Formation of 1,3-diaryltriazene 1-oxides by oxidation of diazoamino-benzenes with peroxybenzoic acid: isomer ratios, kinetics, and mechanism

Abstract

The oxidation of diazoaminobenzenes with peroxybenzoic acid in ether gives diaryltriazene 1-oxides in good yield. An electron-releasing substituent on one of the benzene nuclei directs the oxygen to the nearest nitrogen atom. With diazoaminobenzenes carrying substituents of similar polarity on the two benzene nuclei the two possible isomers are formed in comparable amounts. The plot of logarithms of isomer ratios against the difference between Brown and Okamoto's σ⁺ values for the two substituents in a triazene is a straight line (ρ–1·3). Kinetic studies show that the bimolecular rate constants obey the Hammett law for the sum of the Hammett σ values for the substituents in both benzene rings (ρ–0·87). Analysis of the effect of substituents on the rate and the isomer ratio suggests a mechanism which involves the rate-determining formation of a metastable intermediate, in which the oxygen atom from peroxybenzoic acid is tentatively regarded as bonded to both nitrogen atoms 1 and 3, and which rapidly collapses to isomeric N-oxides in a ratio determined by the nature of the substituents.