Titanium salt

Although titanium compounds are considered to be physiologicaHy inert (21), fluorides in general are considered as toxic above 3 ppm level and extreme care should be taken in handling large amounts of titanium salts as weU as hexafluorotitanic acid. The ACGIH adopted (1992—1993) toxicity limits are as TWA for fluorides as F 2.5 mg/m. ... 

OC-Hydroxycarboxylic Acid Complexes. Water-soluble titanium lactate complexes can be prepared by reactions of an aqueous solution of a titanium salt, such as TiCl, titanyl sulfate, or titanyl nitrate, with calcium, strontium, or barium lactate. The insoluble metal sulfate is filtered off and the filtrate neutralized using an alkaline metal hydroxide or carbonate, ammonium hydroxide, amine, or alkanolamine (78,79). Similar solutions of titanium lactate, malate, tartrate, and citrate can be produced by hydrolyzation of titanium salts, such as TiCl, in strongly (>pH 10) alkaline water isolation of the... 

Titanoiyd, n. titanium oxide, titanieich, a. rich (or high) in titanium. Titansalz, n. titanium salt. 

Used industrially to produce pure titanium and titanium salts, pigments, as an additive in decorative glass, and as a polymerization catalyst. 

The aldol condensation of benzaldehyde with the thioacetamide carbanion (RCHCSNRV), derived from the desilylation of the silyl-thioether with tetra-/i-buty-lammonium fluoride, is stereoselective at—80°C producing the erythro isomer of the p-hydroxy thioamide preferentially (Scheme 6.18, R = Me, erythro threo 95 5) via a conformationally mobile intermediate. However, when R is bulky, a greater amount of the threo isomer is formed. Predictably, as the reaction temperature is raised, so the stereoselectively decreases. This procedure contrasts with the corresponding condensation catalysed by titanium salts, where the complexed intermediate produces the threo isomer [47, 48],... 

The spectrum of di-cyclopentadienyltitanium dichloride is the simple type I spectrum that might be expected of a hypothetical hydrated divalent titanium salt. 

Another drawback of RCM applies in case of certain substitution patterns that lead to preferential complexation of the catalyst by substrate functional groups, thereby rendering it inactive. This may be overcome either by a more active or different catalyst or by precomplexation of the donor groups, e.g. with titanium salts [41]. 

Ziegler-Natta catalysts are primarily complexes of a transition metal halide and an organometallic compound whose structure is not completely understood for all cases. Let us use as an example TiCU and R3AI. The mechanism of the polymerization catalysis is somewhat understood. This is shown in Fig. 14.6. The titanium salt and the organometallic compound react to give a pentacoordinated titanium complex with a sixth empty site of... 

An alternative procedure, which was devised for the synthesis of heteroannulated chromenes, involves the reaction of the titanium salt of the phenol with an a, 3-unsaturated carbonyl compound. " This is illustrated for the reaction of iV-methyl-3-hydroxycarbazole (1.26) with P-phenylcinnamaldehyde, which produces the carbazolopyran (1.27) in 35% yield. ... 

Asymmetric pinacol coupling reactions with a stoichiometric amount of titanium salts have been observed using a combination of TiGL and chiral amines such as A,A,A,A-tetramethyl-l,2-cyclohexanediamine and 2-methoxy-methylpyrrolidine. " " In these reports, the titanium salt is considered to be TiGl2- However, the titanium salt prepared by reduction of TiGU with McsSiSiMcs has proved to be TiGL. The enantioselectivities of the reactions using the chiral amines are modest (Table 2). 

There is evidence that each active center which initiates a polymeric chain (coordination complex between the titanium salt and a metal-ulkyl... 

SCHEME 120. Enantioselective additions mediated by titanium salts... 

Aldehydes are methylenated by bis(iodozincio)methane (3) without the mediation of titanium salt. Commercially available Nysted reagent 1 is also effective for this transformation in this case, the addition of a catalytic amount of BF3 OEt2 improved the yield (Table l)31a c. 

TABLE 2. Titanium salt mediated methylenation of ketones with bis(iodozincio) methane (3)... 

The role of titanium salt is to activate the carbonyl compounds as Lewis acid. As described above, bis(iodozincio)methane (3) is nucleophilic enough to attack the carbonyl group of aldehydes or ce-alkoxyketones. In the reaction with simple ketones or esters, however, the addition of titanium salt is necessary to facilitate the nucleophilic attack. Instead of this Lewis acid activator, simple heating may induce the nucleophilic attack. Treatment of 2-dodecanone with 3 without titanium salt at higher temperature, however, does not improve the yield of alkene (Scheme 13). The reason for the low reactivity of 3 at higher temperature comes from the structural change of 3 into the polymeric methylene zinc 4 through the Schlenk equilibrium shown in equation 740. 

Titanium salts (TiCl ) (Fig. 3.64) Chlorosilanes (trichloromethylsilane) Bore (BFj)... 

Titanium Salt Components Group VB Other Usea... 

Many experiments suggest that the promotional effect of titania is due to formation of Ti—O—Cr bonds, and that this is very dependent on subtle variations in the preparation of the catalyst. For example, most titanium salts are ineffective as promoters when impregnated onto CR/silica as an aqueous solution, but anhydrous titanium esters, which react with silanols, are often highly effective. A uniform monolayer of titania is probably not achieved in the first case. 

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