OXIDATION OF AROMATIC-AMINES WITH HYDROGEN-PEROXIDE CATALYZED BY CETYLPYRIDINIUM HETEROPOLYOXOMETALATES

Various substituted anilines 1 were selectively converted into the corresponding nitrosobenzenes 2 or nitrobenzenes 3 by oxidation with aqueous hydrogen peroxide catalyzed by heteropolyoxometalates. The oxidations of anilines 1 with 35% H2O2 catalyzed by peroxotungstophosphate (PCWP) at room temperature in chloroform under two-phase conditions afforded nitrosobenzenes 2 with high selectivity. When the same reactions were carried out at higher temperature (e.g., refluxing chloroform), nitrobenzenes 3 were obtained in good yields. The oxidation of aniline (1a) with dilute H2O2 catalyzed by PCWP (2 wt %) in an aqueous medium produced azoxybenzene (4a) with high selectivity. Phenylazoxyalkanes 7 were prepared by the first direct cooxidation of la in the presence of primary aliphatic amines 6. For example, the oxidation of a 1:2 mixture of 1a and hexylamine (6b) with 35 % H2O2 (6 equiv) in the presence of PCWP produced phenylazoxyhexane (7b) (51 %) along with a small amount of 4a (8 %). The reaction path for the conversion of anilines to azoxy-, nitroso-, and nitrobenzenes is described.