Preparation, reactions and physical properties of segmented 2-(perfluoroalkyl)ethanesulfinic acids and their derivatives. The role of the perfluoroalkyl group in finding new and useful compounds and in searching out new chemistry

2-(Perfluoroalkyl)ethanesulfinic acids of the formula RFCH2CH2SO2H (2, where RF = n-C6F13, or n-C8F17) are synthesized from the thiol, RFCH2CH2SH (1). These segmented acids 2 have sharp melting point (mp) and can be recrystallized. The C6 or C8 perfluoroalkyl group confers unusual “fluophilic” properties to acids 2 and their derivatives. Water solutions of acids 2 and their Na, K, Cs and Bu4N salts are highly surface active and stable for several days, and are more effective in reducing surface tension at the air/water interface than sodium n-perfluorooctanesulfonate (10). Sodium salts 2 (C6, C8) are converted to K and Cs salts by methathesis in high yield. However, the amphiphilic Bu4N salts of 2 (C6, C8) are best prepared in a biphasic system (C6, 99.6% yield). Acids 2 are synthesized by three methods. (1) Oxidation of the C8 thiol 1 (at −35°C) by m-CPBA gives acid 2 (C8) in 73% yield and unwanted disulfide (3) in 27% yield. The bulky, strongly electronegative RF group of 1 may slow oxidation of the RSOH (intermediate) to allow disproportionation with RSH into disulfide 3 and water. (2) Hydrolysis of RFCH2CH2SO2SCH2CH2RF (4) with strong base gives salt 2 (C6, or C8; 92% yield). (3) Heating sulfone, RFCH2CH2SO2CH2CH2Y (8) with a base (M2CO3) eliminates RFCH2CH2SO2M (2, M = Na, K, Cs) in 95–100% yield (C6, C8). Alternatively, 8 with the sodium thiolate of 1 gives RFCnH2nSCH2CH2Y (7, 90%) and sodium salt 2 (C6, 95%). Conjugate addition of the RFCH2CH2SO2− to CH2CHY gives sulfones 8, and RFCH2CH2SO2− adds stereospecifically to cyclohexene oxide, giving the trans-adduct 13. RFCH2CH2SO2H (2), with azo initiator, telomerizes acrylamide to a water-soluble, surface active product.