Abstract
The Fries rearrangement reactions of acetyloxy- and benzoyloxybenzenes were carried out both under microwave irradiation and conventional heating conditions, and the effect of microwave irradiation was examined. Acceleration of the reaction for the acetyloxy derivatives could not be confirmed, but was successfully demonstrated for the benzoyloxy derivatives. On the Fries rearrangement, the Lewis acid coordinates to the ester oxygens, but also coordinates to the aromatic rings. The microwave is efficiently absorbed by such an adduct between the Lewis acid and substrate, resulting in acceleration of the reaction.
Highlights
The Fries rearrangement reaction reported by Fries et al in 1908 (Blatt, 1942; Clark, Dekamin, & Moghaddam, 2002; Fries & Finck, 1909; Martin, 2009) involves the heating of a phenolic ester of a carboxylic acid in the presence of a Lewis acid catalyst to promote rearrangement of the acyl group to give an aromatic hydroxyketone (Scheme 1)
When the reaction is reversible, even if the positive reaction is accelerated by some factor, the reversible reaction is accelerated at the same time, and so the apparent reaction rate does not change
In the case of the 4-substituted phenyl acetates, no change in the reaction rate was observed under the different the heating conditions regardless of the properties of the substituent, thereby indicating that microwave irradiation did not show any specific effect on the Fries rearrangement of these substrates
Summary
The Fries rearrangement reaction reported by Fries et al in 1908 (Blatt, 1942; Clark, Dekamin, & Moghaddam, 2002; Fries & Finck, 1909; Martin, 2009) involves the heating of a phenolic ester of a carboxylic acid in the presence of a Lewis acid catalyst to promote rearrangement of the acyl group to give an aromatic hydroxyketone (Scheme 1). This rearrangement reaction has much in common with the Friedel-Crafts acylation reaction in terms of both the reaction conditions and the obtained product; both reactions are Lewis acid-catalyzed reactions that yield aromatic ketones. The effects of microwave irradiation will be examined for both acetyloxy and benzoyloxy derivatives
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