Ruthenium tetroxide solvents

The sequence has been applied to the synthesis of 1,4-cyclohexanedione from hydroquinone 10), using W-7 Raney nickel as prepared by Billica and Adkins 6), except that the catalyst was stored under water. The use of water as solvent permitted, after hltration of the catalyst, direct oxidation of the reaction mixture with ruthenium trichloride and sodium hypochlorite via ruthenium tetroxide 78). Hydroquinone can be reduced to the diol over /o Rh-on-C at ambient conditions quantitatively (20). 

Another reagent that finds application of oxidations of alcohols to ketones is ruthenium tetroxide. The oxidations are typically carried out using a catalytic amount of the ruthenium source, e.g., RuC13, with NaI04 or NaOCl as the stoichiometric oxidant.16 Acetonitrile is a favorable solvent because of its ability to stabilize the ruthenium species that are present.17 For example, the oxidation of 1 to 2 was successfully achieved with this reagent after a number of other methods failed. 

When n = 0 or 1, the system appeared to be too rigid to allow the radical pair created upon hydrogen abstraction to form a carbon-carbon bond. Hence a considerable amount of chlorine appears in the product from radical abstraction from the solvent, carbon tetrachloride. When n = 2 the radicals are able to form a carbon-carbon bond. After a five-step workup of the crude irradiation product including reduction with LiAlH4, acetylation, dehydration, oxidation with ruthenium tetroxide, and hydrolysis a 16% yield of previously unreported 12-keto-3a-chlorestanol was obtained. However,... 

In another procedure, oxidation is carried out in the presence of chloride ions and ruthenium dioxide [31]. Chlorine is generated at the anode and this oxidises ruthenium to the tetroxide level. The reaction medium is aqueous sodium chloride with an inert solvent for the alkanol. Ruthenium tetroxide dissolves in the organic layer and effects oxidation of the alkanol. An undivided cell is used so that the chlorine generated at the anode reacts with hydroxide generated at the cathode to form hypochlorite. Thus this electrochemical process is equivalent to the oxidation of alkanols by ruthenium dioxide and a stoichiometric amount of sodium hypochlorite. Secondary alcohols are oxidised to ketones in excellent yields. 1,4- and 1,5-Diols with at least one primary alcohol function, are oxidised to lactones while... 

Cyclic sulfites (68) also are opened by nucleophiles, although they are less reactive than cyclic sulfates and require higher reaction temperatures for the opening reaction. Cyclic sulfite 77, in which the hydroxamic ester is too labile to withstand ruthenium tetroxide oxidation of the sulfite, is opened to 78 in 76% yield by reaction with lithium azide in hot DMF [82], Cyclic sulfite 79 is opened with nucleophiles such as azide ion [83] or bromide ion [84], by using elevated temperatures in polar aprotic solvents. Structures such as 80 generally are not isolated but as in the case of 80 are carried on (when X = N3) to amino alcohols [83] or (when X = Br) to maleates [84] by reduction. Yields are good and for compounds unaffected by the harsher conditions needed to achieve the displacement reaction, use of the cyclic sulfite eliminates the added step of oxidation to the sulfate. 

Catalyzed oxidations.1 In catalytic procedures with Ru04, periodate or hypochlorite are generally used as the stoichiometric oxidants. The addition of acetonitrile, which is inert to oxidation but an effective ligand for lower valent transition metals, results in much higher yields. A third solvent, chloroform, also plays a significant part. The ruthenium tetroxide is generated in situ from RuCl, (H20)n or Ru02 with sodium or potassium metaperiodate sodium hypochlorite is less effective. 

Much of the early work with ruthenium tetroxide also made use of stoichiometric amounts of a solution of the reagent in an inert solvent, such as carbon tetrachloride. Reactions were carried out at room temperature. The general acceptance of the reagent as a powerful wide-ranging oxidant, coupled with the expense of ruthenium me, however, later provided the incentive to develop alternative catalytic... 

Transition metal oxidants such as permanganate, ruthenium tetroxide and diromium(VI) oxide are convenient and efficient reagents for routine cleavage reactions. The use of phase transfer catalysts (quaternary ammonium and phosphonium ions, primarily) has made it possible to solubilize transition metal oxides such as permanganate and chromatt in nonaqueous solvents, and to therdry increase the scope of these reactions substantially. ... 

The physical properties, preparation and reactions of ruthenium tetroxide have been reviewed by Lee and van den Engh, Rylander," Haines and Hetuy and Lange. A more vigorous oxidant than osmium tetroxide, its reaction with double bonds produces only cleavage products. " Under neutral conditions aldehydes are formed from unsaturated secondary carbons while carboxylic acids are obtained under alkaline or acidic conditions. For example, Shalon and Elliott" found that ruthenium tetroxide reacted with compound (11) to give the corresponding aldehyde under neutral conditions, but that a carboxylic acid was formed in acidic or alkaline solvents (equation 23). 

A two-phase system (carbon tetrachloride and water) is often used for these reactions. It q>pears that contact between ruthenium tetroxide and the alkene takes place in the oiganic phase where they are both most soluble. The ruthenium dioxide produced when oxidation occurs is insoluble in all solvents and migrates to the interphase where it contacts the cooxidant (in the aqueous phase) and is reoxidized, as summarized in Scheme 3. Because good contact between all components is essential, best results are obtained when the mixture is shaken or stirred vigorously throughout the course of the reaction. Sharp-less and his coworkers have also found that the addition of acetonitrile to the two-phase mixture improves yields. 

Cation-radicals from 2-arylfurans have been suggested to be involved in the oxidation of these compounds by ruthenium tetroxide. The suggestion is based on the observation of the capture by the heterocycle of the chlorine from chlorinated solvents and of a broad ESR signal which persists for several days. 

Ruthenium tetroxide (RuOa) is also utilized for phenolic oxidation. Sodium 2,6-dichlorophenoxide (750) was oxidized with RuOa in H2O to afford 2,6-dichloro-p-benzoquinone (751) (60%), while the use of acetone as a solvent provided the corresponding biphenol 752 as the only isolatable product (20%) (Scheme 148). 

Oxidation of cyclic amines. Sheehan and Tulis have examined the oxidation of acylated cychc amines with ruthenium tetroxide in a chlorinated solvent (single-phase system) or with ruthenium dioxide—sodium metaperiodate in CHCI3-H2O (two-phase system). Lactams can be obtained in good yield by oxidation of 1-methyloxalylpiperidine or l-methyloxalylpyrroUdine (1) with RUO4. Tlih, protective group is cleaved with sodium methoxide in methanol. The N-carboethoxy derivative of azetidine (n = 0) is oxidized in low yield... 

Ruthenium tetroxide, RuO, is more reactive staining agent that can be used to differentiate between rubber and matrix when the former is essentially saturated. For example, clean glass slides (50 x 10 mm) were dipped in 2 wt% solutions of polymer and the solvent was subsequently evaporated under vacuum at 50°C (323 K) for 24 h. The films were removed from the glass... 

In the solution, americium and curium, most of the FPs are in a single relatively nonextractable valence state. Iodine and ruthenium are important exceptions. Iodine may appear as nonextractable iodide or iodate or as elemental iodine, which would be extracted by the solvent and react with it. Ruthenium may appear in any valence state between 0 (insoluble metal) and 8 (volatile ruthenium tetroxide), and, at valence 4, it may form a number of nitrosyl ruthenium (Ru(IV)NO) complexes of varying extractabil-ity. An important objective of dissolution and the preconditioning of the feed solution prior to extraction is to convert these FP elements into states that will not contaminate uranium, plutonium, or solvent in subsequent solvent extraction (Benedict, Pigford, and Levi, 1981). 

Side reactions can be avoided with a selective oxidizing agent such as ruthenium tetroxide (453) which is soluble in many solvents. It can be used in catalytic quantities in combination with another oxidizing agent, eg, peracetic acid (454). Ruthenium dioxide in combination with periodate can be used in water or in organic solvents in the presence of a phase transfer catalyst (424,425). 

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