Kinetics of the gas-phase unimolecular thermal isomerisation of 1,1-dichloro-2,3-dimethylcyclopropane. Part I. cis-1,1-Dichloro-2,3-di-methylcyclopropane.

Abstract

The gas-phase thermal isomerisation of cis-1,1-dichloro-2,3-dimethylcyclopropane to trans-3,4-dichloropent-2-ene at 264·5–333·4° and 5–60 Torr is first-order and unaffected by changes in surface-to-volume ratio or by the addition of propene. The first-order rate constants fit the Arrhenius equation: log₁₀k(sec.^–1)=(13·65 ± 0·16)–(44,568 ± 221)/4·576T. The reaction is interpreted as a unimolecular process in which migration of the chlorine trans to the methyl groups occurs with simultaneous outward rotation of the methyl groups in a disrotatory manner. The reaction is analogous to the solvolytic rearrangements of cyclopropyltoluene-p-sulphonates.