Sciencemadness Discussion Board

toluene --> benzaldehyde

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frogfot - 25-6-2004 at 08:07

In several threads this came up, so I decided to make a thread :)

In another thread I mentioned one article that mentions oxidation of toluene by a mixture of MnO2 and aqueous H2SO4. However that synth was told to give only 5% yield, so I didn't bother to scan it.

Now, I found a patent that covers this. Search for 1,302,273 at

In patent they use a mix of 92 parts toluene, 100 p MnO2, 150 p H2SO4 diluted by 3 volumes of water. Some catalyst is also added (CuSO4 or FeSO4), in ammount of 5% from MnO2.

The mix is heated and steam is let through. The fumes is then destilled and a heterogenous mix of toluene/benzaldehyde and water is ubtained. The first is separated and fractionated, and toluene is returned back.

This is basically a "continious" process and nearly no benzoic acid is formed. I'm sure that this can be also done in a batch.

Made a little test with 10,6 ml toluene, where I refluxed small ammount of reaction mix (with CuSO4 as catalyst), reaction time was 3-4 h and there was alot of oxidiser left..
I could not prove what the yield was.. But after workup of organic phase I could get about 3 ml liquid with higher bp than toluene and smell of mandel :P
(some benzoic acid may be dissolved in it..)

Another good news is, I neutrolised aqueous layer, filtered, acidifyed, and no benzoic acid was seen to precipitate :)

Next time it's probably wise to use toluene in 1,5 equivalent to oxidiser and wait until all black MnO2 dissapears.
Oh, and I'm not against some benzoic acid that will form as a byproduct, since reagents are cheap.

[Edited on 25-6-2004 by frogfot]

chemoleo - 25-6-2004 at 08:41

Couldnt you purify the resultant benzaldehyde with NaHSO3, to form the crystaline bisulphite adduct? This way you get rid of other impurities...

Anyway- great stuff! Could you describe the reaction a bit more in detail? I.e. was it vigorous, lots of bubbling? I wouldnt like to do that with my valuable dest. equipment, if it becomes too vigorous...
Also, do you have pictures?

frogfot - 25-6-2004 at 08:57

Soz, I didn't make any pics. But it wasn't that spectacular.. Just a black goo refluxing :) (I used vigorous stirring to break upper layer).
Reaction wasn't vigorous, I beleave that ammount I had would need more than 12 h to react.

Wish I had NaHSO3.. btw, how does that adduct look like?
Just guessing.. something like this? : C6H5CH(OH)OSO2

I mixed up small ammount with methanol and some H2SO4 in hope to get some acetal in several days..

Yay, remembered reaction with acetone.. gotta run :o but still that wouldn't give precise aldehyde content..

Is there any other easy ways to convert benzaldehyde to some crystalline stuff?

Organikum - 25-6-2004 at 10:22


Is there any other easy ways to convert benzaldehyde to some crystalline stuff?
Ammonia forms an solid addition product with benzaldehyde.

What kind of MnO2 was used? A natural or a activated form?
MnO2 can be activated by boiling it with DILUTED, say 3% max. HCl. Although some small amounts of MnO2 will be lost the remaining bigger part, 95% or more, will be in an active state. Use it instantly for best results.

frogfot - 25-6-2004 at 23:17

Cool, In which way does the activation proceeds? I used MnO2 from pottery supplyer (even cheap for this country, swe)

If I used aqueous ammonia, would the basiticy of the solution also produce benzyl alcohol and benzoic acid?
Cause benzaldehyde do this in alkali soln..

Marvin - 26-6-2004 at 03:18

The ammonia adduct is the usual method for additional purification for aliphatic aldehydes by passing in anhydrous ammonia and then adding ether causing it to crash out. It assumes you are working with distilled/dried products though, and thus the major contaminant is alcohol.

Benzaldehyde deviates from aliphatic aldehydes in that you cant regenerate the aldehyde afterwards from the ammonia product, which is why for benzaldehyde sodium hydrogen sulphite has to be used instead. You can use the adduct to make lophine though :)

I'm glad the copper sulphate came of something, I was worried when you posted the 5% yeild of the other process. Did you use anhydrous copper sulphate btw?

Organikum - 28-6-2004 at 06:30

Benzaldehyde forms an addition product with ammonia. Check your books Marvin.

If this is a practical method is another question.


Marvin - 28-6-2004 at 21:12

I agree, I just added that you cannot get the aldehyde back afterwards, though you can make lophine with it.

With sodium bisulphite you can get the aldehyde back.

frogfot - 3-7-2004 at 08:37

Originally posted by Marvin
Did you use anhydrous copper sulphate btw?

Yp, weight was corrected accordingly.
I'm a bit late cause I decided to post the next time I had some results.. but it seems this can't be made a batch process. I tested same thing with two stochiometrical ammounts of toluene. After darn 14 h, upper layer was separated and destilled (don't have that small fractional column..). Nearly everything destilled at approx 111*C... I thoat there would be at least a big ammount of benzoic acid..
That residue had strong smell of benzaldehyde.. but that's nothing to be proud of.. :(

Uh, gonna make an effective steam generator to follow the method in patent.
That's a good idea with activation of MnO2, hopefully this will greatly increase speed of reaction. I had also a suspection that MnO2 from pottery store is not pure.. but I have no proof of it's purity..

MnkyBoy - 14-7-2004 at 09:33

Was the Tol free of thiotolenes? (Found in comercial grade Tol)? As they will inhibit or hinder the benz. formation.

frogfot - 15-7-2004 at 02:58

It was labgrade toluene.
Any idea if dichromates/H2SO4 could be used for this? If toluene is taken in like 10 equivalents excess..
There was some method that uses acetic anhydride (to protect forming aldehyde), but thats harder to find than benzaldehyde.

Btw, I've seen a liquid sold in supermarket that is used in food to give a smell of mandel. Package said, contains benzaldehyde.. could it be pure? noo.. or? it's really not that toxic..

MnkyBoy - 15-7-2004 at 10:54

In the local supermarkets Bitter Almond flavoring says it contains Benzalhyde, alcohol and water. I seem to recall reading some posts about the use of this some time ago and the conclusion was that after the time/effort/materials involved to extract the small amount of the goods out it just wasnt worth it

Jedi - 25-7-2004 at 09:39

Not sure where the person or persons who told you that, but the stuff I get(Bitter Almond Extract) is 50% benzyldehyde and 50% ethyl alcohol. And extracting it is a snap. Unless perhaps they like tried with some product that was diluted and polluted with extra garbage. Not sure, I guess it's all about knowing where to look because it's out there no problem kind of like safrole



[Edited on 25-7-2004 by vulture]

Mendeleev - 26-11-2004 at 13:15

The process using manganese dioxide and sulfuric acid apparently yields only 14%. However according to this site 40% can be achieved with cobalt catalyst at 3 atm. 3 atm is well within the range of a champagne/wine bottle or a stoppered filter flask. Perhaps even higher yields can be obtained if pressurized oxygen is used. Pressurized oxygen is used for welding. This article reports on the oxidation of benzaldehyde to benzoic acid using cobalt (II) bromide. Perhaps this process can be adapted to oxidation of toluene.


Tweenk - 7-12-2004 at 14:46

I think a better way would be to
1. chlorinate the toluene with uv irradiation (sunlight exposure), the synth is on rhodium and is fairly straightforward
2. let the resultant benzyl chloride stand with an excess of water until it hydrolyses to benzyl alcohol (not certain if this happens fast enough)
3. use CuO to oxidise it to benzaldehyde.
Certainly the overall yield of this process would be better but the whole thing requires more work than the direct oxidation method.

[Edited on 7-12-2004 by Tweenk]

Mendeleev - 7-12-2004 at 18:55

It is straightforward, but it is also a pain in the ass. Take it from me, it is a PAIN IN THE ASS. For starters the reaction needs to be dry. So you use dry toluene and dry Cl2, which involves at least one, but sometimes two washbottles with concentrated H2SO4, and a suckback trap between the washbottles and the reaction vessel. It would also be a good idea to have a suckback trap between the gas generator and the washbottle, because you wouldn't wan't a sudden splash of sulfuric acid onto permanganate/whatever the hell. Furthermore if you have neighbors within a 50 meter radius, then you probably want to have a few NaOH washbottles on the other end of the apparatus to prevent gassing your house/neighborhood with HCl.

Oh and you have to wait for bright sunlight unless you have a mercury vapor lamp. But be warned they generate very intense UV, and if your reaction is running for two hours or so, you wouldn't want to be near it because you will get some serious burns. This reaction would be simplified greatly if you had cylinders of dry chlorine on hand(not likely), and lived in a deserted area with perpetual sunshine. As long as I'm fantasizing lets throw in endless hemp fields as well ;). This reaction is more suited for industry or for people who have cylinders, or for people who are really good at rigging up apparatti with 60 hoses and 10 washbottles, suckback traps.

I tried this reaction once. Failed. At first I thought that I had screwed up the assembly of the gas generator too hastily or something and it leaked, but no, the source of the problem was the u-tube filled with CaCl2 that I was using to predry the Cl2. The never before used glass u-tube, had a fucking hole in it, which eventually filled the garage with so much Cl2, I had to get the fuck out of there. I might try this again in few weeks, but for now I'll leave this beast be.

There are much better ways to benzyl/benzal chloride and benzaldehyde. The thread with the gargantuan name in the Organic Chemistry section has info on a very easy synth, no need for dry tubes, it's conducted under acqueous conditions, with the most common materials and no heating needed I believe. Check it out.

[Edited on 8-12-2004 by Mendeleev]

Organikum - 8-12-2004 at 06:23

A 500W halogen lamp is cheap and suffices easily as lightsource. Remove any glassplates from the lamp so present - they are to filter UV and thats what we dont want.

A working chlorine generator with gas-drying setup is described here

It works well, I did it quite often now.

Zak McKracken - 10-12-2004 at 15:27

Is benzaldehyde really that hard to get?
As far as I know it´s not watched.

Please teach me if I´m wrong. :)

Polverone - 10-12-2004 at 18:00

In the US, it is a "List I" chemical like phosphorus or ergotamine. Since it is widely used, it isn't hard to buy, but it is prudent to exercise caution, and perhaps the most cautious thing of all would be not to buy it.

solo - 10-12-2004 at 18:46

Here iis a list from rhodium's page on the watched chemicals in the U.S........solo

Attachment: Watched Chemicals in the US.html (14kB)
This file has been downloaded 4174 times

Zak McKracken - 11-12-2004 at 07:18

Wow didn´t know it´s at the same
level as safrole.:o

However here in europe it´s not hard
to get. Nitroethane seems to be a bigger

Organikum - 16-1-2005 at 04:14

Some stuff from the-hive and an old patent:


Toluene to Benzaldehyde by Manganesepersulfate

by: neograviton
(edited by me)

Here is a easy way to do it with Mn(V)sulfate. A way I used many time!

First get some MnO2. You can buy it as "Manganese-Black" a pigment for cement and concrete. Thats about 70% MnO2. Then put it in an equimolar amount of H2SO4 (100%) and heat it up. Make it really hot. (>200°C). Let it be there for about half an hour. When I do this, I let The acid become so hot, that white steam comes out. After that, let it cool down. You just have made Mn(V)SO4. It is soluble in 37% H2SO4 (battery acid) with a deep, chocolate like brown color.
After that put it 1:1 with the toluene in about 60% H2SO4 (enough H2SO4, so that nearly everything dissolves). Heat (or cool) it to about 50-60°C and stirr it well. After 3-4 hours you will have mostly Benzaldehyd (in my cases about 70%)
Distill the Benzaldehyd/Toluene out by a simple steam distillation. (Just boil water out, until there is no oily layer any more)
When you start boiling that stuff, the color of the liquid becomes sand-like. Thats because the rest of the Mn(V)SO4 breaks down to Mn(II)SO4.

And now the best: just put the liquid in a electrolytic cell (in the anode-part) and put some electricity through it, while stirring. The color will chance to chocolate brown once again, and you can use it again!!! About 6 times!


Just another oxidiser - Manganese-(III)-sulfate

by: hermanroempp

Process for the preparation of an oxidiser:

The process implies the dissolution of manganese-IV-dioxide in sulfuric acid of 50-60% strength in the presence of manganese-II-sulfate. To obtain the oxidiser as a solid, a cold saturated solution of manganese-II-sulfate in water is prepared and concentrated sulfuric acid is added (with cooling, of course) until the solution contains 50-60% sulfuric acid.
The purpose of precipitating the manganese-(II)-sulfate by addition of sulfuric acid is to get the sulfate in finely divided particles, but finely ground manganese-(II)-sulfate could also be used with the same results.
To the crystalline sludge such obtained an equimolar part of manganese dioxide is added under strirring, i.e. for 1 Mol MnSO4 1Mol MnO2 is added. The slush is stirred until the manganese dioxide has dissolved under warming (the reaction is exothermic).
On cooling or upon addition of more (cold) concentrated sulfuric acid the oxidiser settles out in the form of lustrous, brown-red needles.
The product such obtained can be dissolved in organic acids, like acetic acid, and can be used in such solution to react with dissolved organic compounds which otherwise would be destroyed by concentrated sulfuric acid.
The oxidiser itself remains unchanged in its solid form if all traces of water are excluded.

[Translated from: D.R.P. 205200, titled "Verfahren zur Herstellung eines Oxidationsmittels"]

The reaction involved in this process is:
MnO2 +MnSO4 +2H2SO4 --> Mn2(SO4)3 +2H2O

The preparation of this compound is comparable to the prep. of Mn-(IV)-sulfate, as described by neograviton, but the need of working with fuming hot sulfuric acid is omitted, which seems to be a little healthier...
Also, like in neograviton's preparation, there is no need for purchasing watched items like potassium permanganate for the preparation of activated manganese dioxide

An educated guess at last:
For the preparation of benzaldehyde from toluene, I think the procedure described by neograviton should work equally well with the use of abovementioned Mn-(III)-sulfate, there is even no need of isolating this compound from the 60% sulfuric acid solution, use it as it is.

hermanroempp´s last guess is not to the point. There is no 60% H2SO4 solution which can be used in his process, he seems to confuse here some things.

neograviton's method is the preferred one.

This should be done outsides or with a tube venting into a solution of lye or sodium carbonate for the fumes from the hot H2SO4 (SO2/SO3) are not healthy. The first 15cm tube should be glass, copper or iron/steel, then any PE/PP/PVC tubing can be used. Or any other setup which guarantees that the tubing does not just melt away.
Also the vessel containing the acid MUST be put in an old pot which is filled at the bottom with salt or sand (1cm), one can add more salt/sand around the vessel for a better heattransfer. This is then put on a gas-stove or a hotplate. The reason is obvious I hope.
When done this way this is quite safe.

But we can do this even better:
Patent DE102221 from 1897

Exampel 1 - Benzaldehyde
300kg toluene and 700kg H2SO4 65% are mixed under stirring. 90kg MnO2 are added as fine powder under strong stirring. Temperature is kept at about 40°C. After all MnO2 is added stirring is continued for some time, toluene and benzaldehyde is recovered by steamdistillation.

Yeah the old boys didnt deal with small amounts...
No yields are named.

In a followup patent they claim that not so large an excess of toluene is necessary.

The remaining soup of manganese sulfate and H2SO4 can be used in the next run I guess, what may afford less MnO2, worth a try. Maybe the sulfate can also be oxidized to the persulfate by H2O2?


[Edited on 16-1-2005 by Organikum]

Direct oxidation of toluene to benzaldehyde using chromyl chloride

Esplosivo - 16-1-2005 at 14:28

Chromyl chloride (chromium (VI) dichloride dioxide) is a red, fuming, toxic liquid produced as follows in the quotes below.


... the oxychloride or chromyl chloride, CrO2Cl2, is well known as a reddish brown liquid which distils over when a dry mixture of a soluble chloride and potassium bichromate is heated with concentrated sulphuric acid. It is best prepared by dissolving the trioxide in conc. hydrochloric acid, and adding excess of conc. sulphuric to the well cooled solution. Chromyl chloride seperates out and forms a layer below the acids. This is separated, air is blown through, and it is distilled.
CrO3 + 2HCl --> CrO2Cl2 + H2O

Exp 36 - Prepare chromy chloride by distilling a mixture of common salt and potassium bichromate with strong sulphuric acid in a small retort. Collect the product which passes over in a small flask. ...

[Intermediate Inorganic Chemistry, Volume II - Mainly Metals, G. H. Bailey and D. R. Snellgrove, 1930 - Pg.355]

A more 'recent' quote of it synthesis:
Quote: is evolved as a red vapour when sulphuric acid acts in a mixture of potassium dichromate and a chloride, such as common salt:
K2Cr2O7 + 4NaCl + 6H2SO4 --> 2KHSO4 + 4NaHSO4 + 2CrO2Cl2 + 3H2O
It is a deep red liquid evolving as a red vapour. It boils at 119 deg celcius.

[Inorganic and Theoretical Chemistry, F. Sherwood Taylor, 1952 - Pg.675-676]

This chromyl chloride can be used directly with toluene to oxidise it to benzaldehyde, similar to the reaction with MnO2. The only disadvantage I can see is that it requires conc. sulfuric acid and a source of dichromate or chromium oxide (the latter is said to be available at paint shops). This is more of a novel synthesis other than a way to 'mass produce' benzaldehyde, but still interesting and since I found no reference to it I felt I should post it somewhere.

S.C. Wack - 16-1-2005 at 14:33

The problem with the Etard is that CCl4 or CS2 is the usual solvent. If anyone knows of any refs using DCM, let us know.

phanchem - 16-1-2005 at 18:33

In Morrison and Boyd, the organic text I was taught from, the most direct... and probably highest yield benzaldehyde was given as toluene plus CrO3 in acetic anhydride (and, I expect, some acetic acid) to give phenyl-CH(OAc)2, which subsequently is hydrolyzed to the benzaldehyde with water and acid.
Hope that helps.

S.C. Wack - 16-1-2005 at 23:19

Went to the library to follow up on some research on oxidations to aldehydes, not looking for toluenes->benzaldehydes at all. So of course I found nothing useful in the area that I was looking for, but with this thread fresh in my mind noticed some references. Looked some up.

JOC 16, 604 (1951) went the MnO2/H2SO4 route to make 3-t-butyl-4-methoxybenzaldehyde from the corresponding toluene. 400 g. of the methylanisole, 221 g. MnO2, and 2000 g. 30% H2SO4 were agitated vigorously for 28 hrs at 62-65C. 226 g. of unreacted precursor and 187 g. of the aldehyde were found in the oil layer. Given cheap or unreacted, recyclable precursor and cheap H2SO4, the low yield may not be so bad.

A reference to NiO2 also caught my eye. Useful stuff considering how easy is is to make, use, and regenerate. Doesn't get much easier, so I am suspicious of

But if that doesn't work out, there is another way to use it to get benzaldehyde. If one goes from benzyl chloride to the alcohol such as in
a nearly quantitative yield can supposedly be had, because those are the kinds of yields of aldehydes that aqueous alkaline NiO2 gives in minutes. Alcohol->aldehyde reagents are a dime a dozen, there are many other options.

EDIT: wow, that is what happens when you stay up too late. Of course I am and was well aware that NiO2 makes acids, not aldehydes, from alcohols. Except when I got to that last paragraph. Which is why I said that I am suspicious of that patent producing much benzaldehyde. How then I came up with that last bit, I don't know. Going from the alcohol to the aldehyde is still a good idea, just not with NiO2.

[Edited on 18-1-2005 by S.C. Wack]

Organikum - 17-1-2005 at 02:37


JOC 16, 604 (1951) went the MnO2/H2SO4 route to make 3-t-butyl-4-methoxybenzaldehyde from the corresponding toluene. 400 g. of the methylanisole, 221 g. MnO2, and 2000 g. 30% H2SO4 were agitated vigorously for 28 hrs at 62-65C. 226 g. of unreacted precursor and 187 g. of the aldehyde were found in the oil layer. Given cheap or unreacted, recyclable precursor and cheap H2SO4, the low yield may not be so bad.

Quite similar to the german patent I posted. Toluene seems to stand an higher acid concentration, all references talk about 50-60% H2SO4.

I will post some practical results lateron, the advantage of MnO2 is its availability.
The electrolytic re-oxidation of the spent sulfate sounds nice but is tedious, if one doesnt have an electrolytic cell around its not worth the effort IMHO.
Reoxidation by 30% H2O2 will be explored for the simple reason that its OTC for me.


frogfot - 17-1-2005 at 09:57

Found an article:

K. Ohkubo, K.Suga, K. Morikawa, S. Fukuzumi; J. Am. Chem. Soc., 2003, 125, 12850-12859

where they oxidise toluene to benzaldehyde photochemically (>300 nm) by oxygene in acetonitrile in presence of a photocatalyst tetrafluoro-p-dicyanobenzene, getting 3% conversion with 100% selectivity after 10 h. (we have lots of time). One could most probably change the solvent. Some articles referred to using acetic acid..

In article there are given 12 different photocatalysts, all are benzene rings with some chlorine and/or fluorine and/or cyano substituents.
As I understand, photochem oxidation begins with exitation of the photocatalyst, and all photocatalysts presented in article seems to be some electron poor benzene rings...
Any idea if this electron poorness is an criteria to select a good photocatalyst? Or am I totally wrong?
Otherwise one could choose 1,3,5-trinitrobenzene as the photocatalyst :o

Btw, in another interesting article on photocatalysis they used TiO2 as catalyst:

G. Marta, V. Augugliaro, S. Coluccia, Studies in Surface Science and Catalysis, 2000, 130A, 665-670.
(havn't printed it yet.. gonna check it out soon..)

Toluene to benzaldehyde

Kinetic - 17-1-2005 at 12:00

A quick search for toluene to benzaldehyde gave me - unsurprisingly - a lot of hits. The extract from the article below is a solvent-free oxidation with potassium permanganate supported on montmorillonite, but does not suffer from the particularly large amounts of oxidant often required for such transformations. Still, it isn't a procedure you'd use on a large scale. The following is exemplified for indane -> indanone, with the same procedure giving benzaldehyde in 60% yield in 18h when applied to toluene. Taken from Tetrahedron Letters, 43, 5165-5167 (2002):

2.1. Oxidation of indan under classical conditions
Potassium permanganate (3.16 g, 20 mmol) and montmorillonite K10 (6 g) were ground together in a mortar until a fine homogeneous powder was obtained. Indan (0.24 g, 2 mmol) was added to this KMnO4/K10 mixture (4.5 g, 9.9 mmol) in a 25 mL round bottomed flask and mixed magnetically at room temperature until TLC (eluent: hexane–ethyl acetate) analysis indicated a completed reaction (20 h). The residue was then washed with CH2Cl2 (2×20 mL). After filtration and removal of the solvent, the crude product was chromatographed on silica gel (eluent: hexane–ethyl acetate) to give purified product (0.22 g, 1.7 mmol, 85%)

Using microwave irradiation, as below, gave benzaldehyde in 54% yield in 12 minutes:

2.3. Oxidation of tetralin under microwave irradiation
In a 25 mL Teflon beaker, tetralin (0.26 g, 2 mmol) was added to KMnO4/K10 (4.5 g, 9.9 mmol). After 3 min of mechanical stirring, the mixture was irradiated at medium power for 25 min. At the end of exposure to microwave irradiation, the mixture was cooled to room temperature and eluted with CH2Cl2 (2×20 mL). After filtration and solvent removal the crude product was chromatographed on silica gel (eluent: hexane–ethyl acetate) to give purified product (0.24 g, 1.7 mmol, 82%).

Some other references for the oxidation of toluene to benzaldehyde are:

Synthetic Communications, 29(7), 1177-1182 (1999), using sodium bromate and cerium dioxide;

Tetrahedron Letters, 28(10), 1067-1068 (1987), using ceric methanesulfonate (91% yield);

DE168291, in which 'air and water' is used;

DE127388, using nickel oxide (edit: duh, of course this is the same as posted by S. C. Wack above);

DE101221 (which appears to be the one cited by Orgy as DE102221), DE107722 and Journal of the Chemical Society, 91, 263 (1907), using manganese dioxide and sulfuric acid;

DE158609, using cerium dioxide and sulfuric acid;

and DE175295, using 'manganese dioxide sulfate'.

That's pretty much it for the easy to get reagents. I haven't read any of the papers (partly as I don't speak German) so I'll keep my fingers crossed that they are of use.

[Edited on 17-1-2005 by Kinetic]

Mendeleev - 17-1-2005 at 20:54


JOC 16, 604 (1951) went the MnO2/H2SO4 route to make 3-t-butyl-4-methoxybenzaldehyde from the corresponding toluene. 400 g. of the methylanisole, 221 g. MnO2, and 2000 g. 30% H2SO4 were agitated vigorously for 28 hrs at 62-65C. 226 g. of unreacted precursor and 187 g. of the aldehyde were found in the oil layer. Given cheap or unreacted, recyclable precursor and cheap H2SO4, the low yield may not be so bad.

This is actually a pretty good yield. Similar could probably be attained with toluene. Is it difficult to separate a mix of toluene/benzaldehyde that contains 226 g toluene and 187 g aldehyde as above?

S.C. Wack - 17-1-2005 at 21:06


Organikum - 18-1-2005 at 03:15

cheaper and more OTC.

first try

Organikum - 19-1-2005 at 10:32

350ml 38% H2SO4
110ml toluene
100g MnO2
8g CuSO4 pentahydrate

This was refluxed for 3 hours, and steamdistilled, toluene stripped and yielded a small residue of benzoic acid.

Nada benzaldehyde.


second try

Organikum - 19-1-2005 at 13:58

150ml 38% H2SO4
110ml toluene
100g MnO2
8g CuSO4 pentahydrate

This was refluxed for 3 hours, and steamdistilled, toluene stripped and yielded some benzoic acid and a neglectible amount of benzaldehyde.

I would like to say that - at least with somehow bigger amounts - high temperature/refluxing will end in benzoic acid and no stirring will give lousy results anyways.

More the next days.
/ORG :mad:

S.C. Wack - 20-1-2005 at 00:15

Looked up Kinetic's JCS ref. There were other oxidants in that article as well. Looked in CA and found some things. Found Beilstein (all versions except online, stingy Uni), the sometimes helpful Richter's Organic Chemistry, and the Fiesers' Reagents... of no use. Looked strictly for toluene->benzaldehyde without high temps and in English.

First in the JCS was PbO2. 280 g of it and 300 ml of H2SO4 (sp. gr. 1.52) were mixed in a lead vessel with ice bath cooling. CO2 was blown in to the reactor. With stirring, 50 g toluene was added. This was steam distilled after 3 hrs and a 24% yield of benzaldehyde was isolated with bisulfite. They got an 18% yield without the ice bath and with slow addition of the toluene. The temp got up to 40C either way.

Also in lead, 100 g MnO2, 300 ml of the 1.52 H2SO4, and 50 g toluene were stirred for 5 hrs. Less than 1% yield. Repeating with "freshly precipitated" MnO2 and 6.5 hrs, a 5% yield.

Then 40 g toluene in 2X its volume of CHCl3 was added slowly with stirring to 140 g CrO2Cl2 in 200 ml CHCl3 on a cold water bath. After standing overnight, H2SO3 was added with stirring, the whole was steam distilled, CHCl3 evaporated, and a 44% yield of benzaldehyde was isolated via bisulfite. Their description of this Etard looks different than others that I have seen in the journals. BTW, when I mentioned the Etard earlier, I was only asking for a ref specifically for DCM/toluene. DCM and other chlorinated solvents often work, usually not as well, on various substrates. The Etard will give phenylacetaldehyde with ethylbenzene, and phenylacetone with propylbenzene. Styrene also gives benzaldehyde.

And last, they mixed 200 g ammonium persulfate, 500 ml 4N H2SO4, 2 g Ag2SO4, and 40 g toluene with stirring. Steam distillation and bisulfite gave a 78% yield of the aldehyde.

CA 23(4), 3217 (1929) abstracts an obscure (outside of Japan, maybe inside it as well) journal. Unfortunately not the experimental details. The abstractor or author was kind enough to tell of the huge amount of experimentation, with the ideal conditions for benzaldehyde production determined, all experimental variables being explored, without actually giving any clue as to what the magic combination is. What it does say is that MnO2 from heating of Mn(NO2)2, or from KClO3, were both tried. Also from MnSO4 and Cl2 or KMnO4. Mn2O3 and Mn3O4 were also tried. It speaks of "oxidizing power", not yield of aldehyde. Mn2O3 was best with 70%, and the MnO2 from simple heating the worst. Other forms, 40%. I'll look up the author later, he promised to give more details.

Later in that volume (p. 3680), the first of a series of Soviet J. Chem. Ind. abstracts. The author claims almost 100 experiments to tell us the most favorable: temp, 18-19C; H2SO4 conc., 65%; ratio of toluene:MnO2, 4:1; yield based on MnO2, 55%. Catalytic amounts of HNO3 had a slight accelerating effect. CuSO4 and KI were found without effect. Different types of MnO2 gave different activity, pyrolusite is to be avoided, except perhaps to make MnSO4 and precipitate MnO2 from that.

In the next one, 150 g toluene, and 300 g of H2SO4 (sp. gr. 1.57) were stirred up, and CuSO4 catalyst and a mix of 45 g MnO2 and 50 g H2SO4 (1.57) was added gradually. After no more than 2 hrs (when the color lightens the reaction is done, it says) steam distillation was done, the organic layer decanted and washed with Na2CO3, and an amazing 15 g of benzaldehyde was isolated from the bisulfite intermediate.

Last, a comrade mixed up 60% H2SO4 with toluene, and added pyrolusite gradually with rapid stirring and some heating. He said that conc. of the acid should not vary far from 60%, temp should not go much above 35C, excess MnO2 hurts, and long reaction time favors production of the acid. Again, if there are details, little things like isolated yield, they aren't in the abstract.

High yields can be had by applying some electrons to the situation, if you're into that kind of thing - it's been done in a few articles with the Mn sulfates, but I thought this of not much interest even here.

[Edited on 20-1-2005 by S.C. Wack]

frogfot - 20-1-2005 at 05:48

Yay, S.C.Wack, the persulfate route seems very interesting specially because ammonium persulfate seems easy to prepare. Can you please give the reference to this?

As for ammonium persulfate preparation, heres what my nonorg book told:

It is prepared electrolytically:
2(NH4)2SO4 - 2e- --> (NH4)2S2O8 + 2NH4+

A glass jar is filled with cold 50% H2SO4. Into the solution, a clay pot is placed, filled with saturated soln of ammonium sulfate.
As anode, a platinum wire is used (dipped into ammonium sulfate soln). As cathode, theyre using a lead pipe which is coiled several times around the clay pot. Through the pipe, cold water is led to make efficient cooling.
Electrolysis is done at 2,5-3 A/cm2 (does not say if it's on cathode or anode). Voltage depends on the resistance of cell, usually 10-20V is enough.
On the anode there will evolve some oxygene and ozone.
Because of low solubility of persulfate, it will precipitate. After 4-6 hours electrolysis is ceased. Colorless solid is filtered through porous glass filter, washed once with cold water and dried at 50-60*C. Salt is stable in air.

So, this seems doable. If only we could change anode to graphite and cathode to copper tubing... In my experience copper is quite ok as cathode in sulfuric acid solutions.. though I'm not sure if the oxidaton of sulfate requires Pt anode..

[Edited on 20-1-2005 by frogfot]

Organikum - 20-1-2005 at 07:06

I posted two methods for manganese persulfate preparation before here - nonelectrolytically ones.

Electrolytically ways for (subst.)toluene to benzaldehyde are abundant in the patent literature:

Subst. Toluenes are far easier oxdized to benzaldehydes than plain toluene, this should not be forgotten.

I personally would favor a non-electrolytically way, manganese persulfate seems advantageous over MnO2 anyways.
An interesting question is if Mn(II)sulfate can be oxidized to Mn(III)sulfate by means of H2O2, what would be nice. I remember having read that vanadium-sulfate catalysts can be treated this way - maybe manganese behaves similar?

I also prefer a 30% yield method successfully done by me in my kitchen over any 95% yielding method in literature or somebodies else´s kitchen.


frogfot - 20-1-2005 at 09:27

Manganese persulfate route is good if one has lots of conc H2SO4. When massproducing benzaldehyde (which I planned to do..) I'd prefer using electrolytical route since there are needed only dilute H2SO4 both in prep of ammonium persulfate and oxidation itself.
(I can "safely" evap battery acid to max 70%).

I've just bought a proper clay pot to test this out :P

Btw, was that second oxidiser you've posted (manganese(III)sulfate) actually tested in oxidation of toluene? Sorry if I overlooked something.

Organikum - 20-1-2005 at 10:17

The concentrated H2SO4 is actually only needed for turning the MnO2 into Mn(II)sulfate.
The further oxidation to Mn(III)sulfate can be done with strong oxidizers like MnO2, KMnO4 (dangerous), hopefully with H2O2 (has to be tried) or for sure electrolytically (more tedious as it sounds).

neogravitron does it just one step, turning MnO2 into the sulfate and this into the persulfate, its all in this post with the-hive quotes of mine.

My experiences with electrolytic methods are not so very promising, not with this special synthesis but overall. For this reason I will avoid this so any possible.
But feel free to do otherwise if you like to, no problem.


PS: For the steamdistillation you need a setup which should allow you to concentrate the battery-acid to 98%.

S.C. Wack - 20-1-2005 at 22:46

A Soviet abstract stated that they got Mn sulfate to work best with 1.500 sp gr. H2SO4, 50C, and a Pb anode current density of 2A, per what they don't say. They got 1 part benzaldehyde from less than 2 parts toluene.

That is close to an earlier Japanese abstract that said that the perfect conditions were 800 ml MnSO4 in H2SO4 (from 100 g in 1 L 55% H2SO4) mixed with 250 ml (217 g) toluene, separated with a diaphragm, a catholyte of 55% H2SO4, 400 cm2 porous Pb plate electrodes, a current of 2A (1A/ 300-400 ml anolyte) 2.75 - 2.8 V, vigorous stirring for 5 hrs, and a temp of 53-55.

An abstracted Formosan journal reported that anodic oxidation with Mn2(SO4)3 gave a 77% yield of bisulfite-isolated benzaldehyde, or a 70% yield based on the Mn, which was prepared in 97% yield from electrolytic oxidation of MnSO4.4H2O.The yield was 86% with Mn2(SO4)3.H2SO4.H2O (separated from the anode in H2SO4) in 55% H2SO4, or a 55% yield based on the Mn.

Also see DE189178

In JCS 1336 (1960), 69 g of toluene was vigorously stirred for 2 hrs at 60C with 360 g of Na persulfate in 600 ml of a .01M AgNO3 soln. It was mostly done at 30 minutes, it seemed. After extraction with benzene, base and acid washes, and distillation, 40 g of benzaldehyde and 2 g of toluene were isolated.

With 13.5 g benzyl alcohol, 60 g of Na persulfate, 0.17 g AgNO3, 100 ml H2O, and stirring for 2 hrs at 30C, a 75% yield of benzaldehyde was isolated by distillation.

[Edited on 21-1-2005 by S.C. Wack]


ballzofsteel - 20-1-2005 at 22:52

Just breezing through so excuse me if this has been posted already.(likely)

Patent GB190317982

17,982. Johnson, J. Y., [Badische Anilin & Soda Fabrik]. Aug. 19. Aldehydes; carboxylic acids.-The methyl groups of aromatic hydrocarbons or of substituted aro- matic hydrocarbons are oxidized to aldehydes or acids by the use of so-called " manganese super- " oxide sulphate." The acids are obtained by using either an excess of the sulphate or a higher temperature, or both. The sulphate is prepared by electrolytically treating a mixture of manganous sulphate and sulphuric acid, until the red solution, or the precipitate, of manganic sulphate is con- verted into a brown solution. The process may be such as is described in Specification No. 17,981, A.D. 1903, [Abridgment Class Electrolysis]. The acid solution thus obtained, when run slowly into o-nitrotoluene at a temperature of from 50 to 60 C., which is subsequently raised to 100 -110 C. during stirring, forms o-nitrobenzaldehyde, which is distilled off by steam and separated from the excess of o-nitrotoluene which distils over with it. The acid residue may be electrolytically recon- verted into the " manganese superoxide sulphate," as above. If the acid solution is slowly added to toluene while stirring at 40 to 50 C., and the product distilled in a current of steam, benzalde- hyde and toluene pass over. These can be sepa- rated. To obtain benzoic acid, either benzaldehyde or toluene must be added slowly to a sufficiency of the "manganese superoxide sulphate." The reac- tion is slow, but is quantitative. A sulphuric-acid emulsion of benzyl alcohol is similarly oxidized at a temperature of from 40 to 50 C. to benzalde- hyde, which is driven off along with the excess of alcohol by means of steam. To separate the benzaldehyde from the alcohol, the former is con- verted into its bisulphite compound. Or an emul- sion of benzyl chloride and sulphuric acid may be oxidized by adding gradually the " manganese " superoxide sulphate," and heating on the boiling water-bath. Benzoic acid forms.

Worth a read perhaps.

Electrolytic (su)persulfate:

For those who speak Chinese
Patent CN1415592

A process for preparing benzaldehyde compounds includes such steps as reaction between manganese sulfate and ammonium carbonate to obtain manganese carbonate, calcining at 200-800 deg.c to obtain Mn2O3, and liquid-liquid-solid three phase reactino on sulfuric acid and teluene to oxidize the toluene into benzaldehyde compounds. Its advantages are simple process, high utilization rate of raw materials and low cost.

Patents piss me off!

Organikum - 21-1-2005 at 04:45

Some corrections:
MnSO4 aka Mn(II)sulfate aka manganosulfate
Mn2(SO4)3 aka Mn(III)sulfate aka manganisulfate
Mn(SO4)2 aka Mn(IV)sulfate aka manganperoxidisulfate aka manganese persulfate

I hope I got this right now.

btw. ammonium persulfate is made by electrolysis of ammoniumhydrogensulfate says the Kirk-Othmer, if it can be made from plain ammoniumsulfate I dont know.

MnO2 + 2H2SO4 = Mn(SO4)2 + 2H2O
But neogravitron says H2SO4 and MnO2 are to be used in equimolar ratio?

Experiment will show.

JohnWW - 21-1-2005 at 12:50

I think it is unlikely that Mn(SO4)2 could exist, especially in solution. The Mn++++ ion has too high a charge density to exist without hydrolysis. I think that a basic Mn(IV) sulfate, MnOSO4, would be more likely

Organikum - 21-1-2005 at 13:15

I took the information from the german patent DE163813 which says that Mn(SO4)2 is only stable in H2SO4 of 40°Be to 55°Be what should be 60% to 70% when I remember this right. The color of the solution is deep-brown to black.
Solubility is 15% with 40°Be and 5-6% with 55°Be, its stable up to 60°-80°C.
Under boiling of the solution oxygen escapes and Mn2(SO4)3 is formed what can be recognized by its reddish color.
When the acidic solution is poured into water a brownish solution results which discolors and manganese superoxydhydrate precipitates:
Mn(SO4)2 + H2O = MnO3H2 + 2H2SO4

With conc. H2SO4 "Manganoxydsulfat" (whats this now? Manganisulfat again?) is formed and oxygen escapes.

Yes, thats it, or that was it in 1903 :D
It correspondends well with the preparation of Mn2(SO4)3 in the "Brauer".

PS: Does anybody know what "Eisenoxydulsalz" is?
I also found no °Be to % H2SO4 table, is my estimation of 40°Be ~ 60% and 55°Be ~ 70% H2SO4 ok?

[Edited on 21-1-2005 by Organikum]

Mephisto - 21-1-2005 at 15:12

With conc. H2SO4 "Manganoxydsulfat" (whats this now? Manganisulfat again?) is formed and oxygen escapes.
It's the common Mn(II)-sulfate (MnO3H2 ≡ MnO2 • H2O):
MnO2 + H2SO4 '+ Δ' → MnSO4 + ½ O2 + H2O

And "Eisenoxydulsalz" is simply a Fe(II)-salt; the sulfate in this context.

S.C. Wack - 21-1-2005 at 16:23

Ancient CRC H2SO4 tables, in whole Be, or whole %.

Attachment: h2so4_tables.pdf (163kB)
This file has been downloaded 2855 times

Tetramer - 25-1-2005 at 18:08

There is another oxidant worth trying: persulphates are used in electronics etching and easy available. I read a patent that used persulphates and compounds of copper, silver, or iron as catalysts for the toluene->benzaldehyde. I tried without succes before using ammonium persulphate like patent.

Problem was that I did not follow the given methods closely enough. Now I can make a better try but I have lost the patent. It was from the hive before. Does anyone recall this patent and give advices? I need to know patent number. It looked good for OTC and simple equipment.

Icarus - 25-1-2005 at 22:59

There is another oxidant worth trying: persulphates are used in electronics etching and easy available. I read a patent that used persulphates and compounds of copper, silver, or iron as catalysts for the toluene->benzaldehyde. I tried without succes before using ammonium persulphate like patent.

Tetramer, I am not quite sure of your answer.

Are you stating that this reaction was successful?

Benzaldehyde via Cl2/toluene

CycloKnight - 26-1-2005 at 04:56

Hi folks,
what follows is some discouragement for the Cl2/toluene method and then a procedure for making benzaldehyde using electricity.

I would just like to add that anyone attempting to make benzaldehyde using the toluene chlorination route to think again, unless you know EXACTLY what you are doing. It is a bitch and a half.
I've done it, twice. It will take months to get rid of the benzyl chloride smell off the glassware & general lab area.
First time I did this experiment, my method for checking the progress of the chlorination was to intermittently weigh it out (and measure the volume), to measure the density. It works, but the stuff is tear gas'n a half. Within seconds of opening the reaction vessel, my eyes were involuntarily fused shut, with tears running down my face...Ahh the joys of chemistry. I would say working with benzyl chloride is about 5 times worse than working with chlorine, at least.
By the end of the first experiment, I'd been chlorinating for days and I had fairly pure benzyl chloride (at least 70%, pre distillation) which is only half way there - "To hell with this!" I thought. I dumped my benzyl chloride, only to learn a month later that I could have reacted it with my Kg of hexamine to make benzaldehyde!!!!! (Instead of the benzal chloride route I was aiming for.)

During the second experiment, I used a hydrometer actually inside the 3L 3neck RBF to measure the density without actually having to open the RBF. This is a genuinely good idea. It was held in place by allowing the top couple inches of the hydrometer to fit inside a large tube that was fixed to the cork of the middle neck. The idea is that as the hydrometer bobs around (up and down) inside the refluxing flask it can't go anywhere but up and down (so it can't smash against the side of the flask during reflux).
But, in the end I got fed up and decided to go electrochemical instead.
At first the chlorination thing seemed quite tempting, but halfway through I thought the electrochemical route (which I'd done before) was like a dream come true! And it is by comparison, unless you live in a desert like Mendeleev said.

A good way of doing this reaction is by using US patent 808095. Its the electrochemical route, but runs 24 hours a day, and with my 2amp DC power supply, takes around 60 hours to fully regenerate. It produces around 100ml benzaldehyde per run (based on 1Kg of regenerable oxidizer).
I've done this many times, and it works like a charm. Basically, I do it in a giant 3L pyrex beaker, with 2 lead electrodes (the positive anode is larger with a much larger surface area than the cathode). This requires no membrane!
It is absolutely fool proof! If anyone wants to see pictures, I will take them and post them here - just say.

I use approximately 1Kg of manganese ammonium alum, made by adding manganese sulfate to sulfuric acid (60%+) which already has an excess of ammonium sulfate dissolved in it. The molar ratio for MAA is 2 moles manganese sulfate to 1 mole ammonium sulfate. It is a orangy-yellow precipitate. When you pass a current through it - it oxidizes and turns dark red. Its really cool to watch, you see the dark red pouring off the anode, gradully turning the yellow mix dark red. It lasts a long time, I've never worn it out - getting used over and over and over again!
The ratios (from the patent, scale down accordingly) are: 47.5 Kg mangano-ammonium sulfate, 45 Kg water, 79Kg of 98% sulfuric acid.
The reaction mix is heated to 50 C, and with stirring 4Kg toluene are added. When the dark red solution has turned yellow again - reaction is finished!!! The solution REAKS of cherries!
The patent says steam distil, but don't. Use solvent extraction, the steam will leach out your acid from the mixture. The product (from 4kg toluene) is 3.7Kg benzaldehyde, 0.6 Kg toluene, of course if you are using 1Kg of oxidant instead of 47.5 then you will get about 100ml or so.
My experience is that this is a little on the high side, but that may be due to the impurity of the MAA I'm using (i didn't isolate the yellow precipitate before making up my electrochemical solution, I just added molar ammount of manganese sulfate to excess of ammounium sulfate in sulfuric acid)

Now, what is brilliant about this electrochemical cell is that is can be used for all kinds of oxidations! It can turn alcohols into aldehydes, ie formaldehyde, acetaldehyde, eugenal into vanillin (haven't tried that yet), etc. It can also be used for producing organic acids by adjust the reaction temperature and acid concentration.
The only things this cell consumes is reactant (ie. toluene, methyl alcohol, ethyl alcohol, etc) and electricity...My point exactly.

I see that people are looking for non-electrochemical methods for making benzaldehyde, but I suggest taking a closer look at this procedure, I've used it many, many times and it is quite versatile. It is the real mckoy.
I made my manganese sulfate from dismantled D size alkaline batteries, by reacting the MnO2 (100g per battery) with HCl to make the chloride (vent chlorine outside!), and then reacting the chloride with sulfuric acid to make the sulfate.
BTW, I then used most of that sulfate to make the carbonate (by reacting it with sodium bicarbonate) and then with acetic acid to form the acetate, but that is for another experiment that I won't go into detail here....Maybe down at the hive when it's up and running again. Hey hive guys, I'm wondering if this oxidizer (MAA) can be used to react benzene+acetone in the same way manganese(III)acetate can. That is my next project.

Anyway, the sulfate isn't hard to make from scratch, and ammonium sulfate from the garden centre was first purified by doing the following:
The crude brown ammounium sulfate was dissolved in water (almost saturated), then vacuum filtered (any filter will do, really) a couple of times to remove most of the gunk. Then I boiled it down to a mushy mix with constant stirring, then let it cool a bit. Then I added methylated spirits (or denatured alcohol if you are in the US) and all that brown crap just floats to the top, carefully remove it with a baster/syringe/dropper. I used a dropper, which took a while!
When your crystals are reasonably white, just boil off all the alcohol, done!! You can use your purified ammonium sulfate (as is)for the electrochemical cell. That wasn't hard, was it?
I made my electrodes by making a form out of Al foil, and then melting lead in a crucible made from a STEEL deodorant can cut in half, with a handle made from a C-clamp stuck on the top. I used a blow lamp to melt the lead (I put the lead fishing weights in the can and heated), then just poured the lead into the Al foil mold on a disused wooden breadboard, mmm - I love the smell of burnt wood.
Or you could just buy lead sheet, but I couldn't be bothered.

[Edited on 2-13-2005 by Polverone]

Organikum - 26-1-2005 at 05:27

The electrolytic method described is the one presented by Uncle Fester, patent US808095.
It has the same drawback like many electrolytic pathways and like the ammonium-persulfate method:
The amounts of oxidant etc. used are a little large - scaling up to interesting amounts of benzaldehyde - 500ml or more - calls for quite bulky setups, lots of H2SO4 etc.
Ok when you have a spare garage to dedicate for benzaldehyde production though.

You can do the math yourself to find this out.

When going technical/continous, the toluene oxidation by air in the gasphase as posted by Polverone are probably much better, when doing batches - we will see.

I agree that BzCl is a bitch. Therefor I by now experiment to find and later to present a WORKING OTC kitchen method with MnO2 (pigment quality - pyrolusite) in the 100ml product range.


Attachment: us808095_bdehyde_alectro1908UF.djvu (66kB)
This file has been downloaded 3874 times

Electric benzaldehyde

CycloKnight - 26-1-2005 at 06:39

Yes, i agree that there is a vast excess of oxidant. Though, it is perfectly regenerable and not too much of a bother - but scaling up is a problem...for single batch runs. My cell holds exactly 2.2 litres of acid-oxidant mix, I don't think it's alot of work for 100ml - though that does depend on what you want it for. It's really just a case of switch on, and let stir on the stirrer plate. A couple days later react and extract. Practically a one pot synth, and able to produce all kinds of compounds. If you need such a unit to produce formaldehyde, why not use it to make benzaldehyde as well? Or benzoic acid? I did a little bit of critical path management, and I ended up with the above method as the path of least resistance (For me, at least).
Also, should you get busted - your lawyer could always argue that you use the cell for making formaldehyde...Or whatever, there is a long list to choose from.

I am thinking of working on some kind of 2 phase oxidizing mixture, whereby the cell (stirred) is continuously run with a very large excess of toluene floating on top which is continously removed and extracted (distilled).
Excess toluene simply being returned to the cell. The benefit of this is that the cell runs constantly, but only needs a relatively TINY amount of acid-oxidant mix (tiny compared to industrial sized single batches). Intead of having the large excess of oxidant that sits in the bottom of the beaker, only enough that dissolves is necessary here, since it's continuously regenerated!
Larger current means more mix (or larger + electrode) - but you see my point. Also, the lead electrodes do not corrode. At least not to an obvious extent - they change from shiny to grey.

Over time alot of benzaldehyde could be made and the process could be made mostly maintenance-free. Occasionally acid and oxidant carryover will need to be removed from the benzaldehyde extractor/distiller, but that's not much maintentenance. This process (if workable) is mainly limited by the anode surface area and the amount of current you are able to supply! (and corresponding cooling of course...)
However, after a trial run it may be found that the oxidant needs to be toluene-free when it is regenerated by the anode, which would mean a separate vessel (with heating and cooling inbetween to drive off toluene prior to regneration) for regenerating. I suspect that benzoic acid by-product could be generated if toluene is present in the mix while current is passed - but I don't know yet.
Maybe someone else knows?


Polverone - 26-1-2005 at 13:41

Yes, let's see some pictures. I always enjoy gazing upon others' DIY setups. Upload to the "scipics" account <A HREF="">as described here</A> so that you can place multiple, inline images in your post instead of using attachments.

Tetramer - 26-1-2005 at 15:58

Originally posted by Icarus
There is another oxidant worth trying: persulphates are used in electronics etching and easy available. I read a patent that used persulphates and compounds of copper, silver, or iron as catalysts for the toluene->benzaldehyde. I tried without succes before using ammonium persulphate like patent.

Tetramer, I am not quite sure of your answer.

Are you stating that this reaction was successful?

Reaction worked some. I smell benzaldehyde. I was unable to isolate it but I think I make mistakes. Persulphate is oxidant and other metals are catalyst. I use ammonium persulphate since I had not sodium persulphate. Maybe this is part of my trouble. I want to try again but cannot find lost patent :( :(

Organikum - 26-1-2005 at 23:13

Posted by Osmium at the-hive:


Ferrous-Copper Catalyst: Toluene (7.6 g.), water (35 ml.), ferrous sulphate
(0.110 g.) heptahydrate, cupric acetate (0.072 g.) and methanol (8 ml.) are
placed in a 250 ml. reactor.

Sodium persulphate (47.05 g.) in an aqueous-methanol solution of sodium
persulphate is added slowly to the mixture which is maintained at
C., in an atmosphere of nitrogen and under agitation.

The organic phase is separated after two hours and the aqueous phase is
extracted with ethyl ether.

The combined organic phases are distilled to afford 8.29 g. (95% yield) of
very pure benzaldehyde (compared against a pure sample).

US-Pat 4,146,582


PS: Ammonium-persulfate should work too. Pleasse notive the big amount of persulfate needed. Smell of bitter almonds doesnt say much - it smells already in strong in traces in special when warm and with water.

[Edited on 27-1-2005 by Organikum]


S.C. Wack - 27-1-2005 at 01:01

NiO2: Eng. Pat. 22887, 1900
MnO2, H2SO4, and catalyst: GB138999
Belongs in the chlorination thread, if anywhere: GB816253
H2O2 and catalyst: US3531519
benzyl bromide and sodium nitrate: US1272522

CycloKnight - 27-1-2005 at 13:48


[Edited on 29-1-2005 by CycloKnight]

cell.jpg - 134kB

Icarus - 27-1-2005 at 19:56

"PS: Ammonium-persulfate should work too. Pleasse notive the big amount of persulfate needed. Smell of bitter almonds doesnt say much - it smells already in strong in traces in special when warm and with water. "

Someone who has forgoten more about chemistry, than I know about it, once said that there may be issues with the Cu salt and NH 3 complexing.

Only one way to find out I suppose.

[Edited on 28-1-2005 by Icarus]

[Edited on 28-1-2005 by Icarus]

Manganese ammonium alum cell

CycloKnight - 29-1-2005 at 14:58

Okay, as promised here is my photo essay of the mananese-ammonium alum cell, which can be used for the oxidation of various compounds.

Here is the anode:
(before dark red oxidizer is electrolytically generated, this picture was taken after reaction was complete)

Here is the power supply:

Here is the overall setup:

The white powder in the coffee jar is the ammonium sulphate I made from the brown garden stuff using the simple purification procedure I described 2 posts ago in this thread.

Here is the cell a few hours after the reaction has commenced:

It took about 3 days to convert all of the yellow mangano-ammonium sulphate into the dark red manganese ammonium alum.
Reaction takes place with vigorous stirring (50 degrees C), the 2 phases MUST be mixed for reaction to occur, I used magnetic and manual stirring to whip up the mixture. I let the reaction proceed for 1 day before finishing it up by heating to over 60 C and applying vigorous manual stirring with a nickel lab spatula.

(note the organic top layer, due to incomplete mixing)

During reaction (sealed with foil to minimise losses):

The orange tinge to the toluene is indicative of the reaction progress. Not sure what the tinge is, condensation products of some kind I suppose?

Reaction is now complete:

Extraction of the goods:

Extraction almost finished!! :
[img] blob.jpg[/img]

Total organics extracted (including a few hundred ml toluene used for extracting):

Vacuum distillation:


Cell is ready for re-use:
Eggnog anyone? Just kidding - don't drink that!

It is important to get as much of the organic material out of the cell as possible, otherwise it will get oxidized to the acid. This cell smells a bit like formic acid, due to benzoic acid being gererated when the current is switched on. It may be wise to do the final extraction with something like ether, so it will boil off easily after wards. Not so with toluene, enough always remains to interfere with the regeneration process for a while.

Let us have some more!
Sir yes sir, regenerating right away sir!

Current of 2 amps (at 5 volts) is flowing through the mix.

The black floating bits have nothing to do with this process. They are bits of carbon (dehydrated organics), the result of another experiment that I carried out immediately after the toluene oxidation run. Please ignore them.

[Edited on 30-1-2005 by CycloKnight]


CycloKnight - 29-1-2005 at 15:30

Okay, I would just like to say that the yield was a little on the low side, however please take the following into account:

1) Toluene wasn't toluene, it was a mixture of toluene, hexane and water.

2) The product was not washed prior to distillation, so I ended up with quite alot of black polymerised gunk (which appeared out of nowhere) in my flask.

In fact, I ended up with more gunk than product, oops. I thought that by using a vacuum this time I could avoid the high temperatures which would cause the product to degrade - I was mistaken.
The toluene I used for the extractions was wet and had a boiling pt of around 86 C. Since the cell is mostly sulfuric acid it dried it (which I thought was a bonus!), so I didn't want to wash it - I wanted to recover dry toluene for other purposes.
See what happens when one takes shortcuts? So, most of my product was ruined, oh well - I'll just have to wait another 3 days...

I should also say that toluene is a bit hard for me to get. I've been using this OTC solvent formulation called "Evo-Stik Cleaner 191".
Evo-Stik is a contact adhesive used in the UK, but the cleaning formulation is a mixture of solvents (and water too!). The solvents are toluene, hexane and small amounts of other solvents.

For the reaction carried out in the photo essay above, I used 250ml of Evo-Stik solvent. Then I used a further 150ml or so for the extractions - though I could have extracted a bit more!
I did the extractions by adding the "toluene" to the 3L beaker, mixing it up real good and then just removing the top layer with a dropper. Doing it that way removes the need to pour the whole mix into a separating funnel and shake. An unnecessary risk (in my opinion).
I would say that as long as everything has been done correctly, the yield is much higher than what I managed, though I can't give a figure because of the lack of control conditions. My last cell contained an unknown quantity of oxidizer, and this is the first run with my new cell! So, this is the first run I've carried out in about 2 years.
I can say that practically no benzoic acid is produced is the temperature if kept at 50 C and no higher.
The benzaldedhyde odour begins from about 30 sec after the toluene is added to the oxidizer mix.
The reaction takes several hours to complete. The heater on my hotplate isn't functional right now due to a damaged thermocouple probe, so I had to keep putting it on the stove ever few hours to heat it up a bit. My other hotplate has a weak stirrer and can't properly stir the mix...
In a couple days or so, the cell should be regenerated and I will try again and post the results here.

[Edited on 30-1-2005 by CycloKnight]

CycloKnight - 1-2-2005 at 01:29

Okay, I did another run last night and it was a success. However, it was only a partial run.
I estimated that the cell was no more than 25% regenerated and I managed to get 25ml of benzaldehyde from the mixture. The cell was only medium pink, as opposed to dark dark red when it is fully regenerated. The partial regeneration is due to organic acids which have been generated when the mixture is heated over 60 C.
I washed the toluene extracts twice, and there was negligible degradation of the benzaldehyde during distillation, and no scent of benzoic acid.
I started the distillation under normal pressure, as soon as the toluene was mostly gone (I let it run to 115 C) I then cranked up the vacuum and boiled off the remaining benzaldehyde until orange distillate just started to distill over.
There is a small problem I'm trying to work a solution for. Steam distillation is the way around it, but I want to avoid it at all costs.
The problem is that as the cell regenerates, some of the dark red oxidizer forms clumps on the anode, these clumps break off and settle to the bottom.
During the reaction these clumps of oxidizer don't react (unless they have first been pulverized) since they aren't dissolved.
After the toluene has been reacted and the reaction is finished, I have been heating up the mixture to drive off the excess toluene before regenerating. What has been happening is that the "clumps" have then been reacting at the higher temperature with residual toluene to form benzoic acid which stays in the cell.
I used to use steam distillation, which would just steam distill out all of the garbage, but it also leached out the cell acid - so I am keen to avoid it this time.
The benzoic acid interferes with the regeneration process by acting as a competing current carrier; some of the current produces dark red salt, and some of the current produces oxygen due to the benzoic acid. Obviously killing the cell efficiency and lengthening the regeneration time considerably.
This evening, I plan to try an ether extraction of the mix, and failing that - I will dump the whole mix into my 3L RBF and steam distill it. I've never tried ether before, I think it is worth a try.
Steam distilling really does drive out all the oils and junk which can accumulate in the cell after a while, but it is not convenient for everyone.

One solution would be to use a glass rod with a flat end to pulverize all oxidizer before reacting with the toluene.
That way, no benzoic acid will be generated when the mixture is heated to drive off any excess solvent.

Another may be to use a more inert solvent (i.e. diethyl ether)to remove the residual toluene before heating it up. That way, the ether should just boil off without reacting with any excess oxidizer still in the mixture.

Or perhaps, the normal technique I've been using could be applied, the benzoic acid is allowed to form as usual during heating, but is extracted out with another (inert) solvent just before regeneration.

I dare say that another possibility would be to apply a vacuum to the mixture to drive out excess toluene, intead of heating it!

As soon as I have found a working way around this (and it will be soon), I will post more pictures.

frogfot - 1-2-2005 at 03:56

That was very interesting, CycloKnight. One thing I wonder, can you tell the amounts of MnSO4, (NH4)2SO4 and 60% H2SO4 that you've used to prepare manganese ammonium alum? It's quite ignorant question but I'm low on the precursors and wanna do this with bigger yields.. Also the patent didn't describe this in detail eather..

If I understand correctly manganese ammonium alum is MnSO4*1/2(NH4)2SO4, right? Couldn't one than simply use a mixture of these two salts? They dissociate in water anyway..

Extracting with a solvent would be very convenient nearly for anyone.. Instead of ether one could use ethyl acetate of low boiling petroleum distillate..

Only thing I could suggest to the synth is using a mechanical stirrer overhead instead of magnetic..

CycloKnight - 1-2-2005 at 12:30

For the manganese-ammonium sulphate mixture, the ingredients I have used are based on the patent ratios and are approximately as follows:

680g MnSO4
310g (NH4)2SO4
700g H2O
1850g 91% H2SO4

this requires approximately 120 amp hours to fully regenerate.

These are the figures I recorded, though I had carried out an "on the spot" conversion of the patents 98% acid ratio to my 91% ratio, since 91% was all the hardware store had.

But a little bit more ammonium sulphate was added, and I've since had to add a little bit more water(200 ml approx). If the acid concentration is too high, you will know because only hydrogen and oxygen will form at the electrodes, no dark red oxidizer at the anode. Even if you have alot of organic acid in the mix, you will still see SOME red oxidizer forming so if you don't see any - then add more water.
I'm unsure why I had to add more water to get the cell to produce oxidizer, it is either because more sulphuric acid was generated in the cell (perhaps from excess sulphate), or the organic acid that was produced after the first run adds to the overall acidity in such a way as to require dilution in order to produce oxidizer?

I made the mixture up by first adding the ammonium sulphate to the acid/water(the acid was added to only about half of the water) mix, allowing it all to dissolve. Then to that I added the manganese sulphate, the mix will then turn yellow as the manganese-ammonium sulphate precipitate forms. Then I added the rest of the water. One piece of advice here - grind up the manganese sulphate BEFORE adding it to the ammonium sulphate/acid mix. Or you will spend all night trying to get it to dissolve and form the precipitate.

I have learned that when reacting the final oxidizer and toluene, the reaction will take place in minutes rather than hours if the mixing is thorough enough. I managed to get the last batch to fully react within about an hour at 50 C by manually mixing the two phases quite aggressively with a nickel spatula.
Overhead stirring is definitely recommended. I don't yet have that as an option, but if I had it I would definitely use it. For a 2L size, magnetic stirring is quite insufficient and leads to long reaction times. Strong stirring is essential for scaling up.

This evening I was going to use ether to extract out the last of the organic acid (benzoic, mostly) from the mix, however I have come home to find that the cell is functioning just fine, several shades of pink darker that it was this morning - which is typical.
What I think I will do is make sure that ALL of the OXIDIZER is reacted before heating to drive off the excess solvent before regeneration (from now on). I will melt up a section of glass tubing, giving one end a flat surface so I can grind up all the little chunks of oxidizer, before doing the aldehyde reaction. That way no benzoic acid will form at any time (in theory, we shall see...).

My plan is to:
1) Let my cell regenerate as usual, should take another couple days at most.
2) Do the toluene reaction only this time make sure no oxidizer is left unreacted, accomplished by grinding up everything before doing the reaction.
3) Extract with toluene (or toluene hexane mixture) until no yellow/reddish tinge to the extract.
4) Heat it up to drive off the excess solvent.
5) Confirm that both A) no benzoic acid (or any other organic acid) was formed during the heating and that B) no oxidizable solvent is left in the mix.
6) Electrically regenerate.
7) Repeat steps 2-6 until my 5L pail of toluene/hexane is exhausted...

If this works, then that is a perfectly workable procedure, quite easy to scale up. If not, I will try using other solvents to finish up the extraction of the benzaldehyde and toluene, before regeneration.
In a day or two, the cell should be ready.
Then I will do another run, and post lots of pictures!

Coincidentally, my 1Kg of cinnamon oil just arrived in the post today, the smell permeating the container has made my house smell wonderful.
And, I've been trying to think up a use for my 1Kg of sodium carbonate for months, that I haven't even opened yet.
Yes indeed, if all goes well this place is going to smell like the magical cherry kingdom.


CycloKnight - 3-2-2005 at 13:37

Toluene oxidation...
Take 3.

Okay, regeneration is nearly complete.

This toluene will be used for the reaction, note the considerable excess.

This will be the oxidizing mixture.

This is my glass rod I made for crunching up the little oxidizer grains.

The toluene has been mixed with the oxidizer and has been heated to 50 C, the mixture will be mixed vigorously for the next 60 minutes.

A closer look at the toluene layer...

Reaction is nearly complete.

This is the first extract, it smells very strongly of benzaldehyde. In fact, the whole house smells strongly of benzaldehyde...

All in all, I have about 80g of product, which still contains a little bit of toluene - but I won't redistill it - I'll gather it all up with the rest and then distill it all at once.

However, my interest has been shifted in two ways, in one way I'm really fascinated by the curious oxidizing powers of the dark red salt (manganese ammonium alum), and in another way I'm overwhelmed by the ease by which benzandehyde can be made from cinnamon oil! I'll post those pics in just a few minutes.
Anyway, I observed that there are ways the solid oxidizer can be isolated from the mix, then reacted on its own with the toluene to form a much more managable reaction mix. Judging by the odour generated by small amounts of oxidizer/toluene - it may even be more efficient - I don't know for sure yet.
It is possible to use a far lesser quantity of sulfuric acid, but it means that the mixture is a paste, not a liquid. But, the paste has a much smaller volume and hence can be "worked" in a small vessel with less labour than stirring a much larger two phase mix!
The dark red oxidizer can't be isolated on its own without decomposing, but large chunks at a time are easy to separate from the cell during regeneration (still wet with cell acid, of course). I'm quite sure that an acidic slurry can be regenerated in a special cell (i.e. bottom of the vessel is the anode), making the reaction much easier - and less dangerous due to the lesser quantity of acid and hence better for scaling up!
As I type, my cell is settling. That is, the manganese-ammonium sulfate is settling to the bottom. I will later pour off the top clear solution and try to regenerate the manganese-ammonium sulfate paste in the bottom of the cell, it will be an interesting experiment.
The reason for the fascination is simple, this dark red salt produces benzadhyde on contact with toluene. Mix the two together at room temperature and the characteristic cherry odour is noticed almost within seconds.
I can't help but think "what a handy little oxidizer.."
Heat it up and it oxidizes to the acid, keep it at 50 and it oxidizes just to the aldehyde, for toluene at least.
I'm just not crazy about the large volume of sulfuric acid, manipulations involving this cell are dangerous. The acid is concentrated enough to dissolve cotton cloth ON CONTACT, if my 3L beaker cracked and shattered on my stove during heating, I'd hate to think of the clean up operation! What a mess.

[Edited on 3-2-2005 by CycloKnight]

Benzaldehyde from Cinnamon Oil.

CycloKnight - 3-2-2005 at 14:38

Okay, this is my latest experiment, and let me say - it truly works wonders.
If you are looking for benzaldehyde, and have access to simple lab equipment, then you've got to try this one on for size.

This procedure was posted by Mendeleev and reference to the patent was given,US Patent 4,716,249.
I had been hunting this procedure for a while, but never knew how it was done. Thanks Mendeleev.
I ordered 1 Kg of cinnamon oil the same day.

This reaction converts cinnamon oil in high yields, my cinnamon oil cost me less than $30 for the Kg I ordered and contains close to 90% cinnamon aldehyde and I've used it for this procedure without altering it in any way. This procedure only requires refluxing equipment, water, sodium carbonate, and cinnamon aldehyde (cinnamon oil, cassia oil, cinnamaldehyde, etc).
I haven't yet isolated the benzaldehyde from the mixture, because I am running 3 batches, the third has just been started with 2 already complete. I will separate the benzaldehyde in one single step later on, I will report back the yield, and the extracton/purification method I've used.
As far as yields go, what I can say is that the distinctive cinnamon aroma has been replaced with a sharp, piercing benzaldehyde aroma - no mistaking it. I think I can smell a TRACE of cinnamon, so I'm sure it must be pretty darned good!

This is the magic reagent:

And this is what 60 grams of sodium carbonate looks like:

And this is what 200g of cinnamon oil looks like:

In the oil goes:

Splash goes the oil:

Now reflux for 7+ hours:
(don't forget to use a condenser for refluxing!)

It's really simple, set up your apparatus for reluxing. I've used a 3L mantle heater set up for reflux - the thermometer is not necessary.
I've boiled 2L of WATER in a kettle. Some of which is used to dissolve 60g of SODIUM CARBONATE, the rest will be added later. Once the sodium carbonate is dissolved, the solution is poured into the 3L 3 neck flask. Then the 200g of CINNAMON OIL is added. Then pour in the rest of the hot water.
Add bumping granules, set up for refluxing and gently reflux for at least 7 hours. Reaction done.

Extraction of the goods should not be a problem. Reportedy, the main by-product of this reaction is cinnamon aldehyde, whcih boils at 246 C. Benzaldhyde boils around 178 C.
From literature, the reaction should produce a mixture of 70% benzaldehyde and 30% cinnamon aldehyde.
And it sure smells like it.
I'm hoping the separation won't be difficult. I think I'll simply going to have to recommission the 'ole vigreux column for this one. If distillation is ineffective, I will need to form the addition product to extract the benzaldehyde. I'm hoping distillation will do just fine, though I'll probably use vacuum distillation to minimise decomposition.

After I have finished the third reaction run, I should have produced around 350 ml of benzaldehyde.
I should then have just enough recovered cinnamon aldehyde to run another batch and turn 70% of that into more goodies. To yield 400ml - 450ml benzaldehyde, perhaps.

And it is alot easier and quicker than the acid cell method - though you can't use this procedure to make formaldehyde...

I am very pleased that this reaction actually works - and from cheap, common cinnamon oil.
Here you have it, benzaldehyde by the gallon - if that's what you want.
I'll report back the actual, final yield later on.
This reaction simply proves that things that seem too good to be true, aren't always.

Though, I hope that making benzaldehyde from cinnamon oil isn't considered "cheating..".
On one hand the chemistry is magic, but then on the other hand, perhaps making cherry flavouring from cinnamon flavouring isn't so big a deal, I suppose...
Any comments?

[Edited on 4-2-2005 by CycloKnight]

Cinnamon oil experiment update.

CycloKnight - 5-2-2005 at 12:46

The cinnamon oil to benzaldehyde conversion experiment is not yet complete.
So far I have extracted and distilled all of the product from the reaction mixture.
From the 600g cinnamon oil I started with, I've managed to obtain a 500ml RBF filled to within 1 inch from the top with crude product.
The crude product is a mixture of benzaldehyde and cinnamaldehyde (and lesser quantitiesof other by-products).

What follows are the photos I've taken of the experiment so far.

This is the cinnamaldehyde fraction mixing with the benzaldehyde fraction in the 500ml receiving flask, this is the crude product.

Perhaps this photo sums up why we all love organic chemistry the best.

The photo does not do it justice. To see this process occurring in 3 dimensions with all moving "swirlies" is more information than the human brain is designed to take in at one time. Total visual overload. I think it compares with even the best sunsets I've ever seen...Only this is smaller - in this instance a magnifying glass achieves wonders!
And it makes a good desktop theme, at least on my 17".
I only wish I took one of higher resolution.

More swirlies..

Pure liquid glass.

And again..

Anyway, some photos of the extraction process are as follows:
Soon after the 7 hour reaction was complete.

DCM appears to be a more effective solvent than toluene for this extraction.

DCM extraction #1

DCM extraction #2

DCM extraction #3

DCM coming over...

I repeated the above, 4 times for all 6 litres. So, that's 24 extractions...That took several hours to complete. That does not include the first extraction I did with toluene.
I would suggest to start the extractions after each reaction, rather than waiting until the end, like I did. It's alot of work and time.

However, I did have some issues with emulsions which would only break after strong HCl was added, brine alone would not break the emulsions. I had to keep adding more solvent, until a decent separation occurred.

Have a look:
This one has just been broken and is on the retreat

(top layer is toluene)

Benzaldehyde fraction.

Distilling flask at the end of the vacuum distillation:

I am unclear whether the cinnamaldehyde is degrading or if this is the other 11% of the cinnamon oil + reaction by-products.
My diaghram vacuum pump needs overhauling, the vacuum is quite poor, the temperature in the above flask is well over 200 C.

This is why I have not carried out the final distillation of my product, it's just too valuable to risk. I will overhaul my pump, THEN do the final vacuum distillation.

Distillation apparatus. The vigreux column was used for evaporating the solvents to minimise losses.

This is the pet store aquarium valve I use to control my vacuum distillations - it works very well. They cost about £1.20 each (couple bucks a piece) .
They are used to regulate the air from aquarium air pumps.
I thought I would include this since I keep hearing of how "difficult" it is to regulate a vacuum during distillations. It is simple, try it and I'm sure you will agree.

For the final benz./cinna. separation, I intend to use the column shown ealier but I will need a much stronger vacuum to do it. And I will probably need to insulate the column to avoid excessive reflux.
Vacuum pump overhaul is next on the agenda.

[Edited on 6-2-2005 by CycloKnight]

Manganese-Ammonium cell images

CycloKnight - 5-2-2005 at 19:16

"You tell me man, I only work here." - Hudson, Aliens

These are what I call "anodemites".
They grow on the anode when the electrolysing solution is already saturated.
Potentially, this is a means of extracting PURE oxidizer from the cell. This is important since some cells (including mine) have other impurities present.

Forming the oxidizing paste, without stirring.

With the pasage of more current, the red spreads to envelope the whole cell, by which time the regeneration is complete.

Another shot of the regeneration process.

The light coloured material on the electrodes is manganese-ammonium sulfate "silt" which has coated the electrodes during stirring. In time it will all be converted to dark red manganese-ammonium alum.
What I would like to do, is make an electrode that covers the entire bottom of the vessel (anode) so that the oxidizer will form from the bottom up into a solid red mass of crystals, which can then be removed from the acid easily, to effect toluene oxidation with minimal stirring required.
This way, I believe no stirring is required duing the regeneration. This has yet to be substantiated. I am not making THAT electrode like I did the other 2, so I will need to actually BUY some lead sheet from somewhere, and make the bottom anode. I really want this "paste" variation to work, since it would be so easy to scale up.

A cameras detailed impression of a "Still Experiment".

Note the headline on the newspaper, that poor guy?

[Edited on 6-2-2005 by CycloKnight]

Cinnamon experiment complete

CycloKnight - 6-2-2005 at 14:26

Fractional distillation of the crude product has now been completed.
The fractional distillation was carried out under vacuum, and employing a vigreux column.
The vacuum I was pulling brought the benzaldehyde over at 85 C, and the cinnamaldehyde over at 135 C.

Benzaldehyde coming over...

Cinnamaldehyde coming over...

Thermometer reads 135 C.
Column insulated for this fraction.

Benzaldehyde condensation in the still head.

Benzaldehyde collecting in receiver.

Cinnamaldehyde collecting in receiver, in it's usual, rather vibrant form.

End product.

(cinnamon left, cherry right)

Total product is :
200g benzaldehyde
128g cinnamaldehyde

The cinnamaldehyde fraction was collected until it just started to turn orange. Despite the colour, it is probably reasonably pure.
The benzaldehyde is quite pure, the suspended bubbles are droplets of solvent that came over at the very start of the vacuum distillation.
The benzaldehyde fraction was stopped when the temperature increased from 85 C to 90 C. Everything from 90 to 135 C is in the cinnamaldehyde fraction.
There is very little cinnamaldehyde in the benzaldehyde fraction, but there is bound to be a fair quantity of benzaldehyde in the cinnamon fraction (few to several ml?).
Bumping was quite a problem during this vacuum distillation, even though the vacuum was constant, I had to stop the distillation 4 times, to add more anti-bumping granules. I used both glass AB granules and ground pumice AB granules. This could prove to be a problem for larger batches (distillations) when magnetic stirring is not employed. My electric heating mantles don't have magnetic stirring.

Once the cinnamaldehyde has also been converted to benzaldehyde, the total yield should be around 300g benzaldehyde.
The yield isn't as high as I rather optimistically had hoped. However, I am very pleased with the way this experiment has turned out, especially considering that there are obvious ways the procedure can be improved.
This is the most benzaldehyde I've ever produced at one time, and from a first try!

Improvements I'm going to undertake are as follows:

1) Distill cinnamon oil before using it in the reaction, I think this may really help to avoid emulsions forming during the extraction phase. Garbage in = garbage out. The non-cinnamaldehyde fraction of the cinnamon oil really makes a mess. The tar that is left after the distillations is completely insoluble in spirits, soluble in toluene, but far more so in DCM, which was used to remove it from the flasks. Removing the non-cinn. fraction (dark-brown/black) in the beginning will help to distinguish between reaction by-products and aldehyde that may be degrading at different times during the extractions. If product is degrading, it is important to narrow down the cause.
The crude DCM extracts of the reaction mix were not washed before distillation, so some sodium carbonate will have been present - this may have degraded a fair amount of product. The extracts were not washed because of the emulsions issue, if this is remedied by removal of the non-cinn. fraction in the beginning, then the extracts can be washed with good separations.

2) Use magnetic stirring during the 7 hour reaction. This is based on previous experience of reacting 2 phase mixtures during reflux, yields generally suffer markedly when proper mixing is not employed; reflux alone is not enough to break up those oily droplets.
I will need to make up an oil bath so I can use my mag. stirrer/hotplate during the 7 hour reaction.

3) Use of toluene will be avoided during the extraction. DCM will be used only.

By applying the above improvements, I think the overall yield for this procedure can be drastically improved.

[Edited on 6-2-2005 by CycloKnight]

LOVE the picks

chloric1 - 6-2-2005 at 14:48

I understand fully about the beauty of the reaction! The pink chewed up electrode was a surreal site. Could imagine it as broken tabel leg encased in bubble gum or a stub of a human arm in the garbage disposal. YUK!:P:P But you bring a whole new meaning to digital photgraphy!

Darkfire - 6-2-2005 at 14:51

Cyclo this is an awsome thread and your pictures are amazing but, it would be best to link them instead of embeding them in the thread. They stretch the page and take several minutes to load evn on dsl. This thread is likley not even loadable to people on narrrowband.

chloric1 - 6-2-2005 at 14:56

Well Darkfire I ahve to agree about loading speed but these are pictures that only the finest resolution could do justice. Maybe Cycloknight could use smaller image size with the smae pixel rating. I know sometimes I take fine resolution in small sizes to email them.

Eclectic - 6-2-2005 at 15:25

Why not steam distill the benzaldehyde and acetal from the cinnamon oil, base mixture as it forms? Anyone have an idea how much water is needed to steam distill 100g benzaldehyde vs 100g cinnamaldehyde?


CycloKnight - 7-2-2005 at 06:20

Thanks for the compliments, I really enjoyed taking the pictures, I'll try to take more of future experiments.

I have a narrow band internet connection, although the first time loading the page is slow - it is quite accessible. Future visits to the page just involves loading the new picture(s) recently added. Each image is only about 150kb average. Maybe I should have put at the top of the first page "Narrow band users, stick the kettle on for a cuppa'. "
After all, a watched page never loads...
However, I will do something with the image size, from now on. At first I thought the pictures were expanded by this page, but it turned out to be the other way around..
For any detailed images that are best displayed in a large format, I will simply include the scipics link to click on. That should tidy things up a bit.

Eclectic, I believe that cinnamon oil itself is produced by steam distillation of the plant material, as are most essential oils. Steam distillation of the reaction mixture will distill out everything except the sodium carbonate and bumping granules.
However, if pure cinnamaldehyde was used at the start of the reaction, I'm reasonably sure steam distillation could be used at the end of the reaction to drive out the reaction products. But it would take at least a couple gallons of water (steam) to be put through each 2L quantity of reaction mixture to get out all of the aldehyde. This would be good for processing industrial sized batches, without consuming industrial quantities of solvents.
I may experiment with using a more concentrated solution of sodium carbonate, that way things can be scaled up greatly. I'm quite tempted to process 1L of cinnamaldehyde in 1 reaction just to see what happens. Or maybe 500ml to start with.
The same quantity of sodium carbonate would be added, just less water.
I'm curious to see what effect that would have on overall yield.

[Edited on 7-2-2005 by CycloKnight]

Eclectic - 7-2-2005 at 06:35

I'm thinking that the benzaldehyde would steam distill much faster than the cinnamaldehyde. The water layer could be automatically recycled back into the reaction mixture, and if the condenser temp was held at 30-40 C, the acetaldehyde should leave the reaction, forcing it to completion. Think of it as an azeotrope with water. It might be worth a test run to see what king of separation you get with a mix of water, benzaldehyde, and cinnamon oil. Also the patent recomends a surfactant, lecithin would be good for making food grade flavoring.

Eclectic - 7-2-2005 at 07:15

Also, the sodium carbonate is just a basic catalyst for the reverse Diels-Alder addition of water to cinnamaldeyde to split it into benzaldehyde and acetaldeyde. You could just as well start with a few tablespoons of baking soda (bicarb).

trilobite - 7-2-2005 at 09:06

Retro-aldol, not Diels-Alder.

Eclectic - 7-2-2005 at 09:08

Thanks, my bad. :-)

Increasing yield..

CycloKnight - 7-2-2005 at 14:49

It would be good if it were possible to extract the benzaldehyde out as it forms, it would certainly increase the overall conversion.
But, if it is possible to get a near total conversion using simple means, then it won't be necessary to extract out the benzaldehyde. Perhaps stirring will result in a much higher conversion.
I will find out soon enough, this evening I distilled out the cinnamaldehyde from the rest of the cinnamon oil. Tomorrow, I will add the other 128g to the 300 ml (I haven't weighed it yet) I've just distilled.
What do you folks think will happen if the dilution is decreased?
I'm considering reacting the roughly 430g I have left, in one reaction in a 3 L RBF. If I fill the 3 L RBF with 2.5 L of liquid, then that is a dilution of approx. 40%.
I can also let it react for a few hours longer, I don't yet have any reason to think that would do any harm.
Any ideas?

Here are a couple photos I took of the cinnamon distillate earlier this evening:

[Edited on 7-2-2005 by CycloKnight]

Eclectic - 7-2-2005 at 16:06

Use a surfactant and stir. More surface area between cinnamon oil and water should speed up conversion. Use hot water for reflux if you don't want to try the steam azeotrope distillation idea, as that will at least allow the acealdehyde to escape.

If you use a distillation column and distill off the benzaldehyde as if forms, you won't need to do an extraction or distillation later. You might need some way to return the upper water layer to the boiler automatically though. I don't have the composition of the steam/benzaldehyde at hand, and it could be a lot of water for a small amount of product.


CycloKnight - 8-2-2005 at 06:44

If all goes well, I should have the last batch of cinnamaldehyde (to benza.)started this evening.
I'm leaning towards carrying it out using the higher concentration of sodium carbonate that I mentioned before. That would really speed things up. Could you imagine processing 3 litres of cinnamon oil? That would require a 7 hour reflux for 30 litres! With good mixing remember..
With these new concentrations, it would only require around half of that, not too bad.

I'm very much looking forward to see what kind of yields can be expected from now on using this more concentrated variation.
Things would be more scientific if I were to do exactly what I did before except this time apply the improvements I mentioned. I intend to apply those improvements AND using the higher concentration (less water).
If things turn out bad, it could be difficult to narrow down the cause.
But, I'm in a rather optimistic mood - go for gold shall I?
If anyone can see any reason why I could end up ruining all of my remaining cinnamaldehyde based on the changes I've proposed, please speak now,
or forever hold your peace...

I'm going to use:
1) approx. 430g cinnamaldehyde
2) 125g NaCO3
3) >2L of boiled water

If I use 2 L of water, then I've more than doubled the concentration from before.
Shall I start with say, a 10 hour stirred reflux? Or perhaps I should increase it to 14?
Magnetic stirring will be as rapid as I can get it, as long as the stir bar remains stable.
I dare say, that it may be possible to increase the conversion rate, by adding a solvent to help dissolve the cinnamaldehyde (or the original oil). Such as 10% ethanol?
I won't do that this time though, too many unknown variables.
Maybe next time, depending on the yield I can manage this time.

Now on to the toluene oxidation.

Just as a reminder to those just joining this page, MAA = manganese-ammonium alum, and MAS = manganese-ammonium sulphate. MAA is the dark red oxidizer.
Yellow MAS is converted to dark red MAA in the acid cell when current is applied.

The toluene oxidation cell experiment is still ongoing, and will be for a while. However, I've been observing some rather bizaare things going on. I don't yet have any pictures of this. I am for the first time, now starting to find oxidizer masses growing on the cathode, this happened when the cathode was submerged in MAS silt. I have also observed little masses of oxidizer growing on the sides of the beaker...
Also, when the "anodemites" are allowed to form when STIRRING has been applied, the unoxidized silt gets "cemented" into the precipitating oxidizer as well, to form a wierd, solid conglomerate of MAA, and MAS.
Also, if the anode doesn't have any oxidizer deposit on it, then it takes quite a while for some to form.
But, if there is an oxidizer deposit already formed, then that deposit rapidly grows larger - towards the cathode, with the passage of more current.

I think I may have found a simple, working solution for making up the oxidizing paste.
Basically, a saturated cell (dark red/violet, like blackcurrent juice) is used to turn manganese-ammonium sulphate into MAA which immediately precipitates out. My cell is saturated, any more MAA that forms, just precipitates out or forms on the anode.
Once the cell is made, enough MAS is added so that when enough current has been passed, you will have a saturated solution of MAA.
If too much MAS is added, you will have MAA precipitate, so it is not a problem.
With the saturated cell made up, start oxidizing kg quantities of MAS, that was prepared earlier.
Once it has been converted to the dark red salt, pour off as much of the acid/oxidizer mixture as possible. Remove the dark red salt and store in a sealed acid-proof container until ready to use, then pour the cell acid (that you poured off) back into the cell.
Some of the acid will still be in the dark red "paste" you just removed, that is good since without it the MAA will decompose into MnO2 - but after a few runs there will be no acid left in the cell!
That is fine if you only want a few kg of MAA, but if you want to make more more - you will need to replace that acid, and make sure the acid concentration is unchanged. The occasional titration wouldn't do any harm to work out the acid concentration, over time it will be altered by moisture, and water loss due to electrolysis. I'm reasonably confident this will work, because it's essentially the same process I've been applying all along, only without the benzoic acid issues. But having to replace consumed acid, that's all.
So, you see - with this variation the saturated cell is just used as a "converter", converts MAS into MAA.
This way, no benzoic acid is ever formed!
The cell is NEVER heated! Before returning spent MAA (not MAS) back to the cell, make sure it is clean, and free of organics or you will end up with the benzoic acid complications I encountered before. Avoid it. To clean up the MAS before regeneration, you can :
A) use low boiling solvents to clean up the mixture, then evorate at low temp.
B) Use steam distillation just for cleaning up the mix, but you will lose some of your sulphuric acid. The loss isn't that bad actually, but over time you will have to keep replacing it.

I haven't yet tried my pH meter to work out the cell acid concentration, I would have thought that 60% H2SO4 is right off the scale...

Here is a photo of the MAA that I've been removing from the anode:

The next thing to do, is to work out a procedure for producing the MAS complex, without losses. This will involve mixing up stoichiometric proportions of manganese sulphate and ammonium sulphate in sulphuric acid solution.
Again, the same solution (saturated) can be used over and over for making larger quantities of MAS, I'm sure. Otherwise, you will make up you sulphuric acid, then precipitate your MAS (by adding MS to an excess of AS in sulphuric acid), and then what are you going to do with that acid solution, throw it away? Make some diethyl sulphate? Who knows. It would be good to be able to use the same acid solution for making up ALL of your MAS.

When I first made my cell, like I explained in an earlier post - I simply added MS to an excess of AS in the cell. My justification for doing this was this :
"Well, if I make up the acid solution and collect the yellow MAS precipitate, I need to keep it wet so I still can't weigh it to work out the exact quantity of oxidizer.."

But, if you use the acid solution, you may not know the exact quantity each time, but you can be pretty sure that it is reasonably pure. Again, and again and again - without building up ammonium sulphate in your cell. If ammonium sulphate precipitates in the MAS acid solution, then it should be obvious by it's colour.

However, I have 2 slight problems when it comes to scaling up:
1) I'm all out of MnSO4 reagent.
2) My transformer only puts out 2 amps.
I've been putting alot more than 120 amp hours to get a decent conversion. Probably due to organic acid that is still in the mix.

Needless to say, I won't be heating my cell to drive off solvent any more. Heating just cause more problems than it solves..

Believe me, I would only be too happy to make a 5 batch, 5 Kg, double-regenerating cell system, working on a rotating shift. Everything would be recycled, and this process would run 24/7.
Heck, the more cells the better.

[Edited on 10-2-2005 by CycloKnight]

Mass Production

CycloKnight - 8-2-2005 at 09:23

For mass production of benzaldehyde from toluene, the air oxidation of toluene isn't so bad.
Probably alot easier for some than for others.

But if one wanted to go the electrochemical route, here is one way:

I should emphasise that this assumes recycling of the oxidizer. It is kinder to the environment to recycle the oxidizer, but not at all essential. It could be skipped if one were in a hurry, simply by following the steps outlined in the last post to make a suitable quantity of MAA for a single reaction - to make the desired quantity of benzaldehyde. That would shorten the following process greatly.

For 24/7 mass production, there are 9 main steps involved in this process, and some can be carried out at the same time (multi-tasking = good time management!), and others can be combined - more on that later. Here they are:

1) MAA regeneration. May contain many individual cells, working in shift, with say 1 complete every 2 hours.

2) MAA settling. Pour cell mix into acid-proof container container, it must be left undisturbed for at least several hours to allow the MAA to settle out at the bottom. This stage may be made up of a few containers, each holding one batch. When one is added for settling, one is transfered to the next stage.

3) Pour off the saturated acid/MAA. This liquid will now go back to the cell for the next regeneration. You will now be left with a batch equivalent of dark red paste, it will probably still have an inch of liquid on top, it will not interfere.

4) Put into storage container. It would be a good idea to make this container have a several "batch" capacity. So, lets just say that each "step" involves 1Kg batches. Then build up a "buffer" inventory in this storage container of perhaps a few to several Kg of MAA. That way, if an accident occurs or the power goes out, you can still process toluene 'round the clock; this inventory will act as a buffer for your system - though not essential. Steps 1,2 and 3 simply add to this container, remove oxidizer in portions you are able to react at a time, maybe 3kg reactions at a time will be possible? Probably easier than 3 separate, time consuming 1kg reactions at 50 C.

5) Remove predetermined portion of MAA from storage container, and place in acid proof reaction vessel. This vessel must be fitted with some form of overhead mechanical stirring. It should at lest have a partiall sealed top, to help contain odours (and minimise evaporation of your toluene). A large excess of DRY TOLUENE is added. A large excess will be necessary if you are going to use mechanical stirring. This stirring mechanism would not be hard to make, easy from a power drill and an acid resistant rod. A fast spinning axle with a small impeller should be good for really whipping up the reaction mixture into a toluene/MAA milkshake. (The lower the temperature this reaction can be made to happen, then the better it probably will be).

6) Solvent (with large amount of dissolved benzaldehyde) is poured off. You may wish to add additional toluene to extract out as much of the benzaldehyde as possible. Use the mechanical mixer for each extraction.

7) Washing the solvent. Wash with water to remove excess acid. You may wish to back extract this water to reclaim some residual benzaldehyde/solvent. You could use a different solvent for the back extraction to conserve toluene. The water extracts could be fractionally distilled to recover some cell acid.

***This benzaldehyde laden solvent is the output from this process, it is put into a storage container and is removed when practical to do so, for the distillation process.***

8) MAS is transferred to solvent removal stage. This could be a vacuum vessel, or some kind of evaporator, or a solvent extraction using a low boiling solvent. Preferably low boiling as in < 50 C low boiling, maybe a higher pb could be used, uncertain at this time. A combination of (low boiling point) solvent extraction with subsequent vacuum evaporation could be used, or just plain old evaporation in a lowe humidity area, on a large acid resistant sheet could be used? Lots of possibilities.

9) MAS goes straight back into saturated MAA cell solution (from step 3) for regeneration, in 1 or more separate cells.

***Distillation process is run under vacuum. The first distillation could be run at normal pressure to drive off the toluene, then what remains is transferred to the vacuum distillation stage. Even a rather small vessel could do this, it would not have to be very big. I'm sure even a 250ml vessel could handle the output from this process, unless your regen cells were pumping out one heck of a current...No need for large vac. vessels***

Okay, I bet you're thinking this all sounds kinda complicated, well - it doens't have to be. Some of the steps can not only run at the same time, they can be combined.
For instance, 1 very large single cell could be run with a large hold up, say a few Kg solid material. Then, 1 Kg at a time can simply be removed when needed for the reaction, and the expended oxidizer from the last reaction (MAS) put back into the cell when convenient to do so.
Using that approach solves alot of practical issues, it just means that the cell will never be 100% regenerated at any given time - but who cares? Just keep an eye on the colour of the mix, keep it a dark-ish red, and make sure you keep organic solvent out of the regenerating mixture.
That large cell could also be the settling tank as well. Just switch it off for a while, it will settle pretty good in just a couple hours - if you are in a hurry. A scoop can retrieve the red paste or sludge from teh bottom, it's not difficult, believe me.
For a large single cell, some kind of overhead stirring would be a good idea -though I'm unclear how essential it would be (at this time).
Chunks of oxidizer that collect on the anode could either be A) broken off and mixed EVENLY with the solid material or B) maybe collected and used as the oxidizer. This would avoid the need to switch it off.

It is perhaps worth noting that this roto-batch style process - like most processes - has it's continual process equivalent, I think people oten refer to that as "going technical"
The continual process equivalent would use a MAA saturated solution of cell acid, that is pumped via the process equivalent of all the above steps/stages.
Only that instead of working with a solid mixture, you would be working with an acid solution (at some stages red, at others yellow), which is not without it's own set of acid-resistant pipes, pumps, level regulators, flow controllers, etc. would need to be obtained.

Or the batch system could be miniaturised to produce benzaldehyde more regularly, only on a more manageable scale.

Doing EVERYTHING in single individual stages is alot of work.
Although the above proposal may have a solid material (MAA and MAS) holdup of perhaps 8 or 10Kg, running 10kg batches in single steps would be a nightmare, and very slow. It would be frustrating doing nothing, but waiting for your 10kg to regenerate.
If you were actually able to work with 10Kg batches, you would be thinking, hey I could be reacting another 10kg right now, and then extracting 10Kg, and then washing...
Maybe someone will actually do that, there's an idea?
10 sounds a lot better than 1.

[Edited on 10-2-2005 by CycloKnight]


CycloKnight - 8-2-2005 at 12:48

This is just an update on the reaction I started this evening.

Chemical used:

~430g Cinnamon aldehyde
120g sodium carbonate
2L boiled tap water

The 2 flasks at the front contain (from left to right) cinnamaldehyde and benzaldehyde. At the back: cinnamonaldehyde (green, freshly distilled), undistilled toluene, and benzaldehyde from the last toluene oxidation run. Note the colour change of the cinnamaldehyde, it has changed from orange to burgandy, since it was distilled 2 days ago.!

Fancy a cuppa' benzaldehyde anyone? Great! I'll just pop the kettle on!

The 120g sodiumcarbonate is still dissolving in the dish of hot water.

The magic ingredients.
Yes, thats right - I shop at Tesco supermarket, the best for quality low prices.

Not as high tech as my Heidolph MR 3003, but it will do the job.

Bumping granules. Pumice granules are generally much better for oily mixtures. I found a large lump of pumice in a field, and smashed it to powder with a hammer.

(Glass left, pumice right)

Making up the oil bath.

A closer look at the oily mixture:

A dude's eye view of the overall setup:

[Edited on 9-2-2005 by CycloKnight]

Cinnamon experiment #2, update

CycloKnight - 9-2-2005 at 14:01

I refluxed the mixture for 12 hours straight.
I started the reflux yesterday at 20:00,
and I switched off the hotplate at around 08:30 this morning. I came home from work at lunchtime and switched on the heating only for about 30 minutes and after work I switched off the stirrer at 18:30.

Eclectic had suggested that I try steam distilling the mixture instead of using solvents to do the extraction directly.
This is what I'm doing just now.

There are many ways this could benefit the process.
If benzaldehyde distils off much faster than the residual cinnamaldehyde, then steam distilling will help to get the remaining cinnamaldehyde reacted. At this time, this does APPEAR to be happening.

The magnetic stirring was a fairly subtle process, and I'm sure that any droplets that didn't get broken up overnight, sure are atomised now.

This is the reaction mixture just before I started the steam distillation.

A closer look at the mixed top layer after the reaction, just before the steam distillation.

This is the pot for the pressure cooker that I use to generate the steam.

This is an essential tool for steam distillation. It is just a bent glass tube connected to some rubber tubes, this makes it flexible and so won't get damaged by the very turbulent mixture. The tube is bent 180 deg at the end to prevent rather disturbing back pressures that are produced when a large bubble of steam is sudddenly released, this way the steam is always moving upwards through the mixture. This really helps to maintain a constant flow of steam.

Here is the overall steam distillation setup. I'm sure it fairly self explanatory.

Same again.

The steam is distilling through at a moderate rate.

Oily droplets can be seen running down the inside of the 1L volumetric flask.

A closer look at the oil droplets.

Here is the liquid that has been collected so far. This is the total amount of steam that has been condensed.

I guess the question is: Has the reaction been a success?
I could be real scientific (yawn..) and say that we will have to wait 'till the experiment is finished and the product distilled to work out the composition.
I've tasted the steam condensate a few times, and I can say right now that the steam condensate tastes considerably "hotter" than the pure cinnamaldehyde I started off with!
That must be a good sign.
There is clearly only a small percentage of total oil in the condensate.

Here are the latest images:

These pictures were taken just as the first litre had finished coming over, the oil at the bottom is approximately 50ml or more.

At one stage the cooling water stopped flowing because some of the cooling water boiled in the condenser.
When this occurred the benzaldehyde laden steam didn't condense and filled up the house with a seriously eye stinging cherry aroma, in just several seconds.
I may have just found the world's most wonderful smelling tear gas.

It is now after 11pm where I live, and I will need to continue this tomorrow evening. So far exactly 2 litres have been condensed. It contains at least 100ml of free benzaldehyde laden oil, though I think that is a conservative estimate - it may be as high as 200ml.

[Edited on 10-2-2005 by CycloKnight]

Cinnamon experiment #2 results

CycloKnight - 10-2-2005 at 13:58

Steam distillation has now been completed.

This is the mixture before I resumed the steam distillation this evening.

Rubber tubing dissolved, just used a straight glass tube for the remainder of the distillation. The tube on the left is the same time of tube before being exposed to benzaldehyde, and the tube on the right it how it looks now. Benzaldehyde has turned the rubber tube in a cherry lollipop.
If I didn't know better, I would eat it.

Earlier I added approximately 3g of lecithin. As you can see, some foaming did occur. This was no problem, my vigreux made swift work of it.

This is approximately 80% of the total oil product, not including the oil still mixed with the water. The condensate has yet to be extracted.

After the above photo was taken, about another 40ml of oil was recovered from further condensate.

In total, about 200ml of free oil has been recovered from the steam distillation. With each litre of condensate, there is about a tablespoon of more product. So, here the point of diminishing returns is approaching..
I don't know how much benzaldehyde is still held up in the water, so far - I've condensed 6 litres (~1.5 gal.) of water, which has removed most of the product. There is about another 200ml of oil unaccounted for.
I am quite certain that the free oil so far collected is almost pure benzaldehyde. If there is any cinnamaldehyde in it, it must be less than 5%. It is not even slightly noticable.
If the other 200ml has been degraded and is still in the mix then it could be due to either the increased concentration, or it could be down to the steam distillation - I am unsure.
I could try the reaction again, only shortening the reaction time to 4 hours or less, then start steam distilling. Perhaps a 12hr reaction + a day stirring + steam distillation for 4 hours + cooled + steam distilled again the next day for another 4 hours is a bit too aggressive for the aldehyde mixture. I will do it again, but I will need to wait until I get more cinnamon reagent.
Once I have extracted the 6L of water, I should have a better idea of the overall reaction efficiency.
I think this reaction is a good one to do while you wait for your cell to regenerate.

Speaking of which, now on to the toluene oxidation..

This is a picture of the cell + the pure oxidizer I have been removing from the anode.

Aren't they both so cute? The chemical equivalent of Dr. Evil and Mini Me.
They will both get put to work soon enough.
Note the colour, this is the colour of a fully regenerated cell. If I wanted to run a bigger reaction, all I would need to do is separate the saturated MAA solution from the MAA, then add MAS and electrolyse and repeat until I had the total quantity I desired, topping up with acid solution when necessary.
It just so happens I don't have the reagents to make up more MAS, at the moment at least.

Here is a recent shot of the anode, still encrusted with MAA oxidizer.

Note, that even with constant passage of over 2 A electrical current since this thread was started, there is still no discernible corrosion on either electrode.
Only some discolouring is visible. These electrodes will last a very, very long time.

I may just keep my steam distillation apparatus assembled and use it to recover my benzaldehyde from the next toluene oxidation run, just like I used to do. Having to replace some leached out acid now and again, isn't so bad really.

[Edited on 11-2-2005 by CycloKnight]

CycloKnight - 11-2-2005 at 14:12

Okay, this is what the mix looks like after the steam distillation.

This is the total product, the free oil is on the left, the total DCM extract of the condensate is on the right.

This is the total extract from the condensate, after the DCM was boiled off. The oil weighs approximately 65 grams.

This is a photo of the benzaldehyde distillate, if you look closely you can see it was taken immediately as a drop had splashed into the benzaldehyde.

200g from previous experiment was added to the oil obtained from the steam distillation. Yield from this experiment is approximately 183g in very pure form.
Final product, 383g pure benzaldehyde

The true total is probably closer to 400g, however I let some of the benzaldehyde distil over with the toluene so I would have pure benzaldehyde without any toluene. I added about 50ml toluene to dry the benzaldehyde, hence the water-clear appearance.

183g from 430g isn't too bad. I did not plan to steam distil, it was a last minute decision.
Using a much shorter reflux time, and then steam distilling will no doubt produce much higher yields, IMO. I think it is definitely worth another try.
After I add in the benzaldehyde from my recent toluene oxidation experiments, I will have over 500ml of pure benzaldehyde.
Time well spent, I'd say.

[Edited on 11-2-2005 by CycloKnight]

Not too shabby!

CycloKnight - 11-2-2005 at 15:18

Well, there you have it folks - the end of chapter 1. Now go forth and be fruitful!

I would be very interested to know if anyone else manages to carry out either of these processes.

The more who do, the better. Purely for the benefit of the advancement of amateur science, that is. We amateurs have to look after ourselves ya' know?

Please don’t hesitate to PM me if you have any questions I can help with.
I will carry out another scaled up variation of the cinnamon experiment at some point in the future, but it won't be for a little while yet. It will probably be another steam distillation variation and then I’ll leave this process alone. It’s been done enough, by me at least.
In the mean time, I will be compiling another photo essay for a completely different process for a different thread. I will post it only when it has been completed.
If all goes well, it should make very interesting viewing :cool:.

You may want to read this before your last trial

psychokitty - 12-2-2005 at 23:19

( 1 of 1 )

United States Patent 4,673,766
Buck , et al. June 16, 1987

Method of producing benzaldehyde

A method is disclosed for producing benzaldehyde by fractionally steam distilling benzaldehyde from cinnamaldehyde in the presence of hydroxide catalyst and at a pH on the order of about 11 to about 13. Conversions of cinnamaldehyde to benzaldehyde can be achieved on the order of about 75% or more.

Inventors: Buck; Keith T. (Cincinnati, OH); Boeing; Anthony J. (Cincinnati, OH); Dolfini; Joseph E. (Cincinnati, OH)
Assignee: Mallinckrodt, Inc. (St. Louis, MO)
Appl. No.: 856595
Filed: April 25, 1986

Current U.S. Class: 568/433; 568/458
Intern'l Class: C07C 045/51
Field of Search: 568/433,458


References Cited [Referenced By]

Other References
Guthrie et al., Can. Jour. Chem., vol. 62 (1984), 1441-1445.

Primary Examiner: Helfin; Bernard
Attorney, Agent or Firm: Wood, Herron & Evans




What is claimed is:

1. A method of making benzaldehyde com- prising

dispersing cinnamaldehyde in water,

converting the cinnamaldehyde to benzaldehyde under the action of heat in the presence of a catalytic amount of hydroxide ion and at a pH of about 11 to about 13,

fractionally steam distilling benzaldehyde and acetaldehyde from the cinnamaldehyde, and

recovering benzaldehyde from the distillate.

2. The method of claim 1 which is conducted at a pH in the range of about 12 to about 12.5.

3. The method of claim 1 wherein the benzaldehyde distillate resulting from the steam distillation is fractionally distilled for separation of the benzaldehyde in substantially pure form.

4. The method of claim 1 wherein the acetaldehyde is vaporized during the course of the conversion while the benzaldehyde is condensed.

5. The method of claim 1 conducted in the presence of an anionic surfactant.

6. The method of claim 1 conducted under shearing agitation to facilitate the dispersion of the cinnamaldehyde in the water.

7. A method of making benzaldehyde com- prising

dispersing cinnamaldehyde in water in the presence of an anionic surfactant,

agitating the dispersion under the action of heat in the presence of a catalytic amount of hydroxide ion and at a pH of about 12 to about 12.5 for the conversion of cinnamaldehyde to benzaldehyde,

fractionally steam distilling benzaldehyde and acetaldehyde from the cinnamaldehyde in a still having a pot temperature of about C. and a column temperature of about C., and

fractionally distilling the benzaldehyde from the distillate for the separation of substantially pure benzaldehyde to obtain a yield of at least about 75% based upon the cinnamaldehyde.

8. The method of claim 7 wherein cassia oil is employed as a natural source for the cinnamaldehyde employed in the conversion.




The retroaldol reaction of cinnamaldehyde is well known. In this reaction, cinnamaldehyde is converted to benzaldehyde and acetaldehyde with various potential side reactions. Recently, for example, an investigation of the kinetics of the retroaldol reaction of cinnamaldehyde has been reported by J. Peter Guthrie, et al, Can. J. Chem., Vol. 62, pp. 1441-1445 (1984). While the conversion of the cinnamaldehyde to benzaldehyde has been long known and well studied, it has not been heretofore known to produce benzaldehyde from cinnamaldehyde in substantial yields and favorable reaction conditions for production of such yields have not been reported.


This invention is directed to a method of making benzaldehyde by conversion of cinnamaldehyde in the presence of water with surprisingly high yields heretofore unachieved. The invention involves the dispersion of cinnamaldehyde in water and, in the presence of an effective catalytic amount of hydroxide ion, fractionally steam distilling benzaldehyde from the cinnamaldehyde. The reaction is conducted at a pH on the order of about 11 to about 13 and, unexpectedly, within this pH range it has been discovered that a substantial conversion of cinnamaldehyde to benzaldehyde can be achieved on the order of about 75% or more. It has also been found that the conversion may be achieved at such a high pH without adverse side reactions.

In a preferred mode of conducting the method, the cinnamaldehyde is dispersed in the water in the presence of shearing agitation and a surfactant. In another aspect of this invention, it is preferred to employ an anionic surfactant such as sodium lauryl sulfate. Preferably, the hydroxide ion is furnished by means of sodium hydroxide which also achieves the pH in the range of about 11 to about 13. It has critically been determined that the fractional steam distillation of benzaldehyde from the cinnamaldehyde must be conducted at a pH within the range of about 11 to about 13, preferably about 12 to about 12.5. Below and above this pH range, very poor conversions are obtained of 50% or far less and competing reactions interfere with the production of benzaldehyde. Outside of this critical pH range, side reactions, polymerization and other adverse reactions prohibit any significant yield of benzaldehyde. Yet, within the pH range of about 11 to about 13, especially about 12 to about 12.5, significant yields on the order of 75% or greater are achieved and benzaldehyde is recoverable in substantially pure form free of side reaction products. These results are considered to be unexpected especially at the high pHs of the reaction where it may have been expected that side reactions would have significantly lessened or prevented the yield for the desired product.

During the course of the fractional steam distillation of benzaldehyde from the cinnamaldehyde, acetaldehyde is also vaporized and removed. The removal of acetaldehyde thus prevents the forward polymerization reaction which otherwise competes in the presence of the catalyst. The benzaldehyde which has been steam distilled is then subsequently fractionally distilled for separation of the benzaldehyde from other components in the distillate such as minor amounts of acetaldehyde, terpenes and orthomethoxybenzaldehyde. It has also been found that a natural source for the cinnamaldehyde such as cassia oil may be employed containing a substantial amount of the natural cinnamaldehyde. Thus, a natural product such as cassia oil may be employed in the fractional steam distillation method of this invention and still the significant yields on the order of about 75% or more are achieved.


The following detailed operating example illustrates the practice of the invention in its most preferred form, thereby enabling a person of ordinary skill in the art to practice the invention. The principles of this invention, its operating parameters and other obvious modifications thereof will be understood in view of the following detailed procedure.


A solution was made up from 38.6 lbs. sodium hydroxide, 4 lbs. sodium lauryl sulfate and 10 liters antifoam agent in 760 gallons of water. The solution was stirred until a homogeneous solution was obtained. Then, 1320 lbs. of cassia oil were placed in a 1150 gallon still. The oil contained approximately 72% by weight of cinnamaldehyde. The still had a pot volume of about 1150 gallons onto which was mounted a 4 foot fractionating column containing 1".times.1" ceramic tubes and a water cooled condenser was thereafter connected in series for condensing the benzaldehyde-water azeotrope.

The above prepared sodium hydroxide solution was then added to the cassia oil and introduced into the pot of the still. The pot was equipped with a stirrer. Using pressurized steam and vigorous stirring, the pot was heated to reflux with a pot temperature of C. Reflux was established with a column head temperature of about C. Once reflux was established, it was continued for about 1 hour. During the course of the conversion of the cinnamaldehyde in the cassia oil to benzaldehyde, pH was monitored and was maintained at about 12 to about 12.5. In the event the pH fell below about 12, sodium hydroxide was added to bring the pH back up to the range of about 12-12.5. After refluxing for about 1 hour, take-off of the water-benzaldehyde azeotrope was initiated. The water cooled condenser was operated at F. thereby enabling the water-benzaldehyde azeotrope to be condensed and collected in a chilled receiver. The acetaldehyde by-product was principally vaporized at the temperature of the condenser and was taken off as vapor. The distillate principally containing benzaldehyde in an amount of about 75% or more with minor amounts of cinnamaldehyde, terpenes, orthomethoxybenzaldehyde and acetaldehyde was obtained. The crude benzaldehyde was thus collected in a chilled receiver and, in a continuous feed operation the condensed water was continuously fed back to the still to replace what had been taken off and the distillation of the azeotrope continued. The fractional steam distillation of the crude benzaldehyde continued until about 670 lbs. of crude benzaldehyde were obtained. The crude distillate containing benzaldehyde was then dried under vacuum and fractionally distilled under vacuum of about 29" thereby providing a boiling point for the benzaldehyde at about C. in order to obtain a substantially pure benzaldehyde free from residual terpenes and other impurities.

Thus, by means of practicing the above process, the objectives of this invention are achieved in that cinnamaldehyde is converted into benzaldehyde in substantially pure form even from the natural source of cassia oil. Surprisingly, it has been found that substantial yields in excess of 75% or more of substantially pure benzaldehyde are achieved by this method. Moreover, it has been found that there is a surprising window of high pH at which the conversion may take place in a fractional steam distillation column in order to separate the benzaldehyde and acetaldehyde from the reaction mixture and still avoid the adverse side reactions from occurring.

Having described this invention and its operating parameters, variations may be achieved without departing from the spirit and scope hereof.

* * * * *


Another leap forward...

CycloKnight - 13-2-2005 at 02:06

Very good work psychokitty!
I don't know how you found that, but that looks pretty darned good.
I'll carry out this new procedure for the last trial, with usual pics.
75% yields? Got to be worth a shot.

Toluene to Benzaldehyde

synthetika - 13-2-2005 at 18:14

Hi all,
We too, are really interested in this particular subject,
We are now looking at some similar, and some new methods as well,

These pictures are just too good, They are sharp, and fruitfull with shit loads of needed, sometimes misunderstood info,


I believe that the persufate of Ammonia, works very well, having done it a few times, and the yields are very high

[Edited on 14-2-2005 by synthetika]

cinnamon oil

Taz - 5-3-2005 at 23:28

Would it matter if the cinnamon oil is

derived from the bark or the leaves?


Polverone - 6-3-2005 at 01:41

The leaf oil has a much lower concentration of cinnamaldehyde than the bark oil. You want the bark oil (or pure cinnamaldehyde if you can get it).

[Edited on 3-6-2005 by Polverone]

paccman278 - 8-3-2005 at 04:18

swip came across some mno2 today, how would one get to mnso4 from the mno2. would heatin it with sulfuric work? swip wants it for the electrocell.

Re: Benzaldehyde from toluene

solo - 8-3-2005 at 19:57

I recently ran into this threads about the current subject which may be of some assistance ........or not,....solo


aldol - 10-3-2005 at 01:51

the best way to benz is with bezyl alcohol
and reacting with mno2 works good

garage chemist - 1-4-2005 at 10:54

Today I tried to make some benzaldehyde, just because it smells nice.
In reference to the method from neograviton I mixed 0,1mol MnO2 with 0,1mol conc. H2SO4, added water until it was a paste and evaporated the water until white fumes appeared.
I added a solution of 10ml H2SO4 in 40ml water and stirred it for a while, it dissolved very slowly. After a while, I poured the black sludge into an erlenmeyer flask and added 20ml toluene (reagent grade, extra pure) and stirred it rapidly with a magnetic stirrer.
After 30min. at about 50°C, there was not the slightest smell of benzaldehyde. I have no idea what I have done wrong.

The electrolytic method from CycloKnight is of course ideal for mass production, but the manufacture of the reagents consumes LOTS of H2SO4: first the production of MnSO4, then the ammonium sulfate (I have to prepare this from H2SO4 and ammonia) and the cell again needs lots of H2SO4.

I considered setting up a small- scale electrolytic cell, but a cell containing 47,5g MAA, 45ml H2O and 79g 98% H2SO4 can, after electrolysis, oxidise only 4g of toluene. Separating this very thin organic phase from the electrolyte would be very difficult.

Organikum posted another interesting process:
"300kg toluene and 700kg H2SO4 65% are mixed under stirring. 90kg MnO2 are added as fine powder under strong stirring. Temperature is kept at about 40°C. After all MnO2 is added stirring is continued for some time, toluene and benzaldehyde is recovered by steamdistillation."

Maybe activated MnO2 (obtained by boiling in dilute HCl) is required. I'll try this out soon.

EDIT: Sorry, I didn't read the entire thread. The MnO2 route gives lousy results... hmm, seems like I have no other choice than to use the elektrolytic method.

Didn't Polverone once speak of a catalytic process where toluene is oxidised with air?

[Edited on 1-4-2005 by garage chemist]

garage chemist - 2-4-2005 at 13:51

I am going to try out "activated" MnO2 in H2SO4 because nobody here tried this until now.

I boiled 20g of MnO2 (sold as "manganese black" from a pigment supplier) with 100ml 2,5% HCl for 1h 30min. There was no detectable chlorine smell, but the chlorine might have dissolved in the very dilute HCl.
I tried to filter it and it totally clogged the filter, after 3 hours it still wasn't done. A large amount of MnO2 passed through the filter, too.
I did a second batch and after boiling, I diluted it with 150ml water and I am letting it stand overnight so that the MnO2 can settle. Tomorrow I'll decant it and let it dry.

I'll be away for a week (starting tomorrow evening) so I can't do any experiments.


aldol - 2-4-2005 at 14:30

I no what you mean about hard to filter
you could try to let it settle out over night and then decant most of the filtrate first then filter.
or use a sintered glass funnell this will help heaps.
can anyone tell me why the sodium bisulphite addition is not contenplated
for the seperation of the aldahyde .
i no the yeilds are a little bit down but gee's it will make the seperation easier


transmuter - 18-4-2005 at 18:57

Thanks Organikum.

Tried your "neograviton" posting & achieved a result. Only a small amount at this stage as I need to to make a small modification to equipement. Will do another run within about a week looking for better results. Used MnO2 from a pottery shop, said it was tech grade. Cheap.

In regards the H2O2 method as per Pat. US 3531519, it makes very small quantities.The concern there seems to be the risk of creating to much benzoic acid. Maybe a hybrid could be developed using H2O2 in place of Mn compounds. Pat. US 780404 & Pat. US 808095 both make the claim that under the conditions perscribed no benzoic acid is formed.

Congratulations CycloKnight you have done a super job & thanks for making your progress available. May try the process at a later stage. One step at a time.
Just a guess but maybe the buildup of your "anodemites" are due to the relatively low current being used as against what is recommended i.e. 2 amps instead of closer to 8.

Organikum - 19-4-2005 at 08:17


Garage Chemist wrote:
I mixed 0,1mol MnO2 with 0,1mol conc. H2SO4, added water until it was a paste

This cannot work when you add water and the method didn´t call for this.

The neogravitron method for sure works and it is the only non-electrolytic method known to me which does so with the MnO2 cement pigment of trade as it is available to me.
I am working on reactivating the sulfate with H2O2 by now, as this is OTC here where I live (no good results up to now).


garage chemist - 19-4-2005 at 08:41

So I have to mix the conc. H2SO4 with the MnO2 and heat it.
The problem is how to mix the two substances- I want to conduct the operation in a round bottom flask to minimize fuming from the H2SO4, but a magnetic stirrer is not able to mix the MnO2 under the H2SO4.
Can I use an excess of H2SO4 to decrease the viscosity of the mix and facilitate mixing?

evil_lurker - 20-4-2005 at 00:17

Swim is working on a new route to Benzaldehyde which is completely OTC from patent US 4,146,582.

Ferrous-Copper Catalyst: Toluene (7.6 g.), water (35 ml.), ferrous sulphate (0.110 g.) heptahydrate, cupric acetate (0.072 g.) and methanol (8 ml.) are placed in a 250 ml. reactor.

Sodium persulphate (47.05 g.) in an aqueous-methanol solution of sodium persulphate is added slowly to the mixture which is maintained at C., in an atmosphere of nitrogen and under agitation.

The organic phase is separated after two hours and the aqueous phase is extracted with ethyl ether.

The combined organic phases are distilled to afford 8.29 g. (95% yield) of very pure benzaldehyde (compared against a pure sample).

If this works it will be sooooo easy. The cupric acetate can be made by reacting a 1:2 molar ratio of dissolved copper sulfate (aka septic line root killer) and sodium bicarbonate. The sodium bicarbonate is dissolved in about 2 liters of water and placed in a 5 gallon bucket. The CuSO4 is dissolved in about 2-3 liters of water and then slooowly poured into the bucket. The stuff is allowed to sit over night while the Copper Carbonate Cu03 precipitates. The next day the stuff is washed with water by filling up the bucket and again allowed to sit. The water is decanted the day after and again washed. After several washes, the Cu03 is then filtered out and a wad about the size of a pancake is placed onto a pizza pan sitting on a hot stove eye. The heat breaks down the Cu03 into copper oxide, Cu0. The resulting finely ground Cu0 is then placed into a stainless steel pot of boiling vinegar. The Cupric Acetate which is formed is thus decanted into a separate dish and then slowly evaporated.

The Iron Sulfate is prepared by again taking CuSO4 and dissolving it in water. Some unsoaped steel wool is placed in the vessel, and the CuS04 is allowed to react. Copper precipitates as metal out of the solution and the iron sulfate is left as a green coloring in the water. The iron sulfate is decanted off and dried similarly to the way the cupric acetate was.

The sodium persulfate is obtained at a pool supply store as a shock treatment. If the sodium persulfate is unavailable, it can possibly be substituted with oxone or potassium persulfate and ajusted for weight.

To make the benzaldehyde, the ingredients are thrown in a pressure cooker large enough to hold many times the original formula. The pressure cooker has been adapted in a manner to take out the pressure relief plumbing to fit it with a paint stirrer, and the safety relief is removed and equipped with a rubber grommet and thermometer. While nitrogen atnosphere would be nice, it probably would not be necessary unless one's goal was to minimize over oxidation of the toluene into benzoic acid.

After the reaction the contents of the pressure cooker are handled according to patent.

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