Y-TiCL

Titanium Trichloride. Titanium trichloride [7705-07-9] exists in four different soHd polymorphs that have been much studied because of the importance of TiCl as a catalyst for the stereospecific polymerization of olefins (120,124). The a-, y-, and 5-forms are all violet and have close-packed layers of chlorines. The titaniums occupy the octahedral interstices between the layers. The three forms differ in the arrangement of the titaniums among the available octahedral sites. In a-TiCl, the chlorine sheets are hexagonaHy close-packed in y-TiCl, they are cubic close-packed. The brown P-form does not have a layer stmcture but, instead, consists of linear strands of titaniums, where each titanium is coordinated by three chlorines that act as a bridge to the next Ti The stmctural parameters are as follows ... 

Titanium trichloride is almost always prepared by the reduction of TiCl, most commonly by hydrogen. Other reduciag agents iaclude titanium, aluminum, and 2iac. Reduction begias at temperatures of ca 500°C and under these conditions a-TiCl is formed. The product is cooled quickly to below 450°C to avoid disproportionation to the di- and tetrachlorides. P-TiCl is prepared by the reduction of titanium tetrachloride with aluminum alkyls at low (80°C) temperatures whereas y-TiCl is formed if titanium tetrachloride reacts with aluminum alkyls at 150—200°C. At ca 250°C, the P-form converts to d. d-TiCl is made by prolonged grinding of the d- or y-forms. 

Figure 7. Polymerization of propylene at 60° C. as affected by amount of AIEU used to activate 5 mmole / liter y-TiCL.

Fig. 7. The steady polymerization of ethylene in the presence of a stable Ziegler catalyst (9a). Cyclohexane, 200 ml at 40°C y-TiCls, 0.525 mmole/liter AlEtaCl, 5.25 mmole/liter ethylene, 643 mmHg.

For phenols, the number of chlorines replaced depends in part on the acidity of the phenol. Under mild conditions, phenol or y -nitrophenol displaces only one chlorine from TiCl, whereas -chlorophenol, (9-nitrophenol, -nitrophenol, picric acid, or 2-naphthol gives (ArO)2TiCl2. If the mixtures are heated sufficiently, eg, in refluxing phenol, all four chlorines can be displaced (49—52). 

For values of F > 0.8, the first term n = I) in Eq. (16-96) is generally sufficient. If the controUing resistance is diffusion in the subpai ticles of a bidispersed adsorbent, Eq. (16-96) apphes with /y replacing / p. For a finite fluid volume the solution is ... 

Family of the scientist has presented documentar y materials to Academy of sciences in June 1974. Among them, the most important ar e manuscripts, typewritten copies about 100 scientific works of the scientist and working materials to them. Its includes articles, reports, monographs, the textbooks written by A.K. Babko during last 25 year s working writing-books with extracts, marks on various questions, abstracts of chemical literature responses and reviews on thesis of Ph.D. and doctor s degrees, on ar ticles, books, textbooks. For example, early works Product of solubility , To a technique of definition of strontium in minerals (1940-s), many unpublished works in 1940-1960, etc. 

M. D. Benayoun, A. Y. Eu, and D. A Mzzioti, Invariance of the cumulant expansion under 1-par-ticle unitary transformations in reduced density matrix theory. Chem. Phys. Lett. 387, 485 (2004). 

The most widely studied transition metal is titanium. At various times, all oxidation states of titanium (II, III, IV) have been proposed for the active site of titanium-based initiators. Most of the evidence points to titanium (HI) as the most stereoselective oxidation state, although not necessarily the most active nor the only one [Chien et al., 1982]. (Data for vanadium systems indicate that trivalent vanadium sites are the syndioselective sites [Lehr, 1968].) Initiators based on the a-, y-, and 8-titanium trihalides are much more stereoselective (iso-selective) than those based on the tetrahalide or dihalide. By itself, TiCl2 is inactive as an initiator but is activated by ball milling due to disproportionation to TiCl3 and Ti [Werber et al., 1968]. The overall stereoselectivity is usually a-, y-, 8-TiCl , > TiCL > TiCLj P-TiCl3 [Natta et al., 1957b,c],... 

Heterosubstituted cyclopropanes can be synthesized from appropriate olefins and car-benes. Since cyclopropane resembles olefins in its reactivity and is thus an electron-rich car bo-cycle (p. 76ft). it forms complexes with Lewis acids, e.g. TiCL, and is thereby destabilized This effect is even more pronounced in cydopropanone ketals. If one of the alcohols forming the ketal is a silanol, the ketal is stable and distillable. The O—Si-bond is cleaved by TiCl4 and a d3-reagent is formed. This reacts with a -reagents, e.g. aldehydes or ketals. Various 4-substituted carboxylic esters are available from 1-alkoxy-l-siloxycyclopropanes in this way (E. Nakamura, 1977). If one starts with l-bromo-2-methoxycyclopropanes, the bromine can be selectively substituted by lithium. Subsequent treatment of this reagent with carbonyl compounds yields (2-methoxycyclopropyl)methanols, which can be transformed to /7,y-unsaturated aldehydes (E.J. Corey, 1975B). 

Notes-. hydrothermal treatment, 4dc is the calcination temperature, R is the average radius of TiCL particles, v is the anatase content in a sample (% of TiC>2 by mass), Dp is the average pores diameter, Vs is the total pores volume, Ssp is the specific surface area, and y is the quantum yield of the evolved hydrogen. 

Kim and Somorjai have associated the different tacticity of the polymer with the variation of adsorption sites for the two systems as titrated by mesitylene TPD experiments. As discussed above, the TiCl y/Au system shows just one mesitylene desorption peak which was associated with desorption from low coordinated sites, while the TiCl /MgClx exhibits two peaks assigned to regular and low coordinated sites, respectively [23]. Based on this coincidence, Kim and Somorjai claim that isotactic polymer is produced at the low-coordinated site while atactic polymer is produced at the regular surface site. One has to bear in mind, however, that a variety of assumptions enter this interpretation, which may or may not be valid. Nonetheless it is an interesting and important observation which should be confirmed by further experiments, e.g., structural investigations of the activated catalyst. From these experiments it is clear that the degree of tacticity depends on catalyst preparation and most probably on the surface structure of the catalyst however, the atomistic correlation between structure and tacticity remains to be clarified. 

Deoxygenation of a nitrone. Some years ago Todd and co-workers noted that 1-pyrroline-1-oxides can be obtained by reductive cyclization of a y-nitro ketone. This reaction was used recently in a synthesis of chlonns related to vitamin B,. Thus the nitro ketone 1 on reduction with zinc and acetic acid gives the pyrroline N-oxide 2 in high yield. The N-oxide is stable to triphenylphosphiue or trimethyl phosphite, but is reduced to the imine 3 in high yield by TiCl,. 

Hyuk Im S, Jeong U, Xia Y (2005) Polymer hollow pai ticles witli confrollable holes in tlreir surTaces. Nat Mater 4 671-675. 

The effect of the last monomeric unit of the growing polymer chain on the stereospecificity of the olefin addition has been confirmed by the calculation of the energy of non-bonded interactions and by quantum-chemical calculations (see section 5.2). Corradini et al. have analyzed the possibility of the it-complex formation on the octahedral titanium ions located on different faces of a- andy-TiCla. The possibility of the coordination by both faces of the propylene molecule was studied. It was shown that active centers on the lateral faces of a-TiCls and y-TiClj may be regioselective (primary insertion of propylene) ruther than stereospecific (no predominant CjHs coordination by one face). In the case of active centers located on the edges of the layered modifications of TiClj, CsHg is coordinated with the more accessible (outward) coordination sites of the titanium ions predominantly the polymer chain is then located on the less accessible (inward) octahedral site. This position of the polymer chain results in a fixed orientation of the first carbon-carbon bond of the polymer chain due to its non-bonded interaction with the TiClj surface. This may explain the predominant coordination of propylene molecules by one face and the stereospecificity of such type of active centers. 

In TiClj, each Ti is octahedral in each of the four crystalline modifications identified. The brown, fibrous or jS-form of TiClj is prepared by low temperature reduction of TiCl with trialkylaluminum compounds and consists of (TiClj) polymeric chains composed of confacially linked Ti octahedra. The Ti-Ti separation of 291 pm is similar to that found in elemental Ti, and the RT magnetic moment is half of that found for the a form of TiClj (12.1 x 10 A m ) . Both TiClj andTiClj are antiferromagnetic, with low magnetic moments relative to related monomeric complexes. All three layered forms of TiClj (a, y, S) have Ti-Ti distances greater than 350 pm, and no metal-metal interaction is evident. Reduction of TiCl is the route to reduced Ti chlorides with syntheses of the four TiClj modifications summarized in Table 1 ". Preparations involve collection of the TiClj at low temperature to avoid disproportionation ... 

Conjugate addition. Formation of Y,y-dicyanobutanoic esters from alkylidenemalononitriles and bromoacetic esters is effected by Cp TiCl -Zn (13 examples, 43-93%). 

While selective reaction of aldehydes takes place with the typical Lewis acids TiCL, SnCl4, TMSOTf, etc., lanthanide triflates [Ln(OTf)3] are unique Lewis acids that change the reaction course dramatically aldimine reacts selectively in the coexistence of aldehydes [70]. Among a series of Ln(OTf)3 tested, Yb(OTf)3 exhibited the most prominent chemoselectivity in addition to high chemical yields. The silyl enol ethers of ketones, allyltributylstannane and Me3SiCN are all applicable as chemoselective nucleophiles (Table 2-9). Preferential formation of Yb(OTf)3-aldimine complexes was postulated by C NMR spectral analysis in the presence of PhCHO and Y-benzylideneaniline. 

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