Zirconium tetra-alkoxides

Zirconium tetra-alkoxides were prepared for the first time in 1950 by the ammonia method, as earlier attempts to use the alkali alkoxide method did not give a pure product, owing to the tendency of zirconium to form stable heterobimetallic alkoxides (Chapter 3) with alkali metals. 

By contrast, the alkali alkoxide route appears to be inapplicable for the synthesis of zirconium tetra-alkoxides or niobium (tantalum) penta-aUcoxides, as these tend to form heterobimetallic alkoxides with alkali metal alkoxides (Chapter 3, Section 3.2.1.1), which volatilize out during final purification, whereas alkali titanium alkoxides, even if formed, dissociate readily to give volatile titanium alkoxides. 

Double alkoxides of zirconium with alkah metals of the type MZr2(OR) have been obtained by reaction of alkah metal alkoxides with zirconium alkoxides (220). Although these usually are monomeric derivatives, the reaction between zirconium tetra-/-butoxide [1071 -76-7] and sodium /-butoxide was found (221) to form dimeric NaZr(OC(CH2)2) ]2. 

This method is particularly useful for the synthesis of the alkoxide and phenoxide derivatives of the earlier transition elements. The method is extremely convenient in view of the high volatility of the generated dialkylamines, which are readily removed in vacuum. One major drawback is the synthetic availability of the corresponding metal dialkylamide complex. In some cases the method represents not only the most convenient but also the only synthetic route to an alkoxide derivative. Hence, zirconium tetra-t-butoxide is formed in excellent yield from Zr(NEt2)4 and Bu OH, and the Vlv and CrIV r-butoxides are also readily obtained via this pathway (equation 11).74... 

Vapor decomposition is a powder preparation technique useful in a few cases when a vapor phase precursor exists (often an organometallic compound) which can be decomposed to the desired composition . The vapor decomposition usually takes place at elevated temperatures. Single component oxide powders of high purity can be prepared by vapor decomposition of metal alkoxides for example, Zr02 is prepared by pyrolyzing zirconium tetra-t-butoxide. ... 

Such an alcoholysis reaction from a more branched alkoxide to a less branched alkoxide is sometimes facilitated even further, if the product is significantly more associated than the reactant alkoxide. For example, Mehrotra has shown that the reactions of monomeric zirconium tetra-fert-butoxide with methanol and ethanol in lower stoichiometric ratios are highly exothermic, resulting in almost instantaneous crystallization of the dimeric mixed alkoxide products ... 

Bradley et al pnrified uranium tetra-alkoxides by sublimation under reduced pressure and also tried to correlate the volatility of uranium tetra-alkoxides with those of other tetravalent metal alkoxides as shown in Table 2.6 (which includes for comparison relevant data for tetravalent titanium and zirconium derivatives). 

The following order of the thermal stability of these alkoxides may thus be assigned in which the ethoxide appears to be thermally more stable than the more volatile secondary and tertiary alkoxides Zr(OEt>4 Zr(OPr )4 > Zr(OBu >4 Zr(OAm )4. Furthermore, the kinetics of thermal decomposition of zirconium tetra-teri-amyloxide studied in a clean glass apparatus in the temperature range 208-247°C indicated that the tertiary amyl alcohol formed during decomposition eliminates water a molecule of water produced from one molecule of alcohol would produce another two molecules of alcohol by hydrolysis of zirconium tert-amyloxide and hence a chain reaction would be set up. Since the dehydration of the tertiary alcohol is a rapid first order reaction, it may be the rate controlling step in the thermal decomposition of tertiary alkoxides. 

The recent mass spectral findings of Turevskaya etal. on tetra-alkoxides of zirconium and hafnium are usually in good agreement with their molecular complexity. " " However, the existence of a high intensity of M30(0R)9+ or M40(0R)i3+ ions in the mass spectra of [M(OR>4] tends to indicate the complex nature of such species. The X-ray crystal structure determination of [M(OR)4] is called for to solve such an ambiguity. 

In an early paper, the formation of products of lower chloride zirconium ratios, as compared to the moles of acetyl chloride employed with zirconium tetra-tert-butoxide, was ascribed to steric effects. However, in a careful re-examination, the reactions between metal fert-butoxides and acetyl halides have been found " to follow an entirely different course. For example, the reaction between zirconium tertiary butoxide and acetyl chloride was slow, and complete replacement of even one mole of tertiary butoxo group was not achieved the equimolar reaction product had the average composition, ZrClo.7(OBu )3 3. On the basis of further reaction of zirconium chloride tertiary butoxide with acetyl chloride it appeared that a side reaction occurred and instead of higher chloride alkoxides, mixed-alkoxide acetates were formed ... 

Tetraalkyl titanates are the most commonly used catalysts for PBT polymerization [8], The varieties of titanates include tetraisopropyl titanate (TPT), tetrabutyl titanate (TBT) and tetra(2-ethylhexyl) titanate (TOT). Titanates effectively speed the reaction rate with few detrimental effects on the resin. Alkoxy zirconium and tin compounds, as well as other metal alkoxides, may also be used in PBT polymerization. 

Hydrolysis studies of secondary and tertiary alkoxides (69) indicate that the degree of polymerization of secondary alkoxides in benzene is lower than for the normal alkoxides, whereas the teritary alkoxides are monomeric. Thus the hydrolysis data on tetraisopropoxide zirconium and tetra-sec-butoxide zirconium are consistent with the model (2) hypothesis, while the hydrolysis data of tetra-ter<-amyloxide fit the model (3) hypothesis. Additionally, crystal structure data on tetraisopropoxide... 

During an attempt to prepare tetra-/ert-alkoxides of zirconium and cerium by the reactions of (C5H6N)2MCl6 (M = Zr, Ce) with terf-butyl alcohol, Bradley and co-workers " 444 noticed the formation of MCl(OBu )3.2C5H5N as represented by Eq. (2.38) ... 

In view of an interesting gradation observed (Section 2.4) in the reactivity of tetra-halides of silicon, titanium, zirconium, and thorium with ethyl and isopropyl alcohols, the reverse reactions of alkoxides of these elements with hydrogen chloride (bromide) were investigated by Mehrotra who demonstrated that the reaction products of... 

In this study, ZT powders were obtained from hydrolysis reactions of zirconium n-propoxide (NPZ) and titanium isopropoxide (tetra-isopropyl titanate - TPT). These reactions were performed by hydrolyzing the alkoxides separately, at the molar ratio of ZriTi of 1 1, in n-propanol, using the sol-gel process at ambient temperature (20°C) and... 

Tetra-alkoxy titanates are the most commonly used catalysts for PBT pol)mierization [15, 20]. As opposed to the PET process, where a different catalyst is used in each of the two polymerization phases, in the PBT process, a single catalyst is typically used for both reaction steps. The most frequently used titanates are tet-rabutoxy titanate (Ti(OBu) ) [26, 27, 29, 30] and tetraisopropoxy titanate (Ti(OiPr) ) [31]. Ti(OBu), and Ti(OiPr) are very efficient catalysts which do not generate side effects, especially discoloration. Titanium and zirconium alkoxides are sometimes involved in the same preparation [23]. Other compounds have also been also proposed CHgCOONa [28] Ti(OBu), (95%) + CHjCOONa (5%) [29] Ti(OBu), (50%) + Sn(OBu), (50%) [26] Ti(OBu) + Ca(OAc)2 [32] Ti(OBu) + Mg(OAc)2 [30] TiOj-xH O [25], etc. These catalytic... 

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