Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: horsebox on October 22, 2010, 11:03:15 PM
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In my lab we did a Friedel-Crafts acylation on toluene using phthalic anhydride and AlCl3 as the lewis acid. Everything I've read on Friedel-crafts acylations so far involve acyl chlorides, I've never even heard of acid anhydrides being used, this is a fairly cool reaction. As for the mechanism I'm guessing the AlCl3 snatches 2 electrons from one of the anhydride bonds which breaks it and yields the carbocation. Are there any other alternative mechanisms for FC acylations?
We also did a Friedel-Crafts alkylation using an unconventional mechanism. Instead of using an alkyl halide with AlCl3, we used an alcohol with H2SO4. The H2SO4 protonates the -OH group and the H2O molecule leaves, yielding the carbocation. Are there any other unconventional routes for FC alkylations?
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In my lab we did a Friedel-Crafts acylation on toluene using phthalic anhydride and AlCl3 as the lewis acid. Everything I've read on Friedel-crafts acylations so far involve acyl chlorides, I've never even heard of acid anhydrides being used, this is a fairly cool reaction. As for the mechanism I'm guessing the AlCl3 snatches 2 electrons from one of the anhydride bonds which breaks it and yields the carbocation. Are there any other alternative mechanisms for FC acylations?
We also did a Friedel-Crafts alkylation using an unconventional mechanism. Instead of using an alkyl halide with AlCl3, we used an alcohol with H2SO4. The H2SO4 protonates the -OH group and the H2O molecule leaves, yielding the carbocation. Are there any other unconventional routes for FC alkylations?
As a hint carbocations next to carbonyl groups are unlikely.
Usually in a FC reaction the Lewis acid coordinates to the aromatic ring to give an ate complex which then reacts with a nucleophile.
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You can get to acylium intermediates from carboxylic acids as well by using either a strong acid or some other powerful activator (that essentially makes an acid chloride equivalent in situ). I believe the former strategy is common in industry because handling the acid chlorides can be hazardous.