Process for preparing perfluoroalkyl-alkyl sulfonic acid compounds

#This invention relates to the preparation of perfluoroalkyl-alkyl sulfonic acid compounds and more specifically to their preparation by oxidizing the appropriate perfluoroalkyl-alkyl thiocyanate.

#The perfluoroalkyl-alkyl sulfonic acid compounds of this invention are useful as surface active agents and as intermediates in the preparation of water and oil repellency agents.

#U.S. Pat. No. 3,810,939 discloses a process for preparing segmented fluorocarbon sulfonic acids and related compounds by reacting a perfluoroalkyl-alkyl halide, a perfluoroalkyl olefin or a perfluoroalkyl substituted aromatic hydrocarbon with selected sulfonation reagents including alkali metal sulfites, alkali metal bisulfites, sulfuric acid, sulfur dioxide, sulfuryl chloride and chlorosulfonic acid. Derivatives of the fluorocarbon sulfonic acids including acid anhydrides, metal salts, sulfonyl halides, and sulfonamides are disclosed.

#The following examples further illustrate this invention.

#A one liter three-neck round-bottom glass flask was equipped with the following: agitator, water-cooled reflux condenser, thermometer, nitrogen inlet, and a dropping funnel for peracetic acid. The exit of the condenser was connected to a scrubber containing 400 g of 15% sodium hydroxide to trap the hydrogen cyanide which was evolved. A mixture of thiocyanates with the formula C.sub.n F.sub.2n+1 (CH.sub.2).sub.2 SCN (350 g), where n=4, 6, 8, 10, 12, 14, 16, 18, and 20 with n=8 on average with approximate weight distribution as follows:

#______________________________________ n wt % ______________________________________ 4 4 max. 6 30-42 8 28-33 10 15-17 12 14 16 15.5 max. 18 ______________________________________ and with an average molecular weight of 505 was weighed into the flask. The nitrogen flow was adjusted to approximately 375 cc/min and held at this rate for the entire oxidation. The contents of the flask were heated to 75 degrees Celsius by applying heat to the flask with a heating mantle. Commercial 35% peracetic acid (375 g) was placed in the dropping funnel. (This amount of commercial peracetic acid represented 3.6 moles of active oxygen compounds per mole of thiocyanate intermediate.) The peracetic acid was added dropwise to the thiocyanate with agitation over a period of 3.8 hours while maintaining a reaction temperature of 65 to 70 degrees Celsius by cooling with an ice bath. The reaction mass was then held with agitation at 65 plus or minus 2 degrees Celsius for 19 hours. The resulting reaction mass contained 268 g of the sulfonic acid compounds of this invention which represented a yield of 72.1%.