Experiments upon the Stability of Colour Developing Solutions. Kinetics and Mechanism of the Conversion of N-Substituted Paraphenylene-Diamines into p-Aminophenols and Hydroquinone in Presence of Oxidants in Traces

Abstract

AbstractSolutions of p-phenylenediamine derivatives (PPD) are totally unstable against traces of oxidants. In acid solution the primary oxidation product, quinone diimine (QDI) is deaminated, forming N-substitutcd quinone monoimine (QMI). This is able to react with the residual PPD, giving N-substituted p-aminophenol (PAP). The other reaction product, QDI, is unstable. In this way the reaction proceeds until the total PPD is transformed into PAP. The residual QMI deaminates slowly, too, giving quinone (Q). The latter reacts in the same way with PAP, forming hydroquinone (H20) and other products. In alkaline solution QMI is more unstable than QDI. Therefore QDI is converted directly into Q which reacts in a similar way as before with the residual PPD. The mechanism is discussed by means of potential pH diagrams and formerly measured rate constants of deamination. An important result is that acid and alkaline PPD solutions do not lose their developing but their coupling ability within a rather short time if...