Homogeneous Unimolecular Gas-Phase Elimination Kinetics of 2-Chloro-2-alkylpropanes. The Electronic Effect of Alkyl Substituents on the α-Carbon of Tertiary Chlorides

Article abstract of DOI:10.1021/j100461a011

The pyrolysis kinetics of 2-chloro-2-methylbutane and 2-chloro-2,3-dimethylbutane have been investigated, in a static system and seasoned vessel, over the pressure range of 50-280 torr and the temperature range of 260-320 deg C.The reactions are homogeneous and unimolecular, follow a first-order law, and are invariable to the presence of a cyclohexene inhibitor.The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for 2-chloro-2-methylbutane, logk₁ (s^-1)=(13.77 +/- 0.25)-(184.1 +/- 2.6) kJ mol^-1 (2.303RT)^-1; for 2-chloro-2,3-dimethylbutane, logk₁(s^-1)=(13.33 +/- 0.18)-(175.3 +/- 1.9) kJ mol^-1 (2.303RT)^-1.The distribution of the olefin products from these reactions has been quantitatively determined and reported in details.The alkyl series ((CH3)3C, (CH3)2CH, CH3CH2, CH3, and H) in the tertiary halides, 2-chloro-2-alkylpropanes, influence the rate of elimination by electronic effect.This is similar to those obtained with α- and β-alkyl-substituted ethyl chlorides.The plot of log k/k₀ vs. ?^*_(R) gives a very good straight line with ρ^*=-4.75, r=0.994, and intercept=0.048 at 300 deg C.The previous and present results reveal that, if a reaction center at the transition state of an organic molecule is markedly polar, the +I inductive electron release of alkyl substituents may affect gas-phase elimination processes.