Acylation by carboxylic anhydrides or acids

This often gives better yields than are obtained from the corresponding acyl chloride, e.g., in the case of acetophenone. Boron trifluoride is particularly useful in these reactions as a mild condensing agent.323 516 

Perchloric acid has also been recommended as condensing agent, as, for example, in the case of acetylthiophen 553 

A mixture of acetic anhydride (15.5 g) and 60% perchloric acid (d 1.535 6 drops) is added to thiophen (8.5 g) with stirring, and the mixture is set aside for 30 min and then poured into a mixture of ice and water (50 ml). The organic layer is separated, and the aqueous layer is extracted with ether. The united organic phases are washed with water and then with sodium carbonate solution, dried over sodium sulfate, and distilled, affording 2-acetyl-thiophene, b.p. 209-212°, in 95% yield. 

2-Acetylthiophen can also be prepared from thiophen and acetic anhydride with boron trifluoride (70% yield),32a 516 85% phosphoric acid,554 concentrated phosphoric acid,525 or sulfuric acid.555 

5-Dimethylfuran is acetylated in 87% yield at position 3 by acetic anhydride and tin tetrachloride at room temperature.556 

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Acylation by carboxylic anhydrides or acids. Carboxylic anhydrides can be used in place of acyl chlorides, the reaction being ... 

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