|
1,2,4,5-Tetrabromobenzene
1,2,4,5-Tetrabromobenzene is a bromobenzene with the formula C6H2Br4. It is one of three isomers of tetrabromobenzene. The compound is a white solid. 1,2,4,5-Tetrabromobenzene is an important metabolite of the flame retardant hexabromobenzene. Preparation The synthesis of 1,2,4,5-tetrabromobenzene has already been reported in 1865 from benzene and excess bromine in a sealed tube at 150 °C. However, the clearly reduced melting point of about 160 °C indicates impurities in the final product. In his 1885 dissertation, Adolf Scheufelen published the synthesis of a purer sample using iron(III) chloride FeCl as a catalyst, isolated as "pretty needles" ("schönen Nadeln"). The synthesis can also be carried out in solution in chloroform or tetrachloromethane and yields 1,2,4,5-tetrabromobenzene in 89% yield. This reaction can also be carried out in a laboratory experiment with excess bromine and iron nails (as starting material for iron (III) bromide FeBr). The interm ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bromobenzenes
Bromobenzene is an aryl halide, C6H5Br. It is a colourless liquid although older samples can appear yellow. It is a reagent in organic synthesis. Synthesis and reactions Bromobenzene is prepared by the action of bromine on benzene in the presence of Lewis acid catalysts such as aluminium chloride or ferric bromide. Bromobenzene is used to introduce a phenyl group into other compounds. One method involves its conversion to the Grignard reagent, phenylmagnesium bromide. This reagent can be used, e.g. in the reaction with carbon dioxide to prepare benzoic acid. Other methods involve palladium-catalyzed coupling reactions, such as the Suzuki reaction. Bromobenzene is used as a precursor in the manufacture of phencyclidine. Toxicity Animal tests indicate low toxicity. Little is known about chronic effects. For liver toxicity, the 3,4-epoxide are proposed intermediates. See also *Fluorobenzene *Chlorobenzene *Iodobenzene Iodobenzene is an organoiodine compound consisting of a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Potassium Carbonate
Potassium carbonate is the inorganic compound with the formula K2 CO3. It is a white salt, which is soluble in water. It is deliquescent, often appearing as a damp or wet solid. Potassium carbonate is mainly used in the production of soap and glass. History Potassium carbonate is the primary component of potash and the more refined pearl ash or salts of tartar. Historically, pearl ash was created by baking potash in a kiln to remove impurities. The fine, white powder remaining was the pearl ash. The first patent issued by the US Patent Office was awarded to Samuel Hopkins in 1790 for an improved method of making potash and pearl ash. In late 18th-century North America, before the development of baking powder, pearl ash was used as a leavening agent for quick breads. Production Potassium carbonate is prepared commercially by the reaction potassium hydroxide with carbon dioxide: : 2 KOH + CO2 → K2CO3 + H2O From the solution crystallizes the sesquihydrate K2CO3·H2O ("potash ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solvatochromism
In chemistry, solvatochromism is the phenomenon observed when the colour due to a solute is different when that solute is dissolved in different solvents. The solvatochromic effect is the way the spectrum of a substance (the solute) varies when the substance is dissolved in a variety of solvents. In this context, the dielectric constant and hydrogen bonding capacity are the most important properties of the solvent. With various solvents there is a different effect on the electronic ground state and excited state of the solute, so that the size of energy gap between them changes as the solvent changes. This is reflected in the absorption or emission spectrum of the solute as differences in the position, intensity, and shape of the spectroscopic bands. When the spectroscopic band occurs in the visible part of the spectrum solvatochromism is observed as a change of colour. This is illustrated by Reichardt's dye, as shown in the image. Negative solvatochromism corresponds to a hypsoc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fluorescent Dyes
A fluorophore (or fluorochrome, similarly to a chromophore) is a fluorescent chemical compound that can re-emit light upon light excitation. Fluorophores typically contain several combined aromatic groups, or planar or cyclic molecules with several π bonds. Fluorophores are sometimes used alone, as a tracer in fluids, as a dye for staining of certain structures, as a substrate of enzymes, or as a probe or indicator (when its fluorescence is affected by environmental aspects such as polarity or ions). More generally they are covalently bonded to a macromolecule, serving as a marker (or dye, or tag, or reporter) for affine or bioactive reagents (antibodies, peptides, nucleic acids). Fluorophores are notably used to stain tissues, cells, or materials in a variety of analytical methods, i.e., fluorescent imaging and spectroscopy. Fluorescein, via its amine-reactive isothiocyanate derivative fluorescein isothiocyanate (FITC), has been one of the most popular fluorophores. From a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bildung Von BBI-Salzen Und Benzochinondiiminen
''Bildung'' (, "education", "formation", etc.) refers to the German tradition of self-cultivation (as related to the German for: creation, image, shape), wherein philosophy and education are linked in a manner that refers to a process of both personal and cultural maturation. This maturation is a harmonization of the individual's mind and heart and in a unification of selfhood and identity within the broader society, as evidenced with the literary tradition of ''Bildungsroman''. In this sense, the process of harmonization of mind, heart, selfhood and identity is achieved through personal transformation, which presents a challenge to the individual's accepted beliefs. In Hegel's writings, the challenge of personal growth often involves an agonizing alienation from one's "natural consciousness" that leads to a reunification and development of the self. Similarly, although social unity requires well-formed institutions, it also requires a diversity of individuals with the freedom (i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Triethyl Orthoformate
Triethyl orthoformate is an organic compound with the formula HC(OC2H5)3. This colorless volatile liquid, the orthoester of formic acid, is commercially available. The industrial synthesis is from hydrogen cyanide and ethanol. It may also be prepared from the reaction of sodium ethoxide, formed in-situ from sodium and absolute ethanol, and chloroform: : CHCl3 + 3 Na + 3 EtOH → HC(OEt)3 + H2 + 3 NaCl Triethyl orthoformate is used in the Bodroux-Chichibabin aldehyde synthesis, for example: : RMgBr + HC(OC2H5)3 → RC(H)(OC2H5)2 + MgBr(OC2H5) : RC(H)(OC2H5)2 + H2O → RCHO + 2 C2H5OH In coordination chemistry, it is used to convert metal aquo complexes to the corresponding ethanol complexes: : i(H2O)6BF4)2 + 6 HC(OC2H5)3 → i(C2H5OH)6BF4)2 + 6 HC(O)(OC2H5) + 6 HOC2H5 Triethyl orthoformate (TEOF) is an excellent reagent for converting compatible carboxylic acids to ethyl esters. Such carboxylic acids, refluxed neat in excess TEOF until low-boiler ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optical Brightener
Optical brighteners, optical brightening agents (OBAs), fluorescent brightening agents (FBAs), or fluorescent whitening agents (FWAs), are chemical compounds that absorb light in the ultraviolet and violet region (usually 340-370 nm) of the electromagnetic spectrum, and re-emit light in the blue region (typically 420-470 nm) through the phenomenon of fluorescence. These additives are often used to enhance the appearance of color of fabric and paper, causing a "whitening" effect; they make intrinsically yellow/orange materials look less so, by compensating the deficit in blue and purple light reflected by the material, with the blue and purple optical emission of the fluorophore. Properties The most common classes of compounds with this property are the stilbenes, e.g., 4,4′-diamino-2,2′-stilbenedisulfonic acid. Older, non-commercial fluorescent compounds include umbelliferone, which absorbs in the UV portion of the spectrum and re-emit it in the blue portion of th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Synthese Eines Symmetrischen Tetraalkoxystilbens
''Synthese'' () is a scholarly periodical specializing in papers in epistemology, methodology, and philosophy of science, and related issues. Its subject area is divided into four specialties, with a focus on the first three: (1) "epistemology, methodology, and philosophy of science, all broadly understood"; (2) "foundations of logic and mathematics, where 'logic', 'mathematics', and 'foundations' are all broadly understood"; (3) "formal methods in philosophy, including methods connecting philosophy to other academic fields"; and (4) "issues in ethics and the history and sociology of logic, mathematics, and science that contribute to the contemporary studies". As of 2022, according to Google Scholar's metrics ( h-5 index and h-5 index median), it is the top philosophy journal, but other metrics do not rank the journal as highly. Overview Published articles include specific treatment of methodological issues in science such as induction, probability, causation, statistics, symboli ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tetrahedron Lett
''Tetrahedron Letters'' is a weekly international journal for rapid publication of full original research papers in the field of organic chemistry. According to the ''Journal Citation Reports'', the journal has a 2020 impact factor of 2.415. Indexing ''Tetrahedron Letters'' is indexed in: References See also *''Tetrahedron In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the o ...'' *'' Tetrahedron: Asymmetry'' Chemistry journals Weekly journals Publications established in 1959 Elsevier academic journals {{chem-journal-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dimethylacetamide
Dimethylacetamide (DMAc or DMA) is the organic compound with the formula CH3C(O)N(CH3)2. This colorless, water-miscible, high-boiling liquid is commonly used as a polar solvent in organic synthesis. DMA is miscible with most other solvents, although it is poorly soluble in aliphatic hydrocarbons. Synthesis and production DMA is prepared commercially by the reaction of dimethylamine with acetic anhydride or acetic acid. Dehydration of the salt of dimethylamine and acetic acid also furnishes this compound: : CH3CO2H·HN(CH3)2 → H2O + CH3CON(CH3)2 Dimethylacetamide can also be produced by the reaction of dimethylamine with methyl acetate. : The separation and purification of the product is carried out by multistage distillation in rectification columns. DMA is obtained with essentially quantitive (99%) yield referred to methyl acetate. Reactions and applications The chemical reactions of dimethylacetamide are typical of ''N'',''N''-disubstituted amides. Hydrolysis of the acyl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
1,3-Bis(diphenylphosphino)propane
1,3-Bis(diphenylphosphino)propane (dppp) is an organophosphorus compound with the formula PhP(CH)PPh. The compound is a white solid that is soluble in organic solvents. It is slightly air-sensitive, degrading in air to the phosphine oxide. It is classified as a diphosphine ligand in coordination chemistry and homogeneous catalysis. The diphosphine can be prepared by the reaction of lithium diphenylphosphide and 1,3-dichloropropane (Ph = CH): : 2 PhPLi + CHCl → PhP(CH)PPh + 2 LiCl However, it can be synthesised via a much more controllable (and cheaper) route, via metal-halogen exchange and then metathesis: :Br(CH)Br + 2 BuLi → Li(CH)Li + 2 BuBr :Li(CH)Li + 2 PCl → ClP(CH)PCl + 2 LiCl :ClP(CH)PCl + 4 PhLi → PhP(CH)PPh + 4 LiCl Coordination chemistry and use as co-catalyst The diphosphine serves as a bidentate ligand forming six-membered CPM chelate ring with a natural bite angle of 91°. For example, the complex dichloro(1,3-bis(diphenylphosphino)propane)nic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Co Catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quickly, very small amounts of catalyst often suffice; mixing, surface area, and temperature are important factors in reaction rate. Catalysts generally react with one or more reactants to form intermediates that subsequently give the final reaction product, in the process of regenerating the catalyst. Catalysis may be classified as either homogeneous, whose components are dispersed in the same phase (usually gaseous or liquid) as the reactant, or heterogeneous, whose components are not in the same phase. Enzymes and other biocatalysts are often considered as a third category. Catalysis is ubiquitous in chemical industry of all kinds. Estimates are that 90% of all commercially produced chemical products involve catalysts at some stag ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
