Osmium tetroxide solution, preparation

Harvested samples should be immediately prepared for the SEM by fixation in a 0.5% osmium tetroxide solution in the dark for 1 h. If the sample is collected in the field, store in buffered 3% glutaraldehyde solution (pH 7.2) until samples can be fixed. 

Miscellaneous. Aside from the oxidation chemistry described, only a few catalytic applications are reported, including hydrogenation of olefins (114,115), a, [3-unsaturated carbonyl compounds (116), and carbon monoxide (117) and the water gas shift reaction (118). This is so owing to the kinetic inertness of osmium complexes. A 1% by weight osmium tetroxide solution is used as a biological stain, particulady for preparation of samples for electron microscopy. In the presence of pyridine or other heterocyclic amines it is used as a selective reagent for single-stranded or open-form B-DNA (119) (see Nucleic acids). Osmium tetroxide has also been used as an indicator for unsaturated fats in animal tissue. Osmium tetroxide has seen limited if controversial use in the treatment of arthritis (120,121). 

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. 

Osmium tetroxide is obtained as an intermediate during recovery of osmium metal from osmiridium or other noble metal minerals (See Osmium). In general, oxidation of an aqueous solution of an osmium salt or complex, such as sodium osmate with nitric acid, yields the volatile tetroxide which may be distilled out from the solution. In the laboratory, the compound can be prepared by oxidation of the osmium tetrachloride, OsCh, or other halide solutions with sodium hypochlorite followed by distdlation. 

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... 

Osmium tetroxide is the traditional osmium species used in the dihydroxylation of olefins. For large-scale reactions, osmium tetroxide may be weighed and transferred as the solid. For many catalytic applications on a laboratory scale, the amount of osmium tetroxide required is too small to be weighed conveniently. In these cases, advantage can be taken of the solubility of osmium tetroxide in organic solvents by the preparation of a stock solution of known concentration and the use of an aliquot for the small-scale reaction. 

Note. (1) Osmium tetroxide is extremely irritating and toxic and constitutes a severe eye injury hazard. It may be purchased in sealed ampoules, e.g. 100 mg the solution in t-butyl alcohol must be prepared and dispensed in an efficient fume cupboard, with the added protection of gloves and goggles. This solution is reasonably stable (e.g. the decomposition after one month is about 20%), provided that no 2-methylprop-l-ene arising from the t-butyl alcohol is present as impurity. In the latter case formation of... 

After primary fixation the algal and root samples were rinsed in 0.1 M PIPES buffer, pH 7.0, then twice in 0.1 M sodium cacodylate buffer, pH 6.8, and post-fixed in 1% osmium tetroxide in 0.1 M cacodylate buffer, pH 6.8, overnight at 4°C. The osmium solution prepared for the root samples was added with 0.7% potassium ferricyanide in order to improve osmium penetration in the root tissues. This was particularly necessary for the 2 h control roots and roots from RO-treated seed, due to their relatively low water content. The replacement of PIPES buffer with cacodylate buffer before osmication was necessary, as PIPES reacts with osmium, producing a dark precipitate. 

Potassium osmiamate, K[Os( VIII )03N], is prepared by the addition of aqueous ammonia to a solution of osmium tetroxide, 0s04, in caustic potash solution (6). X-ray studies show the molecule to be basically... 

Osmyl sulphites readily lend themselves to preparation in this manner. Rosenheim and Sasserath2 first prepared sodium osmyl sulphite by passing sulphur dioxide through a solution of osmium tetroxide in caustic soda. 

The precipitated osmium dioxide discloses its unsaturated nature by exploding when heated with organic substances. E. von Meyer5 describes the preparation of an osmium oxysulphide by passage of hydrogen sulphide through a solution of osmium tetroxide. 

Osmium Sulphite, 0sS03.—This salt is prepared by reduction of a solution of osmium tetroxide with sulphur dioxide.6 The solution at first becomes yellow, and finally assumes an indigo-blue colour. On... 

Osmium tetroxide was supplied by Matthey-Bishop, Inc. in 1-g amounts in sealed glass ampuls. The procedure that we describe below should be followed to prepare the osmium tetroxide catalyst solution. Work in a well-ventilated hood. One ampul is scored in the middle, broken open, and the two halves are dropped into a clean, brown bottle containing 39.8 mL of reagent grade terf-butyl alcohol and 0.20 mL of 70 or 90% terf-butyl hydroperoxide (Aldrich). The bottle is capped (use caps with Teflon liners) and then swirled to ensure dissolution of the Os04. These solutions are stored in the hood at room temperature and seem to be very stable. 

In a typical example, sodium periodate (18.2 g, 85 mmol) was added in small portions over a 45 min period to l,4-dioxa-6-acetyl-6-allylspiro[4.5]decane (8.9 g, 40 mmol) and osmium tetroxide (0.10 g, 0.39 mmol) in a solution of THF (126 mL) and water (42 mL) at room temperature. The mixture was stirred for 2 h at this temperature during which time the black slurry turned brown. Water (600 mL) was introduced, and the mixture was extracted with ether. The extract was dried over anhydrous magnesium sulfate and stripped of solvent to give 7.4 g of crude aldehyde. (Because osmium tetroxide is a toxic and volatile irritant, all preparations should be carried out in a fume hood with use of adequate personal protection, gloves and safety glasses.) Other examples of the use of this reagent have b n summarized in Table 5. 

Hydroxylation by hydrogen peroxide in t-butyl alcohol solution is catalyzed by osmium tetroxide. The catalyst is volatile and dangerous to handle but is conveniently used in a solution of the tertiary alcohol. The yields of diols are usually low (30-60%), and the process has not been adapted to large-scale preparations. In contrast to hydroxylation by performic acid, this procedure leads to cis addition of the two hydroxyl groups to the double bond. An extensive study of other catalysts has been made. Some catalysts, e.g., selenium dioxide and pertungstic acid, catalyze addition in the trans direction. Hydroxylation of cyclopentadiene takes place in the 1,4-positions to give 2-cyclopenten-l,4-diol. ... 

Reactions with unsaturated compounds. /-Butyl hydroperoxide decomposes smoothly at 95-105° and hydroxylates double bonds, and even a,)3-unsaturated ketones the reactions are catalyzed by small amounts of osmium tetroxide and afford cir-glycols. In benzene solution in the presence of Triton B as catalyst it converts a ,/3-unsaturated ketones into the corresponding epoxides in yields of 50-90%. The steric requirement of the base-catalyzed reaction are indicated by the failure to react with isophorone or A -3-ketosteroids. Payne effected smooth preparation of /3-phenylglycidaldehyde by allowing cinnamaldehyde and /-butyl... 

Diphenylcarbazide, a well-known reagent for Cr(VI), has been applied for the spectrophotometric determination of Os [79]. Diphenylcarbazide (in ethanol) reacts with OSO4 (in CHCI3) to form a blue-green complex having max 560 nm. A freshly prepared solution of 1,5-diphenylcarbazide does not absorb between 400 and 700 nm. The molar absorptivity of the osmium complex in CHCI3 is 3. MO. The sensitivity has been increased as a result of certain modifications [80,81]. Now, osmium tetroxide is made to react with... 

---