Molecular oxygen as oxidant

An interesting, but hitherto widely neglected feature of CO2 in this context is its ability to chemically interact with metal-oxygen complexes, leading to transition metal peroxocarbonates [4,82]. These complexes are able to transfer one oxygen atom to oxophiles such as phosphines, alkenes and active methylene 

Koda and co-workers [85] studied the catalytic oxidation of cyclohexane with O2 in liquid and supercritical CO2 in the presence of acetaldehyde (cyclo-hexaneracetaldehyde = 4 1) and an iron porphyrin catalyst bearing pentafluor-ophenyl groups. The main oxidation products were cyclohexanone (2.9% yield) and cyclohexanol (2.3 % yield) with the optimum yields being achieved slightly below the estimated critical pressure of the reaction mixture. 

Although the field is clearly still in its infancy, it becomes evident from these examples that a wide variety of oxidation reactions can be carried out in SCFs and in particular in liquid and supercritical CO2. 

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For catalytic oxidations opt for hydrogen peroxide or molecular oxygen as oxidant for catalytic reductions opt for molecular hydrogen as reductant. 

Secondary alcohol oxidases catalyze the oxidation of secondary alcohols to ketones using molecular oxygen as oxidant. A secondary alcohol oxidase from polyvinyl alcohol-degrading bacterium Pseudomonas vesicularis var. povalolyticus PH exhibited activity toward several... 

Platinum supported on carbon (Pt/C) was tested as solid catalysts in the oxidation of sucrose using molecular oxygen as oxidant (Scheme 10). The reaction was carried out in water and under atmospheric pressure. The support strongly influences the reaction and Pt/C was found more efficient than Pt/Alumina at 353 K. Over Pt/C, at a pH of 9, mono-, di-, and tricarboxylate derivatives were mainly obtained with a tricarboxylate yield of 35% [103]. 

Table 9.1 Oxidation of sulfides ArSR to sulfones catalyzed by LDH-OSO4 using molecular oxygen as oxidant.

TiOi Powders Using Molecular Oxygen as Oxidant — 195... 

A stereocontrolled synthesis of the /ra j-tetrahydrofuran units in Annonaceae acetogenins that relies on the Sharpless asymmetric dihydroxylation protocol is outlined in Scheme 60 <1999TA2551>. In the first step, the disubstituted double bond of the starting material is dihydroxylated followed by monoprotection as a methoxymethyl ether. Einally, a cobalt-catalyzed oxidation using molecular oxygen as oxidant furnishes the /ra j-tetrahydrofuran. 

Neumann, R. Levin, M. Molecular Oxygen as Oxidant in Heteropolyanion Catalysed Oxidations. In Dioxygen Activation and Homogenous Catalytic Oxidation, Simandi, L. I., Ed. Elsevier Amsterdam, 1991 pp 121-127. 

In continuation of this study. Farmer and Welton investigated the selective oxidation of alcohols to aldehydes and ketones by TRAP in conjunction with eithCT A-methylmorpholine-N -oxide or molecular oxygen as oxidants [40]. In the case of molecular oxygen (as oxidant), Cu(I) and a diamine ligand must also be added. Under the optimized conditions, benzylic alcohols were oxidized in good to excellent yields, whereas aliphatic alcohols required longer reaction time and gave poor yield. The reaction products were easily removed from the reaction mixture by extraction with diethyl ether. 

Liquid-phase oxidations of alcohols in the presence of supported metal catalysts are potentially very attractive reactions for the preparation of intermediates and fine chemieals because high selectivities can be obtained with environmentally clean processes. Indeed, they proceed under mild conditions, with molecular oxygen as oxidizing agent and water as solvent. Supported catalysts, based mainly on platinum-group metals, are resistant to leaching, are recyclable, and are readily available from catalyst manufacturers in various compositions and forms. 

Oxidation of unsaturated compounds. Methyl ketones are produced from 1-aIkenes using molecular oxygen as oxidant [catalyst Pd(OAc)2-pyridine]. On the other hand, methyl 3,3-dimethoxypropanoate is formed when eth l acrylate is oxidized on activated carbon-supported molybdovanadophosphate and Pd(OAc>2 in acidic ethanol. Treatment of enones with LiAlH4 under dry oxygen gives 1,3-diols. ... 

The oxidation of ethylene to acetaldehyde employing palladium chloride and cupric chloride as catalysts and molecular oxygen as oxidant. The reaction has been extensively developed for the oxidation of terminal alkenes to methyl ketones ... 

CoAPO-5 Framework Co +, which oxidize to Co + with calcination UV-vis, DRS The conversion increased as the cobalt content increased in CoAPO-5. At n(Co)/n(P) = 0.04 the conversion of cyclohexane was 23.3% Oxidation of cyclohexane using molecular oxygen as oxidant (294)... 

N,N,N, N -Tetrasubstituted ureas 1049 have been obtained in variable yields (45-69%) by reaction of lithium aliphatic amides 1047 in THF solution with carbon monoxide under mild conditions (atmospheric pressure, 0 °C) followed by in situ oxidation with oxygen of the intermediate 1048 prior to work-up. The advantages of this method are the short reaction time and the use of molecular oxygen as oxidant [764]. 

Batiot, C. and Hodnett, B. (1996). The Role of Reactant and Product Bond Energies in Determining Limitations to Selective Catalytic Oxidations, A /. Catal. A Gen., 137 pp. 179-191. Cassidy, F. and Hodnett, B. (1998). Selective Oxidation Catalysts An Evaluation of the Discriminating Capacity of Active Sites on Oxide Catalysts with Molecular Oxygen as Oxidant,... 

When used with molecular oxygen as oxidant, an increase in enantioselectivities is observed (compare 46a in Scheme 4.14 with 46b in Scheme 4.15). Jiao et al. developed a protocol for the successful execution of an asymmetric oxidative a-alkylation of enolizable aldehydes (Scheme 4.15). In addition, the authors have given experimental evidence for the formation of an intermediately peroxide, which produces stabilized carbocations [46). 

An isopolyoxovanadate catalyst, [C8Hi7N(CH3)3]3H3Vio028, showed high catalytic activity in the oxidation of dibenzothiophene to its corresponding sulfone using molecular oxygen as oxidant under mild reaction conditions. A radical chain mechanism has been ruled out. Lewis bases suppress the vanadium-polyoxometalate catalysed dioxygenase reaction and catalysed the oxidation reaction of 3,5-di-t-butylcatechol selectively. The rate of autoxidation is increased by the polyoxometalate catalyst. ... 

It was reported that iron salts catalyzed the oxidative a-phosphonation of A,A-dimethylanilines with (R0)2P(0)H in the presence of tert-butylhydroperoxide [196]. In the study electrochemical C-H bond activation was utilized to generate iminium species, followed by C-P bond formation. An efficient dehydrogenative coupling reaction involving iminium salt as a possible intermediate was also reported with copper salt as catalyst and molecular oxygen as oxidant [197]. 

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