Perrhenic acid, concentrated solution

The preparation is the same as for ReOCl3 2P(C6H6)3 except that the perrhenic acid solution is made up by using 10.0 ml. of concentrated hydrobromic acid instead of the hydrochloric acid. The yield is 13.4 g. (86%) of diamagnetic yellow microcrystals, m.p. 181 to 183° with decomposition (checkers report 180°) of similar solubilities to those of the chloride. Anal. Calcd. for ReOBr3-2P(C6H6)3 Br, 24.8 Re, 19.3. Found (by checkers) Br, 24.1 Re, 17.4. 

Rhenium metal powder is oxidized quantitatively to perrhenic acid by dissolution in 6 M nitric acid followed by repeated evaporation with concentrated nitric acid nearly to dryness. On dilution with 25 ml. of water, neutralization with 6 M sodium hydroxide, and the addition of slightly more than the stoichiometric amount of silver nitrate dissolved in as little water as possible, silver perrhe-nate precipitates in the form of colorless crystals. These additions are made in a beaker protected from light. The solution is decanted from the product, which is dried in an oven at 110° for 8 hours. 

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... 

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. 

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... 

The octachlorodirhenate(III) anion, [Reads]2- has been prepared in several ways, including (a) reduction of perrhenate ion in acid solution with molecular hydrogen at high temperature and pressure 1 (b) reduction of perrhenate ion with hypophos-phorus acid, in a solution of constant boiling hydrochloric acid 1,2 (c) displacement of the carboxylate ligands in Re2-(OOCR)4Cl2 with chloride ion in concentrated hydrochloric acid 1,2 (d) reaction of trirhenium nonachloride in molten diethylammonium chloride.3... 

MTO hydrolyzes rapidly in basic aqueous solutions and much more slowly in acidic media. At low concentrations (crMT0 < 0.008 M) the formation of methane gas and perrhenate is detected. The decomposition of MTO seems to be irreversible. At higher concentrations a second reaction, a faster reversible polymerization -precipitation, takes place to yield a golden-colored solid of the empirical composition H05[(CH3)092Re03] (poly-MTO) in about 70% yield (Eq. 1) [10-15]. 

Workup of various solutions To avoid unnecessary contamination of the air with Re, the solution is neutralized and concentrated (if necessary, by boiling). It is then cooled and acidified with hydrochloric acid and the Re precipitated under pressure as RegS . The Re 387 is washed and dissolved in KOH + H sOa and the I e04 is allowed to crystallize out. If the KRe04 Is still not sufficiently pure, it is reduced with Hg and oxidized with Og to RegOy, and the latter is used to obtain Re or the perrhenate. 

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