Potassium ruthenic acid

The orange-colored solution, containing, among other things, potassium ruthenate, was treated with nitric acid, whereupon a black precipitate of osmium dioxide containing from fifteen to twenty per cent of ruthenium oxide was thrown down as a velvety deposit. Klaus distilled this with aqua regia, taking care to condense the osmium tetroxide. The residue... 

Ruthenium Dioxide (by Pichler).190 A mixture of 1 g of ruthenium powder, 10 g of potassium hydroxide, and 1 g of potassium nitrate is fused in a silver (or a nickel) crucible. It is recommended that the potassium nitrate be added not simultaneously but in portion after portion. In 1-2 h the fusion is complete. After cooling, the mass is dissolved with water into a solution. The dark red solution of potassium ruthenate is heated to boiling, and methanol is added to this dropwise. Immediately after the first drop of methanol has been added, the reduction of the ruthenate to ruthenium dioxide takes place and the reduction is completed in a few minutes. After leaving the precipitate for 1-2 h, the precipitate is collected on a glass filter, washed 7 times with a dilute nitric acid solution and then 18 times with distilled water, and dried at 110°C for 24 h in a desiccator. Pichler s dioxide thus prepared does not show any distinct diffraction patterns corresponding to the oxide of ruthenium and is partly soluble into hot concentrated hydrochloric acid. These facts suggest that Pichler s dioxide is a mixture of the oxide and the hydroxide of ruthenium.191... 

It now remains to separate out the ruthenium. This is accomplished by fusing with potassium hydroxide and nitrate, best in a silver crucible, and subsequently dissolving in water. The solution obtained has an orange-yellow colour in consequence of the presence of potassium ruthenate. This colour is removed by the addition of nitric acid, ruthenium oxide separating out. Ignition in a graphite crucible with a little chalk yields the free ruthenium, the chalk combining with any silicon, chromium, and osmium that may have been present. 

The dioxide may also be obtained by heating the sulphate or disulphide in the presence of air. It crystallises in the form of hard, tetragonal pyramids, of density 7-2, and isomorphous with cassiterite and rutile.2 The crystals exhibit a green iridescent metallic lustre. They are not acted upon by acids, but yield potassium ruthenate when fused with potassium hydroxide. 

In solution potassium ruthenate is of a deep orange colour, but in dilute solution assumes a green colour, due to formation of per-ruthenate. Hydrochloric acid effects the precipitation of an oxide, chlorine being simultaneously evolved. The solution stains the skin black owing to separation of oxide. 

Detection.—Metallic Ruthenium is characterised by its ready solubility in a mixture of fused potassium hydroxide and nitrate, yielding a green mass of potassium ruthenate, K2Ru04. This dissolves in water to an orange-coloured solution which leaves a black stain upon the skin owing to the deposition of oxide or hydroxide. Nitric acid precipitates the hydroxide as a black mass from the solution. 

Detection of Ruthenium in Platinum Alloys.—In order to detect the presence of ruthenium in platinum alloys, a portion of the alloy is fused with lead. The melt is extracted with nitric acid and the residue ignited in contact with air in order to volatilise the osmium. The mass may now contain platinum, iridium, rhodium and ruthenium, and is fused with potassium nitrate and hydroxide. The whole is dissolved in water, treated with excess of nitric acid and allowed to stand in a flask covered with filter-paper. In a few hours (12-24) the filter-paper darkens if ruthenium is present, in consequence of the evolution of vapour of its tetroxide. To confirm the presence of ruthenium, the paper is ignited and the ash fused with potassium nitrate and hydroxide. On extraction with water the orange colour of potassium ruthenate is obtained.1... 

Potassium ruthenate, K2RUO4, is prepared in situ from ruthenium trichloride and aqueous persulfate. The reagent catalyzes persulfate oxidations of primary alcohols to acids, secondary to ketones, and primary amines to nitriles or acids at room temperature in high yields [196],... 

Sodium ruthenate [957] and potassium ruthenate [196 oxidize allylic and benzylic alcohols to carboxylic acids at room temperature. Cinnamyl alcohol is transformed into cinnamic acid with sodium ruthenate in 1 M sodium hydroxide at 10 °C after 1 h in 70% yield [957]. In oxidations with potassium ruthenate, only catalytic amounts can be used in the presence of a persulfate, which reoxidizes the reduced ruthenium salt [196. ... 

The unusual oxidant nickel peroxide converts aromatic aldehydes into carboxylic acids at 30-60 °C after 1.5-3 h in 58-100% yields [934. The oxidation of aldehydes to acids by pure ruthenium tetroxide results in very low yields [940. On the contrary, potassium ruthenate, prepared in situ from ruthenium trichloride and potassium persulfate in water and used in catalytic amounts, leads to a 99% yield of m-nitrobenzoic acid at room temperature after 2 h. Another oxidant, iodosobenzene in the presence of tris(triphenylphosphine)ruthenium dichloride, converts benzaldehyde into benzoic acid in 96% yield at room temperature [785]. The same reaction with a 91% yield is accomplished by treatment of benzaldehyde with osmium tetroxide as a catalyst and cumene hydroperoxide as a reoxidant [1163]. 

The tetroxides of ruthenium and osmium are solids of low m.p. (RUO4, 25°. OSO4, 41°). R11O4 volatilises when a stream of Clg is passed through an alkaline solution of a ruthenate and is conveniently prepared by oxidising potassium ruthenate with periodic acid (Martin, 1952) ... 

A particularly satisfactory ruthenium catalyst was prepared as follows. Commercial ruthenium powder was fused with a mixture of potassium hydroxide and potassium nitrate (1 part ruthenium, 10 parts potassium hydroxide, 1 part potassium nitrate) preferably in a silver crucible and stirred with a silver spatula. Pusion was complete after 1 to 2 hours. After cooling, the fused mass was dissolved in water a deep red solution of potassium ruthenate resulted, which was heated to boiling. Methyl alcohol was added dropwise to the boiling solution. The reduction of potassium ruthenate to ruthenium dioxide began with the addition of the first drops and went rapidly to completion. The precipitate settled after a few hours. It was washed on a fritted glass plate, first with water acidified with nitric acid and then with distilled water. Finally the catalyst was dried at 110°C. The reduction to metal proceeds just as smoothly under synthesis conditions as by a hydrogen treatment, which latter is usually required with catalysts of the iron group. 

A feature of both systems is the autocatalysis by SO4 and COa (derived from the reductant) radicals. A simple rate law is observed in the Ag -catalysed oxidation of aspartic acid (Rate = A a[S208 ][Ag ][Asp] ). Medium effects are important with inhibition by ions in the order Mg + > K+ > Na+ > H+ and NOs > S04 . The uncatalysed oxidations of glyoxal and glyoxylic acid have also been investigated. Potassium ruthenate (K2RUO4), which can be readily prepared from reaction of ruthenium trichloride with aqueous persulphate, can be used cata-lytically in the presence of 8208 for the oxidation of organic substrates under mild conditions. RuO " is considered to act as a two-electron oxidant. 

Primary alcohols and aldehydes can also be eflBciently oxidized to acids by catalytic amounts of potassium ruthenate (K2[Ru04]) in the presence of potassium persulphate and aqueous alkali. This method is amenable to large-scale reactions, and seems especially suitable for the preparation of unsaturated and aromatic acids. 

Potassium ruthenate, K2RUO4, can be used catalytically in the presence of persulphate to oxidize primary and secondary alcohols to the corresponding carboxylic acids and ketones. There is no significant reaction with tertiary alcohols, alkenes, or alkynes. The reaction proceeds at room temperature in high yield (>80%), and although catalyst turnover numbers have not been fully determined initial results suggest that they will be reasonable. 

Potassium Aquo-chlor-ruthenate, K2Ru(OH2)CI5, results1 on boiling a slightly acidified solution of potassium chlor-ruthenite, K2RuC15, with alcohol as also by heating the hydrated sesquioxide with hydrochloric acid and alcohol. 

Sodium ruthenate, Na2Ru04, is prepared in situ from ruthenium tetroxide (in solution in carbon tetrachloride) and 1 M sodium hydroxide by shaking for 2 h at room temperature. The reagent remains in the aqueous layer, which acquires bright-orange color [937]. It oxidizes primary alcohols to carboxylic acids and secondary alcohols to ketones and is comparable with but stronger than potassium ferrate [937]. 

---