THE SULFURIC ACID METHOD 163 cyclic ketones. The method usually gives at least some of the cyclized material, although the reaction conditions may sometimes be quite critical. A simple procedure which has been followed frequently con-sists in dissolving the acid to be cyclized in 4 to 10 parts of 80-98% sulfuric acid and warming the mixture on the steam bath for one-half to three hours. Occasionally the introduction of some fuming sulfuric acid 71 or temperatures over 100° 70 may prove efficacious. The yields by the sulfuric acid method generally are lower than by the Friedel-Crafts or hydrogen fluoride methods. The examples in support of this are so numerous that no attempt is made to cite them all (see Table IX). A collection of typical cyclizations with sulfuric acid is given in Table X. One of the disadvantages of sulfuric acid as an acylating agent is its strong tendency to promote ketone condensation reactions. Early attempts to cyclize 0-phenylpropionic acid, for example, resulted
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