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Knoevenagel Condensation
In organic chemistry, the Knoevenagel condensation () reaction is a type of chemical reaction named after German chemist Emil Knoevenagel. It is a modification of the aldol condensation. A Knoevenagel condensation is a nucleophilic addition of an active hydrogen compound to a carbonyl group followed by a dehydration reaction in which a molecule of water is eliminated (hence ''condensation''). The product is often an α,β-unsaturated ketone (a conjugated enone). In this reaction the carbonyl group is an aldehyde or a ketone. The catalyst is usually a weakly basic amine. The active hydrogen component has the forms: * or for instance diethyl malonate, Meldrum's acid, ethyl acetoacetate or malonic acid, or cyanoacetic acid. * , for instance nitromethane. where Z is an electron withdrawing group. Z must be powerful enough to facilitate deprotonation to the enolate ion even with a mild base. Using a strong base in this reaction would induce self-condensation of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Emil Knoevenagel
Heinrich Emil Albert Knoevenagel (; 18 June 1865 – 11 August 1921) was the German chemist who established the Knoevenagel condensation reaction. The Knoevenagel condensation reaction of benzaldehydes with nitroalkanes is a classic general method for the preparation of nitroalkenes, which are very valuable synthetic intermediates. Works * * ''Praktikum des anorganischen Chemikers : Einführung in die anorganische Chemie auf experimenteller Grundlage'' . Veit, Leipzig 2nd ed. 190Digital editionby the University and State Library Düsseldorf The University and State Library Düsseldorf (, abbreviated ULB Düsseldorf) is a central service institution of Heinrich Heine University. Along with Bonn and Münster, it is also one of the three State Libraries of North Rhine-Westphalia. ... External links Reaction description (in German) References * {{DEFAULTSORT:Knoevenagel, Emil 1865 births 1921 deaths 20th-century German chemists Academic staff of Heidelberg Unive ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amine
In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of electrons. Amines can also exist as hetero cyclic compounds. Aniline is the simplest aromatic amine, consisting of a benzene ring bonded to an amino group. Amines are classified into three types: primary (1°), secondary (2°), and tertiary (3°) amines. Primary amines (1°) contain one alkyl or aryl substituent and have the general formula RNH2. Secondary amines (2°) have two alkyl or aryl groups attached to the nitrogen atom, with the general formula R2NH. Tertiary amines (3°) contain three substituent groups bonded to the nitrogen atom, and are represented by the formula R3N. The functional group present in primary amines is called the amino group. Classification of amines Amines can be classified according to the nature and number o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CS Gas
The compound 2-chlorobenzalmalononitrile (also called ''o''-chlorobenzylidene malononitrile; chemical formula: C10H5ClN2), a cyanocarbon, is the defining component of the lachrymatory agent commonly referred to as CS gas, a tear gas which is used as a riot control agent, and is banned for use in warfare due to the 1925 Geneva Protocol. Exposure causes a burning sensation and tearing of the eyes to the extent that the subject cannot keep their eyes open, and a burning irritation of the mucous membranes of the nose, mouth and throat, resulting in profuse coughing, nasal mucus discharge, disorientation, and difficulty breathing, partially incapacitating the subject. CS gas is an aerosol of a volatile solvent (a substance that dissolves other active substances and that easily evaporates) and 2-chlorobenzalmalononitrile, which is a solid compound at room temperature. CS gas is generally accepted as being non-lethal. History CS gas was first synthesized by two Americans, B ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Feist–Benary Synthesis
The Feist–Benary synthesis is an organic reaction between α-Halo ketone, α-halo ketones and β-carbonyl, dicarbonyl compounds to produce substituted furan compounds. This condensation reaction is catalysis, catalyzed by amines such as ammonia and pyridine. The first step in the ring synthesis is related to the Knoevenagel condensation. In the second step the enolate displaces an alkyl halogen in a nucleophilic aliphatic substitution. Modifications In place of α-haloketones, propargyl sulfonium salts can be used to alkylate the diketone. Another modification is the enantioselective interrupted Feist-Benary reaction with a chiral auxiliary based on the cinchona alkaloid quinine based in the presence of proton sponge to the hydroxydihydrofuran. This type of alkaloids is also used in asymmetric synthesis in the AD-mix. The alkaloid is protonation, protonated throughout the reaction and transfers its Chirality (chemistry), chirality by interaction of the acidic ammonium salt, a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gewald Reaction
The Gewald reaction (or the Gewald aminothiophene synthesis) is an organic reaction involving the condensation of a ketone (or aldehyde when R2 = H) with a α-cyanoester in the presence of elemental sulfur and base to give a poly-substituted 2-amino-thiophene. The reaction is named after the German chemist .John A. Joule, Keith Mills: ''Heterocyclic Chemistry'', John Wiley & Sons, 5. Auflage (2010), p. 340, .Bradford P. Mundy, Michael G. Ellerd, Frank G. Favaloro, Jr.: ''Name Reactions and Reagents in Organic Synthesis'', John Wiley & Sons, 2. Auflage (2005) p. 306, .Christopher Hume: ''Applications of Multicomponent Reactions in Drug Discovery – Lead Generation to Process Development'', p. 311−341, see p. 332−334, In Jieping Zhu, Huges Bienaymé: ''Multicomponent Reactions'', Wiles-VCH Verlag, 2005, . Reaction mechanism The reaction mechanism of the Gewald reaction was elucidated 30 years after the reaction was discovered. The first step is a Knoevenagel condensation bet ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hantzsch Pyridine Synthesis
The Hantzsch pyridine synthesis or Hantzsch dihydropyridine synthesis is a multi-component organic reaction between an aldehyde such as formaldehyde Formaldehyde ( , ) (systematic name methanal) is an organic compound with the chemical formula and structure , more precisely . The compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde. It is stored as ..., 2 equivalents of a Keto ester, β-keto ester such as ethyl acetoacetate and a nitrogen donor such as ammonium acetate or ammonia. The initial reaction product is a dihydropyridine which can be organic oxidation, oxidized in a subsequent step to a pyridine. The driving force for this second reaction step is aromatization. This reaction was reported in 1881 by Arthur Rudolf Hantzsch. A 1,4-dihydropyridine dicarboxylate is also called a 1,4-DHP compound or a Hantzsch ester. These compounds are an important class of calcium channel blockers and as such commercialized in for instance nife ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Self-condensation
In organic chemistry, self-condensation is an organic reaction in which a chemical compound containing a carbonyl group () acts both as the electrophile and the nucleophile in an aldol condensation. It is also called a symmetrical aldol condensation as opposed to a mixed aldol condensation in which the electrophile and nucleophile are different species. For example, two molecules of acetone condense to a single compound mesityl oxide in the presence of an ion-exchange resin: : For synthetic uses, this is generally an undesirable, but spontaneous and favored side-reaction of mixed aldol condensation, and special precautions are needed to prevent it. Preventing self-condensation In many cases, self-condensation is an unwanted side-reaction. Therefore, chemists have adopted many ways to prevent this from occurring when performing a crossed aldol reaction. The use of a more reactive electrophile, and a non-enolizable partner If acetophenone and benzaldehyde are put together in the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Enolate Ion
In organic chemistry, enols are a type of functional group or intermediate in organic chemistry containing a group with the formula (R = many substituents). The term ''enol'' is an abbreviation of ''alkenol'', a portmanteau deriving from "-ene"/"alkene" and the "-ol". Many kinds of enols are known. Keto–enol tautomerism refers to a chemical equilibrium between a "keto" form (a carbonyl, named for the common ketone case) and an enol. The interconversion of the two forms involves the transfer of an alpha hydrogen atom and the reorganisation of bonding electrons. The keto and enol forms are tautomers of each other. Enolization Organic esters, ketones, and aldehydes with an α-hydrogen ( bond adjacent to the carbonyl group) often form enols. The reaction involves migration of a proton () from carbon to oxygen: : In the case of ketones, the conversion is called a keto-enol tautomerism, although this name is often more generally applied to all such tautomerizations. Usual ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron Withdrawing Group
The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up and down quarks. Electrons are extremely lightweight particles that orbit the positively charged nucleus of atoms. Their negative charge is balanced by the positive charge of protons in the nucleus, giving atoms their overall neutral charge. Ordinary matter is composed of atoms, each consisting of a positively charged nucleus surrounded by a number of orbiting electrons equal to the number of protons. The configuration and energy levels of these orbiting electrons determine the chemical properties of an atom. Electrons are bound to the nucleus to different degrees. The outermost or valence electrons are the least tightly bound and are responsible for the formation of chemical bonds between atoms to create molecules and crystals. These valence electrons a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nitromethane
Nitromethane, sometimes shortened to simply "nitro", is an organic compound with the chemical formula . It is the simplest organic nitro compound. It is a polar liquid commonly used as a solvent in a variety of industrial applications such as in extractions, as a reaction medium, and as a cleaning solvent. As an intermediate in organic synthesis, it is used widely in the manufacture of pesticides, explosives, fibers, and coatings. Nitromethane is used as a fuel additive in various motorsports and hobbies, e.g. Top Fuel drag racing and miniature internal combustion engines in radio control, control line and free flight model aircraft. Preparation Nitromethane is produced industrially by combining propane and nitric acid in the gas phase at . This exothermic reaction produces the four industrially significant nitroalkanes: nitromethane, nitroethane, 1-nitropropane, and 2-nitropropane. The reaction involves free radicals, including the alkoxyl radicals of the type , whi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cyanoacetic Acid
Cyanoacetic acid is an organic compound. It is a white, hygroscopic solid. The compound contains two functional groups, a nitrile (−C≡N) and a carboxylic acid. It is a precursor to cyanoacrylates, components of adhesives.Harald Strittmatter, Stefan Hildbrand and Peter Pollak Malonic Acid and Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry 2007, Wiley-VCH, Weinheim. Preparation and reactions Cyanoacetic acid is prepared by treatment of chloroacetate salts with sodium cyanide followed by acidification. Electrosynthesis by cathodic reduction of carbon dioxide and anodic oxidation of acetonitrile also affords cyanoacetic acid. Cyanoacetic acid is used to do cyanoacetylation, first convenient method described by J. Slätt. It is about 1000× more acidic than acetic acid, with a pKa of 2.5. Upon heating at 160 °C, it undergoes decarboxylation to give acetonitrile: : {{chem2, HO2CCH2CN → CO2 + CH3CN Applications In its largest scale application, cya ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Malonic Acid
Malonic acid is a dicarboxylic acid with structure CH2(COOH)2. The ionized form of malonic acid, as well as its esters and salts, are known as malonates. For example, diethyl malonate is malonic acid's diethyl ester. The name originates from the Greek word μᾶλον (''malon'') meaning 'apple'. History Malonic acid is a naturally occurring substance found in many fruits and vegetables. There is a suggestion that citrus fruits produced in organic farming contain higher levels of malonic acid than fruits produced in conventional agriculture. Malonic acid was first prepared in 1858 by the French chemist Victor Dessaignes via the oxidation of malic acid. Hermann Kolbe and Hugo Müller independently discovered how to synthesize malonic acid from propionic acid, and decided to publish their results back-to-back in the Chemical Society journal in 1864. This led to priority dispute with Hans Hübner and Maxwell Simpson who had independently published preliminary results on rela ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
