Potassium perrhenate

Potassium perrhenate reacts similarly to KMn04 to give Re03F. Similarly, the mild fluorinating... 

An unusual reaction is used to form a KRe 4 HjO. The reduction of potassium perrhenate in en-H20 solutions by potassium metal yields a white solid containing the Rh ion mixed with KOH. Extraction with isopropyl alcohol gives a colloidal brown liquid containing a mixture of KOH, isopropyl alcohol and the rhenidc. Fractional extraction of the liquid gives a gray solid that contains 5.5-60% KRe 4 HjO... 

Potassium perrhenate (KRe04) is reduced by hydrogen in two stages. The first operation is carried out at 500 to 550 °C. The reduced product is washed to remove the hydroxide. The powder is then subjected to a second reduction at a higher temperature (900 to 1000 °C). The product is washed, first with dilute hydrochloric acid and then with water, and dried in vacuum or in a current of hydrogen. Solid rhenium is made by powder metallurgy techniques. 

Potassium hexafluororhenate (IV), K2ReF6, is, obtained from potassium perrhenate via K2Re(I)6 and subsequent fusion with KHF2 (45), and shows a magnetic moment of 3.3—3.4 B.M. at 298 °K (31, 46). The electronic spectrum in aqueous solution has been studies in some detail by Jergensen and Schwochau (29), and the principle features of their results are listed in Table 11. (See also Fig. 6). 

Potassium perrhenate [10466-65-6] M 289.3. Crystd from water (7ml/g), then fused in a platinum crucible in air at 750°. 

Muller 90) discusses the factor-group analysis of potassium perrhenate KRe04, using previously-published infra-red and Raman spectra. The space group is C%h, where site symmetry of the Re04 ion is S4 there are only two formula units per spectroscopic unit cell, and all eight infra-red active modes are found. 

Two methods are in common use for the production of metallic rhenium. The first of these involves a direct reduction of commercial potassium perrhenate (procedure A) and yields a product that usually contains a small amount of alkali but is pure enough for most preparative purposes. The second method (procedure B) is slightly more complicated in that a preliminary precipitation of rhenium heptasulfide is followed by conversion to ammonium perrhenate which is subsequently reduced to the metal.1,2 Metallic rhenium so produced is usually purer than that prepared by direct reduction of the potassium salt. 

The temperature at which the reduction is carried out must be approached slowly in order to prevent an agglomeration of potassium perrhenate, KReCq. 

Potassium chlororhenite has been prepared by reducing potassium perrhenate with potassium iodide in hydrochloric acid solution.1-4 The identity of the product has been questioned, and various formulae have been assigned to the compound. The difficulties encountered in obtaining a pure product were probably due to the inclusion of a double chloride of potassium and pentavalent rhenium. It is known that the primary reduction involves formation of pentavalent rhenium. 

Eight grams of commercial potassium perrhenate is finely pulverized and intimately mixed with 16 g. of powdered potassium iodide. This mixture is placed in a small casserole, covered with a glass, and treated with 50 ml. of hydrochloric acid (sp. gr. 1.2). The casserole and contents are gently warmed until the bulk of the iodine liberated condenses on the cover glass. The glass is then removed, and the solution heated for 30 minutes at a temperature just below boiling. 

Metallic rhenium, prepared by the reduction of either potassium perrhenate (see synthesis 60A) or ammonium perrhenate (see synthesis 60B), is placed in a previously ignited porcelain boat and inserted in a pyrex combustion tube of the type shown in Fig. 31. All air in the train is displaced with nitrogen that has been passed through alkaline pyrogallol A and sulfuric acid B. 

Ans. ia) Magnesium hypoiodite ib) iron(III) sulfate or ferric sulfate (c) calcium manganate id) potassium perrhenate (e) calcium mngstate if ) cobalt(II) carbonate... 

A 1-L two-necked flask, equipped with magnetic stirrer, addition funnel, and condenser surmounted by a nitrogen-flushed tee tube, is charged with 7.30 g (15 mmol) of rhenium(VII) oxide (or 8.68 g of potassium perrhenate), 50 mL of concentrated hydrochloric acid, and 250 mL of absolute ethanol. The solution is stirred and heated to boiling, and a solution of 45 g (170 mmol) of triphenylphosphine in 250 mL of hot ethanol is added. The mixture becomes green immediately, and a precipitate forms even before the addition is complete. The mixture is boiled for 30 min. It is allowed to cool to 55° and is filtered. The lime-green solid product is extracted with 100 mL... 

Unreacted perrhenate may be recovered from the reaction mixture by stirring in 5 ml. of 20 % aqueous potassium hydroxide and allowing the solution to stand overnight. A precipitate of potassium perrhenate settles out. 

Rhenium. The element rhenium, atomic number 75, was fliscovered by the Gennan chemists Walter Noddack and Ida Tacke in 1925. The principal compound of rhenium is potassium perrhenate, KReO. a colorless substance. In other compounds all oxidation numbers from -f-7 to —1 are represented examples are RCgOj, ReOg, ReClg, Re02, Re20g, Re(OH)2. 

A perrhenic acid solution is obtained from 10.0 g. (0.036 mol) of potassium perrhenate by the method of Watt and Thompson. The perrhenic acid solution is concentrated... 

Dowex 50-WX2 (but not Dowex 50-WX8) may be used in the ion-cxchangc column instead of Dowex 50-WXl, which is no longer available. The use of an ion-exchange column coated with Instatherm," fabricated by the Ace Glass Co., Inc., Vineland, N.J., has been found to facilitate the conversion of potassium perrhenate to perrhenic acid. Thereby, the column can readily be held at a temperature of 95°, at which the potassium perrhen-atc will remain in solution (solubility, about 80 g./l. at 95°). 

Potassium perrhenate is precipitated when KCl is added to a solution of HRe04, or when HRe04 is neutralised with KOH. It is colourless and less soluble (1.2 g/lOOg, 25°) than KCIO4. The sodium and ammonium salts are... 

Typical bath compositions and operating conditions for electrodeposition of Re are listed in Appendix C. An acid sulfate solution, based on potassium perrhenate, was suggested by Fink and Deren. Netherton and Holt worked with similar baths, to which they added either citric acid or ammoniacal citrate. Sligh and Brenner used more concentrated solutions of perrhenate, but still could not increase the FE significantly. Their deposits exfoliated when produced thicker than 10 pm, and oxidized rapidly upon exposure to air. Therefore, it was hypothesized that the elec-trodeposited metal was not pure, but contained oxide inclusions. 

Meyer claimed that both Ni and Co seem to stabilize the presence of ReO4 anions near the cathode. He proposed that there was a catalytic effect of Ni on the decomposition of ReOT. Sadana and Wang studied the effects of bath composition, pH, temperature, stirring, current density and pulsed current on the characteristics of Au-Re deposits, which contained 0.25-63.4 wt.% Re. The solution consisted of citric acid and potassium perrhenate. The Re-content of the deposit was found to increase markedly as a result of stirring, increase in current density, decrease in bath pH and temperature, and the use of pulsed current. In addition, the as-deposited alloys exhibited XRD patterns of supersaturated solid... 

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