Stereospecificity of catalytic systems MCl3AlEt3 in propylene polymerization reactions

Stereoregularity parameters are measured by different i.r. methods for samples of polypropylene, obtained with catalytic systems MCl₃AlEt₃ (M  Ti, V, Cr and Fe). The degree of stereoregularity of the fractions of these polymers insoluble in boiling n-heptane and n-octane decreases in the order α-TiCl₃ ? δ-TiCl₃ > CrCl₃ > VCl₃ > FeCl₃ which is close to the order of the decrease of MCl and MM distances in the MCl₃ lattices.     

Stereospecific polymerization of propylene with group 4 ansa-fluorenylamidodimethyl complexes

Group 4 [η¹:η³-tert-butyl(dimethylfluorenylsilyl)amido]dimethyl complexes [t-BuNSiMe₂Flu]MMe₂ (M = Ti, 1; Zr, 2; Hf, 3) were synthesized in a one-pot synthesis starting from the ligand, MeLi and MCl₄ (M = Ti, Zr, Hf), respectively. The structures of these complexes were determined by X-ray crystallography and the results obtained revealed that the fluorenyl ligand coordinates to center metal in a η³-manner irrespective of center metal employed. Propylene polymerization was conducted at 0 or 20 °C in toluene by 1–3 combined with dried methylaluminoxane (MAO), which was prepared from the toluene solutions of MAO by removing free trialkylaluminiums, and HNMe₂PhB(C₆F₅)₄ in the presence of triisobutylaluminium. The 1–dried MAO system gave the polymer with syndiotactic triad (rr) of 63% at 0 °C, whereas 2 and 3 did not give any polymer in the same conditions. The 2–dried MAO system gave the polymer with the highest syndiotacticity (rr = 97%) at 20 °C, although the activity was low. The 3–dried MAO system did not give any polymer even at 20 °C. When HNMe₂PhB(C₆F₅)₄ was used in place of dried MAO at 20 °C, 1 gave almost atactic polymer, while 2 and 3 gave highly syndiotactic one (rr > 90%). These results indicate that the catalytic performance strongly depended on the center metal of the ansa-fluorenylamidodimethyl complexes as well as cocatalysts employed.     

Studies of Ziegler-type catalysts for the polymerization of ethylene and propylene II The polymerization of ethylene with VOCl3-Et3Al2Cl3 (chlorinated activator) catalysts

VOCl₃-Et₃Al₂C1₃(chlorinated activator) catalysts have been employed for the polymerization of ethylene at T between 15 and 85° in n-hexane. Using butylperchlorocrotonate as the activator, the following catalyst efficiencies (g polymerization, hr, atmosphere ethylene in the cap gas) were achieved: 10^6,1 MFI = 0-00; 10^5,8, e.g. MFI = 1 0 (with 9 per cent H₂ present in the cap gas) and 10^6–9 MFI = 0?4 (with 44 mmole/1 styrene in the hexane medium). Reactions between the aluminium alkyl and the activator molecules produced other chlorinated species of high average activator effectiveness. The catalyst system could be reactivated by further additions of Et₃Al₂Cl₃. The minimum value of the polymerization propagation rate constant is estimated to be 10¹²²?6x10,461 cm³/mole sec.     

Aromatization of propylene and butadiene over MoO3?SiO2 and WO3?SiO2 catalysts

The activity of various MoO₃–SiO₂ and WO₃–SiO₂ catalysts for the aromatization of propylene and butadiene has been investigated. The results obtained show a comparatively high aromatization activity of the catalysts for propylene to benzene and toluene. The direct conversion of butadiene to ethylbenzene, using WO₃ on acid treated silica, is considered to be an alternative reaction pathway to the known metathesis step to ethylene and benzene.

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MoO₃–SiO₂ WO₃–SiO₂ . . , WO₃ .

     

Thermoanalytical study of the systems PbCO3SrCO3 and PbCO3CaCO3

This study concerns the coprecipitation of the PbCO₃SrCO₃ and PbCO₃CaCO₃ systems in different molar relationships carried out under the same experimental conditions as the PbCO₃BaCO₃ system studied previously. The precipitates obtained were studied by chemical analysis, thermogravimetry, differential thermal analysis and X-ray powder diffraction. It has been established that, for the PbCO₃SrCO₃ system, solid solutions are obtained under all the different experimental conditions and for the PbCO₃CaCO₃ system the precipitates obtained are always mixtures of PbCO₃ and CaCO₃.     

Interaction of propylene with a V2O5/Al2O3 catalyst

IR-spectroscopic studies indicate that on the oxidized surface of V₂O₅/Al₂O₃ catalysts propylene interacts mainly with Brönsted acid centers to form an alcoholate type complex transforming into acetone. On the reduced surface propylene is stabilized as a -complex of V³⁺ and V⁴⁺ ions.

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- , V₂O₅/Al₂O₃ , . - V³⁺ V⁴⁺.

     

Stereospecific synthesis of leukotriene B4 (LTB4)

A stereospecific and chirally economical synthesis of LTB₄ starting from 2-deoxy-D-ribose is reported as part of a comprehensive and efficient approach to the Leukotrienes (A, B, C, D, E). The process includes a novel approach to chiral dienic synthons.     

The kinetics of polymerization of cyclopentene by WCl6/AliBu3 catalyst

The kinetics of the polymerization of cyclopentene by WCl₆/AliBu₃ catalysts have been studied and the factors controlling the reproducibility of the rate of polymerization have been ascertained. A significant dependence of the rate of polymerization on the time between the additions of WCl₆ and AliBu₃ was observed. The dependence of the catalyst activity r,i this time delay suggested that WCl₆ reacted with cyclopentene to produce an unstable species (W₁) that could react with AliBu₃ to produce a catalytically active species (W₁¹) or that could react further with cyclopentene to produce another species W₂ that in turn would react with AliBu₃ to produce a much less active catalyst W₂¹. The detailed study of the kinetics of polymerization under controlled conditions suggested a kinetic chain mechanism initiated by two catalyst species; mechanism of polymerization based on the carbene system is suggested.     

Formation mechanism and structure of compounds catalytically active in propylene dimerization and formed in Pd(acac)2?PR3?BF3OEt2 systems

The interaction between the components of catalytic Pd(acac)₂–PR₃–BF₃OEt₂ systems dimerizing propylene to linear hexenes with 59 % selectivity, has been studied by UV and¹H NMR spectroscopy methods. Formation mechanism of catalytically active [R₃P–Pd–H]⁺BF ₄ ^– compounds is suggested.

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, ¹ Pd(acac)₂–PR₃–BF₃OEt₂, 59%, [R₃P–Pd–H]⁺BF ₄ ^– .

     

LiCl-LiBr-LiVO3 and LiCl-LiBr-Li2MoO4 ternary systems

Phase equilibria in the LiCl-LiBr-LiVO₃ and LiCl-LiBr-Li₂MoO₄ ternary systems have been investigated by differential thermal analysis. The following compositions have been revealed (mol %): eutectic in the LiCl-LiBr-LiVO₃ system (18.0% LiCl, 72.0% LiBr, and 10.0% LiVO₃) with a melting point of 464°C and specific enthalpy of melting of 213 kJ/kg, and a minimum in the LiCl-LiBr-Li₂MoO₄ system (27.0% LiCl, 48.0% LiBr, and 25.0% Li₂MoO₄) with a melting point of 444°C. The investigation of ternary systems including salts of alkali metals is of practical interest for chemical industry and metallurgy, where salt mixtures are used as fused electrolytes and heat carriers. Original Russian Text ? T.V. Gubanova, E.I. Frolova, I.K. Garkushin, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 7, pp. 1220–1223.     

Kinetics of C2H4 polymerization on reduced V2O5/Al2O3 catalyst

Kinetic study of C₂H₄ polymerization on reduced V₂O₅/Al₂O₃ catalysts revealed that the rate equation can be expressed as V=k exp (-Y) K_aP_E/(1+K_aP_E) in the temperature range of –20 to 70°C. The deactivation constant, , was found to have a close relation with the yield and molecular weight of the polymer. C₂H₄ V₂O₅/Al₂O₃ –20 +70°C : V_p=k·exp(-Y_p)·K_aP_e/(1+K_aP_e). .     

Phase equilibrium relations in the binary systems LiPO3CeP3O9 and NaPO3CeP3O9

The LiPO₃CeP₃O₉ and NaPO₃CeP₃O₉ systems have been investigated for the first time by DTA, X-ray diffraction, and infrared spectroscopy. Each system forms a single 1:1 compound. LiCe(PO₃)₄ melts in a peritectic reaction at 980°C. NaCe(PO₃)₄ melts incongruently, too, at 865°C. These compounds have a monoclinic unit cell with the parameters: a = 16.415(6), b = 7,042(6), c = 9.772(7)Å; β = 126.03(5)°; Z = 4; space group $\text{C}{}_2\text{c}$ for LiCe (PO₃)₄; and a = 9.981(4), b = 13.129(6), c = 7.226(5) Å, β = 89.93(4)°, Z = 4, space group $\text{P2}{}_1\text{n}$ for NaCe(PO₃)₄. It is established that both compounds are mixed polyphosphates with chain structure of the type |M^I_IM^III_II (PO₃)₄|_∞M^I_I: alkali metal, M^III_II: rare earth.     

Cu-ZnO-Al2O3复合催化剂上甘油选择氢解合成丙二醇

分别采用均匀共沉淀法、沉积-沉淀法和传统的共沉淀法制备了3种具有相似组成的Cu-ZnO-A1₂O₃催化剂（CZA-HP,CAZ-DP和CZA-CP）Ε同时还采用均匀共沉淀法制备了Cu-ZnO催化剂（CZ-HP）以用于比较.X射线衍射表征结果表明,以上方法制备的Cu-Zn-Al碱式碳酸盐前体中Cu²⁺,Zn²⁺和Al³⁺的混合均匀程度的顺序为CZA-DP3+分散程度的提高和A1₂O₃与ZnO的紧密接触使得Cu-ZnO-A1₂O₃催化剂中金属Cu和ZnO具有更小的粒径.但ZnO-A1₂O₃间紧密接触也阻隔了Cu-ZnO-A1₂O₃催化剂中金属Cu与ZnO之间的相互作用.因此A1₂O₃的添加使得CZA-HP样品上的Cu粒子表现出最强的氧化还原能力.在473 K和6.0 MPa H₂的反应条件下,以上三种Cu-ZnO-A1₂O₃催化剂均高选择性地催化甘油氢解为丙二醇（30%甘油转化率下的选择性>90%）.Cu-ZnO-A1₂O₃催化剂表面单位Cu原子的本征活性顺序为CZA-DP2O₃的添加还显著地抑制了Cu粒子在反应过程中的聚集,提高了催化剂的稳定性.经6次循环使用后,CZ-HP中Cu粒子的粒径从13.2增至45.2 nm,活性相应下降了45%:而CZA-HP中Cu粒子的粒径从8.3增至19.0 nm,活性仅下降了10%.     

稀土催化体系Nd(napb)_3-AlEt_2Cl-Al(i-Bu)_3对双烯烃聚合的活性

分析了催化剂Nd(naph)_3-AlEt_2Cl-Al(i-Bu)_3三组分反应产物的组成,用动力学方法研究了其催化异戊二烯聚合的活性。催化剂各组分的配比及制备方法对其活性及利用率有显著影响。催化剂的利用率随它使用时浓度的减小而增大,最后达到恒定链终止反应由体系中过量的AlEt_2Cl吸附于活性体而发生。     

Garnet-perovskite transformations in the Sm2O3Ga2O3 and Gd2O3Ga2O3 systems

The effect of heating garnet melts to various temperatures has been investigated. The previously reported decomposition of the garnet phase due to loss of Ga₂O₃ was corroborated. However, it was also observed that when gallium oxide loss is prevented and the maximum temperature of the melt exceeds a critical value, phase separation of garnet to perovskite and β-gallium oxide occurs:

$\text{RE}{}_3\text{Ga}{}_5\text{O}{}_{12}\text{?3RE}\text{GaO}{}_3\text{+}\text{Ga}{}_2\text{O}{}_3$

.The reverse reaction will occur by reheating the two-phase mixture to the garnet melting point.     

Synthesis and ethylene polymerization behavior of {MeB(3-Ph-pyrazolyl)3}TiCl3

The new methyl-tris(pyrazolyl)borate reagents Li[MeTp^Ph] (1) [MeTp^Ph]⁻ = MeB(3-Ph-pyrazolyl)₃⁻) and Tl[MeTp^Ph] (2) react with TiCl₄ to afford (MeTp^Ph)TiCl₃ (3) in 77% and 81% yield respectively. 2 reacts with ZrCl₄ and HfCl₄ to yield mixtures of products. The reaction of 1 with TiCl₃(THF)₃ proceeds with B-N bond cleavage to afford TiCl₃(3-Ph-pyrazole)(THF)₂ as the major product (30%). The reaction of 3 with MeLi (3 equiv) yields 1 (60%) and reduced Ti species, via apparent displacement of [MeTp^Ph]⁻ and generation of unstable TiCl₄Me_4−x species. Under MAO activation conditions (MAO = methylalumoxane), 3 polymerizes ethylene to linear polyethylene. 3/MAO is significantly more active in ethylene polymerization than the hydrido-tris(pyrazolyl)borate analogue {HB(3-Ph-pyrazolyl)₃}TiCl₃/MAO.     

Stereospecific synthesis of two metabolites of LTB4

The stereospecific synthesis of the recently identified metabolites of LTB₄ 1: 5(S),12(R),20-trihydroxy-6-cis,8,10-trans,14-cis-eicosatetraenoic acid 2 and 5(S),12(R),dihydroxy-6-cis,8,10-trans,14-cis-eicosatetraen-1,20-dioic acid 3, via the synthon 4 has been accomplished; identity of synthetic and natural products has been confirmed.     

Catalytic and physico-chemical properties of a doped MoO3/SiO2 catalyst used in propylene oxidation

Oxygen chamisorbed at low temperature on a doped MoO₃/SiO₂ catalyst has been used to evaluate the dispersity of molybdena. The time on stream seems to increase considerably the dispersity of active phase, also observed by Scanning Electron Microscopt (SEM). IR spectroscopy and X-Ray Diffraction (XRD) analysis have shown interaction between Te and Mo oxides. A weak complex of propylene on the surface, and carboxylate species on the oxidized surface have been detected.

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, MoO₃ SiO₂ , . , . - . - .

     

Crystallographic shear in the Nb2O5WO3 and Ta2O5WO3 systems

Crystallographic shear (CS) phases occurring in the Nb₂O₅WO₃ and Ta₂O₅WO₃ systems near to WO₃ were characterized by X-ray diffraction and high-resolution transmission electron microscopy. The Nb₂O₅WO₃ samples were heated at 1600K. They contained ordered {104} and {001} CS planes and wavy CS which were composed of intergrowths of {104} and {001} CS segments. The composition range over which the {104} CS series extended was from (Nb,W)O_2.954 i.e., (Nb,W)₆₅O₁₉₂, to (Nb,W)O_2.942, i.e., (Nb,W)₅₂O₁₅₃. The composition range over which the {001} CS series extended was from (Nb,W)O_2.9375, i.e., (Nb,W)₁₆O₄₇ to (Nb,W)O_2.875, i.e., (Nb,W)₈O₂₃. The Ta₂O₅WO₃ samples were prepared at 1593, 1623, and 1672K. At lower temperatures ordered {103} CS phases were found, with a composition range extending between (Ta,W)O_2.960, i.e., (Ta,W)₅₀O₁₄₈, to (Ta,W)O_2.944, i.e., (Ta,W)₃₆O₁₀₆. At 1673K ordered {103} CS phases occurred, as did wavy CS composed of intergrowths of {103} and {104} CS segments.