Osmium tetroxide OsO

There are a number of reagents that, overall, add two OH groups to alkenes. Thus osmium tetroxide, OsO, adds to yield cyclic osmic esters (46), which can be made to undergo ready hydrolytic cleavage of their Os—O bonds to yield the 1,2-diol (47) ... 

One of the important properties of osmium is the formation of gases when the metal is exposed to air. These fumes are extremely toxic, which limits osmiums usefulness. Osmium is a hard, tough, brittle, bluish-white metal that is difficult to use except in a powder form that oxidizes into osmium tetroxide (OsO ), which not only has objectionable odor but also is toxic. 

Whereas hydrolysis of epoxides leads to the trans diaxial addition of water and the formation of trans glycols (1,2-diols), cis glycol formation involves the addition of osmium(VIII) oxide (osmium tetroxide, OsO ) or cold dilute aqueous potassium manganate(Vll) (potassium permanganate) to an alkene. 

Several methods of studies have been developed. Osmium-staining technique, pioneered by Kato [1967], is one of the most successful methods for observing crazing in rubber toughened plastics. It depends upon a reaction between osmium tetroxide, OsO, and double bonds in PBD and other unsaturated polymers. However, it is not suitable for saturated rubbers. 

Osmium tetroxide, OsO. This is undoubtedly the most important compound or complex of osmium, and it was as the tetroxide that osmium was first separated and, as explained on p. 522, gave its name to the element. It is industrially important both in the fine organic chemicals industry (for the cis hydroxylation of alkenes) and in biological chemistry and medicine for the fixation or... 

The reaction of alkenes with osmium tetroxide (OsO ) is an example of an oxidation reaction (Following fig.). In this case the alkene is not split, but, a 1,2-diol is obtained which is also called a glycol. The reaction involves the formation of a cyclic intermediate where the osmium reagent is attached to one face of the alkene. On treatment with sodium bisulphite, the intermediate is cleaved such that the two oxygen atoms linking the osmium remain attached. Due to this both the... 

ESCA measurements ESCA(Electron Spectroscopy for Chemical Analysis) spectra were obtained on a Shimazu ESCA Model 650-B electron spectrometer using MgKa radiation. Samples of membranes cast from chloroform (Cf) - trifluoro-ethanol (TFE) 10 1 mixture, followed by fixation and staining of membranes by osmium tetroxide (OsO ) were coated onto plane glass plate, and fixed to the probe by doublesided tape. 

FIGURE 17. ESCA spectra of the products of the reaction of each polymer membrane with osmium tetroxide OsO, vapor (a) PCBL-1, (b) LBL-1, (c) LBL-2, and (d) LBL-5. 

OSMIUM TETROXIDE OsO, 0 mk acid Hydrochloric acid, easily Oiddized organic materiab Not combustible ... 

Caution. Osmium tetroxide, OsO, is a severe poison and must be handled in a well-ventilated hood. 

The double bonds of avermectins react with y -chloroperbenzoic acid to give 3,4-, 8,9-, and 14,15-epoxides. The 8,9-epoxide is the primary product and can be isolated in good yield (45). The 8,9-epoxide was opened by aqueous acids to the 8,9-diol (46). The 3,4-diol can be obtained readily and regiospecificaHy by osmium tetroxide oxidation. Neither peracids nor OsO will attack the 22,23-double bond. 

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... 

The bulk metal is stable in oxygen at ordinary temperatures but reacts at 200°C, forming osmium tetroxide. When further heated to 800 to 1,500°C in air or oxygen, the tetroxide converts to volatde trioxide, OsOs. When the metal is heated in a stream of 0s04 vapor, osmium dioxide is produced ... 

Osmium tetroxide reacts with amines, undergoing partial substitution of NR2 (where R=alkyl group) with O to form compounds such as OsOs (NR) and OsO(NR)3. 

Diammino-osmo-hydroxide, [OsO(NH3)2](OH)2, is prepared from osmium tetroxide and excess of concentrated aqueous ammonia. The yellow liquid obtained is heated in a closed vessel at 50° C. till it becomes dark brown in colour and a black powder is deposited. It is then exposed to the atmosphere and evaporated at low temperature, when a blackish-brown powder is deposited. The dry powder decomposes explosively on heating, with evolution of nitrogen. It dissolves in acids yielding the corresponding salts, and from these the base may be precipitated on the addition of aqueous alkali hydroxide. On boiling with a solution of alkali, however, the base is decomposed, ammonia is liberated, and a precipitate of osmium dioxide remains.1... 

For most cases staining with osmium or rhu-tenium tetroxide (OsO or RuO, respectively) yields sufficient results. OsO reacts with isolated double bonds (C=0, C=C) such as the double bonds in polyisoprene and polybutadiene, but it does not react with conjugated double bonds [Parker and Vesely, 1990]. 

Check to make sure that the osmium tetroxide is fully dissolved. Osmium crystals must be left overnight in distilled H O to dissolve, and then mixed the following morning with 0.2 M phosphate buffer to make a working solution of 1% OsO. Remember to wear gloves and work in the hood when handling osmium... 

To produce contrast between phase domain for electron microscopy the osmium tetroxide technique of Kato (1 18) was employed. Samples were exposed to OsO. vapor for one week, during which time they darkened. The samples were cut... 

M My attraction to the reaction of OsO,f with olefins was inevitable. Osmium tetroxide not only accomplishes an important synthetic transformation, but it does so with a scope and reliability unique among reactions used for organic synthesis. It reacts only with olefins and it reacts with all olefins (slight poetic license here). (Sharpless, 2001) [5] H... 

Now in the foregoing reactions the osmium is used in the form of its tetroxide, in which its valency is 8. The first action is that of the reducing agent, which lowers its valency to six. Then comes the formation of the osmyl derivative. For example, the preparation of potassium osmyl oxalate takes place in two stages, namely, (1) the reduction of 0s04 to OsOs, which, in the presence of the potassium hydroxide, yields potassium osmate, K20s04 and (2) interaction of the last named with 2 molecules of oxalic acid to form the osmyl derivative. These stages may be expressed as follows ... 

Osmium Di-ammine Hydroxide, OsO(NH3)2(OH)2, results when the tetroxide is dissolved in concentrated aqueous ammonia and heated in a closed vessel to 50° C. On opening the vessel and evaporating the excess of ammonia, osmosammine hydroxide is obtained as a dark brown powder.2 It unites with acids to form salts, and upon being heated readily decomposes. When boiled with alkalies ammonia is evolved and hydrated osmium dioxide remains. ... 

Obviously the chemistry here is dominated by that of the tetroxide. We briefly consider the hexa-and penta-oxo species, then Os04, followed by species of the type Os04 L and OsO, . The few tri-, di- and mono-oxo complexes of osmium(VIII) conclude the section, (see Table 23). 

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