62 ALIPHATIC FLUORINE COMPOUNDS remove any residual trace of hydrogen fluoride, the mixture is subjected to distillation. The yield of acetyl fluoride, b.p. 20°, is quantitative. l,l,2-Trichloro-3,3,3-trifluoro-l-propene (CC1 2 ==€C1CF 3 ). 7 In a dry flask equipped with an efficient dephlegmator an equimolecular mixture of hexachloropropene and antimony trifluoride is heated in an oil bath. The temperature of the bath is adjusted to maintain a steady distillation at about 90° at the top of the dephlegmator. The crude distillate is mostly the desired product, distilling at 87.9°, together with a small amount of CC1^=CC1CC1F 2 . If the difluoride is wanted instead of the trifluoride the distillation is adjusted at 130°. If the monofluoride is desired, the distillation is made as rapid as possible. The fluorine utiliza-tion is complete, and there are no side reactions. Benzotrifluoride (C 6 H 5 CF 3 ). Laboratory Procedure.*'-* Benzotrichlo-ride and antimony trifluoride, in the molecular proportion of 1.5 to 1,
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