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Rhenium(VII) Oxide
Rhenium(VII) oxide is the inorganic compound with the formula Re2 O7. This yellowish solid is the anhydride of HOReO3. Perrhenic acid, Re2O7·2H2O, is closely related to Re2O7. Re2O7 is the raw material for all rhenium compounds, being the volatile fraction obtained upon roasting the host ore. Structure Solid Re2O7 consists of alternating octahedral and tetrahedral Re centres. Upon heating, the polymer cracks to give molecular (nonpolymeric) Re2O7. This molecular species closely resembles manganese heptoxide, consisting of a pair of ReO4 tetrahedra that share a vertex, i.e., O3Re–O–ReO3. Synthesis and reactions Rhenium(VII) oxide is formed when metallic rhenium or its oxides or sulfides are oxidized at in air. Re2O7 dissolves in water to give perrhenic acid. Heating Re2O7 gives rhenium dioxide, a reaction signalled by the appearance of the dark blue coloration:O. Glemser "Rhenium" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Manganese(VII) Oxide
Manganese(VII) oxide (manganese heptoxide) is an inorganic compound with the formula Mn2O7. This volatile liquid is highly reactive. It is a dangerous oxidizer and was first described in 1860. It is the acid anhydride of permanganic acid. Properties The crystalline form of this chemical compound is dark green. The liquid is green by reflected light and red by transmitted light. It is soluble in carbon tetrachloride, and decomposes when in contact with water. Structure Its solubility properties indicate a nonpolar molecular species, which is confirmed by its structure. The molecules consist of a pair of tetrahedra that share a common vertex. The vertices are occupied by oxygen atoms and at the centers of the tetrahedra are the Mn(VII) centers. The connectivity is indicated by the formula O3Mn−O−MnO3. The terminal Mn−O distances are 1.585 Å and the bridging oxygen is 1.77 Å distant from the two Mn atoms. The Mn−O−Mn angle is 120.7°. Pyrosulfate, pyrophospha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Methylrhenium Trioxide
Methylrhenium trioxide, also known as methyltrioxorhenium(VII), is an organometallic compound with the formula CH3ReO3. It is a volatile, colourless solid that has been used as a catalyst in some laboratory experiments. In this compound, rhenium has a tetrahedral coordination geometry with one methyl and three oxo ligands. The oxidation state of rhenium is +7. Synthesis Methylrhenium trioxide is commercially available. It can be prepared by many routes, a typical method is the reaction of rhenium heptoxide and tetramethyltin: :Re2O7 + (CH3)4Sn → CH3ReO3 + (CH3)3SnOReO3 Analogous alkyl and aryl derivatives are known. Compounds of the type RReO3 are Lewis acids, forming both 1:1 and 1:2 adducts with halides and amines. Uses Methylrhenium trioxide serves as a heterogeneous catalyst for a variety of transformations. Supported on alumina/silica, it catalyzes olefin metathesis at 25 °C. In solution, MTO catalyses for the oxidations with hydrogen peroxide. Terminal al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rhenium Compounds
Rhenium compounds are compounds formed by the transition metal rhenium (Re). Rhenium can form in many oxidation states, and compounds are known for every oxidation state from -3 to +7 except +2, although the oxidation states +7, +6, +4, and +2 are the most common. Rhenium is most available commercially as salts of perrhenate, including sodium and ammonium perrhenates. These are white, water-soluble compounds. Tetrathioperrhenate anion eS4sup>− is possible. Chalcogenides Oxides Rhenium(IV) oxide (or rhenium dioxide) is an oxide of rhenium, with the formula ReO2. This gray to black crystalline solid is a laboratory reagent that can be used as a catalyst. It adopts the rutile structure. It forms via comproportionation: :2 Re2O7 + 3 Re → 7 ReO2 Single crystals are obtained by chemical transport, using iodine as the transporting agent. At high temperatures it undergoes disproportionation. It forms perrhenates with alkaline hydrogen peroxide and oxidizing acids. In m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amide Reduction
Amide reduction is a reaction in organic synthesis where an amide is reduced to either an amine or an aldehyde functional group. Catalytic hydrogenation Catalytic hydrogenation can be used to reduce amides to amines; however, the process often requires high hydrogenation pressures and reaction temperatures to be effective (i.e. often requiring pressures above 197 atm and temperatures exceeding 200 °C). Selective catalysts for the reaction include copper chromite, rhenium trioxide and rhenium(VII) oxide or bimetallic catalyst. Non-catalytic routes to amines Reducing agents able to effect this reaction include metal hydrides such as lithium aluminium hydride, or lithium borohydride in mixed solvents of tetrahydrofuran and methanol. : Noncatalytic routes to aldehydes N,N-disubstituted amides can be reduced to aldehydes by using an excess of the amide: :R(CO)NRR' + LiAlH4 → RCHO + HNRR' With further reduction the alcohol is obtained. Some amides can be reduced to aldehy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbonyl Reduction
In organic chemistry, carbonyl reduction is the organic reduction of any carbonyl group by a reducing agent. Typical carbonyl compounds are ketones, aldehydes, carboxylic acids, esters, and acid halides. Carboxylic acids, esters, and acid halides can be reduced to either aldehydes or a step further to primary alcohols, depending on the strength of the reducing agent; aldehydes and ketones can be reduced respectively to primary and secondary alcohols. In deoxygenation, the alcohol can be further reduced and removed altogether. Metal hydrides based on boron and aluminum are common reducing agents; catalytic hydrogenation is also an important method of reducing carbonyls. Before the discovery of soluble hydride reagents, esters were reduced by the Bouveault–Blanc reduction, employing a mixture of sodium metal in the presence of alcohols. Carboxylic acid derivatives, aldehydes, and ketones to alcohols Hydride reduction Mechanism The reaction mechanism for metal hydride reductio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ethenolysis
In organic chemistry, ethenolysis is a chemical process in which internal olefins are degraded using ethylene () as the reagent. The reaction is an example of cross metathesis. The utility of the reaction is driven by the low cost of ethylene as a reagent and its selectivity. It produces compounds with terminal alkene functional groups (α-olefins), which are more amenable to other reactions such as polymerization and hydroformylation. The general reaction equation is: :\ce + \longrightarrow \ce + \ce Ethenolysis is a form of methylenation, i.e., the installation of methylene () groups. Applications Using ethenolysis, higher molecular weight internal alkenes can be converted to more valuable terminal alkenes. The Shell higher olefin process (SHOP process) uses ethenolysis on an industrial scale. The SHOP α-olefin mixtures are separated by distillation, the higher molecular weight fractions are isomerized by alkaline alumina catalysts in the liquid phase. The resulting ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quickly, very small amounts of catalyst often suffice; mixing, surface area, and temperature are important factors in reaction rate. Catalysts generally react with one or more reactants to form intermediates that subsequently give the final reaction product, in the process of regenerating the catalyst. Catalysis may be classified as either homogeneous, whose components are dispersed in the same phase (usually gaseous or liquid) as the reactant, or heterogeneous, whose components are not in the same phase. Enzymes and other biocatalysts are often considered as a third category. Catalysis is ubiquitous in chemical industry of all kinds. Estimates are that 90% of all commercially produced chemical products involve catalysts at some s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organic Synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one of the most important branches of organic chemistry. There are several main areas of research within the general area of organic synthesis: ''total synthesis'', ''semisynthesis'', and ''methodology''. Total synthesis A total synthesis is the complete chemical synthesis of complex organic molecules from simple, commercially available petrochemical or natural precursors. Total synthesis may be accomplished either via a linear or convergent approach. In a ''linear'' synthesis—often adequate for simple structures—several steps are performed one after another until the molecule is complete; the chemical compounds made in each step are called synthetic intermediates. Most often, each step in a synthesis refers to a separate rea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Siloxide
Siloxides are chemical compounds with the formula R3SiOM, where R is usually an organic group and M is usually a metal cation. Also called silanoates, they are derived by deprotonation of Silanol, silanols. They also arise by the degradation of Siloxane, siloxanes by base: :R3SiOSiR3 + 2 NaOH → 2 R3SiONa + H2O Cleavage of cyclic siloxanes affords siloxides: :(Me2SiO)3 + MeLi → Me3SiOSiMe2OSiMe2OLi These anions function as ligands for metal ions, forming complexes similar to metal alkoxides. Sodium trimethylsiloxide is useful for generating metal complexes by salt metathesis reactions. A very bulky siloxide is tert-butyl3SiO−, sometimes called silox. Siloxides are weaker net donors than alkoxides because pπ-d donation has to compete with Back bonding, backbonding from the oxygen atom into the low-lying Si-C σ* orbitals.{{cite journal , last1=Krempner , first1=Clemens , title=Role of Siloxides in Transition Metal Chemistry and Homogeneous Catalysis , journal= ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hexamethyldisiloxane
Hexamethyldisiloxane (HMDSO) is an organosilicon compound with the formula O i(CH3)3sub>2. This volatile colourless liquid is used as a solvent and as a reagent in organic synthesis. It is prepared by the hydrolysis of trimethylsilyl chloride. The molecule is the protypical disiloxane and resembles a subunit of polydimethylsiloxane. Synthesis and reactions Hexamethyldisiloxane can be produced by addition of trimethylsilyl chloride to purified water: : 2 Me3SiCl + H2O → 2 HCl + O i(CH3)3sub>2 It also results from the hydrolysis of silylethers and other silyl-protected functional groups. HMDSO can be converted back to the chloride by reaction with Me2SiCl2.Röshe, L.; John, P.; Reitmeier, R. “Organic Silicon Compounds” ''Ullmann’s Encyclopedia of Industrial Chemistry''. John Wiley and Sons: San Francisco, 2003. . Hexamethyldisiloxane is mainly used as source of the trimethylsilyl functional group (-Si(CH3)3) in organic synthesis. For example, in the presence of acid c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tetramethyltin
Tetramethyltin is an organometallic compound with the formula (CH3)4Sn. This liquid, one of the simplest organotin compounds, is useful for transition-metal mediated conversion of acid chlorides to methyl ketones and aryl halides to aryl methyl ketones. It is volatile and toxic, so care should be taken when using it in the laboratory. Synthesis and structure Tetramethyltin is synthesized by reaction of the Grignard reagent methylmagnesium iodide, with tin tetrachloride, which is synthesized by reacting tin metal with chlorine gas. :4 CH3MgI + SnCl4 → (CH3)4Sn + 4 MgICl In tetramethyltin, the metal surrounded by four methyl groups in a tetrahedral structure is a heavy analogue of neopentane. Applications Precursor to methyltin compounds Tetramethyltin is a precursor to trimethyltin chloride (and related methyltin halides), which are precursors to other organotin compounds. These methyltin chlorides are prepared via the so-called Kocheshkov redistribution reaction. Thus ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Technetium(VII) Oxide
Technetium(VII) oxide is the chemical compound with the formula Tc2O7. This yellow volatile solid is a rare example of a molecular binary metal oxide, the other examples being RuO4, OsO4, and the unstable Mn2O7. It adopts a centrosymmetric corner-shared bi-tetrahedral structure in which the terminal and bridging Tc−O bonds are 167pm and 184 pm respectively and the Tc−O−Tc angle is 180°. Technetium(VII) oxide is prepared by the oxidation of technetium Technetium is a chemical element with the symbol Tc and atomic number 43. It is the lightest element whose isotopes are all radioactive. All available technetium is produced as a synthetic element. Naturally occurring technetium is a spontaneous ... at 450–500 °C: :4 Tc + 7 O2 → 2 Tc2O7 It is the anhydride of pertechnetic acid and the precursor to sodium pertechnetate: :Tc2O7 + 2 H2O → 2 HTcO4 :Tc2O7 + 2 NaOH → 2 NaTcO4 + H2O References {{Oxides Technetium compounds Transiti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
