Von Richter reaction

From among the judges reaction refers to a chemical reaction which is the basis for the synthesis of aromatic acids from a nitrobenzene derivative. To this end, the aromatic compound with potassium cyanide in an aqueous or alcoholic medium, is reacted. Product as a carboxyl group in the ortho- position to the previous, but no longer present after the reaction, the nitro group is obtained.

History

The reaction was first described by Victor von Richter in 1871. He realized that the substitution of the carboxylic acid functional group in the ortho position is done to formerly existing nitro group and postulated that the reaction proceeds with the formation of an addition product of aromatics with hydrogen cyanide, which initially results in a substituted benzonitrile after elimination of nitrous acid. This should hydrolyze in water to the corresponding benzoic acid. However, the Benzonitrilzwischenprodukt could not be detected.

JF Bunnett led in the 1950s, extensive studies of the judges reaction. To explain the absence of Benzonitrilzwischenprodukt, 1958, he developed a reaction mechanism that proceeds via cyclic intermediates. As a final step should consist of a Acylnitrit with elimination of nitrous acid, the benzoic acid formed.

Reaction mechanism

In 1960 M. Rosenblum noted that in the reaction of the by-products of ammonia and nitrous acid are undetectable and that instead of nitrogen produced. The reaction mechanism is initially also on the addition of cyanide to the aromatic system and the formation of a cyclic intermediate. By surroundings then creates a Indazolonverbindung, the benzoic acid arises from the following elimination of nitrogen. The mechanism could be supported by the formation of nitrogen composition 15N14N on reaction of a nitro compound with the 15N Isoptop and cyanide with the 14N Isoptop and by the detection of Indazolonverbindungen. A conducting the reaction in isotopically labeled water H218O gave only a partial incorporation of 18O into the resulting benzoic acid, from which it follows that a normal 16O of the nitro group was transferred via the cyclic intermediate. The reaction of o- nitrosobenzamide, prepared by the oxidation of o- aminobenzamide, under conditions which also confirmed by the benzoic acid to judge reaction mechanism via a Indazolonintermediat.

A more recent version of the funnel - reaction starts from the nitrone compounds N- Acylbenzochinonimin - N-oxide. The leaving group is then the corresponding phenol.