The influence of pH on the stability constants values of dyes formed by reaction of imines with diazotized sulphanilic sodium salt

Abstract

The main object of the study , is the determination of stability constants of
some azo dyes formed by the reactions of donor imines with diazotized sulphanilic
sodium salt as an acceptor , using the spectophotometric method. These stability
constants are evaluated under pH values of 5.4 , 7.1 and 9.2 respectively and at five
different temperatures. At pH of 5.4, some experiments are proved the formation of
unstable dyes and the failure evaluation of some of their values. They are attributed to
the partial or complete protonation of donor imines and the formation of
phenoxonium or nitrilium ions or both of them. Other donor imines form a stable dyes
at pH 7.1. The last shows a maximum stability constant values for the dyes , due to
the presence of imine in the enolic form. Conversely , a minimum stability constant
value for the dye is obtained at pH 9.2 , due to the tautomeric conversion of enol form
to keto form in imine.