On the chlorination of chlorobenzene in the gaseous phase at 500-600°; The meta directing influence of the chlorine atom

The chlorination of chlorobenzene vapour in the presence of pumice as a contact substance has been studied at 500°, 550° and 600°. The reaction proceeds violently; even when a large excess of chlorobenzene is used, carbon is formed, especially in the experiments at 550° and at 600°. Besides dichlorobenzenes a considerable quantity of higher chlorinated benzenes is formed; the yields of dichlorobenzenes are low. The mixture of dichlorobenzenes has been isolated from the reaction product and the proportions of isomerides has been determined by thermal analysis. The main product (50%-60%) of the mixture of dichlorobenzenes formed within the range of 500–600°, is meta-dichlorobenzene. Although the chlorination of chlorobenzene at high temperatures is not suitable for an exact quantitative investigation, it is proved in this paper, that this substitution reaction belongs to the meta type at 500–600° in the presence of pumice as a contact substance.