Titanium tetrachloride supported

Present generation high activity Ziegler-Natta catalyst is comprised of titanium tetrachloride supported on magnesium dichloride [1-4]. Performance of the catalyst... 

Fanelli AJ, Burlew JV, Marsh GB (1989) The polymerization of ethylene over titanium tetrachloride supported on alumina aerogels low-pressure results. J Catal 116 318-324... 

Most catalysts for solution processes are either completely soluble or pseudo-homogeneous all their catalyst components are introduced into the reactor as Hquids but produce soHd catalysts when combined. The early Du Pont process employed a three-component catalyst consisting of titanium tetrachloride, vanadium oxytrichloride, and triisobutjlalurninum (80,81), whereas Dow used a mixture of titanium tetrachloride and triisobutylalurninum modified with ammonia (86,87). Because processes are intrinsically suitable for the use of soluble catalysts, they were the first to accommodate highly active metallocene catalysts. Other suitable catalyst systems include heterogeneous catalysts (such as chromium-based catalysts) as well as supported and unsupported Ziegler catalysts (88—90). 

High Density Polyethylene. High density polyethylene (HDPE), 0.94—0.97 g/cm, is a thermoplastic prepared commercially by two catalytic methods. In one, coordination catalysts are prepared from an aluminum alkyl and titanium tetrachloride in heptane. The other method uses metal oxide catalysts supported on a carrier (see Catalysis). 

The dependence of the diastereomeric ratio on the choice of Lewis acid can be understood when considering the geometry of the Lewis acid complex. In the case of the titanium tetrachloride catalysed reaction, the interaction of the ester and the catalyst is strongly supported by the first crystal structure observed of the Lewis acid with a chiral dienophile (Figure 4)118. 

The stereochemical outcome was rationalized by a Zimmerman-Traxler type transition state 45.64 Assuming the titanium enolate of 42 has a Z-geometry and forms a 7-membered metallacycle with a chairlike conformation, a model can be proposed where a second titanium metal coordinates to the indanol and aldehyde oxygens in a 6-membered chairlike conformation. The involvement of two titanium centers was supported by the fact that aldehydes that were not precomplexed with titanium tetrachloride did not react (Scheme 24.7).63 Ghosh and co-workers further hypothesized that a chelating substituent on the aldehyde would alter the transition state 46 and consequently the stereochemical outcome of the condensation, leading to. vyn-aldol products 47.64 Indeed, reaction of the titanium enolate of 42 with bidentate oxyaldehydes proceeded with excellent. s v -diastereo-selectivity (Scheme 24.8).65... 

A study on the scope of the reaction applied to different types of carbonyl compounds (aldehydes, cyclic ketones and some substituted alkyl aryl ketones75) has been published. Two different secondary amines (pyrrolidine, morpholine) were used. Titanium tetrachloride on various supports (e.g. A1203) acted as effective dehydrating agents for the preparation of enamines from hindered ketones and secondary amines76. 

The discovery of active magnesium chloride as the ideal support for the fixation of titanium tetrachloride and its derivatives opened a new era in the field of Ziegler-Natta catalysis, both from the industrial and the scientific viewpoint. During the last 15 years MgCl2-supported catalysts brought about revolutionary industrial developments, as compared to those of the traditional Ziegler-Natta catalysts. 

Longworth and Plesch examined the conductivity of solutions of titanium tetrachloride in methylene chloride and observed that this was directly proportional to the Lewis acid concentration. This correlation was taken as evidence of a 2 2 ionogenic equilibrium involving the monomeric halide. The presence of a TiCls deposit at the cathode seemed to support the presence of TiCl. This type of work is extremely delicate and demands all possible experimental care (purity, dryness, etc.) to provide meaningful results. The interpretation of such results reflecting ionc enic equilibria of various possible stoicheiometry was recently discussed in a very useful paper by Grattan and Plesch ... 

Three types of products have been observed in intermolecular acylations of homoallylic silanes, the major one being cyclopropylmethyl ketones, along with minor amounts of 3-butenyl ketones and -chlo-ro ketones. It is likely that all derive from the carbenium ion formed by acylation of the double bond, which then undergoes cyclodesilylation or hydride transfer followed by 3-elimination (Scheme 14). The former leads to the cyclopropane, which can ring open to give the chloro products. The latter pathway gives the butenyl ketone, and is supported by location of substituent positions on methylated substrates. However, the direct acylation of the carbon-silicon bond should not necessarily be excluded in consideration of more general cases. Titanium tetrachloride seems the preferred catalyst in these cyclodesilyl-ations, and low temperatures minimize the formation of the chloro by-products. Intramolecular versions... 

The titania-silica (1 1 mole ratio) mixed oxide support was prepared by homogeneous precipitation method from acidified mixed solutions of sodium metasfiicate and titanium tetrachloride using urea as the neutralizer [11,12]. More details are described in a previous publication [12 ]. The Ti(OH)4 - Si(OH)4 coprecipitate obtained was oven dried at 393 K for 16 h and calcined at 773 K for 6 h in an open air furnace. 

Slurry processes may use a combination of organo-aluminum and organo-magnesium compounds with titanium tetrachloride. Phillips-type catalysts (supported chromium compounds) are also used. Pressures and temperatures are moderate. 

A rather elaborate machine is required to perform this process. The glass plates and lenses are supported on a heated horizontal rotating disk having a maximum speed of 60 r-p-m. Burners or gas-mixer nozzles are supported and geared to sweep back and forth horizontally across the work pieces, one depositing 2, and the other SiC>2. Mixed oxides can be formed by the simultaneous operation of two nozzles so that 2 and SiC>2 are deposited alternately in very thin films. The titanium dioxide nozzle has two inlets for dry air, one for a mixture of dry air and titanium tetrachloride vapour and one for moist air. To prevent chemical reaction of TiCU with humid air inside the nozzle a concentric curtain of dry air between these two reaction partners is maintained. The glasses to be coated are exposed to a temperature of about 250°C and the mixture from the burner reacts on the heated surface to form 2 film... 

Microwave-aided boric add-catalyzed condensation of isophthalic aldehyde 162a or terephthahc aldehydes 162b with 1,3-dicarbonyl compounds and urea/thiourea, furnished p-[bis(dihydropyrimidin-2(lH)-one-4-yl)] benzene 163 containing two dihydropyrimidinone units linked through their C-4 position (Scheme 62) (05M15). Solid-supported tin chloride and titanium tetrachloride were used as catalysts under solvent-free conditions (10M15). 

A similar reaction affords a simple route to cyclopent[b]indoles. Indole-3-carbinol (68) reacts with j8-methylstyrene in the presence of titanium tetrachloride to give compound (70) <93TL8527>. The presumed four-membered spiroindolenine (69) in this sequence receives support from the observation that the conversion of the D-tryptophan derived compound (71) to its mesylate leads to the formation of racemic cyclopent[b]indole (73) via the achiral intermediate (72) (Scheme 17) <93TL439>. 

A solid catalyst of active magnesium dichloride supported on titanium tetrachloride and solid electron-donor such as 2,2-diisobutyl-l,... 

The first example of supported titanium-catalysed DA reaction was reported by Luis et al. in 1992 (Scheme 7.49). In this work, the authors described the preparation of several polymeric alcohols derived from Merrifield resin and their efficiency as ligand in titanium-catalysed cycloaddition between methacrolein and cyclopentadiene with yields between 83-99% and good exo selectivity. With the aim to evaluate the enantioselectivity of the reaction, catalyst 80 was then prepared almost quantitatively by double esterification of tartaric acid with chloromethylated polystyrene and a 1 1 mixture of titanium tetrachloride/titanium tetraisopropoxide. " Despite the good conversion and selectivity toward the exo-cycloadduct, only 3% enantiomeric excess was recorded, which was attributed to the very high reactivity of the system. Recycling of the catalyst was successfully performed by filtration from the reaction media and washing with dichloromethane, and catalyst 80 was reused seven times without significant loss of catalytic activity. 

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