MECHANISMS OF THE CL-ATOM-INITIATED OXIDATION OF ACETONE AND HYDROXYACETONE IN AIR

The products of the Cl-atom-initiated oxidation of acetone and hydroxyacetone (CH3COCH2OH) in O2-N2 MiXtures at 700 Torr and 298 K have been identified using long-path-length FTIR spectroscopy and long-path-length UV-visible diode array spectroscopy. The oxidation of acetone yields methyl glyoxal (CH3COCHO), HCHO, CO, CO2, CH3COOH, CH3OH, HCOOH and O3 as identifiable products. The data have been analysed, utilising the results of a kinetic study of the oxidation of acetone in air. The mechanism of the oxidation proceeds initially via the production of acetonylperoxy radicals (CH3COCH2O2) which are removed by their self-reaction (3), and reaction with other peroxy radicals [CH3C(O)O2, CH3O2 and HO2] produced by the subsequent chemistry: 2CH3COCH2O2 --> 2CH3COCH2O + O2 (3a) --> CH3COCHO + CH3COCH2OH + O2 (3b) The thermal decomposition of CH3COCH2O radicals produced in channel (3a) into CH3CO radicals and HCHO, is shown to predominate over the alternative reaction with O2, under the conditions of these experiments: CH3COCH2O + M --> CH3CO + HCHO + M (12) CH3COCH2O + O2 --> CH3COCHO + HO2 (13) Measurements of the yields of HCHO and CH3COCHO are consistent with the operation of both channels of reaction (3) and allow certain conclusions to be drawn concerning the reactions of CH3COCH2O2 with CH3O2 and CH3C(O)O2. The only detected primary organic product of the oxidation of CH3COCH2OH is CH3COCHO, formed with a yield of (100 +/- 5)% by the following reaction sequence: Cl + CH3COCH2OH --> HCl + CH3COCHOH (4) CH3COCHOH + O2 --> CH3COCHO + HO2 (5) The concentration-time dependence of a range of secondary organic products, formed in the system was also measured. Identifiable products are CO, CO2, CH3COOH, HCHO, CH3OH, HCOOH and pyruvic acid (CH3COCOOH). These results are consistent with the presence of the CH3COCH(OH)O2 radical, formed as an intermediate in reaction (5): CH3COCH(OH)O2 <-- --> CH3COCHO + HO2 (5'')