Kinetics and Mechanism of Azocoupling between quaternary 1,2,4‐triazolium salts and p‐N,N‐dimethylamino benzenediazonium tetrafluoroborate
Identifieur interne : 001136 ( Main/Exploration ); précédent : 001135; suivant : 001137Kinetics and Mechanism of Azocoupling between quaternary 1,2,4‐triazolium salts and p‐N,N‐dimethylamino benzenediazonium tetrafluoroborate
Auteurs : Becker ; Al Kurdi ; Mun Gwan [Corée du Sud] ; SchützSource :
- Journal für Praktische Chemie [ 0021-8383 ] ; 1991.
Abstract
The kinetics of azocoupling between 1‐benzyl‐4‐phenyl‐, 1,3,4‐triphenyl‐, 4‐benzyl‐1‐methyl‐, 1,4‐dimethyl‐, 1,4‐diphenyl‐3‐methylmercapto‐ and 3‐benzyl‐mercapto‐1,4‐diphenyl‐1,2,4‐triazolium salts, and p‐N,N‐dimethylamino benzenediazonium tetrafluoroborate are studied spectroscopically in methanol/water 1:1 (v/v) at various pH values following up the growing‐in of the respective azodyes. The competing reactions of the diazonium salt with the solvent and the buffer (NH3/NH4Cl), and of some bleaching of the azodye formed were studied separately and accounted for in the kinetic treatment. From the pH dependence of the coupling rate constants and by application of kinetic models it turned out that not the widely accepted one‐step deprotonation mechanism of the quaternary triazolium salts applied but a two‐step mechanism comprising of pseudobase formation and their subsequent deprotonation is valid. Using the pertinent kinetic model the pK values of pseudo‐base formation (pKR+) and their deprotonation (pKA) were determined by non‐linear regression.
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DOI: 10.1002/prac.19913330102
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