138 THE FORMATION OF CYCLIC KETONES boiling point of 79°, it can be removed readily when used in excess. On the other hand, a number of instances are on record 48> Mi Mi 90> M-w describing a deleterious action of thionyl chloride. Among these are six examples in which the use of the reagent directly upon the acid resulted in the formation of tarry decomposition products. In one case 48 the difficulty was eliminated by employing ether as a solvent, and in three others M-90> 91 it was found necessary also to use thionyl chloride of a high degree of purity. 79 The treatment of Y-3-pyrenylbutyric acid with thionyl chloride was found to require exceptional care. In addition to the above precautions the mixture could not be heated much above 40° during removal of the ether without decomposition. 84 When thionyl chloride is used in conjunction with stannic chloride it is usually neces-sary to remove the thionyl chloride completely before cyclization.
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