Photolysis of aqueous solutions of p-benzoquinone: a spectrophotometric investigation

Abstract

The photolysis of aqueous solutions of p-benzoquinone is investigated spectrophotometrically over a wider range of pH, concentration, and the wavelength of irradiation than before. Experimental evidence has been obtained for the formation of benzene-1,2,4-triol as the sole primary photochemical product at all values of pH. Quinol and 2-hydroxy-1,4-benzoquinone are produced in equimolar quantities as secondary products both in acid and alkaline solutions, when the reaction between p-benzoquinone and benzene-1,2,4-triol is very fast. 2-Hydroxy-1,4-benzoquinone at higher concentrations polymerizes to the so-called ‘humic acid’. Between pH 4 and 6 benzene-1,2,4-triol is the chief photoproduct owing to suppression of the secondary reaction.