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33) Boiling point (acid form) (200C at 101 kPa) , Contains NO CBI j 952 FLUORINE COMPOUNDS, ORGANIC DEC 0 9 2003 20. US.Pat. 3,250,807 (May IO, 19661, C. G. Fritz and E. P. Moore (to E. I. du Pont de Nemours & Co., Inc.). 21. US.Pat. 4,102,872 (July 25, 19781, W.R. Griffin (to U.S.Air Force). WARRENR. GRIFFIN I Air Force Materials Laboratory PERFLUOROALKANE SULFONIC ACIDS The perfluoroalkane sulfonic acids were first reported in 1954. Trifluoro- methanesulfonic acid was obtained by oxidation of bis(trifluoromethy1thio)mercury with aqueous hydrogen peroxide (1)(see also Sulfonic acids). The preparation of a - - series of perfluoroalkane sulfonic acids by electrochemicalfluorination (ECF) of alkane sulfonyl halides was also disclosed in the same year (2). HF RS02F RfSOzF wo4 RfSOiK RjS03H ECF aq KOH CF3S03H may also be prepared from trifluoromethanesulfenyl chloride (3). [421-83-0] (2926-30-91 or by the oxidation of methyl trifluoromethyl sulfide under a variety of conditions (4-5). The boiling points of a series of perfluoroalkane sulfonic acids are listed in Table 1(2). TrifluoromethanesulfonicAcid The first member of the series, CF3S03H. has been studied extensively. T w o excellent review articles (6-7) cover the chemistry of the acid and its derivatives in great detail. - -5 Trifluoromethanesulfonic acid is available as Fluorochemical Acid FC-24 (3M Co.). T h e technical brochure (8) is an excellent source for applications, safety, and handling data of the acid. Properties. Trifluoromethanesulfonic acid is a stable, hygroscopic liquid which fumes in air. An equimolar amount of water with the acid results in a stable, distillable monohydrate, mp 34"C, bp 96C at 0.13 kPa (1mm Hg)(9). Measurement of con- ductivity OF strong acids in acetic acid has shown the acid to be one of the strongest simple protic acids known, similar to fluorosulfonic and perchloric acid (10).Triflu- oromethanesulfonic acid is miscible in all proportions in water, and is soluble in many polar organic solvents such as dimethylformamide, dimethyl sulfoxide, and acetonitrile. In addition, it is soluble in alcohols, ketones, ether, and esters, but these generally are not suitably inert solvents. The acid with diethyl ether gives a colorless,liquid oxonium complex, which with further heating, gives the ethyl ester and ethylene. Reaction with ethanol gives the ester, but in addition, dehydration and ether formation occurs. I i 1 ! 1 I I I I 5 t t. I U S & co., tboratory rrifluoro)mercury ation of a of alkane Contains No CBI Vol. 10 I FLUORINECOMPOUNDS,ORCANICDEC 958 2003 1 Table 1. Boiling Points of a Series of Pedluoro Alkane Sulfonic Acids. Compound CAS Reg. No. Boiling pointa "C/kPa aC/lOl kPa CFSSO~H + CzFsS03H n-C4FgS03H n-C5F11S03H n-CeF13S03H n-CaF17S03H [ I493-13-61 [354-88-1] [59933-66-31 [3872-25-11 [355-46-41 [1763-23-11 60/0.4 81/2.9 76-8410.13 110/0.67c 95/0.47 133/0.8 166 175 200b ?+ 212b.d 225 249 [ 72441.89-51 120/0.4 24 1 [41242-13-I] 254 a To convert kPa to mm Hg, multiply by 7.5. Estimated boiling point. ~-C~F~~SO~H.HZO. :onditions ,din Table vely. Two ivatives in 'C-24 (3M afety, and luid which distillable mt of con? strongest .O). Triflu)lein many cetonitrile. nerally are id oxonium action with occurs. The strongly electron-attracting CF3SO; group makes the esters excellent al- kylating agents. Methyl trifluoromethanesulfonate [333-27-71is more than lo4 times as reactive as methyl toluenesulfonate in acetolysis (11).Trifluoromethyl trifluoro- methane sulfonate [3582-05-61was obtained by the reaction of trifluoromethanesul- fonic acid with fluorosulfuric acid (12). The trifluoromethylating ability of the triflate (see below) is limited, benzene at 100C giving only small amounts of benzotrifluo- ride. -5 Derivatives. Alkyl esters of trifluoromethanesulfonic acid, commonly called tri- flates have been prepared primarily from the silver salt [51098-28-31 and an alkyl io- dide, or by reaction of the anhydride with alcohol (9,13). The metallic salts of trifluoromethanesulfonicacid, also called triflates,are prepared by reaction of the acid with the corresponding hydroxide or carbonate. The salts are hygroscopic but can be dehydrated at 100C under vacuum. The sodium salt has a melting point of 248C and decomposes at 425C. The rare earth salts are also obtained from the acid and rare earth metal oxides (14). Organic trifluoromethanesulfonate salts are quantitatively prepared from the acid and amines (9). Triflate salts show promise as electrolytes for nonaqueous electrochemical cells (15),as catalysts for epoxy resins (16),and latent catalysts for cationically polymerizable monomers (17-18). Trifluoromethanesulfonic acid anhydride [358-23-61, bp 84"C, is prepared by refluxing the acid over an excess of phosphorus pentoxide (19). It reacts instanta- neously with ammonia, aqueous ammonium hydroxide, or amines, to form trifluoro- methanesulfonamides. The anhydride is generally a more effective esterification promotor than trifluoroacetic acid anhydride. A number of methods have appeared that allow the introduction of the CF3SOT group on carbon; the synthetic utility of these derivatives in organic chemistry has been reviewed (20). 954 FLUORINE COMPOUNDS, ORGANIC Contains No CBI DEC 0 9 2003 Higher Perfluoroalkane Sulfonic Acids The longer chain perfluoroalkane sulfonic acids ate very hygroscopic oily liquids. Distillation of the acid from a mixture of its salt and HzS04 gives hydrated mixtures with melting points above 100C. The acids show the same polar solvent solubilities as trifluoromethanesulfonicacid but are quite insoluble in benzene, heptane, carbon tetrachloride, and the perfluorinated liquids. Many of the higher perfluoroalkane sulfonic acids have been prepared by electrochemical fluorination as previously described (13). apPerfluoroalkane disulfonic acids can be prepared by aqueous alkali permanganate oxidation of the bis-sulfone, RfSO2(CF2CF2),,SO:R (21). The longer chain acids, particularly C ~ F L ~ S Oan~d Hhigher, are surface-active agents in aqueous media. Derivatives of the acids have unique surface-activeproperties and have formed the basis for a number of commercial fluorochemical surfactants (22). T h e chemical and thermal stability of the perfluorosulfonate salts as well as their surface activity has led to their use in strong acid and base environments. Very low surface tensions in aqueous media, less than 20 mN/m (= dyn/cm), are obtained with most fluorochemical surfactants derived from the perfluoro sulfonic acids. This has led to their use as wetting and leveling agents (see also Surfactants). Safety and Storage Extreme caution should be used when handling the perfluoroalkane sulfonic acids. Eye irritation studies with albino rabbits suggest extreme irritation and permanent eye damage could occur following eye contact, even if the eyes are immediately flushed with water. Acute inhalation toxicity studies (albino rats) indicate that high vapor of mist concentration can cause significant respiratory irritation. All contact of the I acids and alkyl esters with the skin should be avoided. Normal procedures for treat- ment of strong acid burns should be used. -, Contact of the perfluoroalkane sulfonic acids with cork, rubber, cellulosics, and plasticized materials will cause discoloration and deterioration of those materials. Samples are best stored in glass ampuls or glass bottles with Kel-F or Teflon plastic screw-cap linings. Trifluoromethanesulfonic acid in contact with stainless steel, irzn or aluminum typically causes a weight loss of about 20 mg/(mz-d). Use of glass equipment where possible is recommended. BIBLIOGRAPHY 1. R. N.Hazeldine and J. M.Kidd, J. Chem. SOC.,4228 (1954). 2. P.W. Trott and co-workers, 126th National Meeting of the American Chemical Society, New York, 195.1, Abstracts p. 42-M. 3. R. N. Hazeldine and J. M. Kidd, J.Chem. SOC.,2901 (1955). 4. R.N. Hazeldine and co-workers, Chem. Commun., 249 (1972). 5. R.B.Ward, J. Org. Chem. 30,3009 (1965). 6. A.Senning,Chem. Reu. 65,385 (1965). 7 . R. D. Howells and J. D. McCown, Chem. Reu. 77,69 (1977). 8. FLUORAD@Brand Fluorochemical Acid FC-24, 3M Company, St. Paul, Minn. 9. T. Gramstad and R. N. Hazeldine, J. Chem. SOC.4,69 (1957). 10. T. Gramstad, Tidsskr. Kremi Bergues. Metall. 19,62(1959); Chem. Abstr. 54,14102(1960). 11. R.L.Hansen.J. Org. Chem. 30,4322(1965). Contains NOCBI i ! 12. G. A. Olah and T. Ohyama, Synthesis (51,319 (1976). 13. US.Pat. 2,732,398 (Jan, 24,19561, T. J. Brice and P. W. Trott (to 3M Co.). 14. US.Pat. 3,796,738 (Mar. 12, 19741, K. F. Thorn (to 3M Co.). c oily liquids. 15. W. H. Tredman and D. N. Bennion, J.Chern. Engr.,Data 16,368 (1971). ted mixtures it solubilities )tane, carbon fluoroalkane reviously de- 16. US.Pat. 3,842,019 (Oct. 15,1974), J. E. Kropp (to 3M CO.). 17. U.S.Pat. 3,998,763 (Dec. 21,1976), E.Bohnel (to 3M Co.). 18. US.Pat. 3,907,706 (Sept. 3,1975),J. Robbins (to 3h4 Co.). 19. J . Burden and co-workers, J . Chem. Soc., 2574 (1957). 20. J. B. Hendrickson, D. D. Sternbach, and K. W. Bair, Acc. Chern. Res. 10,306 (1977). 21. C.S. Pat. 3,346,606 (Oct. 10, 19671,R. E.Ward (to E. I. duPont de Nemours & Co., Inc.). i queous alkali ). urface-active ive properties :factants (22). well as their 22. R. A. Guenthner and PI. L. Vietor, Ind. Eng. Chern., Product Research and Development Vol. 1,pp. 165-169,1962. RICHARDA. GUENTHNER 3hI Company nts. Very low 3btained with :ids. This has sulfonic acids. id permanent liately flushed .at high vapor contact of the ures for treatellulosics, and ose materials. Teflon plastic 1 or aluminum .ipment where gciety, New York, .02 (1960). PERFLUOROALKYLSULFUR FLUORIDES Compounds containing fluorine bound to both carbon and sulfur with no other elements present are relatively rare and little known substances. Less than fifty ex- amples of these materials are known and none of them have any current commercial utility. In general, they are difficult and costly to prepare. Their properties range from thermally stable and chemically inert to extremely unstable. .- The only member of this group worthy of mention is the parent compound tri- fluoromethylsulfur pentafluoride [373-80-8],CF3SF5, which is a good gaseous dielectric material (11,and this use has been mentioned in two patents (2-3). A bibliography on CF3SFS-is available in ref. 4. i BIBLIOGRAPHY "Perfluoroalkylsulfur Fluorides" under "Fluorine Compounds, Organic" in ECT 2nd ed., Vol. 9, pp. 502-805 by Richard E. Eibeck, Allied Chemical Corporation. 1. R. Geballe and F. S. Linn, J . Appl. Phys. 21,592 (1950). 2. US.Pat. 2,989,577 (June 20, 19611,D. Berg (to Westinghouse Electric Corp.). 3. Ger. Pat. 1,108,779 (June 15. 1961),D. Berg and T. E. Brown (to Westinghouse Electric Corp.). 4. L. S. Cove and R.J. Seffl, Proceedings of the 6th Electrical Insulation Conlerence, New York, Sept. 13-16.1965. RICHARDE.EIBECK Allied Chemical Corporation