Osmium tetroxide catalyst

With osmium tetroxide catalyst [PLATINUM-GROUP METALS, COMPOUNDS] (Vol 19)... 

CARBON - CARBON AND ARTIFICIALGRAPHITE - APPLICATIONS OF BAKED AND GRAPHITIZED CARBON] (Vol 4) -With osmium tetroxide catalyst [PLATINUM-GROUP METALS, COMPOUNDS] (Vol 19)... 

Oscillometry 527 as analytical tool, 528 titrations (H.F.), 527 Osmium tetroxide catalyst 381 Ostwald s dilution law 31 Ovens electric, 97 microwave, 97 Overpotential 506 Overvoltage see Overpotential Oxalates, D. of as calcium carbonate via oxalate, (g) 484... 

In this report we describe the conversion of cyclohexene to cis-diol 2 in 90% yield in a catalytic osmylation using 1 mole equivalent of N-methylmorpholine N-oxide (1) to regenerate the less than 1 mole % of osmium tetroxide catalyst. This procedure avoids the a-ketol by-products encountered with the presently available catalytic processes, and provides the high yields of the stoichiometric reaction without the expense and work-up problems. 

Osmium tetroxide (0s04, sometimes called osmic acid) reacts with alkenes in a concerted step to form a cyclic osmate ester. Oxidizing agents such as hydrogen peroxide (H202) or tertiary amine oxides (R3N+—O-) are used to hydrolyze the osmate ester and reoxidize osmium to osmium tetroxide. The regenerated osmium tetroxide catalyst continues to hydroxylate more molecules of the alkene. 

Osmium tetroxide was supplied by Matthey-Bishop, Inc. in 1-g amounts in sealed glass ampuls. The procedure that we describe below should be followed to prepare the osmium tetroxide catalyst solution. Work in a well-ventilated hood. One ampul is scored in the middle, broken open, and the two halves are dropped into a clean, brown bottle containing 39.8 mL of reagent grade terf-butyl alcohol and 0.20 mL of 70 or 90% terf-butyl hydroperoxide (Aldrich). The bottle is capped (use caps with Teflon liners) and then swirled to ensure dissolution of the Os04. These solutions are stored in the hood at room temperature and seem to be very stable. 

Catalysts are very important to the analytical chemist in a number of reactions that are normally too slow to be analytically useful. An example is the use of an osmium tetroxide catalyst to speed up the titration reaction between arsenic(III) and ceiium(IV), whose equilibrium is very favorable but whose rate is normally too slow to be useful for titrations. The measurement of the change in the rate of a kineti-cally slow reaction in the presence of a catalyst can actually be used for determining the catalyst concentration. 

Pinanediol is the least expensive of the useful chiral directors. a-Pinene (13) reacts with trimethylamine N-oxide and osmium tetroxide catalyst in the presence of pyridine and water to produce pinanediol (14) (Scheme 8.3) [23, 24], A kinetic study has shown that the reaction is first-order in trimethylamine N-oxide, first-order in osmium tetroxide, and zero-order in a-pinene [25]. Trimethylamine N-oxide produced better yields than the less expensive N-methylmorpholine N-oxide [24,26]. Although the first reported solvent was tert-butyl alcohol [24], acetone can be used instead [26, 27], The reflux temperature of tert-butyl alcohol is a little too high, and some over-oxidation to hydroxyketone occurs above about 75 °C. Refluxing in acetone avoids over-oxidation but is slower. Two moles of pinene with a small excess of trimethylamine N-oxide and 1 g of osmium tetroxide produce pinanediol in 95-96% yield in 3-4 days in tert-butyl alcohol, or after about a week in acetone [24, 27]. 

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