Catalytic oxidation of aniline by aqueous hydrogen peroxide in the presence of some heteropolyoxometalates

Abstract

Anilina foi convertida em nitrosobenzeno e nitrobenzeno por oxidação com peróxido de hidrogênio aquoso 30%. A reação foi catalisada por vários heteropolioxometalatos, à temperatura ambiente, em diclorometano, em condições bifásicas. Descobriu-se que H 3 PW 12 O 40 é o melhor catalisador na oxidação da anilina. Na 3 PW 9 Mo 3 O 40 e K 4 SiW 9 Mo 2 O 40 também exibiram alta atividade na oxigenação. Agentes de transferência de fase e temperatura também contribuíram para a eficiência da oxidação.Aniline was selectively converted into the corresponding nitrosobenzene and nitrobenzene by oxidation with 30% aqueous hydrogen peroxide. The reaction was catalyzed by various heteropolyoxometalates, at room temperature, in dichloromethane under two-phase conditions. Findings show that H 3 PW 12 O 40 is the best catalyst in the oxidation of aniline. Na 3 PW 9 Mo 3 O 40 and K 4 SiW 9 Mo 2 O 39 also displayed high reactivity in the oxygenation system. Phase transfer agents and temperature increase also contribute to the efficiency of the oxidation. Keywords: oxidation, polyoxometalates, aniline IntroductionOxidation of organic substrates by aqueous hydrogen peroxide is very attractive from the viewpoint of industrial technology and synthetic purposes.1 Polyoxometalates have been widely studied as small compact oxide clusters. oxidants. The product composition in the oxygenation of amines depends on the oxidant, catalyst, quaternary ammonium salts, and reaction conditions employed. 16Tungsten-and molybdenum-based heteropolyoxometalates have received attention as promising oxidation catalysts in the selective oxygenation of aromatic and aliphatic amines. 24,25 Recently, Ishii and colleagues have reported their results on the oxidation of amines by aqueous hydrogen peroxide under the influence of synthetic PCWP, peroxotungstophosphate, and CWP, tris(cetylpyridinium)12-tungstophosphate. 26 In this system, H 3 PW 12 O 40 revealed little activity in CHCl 3 and its efficacy varied with the reaction conditions.We hereby present our results in the selective and fast oxidation of aniline by hydrogen peroxide in the presence of several simple heteropolyoxometalates at room temperature under simple reaction conditions. Accordingly, Scheme 1 represents the general formulation of the catalytic two-phase system in the oxygenation of aniline. Results and DiscussionIn summary, we have shown that the oxidation of aniline by 35% hydrogen peroxide, catalyzed by H 3 PW 12 O 40 family (under two-phase conditions at room temperature or under reflux) provides a simple and general procedure for the preparation of nitrosoaniline, that is difficult to prepare selectively by conventional methods. The results clearly demonstrate that this oxidation system is more efficient than Ishii system in the selective oxidation of aniline with hydrogen peroxide. 26 ExperimentalAll starting materials were commercially available and were used without further purification. GLC analyses were performed with Shimadzu capillary column equipped with a flame ionization detec...

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