The reaction between triphenylphosphine and 2-bromocyclohexanone

Abstract

In non-hydroxylic solvents a mixture of α- and β-oxophosphonium salts and triphenylphosphine dibromide was formed in the reaction between triphenylphosphine and 2-bromocyclohexanone, probably by initial attack on bromine. The proton n.m.r. spectrum of the dissolved salts showed the presence of a vinylic proton attributed to the quasi-phosphonium salt. The reaction is very strongly catalysed by alcohols and water, under which conditions high yields of phosphine oxide are obtained together with cyclohexanone, 2-cyclohex-1-enylcyclohexanone, and small yields of cyclopentane carboxylic acid. The relative electrophilic reactivity of chlorine and bromine in positive halogen compounds is discussed.