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Aluminoxane
Aluminoxanes are organoaluminium compounds with the formula AlOsub>m n o, where R = organic substituent. The following structural rules apply: Al is tetrahedral and O is three-coordinate. Methylaluminoxane is widely used in the polymerization of alkenes. These compounds are typically obtained by the partial hydrolysis of trialkylaluminium compounds. Aluminoxanes serve as activators for catalytic olefin polymerisation, such as the Ziegler–Natta catalyst. They also serve a function as scavenger for impurities (e.g. water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...) in reactions that are sensitive to these impurities. Aluminoxane, appearing as white solids, are encountered as solutions. References Aluminium compounds Organometallic compounds Coordination complexes [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Methylaluminoxane
Methylaluminoxane, commonly called MAO, is a mixture of organoaluminium compounds with the approximate formula (Al(CH3)O)''n''. It is usually encountered as a solution in (aromatic) solvents, commonly toluene but also xylene, cumene, or mesitylene, Used in large excess, it activates precatalysts for alkene polymerization. Preparation and structure MAO is prepared by the incomplete hydrolysis of trimethylaluminium, as indicated by this idealized equation :''n'' Al(CH3)3 + ''n'' H2O → (Al(CH3)O)''n'' + 2''n'' CH4 Diverse mechanisms have been proposed for the formation of MAO. Well defined analogues of MAO can be generated with tert-butyl substituents. Uses MAO is well known as catalyst activator for olefin polymerizations by homogeneous catalysis. In traditional Ziegler–Natta catalysis, supported titanium trichloride is activated by treatment with trimethylaluminium (TMA). TMA only weakly activates homogeneous precatalysts, such as zirconacene dichloride. In the mid- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organoaluminium Compound
Organoaluminium chemistry is the study of compounds containing bonds between carbon and aluminium. It is one of the major themes within organometallic chemistry. Illustrative organoaluminium compounds are the dimer trimethylaluminium, the monomer triisobutylaluminium, and the titanium-aluminium compound called Tebbe's reagent. The behavior of organoaluminium compounds can be understood in terms of the polarity of the C−Al bond and the high Lewis acidity of the three-coordinated species. Industrially, these compounds are mainly used for the production of polyolefins. History The first organoaluminium compound (C2H5)3Al2I3 was discovered in 1859. Organoaluminium compounds were, however, little known until the 1950s when Karl Ziegler and colleagues discovered the direct synthesis of trialkylaluminium compounds and applied these compounds to catalytic olefin polymerization. This line of research ultimately resulted in the Nobel Prize to Ziegler. Structure and bonding Aluminium( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trialkylaluminium Compound
Organoaluminium chemistry is the study of compounds containing bonds between carbon and aluminium. It is one of the major themes within organometallic chemistry. Illustrative organoaluminium compounds are the dimer trimethylaluminium, the monomer triisobutylaluminium, and the titanium-aluminium compound called Tebbe's reagent. The behavior of organoaluminium compounds can be understood in terms of the polarity of the C−Al bond and the high Lewis acidity of the three-coordinated species. Industrially, these compounds are mainly used for the production of polyolefins. History The first organoaluminium compound (C2H5)3Al2I3 was discovered in 1859. Organoaluminium compounds were, however, little known until the 1950s when Karl Ziegler and colleagues discovered the direct synthesis of trialkylaluminium compounds and applied these compounds to catalytic olefin polymerization. This line of research ultimately resulted in the Nobel Prize to Ziegler. Structure and bonding Aluminium ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ziegler–Natta Catalyst
A Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, is a catalyst used in the synthesis of polymers of 1-alkenes (alpha-olefins). Two broad classes of Ziegler–Natta catalysts are employed, distinguished by their solubility: * Heterogeneous supported catalysts based on titanium compounds are used in polymerization reactions in combination with cocatalysts, organoaluminum compounds such as triethylaluminium, Al(C2H5)3. This class of catalyst dominates the industry. * Homogeneous catalysts usually based on complexes of the group 4 metals titanium, zirconium or hafnium. They are usually used in combination with a different organoaluminum cocatalyst, methylaluminoxane (or methylalumoxane, MAO). These catalysts traditionally contain metallocenes but also feature multidentate oxygen- and nitrogen-based ligands. Ziegler–Natta catalysts are used to polymerize terminal alkenes (ethylene and alkenes with the vinyl double bond): :''n'' CH2=CHR → − H2−CHRsub>' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scavenger (chemistry)
A scavenger in chemistry is a chemical substance added to a mixture in order to remove or de-activate impurities and unwanted reaction products, for example oxygen, to make sure that they will not cause any unfavorable reactions. Their use is wide-ranged: * In atmospheric chemistry, the most common scavenger is the hydroxyl radical, a short-lived radical produced photolytically in the atmosphere. It is the most important oxidant for carbon monoxide, methane and other hydrocarbons, sulfur dioxide, hydrogen sulfide, and most of other contaminants, removing them from the atmosphere. * In molecular laser isotope separation, methane is used as a scavenger gas for fluorine atoms. * Hydrazine and ascorbic acid are used as oxygen scavenger corrosion inhibitors. * Tocopherol and naringenin are bioactive free radical scavengers that act as antioxidants; synthetic catalytic scavengers are their synthetic counterparts * Organotin compounds are used in polymer manufacture as hydrochloric acid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a solvent). It is vital for all known forms of life, despite not providing food, energy or organic micronutrients. Its chemical formula, H2O, indicates that each of its molecules contains one oxygen and two hydrogen atoms, connected by covalent bonds. The hydrogen atoms are attached to the oxygen atom at an angle of 104.45°. "Water" is also the name of the liquid state of H2O at standard temperature and pressure. A number of natural states of water exist. It forms precipitation in the form of rain and aerosols in the form of fog. Clouds consist of suspended droplets of water and ice, its solid state. When finely divided, crystalline ice may precipitate in the form of snow. The gaseous state of water is steam or water vapor. Water co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aluminium Compounds
Aluminium (or aluminum) combines characteristics of pre- and post-transition metals. Since it has few available electrons for metallic bonding, like its heavier group 13 congeners, it has the characteristic physical properties of a post-transition metal, with longer-than-expected interatomic distances.Greenwood and Earnshaw, pp. 222–4 Furthermore, as Al3+ is a small and highly charged cation, it is strongly polarizing and aluminium compounds tend towards covalency;Greenwood and Earnshaw, pp. 224–7 this behaviour is similar to that of beryllium (Be2+), an example of a diagonal relationship.Greenwood and Earnshaw, pp. 112–3 However, unlike all other post-transition metals, the underlying core under aluminium's valence shell is that of the preceding noble gas, whereas for gallium and indium it is that of the preceding noble gas plus a filled d-subshell, and for thallium and nihonium it is that of the preceding noble gas plus filled d- and f-subshells. Hence, aluminium does not suf ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organometallic Compounds
Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and sometimes broadened to include metalloids like boron, silicon, and selenium, as well. Aside from bonds to organyl fragments or molecules, bonds to 'inorganic' carbon, like carbon monoxide (metal carbonyls), cyanide, or carbide, are generally considered to be organometallic as well. Some related compounds such as transition metal hydrides and metal phosphine complexes are often included in discussions of organometallic compounds, though strictly speaking, they are not necessarily organometallic. The related but distinct term " metalorganic compound" refers to metal-containing compounds lacking direct metal-carbon bonds but which contain organic ligands. Metal β-diketonates, alkoxides, dialkylamides, and metal phosphine complexes are repres ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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