Reduction Potentials of Vat Dyes and Their Relation to the Ease of Reduction and Tendering Behavior

Abstract

A method for carrying out potentiometric titration of reduced vat dyes in aqueous alkaline solutions using a potassium ferricyanide solution as the oxidant is described. The standard method is modified on the basis of certain assumptions, and the values of potentials are calculated and termed “Characteristic redox potentials.” An account of the determination of these characterisic redox potential values for a series of purified vat dyes is given. The characteristic redox potential values of vat dyes are compared with the ease of reduction of these dyes and also with their tendering behavior. The effect of substitution on these values is discussed.