Gas-Phase Elimination Kinetics of Ethyl Esters of Chloroacetate, 3-Chloropropionate, and 4-Chlorobutyrate. The Electronic Effects of Substituents at the Acyl Carbon

Article abstract of DOI:10.1021/j150609a030

Several ethyl chloroesters were pyrolyzed in a static reactor in the presence of a propene inhibitor at temperatures between 360 and 420 deg C and pressures between 49 and 209 torr.The reactions are homogeneous, unimolecular, and follow a first-order rate law.The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for ethyl chloroacetate, log k(s^-1) = (12.70+/-0.50) - (197.0+/-6.1)kJ mol^-1 (2.303RT)^-1; for ethyl 3-chloropropionate, log k(s^-1) = (12.54+/-0.22) - 196.8+/-2.7) kJ mol^-1 (2.303RT)^-1; and ethyl 4-chlorobutyrate, log k(s^-1) = (12.67+/-0.31) - (198.7+/-3.8) kJ mol^-1 (2.303RT)^-1.The data from the rate coefficients give an approximate correlation only with ?^* values (ρ^*=0.357, r=0.903, and intercept =0.048 at 400 deg C).The present work together with those reported in the literature suggests, that electron-withdawing substituents at the acyl carbon of ethyl, isopropyl, and tert-butyl esters of substituted acetates enhance the rate of elimination, whereas electron-releasing substituents decrease it.