Titanium alkoxides alkali

Scheme 5-47 Asymmetric hydrophosphonylation of a cyclic imine catalyzed by heterobimetallic rare earth/alkali metal/BI-NOL complexes or by chiral titanium alkoxide complexes...

Single metal and mixed metal oxo alkoxides can also be prepared by reaction between metal halides, oxy halides, and alkali metal alkoxides.47,48 One of the first to be structurally characterized was a series of mixed Cd or Sn containing zirconium, tin, and titanium alkoxides.84,85 These and other examples are shown in skeletal form in Figure 3. 

Hampden-Smith, M. J., Williams, D. S., and Rheingold, A. L., Synthesis and characterization of alkali-metal titanium alkoxide compounds MTi (OiPr)s (M = Li, Na, K) Single-crystal x-ray diffraction structure of [(LiTi(OiPr)s]2, Inorg. Chem., 29, 4076-4081 (1990). 

Zirconia, which is stable as well as titania, especially, in alkali solution, is also one of the promising materials for separation membranes. Several manufacturers have commercialized zirconia UF membranes, but not NF membranes. Zirconium propoxide [30] or butoxide [31], which are mainly used as precursors of zirconia sols, are highly sensitive to water to form suspensions (the reaction rate with water is much faster than titanium alkoxide), the preparation of nanosized sols is difficult. Therefore, very few reports have appeared on the successful preparation of zirconia nanofiltration membranes. Vacassy et al. [30] added acetylacetone to zirconia propoxide to prevent hydrolysis, and reported a successful preparation of porous zirconia membranes showing a water permeability of 3.4 X 10 ms Pa and a rejection of 55% towards saccharose (MW = 342). 

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. 

The effect of metal alkoxides on the properties of initiators for the anionic polymerization of vinyl monomers has also been reported for polymethylmethacrylate, polymethacrylonitrile and poly-2-vinyl pyridine. The polymerization esterification of teiephthaUc acid with glycols is another important industrial process which is catalysed by metal alkoxides, mainly titanium or alkali metal derivatives. Numerous patent applications have appeared over the years. 

Taramasso et al. (5) had originally reported two methods for the hydrothermal synthesis of TS-1. The first method (mixed alkoxide method) involves the preparation of a solution of mixed alkoxides of titanium and silica (preferably ethoxides) followed by hydrolysis with alkali-free solution of tetrapropylammonium hydroxide (TPAOH), distillation of the alcohol and crystallization of the resulting gel at 448 K. In the second method (dissolved or hydrolyzed titanium method) a soluble tetrapropylammonium peroxo-titanate species was prepared initially and then colloidal SiC>2 (Ludox AS-40) was added. This entire operation had to be carried out at 278 K. The TS-1 samples obtained by these two synthesis routes differed, particularly because of the presence of impurities such as Al3+ usually present in colloidal silica (33). 

The synthesis of titanium-containing beta zeolite has been carried out by direct hydrothermal synthesis and by secondary synthesis. In the direct synthesis with aluminum salts and titanium and silicon alkoxides, it is necessary to operate in the absence of alkalies, since these cause the formation of an amorphous precipitate containing Ti02 and Si02. Evidence for the substitution... 

Transesterifications of aliphatic carbonate esters with glycols are catalysed by alkali metal alkoxides. No catalyst is needed for the transesterification of diaryl carbonates with aliphatic diols. Alkyl carbonate esters and p-xylylene glycol undergo transesterification reactions when certain titanium compounds are used as catalysts. The preparation of aromatic polycarbonates by transesterification is best... 

IDouble Alkoxides. Complex double alkoxides are formed when a solution of an alkali or alkaline earth metal alkoxide is added to a solution of an alkoxide of aluminum, titanium, or zirconium and a series of such compounds have been prepared (44). 

Metal alkoxides, also known as alcoholates, constitute a class of compounds in which the metal atom is attached to one or more alkyl groups by an oxygen atom. These substances have the general formula, M—O—R, where M is the metal atom and R, an alkyl group. Many metals in the Periodic Table are known to form alkoxides. However, only a few of them have commercial applications. These include the alkali and alkaline-earth metals, aluminum, titanium, and zirconium. Metal alkoxides have found applications as catalysts, additives for paints and adhesives, and hardening agents for synthetic products. They are also used in organic synthesis. 

Following the procedure of Meerwein and Bersin and others, - - this method has been extended to the bimetallic alkoxides of alkali metals (Lewis bases) with those of less basic metals and metalloids, beryllium, zinc, - boron, aluminium, gallium,tin(n), " tin(iv), antimony(iii), bismuth, titanium," niobium(iv), zirconium, " thorium, niobium(v), tantalum(v) and copper. Equations (3.1)-(3.3) reflect a few typical reactions used in the synthesis of bimetallic alkoxides involving alkali metals (M) ... 

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