Friedel-Crafts A) Alkylation Think of as discrete carbocation that can rearrange AlCl3 Cl Cl AlCl3 δ+ δ− Cl AlCl3 H Cl AlCl3 could also be H2O a WEAK base will suffice HCl AlCl3 Cl B) Acylation O R O AlCl3 Cl O O R R R acylium ion + Cl O AlCl3 R H Comparison of Acylation vs. Alkylation Acyl Group ~ deactivating: will only react once ~ no rearrangements Alkyl Group ~ activating: may react more than once to give disubstituted benzene ~ will rearrange to form most stable carbocation Acylation is more reliable in synthesis O O AlCl3 + R better R Cl acyl ketone + R Cl R R AlCl3 R Note that acyl ketone can be reduced to alkyl benzene O R note: H2 Pd R H2 Pd R we'll talk more about this during section on carbonyls O R NO2 NH2 nitro group is REDUCED to AMINE Synthesis Examples (A) Cl + + AlCl3 (B) O Cl + + H2 Pd O (B) is better AlCl3 Keep in Mind Note that the Lewis acid AlCl3 can complex with certain functional groups and kill the reaction. H NH2 Cl Al H N Cl AlCl3 Cl aniline Strongly e- withdrawing substituents on benzene will deactivate ring and prevent Friedel-Crafts O R NO2 Cl N.R. AlCl3 Alkylation may yield unexpected products (and mixtures of products) by rearrangement Cl H AlCl3 H Cl AlCl3 H