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Originally posted by: SAIBALROUTH
Friedel-Crafts Acylation of Benzene
Reaction type: Electrophilic Aromatic Substitution
- Overall transformation : Ar-H toAr-COR(a ketone)
- Named after Friedel and Crafts who discovered the reaction.
- Reagent : normally the acyl halide (e.g. usually RCOCl) with aluminum trichloride, AlCl3, a Lewis acid catalyst.
- Alternatively, the acid anhydride, i.e. (RCO)2O, can be used instead of the acyl halide.
- The AlCl3 enhances the electrophilicity of the acyl halide by complexing with the halide.
- Electrophilic species : the acyl cation or acylium ion (i.e. RCO + ) formed by the "removal" of the halide by the Lewis acid catalyst
- The acylium ion is stabilised by resonance as shown below. This extra stability prevents the problems associated with the rearrangement of simple carbocations:
- The reduction of acylation products can be used to give the equivalent of alkylation but avoids the problems of rearrangement
- Friedel-Crafts reactions are limited to arenes as or more reactive than mono-halobenzenes
- Other sources of acylium can also be used such as acid anhydrides with AlCl3
Electrophilic aromatic substitution is an organic reaction in which an atom that is attached to an aromatic system (usually hydrogen) is replaced by an electrophile. Some of the most important electrophilic aromatic substitutions are aromatic nitration, aromatic halogenation, aromatic sulfonation, and acylation and alkylating Friedel-Crafts reactions. 😳
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