Titanium Experimental Procedure

This series of reagents is characterized by the use of metals under the appropriate conditions. In this regard, a mixture of zinc dust and titanium tetrachloride in ether provided a useful synthesis of vinyl sulphides43, with the possibility of further substitution alpha to the sulphur atom, as outlined in equation (16). The reaction is easy to carry out and gave yields of 49 to 87%, although the authors do not provide much detail of their experimental procedure and of the purity (chemical or stereochemical) of their products. 

Annual Volume 71 contains 30 checked and edited experimental procedures that illustrate important new synthetic methods or describe the preparation of particularly useful chemicals. This compilation begins with procedures exemplifying three important methods for preparing enantiomerically pure substances by asymmetric catalysis. The preparation of (R)-(-)-METHYL 3-HYDROXYBUTANOATE details the convenient preparation of a BINAP-ruthenium catalyst that is broadly useful for the asymmetric reduction of p-ketoesters. Catalysis of the carbonyl ene reaction by a chiral Lewis acid, in this case a binapthol-derived titanium catalyst, is illustrated in the preparation of METHYL (2R)-2-HYDROXY-4-PHENYL-4-PENTENOATE. The enantiomerically pure diamines, (1 R,2R)-(+)- AND (1S,2S)-(-)-1,2-DIPHENYL-1,2-ETHYLENEDIAMINE, are useful for a variety of asymmetric transformations hydrogenations, Michael additions, osmylations, epoxidations, allylations, aldol condensations and Diels-Alder reactions. Promotion of the Diels-Alder reaction with a diaminoalane derived from the (S,S)-diamine is demonstrated in the synthesis of (1S,endo)-3-(BICYCLO[2.2.1]HEPT-5-EN-2-YLCARBONYL)-2-OXAZOLIDINONE. 

Experimental Procedure 3.2.2. Cyclopropanation with a Titanium Carbene Complex (E)-l-Hexyl-2-(2-phenylethenyl)cyclopropane [33]... 

Apart from the tandem metathesis/carbonyl o[efination reaction mediated by the Tebbe reagent (Section 3.2.4.2), few examples of the use of stoichiometric amounts of Schrock-type carbene complexes have been reported. A stoichiometric variant of cross metathesis has been described by Takeda in 1998 [634]. Titanium carbene complexes, generated in situ from dithioacetals, Cp2TiCl2, magnesium, and triethylphosphite (see Experimental Procedures 3.2.2 and 3.2.6), were found to undergo stoichiometric cross-metathesis reactions with allylsilanes [634]. The scope of this reaction remains to be explored. 

Even at high styrene incorporation, the co-polymers are formed by ethylene blocks and isolated styrene units.627 Half-sandwich titanium complexes such as 35-39 have also been reported to be active in the ethylene/styrene co-polymerization. The performance of the MAO-activated complex 35 is highly dependent on the Al/Ti ratio. At a ratio of 100, a co-polymer composed of polyethylene blocks with essentially isolated styrene units could be fractionated from the homopolymers. By contrast, at Al/Ti ratios of 1000, a co-polymerization at the same feed ratio resulted in the production of only homopolymers, or co-polymers composed of long PE and sPS blocks at most.628 Subsequent 13C NMR analysis of the co-polymers obtained at 20°C indicated that up to 36 mol% of styrene was incorporated.629 However, under very similar conditions, only formation of the homopolymers was reported.630,631 This may be reasonable since catalytic systems 35/MAO and 36/MAO give rise to several active species with different catalytic properties. Thus, remarkably different results can be obtained with small differences in the experimental procedure. 

Although it was stated that allyltrialkylsilanes were unsuccessful in the Lewis acid mediated addition to acryloylFp complexes, a stereoselective procedure has been developed for [3 + 2] cycloadditions of allylsilanes to enones10. The reaction occurs in the presence of titanium(IV) chloride (TiCl4) as Lewis acid and the single cycloaddition product formed is the m-fused eyclopentane with the trimethylsilyl group in the endo orientation. The reaction appears to follow a similar pathway to the previous process although, as yet, yields and experimental procedures have not been documented. 

Typical Experimental Procedures for Generation of Titanium Enolates... 

Much effort has been devoted to the optimization of the polyesterification reaction. For instance, different types of monomeric precursors structurally related to succinic acid (e.g., dimethyl succinate or succinic anhydride) were used. Different kinds of catalysts (e.g., phenolates, titanium alkoxides, tin octanoates) at different concentrations were studied. Different reaction temperatures (130-190 °C) were reached and different procedures for water elimination (vacuum drying under different conditions or toluene distillation) were adopted. Experimental results obtained showed that the use of different catalysts and different monomer precursors (succinic acid derivatives) did not significantly alter the polymerization kinetics or yield, and for this reason, they were abandoned. The procedure finally adopted is summarized below. 

Several authors have addressed the determination of the optical properties of aqueous titanium dioxide suspensions in the context of photoreactor modeling (Brandi et al., 1999 Cabrera et al., 1996 Cured et al., 2002 Salaices et al., 2001, 2002 Satuf et al., 2005 Yokota et al., 1999). Among the determined properties are extinction, scattering, and absorption coefficients, as well as the asymmetry parameter of the scattering phase function. In general the procedures involve fitting of a radiative transfer model to the experimental results for reflectance and transmittance of radiation. 

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