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
✍ Scribed by Rafal Kaminski; Urs Lauk; Peter Skrabal; Heinrich Zollinger
- Publisher
- John Wiley and Sons
- Year
- 1983
- Tongue
- German
- Volume
- 66
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
Abstract
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 (≤10^−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 couplings with 3‐trifluoromethylbenzediazonium 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.