Free-radical addition to olefins. Part VII. Addition of trichloromethyl radicals to chloro-olefins

Abstract

The photochemically induced addition of bromotrichloromethane to a series of chlorine-substituted ethylenes has been studied in gas-phase experiments. Addition to a carbon atom of the olefin not carrying a chlorine atom leads to formation of a normal adduct. When the addition of trichloromethyl radicals or bromine atoms occurs at a carbon atom carrying a chlorine atom the major products are CCl₂CXCX₂ and BrCXCX₂ respectively, where CXClCX₂ represents the original chloro-ethylene. The rate of trichloromethyl radical addition to a chlorine-substituted site is slower than the rate of addition at CF₂ and much slower than addition to CH₂. Arrhenius parameters for the addition of CCl₃· to the CH₂ end of vinyl chloride have been measured:

k(CH₂)=(1·1 ± 0·4)× 10⁷ exp(–3400 ± 200)/RT l mol^–1 s^–1R, the gas constant, is taken to be 1·987 cal mol^–1 K^–1 and subsequent energies are expressed in cal mol^–1(1 cal = 4·19 J).