It is known how to prepare fluorinated ethers by addition of hypofluorite to fluorochloro-olefins, as is described in Italian patent application No.  20781 A/85 in the name of the Applicant hereof.  This kind of reaction is generally conducted under strictly controlled conditions, maintaining the temperature at very low values (from -50.degree.  to +50.degree.  C.), as hypofluorite decomposition reactions can easily occur. 
Furthermore, it should be taken into account that the yields can vary in an unforeseeable manner depending on the selected olefin and hypofluorite owing to other secondary reactions. 
In particular, the reaction of 2-bromoperfluoroethylhypofluorite with difluoro-dichloroethylene was not known. 
The preparation of hypofluorite of formula BrCF.sub.2 --CF.sub.2 OF is disclosed in patent application No.  21632 A/86, fluorine is directly reacted with BrCF.sub.2 --COF on cesium fluoride as a catalyst, in the presence of nitrogen as a diluent to produce BrCF.sub.2 --CF.sub.2 OF. 
Hypofluorite is an unstable compound and easily leads to .beta.  scission reactions; it was observed that by reacting the gas stream of N.sub.2 -diluted hypofluorite with the olefin dissolved in a solvent, even at low temperature, the product did not form.