Acetates titanium alkoxide

Different types of metal compounds can also be used as catalysts for example, zinc acetate, titanium alkoxide, phosphorus derivatives, etc. 

Zinc chloride is a Lewis acid catalyst that promotes cellulose esterification. However, because of the large quantities required, this type of catalyst would be uneconomical for commercial use. Other compounds such as titanium alkoxides, eg, tetrabutoxytitanium (80), sulfate salts containing cadmium, aluminum, and ammonium ions (81), sulfamic acid, and ammonium sulfate (82) have been reported as catalysts for cellulose acetate production. In general, they require reaction temperatures above 50°C for complete esterification. Relatively small amounts (<0.5%) of sulfuric acid combined with phosphoric acid (83), sulfonic acids, eg, methanesulfonic, or alkyl phosphites (84) have been reported as good acetylation catalysts, especially at reaction temperatures above 90°C. 

PZN-PT, and YBa2Cug02 g. For the preparation of PZT thin films, the most frequently used precursors have been lead acetate and 2irconium and titanium alkoxides, especially the propoxides. Short-chain alcohols, such as methanol and propanol, have been used most often as solvents, although there have been several successful investigations of the preparation of PZT films from the methoxyethanol solvent system. The use of acetic acid as a solvent and chemical modifier has also been reported. Whereas PZT thin films with exceUent ferroelectric properties have been prepared by sol-gel deposition, there has been relatively Httle effort directed toward understanding solution chemistry effects on thin-film properties. 

Mn(II) > Mg(II).270 It should be underlined that titanium and zirconium alkoxides are efficient catalysts for both stages of reaction. Lanthanide compounds such as 2,2/-bipyridyl, acetylacetonate, and o-formyl phenolate complexes of Eu(III), La(III), Sm(III), Er(III), and Tb(III) appear to be even more efficient than titanium alkoxides, Ca or Mn acetates, Sb203, and their mixtures.273 Moreover, PET produced with lanthanides has been reported to exhibit better thermal and hydrolytic stability as compared to PET synthesized with the conventional Ca acetate -Sb203 catalytic system.273... 

Modification by acetylacetone is a powerful route, that allows precursor solutions to be stabilized. Interaction of titanium alkoxides with acetylacetone was extensively studied and reviewed in [1391,86]. Study ofreactions, occurring on interaction of Zr(OPrn)4 and Ti-Zr alkoxide mixture with acetylacetone, was performed in [1448] and allowed the authors to simplify the technique for preparation of precursor solution for PZT films application and to overcome the requirement of prolonged refluxing, which certainly decreases reproducibility. After dissolution of titanium and zirconium alkoxides in methoxyethanol, acetylacetone is added to form stable zirconium and titanium stock solutions. The introduction of acetylacetone allowed aqueous lead acetate (and lanthanum acetate for PLZT films) solutions to be added to mixed titanium and zirconium solutions. No reaction steps involving elevated temperatures or distillation or long reaction times are required. The solution could be used both immediately on mixing or after storage for several months. Such solutions were successfully used for application of ferroelectric films. 

Hydroxyalkyl Acids. The first reliable synthesis of 1-hydroxyalkylphos-phonates (241) in high enantiomeric excess has been achieved via titanium alkoxide-catalysed asymmetric phosphonylation of aldehydes then acetylation and enzyme-catalysed kinetic resolution of the acetates (Scheme 63). ... 

In a series of papers, the application of titanium alkoxide catalysts to the synthesis of sugars has been described. Asymmetric epoxidation and kinetic resolution of (48) afforded (+)-(49) (27% >95%e.e.) and (—)-(48) (33% 72%e.e.). The ring-opening reactions of the chiral epoxides that are produced, for example, from cis- and from trans- 50) provide new routes to saccharides. The reagents also find use in the synthesis of pheromones e.g., (+)-disparlure and (+)-2,6-dimethylhepta-l,5-dien-3-ol acetate via the epoxide (52), which was obtained from the dienol (51) by using D-(—)-... 

A Idol reactions. The copper comp l> lketene acetals with (benzyloxy )ac< kn approach to 5-hydroxy-3-ketoester es a titanium alkoxide derived from n imino-BINOL complex 15 is effec... 

An exothermic reaction takes place when acetic acid is added to titanium alkoxide in a 1 1 ratio. A clear solution is obtained. X-ray absorption experiments show that the coordination of titanium increases up to six (Fig. 4a), whereas two Ti-0 distances (l.SOA and 2.06A) and Ti-Ti correlations (3.11 A) are observed on the Fourier transform of the EXAFS spectrum (Fig. 4b). Infrared spectroscopy can be used to study how acetate groups are bonded to tita-... 

Acetate groups actually behave as complexing nucleophilic ligands and react with titanium alkoxides as follows ... 

For example, when Ti(OBu )4 is reacted with one molar equivalent of acetic acid, an exothermic reaction takes place and the acetate-substituted titanium alkoxide (CH3COO)Ti(OBu )3 is formed with a six-coordinate titanium atom. While addition of water to Ti(OBu )4 results in immediate precipitation of titania, stable transparent gels are obtained from acetate-substituted titanium alkoxides with gelation times of several days or months. Similar observations were made for the reaction of Ti(OPr )4 with acetylacetone (acac-H)." The X-ray structure analyses of Ti(OR)3(/3-diketonate) -diketonate = acac, R = Me, Et, Pr -diketonate = Bu C(0)-CHC(0)Bu , R = Me, Pr, and Ti(OR)2(j0-diketonate)2 (,8-diketonate = acac, R = Pr " ... 

The earliest work on polyester synthesis used no catalyst or a simple acid catalyst such as p-toluenesulfonic acid, but use of weakly basic metallic salt catalysts is now almost universal. Many salts have been claimed to be useful in this context, but the best known examples are alkaline earth and transition metal acetates, tin compounds and titanium alkoxides [21-23]. Care must be exercised in selecting ester-interchange catalysts because some may cause degradation/ discoloration in the polymer during the subsequent polymerisation reaction [24], especially for PET and PEN. To prevent this occurrence, catalysts are often sequestered/complexed at the end of the ester-interchange phase by addition of phosphorus compounds such as phosphites, phosphates or polyphosphoric acid [25]. Titanium and tin compounds operate as catalysts for ester-interchange and polymerisation reactions, and in general do not require such procedures. 

Ester interchange can be retarded, particularly when esterification catalysts like zinc or calcium acetate are present by addition of phosphorous acid or triphenyl phosphite [415]. This improves the chances of forming block copolymers. The procedure can be applied to preparation of block copolymers of poly(ethylene terephthalate) with poly(ethylene maleate), poly(ethylene citraconate), and poly(ethylene itaconate) [416]. With ester interchange catalysts, like titanium alkoxides or their complexes, melt randomization may be inhibited by adding arsenic pentoxide that deactivates them [417]. 

Doueff S, Henry M, Sanchez C, Livage J. Hydrolysis of titanium alkoxide modification of the molecular precursor by acetic acid. J Non-Cryst Solids 1987 89(l/2) 206-16. 

Titanium alkoxides feature as catalysts in the esterification of succinic, adipic, azelaic, and sebacic acids with 2-ethyl hexanol and in the production of acetate... 

Williams P.A, Jones A.C., Bickley J.F., Steiner A., Davies H.O., Leedham T.J., Impey SA., Garcia J., Allen S., Rougier A., Blyr A. Synthesis and crystal structures ofdimethylaminoethanol adducts of Ni(ll) acetate and Ni(II) acetylacetonate. Precursors for the sol-gel deposition of electrochromic nickel oxide thin films, J. Mater. Chem. 2001, 11 2329 Yanovskaya M.L, Kotova N.M., Golubko N.V., Turova N.Ya. Reactions of magnesium and titanium alkoxides. Preparation and characterization of alkoxy-derived magnesium titanate powders and ceramics, J. Sol-Gel Sci. Tech. 1998 11 23... 

The acetato-alkoxo Ba-Ti complex, in which titanium alkoxide is associated with barium acetate via acetate bridges (Mosset et al., 1988), yielded BaTiOs ceramic fibers in a similar manner to PbTiOs fibers (Yoko et al., 1990). However, fiber length was limited to several mm probably due to the lack of strong Ba-O-Ti bonds in the precursor gel (later, long BaTiOs fibers were obtained by using the catecohol-complexed alkoxide as a starting material Lu et al., 2002). 

Hydrolysis is most rapid and complete when catalysts are employed [47]. Although mineral acids or ammonia are most generally used in sol-gel processing, other known catalysts are acetic acid, KOH, amines, KF, HF, titanium alkoxides, and vanadium alkoxides and oxides [47]. Many authors report that mineral acids are more effective catalysts than equivalent concentrations of base. However, neither the increasing acidity of silanol groups with the extent of hydrolysis and condensation (acidic silanols may neutralize basic catalysts [48]) nor the generation of unhydrolyzed monomers via base-catalyzed alcoholic or hydrolytic depolymerization processes have generally been taken into acount. 

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