Studies On Selective Oxidation Of Alcohol Catalyzed By Metal Oxides/TEMPO

The catalytic aerobic oxidation of alcohols to the corresponding aldehydes and ketones has received great attention, since this important functional group transformations were applied widely both in fundamental synthesis research and industrial manufacturing, and the use of molecular oxygen as terminal oxidant is of economic and environmental benefits. 2,2,6,6-tetramethyl-piperidyl-1-oxy (TEMPO) is particularly attractive because such small-molecule organocatalyst exhibited very high efficiencies and selectivities in many case of oxidation of alcohols. However, TEMPO-catalyzed oxidation of alcohols always rely on the assistance of various homogeneous cocatalysts.Herein, this dissertation has employed firstly redox metal oxides as heterogeneous cocatalyst in combination with TEMPO for aerobic selective oxidation of alcohols. The achievements are as follows:1. MnO₂/TEMPO were found to be a catalytic system for aerobic selective oxidation of alcohols, by which 81.9%conversion of benzyl alcohol and over 99%selectivity of benzaldehyde were reached at temperature 120°C under 0.8 MPa O₂ pressure in CH₂Cl₂ for twenty-four hours.2. Mn-Cu mixed oxides, prepared by coprecipitation, showed more efficient catalytic activities, probably due to the synergic effect between the well-dispersed Cu and Mn centers. Some Mn-Cu mixed oxides realized over 98% conversions and selectivities in oxidation of benzyl alcohol.3. The molar ratio of Cu to Mn in Mn-Cu mixed oxide displayed significant effect on its catalytic activity. The more the Cu is, the higher activity it obtain. The high-dispersed CuO is the key component.4. The catalytic mechanism of metal oxide/ TEMPO, including a two-stage redox cycle cascade, was suggested, among which the pivotal step is the oxidation of TEMPO to its oxammonium cation by high valence of metal oxide.5. Vairous alcohols were oxidized efficiently by Cu₂MnO_z / TEMPO, the oxidation of some substituted benzyl alcohols and cinnamonic alcohol gave near-quantitative conversions and selectivities.In summary, this dissertation firstly developed active MnO₂ and Mn-Cu mixed oxides as effective heterogeneous co-catalysts for TEMPO-catalyzed aerobic selective oxidation of alcohols.