Kinetic study of OH and NO3 radical reactions with 14 aliphatic aldehydes

Rate coefficients for the reactions of NO3 and OH radicals with 14 aliphatic C2 to C6 aldehydes in purified air at 298 +/-2 K and 1.00 +/-0.01 atm have been determined by the relative rate method using a static reactor equipped with long-path FTIR detection. The aldehydes studied comprise: C2-acetaldehyde; C3-propanal; C4-butanal and 2-methylpropanal; C5-pentanal, 2-methylbutanal, 3-methylbutanal and 2,2-dimethyl-propanal; C6-hexanal, 2-methyl-pentanal, 3-methylpentanal, 4-methylpentanal, 3,3-dimethylbutanal, and 2-ethylbutanal. The new data establish that the gas-phase reactivity of aliphatic aldehydes towards the NO3 and OH radicals follow the linear free energy relationship typical of addition reactions although the net result of the reactions is a H-abstraction. The experiments also indicate that more than 95% of the room temperature NO3 reaction with aliphatic aldehydes proceeds through an abstraction of the aldehydic hydrogen. The structure activity relationship for estimation of rate coefficients of the NO3 radical reaction with saturated organics (J. Phys. Chem. Ref. Data, 1991, 20, 45) fails completely for aliphatic aldehydes.