Ethyl 2-pyridyl disulfide

A very convenient method has been devised [40] for the conversion of thiols to ethyldithio derivatives as a routine procedure for protection of thiol-substituted organic acids. It uses a DMAP-catalysed exchange of the ethylthio group between a thiol and ethyl 2-pyridyl disulfide, prepared from the commercially available 2,2 -dithiobispyridine. Filtration through a macroporous sulfonic acidic resin and evaporation of the solvent yielded the disulfide directly. 

To a solution of 2,2 -dithiobispyridine (4.4 g, 20 mmol) and a catalytic amount of BF3 OEt2 (5 ml) in dichloromethane (25 ml) was added ethanethiol (1.22g, 20mmol). The resulting solution was stirred for 2h at ambient temperature and the solvent was removed under reduced pressure. The lesidue was suspended in a mixture of hexanes and ethyl acetate (50 ml, 7 3), and the insoluble 2-mercaptopyridine was removed by filtration. The filtrate was concentrated under reduced pressure and the residue was purified by chromatography (silica, dichloromethane), affording ethyl 2-pyridyl disulfide (2.84 g, 83%) as a pale-yellow liquid. 

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To a solution of ethyl 2-pyridyl disulfide (55 mg, 0.32 mmol) and DMAP (33 mg, 0.27 mmol) in dichloromethane (2ml) was added 2-mercaptohexadecanoic acid (77 mg, 0.27 mmol). The progress of the reaction was monitored by TLC (silica, CHCl,/MeOH 9 1). Upon completion (1 h) the product mixture was passed through a column (0.5 X 5 cm) of AG MP-50 (0.5 g, 3.5 meq (ml dry resin)1, Bio-Rad Laboratories). Elution with 3 ml of dichloromethane, followed by concentration of the filtrate under reduced pressure, afforded 2-(ethyldithio)hexadecanoic acid (91 mg, 98%) as a colourless oil. 

Whereas 2-(2-pyridyl)ethanethiol is oxidized with hydrogen peroxide to 2-(2-pyridyl)ethyl disulfide, its oxidation by nitric acid yields 2-(2-pyr-idyl)ethanesulfonic acid (equation 549) [474]. 

Aminopropylmorpholine Dimethyl terephthalate Ethylene 2-(5-Ethyl-2-pyridyl)ethyl acrylate Potassium bromide fiber mfg., polyester Diisopropylamine fiber mfg., rayon stable Carbon disulfide fiber mfg., self-extinguishing Benzene phosphinic acid fiber mfg., synthetic Caprolactam... 

Friedman, M., Zahnley, J. C., and Wagner, J. R. (1980). Estimation of the disulfide content of trypsin inhibitors as S-p-(2-pyridyl-ethyl)-L-cysteine. Anal. Biochem. 106, 27-34. 

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