Selective Oxidation Of Alcohols And Alkenes By Green Oxidants

The catalytic selective oxidation of alcohols and alkenes have been a subject of growing interest in the fundamental chemistry and modern industrial processes, since epoxides are key building blocks in organic synthesis. Epoxide compounds are commercially important intermediates used in the synthesis of products such as chiral Pharmaceuticals, pesticides, epoxy paints, agrochemicals, perfume materials and sweeteners. Traditionally, epoxides are produced by the epoxidation of alkenes with stoichiometric amount of peracid as oxidant. However, peracid is very expensive, hazardous, and the acid waste converted from the peracid is environmentally undesirable. Conventionally, stoichiometric oxidants (e.g., chromate or permanganate) have been used for oxidation of alcohols. However, lots of toxic wastes produced from the processes are environmentally undesirable. There has therefore been a drive to identify atom-efficient economic and green chemistry oxidation reaction that can be carried out with molecular oxygen and hydrogen peroxide. The present thesis therefore aims to develop an efficient catalyst, to produce the catalysts that can catalyze aerobic oxidation of alcohols or epoxidation of alkenes with hydrogen peroxide.The Pd nanoparticles supported on MnOx (Pd/MnOx-ads) has been synthesized via adsorption method. The Pd/MnOx-ads exhibited high activity and selectivity to benzaldehyde for aerobic oxidation of benzyl alcohol under free solvent, compared with Pd/Mn3O4, Pd/CeO2and Pd/Fe3O4catalysts. Moreover, the activity of Pd/MnOx-ads catalyst showed remarkably higher than those of catalysts prepared by adsorption-reduction and co-precipitation methods. The catalyst can be reused several times without obvious loss of its activity.The [PdCl4]2-ions were successfully supported on as;synthesized [CTA+]MCM-41materials through adsorption method. Subsequently, the composite materials were reduced by sodium borohydride, followed by being extracted of [CTA+] surfactants with acidified ethanol. The resulted solid (denoted as Pd-M41-AE) could be used as an efficient catalyst for the solvent-free aerobic oxidation of benzylic alcohol under atmospheric pressure.0.4%Pd-M41-AE exhibited high activity (turnover frequency of4,344h-1) for the oxidation of benzyl alcohol, remarkably superior than other kinds of Pd-M41at100℃. Moreover, the superior turnover frequencies (69,162h-1for benzyl alcohol,69,920h-1for1-phenylethanol and117,130h-1for cinnamyl alcohol, respectively) were achieved over0.05%Pd-M41-AE at160℃. Recycling studies proved the recyclability of Pd-M41-AE as a heterogeneous catalyst, which did not lose the catalytic activity after four recycles appreciably.A series of manganese oxides (MnO, Mn3O4, Mn2O3and MnO2) were prepared and firstly applied as heterogeneous catalysts for the liquid phase epoxidation of alkenes with30%H2O2in bicarbonate solution. Under our experimental conditions, MnO exhibited superior activity for the conversion of styrene to achieve ca.100%with92.4%selectivity of epoxide, compared to the other three manganese oxides as well as other metal oxides. Furthermore, recycling studies showed the good recyclability of MnO as a heterogeneous catalyst, which did not lose the catalytic activity after four reuses appreciably.Manganese containing mesoporous materials Mn-MCM-41were prepared by template-ion exchange (TIE), in-situ reduction (ISR), direct hydrothermal (DHT), and wetness impregnation (WI) methods. It has been found that the definite structure of the support was retained after introducing Mn into MCM-41. The catalytic activity and selectivity of the Mn-MCM-41in the epoxidation of styrene with30%H2O2as an oxidant agent are explored. The TIE catalysts showed the highest activity but Mn2+was leaching during the reaction. The ISR catalysts exhibited high activity and its very stability which could be recyclable for4times. However, the DHT and WI catalysts showed poor performance in the catalytic epoxidation of styrene.Manganese oxides supported on γ-Al2O3, amorphous SiO2, MCM-41and TiO2prepared by impregnation method were used as heterogeneous catalysts for epoxidation of alkenes with30%H2O2in the presence of NaHCO3aqueous solution. The effect of support and manganese loading on their activity was studied. The1.3%MnOx/γ-Al2O3exhibited superior epoxidazing activity of styrene, compared with other supported MnOx. Recycling studies showed the catalyst was a heterogeneous one and retained its activity after recycling for4times.