Kinetics and mechanism of the reaction between nitrous acid and arylhydrazines

Abstract

The kinetics of the reaction between nitrous acid and phenylhydrazine and its ring-substituted derivatives correspond to an encounter controlled nitrosation by the nitrosonium or nitrous acidium ion with the arylhydrazinium ion. The primary product, 1-aryl-1-nitrosohydrazine, is converted into aryl azide in an acid-catalysed step, the rate of which is very little affected by meta- or para-substituents. In the presence of excess of nitrous acid substantial yields of diazonium ion are obtained, probably through the formation of a 1-aryl-1,2-dinitrosohydrazine, which can also decompose to give aryl azide.