Chemical Selectivities Disguised by Mass Diffusion. VIII. Influence of pH‐gradients on the product distribution in mixing‐disguised azo coupling reactions. 9th Communication on the selectivity of chemical processes

Abstract

AbstractIn mixing‐disguised azo coupling reactions the protons which are released during the electrophilic substitution steps cause a pH‐gradient in the reaction zone. Since, owing to the acid‐base pre‐equilibria, these pH‐gradients also determine the local concentrations of the reactants in the reaction zone, they also have an influence on the measured product distribution of such fast reactions. In the present work, the product distribution of the azo coupling of 1‐naphthol with 4‐sulfophenyldiazonium ion was experimentally measured and the results were compared with the distributions predicted from our mixing‐reaction model developed previously [1]. Furthermore, some experimental evidence for the existence of isoselectivity points are presented, at which a change of the initial pH‐value has no influence on the product distribution.