Difluorohaloacetyl fluoride

A mixture of either bromine or iodine and sulfur trioxide reacts with either tetrafluoroethylene or chlorotrifluoroethylene to produce an intermediate, which, when treated with fuming sulfuric acid, yields a difluorohaloacetyl fluoride [2] (equation 2) 1,1,2-Trichlorotrifluoroethane can be used as a solvent. 

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