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Lithium Bis(trimethylsilyl)amide
Lithium bis(trimethylsilyl)amide is a lithiated organosilicon compound with the formula . It is commonly abbreviated as LiHMDS or Li(HMDS) (lithium hexamethyldisilazide - a reference to its conjugate acid HMDS) and is primarily used as a strong non-nucleophilic base and as a ligand. Like many lithium reagents, it has a tendency to aggregate and will form a cyclic trimer in the absence of coordinating species. Preparation LiHMDS is commercially available, but it can also be prepared by the deprotonation of bis(trimethylsilyl)amine with ''n''-butyllithium. This reaction can be performed ''in situ''. : Once formed, the compound can be purified by sublimation or distillation. Reactions and applications As a base LiHMDS is often used in organic chemistry as a strong non-nucleophilic base. Its conjugate acid has a p''K''a of ~26, making it is less basic than other lithium bases, such as LDA (p''K''a of conjugate acid ~36), but it is more sterically hindered and hence less nu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hexane
Hexane () is an organic compound, a straight-chain alkane with six carbon atoms and has the molecular formula C6H14. It is a colorless liquid, odorless when pure, and with boiling points approximately . It is widely used as a cheap, relatively safe, largely unreactive, and easily evaporated non-polar solvent, and modern gasoline blends contain about 3% hexane. The term ''hexanes'' refers to a mixture, composed largely (>60%) of hexane, with varying amounts of the isomeric compounds 2-methylpentane and 3-methylpentane, and, possibly, smaller amounts of nonisomeric C5, C6, and C7 (cyclo)alkanes. These ''hexanes'' are cheaper than pure hexane and are often used in large-scale operations not requiring a single isomer (e.g., as cleaning solvent or for chromatography). Isomers Uses In industry, hexanes are used in the formulation of adhesive, glues for shoes, leather products, and roofing. They are also used to extract cooking oils (such as canola oil or soy oil) from seeds, for c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Distillation
Distillation, or classical distillation, is the process of separation process, separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the heating of solid materials to produce gaseous products (which may condense into liquids or solids); this may involve chemical changes such as destructive distillation or Cracking (chemistry), cracking. Distillation may result in essentially complete separation (resulting in nearly pure components), or it may be a partial separation that increases the concentration of selected components; in either case, the process exploits differences in the relative volatility of the mixture's components. In Chemical industry, industrial applications, distillation is a unit operation of practically universal importance, but is a physical separation process, not a chemical reaction. An installation used for distillation, especially of distilled ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sulfuryl Chloride
Sulfuryl chloride is an inorganic compound with the formula SO2Cl2. At room temperature, it is a colorless liquid with a pungent odor. Sulfuryl chloride is not found in nature, as can be inferred from its rapid hydrolysis. Sulfuryl chloride is commonly confused with thionyl chloride, SOCl2. The properties of these two sulfur oxychlorides are quite different: sulfuryl chloride is a source of chlorine whereas thionyl chloride is a source of chloride ions. An alternative IUPAC name is sulfuroyl dichloride. Structure Sulfur is tetrahedral in SO2Cl2 and the oxidation state of the sulfur atom is +6, as in sulfuric acid. Synthesis SO2Cl2 is prepared by the reaction of sulfur dioxide and chlorine in the presence of a catalyst, such as activated carbon. :SO2 + Cl2 → SO2Cl2 The product can be purified by fractional distillation. Legacy routes Sulfuryl chloride was first prepared in 1838 by the French chemist Henri Victor Regnault. Legacy routes include oxidation of thionyl ch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sulfur Dichloride
Sulfur dichloride is the chemical compound with the formula . This cherry-red liquid is the simplest sulfur chloride and one of the most common, and it is used as a precursor to organosulfur compounds. It is a highly corrosive and toxic substance, and it reacts on contact with water to form chlorine-containing acids. Chlorination of sulfur is produced by the chlorination of either elemental sulfur or disulfur dichloride. The process occurs in a series of steps, some of which are: :; ''ΔH'' = −58.2 kJ/mol :; ''ΔH'' = −40.6 kJ/mol The addition of to has been proposed to proceed via a mixed valence intermediate . undergoes even further chlorination to give , but this species is unstable at near room temperature. It is likely that several exist where ''n'' > 2. Disulfur dichloride, , is the most common impurity in . Separation of from is possible via distillation with to form an azeotrope of 99% purity, however sulfur dichloride loses chlorine slowly at room temperatu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tetrasulfur Tetranitride
Tetrasulfur tetranitride is an inorganic compound with the formula . This gold-poppy coloured solid is the most important binary sulfur nitride, which are compounds that contain only the elements sulfur and nitrogen. It is a precursor to many S-N compounds and has attracted wide interest for its unusual structure and bonding. Nitrogen and sulfur have similar electronegativities. When the properties of atoms are so highly similar, they often form extensive families of covalently bonded structures and compounds. Indeed, a large number of S-N and S-NH compounds are known with as their parent. Structure adopts an unusual “extreme cradle” structure, with D2d point group symmetry. It can be viewed as a derivative of a (hypothetical) eight-membered ring (or more simply a 'deformed' eight-membered ring) of alternating sulfur and nitrogen atoms. The pairs of sulfur atoms across the ring are separated by 2.586 Å, resulting in a cage-like structure as determined by single crystal X- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Claisen Condensation
The Claisen condensation is a carbon–carbon bond forming reaction that occurs between two esters or one ester and another carbonyl compound in the presence of a strong base, resulting in a β-keto ester or a β-diketone. It is named after Rainer Ludwig Claisen, who first published his work on the reaction in 1887. Requirements At least one of the reagents must be enolizable (have an α-proton and be able to undergo deprotonation to form the enolate anion). There are a number of different combinations of enolizable and nonenolizable carbonyl compounds that form a few different types of Claisen. The base used must not interfere with the reaction by undergoing nucleophilic substitution or addition with a carbonyl carbon. For this reason, the conjugate sodium alkoxide base of the alcohol formed (e.g. sodium ethoxide if ethanol is formed) is often used, since the alkoxide is regenerated. In mixed Claisen condensations, a non-nucleophilic base such as lithium diisopropylamide, or L ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fráter–Seebach Alkylation
In organic chemistry, the Fráter–Seebach alkylation (also known as Seebach–Fráter alkylation or Fráter–Seebach reaction) is a diastereoselective alkylation of chiral beta-hydroxy esters using strong base (chemistry), bases. The reaction was first published by Georg Fráter in 1979; in 1980, Dieter Seebach reported about a similar reaction with malic acid ester. Outline and mechanism Chiral beta-hydroxy esters can be treated with two equivalents of a strong base (lithium diisopropylamide, lithium diisopropylamide (LDA) or Lithium bis(trimethylsilyl)amide, lithium bis(trimethylsilyl)amide (LHMDS) are popular choices) to both remove the proton on the alcohol and Enolization, enolize the ester. An alkylating agent (methyl iodide in the case of Fráter's publication) is then added. This attacks from the opposite face of the chiral hydroxyl group to avoid steric hindrance as shown below in the 6-membered transition state with Chelation, chelating metal ions. This reaction has ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
LiHMDS EnolateFormation
Lithium bis(trimethylsilyl)amide is a lithiated organosilicon compound with the formula . It is commonly abbreviated as LiHMDS or Li(HMDS) (lithium hexamethyldisilazide - a reference to its conjugate acid Bis(trimethylsilyl)amine, HMDS) and is primarily used as a strong non-nucleophilic base and as a ligand. Like many lithium reagents, it has a tendency to aggregate and will form a Cyclic compound, cyclic Trimer (chemistry), trimer in the absence of coordinating species. Preparation LiHMDS is commercially available, but it can also be prepared by the deprotonation of bis(trimethylsilyl)amine with n-butyllithium, ''n''-butyllithium. This reaction can be performed In situ#Chemistry and chemical engineering, ''in situ''. : Once formed, the compound can be purified by Sublimation (phase transition), sublimation or distillation. Reactions and applications As a base LiHMDS is often used in organic chemistry as a strong non-nucleophilic base. Its conjugate acid has a Acid dissociatio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Enolate
In organic chemistry, enolates are organic anions derived from the deprotonation of carbonyl () compounds. Rarely isolated, they are widely used as reagents in the synthesis of organic compounds. Bonding and structure Enolate anions are electronically related to allyl anions. The anionic charge is delocalized over the oxygen and the two carbon sites. Thus they have the character of both an alkoxide and a carbanion. Although they are often drawn as being simple salts, in fact they adopt complicated structures often featuring aggregates. Preparation Deprotonation of enolizable ketones, aromatic alcohols, aldehydes, and esters gives enolates. With strong bases, the deprotonation is quantitative. Typically enolates are generated from using lithium diisopropylamide (LDA). Often, as in conventional Claisen condensations, Mannich reactions, and aldol condensations, enolates are generated in low concentrations with alkoxide bases. Under such conditions, they exist in low concent ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acetylide
In organometallic chemistry, acetylide refers to chemical compounds with the chemical formulas and , where M is a metal. The term is used loosely and can refer to substituted acetylides having the general structure (where R is an organic side chain). Acetylides are reagents in organic synthesis. The calcium acetylide commonly called calcium carbide is a major compound of commerce. Structure and bonding Alkali metal and alkaline earth metal acetylides of the general formula MC≡CM are salt-like Zintl phase compounds, containing ions. Evidence for this ionic character can be seen in the ready hydrolysis of these compounds to form acetylene and metal oxides, there is also some evidence for the solubility of ions in liquid ammonia. The ion has a closed shell ground state of 1Σ, making it isoelectronic to a neutral molecule N2, which may afford it some stability. Analogous acetylides prepared from other metals, particularly transition metals, show covalent character and are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organolithium
In organometallic chemistry 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 so ..., organolithium reagents are chemical compounds that contain carbon–lithium (C–Li) Chemical bond, bonds. These reagents are important in organic synthesis, and are frequently used to transfer the organic group or the lithium atom to the substrates in synthetic steps, through nucleophilic addition or simple deprotonation. Organolithium reagents are used in industry as an initiator for anionic polymerization, which leads to the production of various elastomers. They have also been applied in asymmetric synthesis in the pharmaceutical industry. Due to the large difference in electronegativity between the carbon atom and the lithium atom, the C−Li bond is highly ionization, ionic. Owing to the polar nat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nucleophilic
In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are Lewis bases. ''Nucleophilic'' describes the affinity of a nucleophile to bond with positively charged atomic nuclei. Nucleophilicity, sometimes referred to as nucleophile strength, refers to a substance's nucleophilic character and is often used to compare the affinity of atoms. Neutral nucleophilic reactions with solvents such as alcohols and water are named solvolysis. Nucleophiles may take part in nucleophilic substitution, whereby a nucleophile becomes attracted to a full or partial positive charge, and nucleophilic addition. Nucleophilicity is closely related to basicity. History The terms ''nucleophile'' and ''electrophile'' were introduced by Christopher Kelk Ingold in 1933, replacing the terms ''anionoid'' and ''cationoid' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
