SYNTHESIS OF POLYMER SUPPORTED METAL CATALYSTS AND OXIDATION OF ORGANIC COMPOUNDS

Abstract

In the present work various transition metal complexes anchored on polymer support were synthesized and their characterization by various physico-chemical techniques has been studied. Different types of catalytic oxidation reactions were carried out and suitable reaction conditions were obtained for the maximum oxidation of organic substrates. First, chloromethylated polystyrene crosslinked with divinylbenzene was used as polymer support. Schiff bases; [Hfsal-dmen] and [Hfsal-aepy] derived from the reaction between 3-formylsalicylic acid and N, N- dimethylethylenediamine or 2-(2-aminoethyl)pyridine were immobilized on polymer support. The anchored ligands then reacted with CuC12.2H20 and MnC12.4H20 metal salts to form the metal complexes, PS-[Cu(Hfsal-dmen)Cl], PS-[Cu(Hfsal-aepy)Cl], PS-[Mn(Hfsal-dmen)Cl] and PS-[Mn(Hfsal-aepy)Cl]. These catalysts were characterized by elemental analysis, atomic absorption spectroscopy (AAS), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray analyses (EDAX), thermo-gravimetric analysis (TGA) and UV-vis spectrophotometer. These characterization techniques confirmed the formation of metal complexes and changes occurred on ligand and metal complexes during various steps of catalyst synthesis. Further, catalytic efficiency of various catalysts was studied for the oxidation of styrene. Oxidation of styrene gives styrene oxide which is an important intermediate for many chemical industries. The effect of various oxidants such as H202, tert-butylhydroperoxide (TBHP) and molecular oxygen (02) on styrene oxidation at atmospheric and in high pressure conditions were studied and the effect of various reaction parameters such as substrate (styrene) to oxidant mole ratio, temperature, pressure and catalyst amount has been discussed in detail and comparisons of different catalysts were carried out at optimum reaction conditions. The activities of polymer anchored catalysts were also compared with non-polymer anchored catalysts. The Cu(II) catalyst PS-[Cu(Hfsal-aepy)Cl] showed the maximum catalytic activity for all the three oxidants. The recyclability study for all the catalysts with II H202, TBHP and 02 oxidants were studied and results showed that catalysts can be recycled three to four times without any appreciable change in their catalytic activity and product selectivity. The second part of the thesis reported the modification of polymer support gas phase nitration of macro porous styrene cross linked with divinylbenzene which were synthesized using suspension polymerization technique. The cross linked resins were initially nitrated with NO,, a mixture of NO and NO2 gas. The nitrated resin was subsequently aminated by hydrazine hydrate and further used as precursor for the preparation of heterogeneous catalyst. This method in comparison with traditional chloromethylation method, increases the mechanical stability of the resin, reduces the reaction time (8 h) and forms strong coordination complex with metal salt, which prevents the leaching of the metal during the catalytic reaction. For this study Co(II) salt was loaded on functional polymers and characterized by various techniques such as elemental analysis, AAS, FTIR, SEM and TGA. The catalysts were tested for the catalytic activity of cyclohexane oxidation in a batch reactor using molecular oxygen as an oxidant. The oxidation products of cyclohexane; cyclohexanol and cyclohexanone, are valuable chemical intermediates for the preparation of adipic acid and caprolactam, which are further used in the manufacture of nylon-6,6 and nylon-6 polymers. Industrially reaction is carried out by cobalt salts with total conversion less than 4 % and selectivity to cyclohexanol and cyclohexanone around 70-85 %. In the present study, effect of various reaction parameters i.e. temperature, pressure and catalyst amount were optimized for maximum conversion and selectivity for cyclohexanol and cyclohexanone. Co(H) catalyst showed 18.4 % conversion at 413 K temperature and 1.2 MPa oxygen pressure with 92.0 % combined selectivity to cyclohexanol and cyclohexanone. The results, therefore, recommend relatively low temperature and pressure conditions for cyclohexane oxidation using polymer supported catalysts achieving improved conversion and selectivity to cyclohexanol and cyclohexanone. The recyclability of the polymer anchored complexes has also been evaluated. The reaction mechanism indicates a free radical mechanism. Finally, summary and over all conclusions based on the achievements . are presented.