Benzaldehyde (missing thread)

[Marvin]

There are 2 good threads missing from this section I think, one is benzaldehyde and I'm dammed if I can remeber the other.

The gist of the thread was,

Turn toluene into benzyl chloride using the hypochlorite route.

Hydrolysis of benzyl chloride would normally get us only benzyl alcohol, so instead use the Sommelet Reaction. The benzyl chloride is reacted with hexamine, forming a quaterary salt, and then this can be hydrolysed under mild conditions to benzaldehyde.

Description of the Sommelet Reaction here,
http://themerckindex.cambridgesoft.com/TheMerckIndex/NameReactions/ONR373.htm

I dont remeber who started the thread and my apologies if they were planning to restart it, but as memory serves they stopped posting only a few days after starting the thread and didnt reply to any of the questions as to specific conditions.

A tentitive suggestion is 42g of benzyl chloride to be added dropwise into a boiling suspension of hexamine 48g in water (unknown, enough to dissolve the salt - all the hexamine should dissolve after addition of the chloride) and the mixture refluxed for 2 hours. Alternativly the benzyl chloride can be simply added to the hexamine in water and then refluxed for a slightly lower yeild. A small amount of HCl solution is added to prevent Schiffs bases in the condensate, and the mixture steam distilled until the condensate is nolonger cloudy, or stops smelling of benzaldehyde. Method reconstructed from fragments of related methods. Yeilds of 80% should be achieveable based on benzyl chloride.

[akinrog]

Dear Marvin,

I found the reference you requsted at the hive.

Here is the link (https://www.the-hive.ws/forum/showflat.pl?Cat=&Number=519043&page=&view=&sb=&part=1&vc=1).
Post number is 515478 I believe.

HTH.

P.S. It might be necessary to become a member to view this thread.
P.S. 2 Funny thing the poster made reference to mega's synthesis and another guy says the method is not correct.
P.S. 3. In the post there is a patent (no 431412) which describes entire process (starting from toluene to Benzaldehyde).

[Bugger]

Or you can hydrolyze the benzyl chloride to benzyl alcohol with a strong alkali, and then oxidize the alcohol to benzaldehyde, preferably using CrO3-pyridine complex in dichloromethane solvent.

It is difficult to go directly from toluene to benzaldehyde, because oxidation of the CH3 in toluene by the usual reagents like hot alkaline KMnO4 (followed by acidification)results in further oxidation to benzoic acid instead.

Bugger.

[Mr Cool]

Damn, I'm out of CrO3 and pyridine at the moment. But I have a few kilo's of hexamine....
I prefer the Sommelet rxn ;).

[Marvin]

akinrog,

Thats a good reference. The essential differences are, the benzyl chloride contains considerable toluene, which helps to extract the benzaldehyde into the organic phase afterwards, this can be seperated and fractionated, avoiding a steam distillation. (The patent talks about tolualdehyde but this is an exact analog of the process). Its possible since no water miscable organic solvent is used the steam distillation can be dispensed with even if no toluene is present. Much more HCl, reducing the pH to 3-4, this prevents amines in the organic phase (I assume). In the information I've read adding HCl was optional before the steam distillation to prevent a cloudy condensate masking the end point of the benzaldehyde coming off.

Being able to use the result of the chlorination directly when using chlorine gas is useful, as it reduces contact with the very toxic benzyl chloride, I have a feeling this is as broad as its long though as venting large amounts of chlorine gas contaminated with toluene and benzyl chloride might turn out to be just as nasty. The hypochlorite/toluene method looks a easier on the face of it.

My references are all 60 years old or more. Interestingly the actual yeild, 80%ish hasnt changed in 40 years and the only innovation is the use of crude benzyl chloride! Maybe BASF had other reasons for trying to reestablish rights to such an old process.

The only possible thing I can see with the Benzal chloride method mentioned, is that hydrolysis is normally done with calcium hydroxide. Maybe the method was adapted from a working benzyl chloride method (to benzyl alcohol) that would be easily hydrolysed by water/CaCO3 or maybe it really does work. I respect Organikum on most matters but from experience on sciencemadness the less sure he is the less likley he is to give a reason for his opinion. I'm sure his ratio for hexamine to benzyl chloride works and its close enough to what I calculated, being a little high on the hexamine.

JohnW,
I'm unsure if the usual safe bets like PCC in aprotic solvents will work for benzaldehyde, regardless, its expensive and unsubtle. The founding principle for those that dont know is that oxidising an acetaldehyde itself is much harder than oxidising the diol it forms in water. If you are doing a complicated molecule and need a high yeild of the aldehyde from the alcohol, PCC and its cohorts are doubtless the way to go. Conversely though, if you need acetaldehyde you can distill it out of a mixture as it forms and get a reasonable yeild from a more convensional oxidising agent at much less cost/complexity. Ethanol is cheap. We cant distill benzaldehyde out of the mixture but we do have more leeway than with aliphatics. Benzaldehyde is a tad harder to oxidise than most aldehydes and this gives us a wider range of reagents and processes. The other key difference is that its not possible to generate the aldehyde from the ammonia addition product, so bisulphite compounds have to be used instead if this level of purification is required.

In the vapour phase we could catalytically oxidise toluene with air/MnO2 at 500C and the product is supposed to be very pure. Out of easy reach as a lab method though.

A mixture of MnO2/Copper sulphate/Sulphuric acid will oxidise toluene to benzaldehyde but its easy to take this too far and get benzoic acid. I'd like a reliable method for this but the only reference Ive found is a passing mention in Karrer. frogfot found a version optimised for a continuous extraction, US1302273, it looks like a lot more experiments need to be done before we have a halfdecent method though. His thread is on sciencemadness here,

http://www.sciencemadness.org/talk/viewthread.php?tid=2223

Chromyl Chloride CrO2Cl2 will take toluene to benzaldehyde and stop. (Karrer)

2-nitropropane will oxidise benzyl bromide (and probably chloride) under strong alkaline conditions (ethoxide) to benzaldehyde but this is another one of rather limited application only. (Organic syntheses)

Copper nitrate will oxidise benzyl alcohol or benzyl chloride to benzaldehyde and stop. I think this has potential.

The method for benzyl chloride is,
250ml flask reflux setup equipped to bubble CO2. Through the condensor is poured 23ml of benzyl chloride and then a solution of 20grams copper nitrate in 125 ml water. CO2 is used to sweap out the oxides of nitrogen and the mixture is refluxed for 8 hours keeping a steady current of CO2. Benzaldehyde is extracted with several small portions of ether in a seperating funnel.

The ether extract is then purified by the sodium hydrogen sulphite addition compound. Most of the ether is removed by heating in a water bath and excess saturated solution of sodium hydrogen sulphite is added. The crystals are rapidly filtered and treated with a slight excess of sodium carbonate solution and the benzaldehyde is extracted with ether, dried over anhydrous CaCl2, ether boiled off and the remainder distilled keeping the fraction between 178 and 180C. Method from Organic chemistry, 3rd Ed, by Stokes. How or if the method needs to be altered for benzyl alcohol isnt stated.

It should be possible to generate the copper nitrate solution in situ, so if a replacement for ether can be found, or the product purified via a different method I think this is a reasonable contender to the Sommelet reaction. Purification of the ether extract is clearly a generic method for benzaldehyde.

[Bugger]

Thanks for your possible alternatives for benzaldehyde. Because of the use of benzaldehyde as a food flavor (oil of bitter almonds), as well as for further organic syntheses where it is desired to introduce benzyl groups or else further groups to the benzene ring, I would be most interested in which method is best for large-scale industrial use - which do you think is most suitable?

BTW Can Organic Chemistry, 3rd Ed., by Stokes, be downloaded from anywhere? Otherwise, do you think you could email it to me?

Bugger.

[organikum]

The Sommelet reference at the HIVE is from me and also mine is the opinion that this sentence:

"The crude benzaldehyde oil is treated with a concentrated solution of sodium bisulfite, after shaking for a long time the oil should have dissolved into solution. If any crystals happen to form during the shaking, add water until they dissolve."

is plain nonsense, may it come from incorrect citation or whatever.
It was asked if this is correct. The answer was and is: NO.
Megalomania or not.

Benzaldehyde is supposed to precipitate as sodium-bisulfite addittion product. "Crude" benzaldehyde wont easily precipitate, if at all - the bisulfute purification works only on fairly clean substrates.

The patent I presented works perfectly well - its tried and true.

Benzalchloride hydrolysis:
The benzalchloride is SLOWLY run INTO a SLURRY of water/calcium-carbonate under STRONG STIRRING, some added calcium hydroxide doesnt hurt but may be helpful. Then the broth is refluxed for some hours water added and steamdistilled.

If you just add water/hydroxide/carbonate and reflux you will not need 2 hours, not 4 not 10, but some days.


Benzalchloride synthesis: DONT try to make banzalchloride by the LOOMIS patent method, heating hypochlorite and toluene. There is a high probability that you will get an explosion. Thats just because so much hypochlorite is needed that the toluene will not cover it completely all time. And thats NOT GOOD, believe me.

[Abigail]

Hey, i have no reference but benzalbromide is a alternative to the chlorine method and bezahl chloride. Dryed bromine is bubbled through boiling toluene, i belive that will do the same.
100 ml toluene to 271,3 g benzalbromide by weight.
I think it is correct when bromine is dropped into boiling toluene to get benzalbromide. You need no chlorine or bromine generator.
I`m not shure you can get benzaldehyde at the same conditions with calcium carbonate.