130 THE FORMATION OF CYCLIC KETONES METHODS OF CYCLIZATION Probably the two most generally useful methods for effecting intra-molecular acylation are by the Friedel-Crafts type of reaction on the acid chloride and the action of anhydrous hydrogen fluoride on the free acid. In addition to these methods, cyclizations have been effected by the use of sulfuric acid and other reagents. The Friedel-Crafts Method Many acid chlorides can be induced easily to eliminate the elements of hydrogen chloride intramolecularly. Thus, in the preparation of the chlorides of 7-arylbutyric acids by warming with phosphorus penta-chloride for a short period, in at least two instances cyclic ketones were obtained in addition to the acid chlorides. 69-60 7-6-Tetralylbutyric acid upon such treatment gave 40% of ketone, along with the expected acid chloride. 69 When heated at about 120° under diminished pressure, the acid chloride lost hydrogen chloride to an extent approximating com-pleteness, so that the total yield of ketonicmaterial was 83%. An extreme
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