158 THE FORMATION OF CYCLIC KETONES gen fluoride, although better yields have been obtained by the Friedel-Crafts method (Table II, examples 8, 9, 10, 11). The cyclization of y-phenylbutyric acid to tetralone-1 (Table III) is perhaps best effected by this new method. General Procedure. Liquid hydrogen fluoride (b.p. 19.4°) containing only 0.1-0.2% of water is available commercially in steel cylinders. It is highly corrosive to tissue, 1820 and the vapors are very toxic. Conse-quently, it should be handled with care; goggles and rubber gloves must be worn. With heed to these precautions hydrogen fluoride can be handled safely and easily. The reactions may be carried out in the hood in an open container without provision for reflux. Platinum vessels appear to be most satis-factory, although copper flasks also may be used. 183 The vessel contain-ing the acid to be cyclized is tared on a rough balance in the hood and filled with 7 to 30 parts (based on the weight of acid) of hydrogen fluoride
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