Gas-phase eliminations. Part XIII. The pyrolysis of 1,1- and 1,2-dibromoethane

Abstract

The kinetics of the thermal decompositions of 1,1- and 1,2-dibromoethane have been studied in a static system seasoned with the products of reaction. The products in each case are vinyl bromide and hydrogen bromide. In the absence of inhibitors, the reactions are catalysed by hydrogen bromide and follow complex kinetics involving reaction chains. However, the chain reactions may be inhibited by cyclohexene. The inhibited reactions follow first-order kinetics and are believed to occur by a unimolecular mechanism. The Arrhenius equation for 1,1-dibromoethane is k₁= 10^{13·25 ± 0·22} exp [(–50,520 ± 600)/RT] sec.^–1, while the rate constant for the pyrolysis of 1,2-dibromoethane at 415·5 °C is 4·9 × 10^–5 sec.^–1. The implications of these results in the light of the heterolytic theory of gas-phase eliminations from alkyl halides are discussed.