Nitrobenzene Reduction to Azobenzene using Silver loaded OMS-2

Abstract

Nitrobenzene reduction to aniline is a well known process with azobenzene as an intermediate product. Many azobenzene derivatives are synthesized by oxidation of aniline. Selectivity to azobenzene during nitrobenzene reduction is very less. Aniline forms as a major product. Thus formation of azobenzene directly with high selectivity from nitrobenzene reduction can provide an economically attractive route. In the current work, this is achieved by using a silver loaded OMS-2. Catalysts with silver, with 5 to 15 (wt%), substituted OMS-2 (Ag-OMS-2) have been synthesized and used for nitrobenzene reduction. The catalysts were characterized by XRD, SEM, EDX, TGA, TPD-TPR, etc. 15% Ag-OMS-2 shows the highest conversion and selectivity for azobenzene. Study of various parameters such as catalyst loading, hydrogen pressure, nitrobenzene concentration and temperature has been studied. A suitable kinetic model was proposed. At reaction conditions of 0.0487 mol Nitrobenzene, 1.0 ml n-Dodecane, 0.005 g/cm3 catalyst loading, make upto 50 ml with IPA, 25 kg/cm2 H2 pressure, 1200 rpm speed of agitation, about 39% conversion of nitrobenzene takes place with 85% selectivity towards azobenzene at 145 oC after 3 h of reaction. Activation energy for nitrobenzene hydrogenation to azobenzene is 14.88 kcal/mol. Thus azobenzene synthesis directly from nitrobenzene reduction using Ag-OMS-2 is an economically attractive root.