Aerobic Oxidation of Alcohols in Carbon Dioxide with Silica-Supported Ionic Liquids Doped with Perruthenate

The replacement of toxic CrVI for O2 and of chlorinated solvents for supercritical carbon dioxide (or ionic liquids) in the oxidation of alcohols remains hindered by the low selectivity and activity of the current heterogeneous catalysts. Using an integrated approach that combines sol–gel entrapped perruthenate as aerobic catalyst, an encapsulated ionic liquid as solubility promoter, and scCO2 as the reaction solvent, we have developed a system capable of rapidly converting different alcohols into carbonyl compounds with complete selectivity, including substrates which are otherwise difficult to oxidise. The methodology is generally applicable and may easily be extended to other waste-free, catalytic syntheses of fine chemicals

Photoinitiated Olefin Epoxidation with Molecular Oxygen, Sensitized by Free Base Porphyrins and Promoted by Hexacarbonylmolybdenum in Homogeneous Solution

The photooxidation of various olefins in homogeneous solution under an oxygen atmosphere, using visible light, a dye sensitizer, and an oxygen-transfer catalyst has been investigated. The oxygen transfer from molecular oxygen to olefin involves the following steps: i) photoinduced singlet-oxygen formation, ii) alkylhydroperoxide formation through ene-reaction, iii) intermediacy of a reactive molybdenum-peroxide, and iv) olefin epoxidation of the remaining substrate or of a second olefin. Among the various sensitizers and catalysts tested, electron deficient free base porphyrin 5,10,15,20-tetrakis(2’,6’-dichlorophenyl)-b-octabromoporphyrin and molybdenum hexacarbonyl showed the best performances in terms of robustness and activity. Under proper conditions, a complete olefin conversion may be obtained, adopting molar ratios of sensitizer/catalyst/substrate=1/50/2000, with the formation of the corresponding epoxide up to 38% yield, which corresponds to 77% of the theoretical maximum. Quite interestingly, olefins reluctant to undergo ene-reaction may be epoxidized in the presence of a second sacrificial olefin yielding the corresponding epoxides with up to 80% total selectivity

Selective catalytic oxidations in supercritical carbon dioxide

Abstract: Conducting catalytic oxidations of organic substrates in supercritical carbon dioxide as reaction medium is one of the most promising strategy for the creation of fundamental chemical transformations that are environmentally benign. There is extensive literature on the use of supercritical carbon dioxide as solvent for unselective hydrocarbons auto-oxidations. Conversely, only a limited number of reports deal with selective oxidations carried out by molecular oxygen or by other primary oxidants such as hydrogen peroxide, alkyl hydroperoxides, monopersulfate, etc. In this paper recent developments in selective catalytic oxidations are reviewed ed in particular those processes in which is formed a metal derivatives, by action of a terminal oxidant which could be oxygen or an organic or inorganic peroxide, capable of selectively oxidizing various substrates

Manganese Porphyrin-catalysed Heterogeneous and Unusually Selective Oxidation of Sulfides by Monopersulfate in Supercritical C02

The oxidation of sulfides by Oxone\uae in the presence of catalytic amount of various manganese porphyrins in supercritical CO2 (scCO2) has been studied. The reactions have been carried out in an anhydrous two phase-system (solid Oxone\uae, solid catalyst/scCO2). In the experimental conditions employed (40 oC, 20 MPa), only the new synthesised 5,10,15,20-tetrakis(heptafluoropropyl)porphyrinate-manganese(III) chloride showed a slight solubility in scCO2. In the absence of manganese porphyrin and/or of an aromatic nitrogen base a slow stoichiometric sulfide oxidation leading mainly to sulfoxide is observed in spite of the extremely low solubility of Oxone\uae in scCO2. Conversely, in the presence of 4-tert.-butylpyridine and catalytic amount of manganese porphyrins (0.6% with respect to sulfide) enhanced reaction rates are observed. Furthermore, the selectivity of sulfide oxidation reverses and sulfone is formed in larger or comparable amount than sulfoxide even when an excess of sulfide over oxidant is employed. The results collected suggest that the local concentration of the intermediate sulfoxide around the catalyst is higher than that of the bulk supercritical phase thus determining unusual high reaction rates for sulfone formation

Highly Efficient Cascade-Oxygen-Transfer from H2O2 to Olefins Mediated by Halogenated Carbonyl Compounds and MetalloPorphyrins

The catalytic oxidation of cyclohexene with hydrogen peroxide promoted by manganese and iron porphyrins has been studied in the presence of halogenated carbonyl compounds as co-catalysts in a dichloromethane/water biphasic medium. The efficiency of the overall catalytic process is strictly related to the nature of the co-catalyst and to the high reactivity of its perhydrate form toward metalloporphyrins in forming an high valent oxo-porphyrin derivative. Hydrogen peroxide fixation by hexafluoroacetone hydrate provides an useful system to hamper catalyst bleaching and/or oxidant decomposition. Thus, a complete olefin conversion into oxygenated products is accomplished with a very limited excess of oxidant respect to the organic substrate

Catalytic Olefin Epoxidation with KHSO5: the First Report on Manganese Hemiporphyrazines as Catalyst in Oxigenation Reactions

The oxidation of cyclooctene to cyclooctene epoxide by Oxone\uae (2KHSO5*KHSO4*K2SO4) as probe for evaluating the catalytic activity of a few manganese hemiporphyrazines has been studied. The oxidations have been carried out in an anhydrous two-phase system (solid Oxone\uae/solid catalyst/1,2-dichloroethane solution). In the absence of manganese hemiporphyrazine and/or of an aromatic nitrogen base only the slow stoichiometric epoxidation by KHSO5 is observed. On the contrary, in the presence of pyridine and catalytic amount of manganese hemiporphyrazine (0.13\ub81% respect with the organic substrate) either suspended in the reaction medium or adsorbed on a suitable polymer (silica gel or poly(vinylpyridine)) enhanced reaction rates are observed. The presence of an axial ligand in the coordination sphere of the catalyst appears to be essential for promoting the catalytic activity of the manganese complex. Moreover, the manganese hemiporphyrazine was subject to a colour change upon addition of the oxidant, thus suggesting the formation of a high valent oxo intermediate that oxidizes the olefin in a successive step. Under the experimental conditions adopted, epoxide yields up to 86% are obtained

Fluorinated Silica Gels Doped with TPAP as Effective Aerobic Oxidation Catalysts in Dense Phase Carbon Dioxide

Abstract: Hybrid organic-inorganic fluorinated silica glasses doped with the ruthenium species TPAP (tetra-n-propylammonium perruthenate) are effective catalysts for the aerial oxidation of benzyl alcohol to benzaldehyde in dense phase CO2. Moderate silica fluorination (10%) by short-chain fluoroalkyl-containing monomers in the sol-gel polycondensation with TMOS affords highly active catalysts which at 75 oC and 220 bar selectively dehydrogenate the alcohol with oxygen as primary oxidant. Both the activity and the stability of the fluorinated materials vary with the degree of fluorination and the nature of the fluoroalkyl residue attached to the silica polymeric network. An explanation of the behaviour of doped sol-gel oxides in supercritical carbon dioxide is proposed which is thought to be of general validity for future practical applications to heterogeneously catalysed aerobic oxidations eliminating the current need for both organic solvents and stoichiometric oxidants