0-TiCla

Crystal structure of solids. The a-crystal form of TiCla is an excellent catalyst and has been investigated extensively. In this particular crystal form of TiCla, the titanium ions are located in an octahedral environment of chloride ions. It is believed that the stereoactive titanium ions in this crystal are located at the edges of the crystal, where chloride ion vacancies in the coordination sphere allow coordination with the monomer molecules. 

LiAlH4. When the substrate is an allylic alcohol, the reaction is not regiospecilic, but a mixture of normal coupling and allylically rearranged products is found. A free-radical mechanism is involved. The TiCla—LiAlUj reagent can also convert... 

The McMurry reaction (the reductive dimerization of carbonyl compounds giving olefins after treatment with the low-valent titanium reagents TiCla/Mg and TiCla/Zn in THF at 40°C) (CR891513) is a key step in the synthesis of photochromic cyclopentene derivatives. Later, it has been shown that TiCU, which is easier to handle than TiCls, can be used. The cyclization products are formed in 50-60% yields (98S1092,03EJO155). The advantages of this method are that the reactions can be scaled and inexpensive starting materials can be used. 

Aliphatic ketones reductively dimerize upon treatment with TiCl3 (reported as TiCla in the literature (vide supra)) and zinc in the presence of pivalonitrile in dichloromethane (Equation (14)). In the reaction, addition of pivaloni-trile produces a dramatic accelerating effect. 

PiQ. 12. Dependency of the Izn index of the adjustment period, on the reciprocal of the propylene polymerization rate in steady. state conditions. Tests performed with unground a-TiCla (sample A). 

Fig. 20. Log of propylene polymerization rate in steady-state conditions as function of l/T (pciH< 1,500 mm. Hg, a-TiCla sample A).

The a-TiCla treated in this way gives reproducible results for the kinetic behavior, the molecular weights, and the steric composition of the polymer. 

Fig. 26. Specific radioactivity (and corresponding values of —CjHj mol. per mol. of polymerized CaH ) of the atactic polypropylene fraction, as function of the square root of the a-TiCla amount in the catalytic system. (Tests performed with K -labeled AKCjHsla at t = 70°, pcia, = 450 mm. Hg, ground a-TiCli sample A.)...

It must be remembered that several compounds or soluble complexes of titanium which, alone, and also in the presence of AIU3, do not polymerize the propylene, can effect the polymerization rate of the catalytic systems containing a-TiCla and the molecular weight of the polymers obtained (10, 11). 

Polymerization of Propylene to Isotactic Polymer with a-TiCla-Al(C2H6)3-n-/fepCatalytic System. Tests Performed at 70°, 950 mm. Hg pciHi, [CaHa] = 0.41 mol./I. 

Number of Conventional Active Centers in a Sample of Ground a-TiCla, Determined by Adsorption Tests of C-Labeled Alkylaluminum Compounds, Followed by Polymerization of Propylene. (a-TiCli-Ground Sample A 0.5 g. Alkylaluminum Compound 0.5 cm. Solvent 30 cm. ). 

Propylene Polymerization with the a-TiCl3-Al(C2H6)a-n-ffe )Catalytic System. Comparison between Two Samples of a-TiCla Sample A Ti/Cl = 2.96 (Initial Sizes of the Crystals <2 y. Sample B Ti/Cl = 3.00 (Initial Sizes of the Crystals within 1 to 200 fi—See fig. 7). 

Fig. 36. Approximate values of the mean lifetime of the chains of polypropylene growing on the active centers of a catalytic system a-TiCla-AUCjHsls-n-heptane at 70° and 950 mm. Hg pcm,. (The calculations were performed assuming the number of conventional active centers C = 1 mol. per 100 mol. of ground a-TiCU sample A and x = 95hJ .)...

The number of isotactic chains growing at the same time, was assumed as being equal to the number of conventional active centers 1 X 10 mol./ mol. of a-TiCla. The results obtained are plotted in Fig. 36. 

If iron is present, a ferric thiocyanate complex will form and the soln will change from light blue to deep red. Back-titrate the ferric thiocyanate complex with 0.2N TiCla soln from the same buret untii the light blue color reappears. Determine the mis of Ti Cl3 soln... 

Danusso s conclusion that the monomer is only weakly polarized in the complex must certainly be true for the stereospecific coordinated anionic catalysts, such as AlR3/TiCl3, which are used for a-olefin polymerization. If it were not so, then rapid termination would take place through hydride abstraction by the strongly polarized monomer. This appears to be the case when strongly acidic alkyl metal chlorides are used in catalysts. For example, low molecular weight polypropylene oils are obtained with RAlCl2/TiCla catalyst (308) and polyethylene oils are obtained with RjA Cla/TiC catalysts in reactive alkyl halide solvents (309). 

The precipitate prepared at 80° C. at about the stoichiometric AlEta/TiCE ratio of H has a reddish-brown color, and, according to x-ray analysis, consists of 3-TiCla, whereas the product prepared at 170° C. at the same Al/Ti ratio has a purple color and the structure of 7-TiCE (4, 24, 26). Analysis further showed that the TiCE thus formed contains an appreciable amount of aluminum compounds, and if prepared at 80° C., also some ethyl groups. These aluminum compounds, which apparently consist mainly of A1CE, and possibly of some AEEtCE, are taken up in the crystal lattice of the TiCE since they could not be removed by washing and hardly show up in the x-ray diagram (4, 24). About one out of every six titanium atoms is replaced by aluminum in the 80° C. solid reaction product (4), whereas in the 170° C. product, this... 

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