Osmic acid

Osmium tetroxide (osmic acid) 71.5°/100mm, 109.3°/400mm,... 

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. 

EFFECT OF CHANGES IN THE CONCENTRATION OF OSMIC ACID ON THE INDUCED REACTION BETWEEN H2O2, OSO4. AND KM11O4 Data of Csinyi et... 

Cis 2-butene (48a) thus yields the meso 1,2-diol (47), i.e. the overall hydroxylation is stereoselectively SYN, as would be expected from Os—O cleavage in a necessarily cis cyclic ester (46). The disadvantage of this reaction as a preparative method is the expense and toxicity of 0s04. This may, however, be overcome by using it in catalytic quantities only, but in association with H202 which re-oxidises the osmic acid, (HO)2OsOz, formed to 0s04. 

Robinow prepared wet smears of Escherichia coli. Slides were fixed in osmic acid vapor, dried, and immersed in normal HC1 for about 9 min. at S3 to SS°C., then washed and stained in 1 20 Giemsa solution for 10 to 60 min., depending on the staining properties of the specimen. 

Oxidation of Divinylglycol with Silver Chlorate and Osmic Acid... Ill... 

Very little was published on the synthesis of hexitols from unsaturated intermediates between the time of Griner s work and 1933, when it occurred to me that it might be possible to add four hydroxyl groups to divinylglycol by means of a solution of silver chlorate containing a small amount of osmic acid. In carrying out this work I had the assistance of one of my students, Joseph Wiemann. We succeeded far beyond our expectations and obtained allitol, unknown up to that time, and d,l-mannitol. 

Another method of synthesis was also used. This involved the action of chloroacetaldehyde on the Grignard reagent derived from acetylene in order to obtain the meso divinylacetylene dichlorohydrin, CH2CI—CHOH—C=C—CHOH—CH C1, from which one passed to the corresponding hexynetetrol, CH2OH—CHOH—C=C—CHOH— CHjOH. This, in turn, was reduced to the hexenetetrol, CHjOH— CHOH—CH=CH—CHOH—CH2OH, by means of Bourguel s catalyst,8 a dispersion of colloidal palladium on starch. When the hexenetetrol was hydroxylated by the use of silver chlorate and osmic acid, two hexitols, dulcitol and allitol, were obtained. 

An amount of 16 g. of the glycol (m. p. 18°) dissolved in 250 ml. of water was oxidized with 18 g. of silver chlorate and 0.3 g. of osmic acid. The reaction mixture yielded 3 g. of allitol and no D,L-mannitol. We may therefore assign the meso configuration to the divinylglycol melting at 18°, since on hydroxylation it yielded allitol, but not D,L-mannitol. 

Oxidation of Divinylglycol with Silver Chlorate and Osmic Acid. In a typical experiment 100 g. of divinylglycol, 118 g. of silver chlorate and 1 g. of osmic acid were dissolved in 6 liters of water. The reaction mixture was kept at room temperature for several days. It was apparently essential that the reaction be carried out rather slowly. 

The reaction is complete when the liquid becomes black, due to reduction of the osmic acid. Silver chloride was then removed by filtration and the... 

Oxidation of l,2,5,6-tetraacetoxyhexene-3 led to the formation of dulcitol tetraacetate. In a typical experiment 22 g. of the tetraacetate was oxidized with 4.4 g. of silver chlorate and 0.1 g. of osmic acid and yielded a sirujj which did not crystallize. The sirup was acetylated again and yielded the corresponding hexitol hexaacetate. The crystals which deposited first were collected and recrystallized from methanol, in which they are difficultly soluble in the cold. The product melted at 166-166.5° and analyzed correctly for a hexitol hexaacetate. Now there was found in the collections of the Ecole Normale Sup rieure an old bottle containing dulcitol hexaacetate, m. p. 167-168°. A mixture of the new and the old hexaacetates was found to melt at 166.5-167.5° the identity of the two compounds was thus beyond doubt. 

CHOAc—CHOAo—CHOH—CH2OH, by the action of silver chlorate and osmic acid. 

Hydrogenation of the pentenynol with Bourguel s catalyst5 gives the corresponding divinylcarbinol, CH2=CH—CHOH—CH=CH2, b. p. 114.5-116°, dig 0.8648, mdw 1.4452. Treatment of this divinylcarbinol with the theoretical quantity of silver chlorate and a little osmic acid yielded a sirup which has not crystallized. From the acetylation of this sirup there was obtained a small quantity of D,L-arabitol pentaacetate and a viscous liquid which has not been studied further but certainly contains one or both of the other pentitol pentaacetates. 

Osmic Acid Anhydride Osmium Oxide Osmium Tetraoxide Osmium Tetroxide OU1 Dry Agent ... 

Procedure Weigh accurately about 0.2 g of arsenic trioxide previously dried at 105°C for 1 hour and transfer to a 500 ml conical flask. Wash down the inner walls of the flask with 25 ml of sodium hydroxide solution, swirl to dissolve, add 100 ml of water and mix. Add 30 ml of diluted sulphuric acid, 0.15 ml of osmic acid solution, 0.1 ml of ferroin sulphate solution and slowly titrate with ceric ammonium sulphate solution until the pink colour is changed to a very pale blue. Each 4.946 mg of arsenic trioxide is equivalent to 1 ml of 0.1 N ammonium ceric sulphate or 0.06326 g of Ce(S04)2. 2(NH4)2S04.2H20. 

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. ... 

With the exception of the neutral halo complexes, which are prepared by direct reaction of the halogen with the metal, and a number of complexes generated by the direct reaction of the metal with a strong acid, coordination complexes of Os are prepared directly or indirectly from [0s04] (2). The latter is a toxic, volatile solid, normally purchased in 1-g ampuls and opened within the reaction mixture contained in a fume hood to prevent escape of the toxic vapor (3) and loss of the reactant. It is also available as an aqueous solution of osmic acid, which is suitable for some reactions. 

The problem of rotational disorder was solved by making an osmyl derivative of buckyball. Osmic acid, OsO. will add across double honds ... 

Osmic acid, osmic acid anhydride, perosmic oxide. 

The aldehydes 346 and 347 were prepared from the methoxyl derivatives by osmic acid sodium chlorate oxidation and deketalization followed by base-catalyzed condensation in an overall yield of 50%. Acetalization of 346 with /i-toluenesulfonic acid and ethylene glycol in refluxing benzene afforded the acetal 348. The latter has an active site at C-6 suitable for the introduction of oxygen substituents at this position. 

Osmium tetroxide (0s04, sometimes called osmic acid) reacts with alkenes in a concerted step to form a cyclic osmate ester. Oxidizing agents such as hydrogen peroxide (H202) or tertiary amine oxides (R3N+—O-) are used to hydrolyze the osmate ester and reoxidize osmium to osmium tetroxide. The regenerated osmium tetroxide catalyst continues to hydroxylate more molecules of the alkene. 

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