Oxidation zirconium compounds

The abihty of magnesium metal to reduce oxides of other metals can be exploited to produce metals such as zirconium, titanium [7440-32-6] and uranium [7440-61-1] (see ZiRCONiUMAND ZIRCONIUM COMPOUNDS Titaniumand titanium alloys Uraniumand uranium compounds). These reactions are... 

Chlorination. In some instances, the extraction of a pure metal is more easily achieved from the chloride than from the oxide. Oxide ores and concentrates react at high temperature with chlorine gas to produce volatile chlorides of the metal. This reaction can be used for common nonferrous metals, but it is particularly useful for refractory metals like titanium (see Titanium and titanium alloys) and 2irconium (see Zirconium and zirconium compounds), and for reactive metals like aluminum. 

Zirconium [7440-67-7] is classified ia subgroup IVB of the periodic table with its sister metallic elements titanium and hafnium. Zirconium forms a very stable oxide. The principal valence state of zirconium is +4, its only stable valence in aqueous solutions. The naturally occurring isotopes are given in Table 1. Zirconium compounds commonly exhibit coordinations of 6, 7, and 8. The aqueous chemistry of zirconium is characterized by the high degree of hydrolysis, the formation of polymeric species, and the multitude of complex ions that can be formed. 

Zirconium forms anhydrous compounds in which its valence may be 1, 2, 3, or 4, but the chemistry of zirconium is characterized by the difficulty of reduction to oxidation states less than four. In aqueous systems, zirconium is always quadrivalent. It has high coordination numbers, and exhibits hydrolysis which is slow to come to equiUbrium, and as a consequence zirconium compounds in aqueous systems are polymerized. 

Zhconium and Zirconium Compounds, 139 ZNO KADOX 720 , zinc oxide, 140... 

Zirkonium-Btahl, m. zirconium steel. ver bindung, /, zirconium compound, Zirkon-lampe, /. zirconium lamp, -licht, n. zircon hght, -oxyd, n. zirconium oxide, prUparat, n. zirconium preparation, -saure, /. zirconic acid, stahl, m, zirconium steel. Zirkulonte,/. (Math.) circulant. 

The oxidation-resistant SiC fiber was prepared from polycarbosilane containing Zr(OC4H9)4 by the same process as that used for the aforementioned tita-nia/silica fiber, except that the calcination was performed in Ar atmosphere at 1400 °C. In this case, the polycarbosilane and Zr(OC4H9)4 were effectively converted into SiC-based bulk ceramic and zirconium oxide (cubic zirconia). Before the conversion, bleed-out of the zirconium compound proceeded effectively. AES depth analysis of the fiber surface showed an increase in the concentration of zirconium towards the surface. This construction was confirmed by the TEM image of the cross-section near the fiber surface. This indicates the direct production of a SiC-based fiber covered with a Zr02 surface layer, which... 

Figure 4.7 SIMS ZrOW and ZrO.W intensity ratios as a function of calcination temperature for the same catalyst as in Fig. 4.6, along with ratios measured from zirconium ethoxide and oxide reference compounds (data from Meijers et al. [151).

Interpretation of the spectra in Fig. 4.6 is best done by comparison with those of zirconium ethoxide and zirconium oxide reference compounds. Figure 4.7 contains the ZrO+/Zr+ and ZrO/Zr+ ratios from the SIMS spectra of the reference compounds, and of the catalysts as a function of the calcination temperature. The figure clearly shows that catalysts calcined at temperatures up to 200 °C have ZrO+/Zr+ and Zr02+ /Zr+ ratios about equal to those measured from a zirconium ethoxide reference compound. However, samples calcined above 300 °C have intensity ratios close to that of Zr02. 

The chemistry of zirconium has some similarities to that of silicon and titanium, since it is in Group IV of the periodic table. Zirconium has a normal oxidation state of 4 with limited redox chemistry and a coordination number of up to 8. Zirconium compounds are normally colourless. 

A number of zirconium compounds are able to catalyze Oppenauer oxidations. For example, zirconium dioxide, when properly conditioned, is able to promote the oxidation of alcohols in variable yields40 and it is reportedly superior than AI2O3. Other zirconium compounds able to induce Oppenauer oxidations in catalytic amounts include Cp2ZrH2,41 Cp2Zr(Oi-Pr)2,41b Zr(Oi-Bu)442 and Zr(0 -Pr)x on Si0242... 

Syntheses of MPc from phthalodinitrile or phthalic anhydride in the presence of urea are the two most important laboratory and industrial methods. They were also used originally by Linstead et al. [8,9], This procedure allows the production of many phthalocyanine compounds [35-37], Catalysts such as boric acid, molybdenum oxide, zirconium and titanium tetrachloride, or ammonium molybdate are used to accelerate the reaction and improve the yield [36,37], Ammonium molybdate is especially effective. Reaction is carried out either in a solvent or by heating the solid components. When metal chlorides and phthalodinitrile are used as starting materials, the reaction products are partially chlorinated (e.g.,7). 

SAFETY PROFILE Flammable when exposed to heat or flame can react vigorously with oxidizing materials. When heated to decomposition it emits toxic fumes of NOx. See also ZIRCONIUM COMPOUNDS and PICRAMIC ACID. 

Why is the prohibition against secondary alkylzirconium relaxed for phenyl substituents Buchwald et al. suggest that the flat phenyl group is less sterically demanding than an alkyl, while others have proposed an electronic effect favoring nzylic zirconium compounds. Evidence supports the latter for internal aromatic alkenes hydrozirconation initially gives mostly the benzylic isomer (25) (based on the alcohol products of oxidation), which slowly (48-96 h at 40 C) converts to the terminal isomer (26 equation 30). ... 

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