Oxidation reactions Osmium tetroxide

Vinyl and ethynyl groups attached to an imidazole ring can be catalytically reduced to the saturated (or less unsaturated) species and cleaved by oxidation. The corresponding 4-carbaldehyde is formed in 71% yield when l-methyl-2,5-diphenyl-4-styrylimidazole is oxidized with osmium tetroxide. However, they may not react like aliphatic alkenes and alkynes not all addition reactions occur normally, Michael additions are known, and the compounds can act as dienophiles in DielsAlder reactions (e.g., Scheme 132). 

The physical properties, preparation and reactions of ruthenium tetroxide have been reviewed by Lee and van den Engh, Rylander," Haines and Hetuy and Lange. A more vigorous oxidant than osmium tetroxide, its reaction with double bonds produces only cleavage products. " Under neutral conditions aldehydes are formed from unsaturated secondary carbons while carboxylic acids are obtained under alkaline or acidic conditions. For example, Shalon and Elliott" found that ruthenium tetroxide reacted with compound (11) to give the corresponding aldehyde under neutral conditions, but that a carboxylic acid was formed in acidic or alkaline solvents (equation 23). 

The acids (IVab) produced from both the barium permanganate reaction and also from treatment with the oxidizing agent osmium tetroxide were found to be identical, as were their phenylhydrazides and these, in turn, were found to differ from the acids (Illab) formed by the hypochlorous acid method. These acids (Illab, IVab) were therefore considered by Glattfeld and Woodruff to be the two theoretically possible dl dihydroxy acids of the 2,3-dihydroxybutanoic acids. 

In the extension of the reaction to polymers 1,2,4,5-cyclo-hexanetetrol was prepared in a 12% over-all yield from 1,4-cyclo-hexadiene by the oxidation with osmium tetroxide. The meso (12/45) diastereomer of (cis/cis) 1,2,4,5-tetrahydroxy-cyclo-hexane (15) was condensed with 1,4-cyclohexanedione to give a 95% yield of a crystalline spiro polymer VI. This material did not melt, but was soluble in hexafluoroisopropanol with an [r ] of 0.056 dl/g (25°, hexafluoroisopropanol). 

OSMIUM(VIII) OXIDE or OSMIUM TETROXIDE (20816-12-0) Contact with hydrochloric acid produces chlorine gas. Explosive reaction with l-methylimidazole. Violent reaction with hydrogen peroxide. Contact with organic and combustible materials may cause fire and explosions. 

Treatment of a solution of 19 in acetone - water with N- methyl morpholine N- oxide and Osmium tetroxide will give the single cis diol which can be cleaved by reaction with lead tetraacetate in benzene to give the sensitive dialdehyde 20. Treatment of 20 with benzylammonium trifluoroacetate in benzene and refluxing will give the alpha,beta unsaturated aldehyde 21. 

Osmium tetroxide also catalyzes the oxidation of organic sulfides to sulfones with NMO or trimethylamine iV-oxide (see Osmium Tetroxide-N-MethylmorphoUne N-Oxide). In contrast, most sulfides are not oxidized with stoichiometric amounts of OSO4. Oxidations of alkynes and alcohols with OSO4 without and in the presence of cooxidants have also been reported. However, these reactions have not found wide synthetic applications because of the availability of other methods. 

Abstract The oxidative functionalization of olefins is an important reaction for organic synthesis as well as for the industrial production of bulk chemicals. Various processes have been explored, among them also metal-catalyzed methods using strong oxidants like osmium tetroxide. Especially, the asymmetric dihydroxylation of olefins by osmium(Vlll) complexes has proven to be a valuable reaction for the synthetic chemist. A large number of experimental studies had been conducted, but the mechanisms of the various osmium-catalyzed reactions remained a controversial issue. This changed when density functional theory calculations became available and computational studies helped to unravel the open mechanistic questions. This mini review will focus on recent mechanistic studies on osmium-mediated oxidation reactions of alkenes. 

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]. 

Dehydration of the tertiary alcohol (290) led to a miicture of approximately equal amounts of the A - and A -isomers (293) and (294) when it was oxidized with osmium tetroxide, all four theoretically possible isomers of the cis-diols (292) and (298) were obtained. At the same time, both in the case of the 16,17-diols (292) and in the case of the 17,17a-diols (298) the amount of the o -isomer was the greater. The cleavage of the first pair of diols (292) with periodic acid led to the ketoaldehyde (295), which, on being boiled in xylene with triethylammonium acetate, cyclized to form dl-5a-A -pregnen-3/S-ol-20-one acetate (296), identical in respect of its IR and UV spectra with the d-enantiomer obtained from natural sources. By a similar series of reactions, the second pair of diols (298) gave the keto-acetate (297) with an acetyl group at Cjg, isomeric with (296) [648, 649,... 

Chemical ingenuity in using the properties of the elements and their compounds has allowed analyses to be carried out by processes analogous to the generation of hydrides. Osmium tetroxide is very volatile and can be formed easily by oxidation of osmium compounds. Some metals form volatile acetylacetonates (acac), such as iron, zinc, cobalt, chromium, and manganese (Figure 15.4). Iodides can be oxidized easily to iodine (another volatile element in itself), and carbonates or bicarbonates can be examined as COj after reaction with acid. 

Oxidation. Maleic and fumaric acids are oxidized in aqueous solution by ozone [10028-15-6] (qv) (85). Products of the reaction include glyoxyhc acid [298-12-4], oxalic acid [144-62-7], and formic acid [64-18-6], Catalytic oxidation of aqueous maleic acid occurs with hydrogen peroxide [7722-84-1] in the presence of sodium tungstate(VI) [13472-45-2] (86) and sodium molybdate(VI) [7631-95-0] (87). Both catalyst systems avoid formation of tartaric acid [133-37-9] and produce i j -epoxysuccinic acid [16533-72-5] at pH values above 5. The reaction of maleic anhydride and hydrogen peroxide in an inert solvent (methylene chloride [75-09-2]) gives permaleic acid [4565-24-6], HOOC—CH=CH—CO H (88) which is useful in Baeyer-ViUiger reactions. Both maleate and fumarate [142-42-7] are hydroxylated to tartaric acid using an osmium tetroxide [20816-12-0]/io 2LX.e [15454-31 -6] catalyst system (89). 

Chemical degradation studies carried out on streptovaricias A and C, which are the primary components of the cmde complex, yielded substances shown ia Figure 1. Streptovaricia A (4), consumes two moles of sodium periodate to yield variciaal A [21913-68-8] (1), 0 2 200, which accounts for the ahphatic portion of the molecule, and prestreptovarone [58074-37-6] (2), C2C)H2C)N02, which accounts for the aromatic chromophore of the streptovaricias (Fig. 2). Streptovaricia G (9) is the only other streptovaricia that yields prestreptovaroae upoa treatmeat with sodium periodate. Treatmeat of streptovaricias A (4), B (5), C (6), E (8), and G (9) with sodium periodate and osmium tetroxide yields streptovarone [36108-44-8] (3), C24H23NO2, which is also produced by the reaction of prestreptovarone with sodium periodate and osmium tetroxide (4,65). A number of aliphatic products were isolated from the oxidation of streptovaricia C and its derivatives (66). 

Thus, Mathis et al. [1, 2] investigated oxidation reactions with 4-nitroperbenzoic acid, sodium hypobromite, osmium tetroxide and ruthenium tetroxide. Hamann et al. [3] employed phosphorus oxychloride in pyridine for dehydration. However, this method is accompanied by the disadvantages that the volume applied is increased because reagent has been added and that water is sometimes produced in the reaction and has to be removed before the chromatographic separation. 

Similar hydroxylation-oxidations can be carried out using a catalytic amount of osmium tetroxide with A-methylmorpholine oxide-hydrogen peroxide or phenyliodosoacetate." A recent patent describes the use of triethylamine oxide peroxide and osmium tetroxide for the same sequence. Since these reactions are of great importance for the preparation of the di-hydroxyacetone side-chain of corticoids, they will be discussed in a later section. 

Osmium Tetroxide Oxidation of a A -Cyanopregnene 20-Cyano-21-hydroxy-5j5-pregn-17(20)-ene-3,l l-dione21-methyl ether (8 g) isdissolved in 100 ml of benzene and 8 ml of pyridine. After the addition of 9.6 g of osmium tetroxide, the reaction mixture is stoppered and allowed to stand at room temperature for 5 days. The mixture is stirred for 24 hr with 160 ml of chloroform, 200 ml of methanol and 280 ml of an aqueous solution... 

With this reaction, two new asymmetric centers can be generated in one step from an achiral precursor in moderate to good enantiomeric purity by using a chiral catalyst for oxidation. The Sharpless dihydroxylation has been developed from the earlier y -dihydroxylation of alkenes with osmium tetroxide, which usually led to a racemic mixture. 

Unfortunately, a serious problem with the osmium tetroxide reaction is that Os04 is both very expensive and very toxic. As a result, the reaction is usually carried out using only a small, catalytic amount of OsO, in the presence of a stoichiometric amount of a safe and inexpensive co-oxidant such as A -methylmorpholine N-oxide, abbreviated NMO. The initially formed osmate intermediate reacts rapidly with NMO to yield the product diol plus... 

Osmium tetroxide, reaction with alkenes, 235-236 toxicity of, 235 Oxalic add, structure of, 753 Oxaloacetic acid, structure of, 753 Oxetane, reaction with Grignard reagents, 680 Oxidation, 233, 348 alcohols, 623-626 aldehydes, 700-701 aldoses, 992-994 alkenes, 233-236 biological, 625-626 phenols, 631 sulfides, 670 thiols, 668... 

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. 

Chloramine-B (CAB, PhS02NClNa) and chloramine-T (CAT, p-Me-C6H4S02NClNa) have also been used for the oxidation of sulphoxides107-115. 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 catalyst115. 

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