Sciencemadness Discussion Board

toluene --> benzaldehyde

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transmuter - 5-5-2005 at 22:03

Did another run with neogravitron method. Used a 25 ltr plastic bucket & fixed a drill with metal stirer over the top. Sealed with a garbage bag. Yield ~ 400mls. :D

Organikum - 6-5-2005 at 03:30

A 25 liter bucket? How much H2SO4 did you use?


garage chemist - 10-5-2005 at 12:39

You may also want to look at this:

At page 236, various methods for the oxidation of toluene to benzaldehyde are described.

transmuter - 13-5-2005 at 00:12

Hey Organikum, sorry for the late reply.

Used 7.8 ltrs of H2SO4 & ~ 3 kg of oxidant. The process appears to use less oxidant than the CycloKnight/US 808095 approach which would be > 5 kg to get the same outcome.

Swim has tried to dream up a suitable diaphram for regeneration of the oxidant but the acid levels hinder using anything to conventional.
Without the ability to regenerate the process would have a relatively high running cost. The "CycloKnight" has a high startup cost but a low running cost (when doing quantity).
One could regenerate enough oxidant with that process to output 1 kg with ~ 100 amps of current. Toroidal transformers are available from electronic component stores & a couple of 500 VA's could be used in parallel which after rectification could provide the 100 amps needed at 4-5 volts. The secondary windings would need to be replaced with less but thicker wire to handle the current.

Swim doesnt have any ideas to help with your H2O2 problem but maybe a different angle may work. US 3531519 does a conversion in small quantities the handicap being the risk of benzoic acid production. Also - Organic Process Research & Development 1998, Vol 2, No 4, 261-269 - converts benzy alcohol to aldehyde + other nunerous oxidations ( incl. THF to GBL ) via H2O2.
Now swim doesnt pretend to have a good background in chemistry but heres some thoughts.
It would appear that the common thread with the manganese methods is a temp. of ~ 50 C & a H2O/H2SO4 ratio of ~ 40/60 creating an environment which minimises benzoic acid formation (an excess of toluene should also help).
If H2O2 was used in leiu of manganese compounds & drip fed into this environment at approx. 2-4/1 mole ratio of oxidant to reactant + ferric sulpate or Br2 as a catalyistn then maybe ........?........?
Swim has no idea whether H2O2 would handle such an environment & evolve O in an orderly fashion or not. If it was viable it would have the advantage of low cost & far smaller oxidant carrier solution being needed i.e. less H2O 7 H2SO4.

Does anyone know a way of converting ethyl nitrite to nitroethane other than the asbestos catalyst method ?

UhhKaipShaltaBlet - 22-6-2005 at 04:39

Is there any straight synth for benzaldehyde from Benzene ? I'm interested in it cause I have good access for benzene ant cheaply.

Sandmeyer - 23-6-2005 at 01:28

There is a paper on oxidation of 3,4,5-trimethoxytoluene to the corresponding aldehyde with Co(OAc)2–Mn(OAc)2 as catalyst.

Kitajima N., Takemura K., Moro-oka Y., Yoshikuni T., Akada M., Tomotaki Y., Taniguchi M., The Selective Liquid-Phase Oxidation of 3,4,5-Trimethoxytoluene to 3,4,5-Trimethoxybenzaldehyde, Bull. Chem. Soc. Jpn., 61(3), 1035–1037 (1988)

S.C. Wack - 11-7-2005 at 18:06

Just a little addition to the Mn acetate/toluene electro-abstracts. Can't believe I missed this before, the reference came from a book. I have a feeling that I've seen this mentioned before:
J. Sci. Ind. Res. (India) 12B, 255-61 (1953)
which is abstracted in CA 47, 12056g (1953).

The book said that the yield of benzaldehyde was 80% and that the electrodes were PbO2. The abstract says Pb and does not mention yield or amount of toluene. It also says that the H2SO4 used was 60%, temp 60-70C, current density 6.8 A/dm2, and the catalyst was Mn2(SO4)3.5H2O (10% by weight, of what it doesn't say) promoted with 1% (mystery weight) Ce(SO4)2. Side products tar and benzoic acid.

Found out today (no previous warnings, signs, etc.) that the library has done away with the cards that non-students buy so that we can use the library photocopiers, which also read university ID's. From now on, only students and staff can use the photocopiers, my non-student ID will not work. The med school library never has allowed non-students to use the computers or check out books, and this is probably coming soon to the main library - and maybe to a "public" university library near you.

benzaldehyde success not easy but high yeild

Ephoton - 23-7-2005 at 00:27

ok were to start.
I would rather go via side chlorination of
toluene then a sommelet reaction of the
benzyl chloride to benzaldehyde.
then I would steam distill the benzaldehyde out of the mixture.

to find exact synthesis info
well ask me and I will post or go to organic sythesis volumes and merk index
I will be hangging around to see what happens to the bees so ask and I will post.

neutrino - 23-7-2005 at 04:35

If you have anything to say (hard to tell with your grammar), please post it in appropriate thread.

enima - 24-7-2005 at 18:20

well the much _easier_ route would be an elb oxidation of toluene using a persulfate salt and a metal catalyst to yield the aldehyde in a 70% yield.

No nasty benzyl chloride, 1 easy step.
A bisulfite adduct could be used for the puritification of the aldehyde as steam distillation is tedious.

But then again who needs benzaldehyde? (those nasty amphetamine chemists thats who).

Benzaldehyde synthesis via phenylalanine

solo - 27-7-2005 at 13:47

Recently Wizard X found this little pearl and made it available over at WD..........solo


Phenylalanine when heated in 5N sodium hydroxide at 110~115° for 5
hours, it decomposes forming benzaldehyde. reported at,

[Edited on 27-7-2005 by solo]

S.C. Wack - 27-7-2005 at 14:11

Yield? Why no Cannizzaro?

trilobite - 27-7-2005 at 14:18

Steam distillation to remove the aldehyde as formed?

Sandmeyer - 27-7-2005 at 14:22

Kornblum is another possibility.

See also: for another method.

[Edited on 27-7-2005 by Sandmeyer]

solo - 27-7-2005 at 14:25

Don't know why this quoted reaction would work since we're starting out with an acid (Phenylalanine)......solo

S.C. Wack - 27-7-2005 at 17:14

solo: My question was, why would the benzaldehyde formed not react with the conc. hydroxide the second that it is formed? There needs to be a little experimental detail here.

solo - 27-7-2005 at 18:58

Sorry , I didn't understand the implied question.......I don't know as you can see the reference was given by a chemist working in a pharmaceutical company.....maybe I'll write him and find out a bit more.......solo

Persulfate oxidations

Antoncho - 22-10-2005 at 10:30

Well bees....

SWIM recently tried that US patent where they speak of oxidazing toluenes with Na2S2O8 with MeOH as a co-colvent and Cu/Fe catalyst.....

Unfortunately, SWIM has no methanol so he tried to sbstitute it for a) AcOH b) DMF c) IPA.

With AcOH, the yield was like 10%, the chief product being benzyl acetate :) That is, as soon as BzOH is produced, it is esterified under the rxn conditions and can no longer oxidize.

With DMF ...... err...... when you mix DMF with persulfate solution, it heats up spontaneously within 10 mins and violently decomposes:o

Same thing happened with IPA - but SWIM decided to try it again adding IPA separately in portions. Yielded only 30%.

It turned out that ALL of the oxidant disappeared from the rxn immediately after addition (tested with acidic KBr) although with MeOH it's supposed to last for 2 hrs more.

EtOH seems not to bee an option since upon contact with persulfate it produces acetaldehyde at once.

That is, all in all, it looks promising (i.e., don't mind the NH4/Na difference, i assure you), but methanol is the only solv't that could work.

It;s heavily controlled in Russia and no matter how hard a bee tries, he can't get his hands on any. But i assume you guys don't have that problem, do you?

Then i encourage you to give it a try. It's going to work.


[Edited on 22-10-2005 by Antoncho]

garage chemist - 22-10-2005 at 11:26

How about ethanol instead of methanol? That should be considerably easier to acquire in Russia (distillation from Vodka?). :P
Interesting thing is that in germany you can buy all the benzaldehyde you'd ever want from chemical suppliers. It's non- regulated and non- scheduled here. Are things so different in Russia?

[Edited on 22-10-2005 by garage chemist]

Antoncho - 22-10-2005 at 11:52

Ahem.... read my post carefully. I mentioned ethanol.

garage chemist - 22-10-2005 at 13:24

Ah, sorry. Didn't read carefully enough.
But very strange that methanol isn't oxidised while ethanol is. Those alcohols are very similar in their behaviour towards oxidisers!
Maybe only a very small part of the ethanol is oxidised to acetaldehyde while the rest can still work as a solvent? Acetaldehyde has a very strong smell, even very small amounts give the mixture the characteristic apple- like smell.

Antoncho - 22-10-2005 at 20:22

I'd say it's not that strange, those alcohols are NOT very similar in their manner of beehaviour towards oxidants: MeOH is much more resistant (being much more "electron-hungry";).

Anyway, the main point is - there's nothing to bee _talking_ about here - we won't know until someone tries this. The rest of the dicussion is useless crap ;)

If anyone wishes, i can post a write-up of SWIM's own experience, so that may bee of help.

frogfot - 24-10-2005 at 10:33

Any idea on how one could prevent the runaway (mentioned on synthetikal) of this persulfate oxidation?
I asked the same question on synthetikal without any luck...

IPN - 24-10-2005 at 10:40

Posted at Synthetikal by IndoleAmine:


Just wanted to mention that Na2S2O8 oxidations of toluene behave really strange, seen from a kinetic point of view: a 5 mol persulfate oxidation of toluene seemed to run nicely, until the chemist decided to intetionally crank up the heat control from 65°C to 80°C after having added all the persulfate solution over the course of 2.5 hours (he really thought it would be a good idea). Result was a really incontrollable exothermic rxn that kicked in suddenly as a certain temp. threshold was reached, resulting in a giant "whooosh" sound and maybe 3-4 liters of boiling persulfate/toluene/MeOH/BzOH/BzCHO/water solution were shot to the ceiling in an arm-thick fountain,in a matter of 10-20 seconds (a 29/32 stopper was blown off too, and the fountain actually spit out of the condenser AND one side neck too - frightening when you consider the rxn vessel nominal volume of 5L..)

--Conclusion: better partition the Na2S2O8 solution into two equal parts when doing large scale oxidations - since the rxn proceeds via an OH intermediate anyway, this means that you first make BzOH and then oxidize further to BzCHO in two steps. Also make sure to heat to at least 75°C BEFORE dripping in any oxidant. Hopefully the rxn can be controlled better this way...

I have tried this procedure as well but only got a very low yeild. Probably kept the persulfate solution (MeOH/H2O) too long before using.. :(

bio2 - 26-10-2005 at 01:25

...Any idea on how one could prevent the runaway (mentioned on synthetikal) of this persulfate oxidation? .....

Persalts undergo rapid decomposition at a certain temp and more slowly in contact with moisture. Alcohol also decomposes pesulfate.

There are two ways to prevent an uncontrolled reaction which work with perborate (decomp ca 65deg). Also if the Oxygen escapes rather than reacts yields will be low.

The problem is an induction period which becomes uncontrollable if too much persalt decomposes at once. The perborate after say about 2moles needs to be added in portions at the rate that sustains the desired temperature with adequate cooling. Running cooler and longer works well with perborate with only tap water cooling needed.

The other method is as indoleamine indicated and I do know that this procedure works per the patent although the 90% plus yields may be exagerated. If the reaction mix is heated to the decomposition temp before any persalt is added then there is no induction period and with portionwise addition it's easy to control
the temp. Just remove the heat after it kicks in and place in a water bath with a bucket of ice available to toss in a little at a time.

The cooler, longer method works better for more sensitive compounds and less excess is needed due to minimized O losses.

With a little practice you can fine tune your technique using the method which suits the optimum temperature for your reaction.

Mendeleev - 13-11-2005 at 18:03

Hello forumites, i've been gone for a while but i'm in college now and taking a bunch of interesting chemistry classes and I remembered the good ole forum. Anyway back to benzaldehyde, I found pretty interesting and easy looking procedure for producing benzaldehyde, in Rhodium's archive.

You need benzyl alcohol, DMSO, and aqueous 48% HBr. Now benzyl alcohol isn't exactly toluene, but if you can get that from toluene or just get straight up benzyl alcohol(photo supply). I'm not at my computer so I can't pull up any references at the moment, but the procedure they gave used 550 mg benzyl alcohol in 5 mL DMSO and I think a 3:1 ratio of benzyl alcohol:HBr.

The procedure is pretty straight forward, throw all those reactants in a flask, heat to 100 C for 3 hours, extract with your solvent of choice probaby DCM or ether and distill. The procedure works with substituted benzaldehydes and gives very good yields. The yield they gave from plain benzyl alcohol was 95% or something like 533 mg benzaldehyde from 550 mg benzyl alcohol.

DMSO can be bought OTC, it penetrates skin and whatever you dissolve it will get absorbed into your blood stream so it has veterinary applications(horse liniment) and you could probably find it at petsmart or if not I know for a fact that they have it or used to have it at the tractor supply co. HBr from H2SO4 and pool brominating tablets.

I'll post more details and references next time I pull up the file.

[Edited on 14-11-2005 by Mendeleev]

evil_lurker - 14-11-2005 at 03:24

I just had an idea... why not use bromine instead of chlorine in a photo-cataylized halogenation of toluene?

Bromine is liquid at room temps... brominating toluene would be as simple as pouring it in a flask along with some toluene in the correct proportions, setting the flask out in the sun and turning on the magnetic stirrer.

If one wanted, they could then pump in chlorine gas in the dark, which should displace the bromine and form benzyl/benzal chloride.

The bromine could be caught in water and recycled for later use.

Mendeleev - 15-11-2005 at 10:05

That could probably work but you would probably need some sort of catalyst because the bromine radical isn't as reactive as the chlorine radical.

garage chemist - 15-11-2005 at 10:18

An advantage of bromine is that benzotribromide cannot be formed. So you get nearly quantitative yields of benzal bromide when using a stochiometric amount of bromine (don't forget that half of the bromine is evolved as HBr!).
C6H5-CH3 + 2 Br2 -----> C6H5-CHBr2 + 2 HBr
No special initiators are needed, just slowly add the bromine to refluxing toluene irradiated with bright light.

The disadvantage of bromine is that formation of ringbrominated derivatives is promoted, because the reaction will take longer and cannot be made as hot as the reaction with chlorine (think about the boiling point of bromine).
So the produced benzaldehyde would have to be fractionated thoroughly in order to seperate bromobenzaldehyde.
It is also crucial that the toluene be distilled before use! Any iron contamination will totally screw up the reaction.

For industry, bromine is too expensive, so only methods using chlorine have been used.

But in the laboratory, bromine has the very important advantage of convenience.
All the reagents are liquid, and can be mixed in every desired proportions.
The ringbrominated byproducts can be seperated by fractional distillation, this step would be needed with chlorine too because of the formation of benzotrichloride.

In the lab, bromine is the better choice.

[Edited on 15-11-2005 by garage chemist]

S.C. Wack - 15-11-2005 at 12:06

There are of course a jillion ways to do things...they all have some disadvantage or other...even in the dark

S.C. Wack - 23-11-2005 at 19:55

I've finally gotten around to photocopying the 100 year old French Rec. trav. articles mentioned in the above JACS article, just because I can. In the unlikely event that anyone else wants to see them...

chemoleo - 23-11-2005 at 20:45

SC Wack, don't be discouraged, don't be frustrated. Your efforts are truly noted (and I am not just speaking for myself).
You don't have the 'bibliomaster' title for no reason'. :P
Although this may be in French, I'll always know, if I am ever to run into difficulties of making benzaldehyde from toluene (via bromination), the article you scanned will be one to check; presumably the same for many others here.
Although of course I'd first produce it from benzoylalcohol and K2Cr2O7 :)
Seriously, keep up the good work. Not everyone may appreciate/need it, but still, it doesn't mean it's a waste of time.
The sheer broadness of this forum is what I like about it. Any language, any noteworthy procedure is worth diamonds as long as it works, regardless the language or intention.

Furthermore, I am sure some people are willing to translate if that is required.

Many thanks, and regards.

CherrieBaby - 17-2-2006 at 11:31

Aromatic Aldehydes Via Catalytic Oxidation
R.A. Sheldon, N. de Heij, Andeno B.V.
Summary: The various methods for the oxidation of substituted toluenes to the corresponding benzaldehydes, e.g. autoxidation, catalytic oxygen transfer, electro(catalytic) oxidation and oxidative bromination, are reviewed and evaluated. The cobalt catalyzed autoxidation of para-cresol, in methanolic sodium hydroxide solution at 60°C, is discussed in detail. Under optimal conditions para-hydroxybenzaldehyde is obtained in ca. 90% selectivity at 95% para-cresol conversion.

From: W. Ando and Y. Moro-oka (Eds),
The Role of Oxygen in Chemistry and Biochemistry, Proceedings of an International Symposium on Activation of Dioxygen and Homogeneous Catalytic Oxidations, Tsukuba, Japan, 12-16 July 1987 Studies in Organic Chemistry, Volume 33, pp. 243-256, 1988

Attachment:,243-56(1988).djvu (88kB)
This file has been downloaded 1256 times

Phel - 21-2-2006 at 17:08

While browsing for a journal request for Sandmeyer I found this:

Unusual reactivity of peroxo vanadium complex for catalytic oxidation of aralkenes to benzaldehydes selectively (>99%) in conjunction with aqueous H2O2 as an oxidant is described here for the first time.

Don't know if it's been up before.

[Edited on 22-2-2006 by Phel]

Attachment: Peroxo_vanadium_cat_for_sel_ox_of_aralkenes_to_BzCHO.pdf (162kB)
This file has been downloaded 1582 times

styrene -> benzaldehyde

Flip - 1-3-2006 at 21:28

You could always start with styrene and use ozonolysis or just treatment with acidic KMnO4.

groaner - 8-3-2006 at 20:18

Toluene Trouble

After reading CycloKnights success using the patent 808095/UF method, swim was all fired up with enthusiasm. Swim developed a setup on a slightly less than 1/4 scale of the original patent. The power supply was homemade & delivered ~60 amps. A washing machine motor was used via pulleys to drive a stirer.

Charging the solution worked well & the color turned from a whitish yellow to a very dark red.

On adding the toluene (excess was used) it took 24 + hrs for the solution to loose color. The product was extracted & turned out to be mostly benzoic acid.

Later swim made more oxidant & tried again copying CycloKnights volumein a beaker. There was no benz smell at least for 1/2 an hr & then it was only faint. After 2 hrs swim gave up.

After procurring a small quantity of benzyl alcohol (20 ml), on addition to 200ml of oxidant the smell of benz was almost immediate. So obviously the oxidant is ok.

All inputs used were tech grade including the toluene which according to the supplier was 98.6% pure. Could it be that the toluene in oz is contaminated, perhaps the other 1.4% is thiotolenes or thiophenes & inhibiting the oxidation process.

Swim would be grateful for any help.

bio2 - 9-3-2006 at 04:41

You really need to give more details on the reaction parameters such as electrode material, current density, temperature, faradays passed and etc.

PhCOOH being a two oxygen reaction versus the aldehyde
being only one it seems that somehow you overoxidized the substrate.

Also always a very wise thing to do when doing a new (to you) reaction is using a small scaled say 250ml beaker with everything proportional to the 72 liter tank you will eventually use. Saves a lot of headaches and wastes
few chemicals when something goes wrong. Remember
Murphy's First Law?

groaner - 13-3-2006 at 22:12

You are certainly right there bio2. Murphy is always lurking around the corner.

Swim followed the patent (808095) in most areas, an outer anode & an inner cathode plus a central stirer. The temp used was 50 C +/- 3. The oxidant was charged with 6000/4.3 amp hrs i.e. 62 amps for 22 1/2 hrs. Anode & cathode were copperised lead sheet which is used for flashing in building construction, with the cathode being full of holes drilled out with a hole saw as against using rods, for more stability when stiring. current density at the anode was ~2.5 amps per sq. decimeter.

The original patent says the reaction was complete after 2 to 3 hrs. Regards CycloKnight, one he did took about an hour.

Its as though the oxidant is able to convert the benz to benzoic acid easier than from toluene to benz.

Douchermann - 21-3-2006 at 17:50

I don't know if this was discussed in this thread or not, but
What about turning aniline to benzaldehyde?

The anline can be synthesized, formaldehyde can be bought, along with hydroxylamine

S.C. Wack - 9-4-2006 at 20:51

More alkane oxidations, mostly Mn, just for hahas.

Without electricity-

With (illustrated for anisaldehyde, but a bit different, so)-

Madandcrazy - 15-4-2006 at 07:34

Nice syntheses on

I think benzahdehyde can be prepared by many ways.

phenylcarbinol (benzyl alcohol)

chlorination of toluene to benzalchloride

or maybe chloromethanol is prepared by methanol and HCl ;)
and the chloromethanol is threathed with Clorox bleach and NaOH solution to bezaldehyde.

[Edited on 15-4-2006 by Madandcrazy]

youngOne - 20-4-2006 at 22:14

Could it be that the toluene in oz is contaminated.

Have had many reports of a residue in evaperation dishes in labgrade and service station sources.

Maja - 25-4-2006 at 04:04

Originally posted by Madandcrazy
Nice syntheses on

I think benzahdehyde can be prepared by many ways.

phenylcarbinol (benzyl alcohol)

chlorination of toluene to benzalchloride

or maybe chloromethanol is prepared by methanol and HCl ;)
and the chloromethanol is threathed with Clorox bleach and NaOH solution to bezaldehyde.

[Edited on 15-4-2006 by Madandcrazy]

How hard to prepare CH3Cl ? And I looked at chloromethane msds... It's EVIL ! Look :

Stable. May react violently or explosively with interhalogens, magnesium, zinc, potassium, sodium or their alloys. Incompatible with natural rubber and neoprene composites, but does not attack PVA. Highly flammable. May decompose upon exposure to moist air or water. (So ... HCl must be dried)

Toxic by inhalation - gas is readily absorbed, but very slowly removed from the body. Irritant. Mutagen. Possible carcinogen. Human mutagenic data. May cause systemic effects. Possible teratogen. Gas can be absorbed through the skin.

CycloKnight - 2-5-2006 at 00:40

Originally posted by groaner
You are certainly right there bio2. Murphy is always lurking around the corner.

Swim followed the patent (808095) in most areas, an outer anode & an inner cathode plus a central stirer. The temp used was 50 C +/- 3. The oxidant was charged with 6000/4.3 amp hrs i.e. 62 amps for 22 1/2 hrs. Anode & cathode were copperised lead sheet which is used for flashing in building construction, with the cathode being full of holes drilled out with a hole saw as against using rods, for more stability when stiring. current density at the anode was ~2.5 amps per sq. decimeter.

The original patent says the reaction was complete after 2 to 3 hrs. Regards CycloKnight, one he did took about an hour.

Its as though the oxidant is able to convert the benz to benzoic acid easier than from toluene to benz.

It might be worth having a closer look at the exact acid concentration you are using. If there is much deviation from the stated values, then it could easily have a dramatic effect on the aldehyde yield, with benzoic acid being the main side-product. I ended up producing large quantities of benzoic acid before I realised that I simply needed to adjust the acid concentration for much better results.

Any other Route

technologist - 6-6-2006 at 01:54

May be an Stupid Question?
Can I make it using Benzene & some aldehyde or ....May be any other route leaving Toluene.

Visit my Blog -

Cinnamon oil to benzaldehyde update.

CycloKnight - 6-6-2006 at 11:47

Hi peeps, been off the forum a good while but its good to be back :).

I’ve significantly improved the original batch method I posted last year, what follows is my latest method.

This approach uses the same setup as the last steam distillation variation graphically depicted in in this thread.

Basically, the items used were:
hot plate, pressure cooker steam generator & associated tubing, etc
3L 3-neck RBF & mantle
vigreux column, right angle bend & still head
Vacuum pump & glassware for purfying the final product & recycling unreacted cinnamaldehyde.

chemicals: 2 litres tap water, lecithin, cinnamon oil, NaOH

Essentially, a large reaction vessel and a means of steam & vacuum distilling are all the equipment really required.

Begin by setting up all equipment, add 2 L water & ~1.5g lecithin.
The first variation is to use OTC sodium hydroxide instead of sodium carbonate, simply add the alkali to adjust the pH within the range of 12-13, only small amounts are required.

The second variation is to slowly drip in the cinnamon oil during the course of the reaction, the benzaldehyde being steam distilled as it forms. Begin the addition once the pH adjusted solution has heated to boling temperature and the steam is passing though the solution.

The third variation is to stop the cinnamon oil addition after 5 min, then check the distillate. If benzaldehyde is clearly distilling over, then continue with the addition.
A crude test is to simply taste the steam distillate as it drips into the receiving vessel, if it burns your tongue off, then you're doing well. If it tastes sweet, then significant quantities of cinnamon are being carried over. Should this not change after a short while, then double check the pH !

Provided that the pH is correct and the cinnamaldehyde content is high (70%+) then benzaldehyde laden distillate should start collecting almost immediately after the addition has begun.
However, if it is not, wait for the benzadehyde to start collecting, THEN continue with the addition. This prevents unnecessary amounts of cinnamaldehyde being steam distilled at the start of the process, which is a serious problem with the old batch mode reaction.

Note that by slowly dripping the cinnamon oil instead of adding it all at once to the reaction mix, single run conversion is increased by 20-30%.

Ensure the rate of cinnamon oil drip rate is approximately equivalent to the quantity of oil being steam distilled, thus maintaining high dilution in the reaction mixture.

After 300 to 500 ml of cinnamon oil had been added, the drip rate is stopped and the steam distillation continued until all the aldehyde has been steam distilled from the reaction mix. If using less than 2L of water, then adjust proportionally to maintain the same dilution. At this point, dump the mix and replace with clean pH adusted water with at least ~1.5g lecithin.
This step removes tar and other junk that slows down the reaction and reduces benzaldehyde production. Significantly reduced tar formation will also result from periodically carrying out this step (very imporant if high yields are desired).
Also note that with this method, the pH tends to slowly drop over time during the course of the steam distillation, so check the pH every couple hours, and top up with NaOH if and when required. Its preferable to simply add small amounts concentrated NaOH solution when topping up, using a dropper makes the alkali addition much simpler since NaOH pellets will rapidly collect moisture and stick to the sides of the reaction vessel.

Efficiency is further improved if the steam distillate (after oil separation) is also extracted with DCM, though this isn't absolutely necessary.

Once the the product oil is pooled, vacuum distillation will remove the benzaldehyde - no need to vacuum distill the recycle cinnamon aldehyde, just drip it into the steam distillation vessel, just as with the cinnamon oil feed. Expect the quantity of unreacted cinnamon aldehyde to be circa 25%, but if the reaction mix was kept clean during the process then it may be considerably less. The benzaldehyde distillate is clear, & much purer than the original solvent extraction method that doesn't employ the steam distillation. Give the batch solvent extraction a rest folks, use the steam distillation variation if producing benzaldehyde from cinnamon oil!
Far, far less work.

Using the above approach, overall molar conversion to benzdehyde is at least 80%.

I’ve managed higher conversion efficiencies (~90%), but the reaction efficiency is subject to variation according to varying reaction conditions, i.e. feed rate, reaction mix volume (i.e. dilution), and the quantity of cinnamon oil fed to the reaction mix before changing the solution. >80% seems to be a realistic overall figure.

Remember to keep the reaction mix free of tar & cinnamon oil impurities as much as possible to give consistent high yields.

If dripping the aldehyde into the mixture isn't practical for any reason, you can periodically add the cinnamon oil in small batches, say 20-50 ml at a time to give good conversion, but expect a little more cinnamonaldehyde to distill over.

scientistfromdarkness - 3-7-2006 at 22:43

Why are you guys making so much dust around benzaldehyde ? The general rule in chemistry synthesis is to BUY everything you can. You will loose a lot of money, time and patience in order to prepare stupid benzaldehyde. In Croatia it is very cheap: 30$ per litre, p.a. purity.

Best regards,

evil_lurker - 3-7-2006 at 22:57

Depending on where your at its not as simple as being able to call up a chemical company and have them send it to your doorstep.

In the USA and several other countries it is considered a controlled substance because of its potential use as a drug precursor... phenylpropylamine, amphetamine, methamphetamine, and ephedrine can all be synthesized with benzaldehyde as one of the precursors.

Attempting to purchase it in the USA will result in law enforcement kicking your door down and searching your premises, and if they don't like what they find you can be arrested and sent to jail for a very long time.

JohnWW - 4-7-2006 at 01:00

That proves that Croatians have more sense than Americans! Besides, benzaldehyde, which is the principal constituent of artificial almond essence, has a perfectly legitimate use as almond food flavoring, being often used in the sugar "icing" on cakes.

len - 22-7-2006 at 22:41

John, is benzaldehyde still legal in NZ? For long? In Queensland and WA its now on the same schedule together with such notables as lysergic acid and P2P. That is 15 years maximum for illegal possession of more than 0.1g! Presumably amateur experimentation is included. The list also includes such obviously drug related chemicals as chromic acid, alkali metals, and magnesium. Here were only allowed to dig ore, and you to tend sheep;)

[Edited on 23-7-2006 by len]

[Edited on 23-7-2006 by len]

Organikum - 23-7-2006 at 06:22

CycloKnight, I don´t understand why you use a not even insulated Vigreux in your steamdistillation setup as shown here:

May it have some merits when you directly distill the formed benzaldehyde out albeit I doubt it when the cinnamaldehyde is added through a tube or similar, but in a setup which is just steaming out a compound as in the first procedure the use of a Vigreux makes just no sense, it actually beats the purpose.

In all my steamdistillations I used a as short way as any possible, only with a splashhead so necessary and also then I insulated everything up to over the bend.
That makes it much quicker. IIRC benzaldehyde should come over with water in a ratio of 1:3 with forced steam even 1:1.

Besides this, thats great work, I will post a variation of it the next days.


[Edited on 23-7-2006 by Organikum]

Organikum - 31-7-2006 at 08:00

Ok here we go:

- 800ml water
- 30g sodium carbonate
- 100ml synthetic cassia oil (which I hope to be basically pure cinnamaldehyde)
- 3,6g lecithin as surfactant
- some broken pieces of a clay pot as boiling stones

Now under reflux.

I use the one pot setup for I want to try in the second run to collect the formed acetaldehyde and for technical/equipment purposes.

Sorry no pictures I lent my camera to my girl.

The mixture took a yellow color and is boiling nicely. Foaming is not so bad, no splashhead needed. Dark blobs of oil are visible dancing around in the brew what makes me think I could have added more lecithin.

Or maybe not. Steamdistillation produces excessive foaming even with addition of cooking oil (more oil?).
Distillate comes over containing at least 30% oil, which now at start looks and smells like benzaldehyde.
I wish I could push the distillation more - I am frigging tired. But it´s my own fault, a Erlenmeyer almost full is for sure not the right thing to use. Jawn. Next time....

[Edited on 1-8-2006 by Organikum]

Organikum - 31-7-2006 at 10:45

And a question: As condensing actealdehyde is tedious wouldn´t bubbling the formed acetaldehyde into a solution of sodium bicarbonate form the addition product? Would bubbling through ammonia water form acteldehyde ammonia? Would bubbling through a solution of hydroxylamine form the oxime?
Which of the three methods might be preferred/most practical?

Would be the formation of paraldehyde by bubbling the acetaldehyde into hot HCl/H2SO4 a viable option?

I will of course search myself for answers but I would also appreciate if somebody would be able to talk from experience.


Addon: Acetaldehyde ammonia would require anhydrous ammonia in ether as it seems and is therefor no real option.

[Edited on 31-7-2006 by Organikum]

Organikum - 31-7-2006 at 14:44

Another question: This article "The Oxidation of Cinnamaldehyde with Alkaline Hydrogen Peroxide.pdf" as requested by Wack and posted by Solo here, suggests that the addition of H2O2 transforms all cinnamaldehyde to either benzaldehyde or the epoxide which slowly degrades to benzaldehyde itself. The article shows that after a very short time all cinnamaldehyde is transformed. Sadly I couldn´t find the actual reaction parameters, something like "the necessary amounts of NaOH and H2O2 to reach the wanted conditions are added" doesn´t really help.

Anybody an idea how much H2O2 and NaOH to add and is the epoxide volantile with steam or not?
If not benzaldehyde could be distilled out of the reaction and the epoxide should degrade and so on.
Otherwise I couldn´t find how long it takes until all the epoxide is degraded. Maybe I just overlooked this on first sight.

This might be a nice alternative which would only require one steamdistillation if we are lucky without further separation.

Any ideas?

not_important - 31-7-2006 at 19:14

I assume that by 'bicarbonate' you mean 'bisulfate' ? With a strong solution, yes. Same for hydroxylamine, it will go in water.

I'm thinking that the best optin might be catching it in some solvent. The solution might be directly usable for a desired reaction. Or if the solvent choosen is inert enough, acid could be added to form paraldehyde or metaldehyde .

Organikum - 31-7-2006 at 23:56

Not bicarbonate nor bisulfate but sodium bisulfite of course. I apologize it was late last night.

not_important - 1-8-2006 at 00:03

And it was for me, I too meant bisulfite - the anion whose name can not be typed.

Organikum - 1-8-2006 at 02:58

Update on the running reaction:

After some hours I had to stop the steamdistillation for it got to late and I had to go to bed. The distillate which had come over - not very much - was waterclear with a nice clear blob on the bottom. But the distillation seemed to have slowed down over time and I got the impression that only a part of the cinnamaldehyde got converted into benzaldehyde and so I added some NaOH before restarting the steamdistillation this morning.
Much more distillate started to come over it is turbid, clear blobs at the bottom are slightly yellowish now.

So I ask myself: Does NaOH on the one side speed things up but on the other side produce a decent amount of sideproducts?
Or did I just fuck up something and if - what? Did the NaOH react with the frigging cooking oil I had to add to reduce foaming? Darn!

Suggestions for other anti-foaming agents? Paraffine/Stearine maybe? Or just some margarine or butter?

Addon: The yellow discoloration and the turbidity come most probably from mist (caused by the foaming) driven over. For I cannot fix this in this run now I decided to ignore the issue, to drive the shit forcibly over and to do another steamdistillation on the product. Anything else would be endless.
In the next run I will obmit the splashhead and instead insert some glasswool into the Claisen which hopefully suffices as demister.

Addon2: Well sometimes I should listen to what I tell others and whats written in the basic literature ;)
A second batch is in steamdistillation and it runs quick and easy just from a 2l Erlenmeyer/Claisen/Liebig combo. No splashhead, no oil, no glasswool. Ehem. Steamdistillation, as short way as possible as large diameter as possible. I guess a retort would be perfect. Or something like these irish whiskey stills.

[Edited on 2-8-2006 by Organikum]

Organikum - 4-8-2006 at 08:25

First results from the cinnamaldehyde to benzaldehyde:

- It seems that the conversion was not more then 30% with sodium carbonate.
- Cinnamaldehyde is not easily steamdistilled without forced steam (whats not so bad as it is a easy means of separation)
- Too much lecithin causes excessive foaming and I am not sure if it is actually necessary in the sodium carbonate method as after my understanding the amount of carbonate used is not mainly for basifying but for density adjustment)


not_important - 5-8-2006 at 00:18

Spa supply might get you anti-foaming agents.

Why lecithin as a surfactant? It's a rather complex mix, and not all that stable. Would a low foam sulfonate serve?

Might the VO(AC)2 catalysed H2O2 oxidation of styrenes be useful? With yields in the 80% to 98% range, it would seem to be useful. It was listed in this thread back in feb, I believe.

Organikum - 6-8-2006 at 09:22

Lecithin because I got it around the corner and it is named in the patent.

The sodium carbonate method was not so really successful. Now running the second method as described by CycloKnight and this looks better.

On an additional note:
I don´t think it is necessary to do a solvent extraction on the distillate, simple salting out the benzaldehyde/cinnamaldehyde should do. A saturated solution of NaCl has a density of about 1,2 compared to about 1,05 of the oils, thats no problem.


CycloKnight - 11-8-2006 at 02:46

CycloKnight, I don´t understand why you use a not even insulated Vigreux in your steamdistillation setup as shown

The reason is to increase the reflux rate. The rate of steam flow is very high; the stove heating the pressure cooker steam generator is at a maximum. I reckon the steam is only in the column for about 2 seconds before reaching the condenser, therefore the reflux rate is actually extremely low.
Without forced steam however, it would be far better to use an insulated column or a very short column.

A couple points...
The steam distillation variation requires forced steam, there is no way boiling will produce sufficient steam without excessive foaming, in the necessary time. Too long of a reaction time will destroy your product and turn it into tar.

Also, remember to check the pH now and again. The pH tends to drift - don't ask me why though !
I'm sure that adding vegetable oil will cause the oil to saponify, but I'm unclear how that will consume the alkali.
My experience is that the alkali is consumed somehow: either it is driven out by the steam or is is reacted in some way. In any case I've always found it necessary to top up with NaOH when necessary (usually after several hours).

Using too much NaOH will produce instant benzaldehyde, but it will produce much tar and kill the efficiency. Its best to measure the pH and maintain it between 12 & 13.

hodges - 28-8-2006 at 14:05

I managed to duplicate a good portion of this experiment on a smaller scale, although my attempt to purify the final product failed.

I reacted 0.3 moles of MnO2 with excess HCl in a hot water bath, leading the evolved Cl2 gas into NaOH solution for disposal. It was interesting to watch the Cl2 bubbling into the NaOH solution, but the bubbles never making it to the top of the solution. They appeared to shrink with a jerky motion. There was no smell of chlorine at all until I opened the flask after the reaction was complete. I filtered out a bit of remaining MnO2 and then precipitated Mn(OH)2 using NaOH solution. I placed the precipitate in a 1 liter plastic bottle, where I washed it 10 times by filling the bottle with water, allowing the precipitate to settle, then squeezing off the water. I then added H2SO4 (drain cleaner) slowly until all the precipitate dissolved. At that point I discovered a small amount of MnO2 still remaining so I filtered that out. I dried solution in an oven. Unfortunately, I had a slight excess of H2SO4, so when the MnSO4 was almost dry it started to fume. I decided to stop at that point, so I was not able to weigh the MnSO4.

I added (NH4)2SO4 (which I had remaining from a reaction I did years ago between household ammonia and drain cleaner). The amount I added was just under half the calculated mass of the MnSO4 (which I had been unable to weigh). I then added an appropriately scaled amount of water followed by H2SO4. I ended up with a brown milky precipitate that looked very similar to the pictures previously posted in this thread.

Using small lead sheets left over from a battery experiment, I ran 2 amps of current through the solution for 5 hours. It quickly turned dark red. I stirred occasionally, although I could see that the bubbles on the cathode were doing a pretty good job of stirring alone.

I poured the now-red solution into a flask and added 5ml of toluene. I placed this in hot water (around 50C). I let it react for about an hour, occasionally stoppering the flask and shaking vigorously.

After an hour, I let the mixture settle. There was still some red color left but this all settled to the bottom, leaving a light yellow solution with a darker yellow product on top. I carefully removed the product with a plastic pipette and placed it into another flask. I ended up with about 4ml of product. The product smelled like cherries, although I could also still detect some toluene odor as well. When I let a drop of it sit in the air, the toluene smell went away after about 20 minutes and the only remaining smell was of cherries. Of course, after a couple hours it started to smell like benzoic acid.

So far, everything seems to have worked just as planned. Then I got the idea to try to purify the product by distillation, since I recently acquired a cheap distiller with heating mantle from E-Bay. Since the distiller has a 500ml flask, I figured I would need more than the 4ml or so of product I ended up with. So recharged the manganese compound by running current through it again. I repeated the process 5 more times over the course of a week. I ended up with about 20ml of dark yellow liquid, which I washed twice with water. My plan was to distill this. I expected any remaining toluene to come over at around 110, followed by benzaldehyde around 180. I was surprised when a clear liquid began distilling over at only 76 degrees. I was even more surprised when I was down to just a few ml of liquid left to distill and the temperature had only risen to 82. I didn't distill the last few ml because I was afraid liquid condensing on the thermometer would drip down and break the flask since there was so little liquid left at the bottom.

I can't figure out what I made. Obviously it was not benzaldehyde. It smells sort of like toluene. Given the very low boiling point I figured maybe I had ended up with benzene. I tried burning a drop of it and it burns with an orange, sooty flame. But it did not freeze even at -20C, whereas benzene should freeze around 5C. The product remaining in the distillation flask also does not smell like benzaldehyde. It has a foul odor, but different from benzoic acid.

Presumably it is necessary to use a vacuum or steam distillation to purify benzaldehyde. But can anyone enlighten me as to what product I actually got using regular distillation? I still have the product, as well as a ml or so of the original (pre-distillation) product.


not_important - 28-8-2006 at 14:28

I'm guessing, based on you not mentioning drying the organics. The boiling point is a bit low for the toluene-water azeotrope, but not too far off. Might be toluene-benzaldahyde-water. Water dissolves a bit in benzaldehyde, and slightly in toluene.

To generate benzene you'd oxidise all the way to benzoic acid and then decarboylate than, not really likely.

Try drying the liquid with (sodium or magnesium) sulfate; then measure the boiling point in a test tube, or try distilling again. And maybe pick up a 50 or 100 ml distilling flask, 500 is a little large for that amount of liquid.

Freezing points don't mean much unless you have a fairly pure compound, even a few percent of something else can greatly reduce the melting/freezing point. Boiling oints have similar problems if the several componentes co-distill, which is what makes steam distillation work.

hodges - 29-8-2006 at 16:54

I tried drying and re-distilling the previously distilled product. I added several grams of anhydrous MgSO4 (dried in an oven), shook, waited 10 minutes, then poured off and re-distilled the liquid. It all distilled over at 76 degrees.

I took the re-distilled product and added some 3A molecular sieve to it. No significant heat appeared to be evolved. I poured off the liquid and distilled a 3rd time. This time everything distilled over between 75 and 76 degrees. I added water to the molecular sieve I had used and it immediately heated up noticably. So I'm pretty sure my product was dry.

I then tried distilling some "99% toluene" from the same bottle as I used for my original reactions. It all distilled over at 84 degrees. When I distill pure water, it comes over at between 99 and 100 degrees so I know my thermometer is not far off.


not_important - 29-8-2006 at 21:53

Well, toluene boils at 110.6 C, so you've a problem there. Benzene is 80.1, a bit low but care is needed when doing boiling points. If you're not getting plenty of condensation on the thermometer bulb, or you are using it at the wrong immersion, the reading will be off. Try putting some of that toluene in a tall test tube or smallish flask, heat it in a waterbath so that the organic boils but refluxs in the tube/flask (this means that the water can't cover the upper portion of the tube). Stick the thermometer in so the bulb has condensed liquid running down it and take a reading.

Good job on checking for water and that your process had removed it, nicely methodical.

hodges - 30-8-2006 at 14:12

Thanks, not_important. I need to do some more measurements with my toluene. Since this is off the original topic, I will start another topic on distillation in Beginnings (if one does not already exits) shortly.


2bob - 31-8-2006 at 23:28

Benzaldehyde is produced by the following 'streckert oxidation':

Ca(OCl)2 Chlorination of Toluene [2]

"Toluene and dry Calcium Hypochlorite (bleaching powder) are heated together to 105°C in the abscence of other reagents. This avoids by-product formation. If equal amtounts are used, volume-wise, there is a high conversion. If more bleaching powder is used, the conversion is more robust, but contaminants such as benzal chloride and benzotrichloride are formed [...]"

hell-fire - 10-9-2006 at 15:21

As we all know benzaldehyde can be synthed from methylbenzene but what about dimethylbenzene? Methylbenzene is getting harder to find OTC and dimethylbenzene is basically free for some people.

not_important - 20-9-2006 at 07:53

Originally posted by hell-fire
As we all know benzaldehyde can be synthed from methylbenzene but what about dimethylbenzene? Methylbenzene is getting harder to find OTC and dimethylbenzene is basically free for some people.

Not too easy - you need to chop off one of the methyls without affecting the other or also oxidising it just far enough, which as this thread shows isn't easy.

I think the best solution to the problem is to slowly fractionate xylenes containg AlCl3 or AlBr3. Some intermolecular transalkylation occurs, giving mono- and poly- methylbenzenes. The mono- is distilled off, using a good fractionating column, while the poly concentrates in the pot. After that it's back to converting toluene.

not_important - 20-9-2006 at 08:06

This doesn't seem to have appeared before, and might be interesting. I was researching heteropolyacids for other reasons, and ran into the following


Alkylarenes were catalytically and selectively oxidized to the corresponding benzylic acetates and carbonyl products by nitrate salts in acetic acid in the presence of Keggin type molybdenum-based heteropolyacids, H(3+)(x)()PV(x)()Mo(12)(-)(x)()O(40) (x = 0-2). H(5)PV(2)Mo(10)O(40) was especially effective. For methylarenes there was no over-oxidation to the carboxylic acid contrary to what was observed for nitric acid as oxidant. The conversion to the aldehyde/ketone could be increased by the addition of water to the reaction mixture.
The ArCHR(*) and NO(2) radical species undergo heterocoupling to yield a benzylic nitrite, which undergoes hydrolysis or acetolysis and subsequent reactions to yield benzylic acetates and corresponding aldehydes or ketones as final products.

DOI: 10.1021/ja031710i
J Am Chem Soc. 2004 May 26;126(20):6356-62.

Oxidation of alkylarenes by nitrate catalyzed by polyoxophosphomolybdates: synthetic applications and mechanistic insights.

Khenkin AM, Neumann R.

hell-fire - 27-9-2006 at 23:39

I first thought about getting benzene from xylene then converting to benzyl chloride then using the benzyl chloride to synth benzaldehyde.

Here's some informaton i've put together thanks to rhodium and Vogel, this is nont my work.

Benzene can be obtained from dimethylbenzene by heating with AlCl3.

Synthesis of benzal chloride.
Into a 1-litre three-necked flask, equipped with a reflux (double surface) condenser, a mechanical stirrer (preferably of the Hershberg type, and a gas lead-in tube extending to near the bottom of the flask, place 200 g (227 ml) of dry benzene, 20g of paraformaldehyde (40% Formalin may also be used; the proportions are then 200g of benzene, 38g of 40% formalin and 50g of pulverized zinc chloride.) and 20 g of finely powdered anhydrous zinc chloride. Support the flask on a water bath so arranged that the level of the water in it is about the same height as the reaction. Heat the bath to 60°C and pass in (through an intervening empty wash bottle) a rapid stream of hydrogen chloride until no more gas is absorbed (about 20 minutes): allow to cool. Transfer the reaction mixture to a separatory funnel, wash it successively with two 50 ml. portions of cold water, two 50 ml. portions of saturated sodium bicarbonate solution (It is essential to remove all the zinc salts in the washing process, otherwise the product largely resinifies during the distillation.) and finally with 20 ml. of water. Dry with anhydrous calcium chloride or magnesium sulfate, and distill under normal pressure from a Claisen flask with fractionating side arm until the temperature rises to 100-110°C. After cooling somewhat, distill under reduced pressure and collect the benzyl chloride at 63-65°C at 12 mmHg. The yield is 70 g. Some (about 4 g.) p-xylylene dichloride, m.p. 100°, and a small amount of diphenylmethane are present in the residue in the flask.

Synthesis of benzaldehyde.
Place 45 g. (43 ml.) of benzal chloride (Section IV,22), 250 ml. of water
and 75 g. of precipitated calcium carbonate (1) in a 500 ml. roundbottomed
flask fitted with a reflux condenser, and heat the mixture for
4 hours in an oil bath maintained at 130°. It is advantageous to pass
a current of carbon dioxide through the apparatus. Filter off the calcium
salts, and distil the filtrate in steam (Fig. //, 40, 1) until no more oil
passes over (2). Separate the benzaldehyde from the steam distillate by
two extractions with small volumes of ether, distil off most of the ether
on a water bath, and transfer the residual benzaldehyde to a wide-mouthed
bottle or flask. Add excess of a concentrated solution of sodium bisulphite
in portions with stirring or shaking : stopper the vessel and shake
vigorously until the odour of benzaldehyde can no longer be detected.
Filter the paste of the benzaldehyde bisulphite compound at the pump
and wash it with a little ether. Immediately transfer the bisulphite
compound to a separatory funnel and decompose it with a slight excess
of sodium carbonate solution. Extract the liberated benzaldehyde with
ether, wash the ethereal extract successively with sodium carbonate
solution and water, dry with anhydrous magnesium sulphate or calcium
chloride. Remove the ether on a water bath using the apparatus shown
in Fig. //, 13, 4, and distil the residue. Collect the benzaldehyde at
178-180°. The yield is 25 g.
(1) A little iron powder or ferric benzoate can be used as a catalyst.
(2) If the clear filtrate in the flask is strongly acidified with concentrated hydrochloric
acid and then allowed to cool, benzoic acid (a by-product of the reaction)
separates in glistening plates. Filter at the pump, and recrystallise from hot water;
m.p. 121°.

solo - 7-10-2006 at 03:47

Since this is a very long thread and I haven't the time to read it all and at the risk of being redundant, I was researching I ran into someone's study on gas phase production of benzaldehyde from toluene, I thought this might be of interest...............solo

evil_lurker - 10-10-2006 at 20:57

This should be looked at...

Unfortunatly I don't have access to this document, but according to wikipedia all you need is HBr, H2O2, Toluene, water, and a 40 watt light bulb to crank out 80% yields of benzyl bromide.

And I can't think of the freaking patent to save my life, but I know it exists. You can oxidize the benzyl bromide with common sodium nitrate into benzaldehyde.

Polverone - 10-10-2006 at 23:25

Here's the above paper.

Attachment: h2o2-radical-bromination.pdf (109kB)
This file has been downloaded 7749 times

Ozone - 23-10-2006 at 19:20


Is the trick still to synthesize benzaldehyde from toluene? If it is, I have an oldey-but-goody that has worked well for me in the past.

To a chilled (ice) solution of toluene (or derivative, viz. p-nitrotoluene) and acetic anhydride (1:8 v/v) is added dropwise, sulfuric acid(conc). (~1:1.6 v/v on toluene) This solution is cooled to 0°C (ice). To this is slowly added (do not let the temperature exceed 10°C), with your safety glasses on, chromium trioxide in acetic anhydride (1:4.5 at 2:1 on toluene)--this solution must be prepared slowly and cold or it might run away from you-violently. This should take ~2hr.

What you should have is the benzaldehyde diacetate and a lot of green slop...and acid.

With my stuff I got crystals that I could filter off, then treat with 10% H2SO4 under reflux and then distill off under low vacuum.

The CrO3-AcO2-H2SO4 mixture is known as the Thiele (the same guy as the Thiele melting point apparatus) reagent, and the method I used was taken from

Fieser, L.F. and Fieser, M. (1967). Reagents for Organic Synthesis. John Wiley and Sons, Inc. ISBN 0-471-25875-X, pp. 146.

Undisputably one of the most useful texts arranged for the pragmatic organic chemist.

You can reduce any remaining chrome (VI) with sodium bisulfite (should be OK with the esters, not OK with your aldehyde, viz. in-situ, unless you wish to isolate the water soluble organosulfite, which can be recovered via acidic or alkaline hydrolysis). Do not put the waste down the drain. Chrome salts are nasty for both you and the environment.

I apologize in advance if this one has been previously posted, I checked most of the pages, but the topic was all over the place.



evil_lurker - 23-10-2006 at 23:39

There is only one problem with that... in the USA its actually harder to get acetic anhydride than benzaldehyde.

Ozone - 24-10-2006 at 18:45

Bummer. I can buy acetic anhydride without too much trouble, but, when buying benzaldehyde, I had to write the intended use and sign a form indicating that the chemical was specifically not to be used for the manufacture of drugs or weapons. My boss had to sign it too.

I was using it as a surrogate for phenylacetaldehyde, which was generated via strecker degradation from phenylalanine and glucose. This might be on some interest to someone who wants benzaldehyde.



herbalextractions - 25-10-2006 at 20:07

whats happened to all the pictures? :(

Hilski - 26-10-2006 at 08:37

Originally posted by herbalextractions
whats happened to all the pictures? :(

I can still see them just fine.

Drunkguy - 13-11-2006 at 09:34

I understand that the cassia oil method works because of a retro-aldol. I was just wondering if this only applies to the aldehyde or if the corresponding carboxylic acid can also be used? This is a variation of the Claisen (Ethylacetate + NaOEt + PhCHO), as covered in Vogel p1032. [I know Perkin, Knoevenagel, Reformatsky, Horner/Wadsworth-Emmons, Doebner etc all can be used to get the forward product, although it's a mute point in this post].

Also, on a more theoretical note, is there a way of reducing benzoic acid to PhCHO that is relatively OTC and does not call upon exotic reducing agents?

[Edited on 13-11-2006 by Drunkguy]

Mason_Grand_ANNdrews - 14-11-2006 at 10:34

Great work Organicum, nice equipment setup. More there is
a way of reducing benzoic acid to benzene or the way from
sodium benzoate.

Benzene Extraction

When i`m thinking right, the "Gattermann-Koch" reaction is a
good replacement to make benzaldehyde from benzene
instead of toluenaldehyde. This should be easy with
anhydrous AlCl3 (Friedel-Crafts) to form the intermediate
formyl (C6H5-CHO) and then the aldehyde. I would guess
the synthesis should work when 78 g benzene is combined
with 14,8 g of anhydrous aluminium chloride and 7,5 g
anhydrous copper(II)chloride, the mix is careful heated a
while and then diluted with 500 ml 25% HCl. I don`t
know the crude benzahldehyde can be removed from the
water by a simple distillation ? Might it must separated bevor
distilled above ~179 °C.

Drunkguy - 14-11-2006 at 10:45

My only concern is that the reaction calls on CO(g), that and I dont know what the storage of AlCl3 is like for mothball projects (it's definately not otc).

Nicodem - 14-11-2006 at 15:00

Originally posted by Drunkguy
Also, on a more theoretical note, is there a way of reducing benzoic acid to PhCHO that is relatively OTC and does not call upon exotic reducing agents?

It can be done trough "ketonization" with formic acid (which then becomes "aldehydation" ;) ):

Related patents:
GB382929 (uses Ca salts in a batch process)
GB190411747 (also Ca formates)
(there must be other related patents as well...)

chemoleo - 14-11-2006 at 17:11

I would guess
the synthesis should work when 78 g benzene is combined
with 14,8 g of anhydrous aluminium chloride and 7,5 g
anhydrous copper(II)chloride, the mix is careful heated a
while and then diluted with 500 ml 25% HCl. I don`t
know the crude benzahldehyde can be removed from the
water by a simple distillation ? Might it must separated bevor
distilled above ~179 °C.

Mr Mason, would you like to tell me where your extra carbon comes from?

I think I shall be watching your 'ideas' more closely in the future....

Mason_Grand_ANNdrews - 20-11-2006 at 11:02

I don`t know the correct conditions to the synthesis. A rapidly stirrred
mixture should give the intermediate formyl in
the solution with the carbon monoxide content in the air
and the hydrochloric acid. This should be adequate, when
this not work bubble CO gas through the solution. ;)
Not enough infos are available within the synthesis of
benzene if the formyl is formed by bubbling gently 1 mol of
CO gas into the solution after the HCl is added, the correct
temperatures or how long the synthesis need to complete the process.
I suppose a additional possibility is when the mixture of benzene/aluminium chloride/copper(II)chloride is
stirred between 6 - 10 °C, CO gas (air need longer reaction
time) is bubble into the mixture and over one hour the HCl is
dropped with a funnel into the solution.

[Edited on 20-11-2006 by Mason_Grand_ANNdrews]

[Edited on 20-11-2006 by Mason_Grand_ANNdrews]

[Edited on 21-11-2006 by Mason_Grand_ANNdrews]

Counter_Culture - 28-12-2006 at 18:49

Any suggestions for salvaging acetaldehyde from the cassia oil to benzaldehyde synth when using steam distillation??

If the condenser and reciever are cool enough it would be in the water I assume.

Can they be seperated?

benzaldehyde from toluene

undead_alchemist - 12-1-2007 at 13:12

toluene, water, sodium Chlorite *NaClO2*
reflux, then distill.

Yes, I do know that other compounds are made in the same mix.
but after it sits for a while, I do detect the smell of almonds from it.
Other compounds that may come from the reaction are:
Benzyl Chloride

Nicodem - 13-1-2007 at 04:55

Smell of almonds as a confirmation that you prepared benzaldehyde? You will get that smell even if the reaction mixture contains less than 1% benzaldehyde!
NaClO2 is a general reagent for the oxidation of aldehydes to carboxylic acids so what makes you believe it stops at the aldehyde stage? Have you analysed the product? Any references?

Organikum - 13-1-2007 at 09:31

Originally posted by Counter_Culture
Any suggestions for salvaging acetaldehyde from the cassia oil to benzaldehyde synth when using steam distillation??

If the condenser and reciever are cool enough it would be in the water I assume.

Can they be seperated?
In my rather unsuccessful tries to replicate the cassia oil to benzaldehyde synthesis I have not encountered the typical acetaldehyde smell nor have I been able to collect any distillate at the temperatures acetaldehyde is supposed to come over although the setup was rigged for exactly this purpose. Some benzaldehyde was formed, not very much but anyways.
Thats a bit disturbing as the acetaldehyde smell the same as benzaldehyde smell is already detectable when only traces of the compound are present. The lack of the smell was what alerted me first that something is going really wrong here.
I suspect the acetaldehyde undergoing condensation and that there must be actually some trick not pointed out in the patent to avoid this. US patens are horrible unrelieable if it comes to reproducing them. Well not only US patents, but they are worst IMHO.

[Edited on 13-1-2007 by Organikum]

overoxidisation & aldehyd'ation?

womble - 24-1-2007 at 00:13

It can be done trough "ketonization" with formic acid (which then becomes "aldehydation" ;) ):

This is perhaps the most important patent I have noticed upon this topic. It even describes in some detail the production of the required catalyst(s). In addition to which, it does, somewhat unusually provide a level of detail on the actual reaction sequence.

I assume such a simple reaction should in fact work as well with catchetol based carboxylic acids?

If so, it would appear that the most productive, if not the most elegant route, would in fact be to proceed to over-oxidise past the desired product, without even attempting to stop the reaction, and then to use formic acid (albeit in massive quantities) to 'aldehyde'ise' the product.

The only problem I have is the sheer volume of THF that would be required to perform these reactions at any volume. Surely there must be an alternative solvent?

problem solved 102 years ago

Rosco Bodine - 26-1-2007 at 18:49

There are a couple of patents that tell the tale .

Organikum cited this patent number on page 2 of this thread .

A nearly quantitative yield of benzaldehyde reported
by way of toluene oxidation by Mn(IV) sulfate ,
Mn(SO4)2 , manganese persulfate .....
no benzoic acid byproduct , but a small amount of tar ,
the benzaldehyde readily steam distills from the mixture .

The Bazlen patent US780404 is attached ,
see also the subsequent Bazlen patent US837777 .

Attachment: US780404 Manganic(IV) Sulfate electrolysis regenerated.pdf (173kB)
This file has been downloaded 2142 times

Hilski - 26-1-2007 at 22:06

I wonder if the need for a diaphragm to efficiently produce the persulfate can be done away with if an anode/cathode size ratio of say 5:1 or higher is used. Basically, it would then be a war of attrition of sorts, as the anode with it's much larger surface area would oxidize the Mn(II) sulfate to the Mn(IV) sulfate faster than the small cathode could reduce it back to the Mn(II) sulfate.
Unless I have no idea what I'm talking about (which is likely) the cell would eventually contain a high percentage of the brown Mn persulfate, along with a small amount of the red Mn(II) sulfate.

Rosco Bodine - 27-1-2007 at 06:13

A porous cup around the cathode is unavoidable for this
persulfate because it is soluble in the acid , and therefore
it will be reduced at the cathode if it can contact it .

This should present no difficulty however , as the cathode
can be made of sheet lead formed into a cylinder which
sits immersed inside a clay flower pot filled three quarters full of sulfuric acid catholyte . If the lead sheet is cut into an L shape of proper dimensions , the long leg width is selected which will be just less than the depth of immersion in the catholyte , and it is rolled into a cylinder
shape around an olive bottle or similar sized form ,
leaving the short leg of the L shaped piece of sheet lead
as a riser and connection tab for the immersed cylinder .

If a 4 to 6 ounce glass bottle is used for the form for the cathode , it can be fitted with a two hole rubber stopper
at the top , and a rigid inlet tube nearly reaching the bottom inside the glass bottle , and a short rigid outlet tube reaching just below the stopper inside the bottle ,
so that cooling water may be run through to effect a
water cooled cathode . The flower pot can be suspended from polypropylene mesh netting , or
a suspension bridle can be made for it from polypropylene
cord or teflon insulated wire , so that the whole assembly
can be suspended from a ringstand , or from the center
of a support between two ringstands , one on either side
of the larger " bucket " or battery jar into which the
cathode assembly is lowered for electrolysis .

It would be easiest to manage this on a scale which
uses a 3 to 5 gallon black poly bucket for the anolyte
compartment . An overhead stirrer of adequate capacity
would be a good idea . However , if one of the larger
and heavy duty magnetic stirrers as are used for
fermenters and reactors is available , this could be used .
I would possibly put a glass or corelle dinner or salad plate in the bottom of a plastic bucket as a surface on which the stirbar would run , to prevent any long abrasion from the stirbar wearing a hole through the bottom of the bucket .....if it looked like abrasion there
could be a problem during long running .

Hilski - 27-1-2007 at 06:54

I think I have all the stuff I need to try this on a smaller scale. If I am successful, I will take some photos and post the results here. Then maybe I can scale it up to a bucket size reactor, and try it again. It seems like the last time I went looking for a clay cup for an electrolytic cell that I had a hard time finding one without a drain hole in the bottom. I think that may be the only thing I don't have on hand, so as soon as I find one I can run the experiment.

Rosco Bodine - 27-1-2007 at 07:25

Silicone of the sort that smells of acetic acid while it is
curing can be used to plug the hole in a flower pot .
I know it works for some of the milder sulfuric acid
electrolytes ....but I am not sure about how well it
would hold up to the stronger sulfuric used in this process .

Maybe check with a local ceramic shop and
see if they might provide an unglazed but
fired , coffee mug .

The flower pots that don't have the drain hole are
unusual , but can be found occasionally .....
and I don't recall what specialty of horticulture
is where they are used ....maybe bonsai ?

Also if it is more convenient , the anolyte and anode can be
inside the porous cup , and the cathode can be outside .
It isn't really of any importance what is the arrangement ,
so long as the porous cup , the flower pot , separates the two .

Those unglazed clay , terra cotta wine coolers don't have a drain hole IIRC , and you could probably use one of those as your porous cup .

[Edited on 27-1-2007 by Rosco Bodine]

womble - 29-1-2007 at 00:09

boys and girls,

I think that maybe this might help..... It is one of hte lost PDF's from Rhodium's site and it deals specifically (in great detail) with what does and does not work in the oxidisation of toluene. VERY INTERESTING reading, highly recomended.

Appears that the best option for decent yeilds (toluene ain't so easy to get here as I can afford to waste it) would be to chlorinate the toluene:

Ca2(OCl)2 + 2C6H5CH3 => 2C6H5CH2Cl + ?

then either oxidise the benzyl halide or use caustic soda/potash to remove the halide and oxidise the alcohol?

womble - 29-1-2007 at 00:35

although I do like this one, 20 seconds (MW) with silica doped with MnO2

I assume that the silica gel would be laid out flat, the MnO2 on top of it. Allow it to set (or go off) and then grind it in a mortar t

Tyvek may be the ticket

Hilski - 29-1-2007 at 11:20

Those unglazed clay , terra cotta wine coolers don't have a drain hole IIRC , and you could probably use one of those as your porous cup .

I was looking around the house to see what I may have on hand that would make a good membrane, and I came across a huge stash of Tyvek chem suits I have had for a while. I haven't been able to find any hard data as to the pore sizes etc, but I have a sneaky suspicion that Tyvek may work as a membrane in this case. I know that water in the aqueous phase will not go through the material, so I assume that a solution saturated with MnSO4 and H2SO4 also will not penetrate the material. I searched around a bit and did find one patent that used Tyvek in a battery type electrolytic cell. I'm sure there are more, but this is the only one I have found so far:

Cathode cover for metal-air cell

Granted, this type of cell is not the same thing we are talking about, but it is similar. Another good thing about Tyvek is that it is made out of high density polyethylene (HDPE), so it will stand up to the harsh conditions created by the warm H2SO4. I have an idea for a small scale experiment, so I'll get to work on it soon and post results when I can.
Man I hope this stuff works.

roamingnome - 29-1-2007 at 20:42


I was looking around the house to see what I may have on hand that would make a good membrane, and I came across a huge stash of Tyvek chem suits

yeah i hate when i forget about my huge stash of goods.

i have used ammonia probes that use a PTFE (Teflon) tape as membrane so tyvex might be some good stuff.... but a envelope at the post office will be better then ripping up your suits dude!

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