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The kinetics and mechanisms of the gas‐phase unimolecular eliminations of halogeno esters. Participation of the carbomethoxy group
Author(s) -
Chuchani Gabriel,
Rotinov Alexandra,
Dominguez Rosa M.
Publication year - 1982
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550140406
Subject(s) - chemistry , arrhenius equation , solvolysis , kinetics , dehydrohalogenation , medicinal chemistry , methyl group , reaction rate constant , group (periodic table) , torr , gas phase , atmospheric temperature range , stereochemistry , computational chemistry , thermodynamics , organic chemistry , activation energy , catalysis , quantum mechanics , physics , hydrolysis
The kinetics of the gas‐phase elimination of several chloroesters were determined in a static system over the temperature range of 410–490°C and the pressure range of 47–236 torr. The reactions in seasoned vessels, and in the presence of a free‐radical inhibitor, are homogeneous, unimolecular, and follow a first‐order law. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for methyl 3‐chloropropionate, log k 1 (s −1 ) = (13.22 ± 0.07) ‐ (231.5 ± 1.0) kJ/mol/2.303 RT ; for methyl 4‐chlorobutyrate, log k 1 (s −1 ) = (13.31 ± 0.25) ‐ (221.5 ± 3.4) kJ/mol/2.303 RT ; and for methyl 5‐chlorovalerate, log k 1 (s −1 ) = (13.12 ± 0.25) ‐ (221.7 ± 3.2) kJ/mol/2.303 RT . Rate enhancements and lactone formation reveal the participation of carbonyl oxygen of the carbomethoxy group. The order COOCH 3 ‐5 > COOCH 3 ‐6 > COOCH 3 ‐4 in assistance is similar to the sequence of group participation in solvolysis reactions. The partial rates for the parallel eliminations to normal dehydrohalogenation products and lactones have been estimated and reported. The present results lead us to consider that an intimate ion‐pair mechanism through participation of the carbomethoxy group may well be operating in some of these reactions.