The Relative Rates of Photo-Chlorination of CHCl3 and CDCl3

Abstract

The relative rates of photo‐chlorination of chloroform and deuterochloroform have been determined in the temperature range of −20° to 180°C. The ratio of the rate constants for the two reactions can be fitted by the equation: $$k_1{\mathrm{/k}}_2\text{=1.4±0.2\hspace{0.17em}}\exp \text{(710∓90/RT).}$$ This result is discussed in terms of Eyring's absolute reaction rate theory and also in terms of an alternative mechanistic explanation. The observed difference in activation energy is accounted for in terms of the zero‐point energies of the normal molecules and the activated complexes. It was found that some deuterochloroform was produced when chloroform was chlorinated in the presence of deuterium chloride. This result indicates that the reaction $$\mathrm{HCl}+{\mathrm{CCl}}_3={\mathrm{CHCl}}_3+\mathrm{Cl}$$ must occur to some extent in the gas‐phase chlorination of chloroform, contrary to the conclusions of Schumacher and Wolff. It was also found that appreciable amounts of hexachloroethane were formed in the reaction. Hence, it is concluded that the formation of this substance must be an important chain‐terminating step in the reaction mechanism.