Acids to aldehydes

Aengus · Thu Aug 18, 2005 6:26 pm

There are many ways of converting an aromatic acid or its simple derivatives into the aldehyde: as a purely theoretical example, methyl trimethoxybenzoate to trimethoxybenzaldehyde. Has anyone reviewed them?

Specifically, what is the most recommended method for a chemist who has very limited equipment and materials? No exotic and expensive reagents - no equipment more complicated than reflux. I have a vague idea you can oxidise the acid hydrazide (nice crystalline materials that are easily made), perhaps with a copper salt.

Any suggestions would be welcome.

The best of luck - I hope this website lasts.

anime · Sun Aug 21, 2005 1:35 am

LAH, Pd/BaSO4, SOCl2. All exotic and expensive.

You are going to need a fairly strong reducing agent to reduce the acid to the aldehyde, NaBH4 alone won't touch the carboxylic acid. You could covert the carboxylic acid to an acid chloride and then reduce with Pd/BaSO4 to yield the aldehyde but SOCl2 is pretty nasty and Pd is not cheap.

There is a method which uses NaBH4 and some catalyst that seems to do the job. (I'll look this up, its somewhere on the LT).

But my question is why when there are easier methods.

Lego · Sun Aug 21, 2005 2:20 am

Use zinc borohydride (made from zinc chloride and sodium borohydride) to reduce the acid to the alcohol, then oxidise the alcohol to the aldehyde with manganese dioxide.

No expensive chemicals, everything easy to get, NaBH4 and MnO2 are sold in non-chemical shops, easy to get, not sure for ZnCl2, but can bee prepared easily.

java · Consumer

There is the NaBH4 reduction to alcohol at RT and in water , then oxidise as mentioned by Lego to the aldehyde.......see.

Transition Metal Compound Mediated Reduction of
-Amino Acids to 1,2-Amino Alcohols with NaBH4 in
Water
Ayhan S. DEM_IR, _Idris M. AKHMEDOV, ®O. S ES ENO GLU

Turk J. Chem. (1999),23,2123-126

PDF

Abstract
A new efficient and cost-effective method for the preparation of 1,2-amino alcohols is described.
The reactions of amino acids with NaBH4 in the presence of NiCl 2 or MoO3 in water give 1,2-amino alcohols in high yield. When optically pure amino acids were used, optically pure 1,2-amino alcohols were obtained.

anime · Mon Aug 22, 2005 1:12 am

Reduction of Some Functional Groups with Titanium (V) Chloride/Sodium Borohydride.
Synthetic Communications, Sept. 1980 pp. 695-697

Several functional groups are reduced.
Oximes to amines, acid chlorides to alcohols, carboxylic acids to alcohols, most in high yields.

2-methoxybenzoic acid -> 2-methoxybenzyl alcohol yield: 92%
benzoic acid -> benzyl alchohol: 94%

You can go on and use sodium persulfate for the oxidation of the alcohol into an aldehyde. Persulfate is used for etching boards.

anime · Mon Aug 22, 2005 1:37 am

hmm, apparently NaBH4 and CuSO4 can also be used. It also reduces NO2 -> NH2....would be interesting to see its application in the reduction of nitroalkenes.

fcknut · Mon Aug 22, 2005 2:42 am

what about in-situ borane formation from sodium borohydride and iodine?

reduces to alcohol so you can then oxidise back up.

nice, neat and cheap!

don't have ref to hand though.