Guest-host interactions in the alkaline bleaching of triphenylmethane dyes catalysed by β-cyclodextrin

Abstract

The rates of alkaline bleaching of triphenylmethane dyes crystal violet (CV), malachite green (MG) and rosaniline (RA) have been measured spectrophotometrically in an aqueous medium at 30°C in the presence of β-cyclodextrin (CD). At lower concentrations of CD, CV forms productive 1:1 (G:H) complex. At higher concentrations of CD, it forms unproductive 1:2 (G:H) complex. For the bleaching of MG, CD accelerates or decelerates the rate depending on pH of the medium by forming 1: 1 (G:H) inclusion complex. Analysis of rate data shows that MG undergoes fading by mixed order process. CD decelerates the water reaction and accelerates hydroxide ion reaction. In the case of RA, both water reaction as well as hydroxide ion reaction are retarded by CD by the formation of inclusion complex. © Indian Academy of Sciences.