Oxidation of benzoins with pyridine N-oxide - SbCl5 (1 : 1) complexes

When a mixture of a few benzoins and a pyridine N-oxide- SbCl5 (1 : 1) complex (Complex A) was boiled in nitromethane, the corresponding benzils were obtained in various yields dependent upon the kinds of substituents in each reactant. The yield of benzil becames higher by adding some tertiary amines. In this reaction, tribenzylamine is a good accelerator to promote it.When Complex A, 4-picoline N-oxide-SbCl5 (1 : 1) complex (Complex B) and 4-nitro-pyridine-SbCl5 (1 : 1) complex (Complex C) were used as the oxidant of benzoin, the order of the reaction rate was as follows : Complex C>Complex A>Complex BThe oxidation of benzoin with these pyridine N-oxide - SbCl5 (1 : 1) complexes seems to proceed according to the following there processes ; i) the oxidation by pyridine oxide-SbCl5 (1 : 1) complexes themselves ii) the oxidation by α-OSbCl4 pyridines and iii) the oxidation by the mixure of pyridine N-oxides and antimony (III) chloride.