Oxidation chemistry of perfluoroalkyl-segmented thiols, disulfides, thiosulfinates and thiosulfonates - The role of the perfluoroalkyl group in searching out new chemistry

The oxidation chemistry of perfluoroalkyl-segmented thiols, R-F-R-SH (1), thiosulfinates, R-F-RS(O)S-R-R-F (3), thiosulfonates, R-F-R-S(O-2)S-R-R-F (4) and disulfides, R-F-R-SS-R-R-F (5) tin which R-F=n-C6F13 or n-C8F17 and R=CH2CH2) is studied herein. Base catalyzed reaction of C6 thiol 1 with hydrogen peroxide gives pure disulfide 5, quantitatively. Other, less suitable methods for the oxidation of thiol 1 are also examined and compared. Selective oxidation of disulfide 5 by peroxy acids in chlorinated solvents gives excellent yields of thiosulfinate 3. Unlike their hydrocarbon analogues, which are unstable to heating or storage, the R-F-segmented thiosulfinates 3 are relatively stable, crystalline compounds. Selective oxidation of 3 by sodium metaperiodate gives thiosulfonate 4 in high yield. Side reactions intervene with unfavorable conditions, or when peroxy acetic acid in acetic acid is used as oxidant,. Oxidation of 5 by hydrogen peroxide in low conversion gives 4 and two new compounds, 8 and 9. Compound 8 is n-C6F13S(O)(2)CH2CH2C6F13 (probably the sulfinate ester and not the sulfone), and 9 is most likely the O,S-sulfenyl sulfinate or, possibly an isomer, the vic-disulfoxide. A free radical chain mechanism is proposed for conversion of 4 (or 9) to 8. Compounds 8 and 9 are stable in solution and are identified by MS/GC. in 3, 4 and 5, the v CH bands correlate with NMR of CH2 at C(1) and C(2) positions, both H-1 and C-13 NMR. The R-F-segment in these unique sulfur compounds enhances their utility and modifies their chemical and physical properties in important and interesting ways. (C) 2000 Elsevier Science S.A. All rights reserved.