This section describes the scope of directing groups that may be used to effect site-selective lithiation in substituted benzenes and heterocycles.
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U. Beck, E. Löser "Chlorinated Benzenes and other Nucleus-Chlorinated Aromatic Hydrocarbons" in Ullmann's Encyclopedia of Industrial Chemistry, 2012, Wiley-VCH, Weinheim.
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Some suggested solvent mixtures are polyalkylated benzenes and alkyl phosphates or tetraalkyl ureas, trimethylbenzenes and alkylcyclohexanol esters, and methylnaphthalene and nonyl alcohols.
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In 1984 a new synthetic strategy was developed by Rick Danheiser to address these shortcomings.Chung, Won-jin. "Regioselective [4+2] Benzannulation: Synthesis of Polysubstituted Benzenes ." Chemistry Department.
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595 Gerd Leston(1996), (Polyhydroxy)benzenes. In Kirk‑Othmer Encyclopedia of Chemical Technology, John Wiley & Sons. The product is also called hexaphenol, J.I.G. Codagan, John Buckingham, Finlay J. MacDonald, P. H. Rhodes (1996), Dictionary of organic compounds. CRC Press.
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Polysubstituted benzenes were originally synthesized by substitution reactions on aromatic precursors. However, these reactions can have low regioselectivity and are prone to over substitution. Directed ortho metalation requires precursors that are often unstable to metallating reagents. Both these synthetic routes pose issues in total synthesis.
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Routine screening is not recommended. Individuals with risk factors who undergo repeated testing have higher rates of urologic malignancies. These risks factors include age (>35 years), male gender, previous or current smoking, chemical exposure (e.g., benzenes or aromatic amines), and prior pelvic radiation therapy.
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Although conversion to terephthalic acid is the dominant chemical conversion, xylenes are precursors to other chemical compounds. For instance chlorination of both methyl groups gives the corresponding xylene dichlorides (bis(chloromethyl)benzenes) whilst mono-bromination yields xylyl bromide, a tear gas agent used in World War I.
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Solvay Process Company in Solvay, New York on Onondaga Lake about 1900 The Allied Chemical Corporation contributed greatly to the chemical pollution of Onondaga Lake. The surface water was found to be contaminated with mercury whereas the sediments are contaminated with polychlorinated biphenyls (PCBs), pesticides, creosotes, heavy metals (lead, cobalt, and mercury), polycyclic aromatic hydrocarbons (PAHs), chlorinated benzenes, and BTEX compounds (benzene, ethylbenzene, toluene, xylene). In Onondaga Lake the chlorinated benzenes are located in the southwest portion, in the form of a dense oily liquid that has settled into the sediments. These chemicals were intentionally dumped into the lake or unintentionally seeped in from upland toxic waste sites or from the Solvay wastebeds located at the southwest end of Onondaga Lake.
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Aromatic hydrocarbons show distinct molecular ion peak.benzylic cleavage is pretty common. When alkyl groups are attached to the ring, a favorable mode of cleavage is to lose a H-radical to form the tropylium cation (m/z 91). Benzylic cleavage Alkyl substituted benzenes can fragment via the kinetic controlled process to form C6H5+, C6H6+ ions.
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At Berkeley he also worked on surface science, and he maintained a research facility at the Lawrence Berkeley Laboratory.Klarup, D. G.; Muetterties, E. L.; Stacy, A. M. Thermal desorption studies of methyl- substituted benzenes on nickel(111) and nickel(100) surfaces. Langmuir (1985), 1, 764-6. Muetterties helped establish the American Chemical Society journals Inorganic Chemistry and Organometallics.
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Soot is the primary cause of "ghosting", the discoloration of walls and ceilings or walls and flooring where they meet. It is generally responsible for the discoloration of the walls above baseboard electric heating units. The formation of soot depends strongly on the fuel composition. The rank ordering of sooting tendency of fuel components is: naphthalenes → benzenes → aliphatics.
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J. Organomet. Chem. 2001, 624, 131-135 Macromolecules such as hematin, cobalamin, vitamin B12, and coenzyme F430 are also used for dichlorination of polychlorinated ethylenes and benzenes. Charles and his co-workers reported that vitamin B12 and coenzyme F430 were capable of sequentially dechlorinating tetrachloroethene to ethene, while hematin was demonstrated to dechlorinate tetrachloroethene to vinyl chloride.
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Trimerisation of unsymmetrical alkynes gives two isomeric benzenes. For example, phenylacetylene affords both 1,3,5- and 1,2,4-C6R3H3. The substitution pattern about the product arene is determined in two steps: formation of the metallocyclopentadiene intermediate and incorporation of the third equivalent of alkyne. Steric bulk on the alkyne coupling partners and catalyst have been invoked as the controlling elements of regioselectivity.
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PCNB was originally synthesized in the laboratory in 1868. It was introduced to the agricultural world in the 1930s in Germany by Bayer AG as a substitute to mercurial pesticides. PCNB is prepared by chlorination of nitrobenzene at 60–70 °C in chlorosulfuric acid, with iodine as a catalyst. It can also be produced by the nitration of chlorinated benzenes.
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The xylene ( a group of three dimethyl benzenes) in the BTX are similarly converted to benzene and methane. This requires hydrogen which is supplied in a gaseous stream from the Ethylene plant (see above). The reaction is completed in a pair of reactors in series at high temperature and high pressure. The methane and other gaseous products are separated from the benzene and the other liquids.
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Because of its polymeric structure, ZrCl4 is usually converted to a molecular complex before use. It forms a 1:2 complex with tetrahydrofuran: CAS [21959-01-3], mp 175–177 °C. NaC5H5 reacts with ZrCl4(THF)2 to give zirconocene dichloride, ZrCl2(C5H5)2, a versatile organozirconium complex. One of the most curious properties of ZrCl4 is its high solubility in the presence of methylated benzenes, such as durene.
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Graebe (1869) "Ueber die Constitution des Naphthalins" (On the structure of naphthalene), Annalen der Chemie und Pharmacie, 149 : 20–28; see especially p. 26. In 1870, the German chemist Viktor Meyer first applied Gräbe's nomenclature to benzene.Victor Meyer (1870) "Untersuchungen über die Constitution der zweifach-substituirten Benzole" (Investigations into the structure of di-substituted benzenes), Annalen der Chemie und Pharmacie, 156 : 265–301; see especially pp. 299–300.
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4-hydroxybenzoate 3-monooxygenase is a homodimer with a flavin bound to each monomer. The active site is composed of the flavin and amino acids on the monomer. The structure of this enzyme often serves as a model for structure-reactivity interdependence of other flavin- dependent hydroxylases. The active site limits potential substrates to substituted benzenes, namely 4-hydroxybenzoate (the native substrate), 2,4-dihydroxybenzoate, 4-mercaptobenzoate, and several halogenated aromatic compounds.
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Any 4-substituted pyridine, pyridine itself, 1-substituted pyrazinium ion, diazine, 1-substituted or unsubstituted pyrrole and related aromatic heterocyclics (phospholes, furan, thiophene, etc.) as well as unsubstituted or 1-substituted cyclopentadienes and 1-substituted cyclopentadienides all have the same symmetry framework as para-disubstituted or ortho-homodisubstituted benzenes, and will present chemically equivalent but magnetically inequivalent pairs of protons. In heterocycles and in five- membered rings in general, however, 3J values can be significantly smaller than in benzenes and the manifestation of magnetic inequivalence may be subtle. The rarer seven-membered and higher ring systems may also show the same symmetry property, as can linked and fused aromatic ring systems such as biphenyls, naphthalenes and isoindoles. Similarly, 1-H benzimidazoles have the appropriate symmetry if N1-deprotonated or N3-protonated, or as a result of rapid tautomerization of the neutral form (for instance, in DMSO-d6) where the signals greatly resemble those of 1,2-dichlorobenzene.
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2-Pyrone (α-pyrone or pyran-2-one) is an unsaturated cyclic chemical compound with the molecular formula C5H4O2. It is isomeric with 4-pyrone. 2-Pyrone is used in organic synthesis as a building block for more complex chemical structures because it may participate in a variety of cycloaddition reactions to form bicyclic lactones. For example, it readily undergoes Diels-Alder reactions with alkynes producing, upon loss of carbon dioxide, substituted benzenes.
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Reaction of benzene with propene to cumene in the presence of phosphoric acid supported on silica & promoted with boron trifluoride Since the mid-1990s, commercial production has switched to zeolite-based catalysts.The Innovation Group website, page accessed 15/11/07 In this process, the efficiency of cumene production is generally 70-75%. The remaining components are primarily polyisopropyl benzenes. In 1976, an improved cumene process that uses aluminum chloride as a catalyst was developed.
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Monosubstituted phenyl groups (that is, disubstituted benzenes) are associated with electrophilic aromatic substitution reactions and the products follow the arene substitution pattern. So, a given substituted phenyl compound has three isomers, ortho (1,2-disubstitution), meta (1,3-disubstitution) and para (1,4-disubstitution). A disubstituted phenyl compound (trisubstituted benzene) may be, for example, 1,3,5-trisubstituted, or 1,2,3-trisubstituted. Higher degrees of substitution, of which the pentafluorophenyl group is an example, exist, and are named according to IUPAC nomenclature.
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Victor Meyer (1870) "Untersuchungen über die Constitution der zweifach-substituirten Benzole" (Investigations into the structure of di-substituted benzenes), Annalen der Chemie und Pharmacie, 156 : 265-301 ; see especially pp. 299-300. The current nomenclature was introduced by the Chemical Society in 1879.William B. Jensen (March 2006) "The origins of the ortho-, meta-, and para- prefixes in chemical nomenclature," Journal of Chemical Education, 83 (3) : 356. The German version of this page provides the following details.
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It was noted that interactions between substituted benzenes in the T-shaped configuration were more complex. Finally, Sherill and Sinnokrot argue in their review article that any semblance of a trend based on electron donating or withdrawing substituents can be explained by exchange- repulsion and dispersion terms. Houk and Wheeler's computational model of substituent direct interactions in pi stacking. Houk and Wheeler also provide compelling computational evidence for the importance of direct interaction in pi stacking.
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In addition to dechlorination of CAHs, microbes have also been reported to act on chlorinated aromatic hydrocarbons. An example of a reaction where aromatic AOX content has been reduced is demonstrated in figure 2 above. While little is known about the dehalogenation mechanisms of polyhalogenated phenols (PHPs) and polyhalogenated benzenes (PHBs), regioselectivity for halide location on the aromatic ring was observed. This regioselectivity is however dominated by both redox potentials for the reaction and the microbe's familiarity to the reaction.
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Pterocarpans are derivatives of isoflavonoids found in the family Fabaceae. It is a group of compounds which can be described as benzo-pyrano-furano-benzenes (i.e. 6H-[1]benzofuro[3,2-c]chromene skeleton) which can be formed by coupling of the B ring to the 4-one position.Pterocarpans on the National Library of Medicine - Medical Subject Headings 2'-hydroxyisoflavone reductase is the enzyme responsible for the conversion in Cicer arietinum and glyceollin synthase for the production of glyceollins, phytoalexins in soybean.
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The primary contaminants include organochloride pesticides, organophosphate pesticides, carbamate insecticides, organic solvents and feedstock chemicals used as raw products or intermediates in the manufacturing process (e.g., chlorinated benzenes), heavy metals, chemical warfare material and their related breakdown products and biological warfare agent such as TX. Additionally, ordnance (including incendiary munitions) was manufactured and tested, and asbestos and polychlorinated biphenyls (PCBs) were used at RMA. Today, it is considered a hazardous waste site according to the Colorado Department of Public and Environmental Health.
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In addition, it has synthesized a series of new cluttered metal bases derived from tetramethylpiperidine allowing C-H activations of aromatic and heterocyclic unsaturated systems.Makarov, I. S.; Brocklehurst, C. E.; Karaghiosoff, K.; Koch, G.; Knochel, P., « Synthesis of Bicyclo[1.1.1]pentane Bioisosteres of Internal Alkynes and para-Disubstituted Benzenes from [1.1.1]Propellane », Angew. Chem. Int. Ed., 2017, 56, p. 12774-12777Haag, B.; Mosrin, M.; Hiriyakkanavar, I.; Malakhov, V.; Knochel, P., « Regio- and Chemoselective Metalation of Arenes and Heteroarenes Using Hindered Metal Amide Bases», Angew. Chem. Int.
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Water based pipe coatings, are an environmentally friendly coating that is applied to the inner & outer diameter of ductile iron pipe. They protect against corrosion from the outside and inside, and also protect the product from contamination. The coating is an emulsion manufactured using asphaltene and water primarily, with other raw materials according to the manufacturer's specifications. They came in use in the early 1990s, replacing coatings based on dangerous and environmental harmful solvents, such as benzenes, toluenes, hexanes and other volatile organic compounds.
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These bacteria occur naturally and will act to remove oil from an ecosystem, and their biomass will tend to replace other populations in the food chain. The chemicals from the oil which dissolve in water, and hence are available to bacteria, are those in the water associated fraction of the oil. In addition, oil spills can also harm air quality. The chemicals in crude oil are mostly hydrocarbons that contains toxic chemicals such as benzenes, toluene, poly-aromatic hydrocarbon and oxygenated polycyclic aromatic hydrocarbons.
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February 6–8, 2006; Lanzarote, Spain. In 2006, a field bioremediation assay was conducted by the Department of Microbiology, University of Barcelona on the use of S-200 ten months after the Prestige heavy fuel-oil spill on a beach of the Cantabrian coast in northern Spain. The field survey indicated that the product enhanced the biodegradation rate, particularly of high molecular weight n-alkanes, alkylcyclohexanes, and benzenes, and alkylated PAHs. The most significant molecular bioremediation indicators were the depletion of diasteranes and C-27 sterane components.
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Despite a large variety of volatile and odorant compounds that have been identified in soy sauce, the food product per se does not present a strong aroma. Alcohols, acids, esters, aldehydes, ketones, phenols, heterocyclic compounds, alkynes and benzenes are identified in Chinese soy sauces. An explanation for this observation is that the aroma of soy sauce does not depend largely on the aroma-active compounds. The subtle aroma is a result of a "critical balance" achieved among all volatile and odorant compounds, whose respective concentrations are relatively low.
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Another fungus associated with causing cerebral phaeohyphomycosis; Cladophialophora bantiana, has been isolated in one occasion from sawdust, which could also be a possible source of R. mackenziei. Due to the lack of knowledge about its environmental niche, it has been difficult to isolate R. mackenziei; and selective techniques such as the use of high temperatures, mouse vectors, alkyl benzenes and mineral oils are required. Enrichment of growth media with volatile aromatic hydrocarbons improves recovery of this agent, implying a role for aromatic hydrocarbon degradation in its environmental niche.
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Individual honeys from different plant sources contain over 100 volatile organic compounds (VOCs), which play a primary role in determining honey flavors and aromas. VOCs are carbon-based compounds that readily vaporize into the air, providing aroma, including the scents of flowers, essential oils, or ripening fruit. The typical chemical families of VOCs found in honey include hydrocarbons, aldehydes, alcohols, ketones, esters, acids, benzenes, furans, pyrans, norisoprenoids, and terpenes, among many others and their derivatives. The specific VOCs and their amounts vary considerably between different types of honey obtained by bees foraging on different plant sources.
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Furthermore, it has been shown that a majority of reductive dehalogenase activities lie within the extracellular and membranous components of D. ethenogenes, indicating that dechlorination processes may function semi-independently from intracellular systems. Currently, all known dehalococcoides strains require acetate for producing cellular material, however, the underlying mechanisms are not well understood as they appear to lack fundamental enzymes that complete biosynthesis cycles found in other organisms. Dehalococcoides can transform many highly toxic and/or persistent compounds. This includes tetrachloroethene (PCE) and trichloroethene (TCE) which are transformed to non-toxic ethene, and chlorinated dioxins, vinyl chloride, benzenes, polychlorinated biphenyls (PCBs), phenols and many other aromatic contaminants.
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Dehalococcoides can uniquely transform many highly toxic and/or persistent compounds that are not transformed by any other known bacteria, in addition to halogenated compounds that other common organohalide respirers utilize. For example, common compounds such as chlorinated dioxins, benzenes, PCBs, phenols and many other aromatic substrates can be reduced into less harmful chemical forms. However, dehalococcoides are currently the only known dechlorinating bacteria with the unique ability to degrade the highly recalcitrant, tetrachloroethene (PCE) and tricholoroethene (TCE) compounds into less-toxic forms that are more suitable for environmental conditions, and thus utilized in bioremediation. Their capacity to grow by using contaminants allows them to proliferate in contaminated soil or groundwater, offering promise for in situ decontamination efforts.
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Formation of pentacene by extrusion of carbon monoxide The precursor itself is prepared in three steps from two molecules of α,α,α',α'-tetrabromo-o-xylene with a 7-tert- butoxybicyclo[2.2.1]hepta-2,5-diene by first heating with sodium iodide in dimethylformamide to undergo a series of elimination and Diels–Alder reactions to form the ring system, then hydrolysing the tert-butoxy group to an alcohol and followed by its oxidation to the ketone. Pentacene synthesis The product is reported to have some solubility in chloroform and is therefore amenable to spin coating. Pentacene is soluble in hot chlorinated benzenes, such as 1,2,4-trichlorobenzene, from which it can be recrystallized to form platelets.
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Not only had two drivers been killed, but one of them was a triple world champion and arguably the best F1 driver at the time. The FIA reacted swiftly and harshly with major changes to be enforced from that year onwards, and it was the beginning of the FIA's push to increase safety in Formula One. While significant changes could not be made to cars in 1994, the FIA required all Formula One cars' airboxes to be perforated to reduce their "ram-air" effect, to reduce power. For the same reason special racing fuels, previously an exotic mixture of benzenes and toluenes, were banned and only those with similar characteristics to everyday unleaded petrol would be permitted.
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In organic chemistry, when a molecule with a planar ring obeys Hückel's rule, where the number of π electrons fit the formula 4n + 2 (where n is an integer), it attains extra stability and symmetry. In benzene, the prototypical aromatic compound, there are 6 π bonding electrons (n = 1, 4n + 2 = 6). These occupy three delocalized π molecular orbitals (molecular orbital theory) or form conjugate π bonds in two resonance structures that linearly combine (valence bond theory), creating a regular hexagon exhibiting a greater stabilization than the hypothetical 1,3,5-cyclohexatriene. In the case of heterocyclic aromatics and substituted benzenes, the electronegativity differences between different parts of the ring may dominate the chemical behaviour of aromatic ring bonds, which otherwise are equivalent.
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Benzene, toluene, tert-butylbenzene, halo-benzenes, ortho-nitrotoluene, anisole, phenol and acetanilide are all rapidly nitrated within 30 minutes at room temperature. The ultraviolet spectrum of the liquid shows an absorption band peaking at 208 nm with a shoulder at 242 nm. At 55 °C the gaseous vanadyl nitrate has absorption bands also at 486, 582 and 658 nm in the visual light spectrum. Liquid vanadyl nitrate has absorption lines in the infrared at 1880, 1633, 1612, 1560, 1306, 1205, 1016, 996, 965, 895, 783, 632, 457, 357, 301, 283, 234, 193, 133, 93 and 59 cm−1. Gaseous vanadyl nitrate has absorption bands at 775, 783, 786, 962.5, 994.4, 997.5, 1000.5, 1006.2, 1012, 1016.3, 1020, 1198, 1211, 1216.3, 1564, 1612, 1629, 1632, 1635, 1648 and 1888 cm−1.
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This was a period rich in the development of structural theory and nomenclature, and Gräbe is known for introducing the "ortho", "meta" and "para" nomenclature for naphthalene ring substitution.In 1869, Gräbe first used the prefixes ortho-, meta-, para- to denote specific relative locations of the substituents on a di-substituted aromatic ring (viz, naphthalene): Graebe (1869) "Ueber die Constitution des Naphthalins" (On the structure of naphthalene), Annalen der Chemie und Pharmacie, 149 : 20–28 ; see especially p. 26. In 1870, the German chemist Viktor Meyer first applied Gräbe's nomenclature to benzene: Victor Meyer (1870) "Untersuchungen über die Constitution der zweifach-substituirten Benzole" (Investigations into the structure of di-substituted benzenes), Annalen der Chemie und Pharmacie, 156 : 265–301 ; see especially pp. 299–300. See also: Hermann von Fehling, ed.
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In 2004 one of the five communities of the island commenced civil works to build a sewage treatment plant but since then the construction has not been completed and it is currently stopped. On 14 June 2007 there was a breakage in one of the four high-voltage underwater cables forming the power line maintained by Enel S.p.A — although never authorized by Italian authorities — between Cuma on the Campania coast and Lacco Ameno on the island of Ischia. Inside each cable there is an 18 mm‑diameter channel filled with oil under high pressure. The breakage of the Enel cable resulted in the spillage of oil into the sea and into other environmental matrices — with the consequent pollution by polychlorobiphenyls (PCBs, the use of which was banned by the Italian authorities as long ago as 1984), polycyclic aromatic hydrocarbons (PAHs) and linear alkyl benzenes (aromatic hydrocarbons) — in the ‘Regno di Nettuno’, a marine protected area, and the largest ecosystem in the Mediterranean Sea, designated as a ‘priority habitat’ in Annex I to the Habitats Directive (92/43/EEC) and comprising oceanic posidonia beds.
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