Yield improvements in the electrochemical production of perfluorooctanoic acid

Abstract The current industrial technique for perfluorooctanoic acid production (a precursor of important emulsifying agents for polymerizations) is the electrochemical fluorination of n-octanoyl fluoride in anhydrous HF (Simons process). This process suffers from a poor molar yield of perfluorooctanoyl fluoride (15–20%), due to formation of large amounts of several by-products. F -2- butyl-tetrahydrofuran and F -2-propyl-tetrahydropyran are two of these by- products [A.K. Barbour, in R.E. Banks (ed.), Organofluorine Chemicals and Their Industrial Applications , (1979) 56], whose formation arises from cyclization of the carbonyl oxygen on the carbon atoms 4 or 5 of the linear hydrogenated chain respectively [F.G. Drakesmith and D.A. Hughes, J. Appl. Electrochem. , 9 (1979) 685]. On the basis of the mechanism EC b EC N proposed for this process [J. Burdon, I.W. Parsons and J.C. Tatlow, Tetrahedron , 28 (1972) 43; I.N. Rozhkov , Russian Chem. Rev., 45 (1976) 615], the possibility to reduce significantly this cyclization was confirmed by starting from precursors having the positions 4 and 5 fully fluorinated; in fact, by using 4,4-difluorooctanoyl fluoride [ UK Pat. 1 000 288 (1965)]* or 4-perfluorobutyl-butanoyl fluoride [M. Napoli, L. Conte, G.P. Gambaretto and F.M. Carlini, J. Fluorine Chem., 45 (1989) 213]* as a starting material, a yield decrease of F-2-butyl-tetrahydrofuran or F-2-propyl-tetrahydropyran was observed, so that an improved molar yield of perfluorooctanoyl fluoride was experimentally detected. The results obtained when a new fluorinated compound (2-perfluorohexyl acetic acid) was used as a starting material in the electrofluorination process are presented here and the yields compared with those observed in the above-cited references (*).