Catalytic Aerobic Oxidation Of Alcohols Research Articles

Selective, catalytic aerobic oxidation of alcohols using CuBr2 and bifunctional triazine-based ligands containing both a bipyridine and a TEMPO group

Three novel, bifunctional triazine-based ligands, namely , and , containing both a TEMPO and a bipyridine moiety have been synthesized. These bpy/TEMPO-based molecules have been used as catalyst precursors for the copper-catalyzed aerobic oxidation of alcohols to aldehydes and ketones, in the presence of tert-BuOK as co-catalyst. The complexes obtained in situ from ligands and with copper(II) bromide in a 2:1 acetonitrile/water mixture, selectively catalyze the aerobic oxidation of primary benzylic, allylic and aliphatic alcohols and secondary benzylic alcohols. The rate of oxidation achieved using compound is slightly lower than that of compound . Surprisingly, the [copper/] system is not an efficient catalyst. The distinct catalytic behaviour of the three complexes is most likely due to the different position of the anchoring point of the bipyridine moiety on the triazine core, thereby inducing dissimilar steric effects. The effect of the substitution position of the bipyridine unit is reflected by the Vis-NIR spectra of the corresponding copper(II) complexes, which show similar LMCT and d-d transitions for and , while these absorption bands are significantly red-shifted in the case of the [Cu(II)/] complex. These differences are indicative of different coordination environments around the Cu(II) centres in those compounds.Single-crystal X-ray diffraction studies reveal that [Cu(2)(4-bpyT)(2)Br(4)](CH(3)CN)(7) () and [Cu(2)(5-bpyT)(2)Br(4)](CH(3)CN)(2) () are comparable dinuclear compounds with pentacoordinated copper ions, in a distorted square-pyramidal geometry in and in a distorted trigonal-bipyramidal geometry in . These two coordination geometries are also reflected by their slightly different Vis-NIR results. Cu(6-bpyT)Br(2) () is mononuclear, with the Cu(II) ion in a distorted tetrahedral geometry, suggesting a relationship with its catalytic inactivity.

Aerobic Oxidation of Alcohols to Carbonyl Compounds Catalyzed by Fe(NO3)3/4-OH-TEMPO under Mild Conditions

Abstract Fe(NO3)3/4-OH-TEMPO catalyst system was developed using the inexpensive organocatalyst 4-hydroxy-2,2,6,6-tetramethyl-piperidyl-1-oxy (4-OH-TEMPO) and the co-catalyst Fe(NO3)3·9H2O. The catalytic molecular-oxygen-driven oxidation of a broad range of primary and secondary alcohols, which may contain carbon-carbon double bond, N, O, and S heteroatoms, to the corresponding aldehydes and ketones was investigated. The results showed that reaction is highly selective to the desired products when carried out at room temperature in ambient atmosphere air. The mechanism for the catalytic aerobic oxidation of alcohols by Fe(NO3)3/4-OH-TEMPO was discussed.

Unraveling the Surface Reactions during Liquid-Phase Oxidation of Benzyl Alcohol on Pd/Al2O3: an in Situ ATR−IR Study

The palladium-catalyzed liquid-phase reaction of benzyl alcohol to benzaldehyde was investigated in the presence and absence of oxygen by attenuated total reflection infrared (ATR-IR) spectroscopy. The 5 wt % Pd/Al2O3 catalyst was fixed in a flow-through ATR-IR cell serving as a continuous-flow reactor. The reaction conditions (cyclohexane solvent, 323 K, 1 bar) were set in the range commonly applied in the heterogeneous catalytic aerobic oxidation of alcohols. The in situ ATR-IR study of the solid-liquid interface revealed a complex reaction network, including dehydrogenation of benzyl alcohol to benzaldehyde, decarbonylation of benzaldehyde, oxidation of hydrogen and CO on Pd, and formation of benzoic acid catalyzed by both Pd and Al2O3. Continuous formation of CO and its oxidative removal by air resulted in significant steady-state CO coverage of Pd during oxidation of benzyl alcohol. Unexpectedly, benzoic acid formed already in the early stage of the reaction and adsorbed strongly (irreversibly) on the basic sites of Al2O3 and thus remained undetectable in the effluent. This observation questions the reliability of product distributions conventionally determined from the liquid phase. The occurrence of the hydrogenolysis of the C-O bond of benzyl alcohol and formation of toluene indicates that Pd was present in a reduced state (Pd0) even in the presence of oxygen, in agreement with the dehydrogenation mechanism of alcohol oxidation.

Catalytic Aerobic Oxidation of Alcohols by Fe(NO3)3—FeBr3.

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Catalytic aerobic oxidation of alcohols by Fe(NO 3) 3–FeBr 3

Selective aerobic oxidation of secondary and benzylic alcohols was efficiently accomplished by the binary catalyst system Fe(NO 3) 3–FeBr 3 under air at room temperature. The oxidation developed in mild conditions and showed good yields. A secondary alcohol even in the presence of a primary one was selectively oxidized.

Neutral, non-racemising, catalytic aerobic oxidation of alcohols

A novel procedure for the catalytic aerobic oxidation of alcohols into carbonyl derivatives under neutral, non-racemising conditions, is reported.