Oxidation of glyoxal initiated by OH 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 O 2 C(OH) 2 CH(OH) 2 that splits off HO 2 in a non-rate determining step. The following rate constants have been determined: k{ OH+[CH(OH) 2 ] 2 }=(1.10±0.04)×10 9 dm3 mol -1 s -1 and k[ C(OH) 2 CH(OH) 2 +O 2 ]=(1.38±0.11)×10 9 dm3 mol -1 s -1 . It is concluded that oxidation of glyoxal by OH in cloud water can proceed by a chain reaction involving H 2 O 2 .