text
stringlengths 105
6.5k
| label
int64 0
1
| label_text
stringclasses 2
values |
|---|---|---|
Sodium trifluoromethanesulfinate (CFSONa) as a trifluoromethylation reagent was introduced by Langlois in 1991. The reaction requires t-butyl hydroperoxide and generally a metal and proceeds through a radical mechanism. The reagent has been applied with heterocyclic substrates | 0 | Organic Reactions |
An oxocarbenium ion (or oxacarbenium ion) is a chemical species characterized by a central sp-hybridized carbon, an oxygen substituent, and an overall positive charge that is delocalized between the central carbon and oxygen atoms. An oxocarbenium ion is represented by two limiting resonance structures, one in the form of a carbenium ion with the positive charge on carbon and the other in the form of an oxonium species with the formal charge on oxygen. As a resonance hybrid, the true structure falls between the two. Compared to neutral carbonyl compounds like ketones or esters, the carbenium ion form is a larger contributor to the structure. They are common reactive intermediates in the hydrolysis of glycosidic bonds, and are a commonly used strategy for chemical glycosylation. These ions have since been proposed as reactive intermediates in a wide range of chemical transformations, and have been utilized in the total synthesis of several natural products. In addition, they commonly appear in mechanisms of enzyme-catalyzed biosynthesis and hydrolysis of carbohydrates in nature. Anthocyanins are natural flavylium dyes, which are stabilized oxocarbenium compounds. Anthocyanins are responsible for the colors of a wide variety of common flowers such as pansies and edible plants such as eggplant and blueberry. | 0 | Organic Reactions |
Epoxidation of allyl- and vinylsilanes can be easily accomplished with peracids. Silyl epoxides can be converted into ketones, aldehydes, or alkenes after selective epoxide opening and elimination. When allylsilanes are combined with peracids, the intermediate epoxides are usually converted to allylic alcohols before isolation.
Halogen electrophiles, primarily X, react with vinyl- and allylsilanes to give a number of halogenated products. Further reaction of the initial adducts is common, and may lead, for instance, to conjugated dienes. Dienes may react further with X under the reaction conditions or undergo [4+2] cycloadditions in the presence of dienophiles.
A few metal electrophiles react with allylsilanes to give interesting products. Reactions of allylsilanes with thallium tris (trifluoroacetate) form electrophilic allylthallium(II) compounds. Palladation of allylsilanes provides π-allylpalladium compounds. | 0 | Organic Reactions |
Simmons-Smith cyclopropanation, which employs carbenes derived from diiodomethane, is a popular alternative to rhodium-catalyzed cyclopropanation. In the presence of a chiral diamine, Simmons-Smith cyclopropanation is enantioselective; however, selectivities are not as high as the corresponding rhodium-catalyzed reactions.
Substituted zinc carbenoids can be prepared from the corresponding ketones or aldehydes through a sequence analogous to the mechanism of the Clemmensen reduction. Cyclopropanation of olefins with these intermediates occurs with moderate diastereoselectivity and yield.
Other diazo compounds besides diazocarbonyl compounds have been used for rhodium-catalyzed cyclopropanations; however, these substrates are much more difficult to handle and unstable than diazocarbonyl compounds. Thus, they have not been extensively adopted for organic synthesis. | 0 | Organic Reactions |
As it is only effective for primary amines, the carbylamine reaction can be used as a chemical test for their presence. In this context, the reaction is also known as Saytzeff's isocyanide test. In this reaction, the analyte is heated with alcoholic potassium hydroxide and chloroform. If a primary amine is present, the isocyanide (carbylamine) is formed, as indicated by a foul odour. The carbylamine test does not give a positive reaction with secondary and tertiary amines. | 0 | Organic Reactions |
In organic chemistry, enolates are organic anions derived from the deprotonation of carbonyl () compounds. Rarely isolated, they are widely used as reagents in the synthesis of organic compounds. | 0 | Organic Reactions |
Gallium arsenide (GaAs) is a III-V direct band gap semiconductor with a zinc blende crystal structure.
Gallium arsenide is used in the manufacture of devices such as microwave frequency integrated circuits, monolithic microwave integrated circuits, infrared light-emitting diodes, laser diodes, solar cells and optical windows.
GaAs is often used as a substrate material for the epitaxial growth of other III-V semiconductors, including indium gallium arsenide, aluminum gallium arsenide and others. | 1 | Inorganic Reactions + Inorganic Compounds |
From Isaiah: "And the people shall be as the burnings of lime: as thorns cut up shall they be burned in the fire"
Its use is mentioned in the Book of Amos (2:1): "I will not turn away the punishment thereof, because he burned the bones of the King of Edom into lime."
It was used in ancient formulas for white paint and cosmetic pigments, and in the cupellation process to separate silver from lead. | 1 | Inorganic Reactions + Inorganic Compounds |
Ketones and imines are related functional groups, and effective technologies for the asymmetric hydrogenation of each are also closely related. Early examples are Noyori's ruthenium-chiral diphosphine-diamine system.
For carbonyl and imine substrates, end-on, η coordination can compete with η mode. For η-bound substrates, the hydrogen-accepting carbon is removed from the catalyst and resists hydrogenation.
Iridium/P,N ligand-based systems have been effective for some ketones and imines. For example, a consistent system for benzylic aryl imines uses the P,N ligand SIPHOX in conjunction with iridium(I) in a cationic complex to achieve asymmetric hydrogenation with ee >90%. An efficient catalyst for ketones, (turnover number (TON) up to 4,550,000 and ee up to 99.9%) is an iridium(I) system with a closely related tridentate ligand.
<br />
The BINAP/diamine-Ru catalyst is effective for the asymmetric reduction of both functionalized and simple ketones, and BINAP/diamine-Ru catalyst can catalyze aromatic, heteroaromatic, and olefinic ketones enantioselectively. Better stereoselectivity is achieved when one substituent is larger than the other (see Flippin-Lodge angle). | 0 | Organic Reactions |
GaN is a very hard (Knoop hardness 14.21 GPa), mechanically stable wide-bandgap semiconductor material with high heat capacity and thermal conductivity. In its pure form it resists cracking and can be deposited in thin film on sapphire or silicon carbide, despite the mismatch in their lattice constants. GaN can be doped with silicon (Si) or with oxygen to n-type and with magnesium (Mg) to p-type. However, the Si and Mg atoms change the way the GaN crystals grow, introducing tensile stresses and making them brittle. Gallium nitride compounds also tend to have a high dislocation density, on the order of 10 to 10 defects per square centimeter.
The U.S. Army Research Laboratory (ARL) provided the first measurement of the high field electron velocity in GaN in 1999. Scientists at ARL experimentally obtained a peak steady-state velocity of , with a transit time of 2.5 picoseconds, attained at an electric field of 225 kV/cm. With this information, the electron mobility was calculated, thus providing data for the design of GaN devices. | 1 | Inorganic Reactions + Inorganic Compounds |
The reaction mechanism of decomposition of diazocarbonyl compounds with copper begins with the formation of a copper carbene complex. Evidence for the formation of copper carbenes is provided by comparison to the behavior of photolytically generated free carbenes and the observation of appreciable enantioselectivity in cyclopropanations with chiral copper complexes. Upon formation of the copper carbene, either insertion or addition takes place to afford carbocycles or cyclopropanes, respectively. Both addition and insertion proceed with retention of configuration. Thus, diastereoselectivity may often be dictated by the configuration of the starting material. | 0 | Organic Reactions |
Amination is the process by which an amine group is introduced into an organic molecule. This type of reaction is important because organonitrogen compounds are pervasive. | 0 | Organic Reactions |
Lanthanum(III) oxalate forms colorless crystals that are poorly soluble in water.
The compound forms various crystallohydrates •n, where n = 1, 2, 3, 7, and 10.
The crystallohydrates decompose when heated. | 1 | Inorganic Reactions + Inorganic Compounds |
The stereochemistry involved in the reactions of five-membered rings can be predicted by an envelope transition state model. Nucleophiles favor addition from the "inside" of the envelope, or from the top of the figure on the right. The "inside" addition produces a results in a staggered conformation, rather than the eclipsed conformation that results from the "outside" addition. | 0 | Organic Reactions |
Acetate esters and acetamides are generally prepared by acetylations. Acetylations are often used in making C-acetyl bonds in Friedel-Crafts reactions. Carbanions and their equivalents are susceptible to acetylations. | 0 | Organic Reactions |
Glass reacts slowly with aqueous sodium hydroxide solutions at ambient temperatures to form soluble silicates. Because of this, glass joints and stopcocks exposed to sodium hydroxide have a tendency to "freeze". Flasks and glass-lined chemical reactors are damaged by long exposure to hot sodium hydroxide, which also frosts the glass. Sodium hydroxide does not attack iron at room temperature, since iron does not have amphoteric properties (i.e., it only dissolves in acid, not base).
Nevertheless, at high temperatures (e.g. above 500 °C), iron can react endothermically with sodium hydroxide to form iron(III) oxide, sodium metal, and hydrogen gas. This is due to the lower enthalpy of formation of iron(III) oxide (−824.2 kJ/mol) compared to sodium hydroxide (−500 kJ/mol) and positive entropy change of the reaction, which implies spontaneity at high temperatures (, ) and non-spontaneity at low temperatures (, ). Consider the following reaction between molten sodium hydroxide and finely divided iron filings:
A few transition metals, however, may react quite vigorously with sodium hydroxide under milder conditions.
In 1986, an aluminium road tanker in the UK was mistakenly used to transport 25% sodium hydroxide solution, causing pressurization of the contents and damage to tankers. The pressurization is due to the hydrogen gas which is produced in the reaction between sodium hydroxide and aluminium: | 1 | Inorganic Reactions + Inorganic Compounds |
Alpha hydroxy acids can be converted into amino acids directly using aqueous ammonia solution, hydrogen gas and a heterogeneous metallic ruthenium catalyst. | 0 | Organic Reactions |
The terminus of the double bond in enols is nucleophilic. Its reactions with electrophilic organic compounds is important in biochemistry as well as synthetic organic chemistry. In the former area, the fixation of carbon dioxide involves addition of CO to an enol. | 0 | Organic Reactions |
Many different nucleophiles have been reported to be effective for this reaction. Some of the most common nucleophiles include malonates, enolates, primary alkoxides, carboxylates, phenoxides, amines, azide, sulfonamides, imides, and sulfones. | 0 | Organic Reactions |
HDAC1 & HDAC2 are in the first class of HDACs are most closely related to one another. By analyzing the overall sequences of both HDACs, their similarity was found to be approximately 82% homologous. These enzymes have been found to be inactive when isolated which led to the conclusion that they must be incorporated with cofactors in order to activate their deacetylase abilities. There are three major protein complexes that HDAC 1 & 2 may incorporate themselves into. These complexes include Sin3 (named after its characteristic protein mSin3A), Nucleosome Remodelling and Deacetylating complex (NuRD), and Co-REST. The Sin3 complex and the NuRD complex both contain HDACs 1 and 2, the Rb-associated protein 48 (RbAp48) and RbAp46 which make up the core of each complex. Other complexes may be needed though in order to initiate the maximum amount of available activity possible. HDACs 1 and 2 can also bind directly to DNA binding proteins such as Yin and Yang 1 (YY1), Rb binding protein 1 and Sp1. HDACs 1 and 2 have been found to express regulatory roles in key cell cycle genes including p21.
Activity of these HDACs can be affected by phosphorylation. An increased amount of phosphorylation (hyperphosphorylation) leads to increased deacetylase activity, but degrades complex formation between HDACs 1 and 2 and between HDAC1 and mSin3A/YY1. A lower than normal amount of phosphorylation (hypophosphorylation) leads to a decrease in the amount of deacetylase activity, but increases the amount of complex formation. Mutation studies found that major phosphorylation happens at residues Ser and Ser. Indeed, when these residues were mutated, a drastic reduction was seen in the amount of deacetylation activity. This difference in the state of phosphorylation is a way of keeping an optimal level of phosphorylation to ensure there is no over or under expression of deacetylation. HDACs 1 and 2 have been found only exclusively in the nucleus. In HDAC1 knockout (KO) mice, mice were found to die during embryogenesis and showed a drastic reduction in the production but increased expression of Cyclin-Dependent Kinase Inhibitors (CDKIs) p21 and p27. Not even upregulation of the other Class I HDACs could compensate for the loss of HDAC1. This inability to recover from HDAC1 KO leads researchers to believe that there are both functional uniqueness to each HDAC as well as regulatory cross-talk between factors. | 0 | Organic Reactions |
In organic chemistry, the vicarious nucleophilic substitution is a special type of nucleophilic aromatic substitution in which a nucleophile replaces a hydrogen atom on the aromatic ring and not leaving groups such as halogen substituents which are ordinarily encountered in SAr. This reaction type was reviewed in 1987 by Polish chemists Mieczysław Mąkosza and Jerzy Winiarski.
It is typically encountered with nitroarenes and especially with nucleophiles, resulting in alkylated arenes: the new substituent can take the ortho or para positions, reversing the selectivity for the meta position that is usually observed with such compounds under electrophilic substitution. Carbon nucleophiles carry an electron-withdrawing group and a leaving group: the nucleophile attacks the aromatic ring, and excess base can eliminate to form an exocyclic double bond which is successively protonated under acidic conditions, restoring aromaticity. | 0 | Organic Reactions |
Metal-catalyzed cyclopropanations are chemical reactions that result in the formation of a cyclopropane ring from a metal carbenoid species and an alkene. In the Simmons–Smith reaction the metal involved is zinc. Metal carbenoid species can be generated through the reaction of a diazo compound with a transition metal). The intramolecular variant of this reaction was first reported in 1961. Rhodium carboxylate complexes, such as dirhodium tetraacetate, are common catalysts. Enantioselective cyclopropanations have been developed. | 0 | Organic Reactions |
Electrophilic aminating reagents rely on the presence of an electron-withdrawing functional group attached to nitrogen. A variety of hydroxylamine derivatives have been used for this purpose. Sulfonylhydroxylamines are able to aminate a wide array of carbanions.
Azo compounds afford hydrazines after addition to the N=N bond. These additions have been rendered enantioselective through the use of chiral auxiliaries (see above) and chiral catalysts. Although the enantioselectivity of the proline-catalyzed process is good, yields are low and reaction times are long.
Upon treatment with sulfonyl azides, a variety of Grignard reagents or enolates may be converted into azides or amines. A significant side reaction that occurs under these conditions is the diazo transfer reaction: instead of fragmenting into an azide and sulfinic acid, the intermediate triazene salt may break down to a diazo compound and sulfonamide. Changing workup conditions may favor one product over another. In general, for reactions of enolates substituted with Evans oxazolidinones, trifluoroacetic acid promotes diazo transfer while acetic acid encourages azidation (the reasons for this are unclear). Solvent and the enolate counterion also influence the observed ratio of diazo to azide products.
Other electrophilic aminating reagents include oxaziridines, diazo compounds, and in rare cases, imines. | 0 | Organic Reactions |
Wet etching of GaAs industrially uses an oxidizing agent such as hydrogen peroxide or bromine water, and the same strategy has been described in a patent relating to processing scrap components containing GaAs where the is complexed with a hydroxamic acid ("HA"), for example:
:GaAs + + "HA" → "GaA" complex + + 4
This reaction produces arsenic acid. | 1 | Inorganic Reactions + Inorganic Compounds |
The reaction can be demonstrated by starting with solutions of potassium cyanate and ammonium chloride which are mixed, heated and cooled again. An additional proof of the chemical transformation is obtained by adding a solution of oxalic acid which forms urea oxalate as a white precipitate.
Alternatively the reaction can be carried out with lead cyanate and ammonia. The actual reaction taking place is a double displacement reaction to form ammonium cyanate:
Ammonium cyanate decomposes to ammonia and cyanic acid which in turn react to produce urea:
Complexation with oxalic acid drives this chemical equilibrium to completion. | 0 | Organic Reactions |
In chemistry, halogenation is a chemical reaction which introduces of one or more halogens into a chemical compound. Halide-containing compounds are pervasive, making this type of transformation important, e.g. in the production of polymers, drugs. This kind of conversion is in fact so common that a comprehensive overview is challenging. This article mainly deals with halogenation using elemental halogens (). Halides are also commonly introduced using salts of the halides and halogen acids. Many specialized reagents exist for and introducing halogens into diverse substrates, e.g. thionyl chloride. | 0 | Organic Reactions |
A free radical is formed from the carboxylic acid in an oxidative decarboxylation with silver salts and an oxidizing agent. The oxidizing agent (ammonium persulfate) oxidizes the Ag(+) to Ag(2+) under the acidic reaction conditions. This induces a hydrogen atom abstraction by the silver, followed by radical decarboxylation. The carbon-centered radical then reacts with the pyridinium aromatic compound. The ultimate product is formed by rearomatization. The acylated product is formed from the acyl radical. | 0 | Organic Reactions |
The process was based on the oxidation of hydrogen chloride:
:4 HCl + O → 2 Cl + 2HO
The reaction takes place at about 400 to 450 °C in the presence of a variety of catalysts, including copper chloride (CuCl). Three companies developed commercial processes for producing chlorine based on the Deacon reaction:
*The Kel-Chlor process developed by the M. W. Kellogg Company, which utilizes nitrosylsulfuric acid.
*The Shell-Chlor process developed by the Shell Oil Company, which utilizes copper catalysts.
*The MT-Chlor process developed by the Mitsui Toatsu Company, which utilizes chromium-based catalysts.
The Deacon process is now outdated technology. Most chlorine today is produced by using electrolytic processes. New catalysts based on ruthenium(IV) oxide have been developed by Sumitomo. | 1 | Inorganic Reactions + Inorganic Compounds |
In the conversion of carbon dioxide to useful materials, the water–gas shift reaction is used to produce carbon monoxide from hydrogen and carbon dioxide. This is sometimes called the reverse water–gas shift reaction.
Water gas is defined as a fuel gas consisting mainly of carbon monoxide (CO) and hydrogen (H). The term ‘shift’ in water–gas shift means changing the water gas composition (CO:H) ratio. The ratio can be increased by adding CO or reduced by adding steam to the reactor. | 1 | Inorganic Reactions + Inorganic Compounds |
Reactions of divinylcyclopropanes containing substituted double bonds are stereospecific with respect to the configurations at the double bonds—cis,cis isomers give cis products, while cis,trans isomers give trans products. Thus, chiral, non-racemic starting materials give rise to chiral products without loss of enantiomeric purity. In the example below, only the isomers depicted were observed in each case. | 0 | Organic Reactions |
Barium chlorate can be produced through a double replacement reaction between solutions of barium chloride and sodium chlorate:
:BaCl + 2 NaClO → Ba(ClO) + 2 NaCl
On concentrating and chilling the resulting mixture, barium chlorate precipitates. This is perhaps the most common preparation, exploiting the lower solubility of barium chlorate compared to sodium chlorate.
The above method does result in some sodium contamination, which is undesirable for pyrotechnic purposes, where the strong yellow of sodium can easily overpower the green of barium. Sodium-free barium chlorate can be produced directly through electrolysis:
:BaCl + 6 HO → Ba(ClO) + 6 H
It can also be produced by the reaction of barium carbonate with boiling ammonium chlorate solution:
:2 NHClO + BaCO + Q → Ba(ClO) + 2 NH + HO + CO
The reaction initially produces barium chlorate and ammonium carbonate; boiling the solution decomposes the ammonium carbonate and drives off the resulting ammonia and carbon dioxide, leaving only barium chlorate in solution. | 1 | Inorganic Reactions + Inorganic Compounds |
Like most metal fluorides, UF is a dense highly crosslinked inorganic polymer. As established by X-ray crystallography, the U centres are eight-coordinate with square antiprismatic coordination spheres. The fluoride centres are doubly bridging. | 1 | Inorganic Reactions + Inorganic Compounds |
Neptunium silicide is a binary inorganic compound of neptunium and silicon with the chemical formula . The compound forms crystals and does not dissolve in water. | 1 | Inorganic Reactions + Inorganic Compounds |
Like other iron oxalates, ferrous oxalates feature octahedral Fe centers. The dihydrate FeCO(HO) is a coordination polymer, consisting of chains of oxalate-bridged ferrous centers, each with two aquo ligands.<br />
When heated to 120 °C, the dihydrate dehydrates, and the anhydrous ferrous oxalate decomposes near 190 °C. The products of thermal decomposition is a mixture of iron oxides and pyrophoric iron metal, as well as released carbon dioxide, carbon monoxide, and water.
Ferrous oxalates are precursors to iron phosphates, which are of value in batteries. | 1 | Inorganic Reactions + Inorganic Compounds |
The roast gas is conveyed through the system by means of an exhaust gas fan (VI). Fans in plants provide pressure increases of approx. 200 mbar and are feedback-controlled to maintain a relative pressure of -3 mbar between reactor and atmosphere to avoid any overpressure-related leakage of acid gas.
To rinse the impeller and cool the gas as well as to remove remaining traces of HCl from the roast gas, the exhaust gas fan is commonly supplied with quenching water, which is separated from the exhaust gas stream by means of a mist eliminator (VII) at the pressure side of the fan.
In a final scrubber, commonly consisting of a combination of wet scrubbers such as venturi scrubbers (IX) and scrubber columns (X), remaining traces of HCl and dust are removed.
In some plant, absorption chemicals such as NaOH and NaSO are used to bind HCl and Cl (which is created under certain circumstances in several, but not all spray roasting reactors). | 1 | Inorganic Reactions + Inorganic Compounds |
Boroxine () is a 6-membered heterocyclic compound composed of alternating oxygen and singly-hydrogenated boron atoms. Boroxine derivatives (boronic anhydrides) such as trimethylboroxine and triphenylboroxine also make up a broader class of compounds called boroxines. These compounds are solids that are usually in equilibrium with their respective boronic acids at room temperature. Beside being used in theoretical studies, boroxine is primarily used in the production of optics. | 1 | Inorganic Reactions + Inorganic Compounds |
Neptunium diarsenide is a binary inorganic compound of neptunium and arsenic with the chemical formula . The compound forms crystals. | 1 | Inorganic Reactions + Inorganic Compounds |
The crystal structure of ScS is closely related to that of sodium chloride, in that it is based on a cubic close packed array of anions. Whereas NaCl has all the octahedral interstices in the anion lattice occupied by cations, ScS has one third of them vacant. The vacancies are ordered, but in a very complicated pattern, leading to a large, orthorhombic unit cell belonging to the space group Fddd. | 1 | Inorganic Reactions + Inorganic Compounds |
GaAs may have applications in spintronics as it can be used instead of platinum in spin-charge converters and may be more tunable. | 1 | Inorganic Reactions + Inorganic Compounds |
In 1941, Kharash discovered that Grignard reagents add to cyclohexenone in presence of Cu(I) resulting in 1,4-addition instead of 1,2-addition. This work foreshadowed extensive studies on the conjugate additions to enones with organocuprates. Note that if a Grignard reagent (such as RMgBr) is used, the reaction with an enone would instead proceed through a 1,2-addition. The 1,4-addition mechanism of cuprates to enones goes through the nucleophilic addition of the Cu(I) species at the beta-carbon of the alkene to form a Cu(III) intermediate, followed by reductive elimination of Cu(I). In the original paper describing this reaction, methylmagnesium bromide is reacted with isophorone with and without 1 mole percent of added copper(I) chloride (see figure).
Without added salt the main products are alcohol B (42%) from nucleophilic addition to the carbonyl group and diene C (48%) as its dehydration reaction product. With added salt the main product is 1,4-adduct A (82%) with some C (7%).
A 1,6-addition is also possible, for example in one step of the commercial-scale production of fulvestrant: | 0 | Organic Reactions |
A dearomatization reaction is an organic reaction in which the reactants are arenes and the products permanently lose their aromaticity. It is of some importance in synthetic organic chemistry for the organic synthesis of new building blocks and in total synthesis. Types of carbocyclic arene dearomization include hydrogenative (Birch reduction), alkylative, photochemical, thermal, oxidative, transition metal-assisted and enzymatic. | 0 | Organic Reactions |
The prototypical super leaving group is triflate, and the term has come to mean any leaving group of comparable ability. Compounds where loss of a super leaving group can generate a stable carbocation are usually highly reactive and unstable. Thus, the most commonly encountered organic triflates are methyl triflate and alkenyl or aryl triflates, all of which cannot form stable carbocations on ionization, rendering them relatively stable. It has been noted that steroidal alkyl nonaflates (another super leaving group) generated from alcohols and perfluorobutanesulfonyl fluoride were not isolable as such but immediately formed the products of either elimination or substitution by fluoride generated by the reagent. Mixed acyl-trifluoromethanesulfonyl anhydrides smoothly undergo Friedel-Crafts acylation without a catalyst, unlike the corresponding acyl halides, which require a strong Lewis acid. Methyl triflate, however, does not participate in Friedel-Crafts alkylation reactions with electron-neutral aromatic rings.
Beyond super leaving groups in reactivity lie the "hyper" leaving groups. Prominent among these are λ-iodanes, which include diaryl iodonium salts, and other halonium ions. In one study, a quantitative comparison of these and other leaving groups was conducted. Relative to chloride (k = 1), reactivities increased in the order bromide (k = 14), iodide (k = 91), tosylate (k = 3.7), triflate (k = 1.4), phenyliodonium tetrafluoroborate (, k = 1.2). Along with the criterion that a hyper leaving group be a stronger leaving group than triflate is the necessity that the leaving group undergo reductive elimination. In the case of halonium ions this involves reduction from a trivalent halonium to a monovalent halide coupled with the release of an anionic fragment. Part of the exceptional reactivity of compounds of hyper leaving groups has been ascribed to the entropic favorability of having one molecule split into three.
Dialkyl halonium ions have also been isolated and characterized for simple alkyl groups. These compounds, despite their extreme reactivity towards nucleophiles, can be obtained pure in the solid state with very weakly nucleophilic counterions such as and . The strongly electrophilic nature of these compounds engendered by their attachment to extremely labile (R = alkyl, X = Cl, Br, I) leaving groups is illustrated by their propensity to alkylate very weak nucleophiles. Heating neat samples of under reduced pressure resulted in methylation of the very poorly nucleophilic carborane anion with concomitant expulsion of the leaving group. Dialkyl halonium hexafluoroantimonate salts alkylate excess alkyl halides to give exchanged products. Their strongly electrophilic nature, along with the instability of primary carbocations generated from ionization of their alkyl groups, points to their possible involvement in Friedel-Crafts alkylation chemistry. The order of increasing lability of these leaving groups is . | 0 | Organic Reactions |
The dry distillation of calcium acetate to give acetone was reported by Charles Friedel in 1858 and until World War I ketonization was the premier commercial method for its production.
Ketonic decarboxylation of propanoic acid over a manganese(II) oxide catalyst in a tube furnace affords 3-pentanone. Of commercial interest are related ketonizations using cerium(IV) oxide and manganese dioxide on alumina as the catalysts. 5-Nonanone, which is potentially of interest as a diesel fuel, can be produced from valeric acid. Stearone is prepared by heating magnesium stearate.
An example of intramolecular ketonization is the conversion of adipic acid to cyclopentanone with barium hydroxide.
The synthesis of 4-heptanone illustrates the production of the metal carboxylate in situ. Iron powder and butyric acid are converted to iron butyrate. Pyrolysis of that salt gives the ketone. | 0 | Organic Reactions |
The polymer-supported synthesis of β-mannosides based on the Crich’s protocol has also been studied in the same laboratories. As shown in Scheme 4, diol 17 was first reacted with polystyrylboronic acid (18) to offer the bound donor 19, in which 4,6-O-phenylboronates served as the torsionally disarming protecting group. With that, activation of the thioglycoside 19 was readily achieved, and the coupling reaction with the acceptor alcohol underwent smoothly to provide the bound β-mannoside 20. After removal of the excess reagents and byproducts from the resin, 20 was then treated with aqueous acetone to release 4,6-diol 21. Overall, this is a powerful method for solid-phase synthesis of β-mannosides, which has great potential to be further extended, was established. | 0 | Organic Reactions |
Keto–enol tautomerism is important in several areas of biochemistry.
The high phosphate-transfer potential of phosphoenolpyruvate results from the fact that the phosphorylated compound is "trapped" in the less thermodynamically favorable enol form, whereas after dephosphorylation it can assume the keto form.
The enzyme enolase catalyzes the dehydration of 2-phosphoglyceric acid to the enol phosphate ester. Metabolism of PEP to pyruvic acid by pyruvate kinase (PK) generates adenosine triphosphate (ATP) via substrate-level phosphorylation. | 0 | Organic Reactions |
Potassium sulfides are formed when black powder is burned and are important intermediates in many pyrotechnic effects, such as senko hanabi and some glitter formulations. | 1 | Inorganic Reactions + Inorganic Compounds |
Unlike sodium hydroxide, which is soluble, the hydroxides of most transition metals are insoluble, and therefore sodium hydroxide can be used to precipitate transition metal hydroxides. The following colours are observed:
* Copper - blue
* Iron(II) - green
* Iron(III) - yellow / brown
Zinc and lead salts dissolve in excess sodium hydroxide to give a clear solution of or .
Aluminium hydroxide is used as a gelatinous flocculant to filter out particulate matter in water treatment. Aluminium hydroxide is prepared at the treatment plant from aluminium sulfate by reacting it with sodium hydroxide or bicarbonate. | 1 | Inorganic Reactions + Inorganic Compounds |
Lanthanum(III) oxide, also known as lanthana, chemical formula , is an inorganic compound containing the rare earth element lanthanum and oxygen. It is used in some ferroelectric materials, as a component of optical materials, and is a feedstock for certain catalysts, among other uses. | 1 | Inorganic Reactions + Inorganic Compounds |
Cobalt(II) chloride is an inorganic compound, a salt of cobalt and chlorine, with the formula . The compound forms several hydrates ·n, for n = 1, 2, 6, and 9. Claims of the formation of tri- and tetrahydrates have not been confirmed. The anhydrous form is a blue crystalline solid; the dihydrate is purple and the hexahydrate is pink. Commercial samples are usually the hexahydrate, which is one of the most commonly used cobalt salts in the lab. | 1 | Inorganic Reactions + Inorganic Compounds |
Praseodymium(IV) fluoride can be prepared by the effect of krypton difluoride on praseodymium(IV) oxide:
Praseodymium(IV) fluoride can also be made by the dissolution of sodium hexafluoropraseodymate(IV) in liquid hydrogen fluoride: | 1 | Inorganic Reactions + Inorganic Compounds |
Epoxidations of alkynes and allenes proceed by concerted mechanisms analogous to epoxidations of simple alkenes. Often, these epoxidized products are unstable and undergo further oxidation reactions via different mechanisms, such as Y-H insertion.
Kinetic studies of heteroatom oxidations have demonstrated that their mechanisms likely proceed by an S2 process, rather than a single-electron-transfer pathway. An example of heteroatom oxidation is the nucleophilic decomposition of DMD by N-oxides, a side reaction that regenerates the reduced starting material and converts the oxidizing agent to dioxygen and acetone.
Concerning the mechanism of C-H and Si-H oxidations, two mechanisms have been proposed. The debate centers on whether the oxidation takes place via concerted oxenoid-type insertion or via radical intermediates. A large body of evidence (including analogous oxidations of alkenes and peracid epoxidation) supports the concerted mechanism; however, recent observations of radical reactivity have been made. Complete retention of configuration in oxidations of chiral alkanes rules out the involvement of free, uncaged radicals. However, products of radical decomposition pathways have been observed in some DMD oxidations, suggesting radical intermediates. | 0 | Organic Reactions |
NiI has some industrial applications as a catalyst in carbonylation reactions. It is also has niche uses as a reagent in organic synthesis, especially in conjunction with samarium(II) iodide.
Like many nickel complexes, those derived from hydrated nickel iodide have been used in cross coupling. | 1 | Inorganic Reactions + Inorganic Compounds |
For laboratory use, the N-alkylation reaction is often unselective. A variety of alternative methods have been developed, such as the Delépine reaction, which uses hexamine. The Gabriel synthesis, involving the use of an equivalent to NH, only applies to primary alkyl halides. | 0 | Organic Reactions |
Cyclic α,β-unsaturated ketones are the most commonly employed substrates for vicinal difunctionalization. They tend to be more reactive than acyclic analogues and undergo less direct addition than aldehydes. Amides and esters can be used to encourage conjugate addition in cases when direct addition may be competitive (as in the addition of organolithium compounds).
Because the addition step is highly sensitive to steric effects, β-substituents are likely to slow the reaction. Acetylenic and allenic substrates react to give products with some retained unsaturation. | 0 | Organic Reactions |
The asymmetric hydrogenation of furans and benzofurans is challenging.
<br />
Asymmetric hydrogenation of thiophenes and benzothiophenes has been catalyzed by some ruthenium(II) complexes of N-heterocyclic carbenes (NHC). This system appears to possess superb selectivity (ee > 90%) and perfect diastereoselectivity (all cis) if the substrate has a fused (or directly bound) phenyl ring but yields only racemic product in all other tested cases.
<br /> | 0 | Organic Reactions |
The reaction was originally carried out in diethyl ether and routinely generated high yields due to the inherent irreversibly of the reaction caused by the formation of nitrogen gas. Though these reactions can be carried out at room temperature, the rate does increase at higher temperatures. Typically, the reaction is carried out at less than refluxing temperatures. The optimal reaction temperature is determined by the specific diazoalkane used. Reactions involving diazomethanes with alkyl or aryl substituents are exothermic at or below room temperature. Reactions involving diazomethanes with acyl or aroyl substituents require higher temperatures. The reaction has since been modified to proceed in the presence of Lewis acids and common organic solvents such as THF and dichloromethane. Reactions generally run at room temperature for about an hour, and the yield ranges from 70%-80% based on the choice of Lewis acid and solvent. | 0 | Organic Reactions |
Reactions of linear topology are the most common, and consist of all transformations whose transition states are acyclic, including addition, elimination, substitution, and (some types of) fragmentation reactions. By contrast, in pericyclic reactions, the atoms under chemical change form a single closed cycle, and include reactions like the Diels–Alder reaction and Cope rearrangement, among many others.
In contrast to these types of reactions, a coarctate reaction is characterized by a doubly cyclic transition state, in which at least one atom undergoes the simultaneous making and breaking of two bonds. Thus, the topology of the transition state of a coarctate reaction is a constricted cycle that meets with itself (resembling a figure eight) while the topology of pericyclic and linear reactions are a circle (or Möbius strip) and line segment, respectively. The concept was first proposed by Rainer Herges. | 0 | Organic Reactions |
The development of facile chemical glycosylation protocols is essential to synthesizing complex oligosaccharides. Among many diverse type of glycosidic linkages, the 1,2-cis-β-glycoside, which exists in many biologically relevant glycoconjugates and oligosaccharides, is arguably one of the most difficult to synthesize. The challenges in constructing β-mannose linkage have been well documented in several reviews. To date, a few laboratories have devised efficient methodologies to overcome these synthetic hurdles, and achieved varying degrees of success. Of those elegant approaches, a highly stereoselective β-mannosylation protocol developed by Crich and co-workers was realized as a breakthrough in β-mannoside synthesis. This strategy is based on the initial activation of α-mannosyl sulfoxides 1 with triflic anhydride (TfO) using DTBMP (2,6-di-tert-butyl-4-methylpyridine) as a base, followed by nucleophilic substitution of glycosyl acceptors (HOR) to provide the 1,2-cis-β-glycoside 2 in good yield and selectivity (Scheme 1). | 0 | Organic Reactions |
Lanthanum oxide is used as an additive to develop certain ferroelectric materials, such as La-doped bismuth titanate ( - BLT).
Lanthanum oxide is used in optical materials; often the optical glasses are doped with to improve the glass' refractive index, chemical durability, and mechanical strength.
The addition of the to the glass melt leads to a higher glass transition temperature from 658 °C to 679 °C. The addition also leads to a higher density, microhardness, and refractive index of the glass. | 1 | Inorganic Reactions + Inorganic Compounds |
Many CF-containing metal complexes have been prepared, and some are useful for trifluoromethylation. The most obvious reagent is CFLi, which can be generated by lithium-iodide exchange. This compound is however unstable even at low temperatures. It degrades to lithium fluoride and difluorocarbene. Trifluoromethyl copper(I) reagents are more useful. These reagents are generated in situ by reaction of CFI with copper powder in polar solvents. Hg(CF), prepared by decarboxylation of the trifluoroacetate, has proven useful for the trifluoromethylation of other metals, although for low-temperature reactions it may prove useful to transmetallate to bis(trifluoromethyl)cadmium. | 0 | Organic Reactions |
Praseodymium(III) nitride can be prepared by the reaction of nitrogen and metallic praseodymium on heating:
It can also be prepared from the reaction of ammonia and praseodymium metal on heating: | 1 | Inorganic Reactions + Inorganic Compounds |
For small scale reactions, SF can be inconvenient since it is a gas and stainless steel reaction vessels are required. Many transformations require elevated temperatures. The reaction generates hydrogen fluoride. These concerns have led to interest in alternative fluorinating reagents. Selenium tetrafluoride, a liquid at room temperature, behaves similarly to SF. Diethylaminosulfur trifluoride (DAST) is a derivative of SF that is easier to handle, albeit more expensive. | 0 | Organic Reactions |
Fusion of a cyclooctyne to two aryl rings increases the reaction rate, and the cyclooctyne reagents of the Bertozzi group proceeded through a series of fusions that sought to increase the ring strain even further. DIBO (dibenzo cyclooctyne) was developed as a precursor to BARAC (biarylazacyclooctynone), although calculations had predicted that a single fused aryl ring would be optimal. Attempts to make a difluoro benzo cyclooctyne (DIFBO) were unsuccessful due to the instability of the compound.
The reason for the instability of DIFBO is that it is so reactive that it spontaneously trimerizes to form two asymmetric products that can be characterized by X-ray crystallography. To stabilize the DIFBO, it is trapped by forming a stable inclusion complex with β-cyclodextrin in aqueous media. This complex, formed with the β-cyclodextrin, can then be stored as a lyophilized powder. To obtain the free DIFBO, the lyophilized powder is dissociated with organic solvents to produce the free DIFBO for in situ kinetic and spectroscopic analysis.
Problems with DIFO with in vivo mouse studies illustrate the difficulty of producing bioorthogonal reactions. | 0 | Organic Reactions |
N-linked glycosylation is a very prevalent form of glycosylation and is important for the folding of many eukaryotic glycoproteins and for cell–cell and cell–extracellular matrix attachment. The N-linked glycosylation process occurs in eukaryotes in the lumen of the endoplasmic reticulum and widely in archaea, but very rarely in bacteria. In addition to their function in protein folding and cellular attachment, the N-linked glycans of a protein can modulate a protein's function, in some cases acting as an on/off switch. | 0 | Organic Reactions |
The Boekelheide reaction is a rearrangement of α-picoline-N-oxides to hydroxymethylpyridines. It is named after Virgil Boekelheide who first reported it in 1954. Originally the reaction was carried out using acetic anhydride, which typically required a period at reflux (~140 °C). The reaction can be performed using trifluoroacetic anhydride (TFAA), which often allows for a room temperature reaction. | 0 | Organic Reactions |
Lanthanum acetate is an inorganic compound, a salt of lanthanum with acetic acid with the chemical formula . | 1 | Inorganic Reactions + Inorganic Compounds |
Neopeltolide was originally isolated from sponges near the Jamaican coast and exhibits nanomolar cytoxic activity against several lines of cancer cells. The synthesis of the neopeltolide macrocyclic core displays a hydrogenation controlled by the ground state conformation of the macrocycle. | 0 | Organic Reactions |
Asymmetric Heck reactions establish quaternary or tertiary stereocenters. If migratory insertion generates a quaternary center adjacent to the palladium-carbon bond (as in reactions of trisubstituted or 1,1-disubstituted alkenes), β-hydride elimination toward that center is not possible and it is retained in the product. Similarly, β-hydride elimination is not possible if a hydrogen syn to the palladium-carbon bond is not available. Thus, tertiary stereocenters can be established in conformationally restricted systems. | 0 | Organic Reactions |
Starting with a zerovalent palladium species and a substrate containing a leaving group in the allylic position, the Tsuji–Trost reaction proceeds through the catalytic cycle outlined below.
First, the palladium coordinates to the alkene, forming a η -allyl-Pd Π complex. The next step is oxidative addition in which the leaving group is expelled with inversion of configuration and a η -allyl-Pd is created (also called ionization). The nucleophile then adds to the allyl group regenerating the η -allyl-Pd complex. At the completion of the reaction, the palladium detaches from the alkene and can start again in the catalytic cycle. | 0 | Organic Reactions |
Lanthanum cuprate usually refers to the inorganic compound with the formula CuLaO. The name implies that the compound consists of a cuprate (CuO]) salt of lanthanum (La). In fact it is a highly covalent solid. It is prepared by high temperature reaction of lanthanum oxide and copper(II) oxide follow by annealing under oxygen.
The material adopts a tetragonal structure related to potassium tetrafluoronickelate (KNiF), which is orthorhombic. Replacement of some lanthanum by barium gives the quaternary phase CuLaBaO, called lanthanum barium copper oxide. That doped material displays superconductivity at , which at the time of its discovery was a high temperature. This discovery initiated research on cuprate superconductors and was the basis of a Nobel Prize in Physics to Georg Bednorz and K. Alex Müller. | 1 | Inorganic Reactions + Inorganic Compounds |
Usually, the amine reacts as the nucleophile with another organic compound acting as the electrophile. This sense of reactivity may be reversed for some electron-deficient amines, including oxaziridines, hydroxylamines, oximes, and other N–O substrates. When the amine is used as an electrophile, the reaction is called electrophilic amination. Electron-rich organic substrates that may be used as nucleophiles for this process include carbanions and enolates. | 0 | Organic Reactions |
Common donors in oligosaccharide synthesis are glycosyl halides, glycosyl acetates, thioglycosides, trichloroacetimidates, pentenyl glycosides, and glycals. Of all these donors, glycosyl halides are classic donors, which played a historical role in the development of glycosylation reactions. Thioglycoside and trichloroacetimidate donors are used more than others in contemporary glycosylation methods. When it comes to the trichloroacetimidate method, one of the advantages is that there is no need to introduce heavy metal reagents in the activation process. Moreover, using different bases can selectively lead to different anomeric configurations. (Scheme 2) As to the thioglycosides, the greatest strength is that they can offer temporary protection to the anomeric centre because they can survive after most of the activation processes. Additionally, a variety of activation methods can be employed, such as NIS/ AgOTf, NIS/ TfOH, IDCP (Iodine Dicollidine Perchlorate), iodine, and PhSO/ TfO. Furthermore, in the preparation of 1, 2-trans glycosidic linkage, using thioglycosides and imidates can promote the rearrangement of the orthoester byproducts, since the reaction mixtures are acidic enough. | 0 | Organic Reactions |
Aminosulfuranes are highly selective for the replacement of hydroxyl groups with fluoride, but in the absence of alcohol functionality, they have the ability to transform a wide array of substrates into the corresponding fluorides or acyl fluorides. For example, ketones are converted to geminal difluorides. However, unlike sulfur tetrafluoride, aminosulfuranes do not convert carboxylic acids into trifluoromethyl groups; the reaction halts at the acyl fluoride stage. Silyl ethers are converted to organofluorides in the presence of DAST.
Aldehydes and ketones react with DAST to form the corresponding geminal difluorides. Fluorination of enolizable ketones gives a mixture of the difluoroalkane and vinyl fluoride. In glyme with fuming sulfuric acid, the vinyl fluoride product predominates. Electron-rich carbonyl compounds, such as esters and amides, do not react with DAST or other aminosulfuranes.
Epoxides may yield a variety of products depending on their structure. Generally, the products that form in highest yield are vicinal difluorides and bis(α-fluoroalkyl)ethers. However, this reaction results in low yields and is not synthetically useful.
The polar mechanism of fluorination by DAST implies that certain substrates may suffer Wagner-Meerwein rearrangements. This process has been observed in the fluorination of pivalaldehyde, which affords a mixture of 1,2-difluoro-1,2-dimethylpropane, 1,1-difluoro-2,2-dimethylpropane, and 1-fluoro-2,2-dimethylethylene.
Diols can undergo pinacol rearrangement under fluorination conditions.
When sulfoxides are treated with DAST, an interesting Pummerer-type rearrangement occurs to afford α-fluoro sulfides. | 0 | Organic Reactions |
Simple N-heterocyclic carbene (NHC)-based ligands have proven impractical for asymmetrical hydrogenation.
Some C,N ligands combine an NHC with a chiral oxazoline to give a chelating ligand. NHC-based ligands of the first type have been generated as large libraries from the reaction of smaller libraries of individual NHCs and oxazolines. NHC-based catalysts featuring a bulky seven-membered metallocycle on iridium have been applied to the catalytic hydrogenation of unfunctionalized olefins and vinyl ether alcohols with conversions and ee's in the high 80s or 90s. The same system has been applied to the synthesis of a number of aldol, vicinal dimethyl and deoxypolyketide motifs, and to the deoxypolyketides themselves.
C-symmetric NHCs have shown themselves to be highly useful ligands for the asymmetric hydrogenation. | 0 | Organic Reactions |
The reaction steps are:
* hydrogenation of -glucose to -sorbitol, an organic reaction with nickel as a catalyst under high temperature and high pressure.
* Microbial oxidation or fermentation of sorbitol to -sorbose with acetobacter at pH 4-6 and 30 °C.
* protection of the 4 hydroxyl groups in sorbose by formation of the acetal with acetone and an acid to Diacetone-L-sorbose (2,3:4,6−Diisopropyliden−α−L−sorbose)
* Organic oxidation with potassium permanganate (to Diprogulic acid) followed by heating with water gives the 2-Keto-L-gulonic acid
* The final step is a ring-closing step or gamma lactonization with removal of water.
* Intermediate 5 can also be prepared directly from 3 with oxygen and platinum
The microbial oxidation of sorbitol to sorbose is important because it provides the correct stereochemistry. | 0 | Organic Reactions |
Isomerization of epoxides to allylic alcohols under strongly basic conditions proceeds by a β-elimination process. A model has been advanced that invokes an initial complex between the lithium amide base and epoxide. Concerted C–O bond cleavage and deprotonation proceeds via a syn transition state to give an allylic alkoxide, which is protonated upon workup. Deprotonation typically occurs at the exist in the transition state for cis double bond formation.
Other processes may take place competitively under basic conditions, particularly when β-elimination is slow or not possible. These pathways likely begin with lithiation of a carbon in the epoxide ring, followed by α-elimination to afford a carbene intermediate. 1,2-hydrogen migration leads to ketones, while intramolecular C–H insertion affords cyclic alcohols with the formation of a new carbon-carbon bond.
In many cases when hexamethylphosphoramide (HMPA) is used as an additive with lithium amide bases, selectivity for the formation of allylic alcohols increases. These reactions are believed to proceed through E2 elimination. | 0 | Organic Reactions |
The Sommelet reaction is an organic reaction in which a benzyl halide is converted to an aldehyde by action of hexamine and water. It is named after the French chemist Marcel Sommelet, who first reported the reaction in 1913.
One example, thiophene-2-carboxaldehyde is prepared by the reaction of hexamine with 2-chloromethylthiophene. The reaction is formally an oxidation of the carbon. | 0 | Organic Reactions |
To a stirred mixture of 13.5 mL (4.09 mmol) of a 0.303 N standard solution of silylated N-acetylguanine in 1,2-dichloroethane and 1.86 g (3.7 mmol) of benzoate-protected 1-acetoxy ribose in 35 mL of 1,2-dichloroethane was added 6.32 mL (4.46 mmol) of a 0.705 N standard solution of TMSOTf in 1,2-dichloroethane. The reaction mixture was heated at reflux for 1.5–4 hours, and then diluted with CHCl. On workup with ice-cold NaHCO solution, there was obtained 2.32 g of crude product, which was kept for 42 hours in 125 mL of methanolic ammonia at 24°. After workup, recrystallization from HO gave, in two crops, 0.69 g (66%) of pure guanosine, which was homogeneous (R 0.3) in the partition system n-butanol:acetic acid:HO (5:1:4) and whose H NMR spectrum at 400 MHz in DO showed only traces of the undesired N-anomer of guanosine. H NMR (CDCl): δ 3.55, 3.63, 3.90, 4.11, 4.43, 5.10, 5.20, 5.45, 5.72, 6.52, 7.97, 10.75. | 0 | Organic Reactions |
Wang et al. proposed a novel method for [4+2] annulation via a palladium catalyzed intermolecular pathway. Derivatives are formed in moderate to good yield; acridine is essential for high reaction efficiency. | 0 | Organic Reactions |
A wide variety of enantioselective additions employing chiral, non-racemic Lewis acids are known. The chiral (acyloxy)borane or "CAB" catalyst 1, titanium-BINOL system 2, and silver-BINAP system 3 provide addition products in high ee via the Lewis-acid-promoted mechanism described above. | 0 | Organic Reactions |
crystallizes in two forms (polymorphs). At room temperature, the compound is stable in the orthorhombic cotunnite (Lead(II) chloride|) structure, whereas the cubic fluorite structure (calcium fluoride|) is stable between 925 and 963 °C. Both polymorphs accommodate the preference of the large ion for coordination numbers greater than six. The coordination of is 8 in the fluorite structure and 9 in the cotunnite structure. When cotunnite-structure is subjected to pressures of 7–10 GPa, it transforms to a third structure, a monoclinic post-cotunnite phase. The coordination number of increases from 9 to 10.
In aqueous solution behaves as a simple salt; in water it is a 1:2 electrolyte and the solution exhibits a neutral pH. Its solutions react with sulfate ion to produce a thick white solid precipitate of barium sulfate.
This precipitation reaction is used in chlor-alkali plants to control the sulfate concentration in the feed brine for electrolysis.
Oxalate effects a similar reaction:
When it is mixed with sodium hydroxide, it gives barium hydroxide, which is moderately soluble in water.
is stable in the air at room temperature, but loses one water of crystallization above , becoming , and becomes anhydrous above . may be formed by shaking the dihydrate with methanol.
readily forms eutectics with alkali metal chlorides. | 1 | Inorganic Reactions + Inorganic Compounds |
Many S-N compounds are prepared from . Reaction with piperidine generates :
A related cation is also known, i.e. .
Treatment with tetramethylammonium azide produces the heterocycle :
Cyclo- has 10 pi-electrons.
In a related reaction, the use of the bis(triphenylphosphine)iminium azide gives a salt containing the blue anion:
The anion has a chain structure described using the resonance .
reacts with electron-poor alkynes.
Chlorination of gives thiazyl chloride.
Passing gaseous over silver metal yields the low temperature superconductor polythiazyl or polysulfurnitride (transition temperature (0.26±0.03) K), often simply called "(SN)". In the conversion, the silver first becomes sulfided, and the resulting silver sulfide| catalyzes the conversion of the into the four-membered ring , which readily polymerizes. | 1 | Inorganic Reactions + Inorganic Compounds |
If an unsymmetrical ketone is subjected to base, it has the potential to form two regioisomeric enolates (ignoring enolate geometry). For example:
The trisubstituted enolate is considered the kinetic enolate, while the tetrasubstituted enolate is considered the thermodynamic enolate. The alpha hydrogen deprotonated to form the kinetic enolate is less hindered, and therefore deprotonated more quickly. In general, tetrasubstituted olefins are more stable than trisubstituted olefins due to hyperconjugative stabilization. The ratio of enolate regioisomers is heavily influenced by the choice of base. For the above example, kinetic control may be established with LDA at −78 °C, giving 99:1 selectivity of kinetic: thermodynamic enolate, while thermodynamic control may be established with triphenylmethyllithium at room temperature, giving 10:90 selectivity.
In general, kinetic enolates are favored by cold temperatures, conditions that give relatively ionic metal–oxygen bonding, and rapid deprotonation using a slight excess of a strong, sterically hindered base. The large base only deprotonates the more accessible hydrogen, and the low temperatures and excess base help avoid equilibration to the more stable alternate enolate after initial enolate formation. Thermodynamic enolates are favored by longer equilibration times at higher temperatures, conditions that give relatively covalent metal–oxygen bonding, and use of a slight sub-stoichiometric amount of strong base. By using insufficient base to deprotonate all of the carbonyl molecules, the enolates and carbonyls can exchange protons with each other and equilibrate to their more stable isomer. Using various metals and solvents can provide control over the amount of ionic character in the metal–oxygen bond. | 0 | Organic Reactions |
The Minisci reaction () is a named reaction in organic chemistry. It is a nucleophilic radical substitution to an electron deficient aromatic compound, most commonly the introduction of an alkyl group to a nitrogen containing heterocycle. The reaction was published in 1971 by F. Minisci. In the case of N-Heterocycles, the conditions must be acidic to ensure protonation of said heterocycle. A typical reaction is that between pyridine and pivalic acid with silver nitrate, sulfuric acid and ammonium persulfate to form 2-tert-butylpyridine. The reaction resembles Friedel-Crafts alkylation but with opposite reactivity and selectivity.
The Minisci reaction often produces a mixture of regioisomers that can complicate product purification, but modern reaction conditions are incredibly mild, allowing a wide range of alkyl groups to be introduced. Depending on the radical source used, one side-reaction is acylation, with the ratio between alkylation and acylation depending on the substrate and the reaction conditions. Due to the inexpensive raw materials and simple reaction conditions, the Minisci reaction has found many applications in heterocyclic chemistry. | 0 | Organic Reactions |
Plutonium selenide is a binary inorganic compound of plutonium and selenium with the chemical formula PuSe. The compound forms black crystals and does not dissolve in water. | 1 | Inorganic Reactions + Inorganic Compounds |
Multiple Michael/aldol reaction (or domino Michael/aldol reaction) is a consecutive series of reactions composed of either Michael addition reactions or aldol reactions. More than two steps of reaction are usually involved. This reaction has been used for synthesis of large macrocyclic or polycyclic ring structures.
Gary Posner and co-workers were the first to report using multiple Michael/aldol reactions to construct macrolide structures. Their method utilized a Michael-Michael-Michael-ring closure (MIMI-MIRC) or a Michael-Michael-aldol-ring closure annulation sequences to assemble acrylates and/or aldehydes together to form substituted 9-, 10-, and 11-membered macrolide structures. Besides synthesis of complex ring structures, multiple Michael/aldol reaction can also be used for rapid production of complex compound libraries.
Aldolases have been used to mediate multiple aldol reactions. Chi-Huey Wong and co-workers had shown that 2-deoxyribose-5-phosphate aldolase and fructose-1, 6-diphosphate aldolase could be used together in a one-pot reaction to connect two aldehydes and one ketone together through sequential aldol reactions. This reaction could be used to generate a variety of carbohydrate derivatives. | 0 | Organic Reactions |
Aldehyde substituents suffer nucleophilic addition in the presence of organolithium compounds; however, adducts of aldehydes with lithium diamines can serve as effective directing groups for lateral lithiation. Subsequent treatment with an electrophilic primary alkyl halide and elimination of the diamine provides functionalized aryl aldehydes.
Tertiary amides are highly effective directing groups. After treatment of the resulting benzylic anion with an aldehyde, cyclization leads to lactones. Carboxamides, in which the amide is attached to the aromatic ring through nitrogen rather than carbon, are also effective directing groups.
Related O-aryl carbamates are good directing groups; upon warming, the resulting organolithiums undergo rearrangement to benzylic amides (the Snieckus-Fries rearrangement) via migration of the carbonyl carbon from oxygen to carbon.
Secondary N-aryl carbamates (along with secondary amides, ketones, and other directing groups containing acidic hydrogens) must be treated with two equivalents of organolithium reagent for lateral lithiation to occur. In the case below, sec-butyllithium is used to avoid competitive addition to the Boc group.
Sulfonamides require two equivalents of an organolithium reagent for lateral lithiation, but represent a useful class of directing groups. Treatment with ketones leads to tertiary alcohols in high yield. | 0 | Organic Reactions |
Cellulose is a polyol and thus susceptible to acetylation, which is achieved using acetic anhydride. Acetylation disrupts hydrogen bonding, which otherwise dominates the properties of cellulose. Consequently, the cellulose esters are soluble in organic solvents and can be cast into fibers and films. | 0 | Organic Reactions |
Organometallic nucleophiles used for conjugate additions are most often prepared in situ. The use of anhydrous equipment and inert atmosphere is necessary. Because these factors are sometimes difficult to control and the strength of freshly prepared reagents can vary substantially, titration methods are necessary to verify the purity of reagents. A number of efficient titration methodologies exist.
Usually, vicinal difunctionalizations are carried out in one pot, without the intermediacy of a neutral protected enolate. However, in specific cases it may be necessary to protect the intermediate of β-addition. Before reaching this point, however, solvent and nucleophile screens, order of addition adjustments, and counterion adjustments can be made to optimize the one-pot process for a particular combination of carbonyl compound, nucleophile, and alkylating (or acylating) agent. Solvent adjustments between the two steps are common; if one solvent is used, tetrahydrofuran is the solvent of choice. Polar aprotic solvents should be avoided for the conjugate addition step. Concerning temperature, conjugate additions are usually carried out at low temperatures (-78 °C), while alkylations are carried out at slightly higher temperatures (0 to -30 °C). Less reactive alkylating agents may require room temperature. | 0 | Organic Reactions |
Early investigations of macrocyclic stereocontrol studied the alkylation of 8-membered cyclic ketones with varying substitution. In the example below, alkylation of 2-methylcyclooctanone occurred to yield the predominantly trans product. Proceeding from the lowest energy conformation of 2-methylcycloctanone, peripheral attack is observed from either one of the low energy (energetic difference of 0.5 (kcal/mol)) enolate conformations, resulting in a trans product from either of the two depicted transition state conformations.
Unlike the cyclooctanone case, alkylation of 2-cyclodecanone rings does not display significant diastereoselectivity.
However, 10-membered cyclic lactones display significant diastereoselectivity. The proximity of the methyl group to the ester linkage was directly correlated with the diastereomeric ratio of the reaction products, with placement at the 9 position (below) yielding the highest selectivity. In contrast, when the methyl group was placed at the 7 position, a 1:1 mixture of diastereomers was obtained. Placement of the methyl group at the 9-position in the axial position yields the most stable ground state conformation of the 10-membered ring leading to high diastereoselectivity.
Conjugate addition to the E-enone below also follows the expected peripheral attack model to yield predominantly trans product. High selectivity in this addition can be attributed to the placement of sp centers such that transannular nonbonded interactions are minimized, while also placing the methyl substitution in the more energetically favorable position for cyclodecane rings. This ground state conformation heavily biases conjugate addition to the less hindered diastereoface. | 0 | Organic Reactions |
Regiospecific formation is the controlled enolate formation by the specific deprotonation at one of the α-carbons of the ketone starting molecule. This provides one of the best understood synthetic strategies to introduce chemical complexity in natural product and total syntheses. A prominent example of its use is in the total synthesis of progesterone illustrated in Figure "Regiospecific enolate formation in the total synthesis of progesterone".
When ketones are treated with base, enolates can be formed by deprotonation at either α-carbon. The selectivity is determined by both the steric and electronic effects on the α-carbons as well as the precise base used (see figure ""Masked functionality" for regiospecific enolate formation" for an example of this). Enolate formation will be thermodynamically favoured at the most acidic proton which depends on the electronic stabilization of the resulting anion. However, the selectivity can be reversed by sterically hindering the thermodynamic product and therefore kinetically favouring deprotonation at the other α-carbon centre. Traditional methods for regioselective enolate formation use either electronic activating groups (e.g. aldehydes) or steric blocking groups (e.g. 1,2-ethanedithiol protected ketone).
An enone can also serve as a precursor for regiospecific formation of an enolate, here the enone is a "masked functionality" for the enolate. This process is first described by Gilbert Stork who is best known for his contributions to the study of selective enolate formation methods in organic synthesis. Reacting an enone with lithium metal generates the enolate at the α-carbon of the enone. The enolate product can either be trapped or alkylated. By using "masked functionality", it is possible to produce enolates that are not accessible by traditional methods.
The "masked functionality" approach to regiospecific enolate formation has been widely used in the total synthesis of natural products. For example, in the total synthesis of the steroid hormone progesterone, Stork and co-workers used the "masked functionality" to stereospecifically construct one of the quaternary carbons in the molecule. | 0 | Organic Reactions |
The identity of this complex anion is uncertain, suggestions include [Co(κ-CO)], [Co(κ-COH)(OH)], and [Co(κ-CO)(κ-CO)(OH)]. Thermal gravimetric analysis favors the presence of one aquo ligand, and infra-red spectroscopy indicates the presence of both bi- and unidentate carbonate ligands. The addition of [[hexaamminecobalt(III) chloride|[Co(NH)]Cl]] to fresh solutions of sodium tris(carbonato)cobalt(III) precipitates anhydrous salt [Co(NH)] [Co(κ-CO)]. This salt has been characterized by X-ray crystallography, which established that the anionic complex features three bidentate (κ-) carbonate ligands.
To some extent, the exact description of the title salt is unimportant since it is only used as a synthetic intermediate, it has no intrinsic value. Products include [Co(HO)], [Co(κ-CO)(HO)], and [Co(κ-CO)(HO)] and their derivatives where the aquo ligand has been displaced. The closely related potassium tris(carbonatocobalt(III) has also been used for the preparation of diverse complexes. These derivatives include [Co(NH)(κ-CO)] and [Co(CN)(κ-CO)], rare examples of biscarbonato cobalt(III) complexes. Other derivatives include the dinitrite [Co(NH)(κ-CO)(NO)] and the oxalate [Co(NH)(κ-CO)(CO)]. | 1 | Inorganic Reactions + Inorganic Compounds |
The red form of HgO can be made by heating Hg in oxygen at roughly 350 °C, or by pyrolysis of Hg(NO). The yellow form can be obtained by precipitation of aqueous Hg with alkali. The difference in color is due to particle size; both forms have the same structure consisting of near linear O-Hg-O units linked in zigzag chains with an Hg-O-Hg angle of 108°. | 1 | Inorganic Reactions + Inorganic Compounds |
Hydrogen cyanide is a linear molecule, with a triple bond between carbon and nitrogen. The tautomer of HCN is HNC, hydrogen isocyanide.
Hydrogen cyanide is weakly acidic with a pK of 9.2. It partially ionizes in water to give the cyanide anion, CN. A solution of hydrogen cyanide in water, represented as HCN, is called hydrocyanic acid. The salts of the cyanide anion are known as cyanides.
HCN has a faint bitter almond-like odor that some people are unable to detect owing to a recessive genetic trait. The volatile compound has been used as inhalation rodenticide and human poison, as well as for killing whales. Cyanide ions interfere with iron-containing respiratory enzymes. | 1 | Inorganic Reactions + Inorganic Compounds |
The formation of sodium aluminosilicate makes the Bayer process uneconomical for bauxites high in silica. | 1 | Inorganic Reactions + Inorganic Compounds |
Nontrigonal pnictogen compounds refer to tricoordinate trivalent pnictogen (phosphorus, arsenic, antimony and bismuth: P, As, Sb and Bi) compounds that are not of typical trigonal pyramidal molecular geometry. By virtue of their geometric constraint, these compounds exhibit distinct electronic structures and reactivities, which bestow on them potential to provide unique nonmetal platforms for bond cleavage reactions. | 1 | Inorganic Reactions + Inorganic Compounds |
Azanes are acyclic, saturated hydronitrogens, which means that they consist only of hydrogen and nitrogen atoms and all bonds are single bonds. They are therefore pnictogen hydrides. Because cyclic hydronitrogens are excluded by definition, the azanes comprise a homologous series of inorganic compounds with the general chemical formula .
Each nitrogen atom has three bonds (either N-H or N-N bonds), and each hydrogen atom is joined to a nitrogen atom (H-N bonds). A series of linked nitrogen atoms is known as the nitrogen skeleton or nitrogen backbone. The number of nitrogen atoms is used to define the size of the azane (e.g. N-azane).
The simplest possible azane (the parent molecule) is ammonia, . There is no limit to the number of nitrogen atoms that can be linked together, the only limitation being that the molecule is acyclic, is saturated, and is a hydronitrogen.
Azanes are reactive and have significant biological activity. Azanes can be viewed as a more biologically active or reactive portion (functional groups) of the molecule, which can be hung upon molecular trees. | 1 | Inorganic Reactions + Inorganic Compounds |
Chiral amide bases may be used in catalytic amounts to isomerize meso epoxides to chiral allylic alcohols with high enantioselectivity. | 0 | Organic Reactions |
The primary debate concerning the mechanism of the rearrangement centers on whether it is a concerted (sigmatropic) or stepwise (diradical) process. Mechanistic experiments have shown that trans-divinylcyclopropanes epimerize to the corresponding cis isomers and undergo the rearrangement via what is most likely a concerted pathway. A boat-like transition state has been proposed and helps explain the observed stereospecificity of the process. Whether the initial epimerization of trans substrates occurs via a one- or two-center process is unclear in most cases.
Transition-metal-catalyzed versions of the rearrangement are known, and mechanisms vary. In one example employing rhodium bis(ethylene) hexafluoroacetylacetonate, coordination and formation of a bis-π-allyl complex precede electrocyclic ring closure and catalyst release. | 0 | Organic Reactions |
The transition state model for a six-membered oxocarbenium ring was proposed earlier in 1992 by Woods et al. The general strategy for determining the stereochemistry of a nucleophilic addition to a six-membered ring follows a similar procedure to the case of the five-membered ring. The assumption that one makes for this analysis is that the ring is in the same conformation as cyclohexene, with three carbons and the oxygen in a plane with the two other carbon atome puckered out of the plane, with one above and one below (see the figure to the right). Based on the substituients present on the ring, the lowest energy conformation is determined, keeping in mind steric and stereoelectronic effects (see the section below for a discussion of stereoelectronic effects in oxocarbenium rings). Once this conformation is established, one can consider the nucleophilic addition. The addition will proceed through the low energy chair transition state, rather than the relatively high energy twist-boat. An example of this type of reaction can be seen below. The example also highlights how the stereoelectronic effect exerted by an electronegative substituent flips the lowest energy conformation and leads to opposite selectivity. | 0 | Organic Reactions |