Wallach degradation

Favorskii rearrangement. Base-catalyzed rearrangement of a-haloketones to acids or esters. The rearrangement of a,a -dibromocyclohexanones to 1 -hydroxycyclopentanecarboxylie acids, followed by oxidation to the ketones, is known as the Wallach degradation. 

The reaction of carboxylic acid amides with phosphorus pentachloride, to yield compounds I and II, was investigated extensively by Wallach and his students in 1876-1882, and later by v. Braun, who utilized this reaction to degrade secondary amines to ammonia. The highly reactive imidoyl chlorides have been used, especially by v. Braun, as synthetic tools to produce a variety of compounds which could not easily be synthesized by other procedures. However, imidoyl chlorides never made the headlines in synthetic organic chemistry, most likely because of the inherent difficulty involved in handling these highly reactive compounds. 

Formic acid is a common degradation product of sugars and also the oxidation product of formaldehyde. It is effective as a specific reagent for reductive amination of imminium ions to give secondary amines in the Maillard reaction. The reaction is known as a Wallach or Leuckart reaction (reactions of formates or formamide) R R N+=CH-R - - H-COOH R R N-CH -R + CO,. 

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