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

Abstract

The oxidation chemistry of perfluoroalkyl-segmented thiols, R F–R–SH ( 1), thiosulfinates, R F–R–S(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) (in which R F= n-C 6F 13 or n-C 8F 17 and R=CH 2CH 2) 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-C 6F 13S(O) 2CH 2CH 2C 6F 13 (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 ν CH bands correlate with NMR of CH 2 at C(1) and C(2) positions, both 1 H and 13 C 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.