Kinetic Studies of OH Reactions with a Series of Methyl Esters

Absolute rate constants have been measured for the gas-phase reactions of hydroxyl radicals with a series of methyl esters: methyl propionate ( k 1 ), methyl butyrate ( k 2 ), methyl valerate ( k 3 ), and methyl caproate ( k 4 ). Experiments were carried out using the pulsed laser photolysis−laser induced fluorescence technique over the temperature range 253−372 K. The obtained kinetic data were used to derive the following Arrhenius expressions: k 1 = (1.45 ± 0.42) × 10 -12 exp[−(148 ± 86)/ T ]; k 2 = (0.96 ± 0.29) × 10 -12 exp[(380 ± 91)/ T ]; k 3 = (1.37 ± 0.64) × 10 -12 exp[(401 ± 142)/ T ]; k 4 = (2.46 ± 1.04) × 10 -12 exp[(326 ± 130)/ T ] (in units of cm 3 molecule -1 s -1 ). At room temperature, the rate constants obtained (in units of 10 -12 cm 3 molecule -1 s -1 ) were as follows: methyl propionate (0.83 ± 0.09); methyl butyrate (3.30 ± 0.25); methyl valerate (4.83 ± 0.55); methyl caproate (7.15 ± 0.70). Our results are compared with the previous determinations and discussed in terms of structure−activity relationships.