Premium
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
Author(s) -
Kaminski Rafal,
Lauk Urs,
Skrabal Peter,
Zollinger Heinrich
Publication year - 1983
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19830660712
Subject(s) - chemistry , azo coupling , triazene , tautomer , protonation , ion , aqueous solution , coupling (piping) , aniline , product distribution , micromixing , inorganic chemistry , medicinal chemistry , computational chemistry , polymer chemistry , organic chemistry , analytical chemistry (journal) , catalysis , engineering , mechanical engineering
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.