Osmium toxicity

Flowever, some associated materials might be perceived as toxic. For example, complexes of osmium find frequent use as electron mediators, because of their rich chemistry, stability, and redox activity. Osmium metal and most compounds are considered nontoxic, but the neat tetroxide of osmium is a strong oxidizer and is considered highly toxic in the U.S. and very toxic by the European Union. On the other hand, the aqueous solution, osmic acid, has been injected at 1% concentration in several European clinical trials, starting in the 1970s, for treatment of arthritis and hemophilia. - No toxic effects were observed. Thus, osmium toxicity might be a question not of in vivo chemistry, but of manufacture, where a concentrated form of the oxide might need to be handled. ... 

Because osmium tetraoxide is regenerated m this step alkenes can be converted to vie mal diols using only catalytic amounts of osmium tetraoxide which is both toxic and expensive The entire process is performed m a single operation by simply allowing a solution of the alkene and tert butyl hydroperoxide m tert butyl alcohol containing a small amount of osmium tetraoxide and base to stand for several hours... 

Because osmium tetroxide is expensive, and its vapors are toxic, alternate methods have been explored for effecting vic-glycol formation. In the aliphatic series, olefins can be hydroxylated with hydrogen peroxide with the use of only a catalytic amount of osmium tetroxide. Anhydrous conditions are not necessary 30% hydrogen peroxide in acetone or acetone-ether is satisfactory. The intermediate osmate ester is presumably cleaved by peroxide to the glycol with regeneration of osmium tetroxide. When this reaction was tried on a A -steroid, the product isolated was the 20-ketone ... 

Since osmium tetroxide is expensive and toxic, alternate reagents were also explored. This has led to the use of potassium permanganate by two different groups. ... 

The actual catalyst is a complex formed from osmium tetroxide and a chiral ligand, e.g. dihydroquinine (DHQ) 9, dihydroquinidine (DHQD), Zj -dihydroqui-nine-phthalazine 10 or the respective dihydroquinidine derivative. The expensive and toxic osmium tetroxide is employed in small amounts only, together with a less expensive co-oxidant, e.g. potassium hexacyanoferrate(lll), which is used in stoichiometric quantities. The chiral ligand is also required in small amounts only. For the bench chemist, the procedure for the asymmetric fihydroxylation has been simplified with commercially available mixtures of reagents, e.g. AD-mix-a or AD-mix-/3, ° containing the appropriate cinchona alkaloid derivative ... 

Ruthenium dissolves anodically in alkaline solutions, as predicted by Pourbaix but its corrosion resistance when made anodic in acid solutions is variable. Under some conditions the volatile and toxic tetroxide is evolved. Osmium is even more reactive anodically than ruthenium. 

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... 

The most successful class of active ingredient for both oxidation and reduction is that of the noble metals silver, gold, ruthenium, rhodium, palladium, osmium, iridium, and platinum. Platinum and palladium readily oxidize carbon monoxide, all the hydrocarbons except methane, and the partially oxygenated organic compounds such as aldehydes and alcohols. Under reducing conditions, platinum can convert NO to N2 and to NH3. Platinum and palladium are used in small quantities as promoters for less active base metal oxide catalysts. Platinum is also a candidate for simultaneous oxidation and reduction when the oxidant/re-ductant ratio is within 1% of stoichiometry. The other four elements of the platinum family are in short supply. Ruthenium produces the least NH3 concentration in NO reduction in comparison with other catalysts, but it forms volatile toxic oxides. 

The reagent is toxic and expensive but these disadvantages are minimized by methods that use only a catalytic amount of osmium tetroxide. A very useful procedure involves an amine oxide such as morpholine-A-oxide as the stoichiometric oxidant.41... 

Osmium tetroxide is highly toxic and is very expensive => Osmium tetroxide is used catalytically in conjunction with a cooxidant. 

This new process has one unexpected benefit the rates and turnover numbers are increased substantially with the result that the amount of the toxic and expensive 0s04 is considerably reduced (usually 0.002 mole %). The rate acceleration is attributed to formation of an Os04-alkaloid complex, which is more reactive than free osmium tetroxide. Increasing the concentration of 1 or 2 beyond that of 0s04 produces only negligible increase in the enantiomeric excess of the diol. In contrast quinuclidine itself substantially retards the catalytic reaction, probably because it binds too strongly to osmium tetroxide and inhibits the initial osmylation. Other chelating tertiary amines as well as pyridine also inhibit the catalytic process. 

Osmium (Os, [Xe + 4/ l4]5 /66.v2), name from the Greek oop/ij (osme, smell). Powdered Os slowly gives off 0s04 toxic and with a strong smell. Discovered with... 

Dihydroxylations and aminohydroxylations of alkenes are important reactions in organic synthesis in order to introduce 1,2-functionalization into simple unsaturated precursors. Since these transformations mostly involve toxic osmium tetrox-ide or valuable chiral hgands, attempts to immobilize those reagents are especially appealing. 

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. 

Because of its hard brittle nature, the metal osmium has few uses. However, the powdered form can be sintered under high pressure and temperatures to form some useful products, despite its toxicity and malodor. Its main use is as an alloy to manufacture devices that resist wear and stand up to constant use. As an alloy, osmium loses both its foul odor and toxicity. Some of these products are ballpoint and fountain pen tips, needles for record players, and pivot points for compass needles. Osmium alloys are also used for contact points on special switches and other devices that require reduced frictional wear. 

Most of the oxides of osmium are not noxious, but are toxic if inhaled or ingested. The compound OsO is extremely poisonous. It is a powerful oxidizing agent that is soluble in water and will produce serious burns in skin as it oxidizes the various layers of tissues. 

McLaughlin AIG, Milton R, Perry KMA Toxic manifestations of osmium tetroxide. Br JlndMedl-. 183-186, 1946... 

Platinum is a relatively rare earth metal usually found with related metals osmium and iridium. While it has a number of industrial applications, its common consumer application is in catalytic converters. This application has actually increased platinum concentrations in roadside dust. The ability of platinum and its derivatives to kill cells or inhibit cell division was discovered in 1965. Platinum-based drugs, such as cisplatin, are used to treat ovarian and testicular cancer, and cancers of the head and neck, as well as others. Unfortunately, the toxic side effects of these agents often limit their usefulness. 

P listed wastes Highly toxic chemicals that are rarely used, are banned, or are permitted for limited uses Acrolein, arsenic trioxide, dieldrin, heptachlor, me-thiocarb, osmium tetroxide, 2-propenal... 

Caution. Because of the toxicity of osmium carbonyl compounds, all manipulations should be carried out in an efficient fume hood, wearing gloves and eye protection. 

Caution Care should be taken in handling osmium tetroxide. The vapor is toxic, causing damage to eyes, respiratory tract, and skin. 

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