Oxidative coupling of thiols to disulfides is of interest from both a synthetic and a biological point of view, because disulfides are useful reagent in organic synthesis [1][2][3] and essential moieties of biologically active compounds for peptide and protein stabilization.4) Thiols can be easily over-oxidized, and therefore, several selective methods of converting thiols into disulfides have been developed. For example, iodine/ hydrogen iodide, 5) bromine, 6,7) potassium permanganate/copper(II) sulfate, 8) hydrogen peroxide in trifluoroethanol, 9) and dimethyl sulfoxide [10][11][12] are used for this purpose. Most of the existing methods suffer from drawbacks such as the use of stoichiometric amounts of reagents that generate undesirable waste materials. To overcome these drawbacks, catalytic oxidation using oxygen as a co-oxidant has been developed by several groups. [13][14][15][16][17][18]
Oxidation O 0212Aerobic Oxidation of Thiols to Disulfides Catalyzed by Trichlorooxyvanadium.-Oxidative coupling of several kinds of thiols (I) to disulfides (II) is carried out in the presence of a molecular sieve and the title catalyst in aprotic polar solvents. The disulfides are efficiently obtained, although in relatively slow reaction rates. The coupling reaction can be accelerated by using higher amounts of the catalyst. Remarkably, mercaptoethanol (Ic) is much faster oxidized than the other thiols. The reason for this phenomenon is not yet clear. Other higher valent vanadium catalysts examined do not have sufficient catalytic activity. -(KIRIHARA*, M.; OKUBO, K.; UCHIYAMA, T.; KATO, Y.; OCHIAI, Y.; MATSUSHITA, S.; HATANO, A.; KANAMORI, K.; Chem.
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