Von Richter reaction

[1][2][3] Although it is not generally synthetically useful due to the low chemical yield and formation of numerous side products, its mechanism was of considerable interest, eluding chemists for almost 100 years before the currently accepted one was proposed.

This is followed by ring closure via nucleophilic attack on the cyano group, after which the imidate intermediate is rearomatized.

Elimination of water produces a cyclic azoketone, which undergoes nucleophilic attack by hydroxide to form a tetrahedral intermediate.

This intermediate collapses with the elimination of the azo group to yield an aryldiazene with an ortho carboxylate group, which extrudes nitrogen gas to afford the anionic form of the observed benzoic acid product, presumably through the generation and immediate protonation of an aryl anion intermediate.

Subsequent mechanistic studies have shown that the subjection of independently prepared ortho-nitroso benzamide and azoketone intermediates to von Richter reaction conditions afforded the expected product, lending further support to this proposal.