Osmium tetroxide, as catalyst

Other examples are the use of osmium(VIII) oxide (osmium tetroxide) as catalyst in the titration of solutions of arsenic(III) oxide with cerium(IV) sulphate solution, and the use of molybdate(VI) ions to catalyse the formation of iodine by the reaction of iodide ions with hydrogen peroxide. Certain reactions of various organic compounds are catalysed by several naturally occurring proteins known as enzymes. 

Method A Standardisation with arsenic (III) oxide. Discussion. The most trustworthy method for standardising cerium(IV) sulphate solutions is with pure arsenic(III) oxide. The reaction between cerium(IV) sulphate solution and arsenic(III) oxide is very slow at the ambient temperature it is necessary to add a trace of osmium tetroxide as catalyst. The arsenic(III) oxide is dissolved in sodium hydroxide solution, the solution acidified with dilute sulphuric acid, and after adding 2 drops of an osmic acid solution prepared by dissolving 0.1 g osmium tetroxide in 40mL of 0.05M sulphuric acid, and the indicator (1-2 drops ferroin or 0.5 mL /V-phenylanthranilic acid), it is titrated with the cerium(IV) sulphate solution to the first sharp colour change orange-red to very pale blue or yellowish-green to purple respectively. 

Reaction between arsenic(tll) and chlorate is fairly slow. Although the reaction can be markedly accelerated by osmium tetroxide as catalyst , the quantitative reduction of chlorates takes nearly an hour. In the case of the induced reaction it was assumed that arsenic(III) is oxidized to arsenic(IV) by 1-equivalent oxidizing agents. Chlorate is reduced to chlorine dioxide by the arsenic(IV) intermediate, viz. 

The first heterogeneous osmium catalyst applicable for asymmetric dihydroxylation reactions was described by Kobayashi and coworkers (Table 9, entry 1) [38, 39]. Osmium tetroxide was enveloped in a polymer capsule by microencapsulation techniques [40,41]. The asymmetric dihydroxylation of transmethylstyrene with poly(acrylonitrile-co-butadiene-co-styrene) microencapsulated (ABS-MC) osmium tetroxide as catalyst, NMO as the cooxidant, and (DHQD)2PHAL as the chiral ligand completed in 88% yield with 94% ee [38]. The catalyst and the chiral ligand were reused in five consecutive runs without loss of activity. However, the use of NMO as cooxidant required the slow... 

Osmium tetroxide alone, or hydrogen peroxide with osmium tetroxide as catalyst, oxidizes strychnine to the expected glycol, CCVII, which... 

Chloramine-B (CAB, PhS02NClNa) and chloramine-T (CAT, p-Me-CgH4,S02NClNa) have also been used for the oxidation of sulphoxides " . The required sulphone is produced after initial attack by the sulphoxide sulphur atom on the electrophilic chlorine-containing species, forming a chlorosulphonium intermediate as shown in equation (34). These reactions take place at room temperature, in water and aqueous polar solvents such as alcohols and dioxane, in both acidic and basic media. In alkaline solution the reaction is slow and the rate is considerably enhanced by the use of osmium tetroxide as a catalyst. ... 

With As(III) as the reductant and Ce(IV) as the oxidant in sulfuric acid, the situation is reversed. The oxidized indicator, ferriin, is reduced hardly at all by excess As(III) even in the presence of osmium tetroxide as a catalyst. If a drop of Ce(IV) solution is added, however, the red color of ferroin is rapidly developed, evidently because of an induced reaction. In hydrochloric acid the induced reaction does not occur, ferroin is oxidized by the first drop of Ce(IV), and so the titration fails. A small amount of chloride (for example, 0.1 Af hydrochloric acid in 0.5 Af sulfuric acid) does not interfere. Addition of excess Hg(II) perchlorate prevents the interference by complexation of the chloride, ... 

Dienes may be hydroxylated at one or at both double bonds, depending on the amount of oxidants used. Cyclopentadiene, on treatment with an excess of hydrogen peroxide and osmium tetroxide as a catalyst in tert-butyl alcohol, gives a mixture of 21% of 3,5-cyclopentenediol and 61% of 1,2,3,4-cyclopentanetetrol [152. ... 

The unusual oxidant nickel peroxide converts aromatic aldehydes into carboxylic acids at 30-60 °C after 1.5-3 h in 58-100% yields [934. The oxidation of aldehydes to acids by pure ruthenium tetroxide results in very low yields [940. On the contrary, potassium ruthenate, prepared in situ from ruthenium trichloride and potassium persulfate in water and used in catalytic amounts, leads to a 99% yield of m-nitrobenzoic acid at room temperature after 2 h. Another oxidant, iodosobenzene in the presence of tris(triphenylphosphine)ruthenium dichloride, converts benzaldehyde into benzoic acid in 96% yield at room temperature [785]. The same reaction with a 91% yield is accomplished by treatment of benzaldehyde with osmium tetroxide as a catalyst and cumene hydroperoxide as a reoxidant [1163]. 

The method described is essentially that of Swem, Billen, Findley, and Scanlan. /mM5-l,2-Cyclohexanediol also has been prepared by hydrolysis of cyclohexene oxide. j-l,2-Cydo-hexanediol has been prepared by the reaction of cyclohexene with hydrogen peroxide in tertiary butyl alcohol with osmium tetroxide as a catalyst. Hydrogenation of catechol over Raney nickel catalyst at 150° gives a mixture (m.p. 73-77°) of cis- and trans-1,2-cyclohexanediols. ... 

A new procedure for the v/c-oxyamination of olefins utilizes the trihydrate of chloramine-T and osmium tetroxide as a catalyst (Scheme 7). 

A method was therefore devised to determine the three anions simultaneously. This is based on their oxidation by hexacyanoferrate(III) under different alkali concentration and using osmium tetroxide as a catalyst. The corresponding reactions are ... 

When the alkali concentration is 0.5-1.0M, dithionite can be titrated with standard hexacyanoferrate(IIl) solution. Because of the possibility of oxidation in air, the titration vessel should be provided with an inlet and an outlet for purging and maintaining an oxygen-free nitrogen atmosphere. Under these conditions, the dithionite is oxidised to sulphite. When the alkali concentration is raised to 4-4.5 M and the temperature is raised to 50°-60°C, the sulphite thus produced or already present together with the thiosulphate, the anions are oxidised by the iron(IIl) complex to sulphate. Titration is carried out in presence of osmium tetroxide as a catalyst. A second titration with iodine in acid solution oxidises the thiosulphate to tetrathionate. This can be titrated with the iron(III) complex at 50°C when the alkali concentration is 5 M. The end-point could be detected potentiometrically or by the dead-stop set up. 

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... 

Ruthenium nowadays finds many uses in the electronics industry, particularly for making resistor tracks. It is used as an ingredient in various catalysts and, importantly, in electrode materials, e.g. Ru02-coated titanium elements in the chloralkali industry. Osmium tetroxide is a very useful organic oxidant and, classically, is used as a tissue stain. Both elements are employed in making certain platinum alloys. 

As with chlorine-containing oxidants, JV-bromo species have been used to oxidize sulphoxides to sulphones (with no bromine incorporation) through the initial formation of a bromosulphonium ion, by nucleophilic attack of the sulphoxide sulphur atom on the electrophilic halogen atom. Such reactions involve JV-bromosuccinimide ° bromamine-T, iV-bromoacetamide ° and iV-bromobenzenesulphonamide. All reported studies were of a kinetic nature and yields were not quoted. In acid solution all oxidations occurred at or around room temperature with the nucleophilic attack on the electrophilic bromine atom being the rate-limiting step. In alkaline solution a catalyst such as osmium tetroxide is required for the reaction to proceed . ... 

In summary, the reaction of osmium tetroxide with alkenes is a reliable and selective transformation. Chiral diamines and cinchona alkakoid are most frequently used as chiral auxiliaries. Complexes derived from osmium tetroxide with diamines do not undergo catalytic turnover, whereas dihydroquinidine and dihydroquinine derivatives have been found to be very effective catalysts for the oxidation of a variety of alkenes. OsC>4 can be used catalytically in the presence of a secondary oxygen donor (e.g., H202, TBHP, A -methylmorpholine-/V-oxide, sodium periodate, 02, sodium hypochlorite, potassium ferricyanide). Furthermore, a remarkable rate enhancement occurs with the addition of a nucleophilic ligand such as pyridine or a tertiary amine. Table 4-11 lists the preferred chiral ligands for the dihydroxylation of a variety of olefins.61 Table 4-12 lists the recommended ligands for each class of olefins. 

Other functionalized supports that are able to serve in the asymmetric dihydroxylation of alkenes were reported by the groups of Sharpless (catalyst 25) [88], Sal-vadori (catalyst 26) [89-91] and Cmdden (catalyst 27) (Scheme 4.13) [92]. Commonly, the oxidations were carried out using K3Fe(CN)g as secondary oxidant in acetone/water or tert-butyl alcohol/water as solvents. For reasons of comparison, the dihydroxylation of trons-stilbene is depicted in Scheme 4.13. The polymeric catalysts could be reused but had to be regenerated after each experiment by treatment with small amounts of osmium tetroxide. A systematic study on the role of the polymeric support and the influence of the alkoxy or aryloxy group in the C-9 position of the immobilized cinchona alkaloids was conducted by Salvadori and coworkers [89-91]. Co-polymerization of a dihydroquinidine phthalazine derivative with hydroxyethylmethacrylate and ethylene glycol dimethacrylate afforded a functionalized polymer (26) with better swelling properties in polar solvents and hence improved performance in the dihydroxylation process [90]. 

Finally, osmium tetroxide-loaded, immobihzed DHQ-hgand system (28) disperses activity in the asymmetric aminohydroxylations of trans-cinnamate derivatives (Scheme 4.14) [95]. Here, the reagent system AcNHBr/LiOH was employed as nitrogen source. The immobihzed catalyst could entirely be removed by filtra-... 

Oxepane (1), as a typical ether, is susceptible to oxidation and yields oxepan-2-one (78) as the initial product. Adipic acid was the product finally isolated after oxidation with Ru04 and NaI04 in a two-phase system (80SC205) or oxygen in the presence of a Pt catalyst (76CB3707) (Scheme 9). Oxidation of 2,3,6,7-tetrahydrooxepin (79) has been reported with peroxybenzoic acid or osmium tetroxide to yield the epoxide (80) or the cis diol (81) respectively (Scheme 10) (58JA3132). 

Organometallic reagents and catalysts continue to be of considerable importance, as illustrated in several procedures CAR-BENE GENERATION BY a-ELIMINATION WITH LITHIUM 2,2,6,6-TETRAMETHYLPIPERIDIDE l-ETHOXY-2-p-TOL-YLCYCLOPROPANE CATALYTIC OSMIUM TETROXIDE OXIDATION OF OLEFINS PREPARATION OF cis-1,2-CYCLOHEXANEDIOL COPPER CATALYZED ARYLA-TION OF /3-DICARBONYL COMPOUNDS 2-(l-ACETYL-2-OXOPROPYL)BENZOIC ACID and PHOSPHINE-NICKEL COMPLEX CATALYZED CROSS-COUPLING OF GRIG-NARD REAGENTS WITH ARYL AND ALKENYL HALIDES 1,2-DIBUTYLBENZENE. 

Diols are prepared from alkenes by oxidation with reagents such as osmium tetroxide, potassium permanganate, or hydrogen peroxide (Section 11-7C). However, ethylene glycol is made on a commercial scale from oxacy-clopropane, which in turn is made by air oxidation of ethene at high temperatures over a silver oxide catalyst (Section 11-7D). 

Exercise 16-37 An elegant modification of the two-step procedure to prepare ketones from alkenes by hydroxylation and oxidative cleavage of the diol formed uses a small amount of potassium permanganate (or osmium tetroxide, 0s04) as the catalyst and sodium periodate as the oxidizing agent ... 

---