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Lossen Rearrangement
The Lossen rearrangement is the conversion of a hydroxamic acid, hydroxamate ester to an isocyanate. Typically O-acyl, sulfonyl, or phosphoryl O-derivative are employed. The isocyanate can be used further to generate ureas in the presence of amines or generate amines in the presence of H2O. Reaction mechanism The mechanism below begins with an O-acylated hydroxamic acid derivative that is treated with base to form an isocyanate that generates an amine and carbon dioxide, CO2 gas in the presence of H2O. The hydroxamic acid derivative is first converted to its conjugate base by abstraction of a hydrogen by a base. Spontaneous rearrangement releases a carboxylate anion to produce the isocyanate intermediate. The isocyanate is then hydrolyzed in the presence of H2O. Finally, the respective amine and CO2 are generated by abstraction of a proton with a base and decarboxylation. Hydroxamic acids are commonly synthesized from their corresponding esters. Historical references * * * ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wilhelm Lossen
Wilhelm Clemens Lossen (8 May 1838 in Kreuznach – 29 October 1906 in Aachen) was a German chemist. He was the brother of geologist Karl August Lossen. From 1857 he studied chemistry at the University of Giessen, then continued his education at Göttingen as a pupil of Friedrich Wöhler. After graduation, he worked as an assistant to Karl Weltzien at the polytechnic in Karlsruhe and as an assistant under Wilhelm Heinrich Heintz at the University of Halle. In 1870 he became an associate professor at Heidelberg, then in 1877 accepted a position as professor of chemistry at the University of Königsberg. He is largely known for his work with hydroxylamines; their preparations, properties and derivatives. The eponymous Lossen rearrangement, refers to the decomposition of hydroxamic acids or their derivatives to yield isocyanates. While a student at Göttingen, he conducted research of cocaine with Albert Niemann. After the untimely death of Niemann in 1861, he continued re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ester
In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distinctive functional group. Analogues derived from oxygen replaced by other chalcogens belong to the ester category as well. According to some authors, organyl derivatives of acidic hydrogen of other acids are esters as well (e.g. amides), but not according to the IUPAC. Glycerides are fatty acid esters of glycerol; they are important in biology, being one of the main classes of lipids and comprising the bulk of animal fats and vegetable oils. Lactones are cyclic carboxylic esters; naturally occurring lactones are mainly 5- and 6-membered ring lactones. Lactones contribute to the aroma of fruits, butter, cheese, vegetables like celery and other foods. Esters can be formed from oxoacids (e.g. esters of acetic acid, carbonic acid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
YouTube
YouTube is an American social media and online video sharing platform owned by Google. YouTube was founded on February 14, 2005, by Steve Chen, Chad Hurley, and Jawed Karim who were three former employees of PayPal. Headquartered in San Bruno, California, it is the second-most-visited website in the world, after Google Search. In January 2024, YouTube had more than 2.7billion monthly active users, who collectively watched more than one billion hours of videos every day. , videos were being uploaded to the platform at a rate of more than 500 hours of content per minute, and , there were approximately 14.8billion videos in total. On November 13, 2006, YouTube was purchased by Google for $1.65 billion (equivalent to $ billion in ). Google expanded YouTube's business model of generating revenue from advertisements alone, to offering paid content such as movies and exclusive content produced by and for YouTube. It also offers YouTube Premium, a paid subs ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gabapentin
Gabapentin, sold under the brand name Neurontin among others, is an anticonvulsant medication primarily used to treat neuropathic pain and also for partial seizures of epilepsy. It is a commonly used medication for the treatment of neuropathic pain caused by diabetic neuropathy, postherpetic neuralgia, and central pain. It is moderately effective: about 30–40% of those given gabapentin for diabetic neuropathy or postherpetic neuralgia have a meaningful benefit. Gabapentin, like other gabapentinoid drugs, acts by decreasing activity of the α2δ-1 protein, coded by the CACNA2D1 gene, first known as an auxiliary subunit of voltage gated calcium channels. However, see Pharmacodynamics, below. By binding to α2δ-1, gabapentin reduces the release of excitatory neurotransmitters (primarily glutamate) and as a result, reduces excess excitation of neuronal networks in the spinal cord and brain. Sleepiness and dizziness are the most common side effects. Serious side effects in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Beckmann Rearrangement
The Beckmann rearrangement, named after the German chemist Ernst Otto Beckmann (1853–1923), is a rearrangement reaction, rearrangement of an oxime functional group to substituted amides. The rearrangement has also been successfully performed on haloimines and nitrones. Cyclic oximes and haloimines yield lactams. The Beckmann rearrangement is often catalyzed by acid; however, other reagents have been known to promote the rearrangement. These include tosyl chloride, thionyl chloride, phosphorus pentachloride, phosphorus pentoxide, triethylamine, sodium hydroxide, trimethylsilyl iodide among others. The Beckmann fragmentation is another reaction that often competes with the rearrangement, though careful selection of promoting reagent and solvent conditions can favor the formation of one over the other, sometimes giving almost exclusively one product. The rearrangement occurs Stereospecificity, stereospecifically for ketoximes and N-chloro/N-fluoro imines, with the migrating group be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Schmidt Reaction
In organic chemistry, the Schmidt reaction is an organic reaction in which an azide reacts with a carbonyl derivative, usually an aldehyde, ketone, or carboxylic acid, under acidic conditions to give an amine or amide, with expulsion of nitrogen. It is named after Karl Friedrich Schmidt (1887–1971), who first reported it in 1924 by successfully converting benzophenone and hydrazoic acid to benzanilide. The intramolecular reaction was not reported until 1991 but has become important in the synthesis of natural products. The reaction is effective with carboxylic acids to give amines (above), and with ketones to give amides (below). Reaction mechanism The reaction is closely related to the Curtius rearrangement except that in this reaction the acyl azide is produced by reaction of the carboxylic acid with hydrazoic acid via the protonated carboxylic acid, in a process akin to a Fischer esterification. An alternative, involving the formation of an acylium ion, becomes more im ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hofmann Rearrangement
The Hofmann rearrangement (Hofmann degradation) is the organic reaction of a primary amide to a primary amine with one less carbon atom. The reaction involves oxidation of the nitrogen followed by rearrangement of the carbonyl and nitrogen to give an isocyanate intermediate. The reaction can form a wide range of products, including alkyl and aryl amines. The reaction is named after its discoverer, August Wilhelm von Hofmann, and should not be confused with the Hofmann elimination, another name reaction for which he is eponymous. Mechanism The reaction of bromine with sodium hydroxide forms sodium hypobromite ''in situ'', which transforms the primary amide into an intermediate isocyanate. The formation of an intermediate nitrene is not possible because it implies also the formation of a hydroxamic acid as a byproduct, which has never been observed. The intermediate isocyanate is hydrolyzed to a primary amine, giving off carbon dioxide. #Base abstracts an acidic N-H proto ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Curtius Rearrangement
The Curtius rearrangement (or Curtius reaction or Curtius degradation), first defined by Theodor Curtius in 1885, is the thermal decomposition of an acyl azide to an isocyanate with loss of nitrogen gas. The isocyanate then undergoes attack by a variety of nucleophiles such as water, alcohols and amines, to yield a primary amine, carbamate or urea derivative respectively. Several reviews have been published. Preparation of acyl azide The acyl azide is usually made from the reaction of acid chlorides or anhydrides with sodium azide or trimethylsilyl azide. Acyl azides are also obtained from treating acylhydrazines with nitrous acid. Alternatively, the acyl azide can be formed by the direct reaction of a carboxylic acid with diphenylphosphoryl azide (DPPA). Reaction mechanism It was believed that the Curtius rearrangement was a two-step processes, with the loss of nitrogen gas forming an acyl nitrene, followed by migration of the R-group to give the isocyanate. However, rec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydroxamic Acid
In organic chemistry, hydroxamic acids are a class of organic compounds having a general formula bearing the functional group , where R and R' are typically organyl groups (e.g., alkyl or aryl) or hydrogen. They are amides () wherein the nitrogen atom has a hydroxyl () substituent. They are often used as metal chelators. Common example of hydroxamic acid is aceto-''N''-methylhydroxamic acid (). Some uncommon examples of hydroxamic acids are formo-''N''-chlorohydroxamic acid () and chloroformo-''N''-methylhydroxamic acid (). Synthesis and reactions Hydroxamic acids are usually prepared from either esters or acid chlorides by a reaction with hydroxylamine salts. For the synthesis of benzohydroxamic acid ( or , where Ph is phenyl group), the overall equation is: : Hydroxamic acids can also be synthesized from aldehydes and ''N''-sulfonylhydroxylamine via the Angeli-Rimini reaction. Alternatively, molybdenum oxide diperoxide oxidizes trimethylsilated amides to hydroxamic acid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Decarboxylation
Decarboxylation is a chemical reaction that removes a carboxyl group and releases carbon dioxide (CO2). Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is the first chemical step in photosynthesis, is called carboxylation, the addition of CO2 to a compound. Enzymes that catalyze decarboxylations are called decarboxylases or, the more formal term, carboxy-lyases (Enzyme Commission number, EC number 4.1.1). In organic chemistry The term "decarboxylation" usually means replacement of a carboxyl group () with a hydrogen atom: : Decarboxylation is one of the oldest known organic reactions. It is one of the processes assumed to accompany pyrolysis and destructive distillation. Overall, decarboxylation depends upon stability of the carbanion synthon , although the anion may not be a true chemical intermediate. Typically, carboxylic acids decarboxylate slowly, but carboxylic acids with an α el ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbon Dioxide
Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at normally-encountered concentrations it is odorless. As the source of carbon in the carbon cycle, atmospheric is the primary carbon source for life on Earth. In the air, carbon dioxide is transparent to visible light but absorbs infrared, infrared radiation, acting as a greenhouse gas. Carbon dioxide is soluble in water and is found in groundwater, lakes, ice caps, and seawater. It is a trace gas Carbon dioxide in Earth's atmosphere, in Earth's atmosphere at 421 parts per million (ppm), or about 0.042% (as of May 2022) having risen from pre-industrial levels of 280 ppm or about 0.028%. Burning fossil fuels is the main cause of these increased concentrations, which are the primary cause of climate change.IPCC (2022Summary for pol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
