Oxidation of glyoxal initiated by (OH)-O-. in oxygenated aqueous solution

The kinetics and mechanism of the oxidation of glyoxal, which is a constituent of cloud water, initiated by . OH in oxygenated solution have been investigated using pulse radiolysis with optical and conductivity detection of the transient species, and steady-state radiolysis with spectrophotometric and ion chromatographic analysis of the permanent products. The data obtained are consistent with glyoxal being present in the form of the dihydrate [CH(OH)(2)](2) which is oxidised to glyoxylic acid (pK(a) = 3.4) and hydrogen peroxide via a peroxyl radical . O2C(OH)(2)CH(OH)(2) that splits off HO2 . in a non-rate determining step. The following rate constants have been determined: k{. OH + [CH(OH)(2)](2)} = (1.10 +/- 0.04) x 10(9) dm(3) mol(-1)s(-1) and k[. C(OH)(2)CH(OH)(2) + O-2] = (1.38 +/- 0.11) x 10(9) dm(3) mol(-1)s(-1). It is concluded that oxidation of glyoxal by . OH in cloud water can proceed by a chain reaction involving H2O2.