Kinetics and mechanism of the thermal decomposition of 1-bromo-2-chloroethane

Abstract

The thermal decomposition of 1-bromo-2-chloroethane at 307–358° results in vinyl chloride and hydrogen bromide as the main products, with vinyl bromide and hydrogen chloride as minor products, the latter being formed mainly via a secondary reaction between the main products. Induction periods are evident below 327°, and propene has a marked inhibitory effect upon the decomposition. The rate of decomposition is sensitive to the nature and treatment of the reaction vessel surface and there is autocatalysis owing to hydrogen bromide. In vessels seasoned with the pyrolysis products of allyl bromide, the reaction catalysed by a sufficiently high proportion of hydrogen bromide is of the half-order in substrate and zero-order in catalyst. At 307–358° the rate coefficient is expressible as in equation (A). The catalysed reaction does not show induction periods, but the rate is decreased k0·5= 9·3 × 109 exp (–40,800/RT) mole–½ l.–½ sec.–1(A) slightly in packed vessels. The results are consistent with a radical-chain reaction, and possible mechanisms are discussed.