Kinetics and products of photolysis and reaction with OH radicals of a series of aromatic carbonyl compounds

Abstract

We have investigated the photolysis and OH radical reactions of phthaldialdehyde, 2-acetylbenzaldehyde, and 1,2diacetylbenzene, atmospheric reaction products of naphthalene and alkylnaphthalenes, and of phthalide, a photolysis product of phthaldialdehyde. Using a relative rate method with 1,2,4-trimethylbenzene and 2,2,3,3-tetramethylbutane as reference compounds, measured rate constants for the gas-phase OH radical reactions (in units of 10(-12) cm3 molecule(-1) s(-1)) were as follows: phthaldialdehyde, 23 +/- 3; 2-acetylbenzaldehyde, 17 +/- 3; 1,2-diacetylbenzene, < 1.2; and phthalide, < 0.8. Blacklamp irradiation showed that phthaldialdehyde and 2-acetylbenzaldehyde photolyze, and, combined with absorption spectra measured in n-hexane solution, average photolysis quantum yields of 0.19 and 0.21, respectively, were derived (290-400 nm). No evidence for photolysis of 1,2-diacetylbenzene or phthalide by blacklamps was obtained. The major atmospheric loss process of phthaldialdehyde and 2-acetylbenzaldehyde are estimated to be by photolysis, with photolysis lifetimes of 1.4-1.5 h for a 12-hr average NO2 photolysis rate of 0.312 min(-1). Phthalic anhydride was the major observed product from the OH radical-initiated reactions of all four compounds and was also formed from photolysis of phthaldialdehyde and 2-acetylbenzaldehyde. The major photolysis products observed were phthalide from phthaldialdehyde and 3-methylphthalide from 2-acetylbenzaldehyde.