Radiation Chemistry of Some Sulfonephthalein Dyes

Abstract

Reactions of hydrated electrons $e_{{\rm aq}}^{-}$ with xylenol orange, thymol blue, cresol red, phenol red, and p-benzoquinone and of the OH radical with xylenol orange have been studied, using flash photolysis and gamma irradiation under conditions where the roles of $e_{{\rm aq}}^{-}$ and OH are emphasized. The rate constants of the reactions of $e_{{\rm aq}}^{-}$ with xylenol orange, cresol red, and p-benzoquinone at pH 11 are $5.2\times 10^{9} M^{-1} {\rm sec}^{-1},8.5\times 10^{9} M^{-1} {\rm sec}^{-1}$ , and $4.2\times 10^{9} M^{-1} {\rm sec}^{-1}$ , respectively; k(OH + xylenol orange) = $1.1\times 10^{10} M^{-1} {\rm sec}^{-1}$ . Although xylenol orange reacts rapidly with $e_{{\rm aq}}^{-}$ the principal decolorization reaction is by the OH radical. The decolorization yields of thymol blue, cresol red, and phenol red are very small compared to <t...