Solvent effects on the tautomerization, autoxidation and bond-exchange reactions of 2-mercaptopyridine derivatives

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Tautomerization, autoxidation and bond-exchange reactions of 2-mercaptopyridine derivatives were investigated in solution, by using several kinds of solvents. A 2-mercaptopyridine derivative having an N-benzylamide group was dissolved not only in water but also in cyclohexane, although the solubility toward such solvents was lower than that toward methanol or chloroform. From the UV-Vis spectra, it was confirmed that thione-type isomer was major in these solvents except for cyclohexane. Autoxidation reactions were monitored in methanol or methanol-d₄, and ca. 36% of 2-mercaptopyridyl groups were oxidized into disulfide bonds within a month in ¹H-NMR spectral measurements. Bond-exchange reactions between 2,2’-dipyridyl disulfide and a thiol compound were observed more clearly in methanol than in chloroform, suggesting a solvent effect to dissolution of corresponding disulfide compounds.