Free-radical substitution in aliphatic compounds. Part 20.—Gas-phase photolytic chlorination of butane and 2-methylpropane by t-butyl hypochlorite

Abstract

The light-induced chlorination of butane and 2-methylpropane by t-butyl hypochlorite has been been studied from 10 to 70°C in the gas phase. Light intensity, pressure, reactant concentration and temperature have been varied and the results have been rationalized in terms of chlorination proceeding by way of a t-butoxy radical chain carrier. The relative rates of hydrogen abstraction by the t-butoxy radical, [graphic ommitted] have been obtained per H atom for the primary, secondary and tertiary positions of the two hydrocarbons studied. kS2/kP2= 1.63±0.01 exp (3.81±0.1 kJ/RT); kT2/kP2= 1.73±0.01 exp (4.94±0.1 kJ/RT). It was also possible to relate the rate of hydrogen abstraction k2 to the rate of decomposition of the t-butoxy radical (k4), [graphic ommitted] kP2/k4= 2.7±1.1 × 10–5 exp (38.1±1.7 kJ)/RT. These results are consistent with earlier results for alkyl and alkoxy radicals.