Photooxidation of substituted purines in presence of peroxydisulphate in aqueous solution

Abstract

Photooxication of purine bases, viz .. caffeine, theobromine, theophylline, xanthine, hypoxanthine, adenine and guanine in aqueous solution has been carried out in presence of

peroxydisulphate (PDS). Peroxydisulphate is activated to SO₄^- at 254 nm. The reactions are followed by measuring the absorbance of purine bases at their respective λ_max. The rates of reactions are calculated under different experimental conditions. The light intensity is measured using peroxydisulphate solution as standard chemical actinometer. Using reaction rate and light intensity at 254 nm, the quantum yields are calculated. The rates of

photooxidation of purine bases are found to increase with increase in [PDS] and independent of [purine]. The increase of light intensity has been found to increase the rate of oxidation. The quantum yields are found to depend on [purine] but independent of [PDS] and light intensity. On the basis of experimental results a probable mechanism is suggested in which peroxydisulphate on photolysis gives sulphate radical anion which initiates the reaction

by capturing an electro n from C8 position of purine to form purine radical cation. This radical cation deprotonates and undergoes further oxidation to give C(8) hydroxy purine.