Correlation of Alkyl and Polar Groups in the Gas-Phase Pyrolysis Kinetics of α-Substituted Ethyl Chlorides

Article abstract of DOI:10.1021/j100281a042

The kinetics of the gas-phase pyrolysis of several secondary chlorides were determined in a static system over the temperature range 369.9-490.1 deg C and the pressure range of 28-298 Torr.The reactions in seasoned vessels, with the free radical suppressor propene and/or toluene always present, are homogeneous and unimolecular and obey a first-order rate law.The observed rate coefficients are represented by the following Arrhenius equations: for 2-chloropropionitrile, log k₁ (s^-1) = (13.45+/-0.57)-(236.1+/-8.2) kJ mol-1; for methyl 2-chloropropionate, log k₁ (s^-1) = (12.22+/-0.54) - (217.0+/-7.4) kJ mol^-1 (2.303RT)^-1; for methyl 3-chlorobutyrate, log k^-1 (s^-1) = (13.65 +/-0.39)-(214.9+/-5.0) kJ mol^-1 (2.303RT)^-1.The data of this work together with those reported in the literature confirm previous correlations that α-alkyl substituents of ethyl chloride give a good straight line, when log k/k₀ vs. ?* values (ρ* = -3.58 +/- 0.24, correlation coefficient = 0.996, and intercept = -0.0066 at 360 deg C) are plotted, while α-polar substituents give rise to an inflection point at ?*(CH3) = 0.00 into another straight line (ρ* = -0.46+/-0.06, correlation coefficient = 0.972, and intercept = 0.017 at 360 deg C).Several other polar α-substituents have been found to enhance the dehydrochlorination process by means of their electron delocalization or resonance effect.Revising a work reported on the pyrolysis kinetics of pinacolyl chloride, a Wagner-Meerwein rearrangement appears to be a reasonable explanation for the formation of about 12percent of the 2,3-dimethylbutene products.