The reactions of cyclopropyl(methyl)bromonium ion with benzene in the gas phase

Abstract

The thermal gaseous cyclo-C₃H₅BrCH₃⁺ ion, formed by the reaction of CH₃ClCH₃⁺ ion, but not of CH₃FCH₃⁺ ion, with cyclopropyl bromide, reacts with benzene as a methylating and as an allylating agent with equal facility. The loss of the cyclic structure results either from a concerted ring cleavage during the attack or from rearrangement of cyclopropylarenium ion after the attack. The methylating ability of cyclopropyl(methyl)bromonium ion toward benzene falls between those of dimethylfluoronium and dimethylchloronium ions, i.e. CH₃FCH₃⁺ > cyclo-C₃H₅-BrCH₃⁺ > CH₃ClCH₃⁺.