Thermal cis-trans isomerization reaction of cis-1-bromopropene

Abstract

Thermal cis-trans isomerization reaction of cis-1-bromopropene was studied at temperature from 620.8 to 724.6 K over the pressure range 0.17-50.3 Torr. Although the main product was trans-1-bromopropene, propylene, allyl bromide, and benzene were also observed as a side products. The inhibition effect by cyclohexene, the catalytic effect by HBr, and the collision effect of $CF_4$ manifest that cis-1-bromopropene is thermally isomerized by dual mechanism, i.e., the unimolecular process and the radical process. The rate constant in maximum inhibition is expressed by $k_1 = 10^{13.4\pm0.3} \exp[(-55800 \pm 2500)/Rt] \sec^{-1}$. The pressure dependence was also studied in the presence / absence of inhibitor. The fall-off curve obtained in maximum inhibition condition appeared in the neighbour of 30-40 Torr. The reaction mechanism is proposed to offer a satisfactory explanation for thermal isomerization of cis-1-bromopropene.