Titanium-based catalyst

Catalysts and LLDPE Polymerization Processes LLDPE resins are produced in industry with three classes of catalysts titanium-based catalysts (Ziegler), metallocene-based catalysts (Kaminsky and Dow), and chromium oxide-based catalysts (Phillips). 

The Lewis acid-catalysed addition of trimethylsilyl cyanide to aldehydes has been reported using several different catalysts. Titanium-based Lewis adds have proved to be particularly popular. In a typical reaction, benzaldehyde (6.01) is converted into the cyanohydrin (6.57) usually after removal of the trimethylsilyl group by hydrolysis. A wide variety of ligands have been used for this reaction and... 

One of the most famous chiral titanium complexes is the Sharpless catalyst (16), based on a diisopropyl tartarate complex. Nmr studies suggest that the complex is dimeric ia nature (146). An excellent summary of chiral titanium complexes is available (147). 

Cocatalysts, such as diethylzinc and triethylboron, can be used to alter the molecular-weight distribution of the polymer (89). The same effect can also be had by varying the transition metal in the catalyst chromium-based catalyst systems produce polyethylenes with intermediate or broad molecular-weight distributions, but titanium catalysts tend to give rather narrow molecular-weight distributions. 

Polymers containing 90-98% of a c 5-1,4-structure can be produced using Ziegler-Natta catalyst systems based on titanium, cobalt or nickel compounds in conjuction with reducing agents such as aluminium alkyls or alkyl halides. Useful rubbers may also be obtained by using lithium alkyl catalysts but in which the cis content is as low as 44%. 

Dimerization of ethylene to butene-1 has been developed recently by using a selective titanium-based catalyst. Butene-1 is finding new markets as a comonomer with ethylene in the manufacture of linear low-density polyethylene (LLDPE). 

A new process developed by Institut Francais du Petrole produces butene-1 (1-butene) by dimerizing ethylene.A homogeneous catalyst system based on a titanium complex is used. The reaction is a concerted coupling of two molecules on a titanium atom, affording a titanium (IV) cyclic compound, which then decomposes to butene-1 by an intramolecular (3-hydrogen transfer reaction. ... 

Several aluminum- and titanium-based compounds have been supported on silica and alumina [53]. Although silica and alumina themselves catalyze cycloaddition reactions, their catalytic activity is greatly increased when they complex a Lewis acid. Some of these catalysts are among the most active described to date for heterogeneous catalysis of the Diels-Alder reactions of carbonyl-containing dienophiles. The Si02-Et2AlCl catalyst is the most efficient and can be... 

Inverse electron-demand Diels-Alder reaction of (E)-2-oxo-l-phenylsulfo-nyl-3-alkenes 81 with enolethers, catalyzed by a chiral titanium-based catalyst, afforded substituted dihydro pyranes (Equation 3.27) in excellent yields and with moderate to high levels of enantioselection [81]. The enantioselectivity is dependent on the bulkiness of the Ri group of the dienophile, and the best result was obtained when Ri was an isopropyl group. Better reaction yields and enantioselectivity [82, 83] were attained in the synthesis of substituted chiral pyranes by cycloaddition of heterodienes 82 with cyclic and acyclic enolethers, catalyzed by C2-symmetric chiral Cu(II) complexes 83 (Scheme 3.16). 

The decomposition is significantly accelerated and the temperature of the first decomposition reaction is lowered to 120°C (Fig. 19.7). The decomposition rate is relatively low compared with other titanium-based dopants. The highest activity of a titanium catalyst used in alanate decomposition was observed for ligand-stabilized colloidal titanium metal [42]. 

The metal catalyzed production of polyolefins such as high density polyethylene (HDPE), linear low density polyethylene (LLDPE) and polypropylene (PP) has grown into an enormous industry. Heterogeneous transition metal catalysts are used for the vast majority of PE and all of the PP production. These catalysts fall generally within two broad classes. Most commercial PP is isotactic and is produced with a catalyst based on a combination of titanium chloride and alkylaluminum chlorides. HDPE and LLDPE are produced with either a titanium catalyst or one based on chromium supported on silica. Most commercial titanium-based PE catalysts are supported on MgCl2. 

Thus it seems possible that analogous titanium-based complexes play a role in the activation of the catalyst with AlEts according to ... 

Although the titanium-based methods are typically stoichiometric, catalytic turnover was achieved in one isolated example with trialkoxysilane reducing agents with titanocene catalysts (Scheme 28) [74], This example (as part of a broader study of enal cyclizations [74,75]) was indeed the first process to demonstrate catalysis in a silane-based aldehyde/alkyne reductive coupling and provided important guidance in the development of the nickel-catalyzed processes that are generally more tolerant of functionality and broader in scope. 

The process has been commercially implemented in Japan since 1977 [1] and a decade later in the U.S., Germany and Austria. The catalysts are based on a support material (titanium oxide in the anatase form), the active components (oxides of vanadium, tungsten and, in some cases, of molybdenum) and modifiers, dopants and additives to improve the performance, especially stability. The catalyst is then deposited over a structured support based on a ceramic or metallic honeycomb and plate-type structure on which a washcoat is then deposited. The honeycomb form usually is an extruded ceramic with the catalyst either incorporated throughout the stmcture (homogeneous) or coated on the substrate. In the plate geometry, the support material is generally coated with the catalyst. 

Cyclohexyl- and phenylmethylsilanes do not polymerize, but give dimer. With titanium-based catalysts the value of n is about 10 and does not vary very much with R or experimental conditions with zirconium based catalysts, n can be as high as 20. 

One of the exciting results to come out of heterogeneous catalysis research since the early 1980s is the discovery and development of catalysts that employ hydrogen peroxide to selectively oxidize organic compounds at low temperatures in the liquid phase. These catalysts are based on titanium, and the important discovery was a way to isolate titanium in framework locations of the inner cavities of zeolites (molecular sieves). Thus, mild oxidations may be run in water or water-soluble solvents. Practicing organic chemists now have a way to catalytically oxidize benzene to phenols alkanes to alcohols and ketones primary alcohols to aldehydes, acids, esters, and acetals secondary alcohols to ketones primary amines to oximes secondary amines to hydroxyl-amines and tertiary amines to amine oxides. 

The catalyst activity is so high that uranium concentration lower than 0.1 millimoles per liter allows a complete conversion of butadiene to be obtained in a few hours, at 20°C, The transfer reaction of uranium based catalyst is similar to that of conventional 3d-block elements (titanium, cobalt, nickel) so that the molecular weight of the polymer is affected by polymerization temperature, polymerization time and monomer concentration in the customary way. This is in contrast, as we shall see later on, to some catalysts based on 4 f-block elements. Uranium based catalysts are able to polymerize isoprene and other dienes to high cis polymers the cis content of polyisoprene is 94%, somewhat inferior to titanium based catalysts. In contrast, with 3d-block elements an "all cis", random butadiene-isoprene... 

Alternating Copolymerization. In the last part of this paper we would like to refer briefly to our findings in connection with the alternating copolymerization of dienes with olefins. The alternating copolymerization of butadiene with propylene was first investigated in 1969 by Furukawa and others (15, 16, 17). They used catalyst systems based on titanium or vanadium compounds. 

Certain catalysts promote the reduction of ketones with organosilanes. The reduction of acetophenone with Et3SiH is catalyzed by the diphosphine 65 and gives only a small amount of overreduction to ethylbenzene.377 Aryl alkyl enones and ynones are reduced to the corresponding alcohols with triethoxysilane and the titanium-based catalyst 66.378 Trichlorosilane reduces acetophenone in 90% yield with /V-formylpyrrolidinc catalysis.379... 

Transition metal catalysis plays a key role in the polyolefin industry. The discovery by Ziegler and Natta of the coordination polymerization of ethylene, propylene, and other non-polar a-olefins using titanium-based catalysts, revolutionized the industry. These catalysts, along with titanium- and zirconium-based metallocene systems and aluminum cocatalysts, are still the workhorse in the manufacture of commodity polyolefin materials such as polyethylene and polypropylene [3-6],... 

Biodiesel is a mixture of methyl esters of fatty acids and is produced from vegetable oils by transesterification with methanol (Fig. 10.1). For every three moles of methyl esters one mole of glycerol is produced as a by-product, which is roughly 10 wt.% of the total product. Transesterification is usually catalyzed with base catalysts but there are also processes with acid catalysts. The base catalysts are the hydroxides and alkoxides of alkaline and alkaline earth metals. The acid catalysts are hydrochloride, sulfuric or sulfonic acid. Some metal-based catalysts can also be exploited, such as titanium alcoholates or oxides of tin, magnesium and zinc. All these catalyst acts as homogeneous catalysts and need to be removed from the product [16, 17]. The advantages of biodiesel as fuel are transportability, heat content (80% of diesel fuel), ready availability and renewability. The... 

Epoxidation of FAMEs Over Titanium-based Catalysts The Skills in Milan... 

Furthermore, the environmental impact of PET production should be reduced by substituting the commonly used antimony-based catalyst for an antimony-free catalyst leg, for a titanium-based catalyst. The pollution by liquid effluents could be reduced by installing a reverse-osmosis unit on top of the glycol distillation unit for the purification of water from the esterification process. 

PBT has both hydroxy and carboxylic acid end groups, and it often contains active residual catalyst (usually titanium based). The resin is still capable of reacting, and molecular weight may be increased by solid-state polymerization. 

Syndiotactic Polystyrene. Syndiotactic polystyrene is an interesting material because it has a Tg of 95 °C and a Tm of 260 °C [38], Polystyrene made via radical polymerisation may show some syndiotacticity, but its heat distortion temperature is too low to allow its use in important applications requiring temperatures around 120 °C or higher, such as medical equipment which requires sterilization or hot water storage containers. Idemitsu and Dow have reported titanium-based catalysts such as the one shown in Figure 10.23. We presume that the mechanism is a chain-end controlled "2,1" insertion. 

With reaction conditions of 200-225°F, 150—225 psi, and a palladium chloride-cupric chloride catalyst, MEK yields are 80-90%. The operating costs of the Wacker process for MEK (and acetone and several other petrochemicals as well) are relatively low. But the plant Is made of more expensive materials. Because of the corrosive nature of the catalyst solution, critical vessels, and the piping are titanium-based.(chats expensive ), and the reactor is rubber-lined, acid-resistant brick. ... 

Turning now to titanium based catalysts, solid-state NM R data are quite... 

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