Kinetic Studies of OH Reactions with a Series of Acetates

Absolute rate constants have been measured for the gas phase reactions of hydroxyl radicals with a series of aliphatic acetates: methyl acetate ( k 1 ), ethyl acetate ( k 2 ), n -propyl acetate ( k 3 ), n -butyl acetate ( k 4 ), and n -pentyl acetate ( k 5 ). Experiments were carried out using the pulsed laser photolysis—laser induced fluorescence technique over the temperature range 243−372 K. The obtained kinetic data were used to derive the Arrhenius expressions, and since the Arrhenius plots were slightly curved they were fitted, using a three-parameter expression. The Arrhenius expressions obtained are: k 1 = (0.53 ± 0.09) × 10 -12 exp[−(128 ± 102)/ T ]; k 2 = (0.48 ± 0.09) × 10 -12 exp[(397 ± 103)/ T ]; k 3 = (1.03 ± 0.12) × 10 -12 exp[(370 ± 69)/ T ]; k 4 = (2.10 ± 0.28) × 10 -12 exp[(299 ± 81)/ T ], and k 5 = (2.75 ± 0.46) × 10 -12 exp[(302 ± 102)/ 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 acetate, 0.32 ± 0.03; ethyl acetate, 1.67 ± 0.22; n -propyl acetate, 3.42 ± 0.26; n -butyl acetate, 5.52 ± 0.51; n -pentyl acetate, 7.34 ± 0.91. Our results are compared with the previous determinations and discussed in terms of structure−activity relationships.