Correlation of Alkyl and Polar Substituents at the Alcoholic Side of Tertiary Acetates with the Rate of Pyrolyses in the Gas Phase

Article abstract of DOI:10.1021/j100253a052

The rate coefficients for the gas-phase pyrolysis of several tertiary acetates have been measured in a static system over the temperature range of 220-340 deg C and pressure range of 40-186 torr.In seasoned vessels the reactions are homogeneous, follow a first-order rate law, and are unimolecular.The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for 3,3,3-trichloro-2-methyl-2-propyl acetate, log k₁ (s^-1) = (13.86 +/- 0.35) - (188.8 +/- 3.8) kJ mol^-1 (2.303 RT)^-1; for methyl α-acetoxyisobutyrate, log k₁ (s^-1) = (12.42 +/- 0.28) - (174.6 +/- 3.2) kJ mol^-1 (2.303 RT)^-1; for 2-methyl-2-hexyl acetate, log k₁ (s^-1) = (13.35 +/- 0.33) - (166.1 +/- 3.4) kJ mol^-1 (2.303 RT)^-1; for 2,4-dimethyl-2-pentyl acetate, log k₁ (s^-1) = (12.42 +/- 0.19) - (154.1 +/- 1.9) kJ mol^-1 (2.303 RT)^-1; for 2-methyl-2-acetoxy-4-phenylbutane, log k₁ (s^-1) = (11.97 +/- 0.55) - (151.5 +/-5.6) kJ mol^-1 (2.303 RT)^-1.The effectof substituents in the gas-phase elimination of 2-substituted 2-propyl acetates may be either electronic or steric in nature.The linear correlations for electron-releasing groups and for electron-withdrawing groups are presented and discussed.The results of the present work together with those reported in the literature lead to the establishment of a possible generalization on the influence of substituents at the alcohols side of primary, secondary, and tertiary acetates pyrolyses in the gas phase.