Alkoxides zirconium isopropoxide

Zirconium alkoxides behave similarly in regard to thermal stability. The series zirconium methoxide [28469-78-5] zirconium ethoxide [18267-08-8] zirconium isopropoxide [2171 -98 ] zirconium /r /f-butoxide [2081 -12-1] shows decreasing thermal stability. 

Sol-gel processing techniques have largely been applied to main group alkoxides, particularly Si and Al, but increasingly studies have dealt with early transition metal elements such as Ti and Zr. The preparation of metal alkoxides has been reviewed extensively.46 18 Self-condensation of alkoxides can occur, depending on the steric demands of the alkoxide group for example, Ti methoxide, ethoxide, and isopropoxide are tetrameric, trimeric, and dimeric, respectively,49 while the zirconium isopropoxide is tetrameric.50... 

Fractional distillation of the more volatile este CH3COOR in Eq. (5.15) is required to complete the reaction. Transestoification reactions have been used for the preparation of alkoxides of various metals including Zr, Ti, Ta, Nb, Al, La, Fe, Ga, and V. For example, zirconium rerf-butoxide has been prepared from the reaction between zirconium isopropoxide and terf-butyl ester followed by distillation of isopropyl acetate ... 

Formation of different complexes at different ratios of reactants in the same solvent (THF in this case) can be illustrated by the examples from barium-zirconium isopropoxide system (Vaartstra, 1991) (the authors used barium metal in the presence of solvating alcohol, but application of the ready alkoxide gives the same result (Turevskaya, 1995)) ... 

Kuhlman R., Vaarstra B.A., Streib W.E., Huffman J.C., Caulton K.G. Primary steps in the hydrolyses of two heterometallic alkoxides. Characterization of lithium-titanium and barium-zirconium isopropoxides [LiTiO(0-wo-Pr)3]4 and BaZr4(OH)(O-W0-Pr)i7. Inorg. Chem. 1993 32 ... 

Scheme 20.28) [84, 118]. The first step in this procedure is reduction of the ketone, followed by the acetylation of the formed alkoxide. It may be noted that aluminum(III) isopropoxide and zirconium(IV) isopropoxide do not catalyze the acetylation. With these catalysts, the alcohol is obtained. 

Aluminum alkoxides form few well-behaved adducts with nitrogen bases. However, species of the type [Al2(OR)6(en)] (en = ethylenediamine) have been isolated.230 The parent alcohol itself can in some cases act as the donor group. Hence, the isopropoxide of zirconium can be readily recrystallized from isopropyl alcohol as the adduct Zr(OPri)4 PriOH. 

It was noticed as early as 1925 that alkoxides of calcium, magnesium and particularly aluminum could catalyze the reduction of aldehydes by ethanol as shown in equation (65).242,243 Removal of very volatile acetaldehyde is easily achieved to drive the reaction to the right. In 1926, Ponndorf devised a method in which both aldehydes and ketones could be reduced to alcohols by adding excess alcohol and aluminum isopropoxide.244 Such reductions are today referred to as Meerwein-Ponndorf-Verley reactions. Although alkoxides of a number of metals, e.g. sodium, boron, tin, titanium and zirconium, have been used for these reactions, those of aluminum are by far the best. 

It was quite unexpectedly found that the amorphous samples of zirconium and hafnium alkoxides M(OR)4 contain several types of oxocomplexes, particularly, M3O(OR)i0 and M40(0R)14 [1612], The trinuclear Zr3([l3-0)()i3-OBu XOBu ), was isolated in a crystalline form and turned out to be a structural analog of the known isopropoxide clusters of Th, Mo, and U(IV) -MjOCOPr ),) [1520] (see also Sections 4.3 and 12.12). The inclusion of the solvent molecules inside the cavities of the structures and formation of alcohol solvates in many cases leads to microanalysis data that does not deviate much from those calculated for M(OR)n. 

Ally) ethers are selectively cleaved with titanium(lV) isopropoxide and commercially available Grignard reagents like /i-butyl- or cyclohexylmagnesium chloride [Scheme 4.229].432 Neither benzylidene acetals nor more highly substituted allylic ethers suffer under the reaction conditions. A mechanism for the reaction implicates formation of the titanacyclopropane intermediate 229.1 as the first step. Ligand exchange with an unsubstituted allyl ether affords intermediate 229.2. -Elimination to the allyltitanium(lV) alkoxide 2293 followed by hydrolysis returns the deprotected alcohol. The reaction closely resembles an earlier method based on zirconium.433... 

The metal salts of alcohols are called alkoxides, M(OR), where M is a metal and R is an alkyl group. Typical examples in the synthesis of ferroelectric thin films include titanium isopropoxide [Ti(OPr )4 where Pr represents isopropyl], tantalum ethoxide [Ta(OEt)5 where Et represents ethyl], and zirconium butoxide butanol [Zr(OBu )4 n-BuOH where Bu represents -butyl], an alkoxide/alcohol compound. The structure of this compound, shown in Figure 27.3a, illustrates its dimeric nature, that is, the fact that each molecule contains two metal centers. 

Ceramic powders of exceptional purity with very fine particle sizes (ca. 10 nm) have been prepared by precipitation of hydrolyzed oxides from high purity alkoxides . Yttria-stabilized zirconia is prepared by mixing high purity zirconium and yttrium isopropoxides in n-hexane, with water added dropwise to precipitate the oxides quantitatively. The homogeneity of the oxides results in stabilized cubic Zr02 at very low temperatures. Cyclic organoaluminum amides are used to prepare nonoxides such as sulfides and AIN- . 

Aluminum isopropoxide has been described in a 1958 US patent (39) as an MPV reductant to selectively convert the 7-ethylenedioxy derivative of a substituted dodecahydrophenanthrene to its 4b-methyl-7-ethylenedioxy-l,2,3,4,4a.4b,5,6,7,8,10,10a-dodecahydrophenanthrene-4-ol-l-one. The MPV reduction of pyrimidin-2(lH)-ones to the corresponding 3,4-dihydro- pyrimidin-2(lH)-ones has been accomplished with zirconium tetraalkoxide and with AIP, although the Zr-alkoxide was more effective (40). Aluminum isopropoxide has proven useful in the reduction of 5P-hydroxy-8-oxo-l,4,4aa,5,8,8aa-hexahydronapthalene-lp-carboxylic acid to a preciusor used in the synthesis of reserpine and related comnpoimds (41,42). 

Hydroxide suspensions of mullite with partially stabilized zirconia were prepared from metal alkoxide starting materials. Zirconium isoamyloxide and yttrium isopropoxide were mixed in the proper proportions for the partially stabilized zirconia. Aluminum isopropoxide and silicon ethoxide were added in the proper proportions for mullite. These solutions were refluxed for 4 to 8 h and then hydrolyzed to a pH of 0.5 using HNO3. The solutions were then neutralized to a pH of 8 using NH4OH. The resulting suspensions then contained the proper amount of each component as a hydroxide to form the mullite partially-stabilized zirconia matrix materials. With MgO as a stabilizer, procedures were identical to the above, except that MgO ethoxide was used instead of yttrium isopropoxide. Batch sizes were 25 to 100 g of final material. 

The differences in solubility of metal isopropoxides and their alcoholates have led to the crystallization of pure isopropoxide isopropanolates of some tetravalent elements. For example, zirconium tetraisopropoxide is a viscous supercooled liquid which dissolves in excess of isopropyl alcohol and crystallizes out in the form of pure white crystals which were characterized as Zr(OPr )4.Pr OH. Similarly tin tetraisopropoxide and cerium tetraisopropoxide have been obtained as crystalline alcoholates, Sn(OPr )4.Pr OH ° and Ce(OPP)4.Pr OH which were used as the starting materials for the synthesis of a number of new alkoxides. 

The higher molecular association of zirconium alkoxides compared to those of titanium analogues may be ascribed to the greater atomic radius of zirconium and its tendency to achieve a higher coordination number. It has also been observed by Bradley that the molecular complexities of zirconium alkoxides are reduced to a considerable extent in their parent alcohols, e.g. ethoxide and isopropoxide show association of 2.5 and 2.0 in boiling parent alcohols as against 3.6 and 3.0 observed, respectively, in benzene. The reduction in molecular complexities in alcohols may be due to the coordination of free alcohol molecules to zirconium atoms. It has been found... 

The isopropoxides of cerium and thorium also show higher association (3.1 and 3.8, respectively, in boiling benzene) than titanium, zirconium, and hafnium alkoxides. 

The process of reducing carbonyl compounds (aldehydes or ketones) to alcohols is therefore known as the Meerwein-Ponndorf-Verley reaction. Although alkoxides of a number of metal(loid)s such as sodium, magnesium, titanium, zirconium, iron, boron, aluminium, tin, and antimony have been used for these reactions, those of aluminium are by far preferred, since they tend to give the minimum degree of side reactions. The use of aluminium isopropoxide over other alkoxides was also preferred by Young et al as well as by Adkins and Cox. ... 

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... 

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