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is a yellow-orange solid. It is an unstable compound, with a half-life of about two minutes, disproportionating into xenon trioxide| and xenon gas. Its structure and identity was confirmed by cooling it to −150 °C so that Raman spectroscopy could be performed before it decomposed.
At -78 °C, the majority of XeO decomposed over a period of 72 hours, which was identified by the fading of the original yellow product to a pale yellow. Almost all yellow color indicating pure XeO disappeared over the span of 1 week.
:3 XeO → Xe + 2 XeO | 1 | Inorganic Reactions + Inorganic Compounds |
Polysubstituted benzenes were originally synthesized by substitution reactions on aromatic precursors. However, these reactions can have low regioselectivity and are prone to over substitution. Directed ortho metalation requires precursors that are often unstable to metallating reagents. Both these synthetic routes pose issues in total synthesis. In 1984 a new synthetic strategy was developed by Rick Danheiser to address these shortcomings. | 0 | Organic Reactions |
Within the inner coma of comets, many reactions are theorized to be relevant to the formation and reactivity of the NS radical. | 1 | Inorganic Reactions + Inorganic Compounds |
Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca(OH). It is a colorless crystal or white powder and is produced when quicklime (calcium oxide) is mixed with water. It has many names including hydrated lime, caustic lime, builders' lime, slaked lime, cal, and pickling lime. Calcium hydroxide is used in many applications, including food preparation, where it has been identified as E number E526. Limewater, also called milk of lime, is the common name for a saturated solution of calcium hydroxide. | 1 | Inorganic Reactions + Inorganic Compounds |
The sugar derivatives used for SHJ reactions should be purified, dried, and powdered before use. Intramolecular Friedel-Crafts reaction of the aromatic ring of a benzoate ester at the 2-position of 1-acetoxy ribose in the presence of a Lewis acid has been observed, and represents a potential side reaction. Heterocycles must not be too basic in order to avoid excessive complexation with the Lewis acid; amino-substituted heterocycles such as cytosine, adenine, and guanine react slowly or not at all under SHJ conditions (although their N-acetylated derivatives react more rapidly).
Silylation is most commonly accomplished using HMDS, which evolves ammonia as the only byproduct of silylation. Catalytic or stoichiometric amounts of acidic additives such as trimethylsilyl chloride accelerate silylation; when such an additive is used, ammonium salts will appear in the reaction as a turbid impurity.
Lewis acids should be distilled immediately before use for best results. More than about 1.2-1.4 equivalents of Lewis acid are rarely needed. Acetonitrile is the most common solvent employed for these reactions, although other polar solvents are also common. Workup of reactions employing TMSOTf involves treatment with an ice-cold solution of sodium bicarbonate and extraction of the resulting sodium salts. When tin(IV) chloride is used in 1,2-dichloroethane, workup involves the addition of pyridine and filtering of the resulting pyridine-tin complex, followed by extraction with aqueous sodium bicarbonate. | 0 | Organic Reactions |
In the episode "A No-Rough-Stuff-Type Deal" of the crime drama television series Breaking Bad, Walter White uses thermite to burn through a security lock in order to steal a methylamine drum from a chemical plant. | 1 | Inorganic Reactions + Inorganic Compounds |
A useful alternative to the methods described here that avoids the site selectivity concerns of the SHJ reaction is tandem Michael reaction/cyclization to simultaneously form the heterocyclic base and establish its connection to the sugar moiety.
A second alternative is enzymatic transglycosylation, which is completely kinetically controlled (avoiding issues of chemical transglycosylation associated with thermodynamic control). However, operational complications associated with the use of enzymes are a disadvantage of this method. | 0 | Organic Reactions |
In 2000, Steglich et al. reported an intramolecular Pd(II)-mediated decarboxylative cross-coupling reaction in their synthesis of lamellarin L.
Myers et al. reported decarboxylative olefination of ortho-substituted arene carboxylates in the presence of an oxidant (Ag2CO3) in 2002.
Subsequent studies showed that homogeneous Pd catalysts were able to decarboxylate acids at lower temperatures than their Cu and Ag counterparts, but were limited to electron rich ortho-substituted aromatic carboxylic acids.
Despite this, palladium catalysts are able to promote a wide variety of cross-coupling reactions including biaryl formation and aryl alkyne formation, along with a variety of cross-coupling reactions in which the carboxylic acid is not bonded to an aromatic.
Other Pd-catalyzed decarboxylation cross-coupling reactions include conjugated diene preparation (see dienes and trienes below) and dehydrogenative reactions (with a variety of substrate and catalyst combinations).
Contrarily to Cu-only systems, decarboxylative palladation is the rate-limiting step in the palladium catalytic cycle. | 0 | Organic Reactions |
When connecting the monosaccharides, the oligosaccharides need to be reducing in order to sequentially connect the glycosyl units. The monosaccharides, in nature prefer ɑ-linkages due to anomeric effect, but the disaccharides with ɑ-linkages are non-reducing thus deactivating the consequent connection of the monosaccharides. In order to make the process of glycosylation continuous and automated, the glycosidic linkages must maintain beta so to keep the structure open to coupling with more glycosyl groups.
It is somewhat more difficult to prepare 1, 2-cis-β-glycosidic linkages stereoselectively. Typically, when non-participating groups on O-2 position, 1, 2-cis-β-linkage can be achieved either by using the historically important halide ion methods, or by using 2-O-alkylated glycosyl donors, commonly thioglycosides or trichloroacetimidates, in nonpolar solvents.
In the early 1990s, it was still the case that the beta mannoside linkage was too challenging to be attempted by amateurs. However, the method introduced by Crich (Scheme 4), with 4,6-benzylidene protection a prerequisite and anomeric alpha triflate a key intermediate leaves this problem essentially solved. The concurrently developed but rather more protracted intramolecular aglycon delivery (IAD) approach is a little-used but nevertheless stereospecific alternative. | 0 | Organic Reactions |
Per IUPAC, the term biaryl refers to an assembly of two aromatic rings joined by a single bond, starting with the simplest, biphenyl. Biaryls constitute an important structural motif of physical organic, synthetic, and catalytic interest—for instance, underlying the area of atropisomers in enantioselective synthesis—and they appear in many pharmaceutical, agrochemical, and materials (e.g. LCD) applications. The example of a coupling reaction reaction used in their preparation is an alternative to the traditional Suzuki and Stille cross-coupling reactions, and various catalysts have been employed for this transformation; Goossen et al. reported the formation of biaryls from palladium and copper-catalzyed cross-coupling reactions of an aryl or heteroaryl carboxylic acid and an aryl halide (I, Br, or Cl) in the presence of a base. | 0 | Organic Reactions |
Bone ash is used in foundries for various purposes. Examples include release agents and protective barriers for tools exposed to molten metal, and as a sealant for seams and cracks. Applied as a powder or water slurry, bone ash has many unique characteristics. First of all, the powder has high thermal stability, so it maintains its form in extremely high temperatures. The powder coating itself adheres to metal well and does not drip, run, cause much corrosion, or create noticeable streaks. Using the bone ash is easy as well, as it comes in a powder form, is easy to clean up, and does not separate into smaller parts (therefore requiring no extra mixing). | 1 | Inorganic Reactions + Inorganic Compounds |
The Eschenmoser sulfide contraction is an organic reaction first described by Albert Eschenmoser for the synthesis of 1,3-dicarbonyl compounds from a thioester. The method requires a base and a tertiary phosphine. The method is of some relevance to organic chemistry and has been notably applied in the vitamin B total synthesis.
A base abstracts the labile hydrogen atom in the thioester, a sulfide anion is formed through an episulfide intermediate which is removed by the phosphine. | 0 | Organic Reactions |
Enantioselective dioxirane oxidations may rely on chiral, non-racemic dioxiranes, such as Shis fructose-based dioxirane. Enantioselective oxidation of meso-diols with Shis catalyst, for instance, produces chiral α-hydroxy ketones with moderate enantioselectivity. | 0 | Organic Reactions |
Aza Paternò−Büchi reaction involves an ππ* excited state of alkene reacting with a ground state imine. This strategy was developed by the laboratory Sivaguru and co-workers to overcome the shortcomings involving direct excitation of imines. Traditionally addition of excited imines to carbon-carbon double bonds involves making the imines as part of a carbocycle. | 0 | Organic Reactions |
Dioxiranes are generated by combining the ketone precursor with a buffered aqueous solution of KHSO. The volatile dioxiranes DMD and TFD are isolated via distillation of the crude reaction mixture. Baeyer-Villiger oxidation may compete with dioxirane formation. Once isolated, dioxiranes are kept in solutions of the corresponding ketones and dried with molecular sieves. Air-free technique is unnecessary unless the substrate or product is air-sensitive or hydrolytically labile, and most oxidations are carried out in the open air in Erlenmeyer flasks.
Oxidations with in situ generated dioxiranes are more convenient than isolation methods, provided the substrate is stable towards hydrolysis. Reactions can either be carried out in truly biphasic media with mechanical stirring, or in a homogeneous medium derived from water and a miscible organic solvent, such as acetonitrile. Asymmetric epoxidations are commonly carried out under the latter conditions. Some ketone catalysts are more persistent under slightly basic homogeneous conditions. | 0 | Organic Reactions |
Nickel(II) iodide is an inorganic compound with the formula NiI. This paramagnetic black solid dissolves readily in water to give bluish-green solutions, from which crystallizes the aquo complex [Ni(HO)]I (image above). This bluish-green colour is typical of hydrated nickel(II) compounds. Nickel iodides find some applications in homogeneous catalysis.
__TOC__ | 1 | Inorganic Reactions + Inorganic Compounds |
When orthoborate salts are dissolved in water, the anion converts mostly to boric acid and other hydrogen-containing borate anions, mainly tetrahydroxyborate . The reactions of orthoborate in solution are therefore mostly those of these compounds.
In particular, these reactions include the condensation of tetrahydroxoborate with cis-vicinal diols such as mannitol, sorbitol, glucose and glycerol, to form relatively stable anion esters. This reaction is used in analytic chemistry to determine the concentration of borate anions. | 1 | Inorganic Reactions + Inorganic Compounds |
Demethylation is the chemical process resulting in the removal of a methyl group (CH) from a molecule. A common way of demethylation is the replacement of a methyl group by a hydrogen atom, resulting in a net loss of one carbon and two hydrogen atoms.
The counterpart of demethylation is methylation. | 0 | Organic Reactions |
Pure sodium hydroxide is a colorless crystalline solid that melts at without decomposition and boils at . It is highly soluble in water, with a lower solubility in polar solvents such as ethanol and methanol. Sodium hydroxide is insoluble in ether and other non-polar solvents.
Similar to the hydration of sulfuric acid, dissolution of solid sodium hydroxide in water is a highly exothermic reaction where a large amount of heat is liberated, posing a threat to safety through the possibility of splashing. The resulting solution is usually colorless and odorless. As with other alkaline solutions, it feels slippery with skin contact due to the process of saponification that occurs between and natural skin oils. | 1 | Inorganic Reactions + Inorganic Compounds |
The most important reaction types involving free radicals are:
* Free-radical substitution, for instance free-radical halogenation and autoxidation.
* Free-radical addition reactions
* Intramolecular free radical reactions (substitution or addition) such as the Hofmann–Löffler reaction or the Barton reaction
* Free radical rearrangement reactions are rare compared to rearrangements involving carbocations and restricted to aryl migrations.
* Fragmentation reactions or homolysis, for instance the Norrish reaction, the Hunsdiecker reaction and certain decarboxylations. For fragmentations taking place in mass spectrometry see mass spectrum analysis.
* Electron transfer. An example is the decomposition of certain peresters by Cu(I) which is a one-electron reduction reaction forming Cu(II), an alkoxy oxygen radical and a carboxylate. Another example is Kolbe electrolysis.
* Radical-nucleophilic aromatic substitution is a special case of nucleophilic aromatic substitution.
* Carbon–carbon coupling reactions, for example manganese-mediated coupling reactions.
* Elimination reactions
Free radicals can be formed by photochemical reaction and thermal fission reaction or by oxidation reduction reaction. Specific reactions involving free radicals are combustion, pyrolysis and cracking. Free radical reactions also occur within and outside of cells, are injurious, and have been implicated in a wide range of human diseases (see 13-Hydroxyoctadecadienoic acid, 9-hydroxyoctadecadienoic acid, reactive oxygen species, and Oxidative stress) as well as many of the maladies associated with ageing (see ageing). | 0 | Organic Reactions |
Temperature plays a major role in the conversion of biomass to bio-oil. The temperature of the reaction determines the depolymerization of the biomass to bio-oil, as well as the repolymerization into char. While the ideal reaction temperature is dependent on the feedstock used, temperatures above ideal lead to an increase in char formation and eventually increased gas formation, while lower than ideal temperatures reduce depolymerization and overall product yields.
Similarly to temperature, the rate of heating plays a critical role in the production of the different phase streams, due to the prevalence of secondary reactions at non-optimum heating rates. Secondary reactions become dominant in heating rates that are too low, leading to the formation of char. While high heating rates are required to form liquid bio-oil, there is a threshold heating rate and temperature where liquid production is inhibited and gas production is favored in secondary reactions. | 0 | Organic Reactions |
Stereospecific cis-hydroalumination is possible through the use of dialkylalanes. The most common reagent used for this purpose is di(isobutyl)aluminium hydride (DIBAL-H). Analogous to hydroboration reactions with RBH, hydroalumination with RAlH leads to the attachment of aluminium at the carbon less able to stabilize developing positive charge (anti-Markovnikov selectivity). Metalation of terminal alkynes is a significant side reaction that occurs under these conditions. If metalation is desired, tertiary amine complexes of DIBAL-H are useful.
The use of silyl acetylenes avoids the problem of competitive metalation of terminal alkenes. The stereoselectivity of hydroalumination can be altered through a change in solvent: tertiary amine solvents provide the cis alkenylalane and hydrocarbon solvents provide the trans isomer.
Lithium aluminium hydride hydroaluminates alkynes to afford trans alkenylalanes. In equation (7) hydride adds to the terminal carbon, which places the developing negative charge next to the stabilizing phenyl substituent. | 0 | Organic Reactions |
Trifluoromethyl sulfone (PhSOCF) and trifluoromethyl sulfoxide (PhSOCF) can be used for trifluoromethylations of electrophiles | 0 | Organic Reactions |
Careful storage is needed when handling sodium hydroxide for use, especially bulk volumes. Following proper NaOH storage guidelines and maintaining worker/environment safety is always recommended given the chemical's burn hazard.
Sodium hydroxide is often stored in bottles for small-scale laboratory use, within intermediate bulk containers (medium volume containers) for cargo handling and transport, or within large stationary storage tanks with volumes up to 100,000 gallons for manufacturing or waste water plants with extensive NaOH use. Common materials that are compatible with sodium hydroxide and often utilized for NaOH storage include: polyethylene (HDPE, usual, XLPE, less common), carbon steel, polyvinyl chloride (PVC), stainless steel, and fiberglass reinforced plastic (FRP, with a resistant liner).
Sodium hydroxide must be stored in airtight containers to preserve its normality as it will absorb water from the atmosphere. | 1 | Inorganic Reactions + Inorganic Compounds |
In 1956 a heterogeneous catalyst made of palladium deposited on silk was shown to effect asymmetric hydrogenation. Later, in 1968, the groups of William Knowles and Leopold Horner independently published the examples of asymmetric hydrogenation using a homogeneous catalysts. While exhibiting only modest enantiomeric excesses, these early reactions demonstrated feasibility. By 1972, enantiomeric excess of 90% was achieved, and the first industrial synthesis of the Parkinson's drug L-DOPA commenced using this technology.
The field of asymmetric hydrogenation continued to experience a number of notable advances. Henri Kagan developed DIOP, an easily prepared C-symmetric diphosphine that gave high ees in certain reactions. Ryōji Noyori introduced the ruthenium-based catalysts for the asymmetric hydrogenated polar substrates, such as ketones and aldehydes. Robert H. Crabtree demonstrated the ability for Iridium compounds to catalyse asymmetric hydrogenation reactions in 1979 with the invention of Crabtrees catalyst. In the early 1990's, the introduction of P,N ligands by several groups independently then further expanded the scope of the C-symmetric ligands, although they are not fundamentally superior to chiral ligands lacking rotational symmetry.
Today, asymmetric hydrogenation is a routine methodology in laboratory and industrial scale organic chemistry. The importance of asymmetric hydrogenation was recognized by the 2001 Nobel Prize in Chemistry awarded to William Standish Knowles and Ryōji Noyori. | 0 | Organic Reactions |
The dienone–phenol rearrangement is a reaction in organic chemistry first reported in 1921 by Karl von Auwers and Karl Ziegler. A common example of dienone–phenol rearrangement is 4,4-disubstituted converting into a stable 3,4-disubstituted phenol in presence of acid. A similar rearrangement is possible with a 2,2-disubstituted cyclohexadienone to its corresponding disubstituted phenol. Usually this type of rearrangement is spontaneous unless a dichloromethyl group is present at the 4th position or the process is otherwise blocked. | 0 | Organic Reactions |
The Payne rearrangement is the isomerization, under basic conditions, of 2,3-epoxy alcohols to isomeric 1,2-epoxy alcohols with inversion of configuration. Aza- and thia-Payne rearrangements of aziridines and thiiraniums, respectively, are also known. | 0 | Organic Reactions |
Hydrochloric acid regeneration or HCl regeneration is a chemical process for the reclamation of bound and unbound HCl from metal chloride solutions such as hydrochloric acid. | 1 | Inorganic Reactions + Inorganic Compounds |
Hydrogen bromide is the inorganic compound with the formula . It is a hydrogen halide consisting of hydrogen and bromine. A colorless gas, it dissolves in water, forming hydrobromic acid, which is saturated at 68.85% HBr by weight at room temperature. Aqueous solutions that are 47.6% HBr by mass form a constant-boiling azeotrope mixture that boils at . Boiling less concentrated solutions releases HO until the constant-boiling mixture composition is reached.
Hydrogen bromide, and its aqueous solution, hydrobromic acid, are commonly used reagents in the preparation of bromide compounds. | 1 | Inorganic Reactions + Inorganic Compounds |
The use of metal hydrides (tin, silicon and mercury hydrides) is common in radical cyclization reactions; the primary limitation of this method is the possibility of reduction of the initially formed radical by H-M. Fragmentation methods avoid this problem by incorporating the chain-transfer reagent into the substrate itself—the active chain-carrying radical is not released until after cyclization has taken place. The products of fragmentation methods retain a double bond as a result, and extra synthetic steps are usually required to incorporate the chain-carrying group.
Atom-transfer methods rely on the movement of an atom from the acyclic starting material to the cyclic radical to generate the product. These methods use catalytic amounts of weak reagents, preventing problems associated with the presence of strong reducing agents (such as tin hydride). Hydrogen- and halogen-transfer processes are known; the latter tend to be more synthetically useful.
Oxidative and reductive cyclization methods also exist. These procedures require fairly electrophilic and nucleophilic radicals, respectively, to proceed effectively. Cyclic radicals are either oxidized or reduced and quenched with either external or internal nucleophiles or electrophiles, respectively. | 0 | Organic Reactions |
There are various mechanisms for glycosylation, although most share several common features:
*Glycosylation, unlike glycation, is an enzymatic process. Indeed, glycosylation is thought to be the most complex post-translational modification, because of the large number of enzymatic steps involved.
*The donor molecule is often an activated nucleotide sugar.
*The process is non-templated (unlike DNA transcription or protein translation); instead, the cell relies on segregating enzymes into different cellular compartments (e.g., endoplasmic reticulum, cisternae in Golgi apparatus). Therefore, glycosylation is a site-specific modification. | 0 | Organic Reactions |
It is also possible to synthesise heterocyclic compounds via the Elbs reaction. In 1956 an Elbs reaction of a thiophene derivative was published. The expected linear product was not obtained due to a change in reaction mechanism after formation of the first intermediate which caused multiple free radical reaction steps. | 0 | Organic Reactions |
These principles have been applied in multiple natural product targets containing medium and large rings. The syntheses of cladiell-11-ene-3,6,7-
triol, (±)-periplanone B, eucannabinolide, and neopeltolide are all significant in their usage of macrocyclic stereocontrol en route to obtaining the desired structural targets. | 0 | Organic Reactions |
Lead(II) azide is prepared by the reaction of sodium azide and lead(II) nitrate in aqueous solution. Lead(II) acetate can also be used.
Thickeners such as dextrin or polyvinyl alcohol are often added to the solution to stabilize the precipitated product. In fact, it is normally shipped in a dextrinated solution that lowers its sensitivity. | 1 | Inorganic Reactions + Inorganic Compounds |
Borate anions are largely in the form of the undissociated acid in aqueous solution at physiological pH. No further metabolism occurs in either animals or plants. In animals, boric acid/borate salts are essentially completely absorbed following oral ingestion. Absorption occurs via inhalation, although quantitative data are unavailable. Limited data indicate that boric acid/salts are not absorbed through intact skin to any significant extent, although absorption occurs through skin that is severely abraded. It distributes throughout the body and is not retained in tissues, except for bone, and is rapidly excreted in the urine. | 1 | Inorganic Reactions + Inorganic Compounds |
The dipeptide derived from glycine and (R-)valine is converted into a 2,5-Diketopiperazine (a cyclic dipeptide). Double O-methylation gives the bis-lactim. A proton is then abstracted from the prochiral position on glycine with n-BuLi. The next step decides the stereoselectivity of the method: One face of the carbanionic center is shielded by steric hindrance from the isopropyl residue on valine. The reaction of the anion with an alkyl iodide will form the alkylated product with a strong preference for just one enantiomer. In the final step the dipeptide is cleaved by acidic hydrolysis in two amino acid methyl esters which can be separated from each other.
With valine Schöllkopf selected the natural proteinogenic amino acid with the largest non-reactive and nonchiral residue in order to achieve the largest possible stereoselectivity, generally speaking enantiomeric excess of over 95% ee is feasible.
With the Schöllkopf method all amino acids can be synthesised when a suitable R-I reagent is available. R does not need to be an alkyl group but can also be more complicated. The method is limited to the laboratory for the synthesis of exotic amino acids. Industrial applications are not known. One disadvantage is limited atom economy. | 0 | Organic Reactions |
The so-called inner sphere mechanism entails coordination of the alkene to the metal center. Other characteristics of this mechanism include a tendency for a homolytic splitting of dihydrogen when more electron-rich, low-valent metals are present while electron-poor, high valent metals normally exhibit a heterolytic cleavage of dihydrogen assisted by a base.
The diagram below depicts purposed mechanisms for catalytic hydrogenation with rhodium complexes which are inner sphere mechanisms. In the unsaturated mechanism, the chiral product formed will have the opposite mode compared to the catalyst used. While the thermodynamically favoured complex between the catalyst and the substrate is unable to undergo hydrogenation, the unstable, unfavoured complex undergoes hydrogenation rapidly. The dihydride mechanism on the other hand sees the complex initially hydrogenated to the dihydride form. This subsequently allows for the coordination of the double bond on the non-hindered side. Through insertion and reductive elimination, the product's chirality matches that of the ligand.
The preference for producing one enantiomer instead of another in these reactions is often explained in terms of steric interactions between the ligand and the prochiral substrate. Consideration of these interactions has led to the development of quadrant diagrams where "blocked" areas are denoted with a shaded box, while "open" areas are left unfilled. In the modeled reaction, large groups on an incoming olefin will tend to orient to fill the open areas of the diagram, while smaller groups will be directed to the blocked areas and hydrogen delivery will then occur to the back face of the olefin, fixing the stereochemistry. Note that only part of the chiral phosphine ligand is shown for the sake of clarity. | 0 | Organic Reactions |
Manganese-mediated coupling reactions are radical coupling reactions between enolizable carbonyl compounds and unsaturated compounds initiated by a manganese(III) salt, typically manganese(III) acetate. Copper(II) acetate is sometimes used as a co-oxidant to assist in the oxidation of intermediate radicals to carbocations.
Manganese(III) acetate is effective for the one-electron oxidation of enolizable carbonyl compounds to α-oxoalkyl or α,α'-dioxoalkyl radicals. Radicals generated in this manner may then undergo inter- or intramolecular addition to carbon-carbon multiple bonds. Pathways available to the adduct radical include further oxidation to a carbocation (and subsequent β-elimination or trapping with a nucleophile) and hydrogen abstraction to generate a saturated carbonyl compound containing a new carbon-carbon bond. Copper(II) acetate is sometimes needed to facilitate the oxidation of adduct radicals to carbocations. Yields of these reactions are generally moderate, particularly in the intermolecular case, but tandem intramolecular radical cyclizations initiated by Mn(III) oxidation may generate complex carbocyclic frameworks. Because of the limited functional group compatibility of Mn(OAc), radical couplings employing this reagent have mainly been applied to the synthesis of hydrocarbon natural products, such as pheromones. | 0 | Organic Reactions |
In carbohydrate chemistry carbohydrate acetalisation is an organic reaction and a very effective means of providing a protecting group. The example below depicts the acetalisation reaction of D-ribose 1. With acetone or 2,2-dimethoxypropane as the acetalisation reagent the reaction is under thermodynamic reaction control and results in the pentose 2. The latter reagent in itself is an acetal and therefore the reaction is actually a cross-acetalisation.
Kinetic reaction control results from 2-methoxypropene as the reagent. D-ribose in itself is a hemiacetal and in equilibrium with the pyranose 3. In aqueous solution ribose is 75% pyranose and 25% furanose and a different acetal 4 is formed.
Selective acetalization of carbohydrate and formation of acetals possessing atypical properties is achieved by using arylsulfonyl acetals. An example of arylsulfonyl acetals as carbohydrate-protective groups are phenylsulfonylethylidene acetals. These acetals are resistant to the acid hydrolysis and can be deprotected easily by classical reductive conditions. | 0 | Organic Reactions |
Because many reagents exist for radical generation and trapping, establishing a single prevailing mechanism is not possible. However, once a radical is generated, it can react with multiple bonds in an intramolecular fashion to yield cyclized radical intermediates. The two ends of the multiple bond constitute two possible sites of reaction. If the radical in the resulting intermediate ends up outside of the ring, the attack is termed "exo"; if it ends up inside the newly formed ring, the attack is called "endo." In many cases, exo cyclization is favored over endo cyclization (macrocyclizations constitute the major exception to this rule). 5-hexenyl radicals are the most synthetically useful intermediates for radical cyclizations, because cyclization is extremely rapid and exo selective. Although the exo radical is less thermodynamically stable than the endo radical, the more rapid exo cyclization is rationalized by better orbital overlap in the chair-like exo transition state (see below).
Substituents that affect the stability of these transition states can have a profound effect on the site selectivity of the reaction. Carbonyl substituents at the 2-position, for instance, encourage 6-endo ring closure. Alkyl substituents at positions 2, 3, 4, or 6 enhance selectivity for 5-exo closure.
Cyclization of the homologous 6-heptenyl radical is still selective, but is much slower—as a result, competitive side reactions are an important problem when these intermediates are involved. Additionally, 1,5-shifts can yield stabilized allylic radicals at comparable rates in these systems. In 6-hexenyl radical substrates, polarization of the reactive double bond with electron-withdrawing functional groups is often necessary to achieve high yields. Stabilizing the initially formed radical with electron-withdrawing groups provides access to more stable 6-endo cyclization products preferentially.
Cyclization reactions of vinyl, aryl, and acyl radicals are also known. Under conditions of kinetic control, 5-exo cyclization takes place preferentially. However, low concentrations of a radical scavenger establish thermodynamic control and provide access to 6-endo products—not via 6-endo cyclization, but by 5-exo cyclization followed by 3-exo closure and subsequent fragmentation (Dowd-Beckwith rearrangement). Whereas at high concentrations of the exo product is rapidly trapped preventing subsequent rearrangement to the endo product Aryl radicals exhibit similar reactivity.
Cyclization can involve heteroatom-containing multiple bonds such as nitriles, oximes, and carbonyls. Attack at the carbon atom of the multiple bond is almost always observed. In the latter case attack is reversible; however alkoxy radicals can be trapped using a stannane trapping agent. | 0 | Organic Reactions |
The DeMayo reaction is a photochemical reaction in which the enol of a 1,3-diketone reacts with an alkene (or another species with a C=C bond) and the resulting cyclobutane ring undergoes a retro-aldol reaction to yield a 1,5-diketone:
The net effect is to add the two carbon atoms in the C=C double bond between the two carbonyl groups of the diketone. It is thus useful in syntheses both as a relatively selective way to join two parts of a molecule and as a way to apply the more developed chemistry of 1,3-diketone synthesis to 1,5-diketones. The first part is a [2+2] cycloaddition. The ensuing retro-aldol cleavage is favored by the relative instability of the cyclobutane ring. | 0 | Organic Reactions |
In order to understand how life arose, knowledge is required of the chemical pathways that permit formation of the key building blocks of life under plausible prebiotic conditions. Nam et al. demonstrated the direct condensation of nucleobases with ribose to give ribonucleosides in aqueous microdroplets, a key step leading to RNA formation. Also, a plausible prebiotic process for synthesizing pyrimidine and purine ribonucleosides and ribonucleotides using wet-dry cycles was presented by Becker et al. | 0 | Organic Reactions |
The most synthetically useful aminations of enolate anions employ N-acyloxazolidinone substrates. The chiral auxiliaries on these compounds are easily removed after hydrazine formation (with azo compounds) or azidation (with trisyl azide). Azidation using the latter reagent is more efficient than bromination followed by nucleophilic substitution by the azide anion Palladium on carbon and hydrogen gas reduce both azide and hydrazide products (the latter only after conversion to the hydrazine). | 0 | Organic Reactions |
Carboxylation is a standard conversion in organic chemistry. Specifically carbonation (i.e. carboxylation) of Grignard reagents and organolithium compounds is a classic way to convert organic halides into carboxylic acids.
Sodium salicylate, precursor to aspirin, is commercially prepared by treating sodium phenolate (the sodium salt of phenol) with carbon dioxide at high pressure (100 atm) and high temperature (390 K) – a method known as the Kolbe-Schmitt reaction. Acidification of the resulting salicylate salt gives salicylic acid.
Many detailed procedures are described in the journal Organic Syntheses.
Carboxylation catalysts include N-Heterocyclic carbenes and catalysts based on silver. | 0 | Organic Reactions |
Detection of NS at steady state concentration in the reaction zone of the combustion of methane doped with ammonia and a fuel sulfur such as HS suggests that NS may be an important reactive intermediate in burning of hydrocarbon flames in a reducing atmosphere, which is relevant to coal pyrolysis and combustion.
Fossil fuels contain bound nitrogen, which releases elevated levels of nitric oxide emissions during combustion. NO emissions can be controlled by denitrification of the fuel source, combustion chamber modification, or both. One developing technique is the reburning of NO, which is reduced to N. These fuels also contain variable amounts of sulfur, which is oxidized to SO. Therefore, understanding the reactivity of NO and SO is crucial to the process of reburning. The experimental apparatus to test this involved a primary flame for producing combustion products, which were mixed with NO and SO to mimic coal burning byproducts. This mixture was fed into the burner at atmospheric pressure. 1-2% decrease in NO concentration is observed at various percentages of total fuel inlet (reburn ratio) in the presence of 0.1% SO, which is attributed to the formation of HS, HS, and the resulting reaction with NO, giving rise to NS. Reaction: HS + NO > NS + OH. | 1 | Inorganic Reactions + Inorganic Compounds |
Alkyl substitution can be achieved when alkyl halides are used in conjunction with a Lewis acid; however, only activated (allylic, benzylic) or highly substituted (tert-butyl) halides are useful in this context. Nucleophilic catalysis of alkylation is rare, because protodesilylation tends to occur. Lewis acid activation is more commonly employed.
Allylsilane additions to carbonyl groups are common and synthetically useful. Vinylsilane additions are less common, as a variety of methods to access allylic alcohols are available (including epoxidation of allylsilanes; see below). If the γ position of the allylsilane is substituted, two diastereomeric products may result. In the presence of Lewis acids such as titanium tetrachloride, (E)-allylsilanes are highly selective for the syn diastereomer. (Z)-allylsilanes are much less selective (~60:40), but also favor the syn isomer.
Conjugate addition reactions of allylsilanes are possible, although unsaturated aldehydes undergo only 1,2 addition. The combination of an allylsilane with an α,β-unsaturated ketone in the presence of a Lewis acid is known as the Sakurai reaction. The enolate intermediate that results from addition can be functionalized with a separate electrophile or simply protonated. Intramolecular Sakurai reactions provide ene-6-ones
Acetals and ketals are excellent substrates for additions of allyl- and vinylsilanes. In some cases, these compounds react more cleanly than the corresponding carbonyl compounds.
Iminium ions generated in situ in the presence of protic acid react with allylsilanes to give homoallylic amines. | 0 | Organic Reactions |
Ammonium perrhenate (APR) is the ammonium salt of perrhenic acid, NHReO. It is the most common form in which rhenium is traded. It is a white salt; soluble in ethanol and water, and mildly soluble in NHCl. It was first described soon after the discovery of rhenium. | 1 | Inorganic Reactions + Inorganic Compounds |
Asymmetric ester hydrolysis with pig liver esterase is the enantioselective conversion of an ester to a carboxylic acid through the action of the enzyme pig liver esterase (EC 3.1.1.1). Asymmetric ester hydrolysis involves the selective reaction of one of a pair of either enantiotopic (within the same molecule and related by a symmetry plane of the molecule) or enantiomorphic (in enantiomeric molecules and related as mirror images) ester groups. | 0 | Organic Reactions |
Thermite reactions have many uses. It is not an explosive; instead, it operates by exposing a very small area to extremely high temperatures. Intense heat focused on a small spot can be used to cut through metal or weld metal components together both by melting metal from the components, and by injecting molten metal from the thermite reaction itself.
Thermite may be used for repair by the welding in-place of thick steel sections such as locomotive axle-frames where the repair can take place without removing the part from its installed location.
Thermite can be used for quickly cutting or welding steel such as rail tracks, without requiring complex or heavy equipment. However, defects such as slag inclusions and voids (holes) are often present in such welded junctions, so great care is needed to operate the process successfully. The numerical analysis of thermite welding of rails has been approached similar to casting cooling analysis. Both this finite element analysis and experimental analysis of thermite rail welds has shown that weld gap is the most influential parameter affecting defect formation. Increasing weld gap has been shown to reduce shrinkage cavity formation and cold lap welding defects, and increasing preheat and thermite temperature further reduces these defects. However, reducing these defects promotes a second form of defect: microporosity. Care must also be taken to ensure that the rails remain straight, without resulting in dipped joints, which can cause wear on high speed and heavy axle load lines.
A thermite reaction, when used to purify the ores of some metals, is called the , or aluminothermic reaction. An adaptation of the reaction, used to obtain pure uranium, was developed as part of the Manhattan Project at Ames Laboratory under the direction of Frank Spedding. It is sometimes called the Ames process.
Copper thermite is used for welding together thick copper wires for the purpose of electrical connections. It is used extensively by the electrical utilities and telecommunications industries (exothermic welded connections). | 1 | Inorganic Reactions + Inorganic Compounds |
A decarboxylative Heck coupling by Su et al. can be used to obtain an aryl olefin using benzoquinone as the oxidant. | 0 | Organic Reactions |
In general, enols are less stable than their keto equivalents because of the favorability of the C=O double bond over C=C double bond. However, enols can be stabilized kinetically or thermodynamically.
Some enols are sufficiently stabilized kinetically so that they can be characterized.
Delocalization can stabilize the enol tautomer. Thus, very stable enols are phenols. Another stabilizing factor in 1,3-dicarbonyls is intramolecular hydrogen bonding. Both of these factors influence the enol-dione equilibrium in acetylacetone. | 0 | Organic Reactions |
Sodium hydroxide is sometimes used during water purification to raise the pH of water supplies. Increased pH makes the water less corrosive to plumbing and reduces the amount of lead, copper and other toxic metals that can dissolve into drinking water. | 1 | Inorganic Reactions + Inorganic Compounds |
Diastereoselective DMD epoxidation of a chiral unsaturated ketone was applied to the synthesis of verrucosan-2β-ol.
Enantioselective dioxirane epoxidation is critical in a synthetic sequence leading to an analogue of glabrescol. The sequence produced the glabrescol analogue in 31% overall yield in only two steps. | 0 | Organic Reactions |
The mechanism proceeds in two stages: β-nucleophilic addition to the unsaturated carbonyl compound, followed by electrophilic substitution at the α-carbon of the resulting enolate.
When the nucleophile is an organometallic reagent, the mechanisms of the first step can vary. Whether reactions take place by ionic or radical mechanisms is unclear in some cases. Research has shown that the second step may even proceed via single-electron transfers when the reduction potential of the electrophile is low. A general scheme involving ionic intermediates is shown below.
Lithium organocuprates undergo oxidative addition to enones to give, after reductive elimination of an organocopper(III) species, β-substituted lithium enolates.
In any case, the second step is well described in all cases as the reaction of an enolate with an electrophile. The two steps may be carried out as distinct experimental operations if the initially formed enolate is protected after β-addition. If the two steps are not distinct, however, the counterion of the enolate is determined by the counterion of the nucleophilic starting material and can influence the reactivity of the enolate profoundly. | 0 | Organic Reactions |
Wu et al. reported a C–X cross coupling using CuX (X= Br, Cl) and a silver catalyst to obtain aryl halides. | 0 | Organic Reactions |
In organic chemistry, the Murai reaction is an organic reaction that uses C-H activation to create a new C-C bond between a terminal or strained internal alkene and an aromatic compound using a ruthenium catalyst. The reaction, named after Shinji Murai, was first reported in 1993. While not the first example of C-H activation, the Murai reaction is notable for its high efficiency and scope. Previous examples of such hydroarylations required more forcing conditions and narrow scope. | 0 | Organic Reactions |
An experiment for the preparation of mercuric oxide was first described by 11th century Arab-Spanish alchemist, Maslama al-Majriti, in Rutbat al-hakim. It was historically called red precipitate (as opposed to white precepitate being the mercuric amidochloride).
In 1774, Joseph Priestley discovered that oxygen was released by heating mercuric oxide, although he did not identify the gas as oxygen (rather, Priestley called it "dephlogisticated air," as that was the paradigm that he was working under at the time). | 1 | Inorganic Reactions + Inorganic Compounds |
The carbonatation process is used in the production of sugar from sugar beets.
It involves the introduction of limewater (milk of lime - calcium hydroxide suspension) and carbon dioxide enriched gas into the "raw juice" (the sugar rich liquid prepared from the diffusion stage of the process) to form calcium carbonate and precipitate impurities that are then removed. The whole process takes place in "carbonatation tanks" and processing time varies from 20 minutes to an hour.
Carbonatation involves the following effects:
* The increase in alkalinity coagulates proteins in the juice.
* Calcium carbonate absorbs colourants
* Alkalinity destroys some monosaccharide sugars, mostly glucose and fructose
The target is a large particle that naturally settles rapidly to leave a clear juice. The juice at the end is approximately 15 °Bx and 90% sucrose. The pH of the thin juice produced is a balance between removing as much calcium from the solution and the expected pH drop across later processing. If the juice goes acidic in the crystallisation stages then sucrose rapidly breaks down to glucose and fructose; not only do glucose and fructose affect crystallisation but they are molassagenic taking equivalent amounts of sucrose on to the molasses stage.
The carbon dioxide gas bubbled through the mixture forms calcium carbonate. The non-sugar solids are incorporated into the calcium carbonate particles and removed by natural (or assisted) sedimentation in tanks or clarifiers.
There are several systems of carbonatation, named from the companies that first developed them. They differ in how the lime is introduced, the temperature and duration of each stage, and the separation of the solids from the liquid.
* Dorr (also Dorr-Oliver) - a continuous process using two tanks with recycling ("1st carbonatation") to build up particle size for natural flocculation. The recycling ratio is about 7:1. The particles are separated under gravity in a thickening stage in a clarifier. The clear juice is then gassed further in another tank ("2nd carbonatation") and filtered. The concentrated mud (underflow) from the clarifier is filtered and/or pressed to recover more liquid. The Dorr process is low in maintenance and man-power but susceptible to filtration problems when frost damaged beets are processed. It is favoured in the UK and the USA.
* DDS (Det Danske Sukkerfabrik - "The Danish Sugarfactory") -- multistage process involving pre-liming where the pH of the juice is gradually increased to start precipitation of proteins, followed by addition of further lime and CO gas. The particles are removed at each stage by filtration.
* RT (Raffinerie Tirlemontoise - "Sugar refinery of Tienen") - another multistage process with a pre-liming stage. Particles also removed by filtration.
Both DDS and RT processes are favoured by European factories. The carbonatation system is generally matched to the diffusion scheme; juice from RT diffusers being processed by the RT carbonatation.
The clear juice from carbonatation is generally known as "thin juice". it may undergo pH adjustment with soda ash and addition of sulfur ("sulfitation") prior to the next stage which is concentration by multiple effect evaporation. | 1 | Inorganic Reactions + Inorganic Compounds |
A wide variety of phenols undergo O-methylation to give anisole derivatives. This process, catalyzed by such enzymes as caffeoyl-CoA O-methyltransferase, is a key reaction in the biosynthesis of lignols, percursors to lignin, a major structural component of plants.
Plants produce flavonoids and isoflavones with methylations on hydroxyl groups, i.e. methoxy bonds. This 5-O-methylation affects the flavonoid's water solubility. Examples are 5-O-methylgenistein, 5-O-methylmyricetin, and 5-O-methylquercetin (azaleatin). | 0 | Organic Reactions |
Hexachlorophosphazene has also found applications in research by enabling aromatic coupling reactions between pyridine and either N,N-dialkylanilines or indole, resulting in 4,4'-substituted phenylpyridine derivatives, postulated to go through a cyclophosphazene pyridinium salt intermediate.
The compound may also be used as a peptide coupling reagent for the synthesis of oligopeptides in chloroform, though for this application the tetramer octachlorotetraphosphazene usually proves more effective. | 1 | Inorganic Reactions + Inorganic Compounds |
Lanthanum oxalate is an inorganic compound, a salt of lanthanum metal and oxalic acid with the chemical formula .
__TOC__ | 1 | Inorganic Reactions + Inorganic Compounds |
In inorganic chemistry, an orthoborate is a polyatomic anion with formula or a salt containing the anion; such as trisodium orthoborate . It is one of several boron oxyanions, or borates.
The name is also used in organic chemistry for the trivalent functional group , or any compound (ester) that contains it, such as triethyl orthoborate . | 1 | Inorganic Reactions + Inorganic Compounds |
N-, P-, and S-alkylation are important processes for the formation of carbon-nitrogen, carbon-phosphorus, and carbon-sulfur bonds,
Amines are readily alkylated. The rate of alkylation follows the order tertiary amine < secondary amine < primary amine. Typical alkylating agents are alkyl halides. Industry often relies on green chemistry methods involving alkylation of amines with alcohols, the byproduct being water. Hydroamination is another green method for N-alkylation.
In the Menshutkin reaction, a tertiary amine is converted into a quaternary ammonium salt by reaction with an alkyl halide. Similar reactions occur when tertiary phosphines are treated with alkyl halides, the products being phosphonium salts.
Thiols are readily alkylated to give thioethers via the thiol-ene reaction. The reaction is typically conducted in the presence of a base or using the conjugate base of the thiol. Thioethers undergo alkylation to give sulfonium ions. | 0 | Organic Reactions |
Trimethylenemethane is a neutral, four-carbon molecule composed of four pi bonds; thus, it must be expressed either as a non-Kekulé molecule or a zwitterion. The orbital energy levels of TMM reveal that it possesses singlet and triplet states; generally, these states exhibit different reactivity and selectivity profiles. A singlet (3+2) cycloaddition, when it is concerted, is believed to proceed under frontier orbital control. When electron-rich TMMs are involved, the A orbital serves as the HOMO (leading to fused products if the TMM is cyclic). When electron-poor (or unsubstituted) TMMs are involved, the S orbital serves as the HOMO (leading to bridged products if the TMM is cyclic). Cycloadditions involving the triplet state are stepwise, and usually result in configurational scrambling in the two-atom component.
The rapid closure of TMMs to methylidenecyclopropanes is a general problem that affects the rate and yield of (3+2) cycloaddition reactions involving this class of reaction intermediates. The problem is generally less severe for five-membered, cyclic TMMs due to ring strain in the corresponding MCPs. When ring closure and TMM dimerization can be controlled, (3+2) cycloaddition affords isomeric mixtures of methylenecyclopentanes. Three classes of compounds have been used to generate synthetically useful TMM intermediates: diazenes, silyl-substituted allylic acetates and methylenecyclopropenes. Transition metal catalysis can be used with the latter two classes, although polar MCPs may open under light or heat (see below). | 0 | Organic Reactions |
Epothilone A and B are reported to be highly effective anticancer drugs. Several of their structural derivatives show very promising inhibition against breast cancer with only mild side effect and some of them are now under trials. In 1997, K. C. Nicolaou and coworkers reported the first total synthesis of both Epothilone A and B. Ender's alkylation reaction was utilized at the very beginning of the synthesis to install the stereogenic center at C8. The reaction proceeded with both high yield and high diastereoselectivity. | 0 | Organic Reactions |
There are two main ways in which minerals hydrate. One is conversion of an oxide to a double hydroxide, as with the hydration of calcium oxide—CaO—to calcium hydroxide—Ca(OH), the other is with the incorporation of water molecules directly into the crystalline structure of a new mineral.
The later process is exhibited in the hydration of feldspars to clay minerals, garnet to chlorite, or kyanite to muscovite.
Mineral hydration is also a process in the regolith that results in conversion of silicate minerals into clay minerals.
Some mineral structures, for example, montmorillonite, are capable of including a variable amount of water without significant change to the mineral structure.
Hydration is the mechanism by which hydraulic binders such as Portland cement develop strength. A hydraulic binder is a material that can set and harden submerged in water by forming insoluble products in a hydration reaction. The term hydraulicity or hydraulic activity is indicative of the chemical affinity of the hydration reaction. | 1 | Inorganic Reactions + Inorganic Compounds |
Calcium hydroxide adopts a polymeric structure, as do all metal hydroxides. The structure is identical to that of Mg(OH) (brucite structure); i.e., the cadmium iodide motif. Strong hydrogen bonds exist between the layers.
Calcium hydroxide is produced commercially by treating (slaking) lime with water:
:CaO + HO → Ca(OH)
In the laboratory it can be prepared by mixing aqueous solutions of calcium chloride and sodium hydroxide. The mineral form, portlandite, is relatively rare but can be found in some volcanic, plutonic, and metamorphic rocks. It has also been known to arise in burning coal dumps.
The positively charged ionized species CaOH has been detected in the atmosphere of S-type stars. | 1 | Inorganic Reactions + Inorganic Compounds |
Protein methylation typically takes place on arginine or lysine amino acid residues in the protein sequence. Arginine can be methylated once (monomethylated arginine) or twice, with either both methyl groups on one terminal nitrogen (asymmetric dimethylarginine) or one on both nitrogens (symmetric dimethylarginine), by protein arginine methyltransferases (PRMTs). Lysine can be methylated once, twice, or three times by lysine methyltransferases. Protein methylation has been most studied in the histones. The transfer of methyl groups from S-adenosyl methionine to histones is catalyzed by enzymes known as histone methyltransferases. Histones that are methylated on certain residues can act epigenetically to repress or activate gene expression. Protein methylation is one type of post-translational modification. | 0 | Organic Reactions |
The Tipson–Cohen reaction is a name reaction first discovered by Stuart Tipson and Alex Cohen at the National Bureau of Standards in Washington D.C. The Tipson–Cohen reaction occurs when two neighboring secondary sulfonyloxy groups in a sugar molecule are treated with zinc dust (Zn) and sodium iodide (NaI) in a refluxing solvent such as N,N-dimethylformamide (DMF) to give an unsaturated carbohydrate. | 0 | Organic Reactions |
There are other proteins that have acetylating abilities but differ in structure to the previously mentioned families. One HAT is called steroid receptor coactivator 1 (SRC1), which has a HAT domain located at the C-terminus end of the protein along with a basic helix-loop-helix and PAS A and PAS B domains with a LXXLL receptor interacting motif in the middle. Another is ATF-2 which contains a transcriptional activation (ACT) domain and a basic zipper DNA-binding (bZip) domain with a HAT domain in-between. The last is TAFII250 which has a Kinase domain at the N-terminus region, two bromodomains located at the C-terminus region and a HAT domain located in-between. | 0 | Organic Reactions |
The Riemschneider thiocarbamate synthesis converts alkyl or aryl thiocyanates to thiocarbamates under acidic conditions, followed by hydrolysis with ice water. The reaction was discovered by the German chemist in 1951 as a more efficient method to produce thiocarbamates. Some references spell the name Riemenschneider.
The Riemschneider reaction can also be used to create the corresponding N-substituted thiocarbamate from an alcohol or alkene. | 0 | Organic Reactions |
Concentrated (50%) aqueous solutions of sodium hydroxide have a characteristic viscosity, 78 mPa·s, that is much greater than that of water (1.0 mPa·s) and near that of olive oil (85 mPa·s) at room temperature. The viscosity of aqueous , as with any liquid chemical, is inversely related to its temperature, i.e., its viscosity decreases as temperature increases, and vice versa. The viscosity of sodium hydroxide solutions plays a direct role in its application as well as its storage. | 1 | Inorganic Reactions + Inorganic Compounds |
The carbon-silicon bond is highly electron-releasing and can stabilize a positive charge in the β position through hyperconjugation. Electrophilic additions to allyl- and vinylsilanes take advantage of this, and site selectivity generally reflects this property—electrophiles become bound to the carbon γ to the silyl group. The electron-donating strength of the carbon-silicon bond is similar to that of an acetamide substituent and equal to roughly two alkyl groups. After formation of the carbon-electrophile bond, silicon elimination is assisted by a nucleophile.
A model of the most likely reactive conformation of the allylsilane (see below) suggests that the new double bond that forms will predominantly possess the (E) configuration. However, addition of a nucleophile (such as the counterion of the electrophile) to the intermediate silyl-stabilized carbocation complicates this picture. Because the elimination to generate the double bond is stereospecifically anti, nucleophilic addition to either face of the silyl-stabilized carbanion leads to the formation of mixtures of double bond isomers. Diastereomeric mixtures of double bond isomers are common when Lewis acids are used to activate the electrophile.
Under conditions of nucleophilic catalysis, any intermediate along the reaction pathway may incorporate a silicon-nucleophile bond. This factor does not affect the outcome unless nucleophilic attack liberates free anions or allylic transposition occurs. The latter is known to occur for hypervalent allylsilanes incorporating fluoride. | 0 | Organic Reactions |
Synthesis of xenon trioxide is by aqueous hydrolysis of :
: + 3 → + 6 HF
The resulting xenon trioxide crystals are a strong oxidising agent and can oxidise most substances that are at all oxidisable. However, it is slow-acting and this reduces its usefulness.
Above 25 °C, xenon trioxide is very prone to violent explosion:
:2 XeO → 2 Xe + 3 O (ΔH = −403 kJ/mol)
When it dissolves in water, an acidic solution of xenic acid is formed:
:XeO(aq) + HO → HXeO H +
This solution is stable at room temperature and lacks the explosive properties of xenon trioxide. It oxidises carboxylic acids quantitatively to carbon dioxide and water.
Alternatively, it dissolves in alkaline solutions to form xenates. The anion is the predominant species in xenate solutions. These are not stable and begin to disproportionate into perxenates (+8 oxidation state) and xenon and oxygen gas. Solid perxenates containing have been isolated by reacting with an aqueous solution of hydroxides. Xenon trioxide reacts with inorganic fluorides such as KF, RbF, or CsF to form stable solids of the form . | 1 | Inorganic Reactions + Inorganic Compounds |
In 2005, Meyers et al. Proposed the following mechanism for the decarboxylative cross-coupling reaction. The initial and rate determining step is the decarboxylation. The ipso carbon of the arene ring is thought to coordinate to the palladium centre initially and is followed by the expulsion of carbon dioxide, forming an aryl–palladium intermediate. The olefin then inserts between the arene and palladium center, which then undergoes beta elimination to form the desired vinyl halide, as well as a palladium hydride. This proton is abstracted by silver carbonate, which acts as both a base and an oxidant to regenerate the starting palladium complex completing the catalytic cycle. | 0 | Organic Reactions |
Examples of enzymes capable of arene dearomatization are toluene dixoyhydrogenase, naphthalene dixoyhydrogenase and benzoyl CoA reductase. | 0 | Organic Reactions |
Dioxiranes may be produced through the action of KHSO on carbonyl compounds. Because of their low-lying σ* orbital, they are highly electrophilic oxidants and react with unsaturated functional groups, Y-H bonds (yielding oxygen insertion products), and heteroatoms. The most common dioxiranes employed for organic synthesis are dimethyldioxirane (DMD) and trifluoromethyl-methyldioxirane (TFD). The latter is effective for chemoselective oxidations of C-H and Si-H bonds. Although this class of reagents is most famous for the epoxidation of alkenes, dioxiranes have been used extensively for other kinds of oxidations as well. | 0 | Organic Reactions |
Bougalt's report of iodolactonization represented the first example of a reliable lactonization that could be used in many different systems. Bromolactonization was actually developed in the twenty years prior to Bougalt’s publication of iodolactonization. However, bromolactonization is much less commonly used because the simple electrophilic addition of bromine to an alkene, seen below, can compete with the bromolactonization reaction and reduce the yield of the desired lactone.
Chlorolactonization methods first appeared in the 1950s but are even less commonly employed than bromolactonization. The use of elemental chlorine is procedurally difficult because it is a gas at room temperature, and the electrophilic addition product can be rapidly produced as in bromolactonization. | 0 | Organic Reactions |
Xylose, fucose, mannose, and GlcNAc phosphoserine glycans have been reported in the literature. Fucose and GlcNAc have been found only in Dictyostelium discoideum, mannose in Leishmania mexicana, and xylose in Trypanosoma cruzi. Mannose has recently been reported in a vertebrate, the mouse, Mus musculus, on the cell-surface laminin receptor alpha dystroglycan. It has been suggested this rare finding may be linked to the fact that alpha dystroglycan is highly conserved from lower vertebrates to mammals. | 0 | Organic Reactions |
Trifluoroacetic acid, often used in these reductions, is a strong, corrosive acid. Some hydrosilanes are pyrophoric. | 0 | Organic Reactions |
Since organochlorine compounds are the most abundant organohalides, most dehalogenations entail manipulation of C-Cl bonds. | 0 | Organic Reactions |
Cobalt is essential for most higher forms of life, but more than a few milligrams each day is harmful. Although poisonings have rarely resulted from cobalt compounds, their chronic ingestion has caused serious health problems at doses far less than the lethal dose. In 1966, the addition of cobalt compounds to stabilize beer foam in Canada led to a peculiar form of toxin-induced cardiomyopathy, which came to be known as beer drinkers cardiomyopathy'.
Furthermore, cobalt(II) chloride is suspected of causing cancer (i.e., possibly carcinogenic, IARC Group 2B) as per the International Agency for Research on Cancer (IARC) Monographs.
In 2005–06, cobalt chloride was the eighth-most-prevalent allergen in patch tests (8.4%). | 1 | Inorganic Reactions + Inorganic Compounds |
Members of the SOBER1 family are considered closely related to acyl-protein thioesterases, judged by their protein structure. However, a change in their amino acid sequence renders SOBER1's biochemical properties into a deacetylase; in particular the hydrophobic tunnel, which is found in acyl-protein thioesterases, is impaired by additional amino acids in the lid structure of SOBER1, creating a new surface for binding of the acetyl group. | 0 | Organic Reactions |
The benzyl halide 1 reacts with hexamine to a quaternary ammonium salt 3, each time just alkylating one nitrogen atom. Then the benzylammonium undergoes an acid-catalyzed hydrolysis process.
Depending on the hydrolysis conditions, the hexamine unit might instead break apart, leaving a benzyl amine (the Delépine reaction).
The reaction can also be applied to the oxidation of benzylic amines. In this way, m-xylylenediamine can be converted to isophthalaldehyde. | 0 | Organic Reactions |
Asymmetric hydrogenation is a chemical reaction that adds two atoms of hydrogen to a target (substrate) molecule with three-dimensional spatial selectivity. Critically, this selectivity does not come from the target molecule itself, but from other reagents or catalysts present in the reaction. This allows spatial information (what chemists refer to as chirality) to transfer from one molecule to the target, forming the product as a single enantiomer. The chiral information is most commonly contained in a catalyst and, in this case, the information in a single molecule of catalyst may be transferred to many substrate molecules, amplifying the amount of chiral information present. Similar processes occur in nature, where a chiral molecule like an enzyme can catalyse the introduction of a chiral centre to give a product as a single enantiomer, such as amino acids, that a cell needs to function. By imitating this process, chemists can generate many novel synthetic molecules that interact with biological systems in specific ways, leading to new pharmaceutical agents and agrochemicals. The importance of asymmetric hydrogenation in both academia and industry contributed to two of its pioneers — William Standish Knowles and Ryōji Noyori — being collectively awarded one half of the 2001 Nobel Prize in Chemistry. | 0 | Organic Reactions |
Saturated hydronitrogens can be:
* linear (general formula ) wherein the nitrogen atoms are joined in a snakelike structure
* branched (general formula , n > 3) wherein the nitrogen backbone splits off in one or more directions
* cyclic (general formula , n > 2) wherein the nitrogen backbone is linked so as to form a loop.
According to IUPAC definitions, the former two are azanes, whereas the third group is called cycloazanes. Saturated hydronitrogens can also combine any of the linear, cyclic (e.g. polycyclic), and branching structures, and they are still azanes (no general formula) as long as they are acyclic (i.e., having no loops). They also have single covalent bonds between their nitrogens. | 1 | Inorganic Reactions + Inorganic Compounds |
Boric acid was first registered in the US as an insecticide in 1948 for control of cockroaches, termites, fire ants, fleas, silverfish, and many other insects. The product is generally considered to be safe to use in household kitchens to control cockroaches and ants. It acts as a stomach poison affecting the insects metabolism, and the dry powder is abrasive to the insects exoskeletons. Boric acid also has the reputation as "the gift that keeps on killing" in that cockroaches that cross over lightly dusted areas do not die immediately, but that the effect is like shards of glass cutting them apart. This often allows a roach to go back to the nest where it soon dies. Cockroaches, being cannibalistic, eat others killed by contact or consumption of boric acid, consuming the powder trapped in the dead roach and killing them, too. | 1 | Inorganic Reactions + Inorganic Compounds |
Diazomethane is a popular methylating agent in the laboratory, but it is too hazardous (explosive gas with a high acute toxicity) to be employed on an industrial scale without special precautions. Use of diazomethane has been significantly reduced by the introduction of the safer and equivalent reagent trimethylsilyldiazomethane. | 0 | Organic Reactions |
One variation is called the decarboxylative A coupling. In this reaction the amine is replaced by an amino acid. The imine can isomerise and the alkyne group is placed at the other available nitrogen alpha position. This reaction requires a copper catalyst. The redox A coupling has the same product outcome but the reactants are again an aldehyde, an amine and an alkyne as in the regular A coupling. | 0 | Organic Reactions |
Both the trimer and tetramer in hydrocarbon solutions photochemically react forming clear liquids identified as alkyl-substituted derivatives , where n = 3, 4. Such reactions proceed under prolonged UVC (mercury arc) illumination without affecting the rings. Solid films of the trimer and tetramer will not undergo any chemical change under such irradiation conditions. | 1 | Inorganic Reactions + Inorganic Compounds |
In the laboratory, cobalt(II) chloride serves as a common precursor to other cobalt compounds. Generally, diluted aqueous solutions of the salt behave like other cobalt(II) salts since these solutions consist of the ion regardless of the anion. For example, such solutions give a precipitate of cobalt sulfide upon treatment with hydrogen sulfide . | 1 | Inorganic Reactions + Inorganic Compounds |
Formation of oxocarbenium ions can proceed through several different pathways. Most commonly, the oxygen of a ketone will bind to a Lewis Acid, which activates the ketone, making it a more effective electrophile. The Lewis acid can be a wide range of molecules, from a simple hydrogen atom to metal complexes. The remainder of this article will focus on alkyl oxocarbenium ions, however, where the atom added to the oxygen is a carbon. One way that this sort of ion will form is the elimination of a leaving group. In carbohydrate chemistry, this leaving group is often an ether or ester. An alternative to elimination is direct deprotonation of the molecule to form the ion, however, this can be difficult and require strong bases to achieve. | 0 | Organic Reactions |
Dioxiranes oxidize a wide variety of functional groups. This section describes the substrate scope of dioxirane epoxidation and the products that most commonly result.
Oxidations of alkynes, allenes, arenes, and other unique unsaturated functionality may yield epoxides or other oxidized products. Oxidation of allenes affords allene dioxides or products of intramolecular participation. Minor amounts of side products derived from additional oxidation or rearrangement were also observed.
In oxidations of heteroaromatic compounds, the products obtained depend on reaction conditions. Thus, at low temperatures, acetylated indoles are simply epoxidized in high yield (unprotected indoles undergo N-oxidation). However, when the temperature is raised to 0 °C, rearranged products are obtained.
DMD may oxidize heteroatoms to the corresponding oxides (or products of oxide decomposition). Often, the results of these oxidations depend on reaction conditions. Tertiary amines cleanly give the corresponding N-oxides. Primary amines give nitroalkanes upon treatment with 4 equivalents of DMD, but azoxy compounds upon treatment with only 2 equivalents. Secondary amines afford either hydroxylamines or nitrones.
Oxidation of nitronate anions, generated in situ from nitroalkanes, leads to carbonyl compounds in an example of an oxidative Nef reaction.
Sulfide oxidation in the presence of a single equivalent of DMD leads to sulfoxides. Increasing the amount of DMD used (2 or more equivalents) leads to sulfones. Both nitrogen and sulfur are more susceptible to oxidation than carbon-carbon multiple bonds.
Although alkanes are typically difficult to functionalize directly, C-H insertion with TFD is an efficient process in many cases. The order of reactivity of C-H bonds is: allylic > benzylic > tertiary > secondary > primary. Often, the intermediate alcohols produced are oxidized further to carbonyl compounds, although this can be prevented by trapping in situ with an anhydride. Chiral alkanes are functionalized with retention of configuration.
Dioxiranes oxidize primary alcohols to either the aldehyde or carboxylic acid; however, DMD selectively oxidizes secondary over primary alcohols. Thus, vicinal diols may be transformed into α-hydroxy ketones with dioxirane oxidation.
Epoxidation is usually more facile than C-H oxidation, although sterically hindered allyl groups may undergo selective C-H oxidation instead of epoxidation of the allylic double bond. | 0 | Organic Reactions |
The physical manifestation of leaving group ability is the rate at which a reaction takes place. Good leaving groups give fast reactions. By transition state theory, this implies that reactions involving good leaving groups have low activation barriers leading to relatively stable transition states.
It is helpful to consider the concept of leaving group ability in the case of the first step of an S1/E1 reaction with an anionic leaving group (ionization), while keeping in mind that this concept can be generalized to all reactions that involve leaving groups. Because the leaving group bears a larger negative charge in the transition state (and products) than in the starting material, a good leaving group must be able to stabilize this negative charge, i.e. form stable anions. A good measure of anion stability is the pK of an anions conjugate acid (pK), and leaving group ability indeed generally follows this trend, with a lower pK' correlating well with better leaving group ability.
The correlation between pK and leaving group ability, however, is not perfect. Leaving group ability represents the difference in energy between starting materials and a transition state (ΔG) and differences in leaving group ability are reflected in changes in this quantity (ΔΔG). The pK, however, represents the difference in energy between starting materials and products (ΔG°) with differences in acidity reflected in changes in this quantity (ΔΔG°). The ability to correlate these energy differences is justified by the Hammond postulate and the Bell–Evans–Polanyi principle. Also, the starting materials in these cases are different. In the case of the acid dissociation constant, the "leaving group" is bound to a proton in the starting material, while in the case of leaving group ability, the leaving group is bound to (usually) carbon. It is with these important caveats in mind that one must consider pK to be reflective of leaving group ability. Nevertheless, one can generally examine acid dissociation constants to qualitatively predict or rationalize rate or reactivity trends relating to variation of the leaving group. Consistent with this picture, strong bases such as and tend to make poor leaving groups, due their inability to stabilize a negative charge.
What constitutes a reasonable leaving group is dependent on context. For S2 reactions, typical synthetically useful leaving groups include , , and . Substrates containing phosphate and carboxylate leaving groups are more likely to react by competitive addition-elimination, while sulfonium and ammonium salts generally form ylides or undergo E2 elimination when possible. With reference to the table above, phenoxides () constitute the lower limit for what is feasible as S2 leaving groups: very strong nucleophiles like or have been used to demethylate anisole derivatives through S2 displacement at the methyl group. Hydroxide, alkoxides, amides, hydride, and alkyl anions do not serve as leaving groups in S2 reactions.
On the other hand, when anionic or dianionic tetrahedral intermediates collapse, the high electron density of the neighboring heteroatom facilitates the expulsion of a leaving group. Thus, in the case of ester and amide hydrolysis under basic conditions, alkoxides and amides are commonly proposed as leaving groups. For the same reason, E1cb reactions involving hydroxide as a leaving group are not uncommon (e.g., in the aldol condensation). It is exceedingly rare for groups such as (hydrides), (alkyl anions, R = alkyl or H), or (aryl anions, Ar = aryl) to depart with a pair of electrons because of the high energy of these species. The Chichibabin reaction provides an example of hydride as a leaving group, while the Wolff-Kishner reaction and Haller-Bauer reaction feature unstabilized carbanion leaving groups. | 0 | Organic Reactions |
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bondsthat is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as inorganic chemistry.
Inorganic compounds comprise most of the Earth's crust, although the compositions of the deep mantle remain active areas of investigation.
All allotropes (structurally different pure forms of an element) and some simple carbon compounds are often considered inorganic. Examples include the allotropes of carbon (graphite, diamond, buckminsterfullerene, graphene, etc.), carbon monoxide , carbon dioxide , carbides, and salts of inorganic anions such as carbonates, cyanides, cyanates, thiocyanates, isothiocyanates, phosphates, sulphates, chlorates, etc. Many of these are normal parts of mostly organic systems, including organisms; describing a chemical as inorganic does not necessarily mean that it cannot occur within living things. | 1 | Inorganic Reactions + Inorganic Compounds |
Iodolactonization has been used in the synthesis of many biologically important products such as the tumor growth inhibitors vernolepin and vernomenin, the pancreatic lipase inhibitor vibralactone, and prostaglandins, a lipid found in animals. The following total syntheses all use iodolactonization as a key step in obtaining the desired product.
In 1977, Samuel Danishefsky and coworkers were able to synthesize the tumor growth inhibitors dl-vernolepin and dl-vernomenin via a multistep process in which a lactonization was employed. This synthesis demonstrates the use of iodolactonization to preferentially form a five-membered ring over a four- or six-membered ring, as expected from Baldwin's rules.
In 2006, Zhou and coworkers synthesized another natural product, vibralactone, in which the key step was the formation of a lactone. The stereoselectivity of the iodolactonization sets a critical stereochemical configuration for the target compound.
In 1969, Corey and coworkers synthesized prostaglandin E using an iodolactone intermediate. Again, the stereoselectivity of the iodolactonization plays an integral role in product formation. | 0 | Organic Reactions |
SOBER1 is an enzyme that catalyzes the biochemical reaction of deacetylation. The SOBER (uppressor f AvrsT-licited esistance) 1 protein is conserved in plants and it suppresses the plants ability to carry out the hypersensitive response against infection by certain pathogenic effector proteins from the YopJ family. SOBER1 belongs to the protein superfamily of α/β hydrolases and possesses a canonical serine/histidine/aspartate catalytic triad to carry out the deacetylation reaction. There have been contradicting reports about SOBER1s potential phospholipase activity, with one study claiming phospholipase A activity of the protein and another study being unable to reproduce this result. | 0 | Organic Reactions |
Yttrium oxalate is highly insoluble in water and converts to the oxide when heated. Yttrium oxalate forms crystalline hydrates (colorless crystals) with the formula Y(CO)•n HO, where n = 4, 9, and 10.
Decomposes when heated:
The solubility product of yttrium oxalate at 25 °C is 5.1 × 10.
The trihydrate Y(CO)•3HO is formed by heating more hydrated varieties at 110 °C.
Y(CO)•2HO, which is formed by heating the decahydrate at 210 °C) forms monoclinic crystals with unit cell dimensions a=9.3811 Å, b=11.638 Å, c=5.9726 Å, β=96.079°. | 1 | Inorganic Reactions + Inorganic Compounds |
Enediols are alkenes with a hydroxyl group on each carbon of the C=C double bond. Normally such compounds are disfavored components in equilibria with acyloins. One special case is catechol, where the C=C subunit is part of an aromatic ring. In some other cases however, enediols are stabilized by flanking carbonyl groups. These stabilized enediols are called reductones. Such species are important in glycochemistry, e.g., the Lobry de Bruyn-van Ekenstein transformation.
Ribulose-1,5-bisphosphate is a key substrate in the Calvin cycle of photosynthesis. In the Calvin cycle, the ribulose equilibrates with the enediol, which then binds carbon dioxide. The same enediol is also susceptible to attack by oxygen (O) in the (undesirable) process called photorespiration. | 0 | Organic Reactions |
In ammonia production CO and CO are considered poisons to most commonly used catalysts. Methanation catalysts are added after several hydrogen producing steps to prevent carbon oxide buildup in the ammonia synthesis loop as methane does not have similar adverse effects on ammonia synthesis rates. | 0 | Organic Reactions |