Radiation induced dechlorination of 1,2-dichloroethane and determination of arrhenius parameters for hydrogen atom abstraction from chloroethanes by the cyclohexyl radical

Abstract

The kinetics of the radiation induced free radical chain reactions in solutions of CH₂ClCH₂Cl in cyclohexane (RH) was studied in the temperature range 150–250°C. Chloroethyl and 1,2-dichloroethyl radicals were produced by the reaction of radiolytically generated cyclohexyl (R) radicals with the solute. The reactions studied were R + CH₂ClCH₂Cl → RCl + CH₂CH₂Cl (2), R + CH₂ClCH₂Cl → RH + CHClCH₂Cl (3), CH₂CH₂Cl + RH → CH₃CH₂Cl + R (4), CH₂CH₂Cl → CH₂CH₂+ Cl. (5), The Arrhenius parameters for reactions (2) and (3) are log₁₀(k₃/k₂)=(0.39 ± 0.09)+(11.40 ± 0.79) kJ mol^–1/2.303 RT. The difference in activation energies for reactions (4) and (5), E₅–E₄= 35.5 ± 6.0 kJ mol^–1, was obtained by assigning the value log(A₅/A₄)= 5.4 ± 0.4 based on previously published works.

The Arrhenius parameters for chlorine atom elimination from chloroethyl radicals in the liquid and gas phases are compared. In addition activation parameters for hydrogen atom abstraction from CCl₃CHCl₂, CHCl₂CHCl₂, CH₂ClCHCl₂, CCl₃CH₂Cl and CH₂ClCH₂Cl by cyclohexyl radicals are evaluated based on the present and previously published results. The effect of α and β chlorine atoms on E_H values is discussed in terms of polar and enthalpic factors.