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frogfot
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toluene --> benzaldehyde
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 http://patft.uspto.gov/netahtml/srchnum.htm
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
(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]
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chemoleo
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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?
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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frogfot
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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  but still that wouldn't
give precise aldehyde content..
Is there any other easy ways to convert benzaldehyde to some crystalline stuff?
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Organikum
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| Quote: |
Is there any other easy ways to convert benzaldehyde to some crystalline stuff?
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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.
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frogfot
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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..
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Marvin
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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?
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Organikum
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Benzaldehyde forms an addition product with ammonia. Check your books Marvin.
If this is a practical method is another question.
ORG
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Marvin
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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.
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frogfot
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| Quote: | 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..
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MnkyBoy
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Was the Tol free of thiotolenes? (Found in comercial grade Tol)? As they will inhibit or hinder the benz. formation.
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frogfot
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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..
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MnkyBoy
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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
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Jedi
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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
----------------------------------------------
PLEASE USE READABLE FONTS IN THE FUTURE. Thank You.
[Edited on 25-7-2004 by vulture]
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Mendeleev
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The process using manganese dioxide and sulfuric acid apparently yields only 14%. However according to this site http://www.faizkaskar.8k.com/processelection.html 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 http://pubs.acs.org/ncw/2003/articles/ja00180a005.pdf reports on the oxidation of benzaldehyde to benzoic acid using cobalt (II) bromide. Perhaps
this process can be adapted to oxidation of toluene.
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Tweenk
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Workaround
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]
And now we add powdered sugar to the previously liquefied chlorine dioxide...
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Mendeleev
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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]
Trogdor was a man. A dragon man. Or maybe just a dragon. . .
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Organikum
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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.
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Zak McKracken
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Is benzaldehyde really that hard to get?
As far as I know it´s not watched.
Please teach me if I´m wrong.
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Polverone
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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.
PGP Key and corresponding e-mail address
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solo
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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 4448 times
It's better to die on your feet, than live on your knees....Emiliano Zapata.
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Zak McKracken
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Wow didn´t know it´s at the same
level as safrole.
However here in europe it´s not hard
to get. Nitroethane seems to be a bigger
problem....
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Organikum
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Some stuff from the-hive and an old patent:
| Quote: |
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!
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| Quote: |
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.
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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?
/ORG
[Edited on 16-1-2005 by Organikum]
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Esplosivo
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Direct oxidation of toluene to benzaldehyde using chromyl chloride
Chromyl chloride (chromium (VI) dichloride dioxide) is a red, fuming, toxic liquid produced as follows in the quotes below.
| Quote: |
... 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. ...
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[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: |
...it 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.
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[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.
Theory guides, experiment decides.
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S.C. Wack
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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.
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phanchem
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In Morrison and Boyd, the organic text I was taught from, the most direct... and probably highest yield route...to 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.
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