Pyrolysis of 1,2-dichloroethane in the presence of HBr

Abstract

The pyrolysis of 1,2-dichloroethane is catalyzed by hydrogen bromide over the temperature range 299-350°C in reaction vessels seasoned with the pyrolysis products of allyl bromide. The reaction is of the first-order in substrate (initial pressures, 20-210 mm) and of zero-order in catalyst (initial pressures, 7-380 mm). The rate coefficient is expressible as k₁= 1.3 × 10¹⁰ exp(–37 600/RT) s^–1. A small decrease in rate is caused by an increase in the surface-to-volume ratio of the reaction vessel. The reaction is complex and formally possible homogeneous radical-chain mechanisms are unsatisfactory. An interaction between the allyl bromide “carbon” surface and hydrogen bromide may produce a supply of bromine atoms which promote the radical-chain decomposition of 1,2-dichloroethane.