Catalysts osmium tetraoxide

Vinyl acetate had been hydroxylated by treatment with excess hydrogen peroxide in presence of osmium tetraoxide catalyst. An explosion occurred while excess vinyl acetate and solvent were being removed by vacuum distillation. This was attributed to the presence of peracetic acid, formed by interaction of excess hydrogen peroxide with acetic acid produced by hydrolysis of the vinyl acetate. 

Spiro acetals can also be stereoselectively hydroxylated, in high yield, with osmium tetraoxide and a catalyst. The resultant diol is formed by. vyw-hydroxylation from the least hindered side of the alkene moiety (equation 21)121. 

The most important (and also the most expensive) grapefruit aroma compound is the bicyclic terpene nootkatone. It is manufactured by oxidation of valencene, which is extracted from Valencia oranges. Figure 1.23 shows two routes for this oxidation, a stoichiometric reaction using chromium trioxide, and a catalytic alternative using sodium hypochlorite (bleach) in the presence of 1 mol% osmium tetraoxide catalyst. 

Osmium-catalysed dihydroxylation has been reviewed with emphasis on the use of new reoxidants and recycling of the catalysts.44 Various aspects of asymmetric dihydroxylation of alkenes by osmium complexes, including the mechanism, acceleration by chiral ligands 45 and development of novel asymmetric dihydroxylation processes,46 has been reviewed. Two reviews on the recent developments in osmium-catalysed asymmetric aminohydroxylation of alkenes have appeared. Factors responsible for chemo-, enantio- and regio-selectivities have been discussed.47,48 Osmium tetraoxide oxidizes unactivated alkanes in aqueous base. Isobutane is oxidized to r-butyl alcohol, cyclohexane to a mixture of adipate and succinate, toluene to benzoate, and both ethane and propane to acetate in low yields. The data are consistent with a concerted 3 + 2 mechanism, analogous to that proposed for alkane oxidation by Ru04, and for alkene oxidations by 0s04.49... 

In order to study the reaction, they defined all the different pathways for approaching the olefin to the catalyst. They are depicted in Fig. 5a. There are three ways of approaching the olefin to the osmium tetroxide, each one directed to one of the equatorial oxygens. Thus, the different isomers of the oxetane complex can be created from the osmium tetraoxide-cinchona ligand complex by adding the olefin in a [2+2] fashion, therefore distorting an equatorial oxo... 

This reaction has been improved by addition of 2,6-lutidine to suppress the side reactions and increase the yields of aldehydes. In addition, this oxidation has been modified by using osmium tetraoxide and oxone as oxidants, which directly convert 1,2-disubstituted olefins into two individual carboxylic acids. On the basis of this modification, osmium tetraoxide has been made to be a three-dimensional networked nanomaterial that, in combination with oxone, forms a superior heterogeneous catalyst, which even oxidizes alkynes into carboxylic acids7... 

Note that the HI value in this case is -1. The value for the former case is twice this value because two diol products are formed, so really the two results are equivalent. Since OSO4 is used as a catalyst, it is recovered and it is the Af-methyhnorpholine oxide that is consumed. This paradoxical situation of using a hypothetical redox reaction in place of the real mechanistically correct one is the only way to satisfy both the tracing of oxygen atoms and the observed net consumption of N-oxide in the overall balanced chemical equation. This will also impact on the determination of/(sac) since the N-oxide will be counted as contributing to the target bond structure map and not osmium tetraoxide. 

Commercially available enantiopure acetate 30 was aminated with sodium di-tert-butyloxy diimide by palladium catalyst to give bis-Boc amide 31, which was quantitatively dihydroxylated by using catalytic osmium tetraoxide and A -methyl morpholine A -oxide (NMO) in THF/water resulting in the cw-diol 32. The free base 33 was liberated from 32 by concentrated... 

Several groups have described the fabrication of microcapsules loaded with a catalyst. Catalysts encapsulated include palladium(II) acetate (86) and osmium tetraoxide (87). Microencapsulated catalysts are described as effective, easily isolated from a reaction system by filtration, and reusable. Shchukin and co-workers (88) recognized that chemical processes can be performed within microcapsules to produce imique products that are retained within the microcapsules. They produced crystalline WO3 nanoparticles inside microcapsules with a polyelectrolyte shell. 

Corey, E. J. Noe, M. C. Sarshar, S. The Origin of High Enantioselectivity in the Dihydroxylation of Olefins Using Osmium Tetraoxide and Cinchona Alkaloid Catalysts. J. Am. Chem. Soc. 1993,115, 3828-3829. 

The reaction is slow, but it is accelerated when osmium tetraoxide is present in the reaction vessel. It is a catalyst for the reaction. Oxide AS2O3 is dissolved in a sodium hydroxide solution, and the solution is acidified by the addition of sulfuric acid. Then some drops of an osmium tetraoxide solution are added and the solution under study is titrated with a ceric sulfate solution ... 

Related Reagents. (Diisopropoxymethylsilyl)methylmag-nesium chloride trimethylsilylmethylpotassium (trimethyl-stannylmethyl)lithium trimethylsilylmethyllithium Grubbs catalyst AD-mix or osmium(VIII) tetraoxide cerium(III) chloride nickel(II) acetylacetonate cobalt(II) chloride. 

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