Rhenium, determination metallic

SS). Data for the metals of group VIII and for rhenium in group VIIA are given in Fig. 1, which is divided into three fields separating the metals of the first, second, and third transition series. The specific activity is defined as the activity per unit surface area of metal. Metal surface areas required for the determination of specific activities are derived from measurements... 

Structure determinations of secondary metal alkyl complexes are relatively rare, yet they provide an opportunity to assess interactions of the metal with the /3-atoms of the alkyl. The angles (excluding hydrogen) about C(24) all exceed 109°, ranging from 111.7° to 115.1°. There is no evidence for any Re 0 interaction (compare V), this distance exceeding 3 A. Both the /3-carbon, C(25), and its attached hydrogens are over 3 A from rhenium. The hydrogen on the a-carbon, C(24J, is 2.76 A from rhenium. 

Pertechnetate forms a blue complex and perrhenate a brownish-yellow complex with K4[Fe(CN) ] in presence of bismuth amalgam. This permits the spectrophotometric determination of both elements in the same solution . The adsorption maxima of the technetium and rhenium complexes are at 680 and 420 nm, respectively. The molar extinction coefficients are 10,800 for technetium and 4,000 for rhenium. Metals forming color or precipitates with K4[Fe(CN) ] must first be removed. 

Triazoles have been used extensively in analytical chemistry. Nitron (182) has been used for the determination of boron, rhenium, and tungsten. Nitron has been bonded to a polymer and used for the removal of nitrate from water <79Mi 402-oi >. Other triazoles have been used for the spectrophoto-metric assay of cobalt, rhodium, and platinum <68Mi 402-01,72ZAK2209). Hydroxyphenylazotriazoles form brilliant lakes with a number of metal ions <73AJC1585>. 5-" C-3-Diazotriazole couples only to tryptophane below pH 6.8 and can used for the specific determination of tryptophane in proteins <84M1 402-02). 

Rate-determining step, hydroformylation, 163 Reactivity, enantiomers, 286 Recognition, enantiomers, 278 Reduction and oxidation, 5 Reductive coupling, dissolving metal, 288 Reductive elimination, 5, 111 Resolution. See Kinetic resolution Rhenium-carbene complexes, 288 Rhodium-catalyzed hydrogenation, 17, 352 amino acid synthesis, 18, 352 BINAP, 20... 

The crystal structure of cadmium rhenium(V) oxide, as determined by single-crystal technique,1 is of the face-centered cubic pyrochlore type (a = 10.219 A.). The only positional parameter for the 48 (/) oxygens is x = 0.309 0.007 when rhenium is at the origin. The density, determined pycnometrically, is 8.82 0.03 g./cc., compared with the theoretical value of 8.83 g./cc. for Z = 8. The resistivity between 4.2 K and room temperature is very low (10-3-10-4 J2-cm.) and has a positive temperature coefficient. Over the same temperature range the magnetic susceptibility is low and temperature-independent. These properties indicate that cadmium rhenium(V) oxide exhibits metallic conductivity. 

If benzene is the main product desired, a narrow light naphtha fraction boiling over the range 70 to 104°C is fed to the reformer, which contains a noble metal catalyst consisting of, for example, platinum-rhenium on a high-surface-area alumina support. The reformer operating conditions and type of feedstock determine the amount of benzene that can be produced. The benzene product is most often recovered from the reformate by solvent extraction techniques. 

Phillips and Timms [599] described a less general method. They converted germanium and silicon in alloys into hydrides and further into chlorides by contact with gold trichloride. They performed GC on a column packed with 13% of silicone 702 on Celite with the use of a gas-density balance for detection. Juvet and Fischer [600] developed a special reactor coupled directly to the chromatographic column, in which they fluorinated metals in alloys, carbides, oxides, sulphides and salts. In these samples, they determined quantitatively uranium, sulphur, selenium, technetium, tungsten, molybdenum, rhenium, silicon, boron, osmium, vanadium, iridium and platinum as fluorides. They performed the analysis on a PTFE column packed with 15% of Kel-F oil No. 10 on Chromosorb T. Prior to analysis the column was conditioned with fluorine and chlorine trifluoride in order to remove moisture and reactive organic compounds. The thermal conductivity detector was equipped with nickel-coated filaments resistant to corrosion with metal fluorides. Fig. 5.34 illustrates the analysis of tungsten, rhenium and osmium fluorides by this method. 

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