Acylation reaction of m-cresol with 2-chlorobenzoic acid in PPA occurred through a prior esterification, followed by a Fries rearrangement of ester (3) to give benzophenones 4—7.Ester 3 undergoes the Fries rearrangement in PPA, giving benzophenones 4—7 in about the same yield as can be obtained by direct acylation reaction of m-cresol with 2-chlorobenzoic acid. The benzophenone 5 is not stable in PPA and decomposed to benzophenone (4). The formation of benzophenones 4—7, from Fries rearrangement of the ester 3 was interpreted by an intermolecular mechanism.
间甲酚与
2-氯苯甲酸在
PPA 中发生酰化反应,先发生酯化反应,然后酯(3)发生弗里斯重排反应,得到
二苯甲酮 4-7。酯 3 在
PPA 中发生弗里斯重排反应,得到
二苯甲酮 4-7,收率与
间甲酚与
2-氯苯甲酸直接发生酰化反应得到的收率大致相同。
二苯甲酮 5 在
PPA 中不稳定,会分解成
二苯甲酮 (4)。
二苯甲酮 4-7 是通过酯 3 的弗里斯重排反应生成的,其分子间机理可以解释。