Mechanisms of the Cl-atom-initiated oxidation of acetone and hydroxyacetone in air

Abstract

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″)