THE USE- OF INORGANIC FLUORIDES 53 Vinyl halides are so inert that none has been converted to a fluoride "by halogen exchange. Vinyl fluorides have been synthesized from satu-rated polyhalides by dehalogenation with zinc and by dehydrohalo-^genation with alcoholic alkali, and from acetylene by addition of one molecule of hydrogen fluoride. 12 " 18 Next to allyl halides in ease of replacement are saturated polyhalides of the types RCX 2 R' and RCX 3 . They are transformed to the corre-sponding polyfluorides RCF 2 R' 19 > 20 and RCF 3 Bo ' 21 by long refluxing with antimony trifluoride or hydrogen fluoride. The reaction is so slow, however, that it would be of little practical importance if it could not be accelerated by the addition of small amounts (2Jto 5%) of a pentavalent antimony salt; this procedure, discovered by Swarts about 1890, 22 has plroved the most important means of synthesizing organic fluorides. The pentavalent antimony salt is usually, produced by adding free halo-
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