Preparation of organotitanium compounds

Among widely used organotitanium compounds are tetraalkoxytitaniums, obtained by the etherification of titanium tetrachloride with alcohols  

The production techniques of titanium tetrachloride are described below in detail. 

Titanium tetrachloride was prepared for the first time in 1825 by chlorine acting on titanium at high temperature. Since that time more production techniques have been devised, e.g. the chlorination of titanium carbide and the effect of hydrogen chloride on metallic titanium at a temperature above 300 °C. 

The most widespread technique, however, is the chlorination of titanium dioxide with chlorine or chlorine-containing substances (carbon tetrachloride, chloroform, sulftuyl chloride, phosphorus oxychloride, silicon tetrachloride). These reactions give high yield at high temperatures (800 °C and more) the chlorination with free chlorine occurs at noticeable speed only in the presence of reducing agents (e.g., coal). If there is a lack of coal, the reaction forms carbon dioxide if there is an excess of coal, it releases carbon oxide  

Industrially titanium tetrachloride can be produced both from titanium dioxide by the technique described above and from titanium- and iron-containing ores rutile (Ti02), which contains about 60% of titanium and up to 10% of iron, ilmenite (FeOTi02 with 25-35% of titanium) or titanif-erous magnetites (the mechanical mixture of ilmenite and magnetite or loadstone). 

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A unique titanium(IV)-silica catalyst prepared by impregnating silica with TiCLt or organotitanium compounds exhibits excellent properties with selectivities comparable to the best homogeneous molybdenum catalysts.285 The new zeolite-like catalyst titanium silicalite (TS-1) featuring isomorphous substitution of Si(IV) with Ti(IV) is a very efficient heterogeneous catalyst for selective oxidations with H2C>2.184,185 It exhibits remarkable activities and selectivities in epoxidation of simple olefins.188,304-306 Propylene, for instance, was epoxidized304 with 97% selectivity at 90% conversion at 40°C. Shape-selective epoxidation of 1- and 2-hexenes was observed with this system that failed to catalyze the transformation of cyclohexene.306 Surface peroxotitanate 13 is suggested to be the active spe-... 

Allyltitanium ate complexes.8 In contrast to organotitanium compounds, which are aldehyde selective, the chemoselectivity of allyltitanium ate complexes depends on the ligands attached to titanium. The most aldehyde-selective allyltitanium ate complex prepared to date is CH2=CHCH2Ti[OCH(CH3) >].jMgCl (1) which reacts... 

It has been reported recently that organotitanium compounds prepared conveniently from the corresponding Grignard reagents and titanocene chloride cyclize with an appropriately positioned internal alkene in the presence of ethylaluminium chloride (equation 119) ... 

The carbene complexes thus prepared can be employed for the olefination of a variety of carbonyl compounds. The procedure is operationally simple treatment of the thioacetals with titanocene(II) species at ambient temperature for 5-15 min affords the organotitanium species, which are further treated with ketones and aldehydes in the same reaction vessel to give the olefins or dienes (Table 4.12) [96]. 

There has been no recent comprehensive review of this area, although a book on the organometallic chemistry of titanium, zirconium, and hafnium deals, in part, with some of the hydride derivatives (1). In the present review, the first part of the discussion reflects the fact that much of the early work on organotitanium hydrides was, often unknowingly at the time, interwoven with attempts to prepare titanocene, Cp2Ti (Cp = tj3-C5H5). Subsequent sections deal with similar compounds containing an additional metal (e.g., aluminum), miscellaneous titanium hydride compounds, and a summary of the main properties of the above species. 

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