Tellurium, elemental metal halides

Higher-valent metal halides oxidize diaryl tellurium compounds to diaryl tellurium dihalides. Copper(II) halides can be generated in the reaction mixture from easily accessible copper(II) acetate and hydrohalic acids4. These halogenation reactions are convenient alternatives to the methods using corrosive elemental halogens or sulfuryl halides. 

Class I. ELEMENTS. A. Metals. Cubic copper, silver, gold, iron, platinum, iridium. - Tetragonal tin. - Rhombohedral and Hexagonal arsenic, antimony, bismuth, tellurium, (Os, Ir). - B. Metalloids. Cubic diamond. - Hexagonal graphite. - Orthorhombic sulfur, iodine. - Monoclinic sulfur, selenium. - Class II. SULFIDES. - Class HI. HALIDES. -Class IV. OXIDES, divided into SIMPLE OXIDES and COMPLEX OXIDES, such as CARBONATES, PHOSPHATES, SILICATES, BORATES and SULFATES. 

Precipitation of Ag as chloride, or better as bromide, with a slight excess of precipitant may be a useful method of separation. Traces of Ag have been separated by thallium iodide as the collector. The precipitation can be dissolved in diluted H2SO4-H2O2 solution. A widely applicable method for the isolation of traces of Ag consists in co-precipitation with elemental tellurium formed by adding tin(II) chloride to 2 mol 1 HCl solution of the sample containing Te(IV) (see above). The extraction constant of primary Ag dithizonate is such that Ag can be extracted quantitatively from 6 mol 1 H solution by the use of 0.001%(w/v) dithizone solution in carbon tetrachloride. Anions such as halides and thiocyanates that form slightly soluble or complex Ag salts must be absent when extraction is made in mineral acid medium. Other metals extracted at high acidity are Pd, Au, and Hg. Copper will also be extracted. 

The following metal compounds are used for the preparation of the catalysts oxides, metal carbonyls, halides, alkyl and allyl complexes, as well as molybdenum, tungsten, and rhenium sulfides. Oxides of iridium, osmium, ruthenium, rhodium, niobium, tantalum, lanthanum, tellurium, and tin are effective promoters, although their catalytic activity is considerably lower. Oxides of aluminum, silicon, titanium, manganese, zirconium as well as silicates and phosphates of these elements are utilized as supports. Also, mixtures of oxides are used. The best supports are those of alumina oxide and silica. 

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