PRESSURE AND TEMPERATURE EFFECTS ON THE KINETICS OF THE ALKALINE FADING OF ORGANIC DYES IN AQUEOUS SOLUTION

Abstract

The rates of the alkaline fading of bromphenol blue, phenolphthalein, crystal violet, and malachite green have been studied from atmospheric pressure to 16,000 pounds per square inch. The rates for phenolphthalein and malachite green were also measured over a range of temperatures in order to determine the activation energies and entropies. The reactions went essentially to completion with the exception of the fading of phenolphthalein, for which the effects of temperature and pressure on the back reaction and equilibrium constant were also studied. No effect of pressure was found for the fading of crystal violet, but the reactions of the other three dyes were accelerated by pressure, so that there are negative volumes of activation. These are correlated with the entropies of activation and are interpreted in terms of the reaction mechanisms.