A series of new 5-halo-3-oxaperflnoropentanesulfonyl fluorides from the reaotion of tetrafluoroethano sultone(or flnorooarbonyl-difluoromethane sulfonyl fluoride),fluoroolofins,potassium fluoride and halogens in diethylene glycol dimethyl ether was prepared.The fluoroolofins used were tetrafluoroethlyene,trifluoroohloroethylene,hegafluoropropene,vinylidone fluoride and symmetrioal diflnorodiohloroethylene,and halogens usod wore iodino monoohloride,bromine and ohlorine.