3,776,960 United States Patent Office Patented Dec. 4, 1973 2 It has been found that bis(perfluoroalkanesulfonyl)- 3,776,960 methanes having the general structural formula PREPARATION OF BIS(PERFLUOROALKYL SULFONYL)METHANES (RSO), CH, Robert J. Koshar, Lincoln Township, Washington County, wherein Rf is a monovalent fluorinated straight or and Ronald A. Mitsch, Little Canada, Minn., assignors 5 branched chain alkyl radical containing 1 to 18 carbon to Minnesota Mining and Manufacturing Company, atoms fully fluorinated except for not more than one of St. Paul, Minn. hydrogen, oxygen, trivalent nitrogen or chlorine atoms No Drawing. Filed Dec. 9, 1971, Ser. No. 206,518 for each two carbon atoms, said hydrogen and chlorine Int, C. CO7c I47/02 atoms being non-reactive to methyl magnesium halide U.S.C. 260-607 A 9 Claims O and oxygen and nitrogen being bonded exclusively to car bon, are prepared in yields of 40 to 90% of theoretical ABSTRACT OF THE DISCLOSURE by reaction of a perfluoroalkanesulfonyl fluoride of the A process is provided for obtaining improved yields of general structural formula bis(perfluoroalkylsulfonyl)methanes by the reaction of perfluoroalkanesulfonyl fluorides with methylmagnesium 5 RSOF halide using a non-reactive ether forming an oxonium ion wherein R is as defined above with 1.2 to 7 or more and in aqueous sulfuric acid having an ionization constant as preferably 2.5 to 3.5 equivalents of methyl magnesium expressed by pKa of greater than -3.3. halide at temperatures in the range of from about -20° C. to about 100 C. in a solvent system comprising at 20 least about 40% by volume of an ether forming an This invention relates to a process for obtaining bis oxonium ion in aqueous sulfuric acid having an ioniza (perfluoroalkylsulfonyl)methanes by the reaction of per tion constant as expressed by pKa of greater than about fluoroalkanesulfonyl fluorides with methyl-magnesium -3.3 and preferably greater than about -3.0 when de halide and particularly to a process effected in solvents termined by solvent extraction and gas chromatograhpy. which permit achieving relatively high yields. 25 Examples of perfluoroalkanesulfonyl fluorides include The preparation of the lowest member of the homol perfluoromethanesulfonyl fluoride, perfluoroethanesul ogous series of bis(perfluoroalkylsulfonyl)methanes, spe fonyl fluoride, perfluorobutanesulfonyl fluoride, perfluoro cifically bis(perfluoromethylsulfonyl)methane, is de hexanesulfonyl fluoride, perfluorooctanesulfonyl fluoride, scribed by Brice and Trott in U.S. Pat. No. 2,732,398 perfluorododecanesulfonyl fluoride, perfluorooctadecane (1956) and by Gramstad and Haszeldine in J. Chem. Soc., 30 sulfonyl fluoride, perfluorocyclohexylmethanesulfonyl 4069 (1957). Brice and Trott obtained methyl perfluoro fluoride, 3-(perfluoromerpholino) perfluoropropanesulfon methly sulfone and bis(perfluoromethylsulfonyl)methane yl fluoride, 3-(perfluoropiperidino)perfluoropropanesulfon in yields of 21.3% and 5.2% of the theoretical amount, yi fluoride, perfluoropropane-2-sulfonyl fluoride, 2-per respectively, from one equivalent weight of perfluoro fluoroethoxyethanesulfonyl fluoride, Cl(CF)SOF, methanesulfonyl fluoride and 2 equivalent weights of methylmagnesium iodide in refluxing (34.6. C.) diethyl Cl(CF)2SOF, Cl(CF) SOF, H(CF) SOF, ether. Gramstad and Haszeldine obtained methyl per fluoromethyl sulfone and bis(perfluoromethylsulfonyl) H(CF)SOF and the like. methane in yields of 12% and 7% respectively from one Methylmagnesium halides that may be used are meth equivalent weight of perfluoromethanesulfonyl fluoride 40 ylmagnesium chloride, methylmagnesium bromide and and 2 equivalent weights of methylmagnesium iodide that methylmagnesium iodide. The preferred methylmagnesium had been sealed cold in a reaction tube with diethylether halide is methylmagnesium chloride. and allowed to warm to room temperature and then held It is a novel feature of the present process that the re at 20 for 12 hours before isolation of products. action, which is in theory capable of producing mono-, The preparation of higher bis(perfluoroalkylsulfonyl) 45 bis- and tris-(perfluoroalkylsulfonyl)methanes, produces, methane homologs as well as the lower homologs is de predominantly the middle member of the series, the bis scribed by Heine in U.S. Pat. No. 3,281,472. From the (perfluoroalkylsulfonyl)methanes and is thus different in example given in this patent, yields of butyl perfluorooctyl kind from the process of the prior art above noted. The sulfone and 1,1-bis(perfluorooctylsulfonyl)butane of 8.3% preferred process of the invention employs perfluoroal and 13.2% respectively, are obtained by the reaction of 50 kanesulfonyl fluorides of the formula one equivalent weight of butyllithium with one equivalent CFanSOF weight of perfluorooctanesulfonyl fluoride in diethylether wherein n is 1 to 18. at 0° C. It is thus apparent that conversions of perfluoroalkane Non-reactive ethers that may be used in the process sulfonyl fluorides to bis(perfluoroalkylsulfonyl)methanes of our invention are ethers that do not react under the have been very poor, not even up to 15%, so that the cost conditions of the process with themselves or the compo of the material has necessarily been prohibitively high. nents of the reaction. Suitable ethers are those forming It is an aim of this invention to provide a method oxonium ions in aqueous sulfuric acid having an ioniza whereby bis(perfluoroalkylsulfonyl)methanes are ob tion constant as expressed by pKa of greater than about tained in improved yields. It is another aim of this inven 60 -3.3 and preferably greater than about -3.0 when deter tion to provide a method whereby bis(perfluoroalkylsul mined by solvent extraction and gas chromatography in fonyl)methanes are obtained in yields of 40 to 90% of accordance with the method described by E. M. Arnett the theoretical amount. Other aims and objects of the in a series of three papers, J. Am. Chem. Soc., 84, 1674 invention will become apparent from the disclosure 1680, 1680-1684, 1684-1688 (1962). Examples of suit herein. 65 able ethers and their pKa values are listed in Table 1. 3,776,960 3 4 TABLE 1. dines and acetals as is taught in U.S. Pat. No. 3,586,616. The bis(perfluoroalkylsulfonyl)methanes are also useful Examples of ethers suitable in the process of the for the preparation of organic intermediates. invention and their dissociation constant The following examples serve to illustrate the process Ether: pKa of the invention. 1,2-dimethoxyethane ------------------- 3.27 EXAMPLE 1. Dioxane ------------------------- a mom -3.16 Methyl t-butylether --------------------- -2.84 This example illustrates the preparation of bis(per 7-Oxa(2.2.1 bicycloheptane -------------- -2.80 fluoromethylsulfonyl)methane, (CFSO2)2CH2, by the Tetrahydropyran ----------------------- 2.79 10 “normal' addition process of the invention. 2-methyltetrahydrofuran ---------------- -2.67 A dry 2-liter flask, fitted with a stirrer, Dry Ice con Trans-2,5-dimethyltetrahydrofuran -------- -2.65 denser, thermometer and gas inlet tube, is charged with Cis-2,5-dimethyltetrahydrofuran ---------- -2.44 730 ml. of 3.0 molar methylmagnesium chloride (2.2 Tetrahydrofuran ----------------------- -2.08 moles) in tetrahydrofuran (available from Arapahoe Hexamethyleneoxide ------------------- -2.02 Chemicals, Inc.). Perfluoromethanesulfonyl fluoride (111 5 g; 0.73 mole) is bubbled into the stirred solution over a At least 40% of the solvent must be such as ether period of one hour, controlling the rate of addition so but diluents may be other ethers or even hydrocarbon or that refluxing of the sulfonyl fluoride is not excessive. chlorinated solvents as benzene, heptane, petroleum ether, The temperature (exothermic reaction) of the reaction ligroin, methylene chloride which are inert toward reac mixture is kept at 30 to 40° C. by intermittent external ants and products. 20 cooling. After the addition is complete, the mixture is Bis(perfluoroalkylsulfonyl)methanes are prepared by first stirred at 35° C. for 1.5 hours, then at 50 C. for (1) reacting one gram-molecular weight of perfluoro 0.5 hour and is then cooled to 25 C. and hydrolyzed by alkanesulfonyl fluoride with from 1.2 to 7 or more and slow addition of 375 ml. of 3 N hydrochloric acid to give preferably 2.5 to 3.5 gram-molecular weights of methyl aqueous and organic phases. In larger scale preparations magnesium halide in about 300 to 2000 ml. and preferably 25 up to 12 N hydrochloric acid may be used. The hy about 500 to 1000 ml. of non-reactive ether forming an drolysis is exothermic and accompanied by the evolution oxonium ion in aqueous sulfuric acid having a pKa greater of methane during the first 10 ml. of acid addition. than about -3.3 at from -20° C. to about 100° C. for After the addition of the acid, the upper organic phase 1 to 3 hours or more and (2) hydrolyzing organic mag is separated, discarding the aqueous phase, and the tetra nesium halide and isolating the reaction products. The 30 hydrofuran and water removed by distillation. The or initial concentration may be up to about 3 molar with ganic residue is taken up in 300 ml. of diethyl ether and respect to perfluoroalkanesulfonyl fluoride but decreases washed twice with 100 ml. of 3 N hydrochloric acid. as reaction proceeds to nil. The concentration is limited Other solvents as CHCls or CH2Cl are also useful and by solubility and by the nature of the particular com are preferred for larger batches. The ether layer is dried pound, whether liquid or gas. The concentration of meth 35 over over anhydrous magnesium sulfate and fractionally ylmagnesium halide is usually held sufficiently low that distilled. In repetitive runs, thereare obtained yields of it is completely dissolved. 67 to 74% of the theoretic (68 to 75 g.) of bis(perflu Generally, the reaction is carried out in a reaction ves oromethylsulfonyl)methane, B.P. 99-101° C./2.5 mm. sel equipped to exclude atmoshperic moisture. The reac 40 and 4 g. of methyl perfluoromethyl sulfone.