|
Bischler–Napieralski Reaction
The Bischler–Napieralski reaction is an intramolecular electrophilic aromatic substitution reaction that allows for the cyclization of β-arylethylamides or β-arylethylcarbamates. It was first discovered in 1893 by August Bischler and , in affiliation with Basle Chemical Works and the University of Zurich. The reaction is most notably used in the synthesis of dihydroisoquinolines, which can be subsequently oxidized to isoquinolines. Mechanisms Two types of mechanisms have appeared in the literature for the Bischler–Napieralski reaction. Mechanism I involves a dichlorophosphoryl imine-ester intermediate, while Mechanism II involves a nitrilium ion intermediate (both shown in brackets). This mechanistic variance stems from the ambiguity over the timing for the elimination of the carbonyl oxygen in the starting amide. In Mechanism I, the elimination occurs with imine formation ''after'' cyclization; while in Mechanism II, the elimination yields the nitrilium intermediate ''pri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
August Bischler
August Bischler (29 April 1865 – 26 May 1957) was a Russian Empire-born ethnic Crimea German chemist who later emigrated to Switzerland. He discovered the Bischler–Möhlau indole synthesis reaction in 1892 and, together with Bernard Napieralski, discovered the Bischler–Napieralski reaction in 1893. Life He received his Ph.D. at the University of Zurich 1889 worked at the University of Zurich and from 1899 at the University of Basel. After becoming a Swiss citizen in 1925 he worked in the chemical industry in Geneva. Bernard Napieralski Bernard Napieralski was a Ph.D. student of Bischler at the University of Zurich in 1893. Napieralski was born in Ostrowy, Poland Poland, officially the Republic of Poland, is a country in Central Europe. It is divided into 16 administrative provinces called voivodeships, covering an area of . Poland has a population of over 38 million and is the fifth-most populou ..., 1861. References * 1865 births 1957 deaths Che ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Substitution Reaction
A substitution reaction (also known as single displacement reaction or single substitution reaction) is a chemical reaction during which one functional group in a chemical compound is replaced by another functional group. Substitution reactions are of prime importance in organic chemistry. Substitution reactions in organic chemistry are classified either as electrophilic or nucleophilic depending upon the reagent involved, whether a reactive intermediate involved in the reaction is a carbocation, a carbanion or a free radical, and whether the substrate is aliphatic or aromatic. Detailed understanding of a reaction type helps to predict the product outcome in a reaction. It also is helpful for optimizing a reaction with regard to variables such as temperature and choice of solvent. A good example of a substitution reaction is halogenation. When chlorine gas (Cl2) is irradiated, some of the molecules are split into two chlorine radicals (Cl•), whose free electrons are strongly n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phenanthridine
Phenanthridine is a nitrogen heterocyclic compound that is the basis of DNA-binding fluorescent dyes through intercalation. Examples of such dyes are ethidium bromide and propidium iodide. Acridine is an isomer of phenanthridine. Phenanthridine was discovered by Amé Pictet and H. J. Ankersmit in 1891 by pyrolysis of the condensation product of benzaldehyde and aniline. In the Pictet–Hubert reaction (1899) the compound is formed in a reaction of the 2-aminobiphenyl – formaldehyde adduct (an ''N''-acyl- ''o''-xenylamine) with zinc chloride at elevated temperatures. The reaction conditions for the Pictet–Hubert reaction were improved by Morgan and Walls in 1931, replacing the metal by phosphorus oxychloride and using nitrobenzene as a reaction solvent. For this reason, the reaction is also called the Morgan–Walls reaction.Jie Jack Li (ed.), 2004, ''Name Reactions in Heterocyclic Chemistry'', Wiley. : The reaction is similar to the Bischler–Napieralski reaction and the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Morgan–Walls Reaction
Phenanthridine is a nitrogen heterocyclic compound that is the basis of DNA-binding fluorescent dyes through intercalation. Examples of such dyes are ethidium bromide and propidium iodide. Acridine is an isomer of phenanthridine. Phenanthridine was discovered by Amé Pictet and H. J. Ankersmit in 1891 by pyrolysis of the condensation product of benzaldehyde and aniline. In the Pictet–Hubert reaction (1899) the compound is formed in a reaction of the 2-aminobiphenyl – formaldehyde adduct (an ''N''-acyl- ''o''-xenylamine) with zinc chloride at elevated temperatures. The reaction conditions for the Pictet–Hubert reaction were improved by Morgan and Walls in 1931, replacing the metal by phosphorus oxychloride and using nitrobenzene as a reaction solvent. For this reason, the reaction is also called the Morgan–Walls reaction.Jie Jack Li (ed.), 2004, ''Name Reactions in Heterocyclic Chemistry'', Wiley. : The reaction is similar to the Bischler–Napieralski reaction an ... [...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 vap ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, benzene is classed as a hydrocarbon. Benzene is a natural constituent of petroleum and is one of the elementary petrochemicals. Due to the cyclic continuous pi bonds between the carbon atoms, benzene is classed as an aromatic hydrocarbon. Benzene is a colorless and highly flammable liquid with a sweet smell, and is partially responsible for the aroma of gasoline. It is used primarily as a precursor to the manufacture of chemicals with more complex structure, such as ethylbenzene and cumene, of which billions of kilograms are produced annually. Although benzene is a major industrial chemical, it finds limited use in consumer items because of its toxicity. History Discovery The word "''benzene''" derives from "''gum benzoin''" (benzoin res ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron-donating
In chemistry, electron-rich is jargon that is used in multiple related meanings with either or both kinetic and thermodynamic implications: *with regards to electron-transfer, electron-rich species have low ionization energy and/or are reducing agents. Tetrakis(dimethylamino)ethylene is an electron-rich alkene because, unlike ethylene, it forms isolable radical cation. In contrast, electron-poor alkene tetracyanoethylene is an electron acceptor, forming isolable anions. *with regards to acid-base reactions, electron-rich species have high pKa's and react with weak Lewis acids. *with regards to nucleophilic substitution reactions, electron-rich species are relatively strong nucleophiles, as judged by rates of attack by electrophiles. For example, compared to benzene, pyrrole is more rapidly attacked by electrophiles. Pyrrole is therefore considered to be an electron-rich aromatic ring. Similarly, benzene derivatives with electron-donating groups (EDGs) are attacked by ele ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polyphosphoric Acid
A phosphoric acid, in the general sense, is a phosphorus oxoacid in which each phosphorus (P) atom is in the oxidation state +5, and is bonded to four oxygen (O) atoms, one of them through a double bond, arranged as the corners of a tetrahedron. Two or more of these tetrahedra may be connected by shared single-bonded oxygens, forming linear or branched chains, cycles, or more complex structures. The single-bonded oxygen atoms that are not shared are completed with acidic hydrogen atoms. The general formula of a phosphoric acid is , where ''n'' is the number of phosphorus atoms and ''x'' is the number of fundamental cycles in the molecule's structure, between 0 and (''n''+2)/2. Removal of protons () from ''k'' hydroxyl groups –OH leaves anions generically called phosphates (if ''k'' = ''n''−2''x''+2) or hydrogen phosphates (if ''k'' is between 1 and ''n''−2''x''+1), with general formula ''n''−2''x''+2−''k''P''n''O3''n''+1−''x''sup>''k''−. The fully dissociated ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trifluoromethanesulfonic Anhydride
Trifluoromethanesulfonic anhydride, also known as triflic anhydride, is the chemical compound with the formula (CF3SO2)2O. It is the acid anhydride derived from triflic acid. This compound is a strong electrophile, useful for introducing the triflyl group, CF3SO2. Abbreviated Tf2O, triflic anhydride is the acid anhydride of the strong acid triflic acid, CF3SO2OH. Preparation and uses Triflic anhydride is prepared by dehydration of triflic acid using P4O10. Triflic anhydride is useful for converting ketones into enol triflates. In a representative application, is used to convert an imine into a NTf group. It will convert phenols into a triflic ester, which enables cleavage of the C-O bond. Assay The typical impurity in triflic anhydride is triflic acid, which is also a colorless liquid. Samples of triflic anhydride can be assayed by 19F NMR spectroscopy: −72.6 ppm vs. −77.3 for TfOH (std CFCl3). Safety It is an aggressive electrophile and readily hydrolyzes to the strong ac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Boron Trifluoride
Boron trifluoride is the inorganic compound with the formula BF3. This pungent, colourless, and toxic gas forms white fumes in moist air. It is a useful Lewis acid and a versatile building block for other boron compounds. Structure and bonding The geometry of a molecule of BF3 is trigonal planar. Its D3h symmetry conforms with the prediction of VSEPR theory. The molecule has no dipole moment by virtue of its high symmetry. The molecule is isoelectronic with the carbonate anion, . BF3 is commonly referred to as " electron deficient," a description that is reinforced by its exothermic reactivity toward Lewis bases. In the boron trihalides, BX3, the length of the B–X bonds (1.30 Å) is shorter than would be expected for single bonds, and this shortness may indicate stronger B–X π-bonding in the fluoride. A facile explanation invokes the symmetry-allowed overlap of a p orbital on the boron atom with the in-phase combination of the three similarly oriented p orbitals ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tin(IV) Chloride
Tin(IV) chloride, also known as tin tetrachloride or stannic chloride, is an inorganic compound with the formula Sn Cl4. It is a colorless hygroscopic liquid, which fumes on contact with air. It is used as a precursor to other tin compounds. It was first discovered by Andreas Libavius (1550–1616) and was known as ''spiritus fumans libavii''. Preparation It is prepared from reaction of chlorine gas with tin at . : Sn + 2 Cl2 → SnCl4 Structure Anhydrous tin(IV) chloride solidifies at −33 °C to give monoclinic crystals with the P21/c space group. It is isostructural with SnBr4. The molecules adopt near-perfect tetrahedral symmetry with average Sn–Cl distances of 227.9(3) pm. Reactions Tin(IV) chloride is well known as a Lewis acid. Thus it forms hydrates. The pentahydrate SnCl4·5H2O was formerly known as butter of tin. They all consist of nCl4(H2O)2molecules together with varying amounts of water of crystallization. The additional water molecules link together ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phosphoryl Chloride
Phosphoryl chloride (commonly called phosphorus oxychloride) is a colourless liquid with the formula . It hydrolyses in moist air releasing phosphoric acid and fumes of hydrogen chloride. It is manufactured industrially on a large scale from phosphorus trichloride and oxygen or phosphorus pentoxide. It is mainly used to make phosphate esters such as tricresyl phosphate. Structure Like phosphate, is tetrahedral in shape. It features three P−Cl bonds and one strong P=O double bond, with an estimated bond dissociation energy of 533.5 kJ/mol. On the basis of bond length and electronegativity, the Schomaker-Stevenson rule suggests that the double bond form is dominant, in contrast with the case of . The P=O bond involves the donation of the lone pair electrons on oxygen ''p''-orbitals to the antibonding combinations associated with phosphorus-chlorine bonds, thus constituting ''π'' bonding. Phosphoryl chloride exists as neutral molecules in the solid, liquid and gas s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
2.png "Click for more on -> Benzene")
