Zirconium acid dependence

Amorphous zirconium phosphorous oxide is obtained in the form of gel by addition of a soluble Zr(VI) salt to phosphoric acid. The stoichiometric crystalline zirconium phosphate is prepared by refluxing the amorphous gel in concentrated phosphoric acid. Depending on the reflux conditions, different crystzdline forms result. 

Zirconium alkoxides readily hydrolyze to hydrous zirconia. However, when limited amounts of water are added to zirconium alkoxides, they partially hydrolyze in a variety of reactions depending on the particular alkoxide (222). Zirconium tetraisopropoxide [2171 -98-4] reacts with fatty acids to form carboxjiates (223), and with glycols to form mono- and diglycolates (224). 

The extraction of metals by liquid amines has been widely investigated and depends on the formation of anionic complexes of the metals in aqueous solution. Such applications are illustrated by the use of Amberlite LA.l for extraction of zirconium and hafnium from hydrochloric acid solutions, and the use of liquid amines for extraction of uranium from sulphuric acid solutions.42,43... 

Brindley and Sempels (1), Vaughan et al. (2) and Shabtai (3) have shown that the experimental conditions of Al intercalation influences the physicochemical properties of the clay. The nature, amount and spacial distribution of the pillars change the thermal stability, texture and acidity of the pillared clays. For example, Rausch and Bale (4) have reported that the OH/Al ratio modifies the structure of the Al complex and that monomeric [Al(0H)x(H20)6-x] " or polymeric [A1i304(0H)24(H20)i2] species can be obtained. Clearfield (5) demonstrated that the polymerisation state of Zr species depends on the temperature, concentration and pH of the solutions. In any case, the height of pillars is largely controlled by the polymerisation state of the intercalated complexes. However, in order to maintain the accessibility of the inner surface, the density or spacial distribution of the pillars has to be controlled. This parameter has been studied by Flee et al (5), and Shabtai et al (7) for Al pillared clays and Farfan-Torres et al (8) for zirconium. 

Oxidation of primary, secondary and benzylic alcohols with TBHP or CHP, mainly catalyzed by Mo and Zr derivatives, were performed by different authors. As an example, Ishii, Ogawa and coworkers reported the conversion of secondary alcohols such as 2-octanol to ketones mediated by catalyst 39 and TBHP. The oxidation of cyclic alcohols depended on steric factors. Zirconium alkoxides may act as catalysts in the conversion of different alcohol typologies with alkyl hydroperoxides . Secondary alcohols, if not severely hindered, are quantitatively converted to the corresponding ketones. The selectivity for equatorial alcohols is a general feature of the system, as confirmed by the oxidation of the sole cis isomer 103 of a mixture 103-bl04 (equation 68). Esters and acids could be the by-products in the oxidation of primary alcohols. 

The ZEALEX Process Researchers from KRI have shown that the zirconium salt of dibutyl phosphoric acid (ZS-HDBP) was soluble in Isopar-L in the presence of 30% TBP. This super PUREX solvent, known as ZEALEX, extracts actinides (Np-Am) together with lanthanides and other fission products, such as Ba, Cs, Fe, Mo, and Sr from nitric acid solutions. The extraction yields depend on both the molar ratio between Zr and HDBP in the 30% TBP/Isopar-L mixture and the concentration of HN03 (232). Trivalent transplutonium and lanthanide elements can be stripped together from the loaded ZEALEX solvent by a complexing solution, mixing ammonium carbonate, (NH4)2C03, and ethylenediamine-N.N.N. N -tetraacetic acid (EDTA). An optimized version of the process should allow the separation of... 

The condensation rate depends on the structure of the zirconocene, the temperature, the Al Zr ratio, and the concentration. Methane production is much faster with MAO than with the weaker Lewis acid trimethylalu-minum. More than 2 mol of methane is eliminated per mole of zirconium in 15 min when high Al Zr ratios are applied (Fig. 9). This is complicated by... 

P-Hydroxy esters. 4 The lithium enolate of ethyl-N-methoxyacetimidate (2) reacts with (S)-( — )-l to provide (R)-(4-methylphenylsulfinyl)-ethyI-N-methoxyacetimidate (3). The enolate of 3 reacts with an aldehyde to give the adducts 4, which are converted by desulfuration and hydrolysis into P-hydroxy acids (5). The stereochemical outcome depends on the experimental conditions. The reaction of the lithium enolate of 3 with benzaldehyde under thermodynamic control gives (S)-5 in 75% ee. Use of the zinc enolate also gives (S)-5, in 86% ee, but use of zirconium enolate, obtained by addition of Cp2ZrCl2 to the lithium enolate, results in (R)-5 in 88% ee. 

All salts of zirconium and hafnium tend to hydrolyze in aqueous solutions, though less so than those of titanium. In highly dilute solutions (<10 " M), Zr and Hf exist as the aqueous ions [M(OH) ] " " +, where n is pH-dependent. The hydration energies are 7001 and 7169kJ moU for Zr and Hf respectively. In chloride, perchlorate, and nitrate solutions, hafnium is less hydrolyzed than zirconium, while the reverse is true in sulfate solutions. This is connected with the lower solubility of hafnium compounds in sulfate solutions, even in only slightly acid media. It should be noted that the sulfate anion has a strong affinity for Zr and Hf... 

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