The catalytic isomerization of allylbenzene in the presence of palladium(II) chloride

Abstract

Allylbenzene has been shown to isomerize rapidly in the presence of palladmm(11) chloride in acetic acid, mainly to trans-β-methylstyrene but to a small extent to the cis isomer. The reaction is not simple. The initial formation of an olefin complex is succeeded by a further slow reaction involving the palladium complex before isomerization takes place. The isomerization reaction itself is zero order with respect to allylbenzene except nearing completion when it becomes first order in allylbenzene concentration. The reaction is first order with respect to catalyst. Rates have been measured by a technique involving N.M.R. spectrometry. Substitution in allylbenzene inhibits isomerization in the case of 2-bromoallylbenzene but not entirely in the case of the corresponding methyl derivative. The mechanism is discussed in the light of an intermediate hydrido complex.