Hexafluoropropylene → 1,2-Oxathietane, 3,4,4-trifluoro-3-(trifluoromethyl)-, 2,2-dioxide

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A 100 mL Parr™ reactor was charged with 63.8 g of 65% oleum (0.52 mole SO3), cooled to -45° C., evacuated, and then charged with 62 grams (0.44 mole) liquid hexafluoropropene from a cold trap (-78° C.). The reaction mixture was allowed to warm to room temperature. At 20° C. a slight exotherm was observed which increased to a maximum temperature of 56° C. and a pressure of 965 kPa over a 9 minute period. Following the exotherm the reactor was held at 42° C. for 6 hours while the mixture was agitated. The reactor was then vented of excess HFP (with the recovery of 0.7 g HFP) and the contents of the reactor were decanted to yield 103.8 grams (g) of a two phase reaction product. The upper layer (90.6 g) was separated from the lower layer, washed with concentrated sulfuric acid to remove residual SO3 and then distilled to give 63.3 grams of HFP suitone (66% yield with respect to the consumed olefln) with boiling point (b.p.) 45°-50° C. NMR analysis of a higher boiling fraction (b.p. 50°-167° C., yield 25 g) revealed a mixture oftetrafluoropropionic acid derivatives and fluorosulfonic acid. A small portion of this fraction was refluxed in methanol for one hour to give tetrafluoropropionic acid methyl ester (yield 12% based on hexafluoropropene consumed). HFP sultone, after heating with concentrated sulfuric acid for 17 hours at 40° C., was recovered by distillation with 95% yield.

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