Methylene: gas phase reactions with organic halides

Abstract

A study has been made of the gas phase reactions of methylene (CH 2 ) with certain organic chlorides. The methylene was prepared by the ultraviolet photolysis of ketene, and the reaction products were analysed by vapour phase chromatography. The reaction of methylene with methyl chloride yielded ethane and methylene dichloride as the major products, while in the reaction with ethyl chloride, propyl chloride and methylene dichloride, methyl chloride was the compound formed at the greatest rate. Further hydrocarbons or organic halides were detected as reaction products in each case, and the experimental observations are consistent with a mechanism in which CH 2 abstracts a chlorine or a hydrogen atom from the organic halide: H — R — Cl + CH 2 → H — R● + ●CH 2 Cl or → ●R — Cl + ●CH 3 , Subsequent reactions of the radicals can then give rise to all products detected. On the basis of this mechanism, methylene was found to react about six times more rapidly with ketene than with methyl chloride. The influence upon the reaction with methyl chloride of light intensity and the presence of nitrogen and oxygen was studied, and the results interpreted in terms of radical reactions. The evidence indicates that the direct ‘insertion’ of methylene into either C—H or C—Cl bonds is a relatively unimportant process. It is suggested, that, in any case, the difference between ‘abstraction’ and ‘insertion’ mechanisms may be one of nomenclature only, and that the physical processes are equivalent.