|
Criegee Oxidation
The Criegee oxidation is a glycol cleavage reaction in which vicinal difunctionalization, vicinal diols are organic oxidation, oxidized to form ketones and aldehydes using lead tetraacetate. It is analogous to the use of periodate (Malaprade reaction) but uses a milder oxidant. This oxidation was discovered by Rudolf Criegee and coworkers and first reported in 1931 using ethylene glycol as the substrate. The rate of the reaction is highly dependent on the relative geometric position of the two hydroxyl groups, so much so that diols that are ''cis–trans isomerism, cis'' on certain rings can be reacted selectively as opposed to those that are ''trans'' on them. It was heavily stressed by Criegee that the reaction must be run in anhydrous solvents, as any water present would hydrolyze the lead tetraacetate; however, subsequent publications have reported that if the rate of oxidation is faster than the rate of hydrolysis, the cleavage can be run in wet solvents or even aqueous so ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rudolf Criegee
Rudolf Criegee (23 May 1902 — 7 November 1975) was a German organic chemist. Early life Criegee was born on 23 May 1902 in Düsseldorf to a wealthy family. His father worked as a court director. The family was national liberal, Prussian and Protestant, managing what Rudolf Criegee felt was a great fortune. His happy childhood was ended by the World War I. In March 1915, his eldest brother died on the Western Front, while a second brother was seriously injured in the summer of 1916. Criegee himself was drafted. After the post-war period, he matriculated at the University of Tübingen in chemistry in 1920. After four semesters of study and moderate success, his experience in student fraternity Germania and twelve duels, Criegee changed to the University of Greifswald. He remained there for three semesters and passed his first examination. He moved to the University of Würzburg and received his PhD in December 1925 at Otto Dimroth with a thesis on acridinium salts. His father ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glycerol
Glycerol () is a simple triol compound. It is a colorless, odorless, sweet-tasting, viscous liquid. The glycerol backbone is found in lipids known as glycerides. It is also widely used as a sweetener in the food industry and as a humectant in pharmaceutical formulations. Because of its three hydroxyl groups, glycerol is miscible with water and is Hygroscopy, hygroscopic in nature. Modern use of the word glycerine (alternatively spelled glycerin) refers to commercial preparations of less than 100% purity, typically 95% glycerol. Structure Although chirality, achiral, glycerol is prochirality, prochiral with respect to reactions of one of the two primary alcohols. Thus, in substituted derivatives, the Glycerophospholipid#Nomenclature and stereochemistry, stereospecific numbering labels the molecule with a ''sn''- prefix before the stem name of the molecule. Production Natural sources Glycerol is generally obtained from plant and animal sources where it occurs in triglycerides, est ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sharpless Epoxidation
The Sharpless epoxidation reaction is an enantioselective chemical reaction to prepare 2,3-epoxyalcohols from primary and secondary allylic alcohols. The oxidizing agent is ''tert''-butyl hydroperoxide. The method relies on a catalyst formed from titanium tetra(isopropoxide) and diethyl tartrate. 2,3-Epoxyalcohols can be converted into diols, aminoalcohols, and ethers. The reactants for the Sharpless epoxidation are commercially available and relatively inexpensive. K. Barry Sharpless published a paper on the reaction in 1980 and was awarded the 2001 Nobel Prize in Chemistry for this and related work on asymmetric oxidations. The prize was shared with William S. Knowles and Ryōji Noyori. Catalyst 5–10 mol% of the catalyst is typical. The presence of 3Å molecular sieves (3Å MS) is necessary. The structure of the catalyst is uncertain although it is thought to be a dimer of []. Selectivity The epoxidation of allylic alcohols is a well-utilized conversion in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acetoxy
In organic chemistry, the acetoxy group (abbr. AcO– or –OAc; IUPAC name: acetyloxy), is a functional group with the formula and the structure . As the ''-oxy'' suffix implies, it differs from the acetyl group () by the presence of an additional oxygen atom. The name acetoxy is the short form of ''acetyl-oxy''. Functionality An acetoxy group may be used as a protection for an alcohol functionality in a synthetic route although the protecting group itself is called an acetyl group. Alcohol protection There are several options of introducing an acetoxy functionality in a molecule from an alcohol (in effect protecting the alcohol by acetylation): * Acetyl halide, such as acetyl chloride in the presence of a base like triethylamine * Activated ester form of acetic acid, such as a N-hydroxysuccinimide ester, although this is not advisable due to higher costs and difficulties. * Acetic anhydride in the presence of base with a catalyst such as pyridine with a bit of DMAP added. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Epoxide
In organic chemistry, an epoxide is a cyclic ether, where the ether forms a three-atom ring: two atoms of carbon and one atom of oxygen. This triangular structure has substantial ring strain, making epoxides highly reactive, more so than other ethers. They are produced on a large scale for many applications. In general, low molecular weight epoxides are colourless and nonpolar, and often volatile. Nomenclature A compound containing the epoxide functional group can be called an epoxy, epoxide, oxirane, and ethoxyline. Simple epoxides are often referred to as oxides. Thus, the epoxide of ethylene (C2H4) is ethylene oxide (C2H4O). Many compounds have trivial names; for instance, ethylene oxide is called "oxirane". Some names emphasize the presence of the epoxide functional group, as in the compound ''1,2-epoxyheptane'', which can also be called ''1,2-heptene oxide''. A polymer formed from epoxide precursors is called an ''epoxy''. However, few if any of the epoxy groups i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Free Radical
A daughter category of ''Ageing'', this category deals only with the biological aspects of ageing. Ageing Biogerontology Biological processes Causes of death Cellular processes Gerontology Life extension Metabolic disorders Metabolism Old age Time in life {{CatAutoTOC ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Keto Acid
In organic chemistry, keto acids or ketoacids (also called oxo acids or oxoacids) are organic compounds that contain a carboxylic acid group () and a ketone group ().Franz Dietrich Klingler, Wolfgang Ebertz "Oxocarboxylic Acids" in Ullmann's Encyclopedia of Industrial Chemistry 2005, Wiley-VCH, Weinheim. In several cases, the keto group is hydrated. The alpha-keto acids are especially important in biology as they are involved in the Krebs citric acid cycle and in glycolysis. Common types of keto acids include: *Alpha-keto acids, alpha-ketoacids, or 2-oxoacids have the keto group adjacent to the carboxylic acid. They often arise by oxidative deamination of amino acids, and reciprocally, they are precursors to the same. Alpha-keto acids possesses extensive chemistry as acylation agents. Furthermore, alpha-keto acids such as phenylpyruvic acid are endogenous sources for carbon monoxide (as a gasotransmitter) and pharmaceutical prodrug scaffold. Important representatives: ** ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydroxy Ketone
In organic chemistry, a hydroxy ketone (often referred to simply as a ketol) is a functional group consisting of a ketone () flanked by a hydroxyl group (). Chemicals in this group can be classified by the position of the hydroxyl relative to the ketone. The two main classes have the hydroxyl on the alpha or beta carbon, that is, on the immediately adjacent carbon or the next-further carbon, respectively. Thus, the general structure of the two main classes are (alpha) and (beta). Alpha-hydroxy ketones are also called acyloins. They are commonly formed by condensation or reductive coupling of two carbonyl () compounds or oxidation of ketones. The simplest such compound is hydroxyacetone. If the alcohol is primary, alpha-hydroxy ketones give a positive Fehling's test. Beta-hydroxy ketones are a type of aldol. They are commonly formed by an aldol reaction between two carbonyl compounds. A simple example is diacetone alcohol Diacetone alcohol is an organic compound with the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alkanolamine
In organic chemistry, alkanolamines (amino alcohols) are organic compounds that contain both hydroxyl () and amino (, , and ) functional groups on an alkane backbone. Alkanolamine's bifunctionality and physicochemical characteristics lead to its use in many applications, such as textiles, cosmetics, agricultural chemical intermediates, drugs, and metal working fluids. Many aminoalcohols derivatives also have chemotherapeutic properties. Methanolamine.svg, Methanolamine, from the reaction of ammonia with formaldehyde Ethanolamine.svg, Ethanolamine 2-amino-2-methyl-1-propanol.svg, 2-Amino-2-methyl-1-propanol is a precursor to oxazolines valinol.svg, Valinol is derived from the amino acid valine Sphingosine structure.svg, Sphingosine is a component of some cell membranes. Alkanolamines usually have high-solubility in water due to the hydrogen bonding ability of both the hydroxyl group and the amino group. Alkanoamines have also shown a broad toxicity for a variety of organism ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Criegee Mechansim
Rudolf Criegee (23 May 1902 — 7 November 1975) was a German organic chemist. Early life Criegee was born on 23 May 1902 in Düsseldorf to a wealthy family. His father worked as a court director. The family was national liberal, Prussian and Protestant, managing what Rudolf Criegee felt was a great fortune. His happy childhood was ended by the World War I. In March 1915, his eldest brother died on the Western Front, while a second brother was seriously injured in the summer of 1916. Criegee himself was drafted. After the post-war period, he matriculated at the University of Tübingen in chemistry in 1920. After four semesters of study and moderate success, his experience in student fraternity Germania and twelve duels, Criegee changed to the University of Greifswald. He remained there for three semesters and passed his first examination. He moved to the University of Würzburg and received his PhD in December 1925 at Otto Dimroth with a thesis on acridinium salts. His father ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Encyclopedia Of Reagents For Organic Synthesis
The ''Encyclopedia of Reagents for Organic Synthesis'' is published in print and online by John Wiley & Sons Ltd. The online version is also known as e-EROS. The encyclopedia contains a description of the use of reagents used in organic chemistry. The eight-volume print version includes 3500 alphabetically arranged articles and the online version is regularly updated to include new reagents and catalyst Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...s. References External links *Print version Encyclopedias of science Chemistry books {{encyclopedia-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Conformational Isomerism
In chemistry, rotamers are chemical species that differ from one another primarily due to rotations about one or more single bonds. Various arrangements of atoms in a molecule that differ by rotation about single bonds can also be referred to as conformations. Conformers/rotamers differ little in their energies, so they are almost never separable in a practical sense. Rotations about single bonds are subject to small energy barriers. When the time scale for interconversion is long enough for isolation of individual rotamers (usually arbitrarily defined as a half-life of interconversion of 1000 seconds or longer), the species are termed atropisomers (''see:'' atropisomerism). The Ring flip, ring-flip of substituted cyclohexanes constitutes a common form of conformers. The study of the energetics of bond rotation is referred to as conformational analysis. In some cases, conformational analysis can be used to predict and explain product selectivity, mechanisms, and rates of reaction ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
