George V. Buxton, Treena N. Malone and G. Arthur Salmon
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 (pKa=3.4) and hydrogen peroxide via a peroxyl radical O2C(OH)2CH(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)×109 dm3 mol-1 s-1 and k[C(OH)2CH(OH)2 +O2]=(1.38±0.11)×109 dm3 mol-1 s-1. It is concluded that oxidation of glyoxal by OH in cloud water can proceed by a chain reaction involving H2O2.