Active metals reduction

In addition to Ta205, another oxide is known, Ta02, which may be formed by active-metal reduction las is the tetrachloride), except that the pentoxide is heated with magnesium rather than aluminum. It forms with alkali metals the metatantalates. MTa03, the orthotantalates. MjTaO and pyrotantalates, M4T 207, as well as such polytantalates as MgTaeOju. the latter requiring fusion with the alkali hydroxides,... 

Active metal reduction of organic compounds in HjO, e.g., alkyl halides with Zn , occurs ... 

Active metal reductions, e.g., that of an amide, occur ... 

Active metal reduction (Zn, Mg or Zn amalgam) of trialkyl- and triarylger-manium halides or (MejGeS)2 in aq acid yields the respective germanes, e.g. ... 

Most of the metals and metalloids have been isolated from their halides by reaction with sodium. In fact, sodium reduction of metal halides can be considered almost a universal method for preparing metals or metalloids in an elemental state. In many cases, imfavorable economics prevents commercialization of processes involving reduction of a metal halide with an active metal, when compared with processes that involve electrolysis, carbon reduction, or hydrogen reduction, and active metal reduction must be relegated to the role of a laboratory procedure. 

Ultrasound can give useful improvements in the yield, reaction time, and convenience of organometallic reactions, and these facets of the technique are demonstrated well in its application to the Reformatsky reaction. Yields are improved by up to almost 100 % over the conventional method, and are nerally superior even to those of the trimethyl borate method. Reaction times are reduced by a factor of 5-10, and the need to prepare zinc powder by the active-metal reduction of anhydrous zinc chloride is eliminated. This technique has also been applied to the zinc-mediated dimerization of a,a -dibromo -xylene, although only low yields are obtained, and to the Pd-catalysed zinc coupling of allyl or aryl halides with perfluoroalkyl iodides. ... 

Qualitative Analysis. Nitric acid may be detected by the classical brown-ring test, the copper-turnings test, the reduction of nitrate to ammonia by active metal or alloy, or the nitrogen precipitation test. Nitrous acid or nitrites interfere with most of these tests, but such interference may be eliminated by acidifying with sulfuric acid, adding ammonium sulfate crystals, and evaporating to alow volume. 

Solvent plays a key role in the course of reductions by active metals Changing the solvent of the reaction of hexafluoroacetone with magnesium from tetrahydro turan to dimethylformamide induces bimolecular reduction to the pinacol [5] (equation 2)... 

Reductive cleavages of carbon-chlorine bonds by active metals and with photochemical activation figure in recent studies aimed at HFCs and HCFCs Sodium amalgam [3J] (equation 25), zinc powder [34] (equation 26), and alumi-mun/tin chloride [35] (equation 26) are all used in conjunction with protic solvents in reactions giving high yields and conversions... 

Calcium metal is the usual reducing agent used in stripping plutonium and americium from these residue salts. Other active metals, such as sodium metal, show good potential for use as a reducing agent. In the case of sodium metal, the reduction byproduct would be NaCl per the following reaction. 

Since the catalytically active phase is frequently quite expensive (e.g. noble metals) it is clear that it is in principle advantageous to prepare catalysts with high, approaching 100%, catalyst dispersion Dc. This can be usually accomplished without much difficulty by impregnating the porous carrier with an aqueous solution of a soluble compound (acid or salt) of the active metal followed by drying, calcination and reduction.1... 

Diols (pinacols) can be synthesized by reduction of aldehydes and ketones with active metals such as sodium, magnesium, or aluminum. Aromatic ketones give better yields than aliphatic ones. The use of a Mg—Mgl2 mixture has been called the Gomberg-Bachmann pinacol synthesis. As with a number of other reactions involving sodium, there is a direct electron transfer here, converting the ketone or aldehyde to a ketyl, which dimerizes. 

The performance of a supported metal or metal sulfide catalyst depends on the details of its preparation and pretreatraent. For petroleum refining applications, these catalysts are activated by reduction and/or sulfidation of an oxide precursor. The amount of the catalytic component converted to the active ase cind the dispersion of the active component are important factors in determining the catalytic performance of these materials. This investigation examines the process of reduction and sulfidation on unsupported 00 04 and silica-supported CO3O4 catalysts with different C03O4 dispersions. The C03O4 particle sizes were determined with electron microscopy. X-ray diffraction (XRD), emd... 

FIGURE 22.2 Schematic polarization curves for spontaneous dissolution (a) of active metals (h) of passivated metals. (1,2) Anodic curves for active metals (3) cathodic curve for hydrogen evolution (4) cathodic curve for air-oxygen reduction (5) anodic curve of the passivated metal. 

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