Rate coefficients for the gas-phase reaction of hydroxyl radicals with the dimethylbenzaldehydes

Rate coefficients for the reactions of hydroxyl (OH) radicals with the dimethylbenzaldehydes have been determined at 295 ± 2K and atmospheric pressure using the relative rate technique. Experiments were performed in an atmospheric simulation chamber using gas chromatography for chemical analysis. The rate coefficients (in units of cm³ molecule^-1 s ^-1) are: 2.3-dimethylbenzaldehyde, (25.9 ± 2.8) × 10^-12; 2,4-dimethylbenzaldehyde., (27.5 ± 4.4) × 10 ^-12; 2,5-dimethylbenzaldehyde, (27.6 ± 5.1) × 10 ^-12; 2,6-dimethylbenzaldehyde, (30.7 ± 3.0) × 10 ^-12; 3,4-dimethylbenzaldehyde, (24.6 ± 4.0) × 10 ^-12; and 3,5-dimethylbenzaldehyde, (28.2 ± 2.5) × 10^-12. The reactivity of the dimethylbenzaldehydes is compared with other aromatic compounds and it is shown that the magnitude of the OH rate coefficients does not depend significantly on the position of the CH₃ substituent on the aromatic ring. The rate coefficient data are explained in terms of known mechanistic features of the reactions and the atmospheric implications are also discussed.