Perrhenic acid

HCIO2 chlorous acid HRe04 perrhenic acid... 

Salts of perrhenic acid may be obtained in acid—base reactions, and may include the tetrahedral ReO anion or the octahedral anion ReO , eg, in Ba (ReOg)2 [13598-09-9], Ammonium perrhenate and perrhenic acid, as well as rhenium metal, are sold by the primary suppHers of this element. 

World production of rhenium in 1993 and 1994 was estimated to be 34 and 35 metric tons, respectively. The price of rhenium metal in 1995 varied in the range 825— 1600/kg. Price is based on form, purity, and quantity. The price for the most commonly used salt, NH ReO, was 550— 770/kg. Dirhenium decacarbonyl and perrhenic acid are also commercially available. 

Rh(N03)3 stock solution (10.37% Rhby wt.) - Engelhard Corp. Perrhenic Acid stock solution (52.091% Re by wt.) - Engelhard Corp. Zirconyl Nitrate, hydrate - Aldrich Chemical Co. 

An ideal derivation would be via direct fluorination of Re and hydrolysis of ReF7 to perrhenic acid, especially since A/2f (Re207) has been determined by oxygen combustion of Re. However, ReF6 is the main fluorination product under normal conditions. It seems that further work on iodine fluorination to produce enhanced yields of the hepta-fluoride, and the hydrolysis of IF7 to periodic acid, is potentially the best route for improving the AHf(F( aq)) value. 

Knapp, F. F., Jr. Lisic, E. C. Mirzadeh, S. Callahan, A. P. Tungsten-188/carrier-free rhenium-188 perrhenic acid generator system. World Pat. Appl. 219541, 1992. 

Rhenium is attacked by neither hydrochloric acid nor by cold sulfuric or hydrofluoric acid. However, oxidizing acids, such as nitric acid or hot sulfuric acid, vigorously react with the metal forming perrhenic acid, HRe04. The metal is oxidized by hydrogen peroxide in ammoniacal solution forming ammonium perrhenate, NH4Re04. 

A quantity of tetrabutylammonium hydrogen sulfate 28.7 g (Aldrich), that has been recrystallized from acetone, is added to 300 mL of warm methanol in a 500-mL beaker. To this is added a solution of aqueous perrhenic acid (28.0 g, 80 to 85%, titrated 75.7%) (Alfa) with stirring. The total volume is then reduced by boiling to 125 mL, and the solution is then cooled slowly to 0 °C yielding white needles of [CH3(CH2)3]4NRe04. The supernatant liquid is further condensed to 50 mL and the resulting needles are combined with the initial crystalline product and twice recrystallized from methanol to give 30.8 g (74% yield) of product (mp 236-237 °C). 

PERRHENIC ACID. HreC>4. Exists only in solution, commercially available as aqueous syrup. Strong very stable, monobasic acid extremely soluble in water and organic solvents. 

The rapid formation of the perrhenic acid (HRe04) and a gas chromatographic transport of the rather volatile HRe04 governed by mobile adsorption processes to relatively low deposition temperatures of less than 100 °C (deposition peak D in Figure 17). This behavior is observed if the employed quartz columns are pretreated in excess of 1000 °C with H2 and with O2/H2O or H202 as reactive component of the carrier gas. 

Salts of the perrhenate anion (including perrhenic acid) are not only the single most important group of starting materials for the synthesis of other rhenium compounds but are also of importance in catalysis and other commercial processes. Although they are formally coordination complexes of Revn and they appear quite extensively in the chemical literature (e.g. see Chemical Abstracts), much of the interest in them is outside the confines of the topic of coordination chemistry as it is commonly accepted. Accordingly, an effort has been made here to keep the coverage of their chemistry to a minimum. 

The aqueous chemistry of both elements is dominated by the M04 ions. They are the ultimate products of oxidizing other Tc and Re compounds. Solutions of the pure acids, HMO4, can be obtained by dissolving the heptoxides in water. Pure perrhenic acid has not been isolated, but dark red, hygroscopic crystals of HTc04 have been described. However, in the absence of structural data, the exact nature of this substance is uncertain. 

Nitriles can be prepared by dehydration of primary amides (reaction 8) or of aldoximes (reaction 9), catalyzed by the Re trioxo compounds [ReOsX] (X = OSiMes, OReOs, OH) in azeotropic (e.g. toluene/water or mesitylene/water) reflux. Aqueous perrhenic acid (X = OH) is the most convenient catalyst in view of the moisture sensitivity of the others. The oxophilicity of the Re(VII) oxo-complexes is believed to play a determining role in the reactions, which are proposed to involve six-membered cyclic transition states formed upon preferential (9-coordination, relative to A-coordination, of the amide or oxime. ... 

Complexes of rhenium (V) have generally been prepared by careful reduction of perrhenic acid or perrhenates or by oxidation of rhenium(IV) compounds. - These procedures involve some difficulties, as in the former case compounds of rhenium (IV) may be produced, and in the latter, complete oxidation to perrhenate may occur. 

The complexes described here, which are very easy to prepare in a pure state, are useful starting materials for the preparation of most compounds of rhenium (V) and should be considered with perrhenic acid, potassium hexahalorhe-nate(IV) salts, rhenium(III) chloride, rhenium(V) chloride, and dirhenium decacarbonyl as basic source materials in rhenium chemistry. The procedure is a modification of that originally used by Freni and Valenti, although the nature of the compounds obtained was clarified only by subsequent studies. - ... 

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