Osmium tetroxide examples

The reagent Is expensive and poisonous, consequently the hydroxylation procedure is employed only for the conversion of rare or expensive alkenes (e.g., in the steroid field) into the glycols. Another method for hydroxylation utilises catalytic amounts of osmium tetroxide rather than the stoichiometric quantity the reagent is hydrogen peroxide in tert.-butyl alcohol This reagent converts, for example, cyc/ohexene into cis 1 2- t/ohexanedlol. 

Other examples are the use of osmium(VIII) oxide (osmium tetroxide) as catalyst in the titration of solutions of arsenic(III) oxide with cerium(IV) sulphate solution, and the use of molybdate(VI) ions to catalyse the formation of iodine by the reaction of iodide ions with hydrogen peroxide. Certain reactions of various organic compounds are catalysed by several naturally occurring proteins known as enzymes. 

Osmium tetroxide used in combination with sodium periodate can also effect alkene cleavage.191 Successful oxidative cleavage of double bonds using ruthenium tetroxide and sodium periodate has also been reported.192 In these procedures the osmium or ruthenium can be used in substoichiometric amounts because the periodate reoxidizes the metal to the tetroxide state. Entries 1 to 4 in Scheme 12.18 are examples of these procedures. Entries 5 and 6 show reactions carried out in the course of multistep syntheses. The reaction in Entry 5 followed a 5-exo radical cyclization and served to excise an extraneous carbon. The reaction in Entry 6 followed introduction of the allyl group by enolate alkylation. The aldehyde group in the product was used to introduce an amino group by reductive alkylation (see Section 5.3.1.2). 

Worked Example 8.17 The following kinetic data were obtained for the second-order reaction between osmium tetroxide and an alkene, to yield a 1,2-diol. Values of k are pseudo-order rate constants because the 0s04 was always in a tiny minority. Determine the second-order rate constant k2 from the data in the following table ... 

Another familiar example of the reaction proceeding in cis fashion is the hydroxylation of alkenes which occurs by osmium tetroxide or by the action of KMn04. 

For this purpose it is necessaiy to give sufficient contrast to a thin film of the frozen sample, for example, by use of osmium tetroxide. Then the sample can be viewed directly in the TEM (at — 196°C). The adjustment of the temperature to — 196°C produces a very low vapor pressure, especially of water, so that the examination of the probe is possible by preservation of the microstructure despite the high vacuum. A disadvantage of cryo-TEM is the classification of vesicles according to their size. Due to the fluid property of the vesicle dispersion prior to freezing, the thickness of the sample film varies from the center to the outside. Hence the smaller vesicles stay in the center, where the film is thin, while the larger ones remain at the outside margin in the thicker part of the film. In this outer part, the vesicles evade... 

Grafting a modified cinchona alkaloid to hexagonal mesoporous molecular sieve SBA-15 afforded catalyst (27) with excellent activity. 1-Phenyl-1-propene was converted to the corresponding diol in 98% yield (98% ee), while trans-stilbene yielded the desired product in 97% yield (99% ee) [92]. Other examples in this field are the utilization of microencapsulated osmium tetroxide by Kobayashi [93] and the application of continuous dihydroxylation mns in chemzyme membrane reactors described by Woltinger [94]. 

Butyl hydroperoxide,37 barium chlorate,38 or potassium ferricyanide39 can also be used as oxidants in catalytic procedures. Scheme 12.6 provides some examples of oxidations of alkenes to glycols by permanganate and by osmium tetroxide. 

Osmium tetroxide used in combination with sodium periodate can also effect alkene cleavage.135 Successful oxidative cleavage of double bonds using ruthenium tetroxide and sodium periodate has also been reported.136 In these procedures, the osmium or ruthenium can be used in substoichiometric amounts because the periodate reoxidizes the metal to the tetroxide state. Entries 1 4 in Scheme 12.17 are examples of these procedures. 

Under the conditions of Example 5-23 the rubber phase of the end product shows an interesting micro-morphology. It consists of particles of 1-3 microns diameter into which polystyrene spheres with much lower diameters are dispersed. These included polystyrene spheres act as hard fillers and raise the elastic modulus of polybutadiene. As a consequence, HIPS with this micro-morphology has a higher impact resistance without loosing too much in stiffness and hardness. This special morphology can be visualized with transmission electron microscopy. A relevant TEM-picture obtained from a thin cut after straining with osmium tetroxide is shown in Sect. 2.3.4.14. 

Reaction with fluoride ion forms the adduct oxofluoro ion, [0s04F2]2. For example, osmium tetroxide reacts with sodium fluoride to form an oxofluoro salt of sodium ... 

Osmium tetroxide forms various complexes with donor molecules under varying conditions. For example, with pyridine(py) it forms a bridged complex, [(py)0s02(p-0)]2. ... 

Osmium tetroxide reacts with phenyl Grignard reagent to produce a reactive intermediate, serving as a synthetic route to prepare polyphenyl osmium complexes. For example, reaction with o-tolyl magnesium bromide, o-tolMgBr, forms a purple, tetracoordinated osmium ort/io-tolyl complex, Os(o-tol)4, which reacts with trimethylphosphine or carbon monoxide to yield osmium n-aryl complexes. 

Phthalazines are commonly used as ligands in transition metal cataysis since the structure provides a planar backbone with coordinating nitrogens. One of the most prevalent phthalazine-based ligands is known as (DHQD)2PHAL (154) <94CR2483>. A recent example of the use of 154 was in the catalytic asymmetric dihydroxylation by osmium tetroxide with air as the ultimate oxidant reported by Krief and co-worker <99TL4189>. 

There are other stereospecific olefin addition processes which occur with cis or syn stereochemistry. Common examples include catalytic hydrogenation, hydroboration/oxidation, and dihydroxylation using osmium tetroxide. The stereospecificity of these syn additions requires that die facial properties of the olefinic bond be maintained throughout die addition process and that both new bonds are formed to the same face of the olefin. This is normally accomplished by a concerted syn addition to the n system. 

Several common examples show the power of diis reasoning. The reaction of osmium tetroxide widi olefins followed by reduction gives diols resulting exclusively from syn addition to the double bond. The reaction is hence stereospecific The addition stereochemistry is clearly seen in cyclic olefins, but it is also seen in acyclic olefins where single diastereomers are produced [reaction (6.4)]. 

A second class of reactions of this kind are ones involving cycloaddition to double bonds. The Diels-Alder reaction can be regarded as an example if we are concerned primarily with the fate of the dienophile. It is generally believed that various oxidations of olefins, e.g. by osmium tetroxide, also take place in this way, i.e. 

The stereochemistry of the product of a reaction will be influenced by the structures of the reagent and substrate and the mechanisms by which they react. For example, the hydroxylation of but-2-ene by osmium tetroxide and water yields a racemate whilst bromination of the same compound with bromine produces a meso compound (Figure 10.5). Flowever, a stereoselective reaction is most likely to occur when steric hindrance at the reaction centre restricts the approach of the reagent to one direction (Figure 10.6). Furthermore, the action of both enzyme and non-enzyme catalysts may also be used to introduce specific stereochemical centres into a molecule. 

The reaction of alkenes with osmium tetroxide (0s04) 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... 

Fig. 3. Example of electron micrograph of a hexagonal structure. Copolymer polystyrene-poly-butadiene SB. 32 containing 30,5% of polybutadiene, swollen with 29% of MMA and post-polymerized. Main figure section along the plane perpendicular to the direction of the axis of the insoluble poly butadiene cylinders insert section by a plane parallel to the axis of the cylinders. Polybutadiene stained by osmium tetroxide in dark...

Fig. 37. Example of an electron micrograph of copolymers with a polyvinyl block and a polypeptide block. Copolymer polybutadiene-poly(benzyl-L-glutamate) BG.530 containing 33% polypeptide with polydiene chains have been stained with osmium tetroxide...

It is a chiral version of the syn dihydroxylation of alkenes by osmium tetroxide. Here is an example— though the concept is quite simple, the recipe for the reactions is quite complicated so we need to approach it step by step. 

Osmium tetroxide and permanganate are the textbook examples for the direct addition of the hydroxyl function to double bonds as shown in Scheme 3. They have been rationalized to be feasible because of their large thermodynamic exothermi-cities,30 and the existence of a low-energy pathway discussed in Section 2.1 for the transfer of two oxygen atoms from the metal to the adjacent alkene carbons. 

The oxidation of alkenes by permanganate is one of the frequently used examples in freshman chemistry. It is also well known as the Baeyer test for unsaturation. There are many reagents that add two hydroxyl groups to a double bond,44 but osmium tetroxide and permanganate are the most prominent ones. The mechanism of the permanganate oxidation is believed to be similar to the oxidation of alkenes by 0s0445 46... 

Osmium tetroxide catalytically assists the oxidation of certain oxidisable substances. For example,8 a mixture of 15 grams of arsenic with 10 grams of potassium chlorate in 50 e.c. of water remains unaltered even after addition of a few drops of dilute sulphuric acid. Upon introducing a trace of osmium tetroxide (c. 0-015 gram) in solution, the temperature immediately rises, the arsenic being rapidly oxidised to... 

The potassium salts may he obtained by the action of a suitable reducing agent upon osmium tetroxide in the presence of a simple potassium salt or its hydroxide. Thus, for example, potassium osmyl nitrite results when the tetroxide is reduced by nitric oxide in the presence of potassium nitrite solution ... 

Osmium tetroxide dissolves in wrater, yielding a neutral solution possessed of oxidising activity. For example, it oxidises ferrous sulphate to the ferric condition, being itself reduced to the dioxide and thrown out of solution in the black hydrated condition, Os(OH)4 or 0s02.2H20. 

CXXXI. Its properties are those to be expected of such a structure for example, the UV-spectrum shows absorption at 224 m/u. (e = 14000) corresponding to one diene chromophore in the C4o-molecule, and oxidation by osmium tetroxide-sodium chlorate followed by periodate fission gives both acetaldehyde and formaldehyde. The Hofmann degradation can be completed by treatment of descurarine with alkali to yield the ditertiary ether base CXXVIII (129). 

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