PURPOSE: To produce arom. ketone in an efficient and profitable manner and to reutilize a catalyst and a solvent by acylating an arom. reactant with boron trifluoride as the catalyst in the solvent of anhydrous liq. sulfur dioxide.

CONSTITUTION: An arom. reactant represented by formula I [where X is H, OH, halogen, alkyl or alkoxy, (n) is 5-9 and Ar is phenylene, naphthylene or an arom. group represented by formula II (where Z is a C-C conjugated bond, O, S, SO2 or C=O], e.g. isobutylbenzene, is allowed to react with an acyl compd. represented by formula III (where R is alkyl and Y is OH, acyloxy or halogen), e.g. acetic acid, in a solvent of anhydrous sulfur dioxide in the presence of boron trifluoride as a catalyst to obtain arom. ketone represented by formula IV, e.g. 4-isobutylacetophenone. The amts. of the acylating agent, BF3 and anhydrous SO2 are preferably about 0.5-4 mol, 1-15 mol and 5-7 mol, respectively, per 1 mol of the arom. starting material. By this process, anhydrous SO2 as well as a large amt. of BF3 can be recovered and reutilized.