Free radical substitution in aliphatic compounds. Part XXX. A reinvestigation of the gas-phase chlorination of alkanes by t-butyl hypochlorite and a study of the chlorination of 1-chloro-, 1-fluoro-, and 1-cyano-butane by the same reagent

Abstract

The chlorination of hexane and 2,3-dimethylbutane using t-butyl hypochlorite in the gas phase has been studied using the method reported previously. However the relative selectivities [equations (ii) and (iii)] for the hydrogen abstraction (i) differ slightly from those reported previously (RS^T:P=k^T₂/k^P₂ where k^T₂ and k^P₂ are the rate constants per hydrogen for abstraction from the tertiary and primary positions; superscript S referring similarly to secondary hydrogen). R^PH(R^SH,R^TH)+ Bu^tO· [graphic omitted] R^P(S,T)·+ Bu^tOH (i), log₁₀ RS^S:P=– 0·05 ± 0·11 –(5·68 ± 0·7 kJ)/2·3RT(ii), log₁₀ RS^T:P=– 0·2 ± 0·2 –(10·0 ± 1·2 kJ)/2·3RT(iii) The reasons for the small discrepancy with the earlier work is discussed. The absolute rates [equation (iv)] can be derived from the experimentally determined ratio k^P₂/k₄ using the recent literature value for k₄(the decomposition of the t-butoxyl radical). log k^P₂= 8·28 ± 0·7 –(34·7 ± 4·4 kJ)/2·3RT(iv) The investigation was extended to a qualitative study of the chlorination of 1-chloro-, 1-fluoro-, and 1-cyano-butane. The observed selectivities are discussed in terms of relative bond strengths and polarity.