Addition–elimination reactions in heterolytic chlorinations of p-xylene

Abstract

Chlorinations of p-xylene and chloro-p-xylene with molecular chlorine at 20–21 °C in the dark and in acetic acid and, second, of p-xylene in nitrobenzene and neat with or without weak catalysts, have been carried out. The results are compared with those obtained for the FeCl₃-catalysed chlorinations of p-xylene and chloro-p-xylene and reveal that dichloro derivatives (especially 2,3-dichloro-p-xylene) are obtained directly from p-xylene, probably by an addition–elimination mechanism which occurs in all the media used except for the FeCl₃-catalysed chlorination. The direct formation of dichloro derivatives from p-xylene, as well as that of trichloro-p-xylene from chloro-p-xylene, is shown by chlorination of an equimolar mixture of [²H₁₀]-p-xylene and chloro-p-xylene. The separation and evaluation of deuteriated and non-deuteriated chloro derivatives are carried out by g.l.c. on capillary columns.