Preparation of perfluoroallyl fluorosulfate

Method of preparing perfluoroallyl fluorosulfate which comprises reacting hexafluoropropene with sulfur trioxide in a mole ratio of 100:1 to 1:2 under anhydrous conditions in the presence of 0.1 to 5% by weight, based on the sulfur trioxide, of a trivalent boron compound selected from the group consisting of boric oxide, boron trichloride, boron trifluoride, tri(lower alkyl) borates where the alkyl groups contain 1 to 6 carbon atoms, boron oxychloride and boron oxyfluoride at a temperature of 0.degree. to 100.degree. C. for a time sufficient to produce perfluoroallyl fluorosulfate, and recovering perfluoroallyl fluorosulfate from the reaction mixture.