Alkylation mechanism of benzene with 1-dodecene in [Bmim]Br-AlCl3 was investigated. Alkylation of C6D6 with 1-dodecene using [Bmim]Br-ALCl3 as a catalyst was firstly carried out. Molecular structures of products, dodecylbenzene isomers, were analyzed by GC-MS and NMR, and the deuterated atom in the dodecylbenzenes was verified to be connected with 1-carbon of the side chain. Alkylation mechanism was deduced by tracing the deuterated atom. Results demonstrated that alkylation was induced by AlCl3, which was generated by the dissociation of [Al2Cl6Br]－. The role of AlCl3 in attracting electrons pushs π electrons to 1-carbon of 1-dodecene, and the positive center is formed at 2-carbon. The carbonium ion reacts with benzene to form a σ complex, which is instable and D＋ connected to the σ carbon of ring is transferred into electronegative 1-C of the side chain to form a C—D bond, accordingly AlCl3 leaves. 2-Dodecylbenzene is formed. The Lewis acid mechanism provides the evidences for the higher selectivity of 2-dodecylbenzene using ionic liquid as catalyst than that using H＋ as catalyst.

Key words: deuterated benzene, ionic liquid, alkylation, reaction mechanism