Kinetics and Mechanism of Elimination of Primary Alkyl Methanesulfonates in the Gas Phase. Correlation of Alkyl Substituents

Article abstract of DOI:10.1021/j100338a042

The gas-phase elimination kinetics of eight primary alkyl methanesulfonates were studied in a seasoned, static reaction vessel over the temperature range of 280.6-350.2 deg C and the pressure range of 32-178 Torr.The reactions are homogenous and unimolecular, follow a first-order rate law, and are invariant to the presence of equal or excess amount of the radical chain suppressor cyclohexene and/or propene.The observed overall rate coefficients are represented by the following Arrhenius equations: For ethyl methanesulfonate, log k₁(s^-1) = (12.18+/-0.12)-(171.7+/-1.3) kJ mol^-1 (2.303RT)^-1; for n-propyl methanesulfonate, log k₁(s^-1) = (12.36+/-0.28)-(171.6+/-3.3) kJmol^-1 (2.303RT)^-1; for n-butyl methanesulfonate, log k₁(s^-1) = (12.16+/-0.20)-(168.7+/-2.3) kJmol^-1 (2.303RT)^-1; for n-pentyl methanesulfonate, log k₁(s^-1) = (12.25+/-0.09)-(169.4+/-1.0)kJmol^-1 (2.302RT)^-1; for n-hexyl methanesulfonate, log k₁(s^-1) = (12.21+/-0.19)-(168.9+/-3.3)kJmol^-1 (2.303RT)^-1; for 3-methyl-1-butyl methanesulfonate, log k₁(s^-1) = (12.74+/-0.19)-(174.7+/-2.2)kJmol^-1(2.303RT)^-1; for 3-methyl-1-pentyl methanesulfonate, log k₁(s^-1) = (12.28+/-0.17)-(167.9+/-1.9)kJmol^-1(2.303RT)^-1; for 3,3-dimethyl-1-butyl methanesulfonate, log k₁(s^-1) = (12.14+/-0.11)-(165.2+/-1.3) kJmol^-1 (2.303RT)^-1.The present data give good correlation lines when log k/k₀ are plotted against several steric parameters E_s and E_s^c and $v values.Apparently, steric factors seem to be operating in these elimination reactions.The primary alkyl methanesulfonates are found to be faster in rates of olefin formation when compared to other primary organic esters.The reaction of this work is interpreted in terms of an intimate ion pair type of mechanism.