The intimate ion pair mechanism in the maximally inhibited elimination kinetics of methyl 4‐chlorobutyrate and methyl 5‐chlorovalerate in the gas phase

Abstract

AbstractThe gas phase elimination of methyl 4‐chlorobutyrate and methyl 5‐chlorovalerate has been reexamined, in a static system and seasoned vessel, over the temperature range of 419.6–472.1°C and pressure range of 45–108 torr. The reactions, under maximum inhibition with propene, are homogeneous, unimolecular, and obey a first‐order rate law. The rate coefficients are given by the following Arrhenius equations: for methyl 4‐chlorobutyrate, log (k1(s−1) = (13.41 ± 0.60) ‐ (226.8 ± 8.2) kJ/mol/2.303RT; and for methyl 5‐chlorovalerate, log k1(s−1) = (13.20 ± 0.02) ‐ (227.6 ± 0.3) kJ / mol / 2.303RT. The pyrolysis rates are found to be about a half of the rates reported in a previous work. As already advanced, the carbomethoxy substituent appears to provide anchimeric assistance in the elimination process, where normal dehydrochlorination and lactone formation arise from an intimate ion pair type mechanism. The partial rates towards each of these products have been determined and reported.