OsO4 Osmium oxide

Osmium—Os—198.5- occurs in combination with Ir in Pt ores combustible and readily oxidized to OSO4. This oxid, known as osmie acid, forms colorless crystals, soluble in HaO, which give off intensely irritating vapors. It is used as a staining agent by histologists, and also in dental practice. 

Other volatile compounds of elements can be used to transport samples into the plasma flame. For example, hydride reduction of mercury compounds gives the element (Hg), which is very volatile. Osmium can be oxidized to its volatile tetroxide (OSO4), and some elements can be measured as their volatile acetylacetonate (acac) derivatives, as with Zn(acac)2. 

The most interesting oxides of Ru and Os, however, are the volatile, yellow tetroxides, RUO4 (mp 25°C, bp 130°C< 3>) and OSO4 (mp 40°C, bp 130°C). They are tetrahedral molecules and the latter is perhaps the best-known compound of osmium. It is produced by aerial oxidation of the heated metal or by oxidizing other compounds of osmium with... 

The excellent resistance of platinum, rhodium and iridium to oxidation at high temperatures finds numerous applications in technology, in particular in the form of platinum-based alloys. Osmium and ruthenium form volatile oxides which may be isolated (OSO4 and RujOj), and they are not widely used. 

Oxidative cleavage of alkenes using sodium periodate proceeds effectively in a monophasic solution of acetic acid, water, and THF with very low osmium content or osmium-free. The orders of reactivity of alkenes are as follows monosubstituted trisubstituted >1,2 disub-stituted > 1,1-disubstituted > tetrasubstituted alkynes.100 Cleavage with polymer-supported OSO4 catalyst combined with NaI04 allows the reuse of the catalyst.101... 

Oxidation of alkenes with osmium tetraoxide is much more moderate than similar oxidations with permanganate. This makes OSO4 a very reliable reagent for cis dihydroxylation. 

Many ruthenyl and osmyl complexes with O donor ligands are known. The ruthenium compounds are usually prepared from [RuOJ, which can be generated by the oxidation of RuCl3 xH20 or [RUO2] with [104] . The osmium compounds are usually prepared from [OSO4] or K2[0s(0)2(0H)4]. 

Formula OSO4 MW 254.23 Synonym osmium(VIII) oxide. 

Dihydroxylation with catalytic osmium tetroxide and stoichiometric oxidant such as NMO (TV -methylmorpholine-A -oxide) gives diols that can be cleaved to the same aldehydes with sodium periodiate or lead tetra-acetate. It is also possible to combine either KMnC>4 or catalytic OSO4 with an excess of NaIC>4 and complete the operation in one pot. 

Expensive OSO4 may be used in catalytic amounts to oxidize alkenes to diols if MesNO is added. This reagent efficiently reoxidizes the osmium back to 0s04 during the course of the reaction. 

OSO4 is obtained on oxidation of any osmium compound or by direct synthesis at 300-800°C from the elements [50], Its solubility in CCI4 and volatility make it easy to purify it forms pale yellow crystals (m.p. 40.46°C, b.p. 131°C). Like RUO4 it forms tetrahedral molecules with Os-O 1.684-1.710 A, O—Os—O 106.7-110.7° in the solid state Os-O 1.711A in the gas phase [51], It is soluble in water as well as in CCI4 and is very toxic (TLV 2.5 ppm), affecting the eyes. (Its use as a biological stain involves its reaction with tissue.)... 

C. Powdered osmium is slowly attacked by oxygen at room temperature, yielding OSO4 (though not below 400°C if in bulk). Osmium reacts with fluorine and chlorine at about 100°C. Both metals are attacked by molten alkalis and oxidizing fluxes. 

It has been known for decades that osmium tetroxide catalyzes the H2O2 oxidation of olefins to c -l,2-diols but the cost, toxicity and volatility of OSO4 have limited its use to the organic research laboratory. Industrial interest was aroused in the 1990 s by i) the invention of a system for vicinal hydro-xylation using an electrochemical device as the ultimate oxidant and ii) the discovery of conditions to carry out the reaction enantioselectively, mainly by Sharpless and his group. The reaction is currently carried out by Chirex to... 

In the only studies so far reported (2005), hassium atoms were oxidized to a very volatile oxide (thought to be HSO4 by analogy with Ru and Os - its absorption enthalpy is comparable with that of OSO4), and deposited on an NaOH surface. Six correlated o -decay chains of Hs were observed and attributed to Na2[Hs04(OH)2], sodium hassate(viii), by analogy with osmium, the 5d homologue of Hs. 

The maximum oxidation number for any element is -1- 8, as for osmium in OSO4 the maximum charge on a monatomic cation is 4-H, as for Ce". Explain the difference. 

The highest oxidation numbers are associated with covalent bonding. The four oxygen atoms in OSO4 are covalently bonded to the osmium atom, and no ions are formed. For any monatomic ion, 41- is the maximum charge. 

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