|
Pechmann Condensation
The Pechmann condensation is a synthesis of coumarins, starting from a phenol and a carboxylic acid or ester containing a β- carbonyl group. The condensation is performed under acidic conditions. The mechanism involves an esterification/transesterification followed by attack of the activated carbonyl ortho to the oxygen to generate the new ring. The final step is a dehydration, as seen following an aldol condensation. It was discovered by the German chemist Hans von Pechmann . With simple phenols, the conditions are harsh, although yields may still be good. With highly activated phenols such as resorcinol, the reaction can be performed under much milder conditions. This provides a useful route to umbelliferone derivatives: For coumarins unsubstituted at the 4-position, the method requires the use of formylacetic acid or ester. These are unstable and not commercially available, but the acid may be produced ''in situ'' from malic acid and sulfuric acid above 100 ° ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hans Von Pechmann
Hans von Pechmann (1 April 1850 – 19 April 1902) was a German chemist, renowned for his discovery of diazomethane in 1894. Pechmann condensation and Pechmann pyrazole synthesis. He also first prepared 1,2-diketones (e.g., diacetyl), acetonedicarboxylic acid, methylglyoxal and diphenyltriketone; established the symmetrical structure of anthraquinone. Von Pechmann also produced the first example of solid polyethylene serendipitously in 1898, via the decomposition of diazomethane. He was born in Nürnberg. After studying with Heinrich Limpricht at the University of Greifswald he became professor at the University of Munich till 1895. He was professor at the University of Tübingen from 1895 until his death. He killed himself by taking cyanide, aged 52. Works * ''Volhard's Anleitung zur Qualitativen chemischen Analyse'' . Chemisches Labolatorium des Staates, München 9th & 10th ed. 190Digital editionby the University and State Library Düsseldorf * ''Anleitung zur quanti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pechmann 4methylumbelliferone
Pechman or Pechmann is a surname of German origin. Notable persons with that name include: *Joseph A. Pechman (1918–1989), American economist * Hans von Pechmann (1850–1902), German chemist *Marsha J. Pechman Marsha J. Pechman (born 1951) is a Senior United States district judge of the United States District Court for the Western District of Washington. Education and career Born in Salem, Oregon, Pechman received a Bachelor of Arts degree from Cornel ... (born 1951), American judge * Matthias Pechmann, East German swimmer {{Authority control German-language surnames ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxygen Heterocycle Forming Reactions
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well as with other compounds. Oxygen is Earth's most abundant element, and after hydrogen and helium, it is the third-most abundant element in the universe. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula . Diatomic oxygen gas currently constitutes 20.95% of the Earth's atmosphere, though this has changed considerably over long periods of time. Oxygen makes up almost half of the Earth's crust in the form of oxides.Atkins, P.; Jones, L.; Laverman, L. (2016).''Chemical Principles'', 7th edition. Freeman. Many major classes of organic molecules in living organisms contain oxygen atoms, such as proteins, nucleic acids, carbohydrates, and fats, as do ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Perkin Reaction
The Perkin reaction is an organic reaction developed by English chemist William Henry Perkin that is used to make cinnamic acids. It gives an α,β-unsaturated aromatic acid or α-substituted β-aryl acrylic acid by the aldol condensation of an aromatic aldehyde and an acid anhydride, in the presence of an alkali salt of the acid. The alkali salt acts as a base catalyst, and other bases can be used instead. Several reviews have been written. Reaction mechanism Cleary from the reaction mechanism, the anhydride of aliphatic acid must contain at least 2 α-H for the reaction to occur. The above mechanism is not universally accepted, as several other versions exist, including decarboxylation without acetic group transfer.Bansal, Raj K. (1998) ''Organic Reaction Mechanisms'', Tata McGraw Hill, 3rd Edition , pp. 199–201, . Applications *Benzaldehyde reacts with acetic anhydride in the presence of sodium or potassium acetate to form cinnamic acid. *One notable application f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kostanecki Acylation
The Kostanecki acylation is a method used in organic synthesis to form chromones or coumarins by acylation of ''O''-hydroxyaryl ketones with aliphatic acid anhydrides, followed by cyclization. If benzoic anhydride (or benzoyl chloride) is used, a particular type of chromone called a flavone is obtained. Mechanism The mechanism consists of three well-differentiated reactions:Ellis, G. P. (1977) ''Chromenes, Chromanones, and Chromones from The Chemistry of Heterocyclic Compounds'', Weissberger, A. and Taylor, E. C., eds.; Wiley & Sons: New York, vol. 31, p. 495. # Phenol ''O''-acylation with formation of a tetrahedral intermediate # Intramolecular aldol condensation to cyclize and to form a hydroxydihydrochromone # Elimination of the hydroxyl group to form the chromone (or coumarin) Examples *Alvocidib (flavopiridol) *Dimefline * Flavoxate See also * Allan–Robinson reaction The Allan–Robinson reaction is the chemical reaction of o-hydroxyaryl ketones with aromatic anhydri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aldol Condensation
An aldol condensation is a condensation reaction in organic chemistry in which two carbonyl moieties (of aldehydes or ketones) react to form a β-hydroxyaldehyde or β-hydroxyketone (an aldol reaction), and this is then followed by dehydration to give a conjugated enone. The overall reaction is as follows (where the Rs can be H): Aldol condensations are important in organic synthesis and biochemistry as ways to form carbon–carbon bonds. In its usual form, it involves the nucleophilic addition of a ketone enolate to an aldehyde to form a β-hydroxy ketone, or "aldol" (aldehyde + alcohol), a structural unit found in many naturally occurring molecules and pharmaceuticals. The term ''aldol condensation'' is also commonly used, especially in biochemistry, to refer to just the first (addition) stage of the process—the aldol reaction itself—as catalyzed by aldolases. However, this is formally an addition reaction rather than a condensation reaction because it does n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Simonis Chromone Cyclisation
Simonis is both a surname and a given name. Notable people with the name include: *Adrianus Johannes Simonis, Dutch Roman Catholic cardinal and former archbishop of Utrecht * Eugène Simonis or Eugen Simonis, Belgian sculptor and architect *Heide Simonis, German politician *Kazys Šimonis, Lithuanian artist *Simonis Palaiologina, Byzantine princess and third wife of Stefan Uroš II Milutin of Serbia *Simonis Starovolsci, Polish scholar See also *Simono The Simono were an indigenous people who lived in what is now part of the Mexican state of Nuevo Leon and the U.S. state of Texas from at least the 16th century in the 18th century. In the late 1580s or maybe slightly earlier the pressure of the ..., a Native American group that lived in Nuevo León and later in eastern Texas. {{given name, type=both Surnames from given names ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chromone
Chromone (or 1,4-benzopyrone) is a derivative of benzopyran with a substituted keto group on the pyran ring. It is an isomer of coumarin. Derivatives of chromone are collectively known as ''chromones''. Most, though not all, chromones are also phenylpropanoids. Examples * 6,7-dimethoxy-2,3-dihydrochromone has been isolated from '' Sarcolobus globosus''. * Eucryphin, a chromone rhamnoside, can be isolated from the bark of ''Eucryphia cordifolia''. * Cromolyn (disodium cromoglicate) was found to inhibit antigen challenge as well as stress induced symptoms.HOWELL, J.B. & ALTOUNYAN, R.E. (1967). A double-blind trial of disodium cromoglycate in the treatment of allergic bronchial asthma. Lancet, 2, 539–542Abstract/ref> Cromoglicate is used as a mast cell stabilizer in allergic rhinitis, asthma and allergic conjunctivitis. * Nedocromil sodium was found to have a somewhat longer half-life than cromolyn; however, production was discontinued in the US in 2008. * Xanthone with ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phosphorus Pentoxide
Phosphorus pentoxide is a chemical compound with molecular formula P4 O10 (with its common name derived from its empirical formula, P2O5). This white crystalline solid is the anhydride of phosphoric acid. It is a powerful desiccant and dehydrating agent. Structure Phosphorus pentoxide crystallizes in at least four forms or polymorphs. The most familiar one, a metastable form (shown in the figure), comprises molecules of P4O10. Weak van der Waals forces hold these molecules together in a hexagonal lattice (However, in spite of the high symmetry of the molecules, the crystal packing is not a close packing). The structure of the P4O10 cage is reminiscent of adamantane with ''T''d symmetry point group. It is closely related to the corresponding anhydride of phosphorous acid, P4O6. The latter lacks terminal oxo groups. Its density is 2.30 g/cm3. It boils at 423 °C under atmospheric pressure; if heated more rapidly it can sublimate. This form can be made by condensing the va ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pechmann Umbelliferone
Pechman or Pechmann is a surname of German origin. Notable persons with that name include: *Joseph A. Pechman (1918–1989), American economist * Hans von Pechmann (1850–1902), German chemist *Marsha J. Pechman Marsha J. Pechman (born 1951) is a Senior United States district judge of the United States District Court for the Western District of Washington. Education and career Born in Salem, Oregon, Pechman received a Bachelor of Arts degree from Cornel ... (born 1951), American judge * Matthias Pechmann, East German swimmer {{Authority control German-language surnames ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sulfuric Acid
Sulfuric acid ( American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formula . It is a colorless, odorless and viscous liquid that is miscible with water. Pure sulfuric acid does not exist naturally on Earth due to its strong affinity to water vapor; it is hygroscopic and readily absorbs water vapor from the air. Concentrated sulfuric acid is highly corrosive towards other materials, from rocks to metals, since it is an oxidant with powerful dehydrating properties. Phosphorus pentoxide is a notable exception in that it is not dehydrated by sulfuric acid, but to the contrary dehydrates sulfuric acid to sulfur trioxide. Upon addition of sulfuric acid to water, a considerable amount of heat is released; thus the reverse procedure of adding water to the acid should not be performed since the heat released ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Malic Acid
Malic acid is an organic compound with the molecular formula . It is a dicarboxylic acid that is made by all living organisms, contributes to the sour taste of fruits, and is used as a food additive. Malic acid has two stereoisomeric forms (L- and D-enantiomers), though only the L-isomer exists naturally. The salts and esters of malic acid are known as malates. The malate anion is an intermediate in the citric acid cycle. Etymology The word 'malic' is derived from Latin ' mālum', meaning 'apple'. The related Latin word , meaning 'apple tree', is used as the name of the genus ''Malus'', which includes all apples and crabapples; and the origin of other taxonomic classifications such as Maloideae, Malinae, and Maleae. Biochemistry L-Malic acid is the naturally occurring form, whereas a mixture of L- and D-malic acid is produced synthetically. File:L-Äpfelsäure.svg, L-Malic acid File:D-Äpfelsäure.svg, D-Malic acid Malate plays an important role in biochemistry. In th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
