Question

4. The first reaction is a Friedel-Craft acylation (or C-acylation) of benzene. The second and third reactions involve phenol. Explain why the second reaction (C-acylation) is a very poor reaction, even in the presence of AlCl3, and why the third reaction (0-acylation) is preferred. H3C0 + HCI Friedel-Craft acylation (or C-acylation) 8. Mode - 13 + HCI HCCI Extremely poor yield. Decent yield (0-acylation)

Answer 1

The given reactions are → Reaction - I I +Hi Extremely port yield c-acylation. tid och mild Co-aulatim) In the case of reaction-I, c-acylation takes place via electrophilic aromatic substitution. Whereas, in Cape - 2, o-acylation takes place through nucleoph acyl substin. acleophilic In the case of phenols, due to the presence of lone pair of electrony on oxygen atom, it will co-ordinate to the lewis acidy (eg: Alde) and hence the aromatic ring will become more electrom deficient due to pulling of the ring electrony teady to by the lewrs auid co-ordinated phenol oxygen atous. Therefore, it will because t h e rebent every cameboration difficult to the acyl carbocation to attack on the be aromatic ring. Hence, phenols undergo friedel-craft acylation very poorly even in presunce of Alely. Whereas, the acyl group can redily be attacked by the nucleophilic oxygen atom of phenol leading to the corresponding ester. Hence, the reaction of phend with acyl chlonce always leads to the estes rather than to the c-acylated product (Reaction-I). However, c-acylated product can be obtained through the following Fries-Rearrangement.