Titanium salts catalysts

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

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... 

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. 

This was one of the first classes of catalyzed reactions that were shown to give rise to strong asymmetric amplifications (vide supra, Scheme 9).33 Many subsequent studies have been performed with variations in the structure of the chiral catalyst, generated from BINOL and titanium salts.50-52 Asymmetric amplification is frequently observed with these catalysts in the glyoxylate-ene reaction (Table 5). 

The large-scale production of esomeprazole is now successfully achieved by asymmetric oxidation of the same sulfide intermediate as is used in the production of omeprazole (Scheme 2.5). Using the titanium-based catalyst originally developed by K. Barry Sharpless for allyl alcohol oxidation [56] and by H.B. Kagan for certain sulfide oxidations [57], a process was developed that could achieve initial enantiomeric excesses of about 94% [53]. During the production process, the optical purity is further enhanced by the preparation of esomeprazole magnesium salt, with subsequent re-crystallization. 

Arco have developed an integrated process for the production of industrially important epoxides via an adapted AO process (Figure 1.13).33 34 A sulfonic acid substituted alkylhydroanthraquinone alkylammonium salt is reacted with molecular oxygen to form the alkylanthraquinone and hydrogen peroxide. The hydrogen peroxide is then reacted with an alkene in the presence of a titanium zeolite catalyst (TS-1 see Chapter 4). The epoxide product is then separated, and the anthraquinone salt recycled to a hydrogenator for reaction with... 

Inorganic precursors are much cheaper and easier to handle than metal alkoxides. Therefore the industrial production of oxide powders for ceramics and catalysts is mainly based on the precipitation or coprecipitation of inorganic salts from aqueous solutions. Gibbsite, Al(OH)3, (see Aluminum Inorganic Chemistry) is precipitated from aluminate solutions. Ti02 powders are made via the controlled hydrolysis of titanium salts. Stabilized zirconia is coprecipitated from aqueous solutions of zirconium oxychloride, ZrOC, and yttrium nitrate, YlKOsjs. 

The Diels-Alder reaction is one of the most fundamental means of preparing cyclic compounds. Since discovery of the accelerating effect of Lewis acids on the Diels-Alder reaction of a,)3-unsaturated carbonyl compounds [341-344], its broad and fine application under mild reaction conditions has been amplified. Equations (140) [341] and (141) [345], respectively, illustrate typical dramatic effects from an early reaction and from one reported more recently. Lewis acid-promoted Diels-Alder reactions have been reviewed [7,8,346-353]. In addition to the acceleration of the reaction, other important feature is its alteration of chemo-, regio-, and diastereoselectivity this will be discussed below. The titanium compounds used in Diels-Alder reaction are titanium halides (TiX4), alkoxides (Ti(OR)4), or their mixed salts (TiX (OR)4 n = 1-3). A cyclopentadienyl complex such as Cp2Ti(OTf)2 is also documented as a very effective promoter of a Diels-Alder reaction [354], In addition to these titanium salts, a few compounds such as those in Eq. (142) [355] have recently been reported to effect the Diels-Alder reaction. The third, [(/-PrO)2Ti(bpy)(OTf)(i-PrOH)] (OTf), was estimated to be a more active catalyst than Cp2Ti(OTf)2. 

Use Pure titanium and titanium salts, iridescent effects in glass, smoke screens, titanium pigments, polymerization catalyst. 

Reetz et al. reported that a chiral Ti complex prepared from TiCL). and the dilithium salt of (S)-BINOL promoted the aldol reaction of 3-mefhylbutanal with KSA 48 with only poor enantioselectivity (60%, 8% ee) [115 b]. After this pioneering work, the titanium-based catalyst system has been intensively improved to attain an efficient catalytic cycle and high stereoselectivity [147-155]. 

S. Kasaoka, E. Sasaoka, and H. Nanba, "Deactivation Mechanism of Vanadium Pentoxide-Titanium Dioxide Catalyst by Deposited Alkali Salts and Regeneration Method of Deactivated Catalyst in Reduction of Nitric Oxide with Ammonia", Nippon Kagaku Kaishi. Japan, 1984,3, 486-494. 

TaUe 6 Catalyst Systems Containing Titanium Salts ... 

The effect of various metal salt catalysts [29-33] on the production of olefin-sulfiir dioxide copolymers was studied earlier by Frey, Snow, and Schulze [33]. It was found that the soluble catalysts (silver nitrate, lithium nitrate, ammonium nitrate, and dilute alcoholic nitric acid) are much more effective than insoluble salts (barium nitrate, zirconium nitrate, titanium nitrate, strontium nitrate, and mercuric nitrate) which usually have long induction periods for reactions as shown in Table III [33]. 

Sharpless epoxidation of allyl alcohols (Sharpless, 1985, 1988 Pfenninger, 1986 Rossiter, 1985 Woodard et al., 1991 Finn and Sharpless, 1991 Corey, I990a,b), an example of which is included in Table 9.6, is perhaps the most recent and one of the most remarkable applications of asymmetric catalysis. The reaction is normally performed at low temperatures (-30 to 0°C) in methylene chloride with a titanium complex consisting of a chiral component [diethyl tartrate (DET) or diisopropyl tartrate (DIPT)] and a titanium salt (titanium tetraisopropoxide) as the catalyst. The beauty of the synthesis is that both enantiomers of the tartrate are available so that either form of the product can be prepared in more than 90% ee. 

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. 

Fig. 3.19. (a) Calibrated silica particles of diameter 500 nm obtained by the Stober process, (b) Titanium oxide particles adapted to paint applications (mean diameter 200 nm). (c) Titanium oxide fibres of thickness 200 nm and length several microns, usable as a catalyst. The objects in (b) and (c) were obtained from the same titanium salt precursor solution, but under different conditions (photo courtesy of Rhone Poulenc)... 

Nitroparaffins are used with catalysts such as alkyl-metal (e.g., triethylaluminum, vanadium, or titanium) salts in the polymerization reactions... 

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