Selective Oxidation Of Alcohols,Furfural, Benzene By Molecular Oxygen

The oxidation reaction is very important in organic synthesis, and it has wide range of applications in the petrochemical industry. With the increasingly high demands on the environment and continuous depletion of oil resources, developing green synthesis methods become very important. In this paper, using oxygen as oxidant, we developed a simple, efficient catalytic system for oxidation of alcohols, a new reaction to synthesize maleic acid from furfural in liquid-phase and a new strategy for the design of oxidation catalysts using oxidation of benzene to phenol as a model reaction.In Chapter Ⅱ, a simple and efficient catalytic system for oxidation of primary and secondary alcohols to the corresponding aldehydes and ketones has been developed. Using RuCl3/Et3N as catalyst, the turnover frequency of oxidation of benzyl alcohol with molecular oxygen as oxidant could be achieved as high as332h-1in the absence of solvent. The influence of versatile N-containing additives on the catalytic efficiency has been discussed. There are two roles of the ligand:1) in coordination with the Ru(Ⅲ) cation to modulate its redox properties2) as base to help the formation of Ru(Ⅲ) alcoholate. The presence of minor water would substantially promote the catalytic efficiency, and its role is to promote the dissociation of chloride anion from the coordination sphere of the Ru(Ⅲ) cation to facilitate metal alcoholate formation, and thus modulate the redox properties of the Ru(Ⅲ) cation. The insensitive Hammett correlations of the substituted benzyl alcohols, the normal substrate isotope effect and the linear relationship between O2pressure and turnover frequency imply that the reoxidation of the Ru(Ⅲ) hydride intermediate to the active species shares the low reaction step with the hydride transfer in the catalytic cycle.Chapter Ⅲ introduced a new reaction to synthesize maleic acid from the renewable furfural. The current data revealed that the combination of copper nitrate with phosphomolybdic acid with oxygen as oxidant could achieve a49.2%yield of maleic acid with selectivity of51.7%. To avoid the polymerization of furfural to resins under oxidative conditions, catalytic aerobic oxidation of furfural to maleic acid was investigated with phosphomolybdic acid catalyst in the aqueous/organic bi-phase system. Under the optimized conditions,34.5%yield of maleic acid could be obtained with68.6%of selectivity, and the conversion of furfural is50.4%. Because furfural and maleic acid dominantly exist in two different phases, the product separation and reactant recycle would be very simple in its potential application. The FT-IR and31P NMR technologies were applied to characterize the phosphomolybdic acid catalyst, and the pathway of maleic acid formation was also discussed based on obtained mechanistic information.Chapter IV provided a new strategy of redox inactive Lewis acid promotes the oxidizing capability of catalyst. The different catalytic efficiency between catalyst PdⅡ(bpym) and PdⅡ(bpym)/Al(OTf)3proved its feasibility. In Pd(Ⅱ)-catalyzed oxidation of benzene to phenol with oxygen as the sole oxidation, using palladium acetate alone as catalyst, biphenyl was main product after reaction. Using2,2’-bipyrimidine as ligand, the catalyst PdⅡ(bpym) showed inactivity to the reaction and there are neither formation of phenol nor formation of biphenyl. The presence of the redox inactive metal ions like AlⅢ might modulate the properties of Pd(Ⅱ) cation and greatly promote the oxidizing capability of Pd"(bpym) with regard to benzene activation, and tune the reactivity of the PdⅡ ion from benzene coupling to hydroxylation. After reaction, phenol was main product. In the catalytic cycle, C-H bond activation was a rapid equilibrium step and the formation of phenol from Pd"-Ph is the rate-limiting step.