Kinetics and product orientation in oxidation of aldehyde 2,4-disubstituted phenylhydrazones by lead tetra-acetate; hydrazone azo tautomers

Abstract

Oxidation of aliphatic aldehyde phenylhydrazones containing ortho-substituents (NO₂, Br, or Me) in the N-phenyl ring with lead tetra-acetate-gives significant yields of α-unsubstituted azo-acetates which are azo tautomers of hydrazones. With aromatic aldehyde derivatives the product-orienting influence of the ortho-substituent in the N-phenyl ring was negated or reduced by the aromatic methine substituent. Kinetic measurements were made on series of aliphatic aldehyde 2,4-dinitrophenylhydrazones and 2-bromo-4-nitrophenylhydrazones. Strong steric effects (δ 0.83) for methine substituents were detected for the 2,4-dinitrophenylhydrazone series. The relative influences of the 2-NO₂ and 2-Br substituents on the rates were examined. The 2-NO₂ group had an exceptionally large rate-retarding effect. The mechanism of the reaction is discussed.