Efficient Oxidation of 2-Mercaptopyridine Catalyzed by Heptylviologen and Application to Photosensitized Carbon Dioxide F ixation

Abstract

In acetonitrile solution, efficient oxidation of 2-mercaptopyridine (PySH) to disulfide was accomplished in the presence of catalytic amount of heptylviologen (HV²⁺). The reaction gave the MichaelisMenten type kinetics, which suggests that an electron is transferred from PyS^- to HV²⁺ via the complex formation between these two species. This reaction was applied to the formation of 2-oxazolidinone derivative from carbon dioxide and _L-phenylalaninol. Contrary to the expectation, however, the reaction scarcely proceeded. This may be due to the coordination of coexisting Ph₃P to HV₂₊, which prevents the complex formation between HV²⁺ and PyS^-. When the above system was irradiated ( >370nm), however, the reaction was enhanced. The excited PyS^-* with higher reducing power probably can give an electron to HV²⁺ even in the absence of HV²⁺-PyS^- complex.