Kinetics of the gas-phase unimolecular thermal isomerisation and decomposition of 1,1-dichloro-2,3-dimethylcyclopropane. Part II. trans-1,1-Dichloro-2,3-dimethylcyclopropane

Abstract

At temperatures between 268·6 and 364·0 °C, trans-1,1-dichloro-2,3-dimethylcyclopropane undergoes isomerisation to trans-3,4-dichloropent-2-ene and also decomposition to produce trans-3-chloropenta-1,3-diene and hydrogen chloride. In this temperature range the decomposition is the more important reaction, unlike the case of cis-1,1-dichloro-2,3-dimethylcyclopropane which undergoes mainly isomerisation. It is shown that the trans-3-chloropenta-1,3-diene is a primary product from the trans-starting material. The decomposition reaction in a seasoned reaction vessel is first order up to ca. 35% decomposition and the rate constants are independent of pressure from 4 to 55 Torr, and unaffected by added propene or by change in the surface: volume ratio. The rate constants fit the Arrhenius expression log₁₀K_diene/S^–1=(14·11 ± 0·34)–(47,726 ± 888)/4·576T.