Kinetics of free radical chain reactions in solutions of trichloroacetonitrile in cycloalkanes. Effect of cyano-group substitution on metathetical reactions

Abstract

The kinetics of γ-radiation induced free-radical chain reactions in solutions of CCl₃CN in cyclohexane and cyclopentane were studied in the temperature range 100–250°C. CCl₂CN radicals were produced by the reaction of radiolytically generated cycloalkyl radicals with CCl₃CN. The kinetics of the following reactions were investigated, CCl₂CN + c-C₆ H₁₂→ CHCl₂CN + c-C₆H₁₁(3), CCl₂CN + c-C₅ H₁₀→ CHCl₂CN + c-C₅H₉(6), CCl₂CN + CCl₂CN →(CCl₂CN)₂(4) The following rate expressions were obtained for the above reactions of dichloroacetonitrile radicals; log₁₀{[k₃/(2k₄)^½]/dm mol^–½ s^–½}= 3.80 ± 0.3 –[(57 380 ± 2 590) J mol^–1/2.3 RT] log₁₀{[k₆/(2k₄)^½]/dm mol^–½ s^–½}= 3.22 ± 0.36 –[(53 110 ± 2 890) J mol^–1/2.3 RT].

In competitive experiments in ternary solutions of CCl₃CN and C₂Cl₄ or CHBr₃ in cyclohexane the following reactions of cyclohexyl radicals were studied; c-C₆H₁₁+ CCl₃CN → c-C₆H₁₁Cl +CCl₂CN (2), c-C₆H₁₁+ C₂Cl₄→ c-C₆H₁₁C₂Cl₄(7), c-C₆H₁₁+ CHBr₃→ c-C₆H₁₁Br + CHBr₂ where c- denotes cyclo.

The following rate expressions were obtained: log₁₀(k₇/k₂)= 0.38 ± 0.47 –[(25 050 ± 4 180) J mol^–1/2.3 RT] log₁₀(k₁₀/k₂)= 0.37 ± 0.05 –[(900 ± 440) J mol^–1/2.3 RT] where the error limits are the 95% confidence limit (2σ).

The effect of CN substitution on the activation energies of reaction (2) was evaluated by combining (E₇–E₂) with (E₇–E(c-C₆H₁₁+ CCl₄)) and (E₁₀–E₂) with (E₁₀–E(c-C₆H₁₁+CCl₄)). The effect on reaction (3) was estimated by assuming E₄=E_diffusion and comparing E₃ with E(CCl₃+ c-C₆H₁₂).