Several aspects of the mechanism of the Friedel-Crafts acetylation of benzene were studied by in situ spectroscopic methods in ionic liquids, prepared from MCl3 (M = Al or Fe) and 1-butyl-3-methylimidazolium chloride ([bmim]Cl). Mössbauer measurements have revealed that the addition of FeCl3 to [bmim]Cl leads to an equilibrium mixture that contains solid FeCl3, [bmim][Fe2Cl7], and Fe2Cl6 and/or [bmim][FeCl4], depending on the molar ratio of FeCl3 and [bmim]Cl. The formation of [(CH3CO)2CHCO]+[MCl4] -, a potential side product in the Friedel-Crafts acetylation of benzene, was shown to require the presence of both the acetylium ion [CH3CO]+[MCl4]- and free acetyl chloride. We have confirmed that [(CH3CO)2CHCO]+[MCl4]- does not involve in the Friedel-Crafts acetylation of benzene. Experimental data and theoretical calculations indicate that the acetylium ion [CH3CO]+[MCl4]- is the key intermediate in the Friedel-Crafts acetylation of benzene and the reaction proceeds through an ionic mechanism.
|Number of pages||6|
|Journal||Journal of the Chemical Society, Dalton Transactions|
|Publication status||Published - Nov 19 2002|
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