Ch_322b_15.08

Ch_322b_15.08 - by the usual mechanism. During the work up...

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Acid Anhydrides in the Friedel-Crafts Acylation Reaction Acid anhydrides are alternatives to acid chlorides in the Friedel-Crafts acylation reaction as illustrated below. Example: The Friedel-Crafts Reaction of Benzene and Acetic Anhydride + CH 3 COCCH 3 O = O acetic anhydride (i) AlCl 3 CCH 3 O + CH 3 COOH (ii) H 2 O
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The acid anhydride acts as a "pseudo acid chloride" in many reactions because the carboxyl leaving group mimics the chloride leaving group. In the Friedel-Crafts reaction, complexation with the AlCl 3 promotes bond cleavage and formation of an acylium ion intermediate . C O C CH 3 CH 3 :O: = :O: + AlCl 3 C O C CH 3 CH 3 :O: :O-AlCl 3 - + C O C CH 3 CH 3 :O: :O-AlCl 3 - + CH 3 C O: + acylium ion + CH 3 C-O-AlCl 3 :O: - aluminate salt After formation of the acylium ion, the acylation reaction proceeds
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Unformatted text preview: by the usual mechanism. During the work up with water, the aluminate salt is hydrolyzed to produce an equivalent of the carboxylic acid. Friedel-Crafts Syntheses with Cyclic Anhydrides Cyclic anhyrides are starting points for the multi-step synthesis of carboxylic acids. + succinic anhydride (i) AlCl 3 (ii) H 2 O CH 2 CH 2 C C O O O CCH 2 CH 2 COOH = O 3-benzoylpropanoic acid (88%) Zn(Hg), HCl reflux CH 2 CH 2 CH 2 COOH 4-phenylbutanoic acid (90%) CH 2 CH 2 C C O via AlCl 3 CH 2 C O: CH 2 C : :O AlCl 3-+ acylium ion O . . . . O . . . . O . . . ....
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Ch_322b_15.08 - by the usual mechanism. During the work up...

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