A Destructive Ethylation Reaction of Benzene with 3-Methylpentane-1-14C

The destructive alkylation reaction of benzene with 3-methylpentane to give ethylbenzene in the presence of aluminum chloride was investigated. When 3-methylpentane-1-14C was employed, radioactive ethylbenzene was obtained. A radioassay of radioactive ethylbenzene showed that: a) the specific radioactivity of the ethylbenzene was about one-third that of the starting 3-methylpentane-1-14C, and b) more than 90% of the radioactivity of the ethylbenzene was present on the β-carbon atom of the ethyl group. These findings suggested a preceding equilibrium between 3-methylpentane and 2-methylpentane, which resulted in an equivalent localization of the radioactive label on three methyl groups of these C6-hydrocarbons. A carbonium-ion mechanism including an intermediate ethyl cation was discussed in detail.