Mechanism of Azo Coupling Reactions XXXIII. pH-Dependence and Micromixing Effects on the Product Distribution of Couplings with 6-Amino-4-hydroxy-2-naphthalenesulfonic Acid. Evidence for N-Coupling of a Naphthylamine Derivative

Article abstract of DOI:10.1002/hlca.19830660712

Azo coupling of 6-amino-4-hydroxy-2-naphthalenesulfonic acid (1) with 3-trifluoromethyl- and 4-nitrobenzenediazonium ion in relative highly concentrated aqueous alkaline solutions gave ratios of aminoazo to hydroxyazo compounds which are much higher than expected on the basis of the acid-base pre-equilibria of 1.These product ratios are disguised by effects of micromixing.In dilute solution (-2 mol/l) product ratios and kinetics both correspond to the theory of acid-base pre-equilibria.A bisazo dye 10 was formed as a by-product in coupling with 3-trifluoromethylbenzenediazonium ion, as expected for reactions with micromixing effects.In the reaction with benzenediazonium ions, the products of azo coupling of diazotized 1 with 1 (compound 8) and of the monoazo compound 8 with benzenediazonium ion (compound 9) were found.It is likely that diazotized 1 is formed by N-coupling of 1 with benzenediazonium ion, tautomeric rearrangement and protonation of the triazene to diazotized 1 and aniline.This seems to be the first case of N-coupling of a naphthylamine which was assumed to be capable of C-coupling only.