Kinetics of the gas-phase homogeneous unimolecular elimination of selected ethyl esters of 2-oxo-carboxylic acids

摘要

The gas-phase elimination kinetics of selected ethyl esters of 2-oxo-carboxylic acid have been studied over the temperature range of 270-415 °C and pressures of 37-114 Torr. The reactions are homogeneous, unimolecular, and follow a first-order rate law in a seasoned static reaction vessel, with an added free radical suppressor toluene. The observed overall and partial rate coefficients are expressed by the following Arrhenius equations: Ethyl oxalyl chloride log k_(overall) (s~(-1))=(13.22 ± 0.45) - (179.4 ± 4.9) kJ mol~(-1) (2.303 RT)~(-1) Ethyl piperidineglyoxylate log k_((CO2)) (s~(-1))=(12.00 ± 0.30) - (191.2 ± 3.9) kJ mol~(-1) (2.303 RT)~(-1) log k_((CO)) (s~(-1))=(12.60 ± 0.09) - (210.7 ± 1.2) kJ mol~(-1) (2.303 RT)~(-1) log k_(t(overall)) (s ~(-1))=(12.22 ± 0.26) - (193.4 ± 3.4) kJ mol~(-1) (2.303 RT)~(-1) Ethyl benzoyl formate log k_((CO2)) (s ~(-1))=(12.89 ± 0.72) - (203.8 ± 9.0) kJ mol~(-1) (2.303 RT)~(-1) log k_((CO)) (s~(-1))=(13.39 ± 0.31) - (213.3 ± 3.9) kJ mol~(-1) (2.303 RT)~(-1) log k_(t(overall)) (s~(-1))=(13.24 ± 0.60) - (205.8 ± 7.6) kJ mol~(-1) (2.303 RT)~(-1) The kinetic and thermodynamic parameters of these reactions, together with those reported in the literature, lead to consider three different mechanistic pathways of elimination.