Extraction perrhenate

Arsonium salts have found considerable use in analytical chemistry. One such use involves the extraction of a metal complex in aqueous solution with tetraphenyiarsonium chloride in an organic solvent. Titanium(IV) thiocyanate [35787-79-2] (157) and copper(II) thiocyanate [15192-76-4] (158) in hydrochloric acid solution have been extracted using tetraphenyiarsonium chloride in chloroform solution in this manner, and the Ti(IV) and Cu(II) thiocyanates deterrnined spectrophotometricaHy. Cobalt, palladium, tungsten, niobium, and molybdenum have been deterrnined in a similar manner. In addition to their use for the deterrnination of metals, anions such as perchlorate and perrhenate have been deterrnined as arsonium salts. Tetraphenyiarsonium permanganate is the only known insoluble salt of this anion. 

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... 

Koide et al. [537] have described a graphite furnace atomic absorption method for the determination of rhenium at picomolar levels in seawater and parts-per-billion levels in marine sediments, based upon the isolation of heptavalent rhenium species upon anion exchange resins. All steps are followed with 186-rhenium as a yield tracer. A crucial part of the procedure is the separation of rhenium from molybdenum, which significantly interferes with the graphite furnace detection when the Mo Re ratio is 2 or greater. The separation is accomplished through an extraction of tetraphenylarsonium perrhenate into chloroform, in which the molybdenum remains in the aqueous phase. 

These include the simplest ion-association systems in which bulky cations and anions are extracted as pairs or aggregates without further coordination by solvent molecules. An example of this type of system is the extraction of manganese or rhenium as permanganate or perrhenate into chloroform by association with the tetraphenylarsonium cation derived from a halide salt... 

Since the extraction behavior of pertechnetate is nearly equal to that of perrhenate, the separation of both elements is difficult and often involves reduction of Tc (VII) to lower oxidation states. 

Salaria et al. suggest the separation of technetium and rheniiun as cupfer-ronates of pertechnetate and perrhenate which have different solubilities in chloroform. Pertechnetate can partially be extracted from 4 M H SO by shaking the solution with chloroform, which is pre-equilibrated with a solution of 1 % cupfer-ron in 4 M H SO. The main part of perrhenate remains unextracted. 

An efficient method has been developed by Pozdnyakov and Spivakov . In alkaline solution pertechnetate, in contrast to perrhenate, is reduced by hydrazine sulfate. After reduction technetiiun is no more extracted by methyl ethyl ketone. The distribution coefficient of technetium is by a factor up to 2500 smaller than that of rhenium. 

Procedure Hydrazin sulfate is added to a mixture of pertechnetate and perrhenate in 3-6 N NaON or KOH until its concentration is about 3 x 10 M. The solution is stirred and, after 10 min, rhenium is extracted by an equal voliune of methyl ethyl ketone. For complete separation of rhenium from technetium the extraction must be repeated 2-3 times. After a twofold extraction 99% of technetium and only 0.8 % of rhenium remain in the aqueous phase. 

Beer, P D., Hopkins, P K., McKinney, J. D., Cooperative halide, perrhenate anion-sodium cation binding and pertechnetate extraction and transport by a novel tripodal tris(amido benzo-15-crown-5) ligand. Chem. Commun. 1999, 1253-1254. 

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... 

Short-lived technetium Isotopes, produced as a daughter product of molybdenum radioisotopes or as fission products of U255 were extracted as the tetraphenylarsonlum salt In chloroform together with perrhenate carrier (91,262). 

The tren-based heteroditopic receptor 22, featuring a tripodal tetrahedral amide hydrogen-bond anion-recognition site in combination with benzo-15-crown-5 ether cation-binding moieties, has been found to cooperatively bind chloride, iodide, and perrhenate anions via co-bound crown ether-complexed sodium cations. It also can efficiently extract the radioactive sodium pertechnetate from simulated aqueous nuclear waste streams. The anion-binding affinity of 22 is considerably reduced in the absence of a co-bound cation <1999CC1253>... 

In their protonated form polyamines are often attractive receptors for a variety of anions, as exemplified by many examples now known in nature, industry and model systems [34, 36]. The characteristic extraction properties of a range of such ligands toward halide, pertechnetate and perrhenate ions are strongly influenced by the ligand s protonation behavior and lipophilicity. Extraction therefore shows a pH-dependence, as well as being influenced by all manner of structural factors [35, 37, 38]. Some results for the perrhenate extraction by three different substituted tripodal tetraamines 7a-c and two structure-related octaamino cryptands 7d,e (Fig. 4.11) are shown in Fig. 4.12 [35, 37]. 

N aqueous solution of HCl, H2SO4 or H( I04, from which more than 99 % of technetium could be extracted into carbon tetrachloride at 20 C. The concentration of potassium xanthate was 0.1 M. Perrhenate remained entirely in the aqueous phase, thus separation from technetium could be readily achieved. Instead of carbon tetrachloride. other extractants like chloroform. 1,1,1-trichlorocthane, xylene or isopropyl ether are also suitable [153[. 

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