Rhodium sulphate

Titanium sulphate Srconiuin sulphate Rhodium sulphate... 

Rhodium Sulphate, Rh3(S04)3, may be prepared by dissolving the sesquioxide in sulphuric acid, and evaporating the solution to a syrupy consistence over a flame, finally expelling the excess of sulphuric acid at a temperature not exceeding 440° C. Obtained in this way, rhodium sulphate is a brick-red powder, which is not hygroscopic. It is not very soluble in water, by excess of which it is decomposed. When heated to 500° C. it begins to decompose.1... 

Basic Rhodium Sulphate.—When the neutral rhodium sulphate is boiled with excess of water until the wash waters are not appreciably coloured, and cease to be acid towards indicators, a citron-yellow powder is obtained, insoluble in water. This is a basic sulphate, for which the formula Rh203.RhE(S04)3 is given by Leidie.1... 

Sodium Rhodium Sulphate, NasS04.Rh2(S04)3, was first prepared by Bunsen3 by heating sodium rhodium sulphite with concentrated sulphuric acid. Tliis salt was regarded by Seubert and Kobbe 4 as an anhydrous rhodium alum. Since then, however, true rhodium alums have been obtained. 

Rhodium sulphate, like its analogues the sulphates of cobalt and iridium, yields stable salts with sulphates of the alkali metals known as alums. These are well-defined crystalline salts, isomorphous with the better known iron and aluminium alums. They thus form an interesting link between these metals and the central vertical column in Group VIII, of which rhodium is the middle member. These alums... 

In addition to the rhodium sulphate the water will have extracted a small quantity of platinum in the form of sulphate. 

The absorption maximum of the Rh complex with SnCb" is at 470 nm. The molar absorptivity, s = 4.2-10 (a = 0.041). If rhodium is present in solution as the sulphate complex, the solution should be heated for some time after the addition of HCl to allow the rhodium sulphate complex to be converted into the chloride complex. The other platinum metals interfere in the determination. 

Z 1 Niobium 1 Nitrate 1 Osmium 73 a. I Perchlorate Phenols u a o Platinum o 0. 1 5 u 1 Rhodium 1 Rubidium Ruthenium Scandium 1 Selenium Silver I Sodium 1 Strontium 1 Sulphate Sulphides, organic Sulphur dioxide 1 Tantalum 1 Tellurium 1 Thallium Thorium e H 1 Titanium a u ab a 1- I Uranium 1 Vanadium 1 Yttrium 1 Zinc Zirconium... 

The metal-catalysed autoxidation of alkenes to produce ketones (Wacker reaction) is promoted by the presence of quaternary ammonium salts [14]. For example, using copper(II) chloride and palladium(II) chloride in benzene in the presence of cetyltrimethylammonium bromide, 1-decene is converted into 2-decanone (73%), 1,7-octadiene into 2,7-octadione (77%) and vinylcyclohexane into cyclo-hexylethanone (22%). Benzyltriethylammonium chloride and tetra-n-butylammo-nium hydrogen sulphate are ineffective catalysts. It has been suggested that the process is not micellar, although the catalysts have the characteristics of those which produce micelles. The Wacker reaction is also catalysed by rhodium and ruthenium salts in the presence of a quaternary ammonium salt. Generally, however, the yields are lower than those obtained using the palladium catalyst and, frequently, several oxidation products are obtained from each reaction [15]. 

The acid sulphate, [Rh(NH3)5N02]S04.TI2S04, crystallises in long white needles. These decompose on heating, leaving a residue of rhodium. The nitrito-salts, like all the rhodium salts, resemble those of cobalt and chromium, but are more stable, the nitrate being particularly stable. This fact Jorgensen attributes partly to the nature of the central atom.1... 

Platinum in a finely divided form is obtained by the in situ reduction of hydrated platinum dioxide (Adams catalyst) finely divided platinum may also be used supported on an inert carrier such as decolourising carbon. Finely divided palladium prepared by reduction of the chloride is usually referred to as palladium black. More active catalysts are obtained however when the palladium is deposited on decolourising carbon, barium or calcium carbonate, or barium sulphate. Finely divided ruthenium and rhodium, usually supported on decolourising carbon or alumina, may with advantage be used in place of platinum or palladium for some hydrogenation reactions. 

Cobalt, rhodium, and iridium yield sulphates of the type R2(S04)a, and these combine with sulphates of the alkali metals to produce alums, of the general formula MaS01.R2(S01)3.24H80. These are well-defined... 

Fusion with potassium hydrogen sulphate is without effect upon ruthenium, although in like circumstances rhodium, palladium, and iridium are attacked. 

Rhodium is insoluble in acids, even in aqua regia, although when its alloys are attacked by this latter mixture a portion of the rhodium passes into solution. When fused -with potassium hydrogen sulphate, rhodium dissolves, yielding the sulphate. This reaction is interesting as affording a convenient method of separating the metal from iridium and platinum (see p. 34-1). 

Colloidal rhodium may also be prepared by reduction of pure rhodium salts with hydrazine hydrate. Traces of impurity prevent the formation of the hydrosol, which is very unstable. Addition of a protective colloid, such as a 1 per cent, solution of gum acacia, renders the hvdrosol stable, so much so that it admits of concentration over sulphuric acid in vacuo, yielding a dark brown solid mass of colloidal metal, containing 99-4 per cent, of rhodium, and almost completely soluble in water.5 Shaking the colloidal solution with barium sulphate or animal charcoal serves to coagulate the metal. 

This alum is of interest inasmuch as its formation renders it easy to separate rhodium from iridium. The sulphates of the metals, dissolved in acidulated water, are treated with caesium sulphate and evaporated. The rhodium alum crystallises out in a pure state, entirely free from iridium.1... 

Thallium Rhodium Alum, Tl2S04.Rh3(S04)3.24H20, is somewhat difficult to prepare, partly on account of the small solubility of thallous sulphate. The alum is very soluble in water, and not altogether permanent in air, becoming converted into a whitish powder on prolonged exposure.1... 

Palladium, like rhodium, but unlike platinum, dissolves in fused potassium hydrogen sulphate, yielding palladous sulphate. Fusion with sodium peroxide converts it into palladium monoxide. Heated with sulphur combination takes place with incandescence. 

This is fused with potassium hydrogen sulphate at a high temperature, which treatment removes practically all the rhodium, any remaining traces being taken out with the iron at a later stage. 

Metallic iridium is thus obtained together with oxide of iron. The whole is heated to redness with potassium hydrogen sulphate, which removes the iron and any remaining traces of rhodium. The residue is well washed with water, then with chlorine water to remove any traces of gold, and finally with hydrochloric acid to take out any silica which may have accidentally been introduced with the alkalies or have come from the vessels employed. The resulting iridium is calcined with charcoal and melted into an ingot. 

Digestion with dilute aqua regia effects the solution of the platinum and lead, leaving a residue of impure iridium. The solution is filtered, evaporated, and the lead converted into sulphate by addition of sulphuric acid in requisite quantity. The platinic chloride is extracted with water, and ammonium chlor-platinate precipitated in the usual way with excess of ammonium chloride containing sodium chloride. The whole is heated to 80° C. and allowed to stand for several days, most of the rhodium remaining in solution and imparting to the liquid a rose-coloured hue. 

The precipitated ammonium chlor-platinate is repeatedly washed with a saturated solution of ammonium chloride, and subsequently with dilute hydrochloric acid. It still contains small quantities of rhodium, however, as ammonium chlor-rhodate. The salt is mixed with potassium hydrogen sulphate to which a small quantity of ammonium... 

Upon evaporating the solution to dryness and heating to redness the platinum sulphate is reduced to the metallic condition, the rhodium salt being unaffected. Digestion with water leaves a residue of pure platinum which may be added to the previous residue. 

Fused potassium hydrogen sulphate, which readily attacks rhodium, palladium and iridium, is without action upon ruthenium. 

Detection.—Metallic Iridium, like rhodium, is insoluble in all acids, save that in a very finely divided condition it is slowly attacked by aqua regia. Fusion with potassium hydrogen sulphate oxidises the metal but does not effect its solution (contrast ruthenium and rhodium). When fused with a mixture of potassium nitrate and hydroxide an insoluble residue containing the sesquioxide, lr203, with alkali is obtained. 

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