text
stringlengths 105
6.5k
| label
int64 0
1
| label_text
stringclasses 2
values |
|---|---|---|
is reduced by acetonitrile:
Although it polymerizes tetrahydrofuran, is stable in diethyl ether. Reduction of such solutions with tin gives and , depending on conditions. | 1 | Inorganic Reactions + Inorganic Compounds |
Liu et al. reported the C-S coupling of aryl carboxylic acids with disulphides or thiols using a Pd/Cu catalyst system. | 0 | Organic Reactions |
Yttrium oxalate is an inorganic compound, a salt of yttrium and oxalic acid with the chemical formula Y(CO). The compound does not dissolve in water and forms crystalline hydrates—colorless crystals. | 1 | Inorganic Reactions + Inorganic Compounds |
Electrophilic amination reactions can be classified as either additions or substitutions. Although the resulting product is not always an amine, these reactions are unified by the formation of a carbon–nitrogen bond and the use of an electrophilic aminating agent. A wide variety of electrophiles have been used; for substitutions, these are most commonly amines substituted with electron-withdrawing groups: chloramines, hydroxylamines, hydrazines, and oxaziridines, for instance. Addition reactions have employed imines, oximes, azides, azo compounds, and others. | 0 | Organic Reactions |
Bone ash can be used alone as an organic fertilizer or it can be treated with sulfuric acid to form a "single superphosphate" fertilizer which is more water soluble:
:Ca(PO) + 2 HSO + 5 HO → 2 CaSO·2HO + Ca(HPO)·HO
Similarly, phosphoric acid can be used to form triple superphosphate, a more concentrated phosphorus fertilizer which excludes the gypsum content found in single superphosphate:
:Ca(PO) + 4 HPO → 3 Ca(HPO) | 1 | Inorganic Reactions + Inorganic Compounds |
Fluoroantimonic acid is the strongest superacid based on the measured value of its Hammett acidity function (H), which has been determined for various ratios of HF:SbF. The H of HF is −15. A solution of hf.rst.imntaining 1 mol % of SbF is −20. The H is −21 for 10 mol%. For > 50 mol % SbF, the H is between −21 and −23. The lowest attained H is about -28. The following H values show that fluoroantimonic acid is stronger than other superacids. Increased acidity is indicated by smaller (in this case, more negative) values of H.
* Fluoroantimonic acid (−23 > H > −28)
* Magic acid (H = −23)
* Carborane acid (H < −18)
* Fluorosulfuric acid (H = −15)
* Triflic acid (H = −15)
* Perchloric acid (H = −13)
Of the above, only the carborane acids, whose H could not be directly determined due to their high melting points, may be stronger acids than fluoroantimonic acid.
The H value measures the protonating ability of the bulk, liquid acid, and this value has been directly determined or estimated for various compositions of the mixture. The pK on the other hand, measures the equilibrium of proton dissociation of a discrete chemical species when dissolved in a particular solvent. Since fluoroantimonic acid is not a single chemical species, its pK value is not well-defined.
The gas-phase acidity (GPA) of individual species present in the mixture have been calculated using density functional theory methods. (Solution-phase pKs of these species can, in principle, be estimated by taking into account solvation energies, but do not appear to be reported in the literature as of 2019.) For example, the ion-pair [HF]· was estimated to have a GPA of 254 kcal/mol. For comparison, the commonly encountered superacid triflic acid, TfOH, is a substantially weaker acid by this measure, with a GPA of 299 kcal/mol. However, certain carborane superacids have GPAs lower than that of [HF]·. For example, H(CHBCl) has an experimentally determined GPA of 241 kcal/mol. | 1 | Inorganic Reactions + Inorganic Compounds |
The iodolactonization reaction includes a number of nuances that affect product formation including regioselectivity, ring size preference, and thermodynamic and kinetic control. In terms of regioselectivity, iodolactonization preferentially occurs at the most hindered carbon atom adjacent to the iodonium cation. This is due to the fact that the more substituted carbon is better able to maintain a partial positive charge and is thus more electrophilic and susceptible to nucleophilic attack. When multiple double bonds in a molecule are equally reactive, conformational preferences dominate. However, when one double bond is more reactive, that reactivity always dominates regardless of conformational preference.
Both five- and six-membered rings could be formed in the iodolactonization shown below, but the five-membered ring is formed preferentially as predicted by Baldwin's rules for ring closure.
According to the rules, 5-exo-tet ring closures are favored while 6-endo-tet ring closures are disfavored. The regioselectivity of each iodolactonization can be predicted and explained using Baldwin's rules.
Stereoselective iodolactonizations have been seen in literature and can be very useful in synthesizing large molecules such as the aforementioned vernopelin and vernomenin because the lactone can be formed while maintaining other stereocenters. The ring closure can even be driven by stereocenters adjacent to the carbon-carbon multiple bond as shown below.
Even in systems without existing stereocenters, Bartlett and coworkers found that stereoselectivity was achievable. They were able to synthesize the cis and trans five membered lactones by adjusting reactions conditions such as temperature and reaction time. The trans product was formed under thermodynamic conditions (e.g. a long reaction time) while the cis product was formed under kinetic conditions (e.g. a relatively shorter reaction time). | 0 | Organic Reactions |
NaOH and its monohydrate form orthorhombic crystals with the space groups Cmcm (oS8) and Pbca (oP24), respectively. The monohydrate cell dimensions are a = 1.1825, b = 0.6213, c = 0.6069 nm. The atoms are arranged in a hydrargillite-like layer structure, with each sodium atom surrounded by six oxygen atoms, three each from hydroxide ions and three from water molecules. The hydrogen atoms of the hydroxyls form strong bonds with oxygen atoms within each O layer. Adjacent O layers are held together by hydrogen bonds between water molecules. | 1 | Inorganic Reactions + Inorganic Compounds |
The reaction is usually initiated by copper(II) chloride (CuCl), which is the most common catalyst in the production of 1,2-dichloroethane. In some cases, CuCl is supported on silica in presence of KCl, LaCl, or AlCl as cocatalysts. Aside from silica, a variety of supports have also been used including various types of alumina, diatomaceous earth, or pumice. Because this reaction is highly exothermic (238 kJ/mol), the temperature is monitored, to guard against thermal degradation of the catalyst. The reaction is as follows:
:CH=CH + 2 CuCl → 2 CuCl + ClHC-CHCl
The copper(II) chloride is regenerated by sequential reactions of the cuprous chloride with oxygen and then hydrogen chloride:
:½ O + 2 CuCl → CuOCuCl
:2 HCl + CuOCuCl → 2 CuCl + HO | 0 | Organic Reactions |
Metals, under the right conditions, burn in a process similar to the combustion of wood or gasoline. In fact, rust is the result of oxidation of steel or iron at very slow rates. A thermite reaction results when the correct mixtures of metallic fuels combine and ignite. Ignition itself requires extremely high temperatures.
Ignition of a thermite reaction normally requires a sparkler or easily obtainable magnesium ribbon, but may require persistent efforts, as ignition can be unreliable and unpredictable. These temperatures cannot be reached with conventional black powder fuses, nitrocellulose rods, detonators, pyrotechnic initiators, or other common igniting substances. Even when the thermite is hot enough to glow bright red, it does not ignite, as it has a very high ignition temperature. Starting the reaction is possible using a propane torch if done correctly.
Often, strips of magnesium metal are used as fuses. Because metals burn without releasing cooling gases, they can potentially burn at extremely high temperatures. Reactive metals such as magnesium can easily reach temperatures sufficiently high for thermite ignition. Magnesium ignition remains popular among amateur thermite users, mainly because it can be easily obtained, but a piece of the burning strip can fall off into the mixture, resulting in premature ignition.
The reaction between potassium permanganate and glycerol or ethylene glycol is used as an alternative to the magnesium method. When these two substances mix, a spontaneous reaction begins, slowly increasing the temperature of the mixture until it produces flames. The heat released by the oxidation of glycerine is sufficient to initiate a thermite reaction.
Apart from magnesium ignition, some amateurs also choose to use sparklers to ignite the thermite mixture. These reach the necessary temperatures and provide enough time before the burning point reaches the sample. This can be a dangerous method, as the iron sparks, like the magnesium strips, burn at thousands of degrees and can ignite the thermite, though the sparkler itself is not in contact with it. This is especially dangerous with finely powdered thermite.
Match heads burn hot enough to ignite thermite. Use of match heads enveloped with aluminium foil and a sufficiently long viscofuse/electric match leading to the match heads is possible.
Similarly, finely powdered thermite can be ignited by a flint spark lighter, as the sparks are burning metal (in this case, the highly reactive rare-earth metals lanthanum and cerium). Therefore, it is unsafe to strike a lighter close to thermite. | 1 | Inorganic Reactions + Inorganic Compounds |
Potassium pentasulfide is the inorganic compound with the formula . It is a red-orange solid that dissolves in water. The salt decomposes rapidly in air.
It is one of several polysulfide salts with the general formula , where M = Li, Na, K and n = 2, 3, 4, 5, 6. The polysulfide salts of potassium and sodium are similar. | 1 | Inorganic Reactions + Inorganic Compounds |
Fluorinations with DAST can be carried out in conventional glass equipment, although etching of the glass may result from reaction byproducts. Reactions are typically carried out in aprotic or non-polar solvents. Moisture and atmospheric oxygen should be excluded from the reaction. Reactions are generally started at -78 °C and warmed to room temperature or above; however, reactions should not be heated above 80 °C, as decomposition of the fluorinating reagent begins to occur at this temperature. Workup usually involves pouring the reaction mixture over water or ice, followed by neutralization of acidic byproducts with sodium bicarbonate. Standard purification methods can be used to isolate the desired fluorinated products. | 0 | Organic Reactions |
The general mechanism is shown below. The resonating arrow (1) shows a resonance contributor of the diazo compound with a lone pair of electrons on the carbon adjacent to the nitrogen. The diazo compound then does a nucleophilic attack on the carbonyl-containing compound (nucleophilic addition), producing a tetrahedral intermediate (2). This intermediate decomposes by the evolution of nitrogen gas forming the tertiary carbocation intermediate (3).
The reaction is then completed either by the reformation of the carbonyl through an 1,2-rearrangement or by the formation of the epoxide. There are two possible carbonyl products: one formed by migration of R (4) and the other by migration of R (5). The relative yield of each possible carbonyl is determined by the migratory preferences of the R-groups.
The epoxide product is formed by an intramolecular addition reaction in which a lone pair from the oxygen attacks the carbocation (6).
This reaction is exothermic due to the stability of nitrogen gas and the carbonyl containing compounds. This specific mechanism is supported by several observations. First, kinetic studies of reactions between diazomethane and various ketones have shown that the overall reaction follows second order kinetics. Additionally, the reactivity of two series of ketones are in the orders ClCCOCH > CHCOCH > CHCOCH and cyclohexanone > cyclopentanone > cycloheptanone > cyclooctanone. These orders of reactivity are the same as those observed for reactions that are well established as proceeding through nucleophilic attack on a carbonyl group. | 0 | Organic Reactions |
LSAT was originally developed as a substrate for the growth of high T cuprate superconductors thin films, mostly of yttrium barium copper oxide (YBCO), for microwave device applications. The motivation for its development was to create a lattice-matched substrate with a similar thermal expansion coefficient and no structural phase transition over a wide temperature range, spanning from the high temperatures used for the growth of cuprates, to the cryogenic temperatures where they are superconducting. | 1 | Inorganic Reactions + Inorganic Compounds |
Some chemicals contain another anion in addition to borate. These include borate chlorides, borate carbonates, borate nitrates, borate sulfates, borate phosphates. | 1 | Inorganic Reactions + Inorganic Compounds |
The Strecker degradation is a chemical reaction which converts an α-amino acid into an aldehyde containing the side chain, by way of an imine intermediate. It is named after Adolph Strecker, a German chemist.
The original observation by Strecker involved the use of alloxan as the oxidant in the first step, followed by hydrolysis:
The reaction can take place using a variety of organic and inorganic reagents. | 0 | Organic Reactions |
Metal sulfides are usually prepared by heating mixtures of the two elements, but in the case of scandium, this method yields scandium monosulfide, ScS. ScS can be prepared by heating scandium(III) oxide under flowing hydrogen sulfide in a graphite crucible to 1550 °C or above for 2–3 hours. The crude product is then purified by chemical vapor transport at 950 °C using iodine as the transport agent.
:ScO + 3HS → ScS + 3HO
Scandium(III) sulfide can be prepared by reacting scandium(III) chloride with dry hydrogen sulfide at elevated temperature:
:2 ScCl + 3 HS → ScS + 6 HCl | 1 | Inorganic Reactions + Inorganic Compounds |
The formose reaction, discovered by Aleksandr Butlerov in 1861, and hence also known as the Butlerov reaction, involves the formation of sugars from formaldehyde. The term formose is a portmanteau of formaldehyde and aldose. | 0 | Organic Reactions |
Boron is used in pyrotechnics to prevent the amide-forming reaction between aluminium and nitrates. A small amount of boric acid is added to the composition to neutralize alkaline amides that can react with the aluminium.
Boric acid can be used as a colorant to make fire green. For example, when dissolved in methanol it is popularly used by fire jugglers and fire spinners to create a deep green flame much stronger than copper sulfate. | 1 | Inorganic Reactions + Inorganic Compounds |
HDAC8 has been found to be most similar to HDAC3. Its major feature is its catalytic domain which contains an NLS region in the center. Two transcripts of this HDAC have been found which include a 2.0kb transcript and a 2.4kb transcript. Unlike the other HDAC molecules, when purified, this HDAC showed to be enzymatically active. At this point, due to its recent discovery, it is not yet known if it is regulated by co-repressor protein complexes. Northern blots have revealed that different tissue types show varying degrees of HDAC8 expression but has been observed in smooth muscles and is thought to contribute to contractility. | 0 | Organic Reactions |
Calcium hydroxide is typically added to a bundle of areca nut and betel leaf called "paan" to keep the alkaloid stimulants chemically available to enter the bloodstream via sublingual absorption.
It is used in making naswar (also known as nass or niswar), a type of dipping tobacco made from fresh tobacco leaves, calcium hydroxide (chuna or soon), and wood ash. It is consumed most in the Pathan diaspora, Afghanistan, Pakistan, India and Bangladesh. Villagers also use calcium hydroxide to paint their mud houses in Afghanistan, Pakistan and India. | 1 | Inorganic Reactions + Inorganic Compounds |
Hydrogen cyanide has been discussed as a precursor to amino acids and nucleic acids, and is proposed to have played a part in the origin of life. Although the relationship of these chemical reactions to the origin of life theory remains speculative, studies in this area have led to discoveries of new pathways to organic compounds derived from the condensation of HCN (e.g. Adenine). | 1 | Inorganic Reactions + Inorganic Compounds |
is prepared by chlorination of Mo metal but also chlorination of . The unstable hexachloride is not produced in this way.
is reduced by acetonitrile to afford an orange acetonitrile complex, . This complex in turn reacts with THF to give , a precursor to other molybdenum-containing complexes.
Molybdenum(IV) bromide is prepared by treatment of with hydrogen bromide:
The reaction proceeds via the unstable molybdenum(V) bromide, which releases bromine at room temperature.
is a good Lewis acid toward non-oxidizable ligands. It forms an adduct with chloride to form . In organic synthesis, the compound finds occasional use in chlorinations, deoxygenation, and oxidative coupling reactions. | 1 | Inorganic Reactions + Inorganic Compounds |
Although the substrate scope of PLE is broad, enantioselectivity varies as a function of the structure of the substrate. This section describes substrates that are hydrolyzed by PLE with the highest enantioselectivity, as well as sensitive substrates that may be hydrolyzed to achiral carboxylic acids in high yield without side reactions.
Glutarates were the first substrates to be hydrolyzed with PLE in high enantioselectivity. Although yields are moderate, enantioselectivity is extremely high.
3-Alkyl glutarates with small alkyl substituents are hydrolyzed to the (R)-monoester; however, when a large alkyl substituent is present, the (S)-monoester forms. This switch in enantioselectivity is accurately predicted by the active site model given above.
An opposite trend is observed in desymmetrizing hydrolyses of 2-methyl malonates, which afford the (S) enantiomer when the other substituent on C-2 is small, and the (R) enantiomer when the other C-2 substituent is large.
A number of meso diesters other than the substrates described above may be hydrolyzed by PLE with high enantioselectivity. Cyclic meso diesters tend to be hydrolyzed more selectively than acyclic diesters. The predominant enantiomer of product depends on ring size.
7-Oxabicyclo[2.2.1]heptane-2,3-dicarboxylates are an interesting class of diesters that are hydrolyzed by PLE with high enantioselectivity. These substrates have been used for the enantioselective construction of biologically relevant sugars (see Synthetic Applications below).
Racemic mixtures of all of the substrates described above, as well as additional chiral diesters (such as the epoxy ester in equation (8)), may be resolved using PLE for kinetic resolution. A significant disadvantage of kinetic resolution is a maximum yield of hydrolyzed product of 50%. However, if rapid racemization is occurring alongside hydrolysis (an example of dynamic kinetic resolution), a maximum yield of 100% is possible.
Esterase enzymes may also be used for hydrolysis of base-sensitive monoesters. PLE has been applied to the synthesis of prostaglandins for the selective hydrolysis of the ester without destruction of the β-hydroxy ketone moiety. | 0 | Organic Reactions |
Most asymmetric Heck reactions employing chiral phosphines proceed by the cationic pathway, which does not require the dissociation of a phosphine ligand. Oxidative addition of an aryl perfluorosulfonate generates a cationic palladium aryl complex V. The mechanism then proceeds as in the neutral case, with the difference that an extra site of coordinative unsaturation exists on palladium throughout the process.
Thus, coordination of the alkene does not require ligand dissociation. Stoichiometric amounts of base are still required to reduce the palladium(II)-hydrido complex VIII back to palladium(0). Silver salts may be used to initiate the cationic pathway in reactions of aryl halides. | 0 | Organic Reactions |
In ene-yne activation, the least common of the five modes, a single metal species coordinates with the enol alkene and the tethered alkyne, simultaneously activating both moieties for reaction. Nickel, cobalt, and rhenium complexes have all been employed in this manner. A representative example was reported by Malacria et al. in 1994, in which an alkynyl substituted β-ketoester was treated with cyclopentadienyl cobalt complex and irradiation to give disubstituted methylene cyclopentane. | 0 | Organic Reactions |
Electrophilic amination is a chemical process involving the formation of a carbon–nitrogen bond through the reaction of a nucleophilic carbanion with an electrophilic source of nitrogen. | 0 | Organic Reactions |
Organic esters, ketones, and aldehydes with an α-hydrogen ( bond adjacent to the carbonyl group) often form enols. The reaction involves migration of a proton () from carbon to oxygen:
In the case of ketones, the conversion is called a keto-enol tautomerism, although this name is often more generally applied to all such tautomerizations. Usually the equilibrium constant is so small that the enol is undetectable spectroscopically.
In some compounds with two (or more) carbonyls, the enol form becomes dominant. The behavior of 2,4-pentanedione illustrates this effect:
Enols are derivatives of vinyl alcohol, with a connectivity. Deprotonation of organic carbonyls gives the enolate anion, which are a strong nucleophile. A classic example for favoring the keto form can be seen in the equilibrium between vinyl alcohol and acetaldehyde (K = [enol]/[keto] ≈ 3). In 1,3-diketones, such as acetylacetone (2,4-pentanedione), the enol form is favored.
The acid-catalyzed conversion of an enol to the keto form proceeds by proton transfer from O to carbon. The process does not occur intramolecularly, but requires participation of solvent or other mediators. | 0 | Organic Reactions |
Nitrosation is a process of converting organic compounds into nitroso derivatives, i.e., compounds containing the R-NO functionality. | 0 | Organic Reactions |
Nucleosomes are portions of double-stranded DNA (dsDNA) that are wrapped around protein complexes called histone cores. These histone cores are composed of 8 subunits, two each of H2A, H2B, H3 and H4 histones. This protein complex forms a cylindrical shape that dsDNA wraps around with approximately 147 base pairs. Nucleosomes are formed as a beginning step for DNA compaction that also contributes to structural support as well as serves functional roles. These functional roles are contributed by the tails of the histone subunits. The histone tails insert themselves in the minor grooves of the DNA and extend through the double helix, which leaves them open for modifications involved in transcriptional activation. Acetylation has been closely associated with increases in transcriptional activation while deacetylation has been linked with transcriptional deactivation. These reactions occur post-translation and are reversible.
The mechanism for acetylation and deacetylation takes place on the NH groups of lysine amino acid residues. These residues are located on the tails of histones that make up the nucleosome of packaged dsDNA. The process is aided by factors known as histone acetyltransferases (HATs). HAT molecules facilitate the transfer of an acetyl group from a molecule of acetyl-coenzyme A (Acetyl-CoA) to the NH group on lysine. When a lysine is to be deacetylated, factors known as histone deacetylases (HDACs) catalyze the removal of the acetyl group with a molecule of HO.
Acetylation has the effect of changing the overall charge of the histone tail from positive to neutral. Nucleosome formation is dependent on the positive charges of the H4 histones and the negative charge on the surface of H2A histone fold domains. Acetylation of the histone tails disrupts this association, leading to weaker binding of the nucleosomal components. By doing this, the DNA is more accessible and leads to more transcription factors being able to reach the DNA. Thus, acetylation of histones is known to increase the expression of genes through transcription activation. Deacetylation performed by HDAC molecules has the opposite effect. By deacetylating the histone tails, the DNA becomes more tightly wrapped around the histone cores, making it harder for transcription factors to bind to the DNA. This leads to decreased levels of gene expression and is known as gene silencing.
Acetylated histones, the octomeric protein cores of nucleosomes, represent a type of epigenetic marker within chromatin. Studies have shown that one modification has the tendency to influence whether another modification will take place. Modifications of histones can not only cause secondary structural changes at their specific points, but can cause many structural changes in distant locations which inevitably affects function. As the chromosome is replicated, the modifications that exist on the parental chromosomes are handed down to daughter chromosomes. The modifications, as part of their function, can recruit enzymes for their particular function and can contribute to the continuation of modifications and their effects after replication has taken place. It has been shown that, even past one replication, expression of genes may still be affected many cell generations later. A study showed that, upon inhibition of HDAC enzymes by Trichostatin A, genes inserted next to centric heterochromatin showed increased expression. Many cell generations later, in the absence of the inhibitor, the increased gene expression was still expressed, showing modifications can be carried through many replication processes such as mitosis and meiosis. | 0 | Organic Reactions |
The following reactions describe the methanation of carbon monoxide and carbon dioxide respectively:
: -206 kJ/mol
: -164 kJ/mol
The methanation reactions are classified as exothermic and their energy of formations are listed.
There is disagreement on whether the CO methanation occurs by first associatively adsorbing an adatom hydrogen and forming oxygen intermediates before hydrogenation or dissociating and forming a carbonyl before being hydrogenated. CO is believed to be methanated through a dissociative mechanism where the carbon-oxygen bond is broken before hydrogenation with an associative mechanism only being observed at high H concentrations.
Methanation reaction over different carried metal catalysts including Ni, Ru and Rh has been widely investigated for the production of CH from syngas and other power to gas initiatives. Nickel is the most widely used catalyst due to its high selectivity and low cost. | 0 | Organic Reactions |
Enolate ions are more useful than enols for two reasons. First, pure enols can't normally be isolated but are instead generated only as short lived intermediates in low concentration. By contrast, stable solutions of pure enolate ions
are easily prepared from most carbonyl compounds by reaction with a strong base. Second, enolate ions are more reactive than enols and undergo many reactions that enols don't. Whereas enols are neutral, enolate ions are negatively charged, making them much better nucleophiles. As a result, enolate ions are more common than enols in both laboratory and biological chemistry.
Because they are resonance hybrids of two nonequivalent forms, enolate ions can be looked at either as vinylic alkoxides (C=C- O) or as α-ketocarbanions (C-C= O). Thus, enolate ions can react with electrophiles either on oxygen or on carbon. Reaction on oxygen yields an enol derivative, while reaction on carbon yields an α-substituted carbonyl compound. Both kinds of reactivity are known, but reaction on carbon is more common. | 0 | Organic Reactions |
In chemistry, a transition metal chloride complex is a coordination complex that consists of a transition metal coordinated to one or more chloride ligand. The class of complexes is extensive. | 1 | Inorganic Reactions + Inorganic Compounds |
The Kostanecki acylation is a method used in organic synthesis to form chromones or coumarins by acylation of O-hydroxyaryl ketones with aliphatic acid anhydrides, followed by cyclization. If benzoic anhydride (or benzoyl chloride) is used, a particular type of chromone called a flavone is obtained. | 0 | Organic Reactions |
In a typical TAP pulse-response experiment, very small (~10 mol) and narrow (~100 μs) gas pulses are introduced into the evacuated (~10 torr) microreactor
containing a catalytic sample. While the injected gas molecules traverse the microreactor packing through the interstitial voids,
they encounter the catalyst on which they may undergo chemical transformations. Unconverted and newly formed gas molecules eventually
reach the reactor's outlet and escape into an adjacent vacuum chamber, where they are detected with millisecond time resolution
by the QMS. The exit-flow rates of reactants, products and inert molecules recorded by the QMS are then
used to quantify catalytic properties and deduce reaction mechanisms. The same TAP instrument can
typically accommodate other types of kinetic measurements, including atmospheric pressure flow experiments (10 Pa),
Temperature-Programmed Desorption (TPD), and Steady-State Isotopic Transient Kinetic Analysis (SSITKA). | 1 | Inorganic Reactions + Inorganic Compounds |
The reaction is initiated by homolytic cleavage of a radical initiator, in this case 2,2'-azobisisobutyronitrile (AIBN), upon heating. A hydrogen is then abstracted from the hydrogen source (tributylstannane in this case) to leave a tributylstannyl radical that attacks the sulfur atom of the thiohydroxamate ester. The N-O bond of the thiohydroxamate ester undergoes homolysis to form a carboxyl radical which then undergoes decarboxylation and carbon dioxide (CO) is lost. The remaining alkyl radical (R·) then abstracts a hydrogen atom from remaining tributylstannane to form the reduced alkane (RH). (See Scheme 2) The tributyltin radical enters into another cycle of the reaction until all thiohydroxamate ester is consumed.
N-O bond cleavage of the Barton ester can also occur spontaneously upon heating or by irradiation with light to initiate the reaction. In this case a radical initiator is not required but a hydrogen-atom (H-atom) donor is still necessary to form the reduced alkane (RH). Alternative H-atom donors to tributylstannane include tertiary thiols and organosilanes. The relative expense, smell, and toxicity associated with tin, thiol or silane reagents can be avoided by carrying the reaction out using chloroform as both solvent and H-atom donor.
It is also possible to functionalize the alkyl radical by use of other radical trapping species (X-Y + R· -> R-X + Y·). The reaction proceeds due to the formation of the stable S-Sn bond and increasing aromaticity of the thiohydroxamate ester. There is also an overall increase in entropy due to the formation of gas which drives the reaction forward. | 0 | Organic Reactions |
Many drugs which are substrates for glucuronidation as part of their metabolism are significantly affected by inhibitors or inducers of their specific glucuronisyltransferase types: | 0 | Organic Reactions |
The very high breakdown voltages, high electron mobility, and high saturation velocity of GaN has made it an ideal candidate for high-power and high-temperature microwave applications, as evidenced by its high Johnson's figure of merit. Potential markets for high-power/high-frequency devices based on GaN include microwave radio-frequency power amplifiers (e.g., those used in high-speed wireless data transmission) and high-voltage switching devices for power grids. A potential mass-market application for GaN-based RF transistors is as the microwave source for microwave ovens, replacing the magnetrons currently used. The large band gap means that the performance of GaN transistors is maintained up to higher temperatures (~400 °C) than silicon transistors (~150 °C) because it lessens the effects of thermal generation of charge carriers that are inherent to any semiconductor. The first gallium nitride metal semiconductor field-effect transistors (GaN MESFET) were experimentally demonstrated in 1993 and they are being actively developed.
In 2010, the first enhancement-mode GaN transistors became generally available. Only n-channel transistors were available. These devices were designed to replace power MOSFETs in applications where switching speed or power conversion efficiency is critical. These transistors are built by growing a thin layer of GaN on top of a standard silicon wafer, often referred to as GaN-on-Si by manufacturers. This allows the FETs to maintain costs similar to silicon power MOSFETs but with the superior electrical performance of GaN. Another seemingly viable solution for realizing enhancement-mode GaN-channel HFETs is to employ a lattice-matched quaternary AlInGaN layer of acceptably low spontaneous polarization mismatch to GaN.
GaN power ICs monolithically integrate a GaN FET, GaN-based drive circuitry and circuit protection into a single surface-mount device. Integration means that the gate-drive loop has essentially zero impedance, which further improves efficiency by virtually eliminating FET turn-off losses. Academic studies into creating low-voltage GaN power ICs began at the Hong Kong University of Science and Technology (HKUST) and the first devices were demonstrated in 2015. Commercial GaN power IC production began in 2018. | 1 | Inorganic Reactions + Inorganic Compounds |
Sodium orthovanadate is the inorganic compound with the chemical formula . It forms a dihydrate . Sodium orthovanadate is a salt of the oxyanion. It is a colorless, water-soluble solid. | 1 | Inorganic Reactions + Inorganic Compounds |
With the addition of heat, strontium oxalate will decompose based on the following reaction:
Strontium oxalate is a good agent for use in pyrotechnics since it decomposes readily with the addition of heat. When it decomposes into strontium oxide, it produces a red flame color. Since this reaction produces carbon monoxide, which can undergo a further reduction with magnesium oxide, strontium oxalate is an excellent red flame color producing agent in the presence of magnesium. If it is not in the presence of magnesium, strontium carbonate has been found to be a better option to produce an even greater effect. | 1 | Inorganic Reactions + Inorganic Compounds |
The anhydrous material crystallizes in the CdCl motif, featuring octahedral coordination geometry at each Ni(II) center. NiI is prepared by dehydration of the pentahydrate.
NiI readily hydrates, and the hydrated form can be prepared by dissolution of nickel oxide, hydroxide, or carbonate in hydroiodic acid. The anhydrous form can be produced by treating powdered nickel with iodine. | 1 | Inorganic Reactions + Inorganic Compounds |
Colloidal suspensions of nanoparticles of boric acid dissolved in petroleum or vegetable oil can form a remarkable lubricant on ceramic or metal surfaces with a coefficient of sliding friction that decreases with increasing pressure to a value ranging from 0.10 to 0.02. Self-lubricating films result from a spontaneous chemical reaction between water molecules and coatings in a humid environment. In bulk-scale, an inverse relationship exists between friction coefficient and Hertzian contact pressure induced by applied load.
Boric acid is used to lubricate carrom and novuss boards, allowing for faster play. | 1 | Inorganic Reactions + Inorganic Compounds |
The zinc chloride smoke mixture ("HC") used in smoke grenades contains zinc oxide, hexachloroethane and granular aluminium powder, which, when ignited, react to form zinc chloride, carbon and aluminium oxide smoke, an effective smoke screen. | 1 | Inorganic Reactions + Inorganic Compounds |
In chemistry, a leaving group is defined by the IUPAC as an atom or group of atoms that detaches from the main or residual part of a substrate during a reaction or elementary step of a reaction. However, in common usage, the term is often limited to a fragment that departs with a pair of electrons in heterolytic bond cleavage. In this usage, a leaving group is a less formal but more commonly used synonym of the term nucleofuge. In this context, leaving groups are generally anions or neutral species, departing from neutral or cationic substrates, respectively, though in rare cases, cations leaving from a dicationic substrate are also known.
A species' ability to serve as a leaving group depends on its ability to stabilize the additional electron density that results from bond heterolysis. Common anionic leaving groups are halides such as and , and sulfonate esters such as tosylate (), while water (), alcohols (), and amines () are common neutral leaving groups.
In the broader IUPAC definition, the term also includes groups that depart without an electron pair in a heterolytic cleavage (groups specifically known as an electrofuges), like or , which commonly depart in electrophilic aromatic substitution reactions. Similarly, species of high thermodynamic stability like nitrogen () or carbon dioxide () commonly act as leaving groups in homolytic bond cleavage reactions of radical species. A relatively uncommon term that serves as the antonym of leaving group is entering group (i.e., a species that reacts with and forms a bond with a substrate or a substrate-derived intermediate).
In this article, the discussions below mainly pertain to leaving groups that act as nucleofuges. | 0 | Organic Reactions |
Praseodymium(III) oxalate forms crystalline hydrates (light green crystals): Pr(CO)•10HO. The crystalline hydrate decomposes stepwise when heated: | 1 | Inorganic Reactions + Inorganic Compounds |
Neptunium silicide forms crystals of tetragonal crystal system, space group I4/amd, cell parameters: a = 0.396 nm, c = 1.367 nm, Z = 4.
Neptunium disilicide does not dissolve in water. | 1 | Inorganic Reactions + Inorganic Compounds |
Tobermorite is often used in thermodynamical calculations to represent the pole of the most evolved calcium silicate hydrate (C-S-H). According to its chemical formula, its atomic Ca/Si or molar CaO/SiO (C/S) ratio is 5/6 (0.83). Jennite represents the less evolved pole with a C/S ratio of 1.50 (9/6). | 1 | Inorganic Reactions + Inorganic Compounds |
The origin of diastereoselectivity in reductions of chiral ketones has been extensively analyzed and modeled. According to a model advanced by Felkin, diastereoselectivity is controlled by the relative energy of the three transition states I, II, and III. Transition state I is favored in the absence of polar groups on the α carbon, and stereoselectivity increases as the size of the achiral ketone substituent (R) increases. Transition state III is favored for reductions of alkyl ketones in which R is an electron-withdrawing group, because the nucleophile and electron-withdrawing substituent prefer to be as far away from one another as possible.
Diastereoselectivity in reductions of cyclic ketones has also been studied. Conformationally flexible ketones undergo axial attack by the hydride reagent, leading to the equatorial alcohol. Rigid cyclic ketones, on the other hand, undergo primarily equatorial attack to afford the axial alcohol. Preferential equatorial attack on rigid ketones has been rationalized by invoking "steric approach control"—an equatorial approach of the hydride reagent is less sterically hindered than an axial approach. The preference for axial attack on conformationally flexible cyclic ketones has been addressed by a model put forth by Felkin and Anh. The transition state for axial attack (IV) suffers from steric strain between any axial substituents and the incoming hydride reagent. The transition state for equatorial attack (V) suffers from torsional strain between the incoming hydride reagent and adjacent equatorial hydrogens. The difference between these two strain energies determines which direction of attack is favored, and when R is small, torsional strain in V dominates and the equatorial alcohol product is favored. | 0 | Organic Reactions |
The divinylcyclopropane-cycloheptadiene rearrangement is an organic chemical transformation that involves the isomerization of a 1,2-divinylcyclopropane into a cycloheptadiene or -triene. It is conceptually related to the Cope rearrangement, but has the advantage of a strong thermodynamic driving force due to the release of ring strain. This thermodynamic power is recently being considered as an alternative energy source. | 0 | Organic Reactions |
The mechanism consists of three well-differentiated reactions:
# Phenol O-acylation with formation of a tetrahedral intermediate
# Intramolecular aldol condensation to cyclize and to form a hydroxydihydrochromone
# Elimination of the hydroxyl group to form the chromone (or coumarin) | 0 | Organic Reactions |
In the presence of lithium or aluminum amide bases, epoxides may open to give the corresponding allylic alcohols. Removal of a proton adjacent to the epoxide, elimination, and neutralization of the resulting alkoxide lead to synthetically useful allylic alcohol products. In reactions of chiral, non-racemic epoxides, the configuration of the allylic alcohol product matches that of the epoxide substrate at the carbon whose C–O bond does not break (the starred carbon below). Besides β-elimination some other reactions are possible, as metalation of the epoxide ring can take place competitively. Vinylogous eliminations are possible when the epoxide substrate is substituted with vinyl or dienyl groups. Unconstrained systems tend to form trans double bonds, as significant non-bonding interactions are avoided in the transition state for the formation of trans products (see equation (2) below). The strongly basic conditions required for most isomerizations of this type represent the reaction's primary disadvantage. | 0 | Organic Reactions |
No heterogeneous catalyst has been commercialized for asymmetric hydrogenation.
The first asymmetric hydrogenation focused on palladium deposited on a silk support. Cinchona alkaloids have been used as chiral modifiers for enantioselectivity hydrogenation.
An alternative technique and one that allows more control over the structural and electronic properties of active catalytic sites is the immobilization of catalysts that have been developed for homogeneous catalysis on a heterogeneous support. Covalent bonding of the catalyst to a polymer or other solid support is perhaps most common, although immobilization of the catalyst may also be achieved by adsorption onto a surface, ion exchange, or even physical encapsulation. One drawback of this approach is the potential for the proximity of the support to change the behaviour of the catalyst, lowering the enantioselectivity of the reaction. To avoid this, the catalyst is often bound to the support by a long linker though cases are known where the proximity of the support can actually enhance the performance of the catalyst.
The final approach involves the construction of MOFs that incorporate chiral reaction sites from a number of different components, potentially including chiral and achiral organic ligands, structural metal ions, catalytically active metal ions, and/or preassembled catalytically active organometallic cores. One of these involved ruthenium-based catalysts. As little as 0.005 mol% of such catalysts proved sufficient to achieve the asymmetric hydrogenation of aryl ketones, although the usual conditions featured 0.1 mol % of catalyst and resulted in an enantiomeric excess of 90.6–99.2%.
<br /> | 0 | Organic Reactions |
Cadmium sulfide can be prepared by the precipitation from soluble cadmium(II) salts with sulfide ion. This reaction has been used for gravimetric analysis and qualitative inorganic analysis.<br />The preparative route and the subsequent treatment of the product, affects the polymorphic form that is produced (i.e., cubic vs hexagonal). It has been asserted that chemical precipitation methods result in the cubic zincblende form.
Pigment production usually involves the precipitation of CdS, the washing of the solid precipitate to remove soluble cadmium salts followed by calcination (roasting) to convert it to the hexagonal form followed by milling to produce a powder. When cadmium sulfide selenides are required the CdSe is co-precipitated with CdS and the cadmium sulfoselenide is created during the calcination step.
Cadmium sulfide is sometimes associated with sulfate reducing bacteria. | 1 | Inorganic Reactions + Inorganic Compounds |
Barium chloride is an inorganic compound with the formula . It is one of the most common water-soluble salts of barium. Like most other water-soluble barium salts, it is a white powder, highly toxic, and imparts a yellow-green coloration to a flame. It is also hygroscopic, converting to the dihydrate , which are colourless crystals with a bitter salty taste. It has limited use in the laboratory and industry. | 1 | Inorganic Reactions + Inorganic Compounds |
All syntheses start from the perxenates, which are accessible from the xenates through two methods. One is the disproportionation of xenates to perxenates and xenon:
: 2 + 2 OH → + Xe + O + 2 HO
The other is oxidation of the xenates with ozone in basic solution:
: + O + 3 OH → + O + 2 HO
Barium perxenate is reacted with sulfuric acid and the unstable perxenic acid is dehydrated to give xenon tetroxide:
Any excess perxenic acid slowly undergoes a decomposition reaction to xenic acid and oxygen: | 1 | Inorganic Reactions + Inorganic Compounds |
In petrochemistry, petroleum geology and organic chemistry, cracking is the process whereby complex organic molecules such as kerogens or long-chain hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carbon-carbon bonds in the precursors. The rate of cracking and the end products are strongly dependent on the temperature and presence of catalysts. Cracking is the breakdown of large hydrocarbons into smaller, more useful alkanes and alkenes. Simply put, hydrocarbon cracking is the process of breaking a long chain hydrocarbon into short ones. This process requires high temperatures.
More loosely, outside the field of petroleum chemistry, the term "cracking" is used to describe any type of splitting of molecules under the influence of heat, catalysts and solvents, such as in processes of destructive distillation or pyrolysis.
Fluid catalytic cracking produces a high yield of petrol and LPG, while hydrocracking is a major source of jet fuel, diesel fuel, naphtha, and again yields LPG. | 0 | Organic Reactions |
The carbylamine reaction (also known as the Hoffmann isocyanide synthesis) is the synthesis of an isocyanide by the reaction of a primary amine, chloroform, and base. The conversion involves the intermediacy of dichlorocarbene.
Illustrative is the synthesis of tert-butyl isocyanide from tert-butylamine in the presence of catalytic amount of the phase transfer catalyst benzyltriethylammonium chloride.
:MeCNH + CHCl + 3 NaOH → MeCNC + 3 NaCl + 3 HO
Similar reactions have been reported for aniline. It is used to prepare secondary amines. | 0 | Organic Reactions |
Reductions with hydrosilanes are methods used for hydrogenation and hydrogenolysis of organic compounds. The approach is a subset of ionic hydrogenation. In this particular method, the substrate is treated with a hydrosilane and auxiliary reagent, often a strong acid, resulting in formal transfer of hydride from silicon to carbon. This style of reduction with hydrosilanes enjoys diverse if specialized applications. | 0 | Organic Reactions |
This reaction is a considerable subject area of research with implications for fuel cell design.
Its main utility lies in the removal of carbon monoxide (CO) from the fuel cell's feed gas. CO poisons the catalyst of most low-temperature fuel cells.
Carbon monoxide is often produced as a by-product from steam reforming of hydrocarbons, which produces hydrogen and CO.
It is possible to consume most of the CO by reacting it with steam in the water-gas shift reaction:
:CO + HO H + CO
The water-gas shift reaction can reduce CO to 1% of the feed, with the added benefit of producing more hydrogen, but not eliminate it completely.
To be used in a fuel cell, feed gas must have CO below 10 ppm. | 1 | Inorganic Reactions + Inorganic Compounds |
[Co(NH)] is diamagnetic, with a low-spin 3d octahedral Co(III) center. The cation obeys the 18-electron rule and is considered to be a classic example of an exchange inert metal complex. As a manifestation of its inertness, [Co(NH)]Cl can be recrystallized unchanged from concentrated hydrochloric acid: the NH is so tightly bound to the Co(III) centers that it does not dissociate to allow its protonation. In contrast, labile metal ammine complexes, such as [Ni(NH)]Cl, react rapidly with acids, reflecting the lability of the Ni(II)–NH bonds. Upon heating, hexamminecobalt(III) begins to lose some of its ammine ligands, eventually producing a stronger oxidant.
)] is a moderately strong Bronsted acid.
The chloride ions in [Co(NH)]Cl can be exchanged with a variety of other anions such as nitrate, bromide, iodide, sulfamate to afford the corresponding [Co(NH)]X derivative. Such salts are orange or bright yellow and display varying degrees of water solubility. The chloride ion can be also exchanged with more complex anions such as the hexathiocyanatochromate(III), yielding a pink compound with formula [Co(NH)] [Cr(SCN)], or the ferricyanide ion. | 1 | Inorganic Reactions + Inorganic Compounds |
Relevant to the inner sphere mechanism are the two modes by which imines can coordinate, as a π or as a σ-donor ligand. The pi-imines are also susceptible to conversion to iminium ligands upon N-protonation. The binding mode for the imine is unclear, both η (σ-type) and η (π-type). The final step in the mechanism is release of the amine. In some iridium-catalyzed hydrogenations, the mechanism is believed to proceed via a monohydride species. The oxidation state of iridium is always +3.
Examples: | 0 | Organic Reactions |
Industrially, most alkylations are typically conducted using alcohols, not alkyl halides. Alcohols are less expensive than alkyl halides and their alkylation does not produce salts, the disposal of which can be problematic. Key to the alkylation of alcohols is the use of catalysts that render the hydroxyl group a good leaving group. The largest scale N-alkylation is the production of the methylamines from ammonia and methanol, resulting in approximately 500,000 tons/y of methylamine, dimethylamine, and trimethylamine. The reaction is poorly selective, requiring separation of the three products. Many other industrially significant alkyl amines are produced, again on a large scale, from the alcohols. Epoxides are another class of halide-free N-alkylating agents, useful in the production of ethanolamines. | 0 | Organic Reactions |
In the late 1960s, the laboratory of chemist Jean-Marie Conia investigated small carbocyclic molecules, specifically as products of ene-type reactions with carbonyls. These efforts culminated in a 1975 review paper titled “The Thermal Cyclisation of Unsaturated Carbonyl Compounds.”
In its original manifestation, the Conia-ene reaction comprised the intramolecular cyclization of ε,ζ-unsaturated ketones or aldehydes to functionalized cyclopentanes upon intense heating. The proposed mechanism invoked a six-membered, ene reaction-like transition state in which the enol tautomer reacts concertedly with the pendant alkene.
The same conditions were found to give six- and nine-membered rings with the appropriate substrates, although with lower yields and diastereoselectivity. In the case of γ,δ- and δ,ε-unsaturated ketones, equilibrium favored the linear product over the cyclopropane or cyclobutane. Alkynyl ketones were also found to cyclize under thermal conditions, giving a mixture of the conjugated and skipped cyclic enones.
Two key drawbacks prevented wider implementation of the initial Conia-ene reaction. First, molecules with additional functional groups were often incompatible with the high temperatures required for conversion. Second, regio- and diastereoselectivity depended entirely on the substrate, offering little to no control over the orientation of the product. | 0 | Organic Reactions |
The Histone code hypothesis suggests the idea that patterns of post-translational modifications on histones, collectively, can direct specific cellular functions. Chemical modifications of histone proteins often occur on particular amino acids. This specific addition of single or multiple modifications on histone cores can be interpreted by transcription factors and complexes which leads to functional implications. This process is facilitated by enzymes such as HATs and HDACs that add or remove modifications on histones, and transcription factors that process and "read" the modification codes. The outcome can be activation of transcription or repression of a gene. For example, the combination of acetylation and phosphorylation have synergistic effects on the chromosomes overall structural condensation level and, hence, induces transcription activation of immediate early gene.
Experiments investigating acetylation patterns of H4 histones suggested that these modification patterns are collectively maintained in mitosis and meiosis in order to modify long-term gene expression. The acetylation pattern is regulated by HAT and HADC enzymes and, in turn, sets the local chromatin structure. In this way, acetylation patterns are transmitted and interconnected with protein binding ability and functions in subsequent cell generation. | 0 | Organic Reactions |
Diastereoselective conjugate addition reactions of chiral organocuprates provide β-functionalized ketones in high yield and diastereoselectivity. A disadvantage of these reactions is the requirement of a full equivalent of enantiopure starting material.
More recently, catalytic enantioselective methods have been developed based on the copper(I)-catalyzed conjugate addition of Grignard reactions to enones. The proposed mechanism involves transmetalation from the Grignard reagent to copper, conjugate addition, and rate-determining reductive elimination (see the analogous upper pathway in equation (2)). | 0 | Organic Reactions |
Methyl metabolism is very ancient and can be found in all organisms on earth, from bacteria to humans, indicating the importance of methyl metabolism for physiology. Indeed, pharmacological inhibition of global methylation in species ranging from human, mouse, fish, fly, roundworm, plant, algae, and cyanobacteria causes the same effects on their biological rhythms, demonstrating conserved physiological roles of methylation during evolution. | 0 | Organic Reactions |
In 1962, Smidt published work on the palladium-catalysed oxidation of alkenes to carbonyl groups. In this work, it was determined that the palladium catalyst activated the alkene for the nucleophilic attack of hydroxide. Gaining insight from this work, Tsuji hypothesized that a similar activation could take place to form carbon-carbon bonds.
In 1965, Tsuji reported work that confirmed his hypothesis. By reacting an allylpalladium chloride dimer with the sodium salt of diethyl malonate, the group was able to form a mixture of monoalkylated and dialkylated product.
The scope of the reaction was expanded only gradually until Trost discovered the next big breakthrough in 1973. While attempting to synthesize acyclic sesquiterpene homologs, Trost ran into problems with the initial procedure and was not able to alkylate his substrates. These problems were overcome with the addition of triphenylphosphine to the reaction mixture.
These conditions were then tested out for other substrates and some led to "essentially instantaneous reaction at room temperature." Soon after, he developed a way to use these ligands for asymmetric synthesis. Not surprisingly, this spurred on many other investigations of this reaction and has led to the important role that this reaction now holds in synthetic chemistry. | 0 | Organic Reactions |
Hydrothermal hydrolysis of hydrochloric SPL from carbon-steel pickling lines is a hydrometallurgical reaction, which takes place according to the following chemical formula: | 1 | Inorganic Reactions + Inorganic Compounds |
The hexahydrate and the anhydrous salt are weak Lewis acids. The adducts are usually either octahedral or tetrahedral. It forms an octahedral complex with pyridine ():
With triphenylphosphine (), a tetrahedral complex results:
Salts of the anionic complex CoCl can be prepared using tetraethylammonium chloride:
: + 2 [(CH)N]Cl → [(CH)N)][CoCl]
The tetrachlorocobaltate ion [CoCl] is the blue ion that forms upon addition of hydrochloric acid to aqueous solutions of hydrated cobalt chloride, which are pink. | 1 | Inorganic Reactions + Inorganic Compounds |
PROX is an acronym for PReferential OXidation, that refers to the preferential oxidation of carbon monoxide in a gas mixture by a catalyst. It is intended to remove trace amounts of CO from H/CO/CO mixtures produced by steam reforming and water-gas shift. An ideal PROX catalyst preferentially oxidizes carbon monoxide (CO) using a heterogeneous catalys<nowiki/>t placed upon a ceramic support. Catalysts include metals such as platinum, platinum/iron, platinum/ruthenium, gold nanoparticles as well as novel copper oxide/ceramic conglomerate catalysts. | 1 | Inorganic Reactions + Inorganic Compounds |
The reaction was discovered in the 1970s as part of a synthetic route to certain prostanoids. The reaction required tin tetrachloride and a stoichiometric amount of Wilkinson's catalyst:
An equal amount of a cyclopropane was formed as the result of decarbonylation.
The first catalytic application involved cyclization of 4-pentenal to cyclopentanone using (again) Wilkinson's catalyst. In this reaction the solvent was saturated with ethylene.
:CH=CHCHCHCHO → (CH)CO | 0 | Organic Reactions |
Deacylations "play crucial roles in gene transcription and most likely in all eukaryotic biological processes that involve chromatin".
Acetylation is one type of post-translational modification of proteins. The acetylation of the ε-amino group of lysine, which is common, converts a charged side chain to a neutral one. Acetylation/deacetylation of histones also plays a role in gene expression and cancer. These modifications are effected by enzymes called histone acetyltransferases (HATs) and histone deacetylases (HDACs).
Two general mechanisms are known for deacetylation. One mechanism involves zinc binding to the acetyl oxygen. Another family of deacetylases require NAD, which transfers an ribosyl group to the acetyl oxygen. | 0 | Organic Reactions |
In organic chemistry, the desulfonation reaction is the hydrolysis of sulfonic acids:
:RCHSOH + HO → RCH + HSO
The reaction applied to aryl and naphthylsulfonic acids. It is the reverse of sulfonation. The temperature of desulfonation correlates with the ease of the sulfonation. | 0 | Organic Reactions |
Barium iodate can be derived either as a product of a reaction of iodine and barium hydroxide or by combining barium chlorate with potassium iodate. | 1 | Inorganic Reactions + Inorganic Compounds |
Cyclopropanation of olefins with diazocarbonyl compounds is commonly accomplished using rhodium carboxylate complexes, although copper was originally used. The scope of the olefin is generally quite broad—electron-rich, neutral, and electron-poor olefins have all been cyclopropanated efficiently using rhodium-based catalyst systems. This section describes the various classes of diazocarbonyl compounds that react with olefins under rhodium catalysis to afford cyclopropanes.
Diazoacetates that possess a single carbonyl substituent attached to the diazo carbon, have been used for the cyclopropanation of a wide array of olefins. Diastereoselectivity for the (E) cyclopropane increases as the size of the ester group increases. In addition, adding electron density to the catalyst (for instance by replacing acetate ligands with acetamide, acam) increases the diastereoselectivity of the reaction.
Diazocarbonyl compounds substituted with two electron-withdrawing groups, such as diazomalonates, are prone to experience side reactions under cyclopropanation conditions. [3+2] Cycloaddition and C-H insertion side products have been observed.
Diazoacetates substituted with a vinyl or aryl group on the diazo carbon are unreactive towards trans-alkenes. This result has been explained by invoking the transition state model in Eq. (2). Reactions of these substrates are highly selective for the (E) cyclopropane isomer.
Vinyl diazoacetates react with dienes to afford divinyl cyclopropanes, which undergo Cope rearrangement to afford cycloheptadienes. The more substituted double bond of the diene reacts preferentially.
Furans react similarly with vinyl diazoacetates, although the intermediate cyclopropane may transform either into the Cope rearrangement product or an opened unsaturated carbonyl compound. The distribution of these products is highly dependent on the substitution pattern of the furan.
Pyrroles react with vinyl diazoacetates to form nitrogen-bridged cycloheptadienes. The use of methyl lactate as a chiral auxiliary on the vinyl diazoacetate led to moderate diastereoselectivity in the tandem cyclopropanation/Cope rearrangement of Boc-protected pyrrole.
The enantioselectivity of asymmetric cyclopropanations may depend profoundly on the solvent. | 0 | Organic Reactions |
In 1920 Armstrong and Hilditch first proposed the associative mechanism. In this mechanism CO and HO are adsorbed onto the surface of the catalyst, followed by formation of an intermediate and the desorption of H and CO. In general, HO dissociates onto the catalyst to yield adsorbed OH and H. The dissociated water reacts with CO to form a carboxyl or formate intermediate. The intermediate subsequently dehydrogenates to yield CO and adsorbed H. Two adsorbed H atoms recombine to form H.
There has been significant controversy surrounding the kinetically relevant intermediate during the associative mechanism. Experimental studies indicate that both intermediates contribute to the reaction rate over metal oxide supported transition metal catalysts. However, the carboxyl pathway accounts for about 90% of the total rate owing to the thermodynamic stability of adsorbed formate on the oxide support. The active site for carboxyl formation consists of a metal atom adjacent to an adsorbed hydroxyl. This ensemble is readily formed at the metal-oxide interface and explains the much higher activity of oxide-supported transition metals relative to extended metal surfaces. The turn-over-frequency for the WGSR is proportional to the equilibrium constant of hydroxyl formation, which rationalizes why reducible oxide supports (e.g. CeO) are more active than irreducible supports (e.g. SiO) and extended metal surfaces (e.g. Pt). In contrast to the active site for carboxyl formation, formate formation occurs on extended metal surfaces. The formate intermediate can be eliminated during the WGSR by using oxide-supported atomically dispersed transition metal catalysts, further confirming the kinetic dominance of the carboxyl pathway. | 1 | Inorganic Reactions + Inorganic Compounds |
Recent work has demonstrated that the scope of "soft" nucleophiles can be expanded to include some pronucleophiles that have much higher than ~ 25. Some of these "soft" nucleophiles have ranging all the way to 32, and even more basic pronucleophiles (~44) have been shown to act as soft nucleophiles with the addition of Lewis acids that help to facilitate deprotonation. The improved pKa range of "soft" nucleophiles is critical because these nucleophiles are the only ones that have been explored for enantioselective reactions until very recently (although non-enantioselective reactions of "hard" nucleophiles have been known for some time). By increasing the scope of pronucleophiles that act as "soft" nucleophiles, these substrates can also be incorporated into enantioselective reactions using previously reported and well characterized methods. | 0 | Organic Reactions |
The cyclic trimer anions dissociate almost completely in aqueous solution giving mainly tetrahydroxyborate anions:
Other molecules and anions, such as , , , and are less than 5% at 26 °C.
In 1937, Nielsen and Ward claimed that the metaborate anion in solution has a linear symmetric structure with negative charges on the oxygens and a positive charge on the boron, or with negative charge on the boron. However, this claim has been disproved. | 1 | Inorganic Reactions + Inorganic Compounds |
In electrophilic trifluoromethylation the active trifluoromethyl donor group carries a positive charge. Production of an CF cation has been described as "extremely hard" The first relevant reagent, a diaryl(trifluoromethyl) sulfonium salt (ArSCFSbF) was developed in 1984 by reaction of an aryltrifluoromethyl sulfoxide 1 with SFSbF followed by reaction with an electron-rich arene. The reagent was used in trifluoromethylation of a thiophenolate.
S-(trifluoromethyl)dibenzothiophenium tetrafluoroborate is a commercially available and known trifluoromethylation reagent based on the same principle first documented in 1990. In this type of compound sulfur has been replaced by oxygen, selenium and tellurium. Examples of substrates that have been investigated are pyridine, aniline, triphenylphosphine and the lithium salt of phenylacetylene.
Another group of trifluoromethyl donors are hypervalent iodine(III)–CF reagents for example 3,3-dimethyl-1-(trifluoromethyl)-1,2-benziodoxole. Some of these are known as Togni reagents, such as Togni reagent II. Substrates are thiols, alcohols, phosphines, (hetero) arenes, unactivated olefins and unsaturated carboxylic acids.
The reaction mechanism of electrophilic trifluoromethylations has been described as controversial with polar substitution or single electron transfer as likely candidates. | 0 | Organic Reactions |
Manganese(III)-mediated radical reactions begin with the single-electron oxidation of a carbonyl compound to an α-oxoalkyl radical. Addition to an olefin then occurs, generating adduct radical 2. The fate of 2 is primarily determined by reaction conditions—in the presence of copper(II) acetate, this intermediate undergoes further oxidation to a carbocation and may eliminate to form β,γ-unsaturated ketone 4. Manganese acetate itself can effect the second oxidation of resonance-stabilized adduct radicals to carbocations 5; unstabilized radicals undergo further transformations before reacting with Mn(OAc). Atom transfer from another molecule of substrate may generate saturated compound 3. Adduct radicals or carbocations may undergo ligand-transfer reactions, yielding γ-functionalized carbonyl compounds. When lithium chloride is used as an additive, chlorination takes place. Alternatively, carbocations may be trapped intramolecularly by the carbonyl oxygen to form dihydrofurans after β-elimination. | 0 | Organic Reactions |
HCN has been detected in the interstellar medium and in the atmospheres of carbon stars. Since then, extensive studies have probed formation and destruction pathways of HCN in various environments and examined its use as a tracer for a variety of astronomical species and processes. HCN can be observed from ground-based telescopes through a number of atmospheric windows. The J=1→0, J=3→2, J= 4→3, and J=10→9 pure rotational transitions have all been observed.
HCN is formed in interstellar clouds through one of two major pathways: via a neutral-neutral reaction (CH + N → HCN + H) and via dissociative recombination (HCNH + e → HCN + H). The dissociative recombination pathway is dominant by 30%; however, the HCNH must be in its linear form. Dissociative recombination with its structural isomer, HNC, exclusively produces hydrogen isocyanide (HNC).
HCN is destroyed in interstellar clouds through a number of mechanisms depending on the location in the cloud. In photon-dominated regions (PDRs), photodissociation dominates, producing CN (HCN + ν → CN + H). At further depths, photodissociation by cosmic rays dominate, producing CN (HCN + cr → CN + H). In the dark core, two competing mechanisms destroy it, forming HCN and HCNH (HCN + H → HCN + H; HCN + HCO → HCNH + CO). The reaction with HCO dominates by a factor of ~3.5. HCN has been used to analyze a variety of species and processes in the interstellar medium. It has been suggested as a tracer for dense molecular gas and as a tracer of stellar inflow in high-mass star-forming regions. Further, the HNC/HCN ratio has been shown to be an excellent method for distinguishing between PDRs and X-ray-dominated regions (XDRs).
On 11 August 2014, astronomers released studies, using the Atacama Large Millimeter/Submillimeter Array (ALMA) for the first time, that detailed the distribution of HCN, HNC, HCO, and dust inside the comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON).
In February 2016, it was announced that traces of hydrogen cyanide were found in the atmosphere of the hot Super-Earth 55 Cancri e with NASA's Hubble Space Telescope.
On 14 December 2023, astronomers reported the first time discovery, in the plumes of Enceladus, moon of the planet Saturn, of hydrogen cyanide, a possible chemical essential for life as we know it, as well as other organic molecules, some of which are yet to be better identified and understood. According to the researchers, "these [newly discovered] compounds could potentially support extant microbial communities or drive complex organic synthesis leading to the origin of life." | 1 | Inorganic Reactions + Inorganic Compounds |
[Co(NH)] is a component of some structural biology methods (especially for DNA or RNA, where positive ions stabilize tertiary structure of the phosphate backbone), to help solve their structures by X-ray crystallography or by nuclear magnetic resonance. In the biological system, the counterions would more probably be Mg, but the heavy atoms of cobalt (or sometimes iridium, as in ) provide anomalous scattering to solve the phase problem and produce an electron-density map of the structure.
[Co(NH)] is used to investigate DNA. The cation induces the transition of DNA structure from the classical B-form to the Z-form. | 1 | Inorganic Reactions + Inorganic Compounds |
Pressure (along with temperature) determines the super- or subcritical state of solvents as well as overall reaction kinetics and the energy inputs required to yield the desirable HTL products (oil, gas, chemicals, char etc.). | 0 | Organic Reactions |
Hydrodefluorination (HDF) is a type of organic reaction in which in a substrate of a carbon–fluorine bond is replaced by a carbon–hydrogen bond. The topic is of some interest to scientific research. In one general strategy for the synthesis of fluorinated compounds with a specific substitution pattern, the substrate is a cheaply available perfluorinated hydrocarbon. An example is the conversion of hexafluorobenzene (CF) to pentafluorobenzene (CFH) by certain zirconocene hydrido complexes. In this type of reaction the thermodynamic driving force is the formation of a metal-fluorine bond that can offset the cleavage of the very stable C-F bond. Other substrates that have been investigated are fluorinated alkenes.
Another reaction type is oxidative addition of a metal into a C-F bond followed by a reductive elimination step in presence of a hydrogen source. For example, perfluorinated pyridine reacts with bis(cyclooctadiene)nickel(0) and triethylphosphine to the oxidative addition product and then with HCl to the ortho-hydrodefluorinated product.
In reductive hydrodefluorination the fluorocarbon is reduced in a series of single electron transfer steps through the radical anion, the radical and the anion with ultimate loss of a fluorine anion. An example is the conversion of pentafluorobenzoic acid to 3,4,5-tetrafluorobenzoic acid in a reaction of zinc dust in aqueous ammonia.
Specific systems that have been reported for fluoroalkyl group HDF are triethylsilane / carborane acid, and NiCl(PCy) / (LiAl(O-t-Bu)H) | 0 | Organic Reactions |
Gallium arsenide (GaAs) transistors are used in the RF power amplifiers for cell phones and wireless communicating. | 1 | Inorganic Reactions + Inorganic Compounds |
Zinc chloride is used as a catalyst or reagent in diverse reactions conducted on an industrial scale. The partial hydrolysis of benzal chloride in the presence of zinc chloride is the main route to benzoyl chloride. It serves as a catalyst for the production of methylene-bis(dithiocarbamate).
The combination of hydrochloric acid and , known as the "Lucas reagent", is effective for the preparation of alkyl chlorides from alcohols. Similar reactions are the basis of industrial routes from methanol and ethanol respectively to methyl chloride and ethyl chloride. | 1 | Inorganic Reactions + Inorganic Compounds |
Anhydrous zinc chloride or its hydrates is not known in nature. However, the related zinc chloride hydroxide monohydrate is known as simonkolleite in nature. | 1 | Inorganic Reactions + Inorganic Compounds |
Steric effects of the alkyl substituents on the carbonyl reactant have been shown to affect both the rates and yields of Büchner–Curtius–Schlotterbeck reaction. Table 1 shows the percent yield of the ketone and epoxide products as well as the relative rates of reaction for the reactions between several methyl alkyl ketones and diazomethane.
The observed decrease in rate and increase in epoxide yield as the size of the alkyl group becomes larger indicates a steric effect. | 0 | Organic Reactions |
The synthesis of hexachlorophosphazene was first reported by von Liebig in 1834. In that report he describes experiments conducted with Wöhler. They found that phosphorus pentachloride and ammonia react exothermically to yield a new substance that could be washed with cold water to remove the ammonium chloride coproduct. The new compound contained P, N, and Cl, on the basis of elemental analysis. It was sensitive toward hydrolysis by hot water.
Modern syntheses are based on the developments by Schenk and Römer who used ammonium chloride in place of ammonia and inert chlorinated solvents. By replacing ammonia with ammonium chloride allows the reaction to proceed without a strong exotherm associated with the / reaction. Typical chlorocarbon solvents are 1,1,2,2-tetrachloroethane or chlorobenzene, which tolerate the hydrogen chloride side product. Since ammonium chloride is insoluble in chlorinated solvents, workup is facilitated. For the reaction under such conditions, the following stoichiometry applies:
where n can usually take values of 2 (the dimer tetrachlorodiphosphazene), 3 (the trimer hexachlorotriphosphazene), and 4 (the tetramer octachlorotetraphosphazene).
Purification by sublimation gives mainly the trimer and tetramer. Slow vacuum sublimation at approximately 60 °C affords the pure trimer free of the tetramer. Reaction conditions such as temperature may also be tuned to maximise the yield of the trimer at the expense of the other possible products; nonetheless, commercial samples of hexachlorophosphazene usually contain appreciable amounts of octachlorotetraphosphazene, even up to 40%. | 1 | Inorganic Reactions + Inorganic Compounds |
In his work at the University of Giessen, Kröhnke observed condensation of α-pyridinium methyl ketone salts 1 with α,β-unsaturated carbonyl compounds 2 via a Michael reaction when treated with ammonium acetate to give 2,4,6-trisubstituted pyridines in high yields under mild reaction conditions. The proposed intermediates, 1, 5-dicarbonyl compound 3, have not been isolated. Since its discovery, the Kröhnke synthesis has enjoyed broad applicability to the preparation of di-,tri- and tetrapyridine derivatives, demonstrating a number of advantages over related reactions such as the Hantzsch pyridine synthesis. | 0 | Organic Reactions |
Organolithium reagents are sensitive to moisture and thus should be handled under inert atmosphere in anhydrous conditions. Tetrahydrofuran is the most common solvent employed for lateral lithiation reactions. Measurement of the concentration of commercial or prepared alkyllithium solutions may be accomplished using well-established titration methods.
A useful indicator for the progress of lateral lithiations is the color of the reaction mixture. Benzyllithium compounds range in color from red to deep purple, and in many cases the lack of a color change upon addition of an organolithium reagent to the substrate may indicate the presence of an undesired proton source in solution. | 0 | Organic Reactions |
Alkene carboamination is the simultaneous formation of C–N and C–C bonds across an alkene. This method represents a powerful strategy to build molecular complexity with up to two stereocenters in a single operation. Generally, there are four categories of reaction modes for alkene carboamination. The first class is cyclization reactions, which will form a N-heterocycle as a result. The second class has been well established in the last decade. Alkene substrates with a tethered nitrogen nucleophile have been used in these transformations to promote intramolecular aminocyclization. While intermolecular carboamination is extremely hard, people have developed a strategy to combine the nitrogen and carbon part, which is known as the third class. The most general carboamination, which takes three individual parts and couples them together is still underdeveloped. | 0 | Organic Reactions |
The Danheiser benzannulation is a chemical reaction used in organic chemistry to generate highly substituted phenols in a single step. It is named after Rick L. Danheiser who developed the reaction. | 0 | Organic Reactions |
A variety of experimental concerns exist for IMHR reactions. Although most of the common Pd(0) catalysts are commercially available (Pd(PPh), Pd(dba), and derivatives), they may also be prepared by simple, high-yielding procedures. Palladium(II) acetate is cheap and may be reduced in situ to palladium(0) with phosphine. Three equivalents of phosphine per equivalent of palladium acetate are commonly used; these conditions generate Pd(PR) as the active catalyst. Bidentate phosphine ligands are common in asymmetric reactions to enhance stereoselectivity.
A wide variety of bases may be used, and the base is often employed in excess. Potassium carbonate is the most common base employed, and inorganic bases are generally used more often than organic bases. A number of additives have also been identified for the Heck reaction—silver salts may be used to drive the reaction down the cationic pathway, and halide salts may be used to convert aryl triflates via the neutral pathway. Alcohols have been shown to enhance catalyst stability in some cases, and acetate salts are beneficial in reactions following the anionic pathway. | 0 | Organic Reactions |
Inductive cleavage, in organic chemistry, is the charge-initiated counterpoint to radical initiated alpha-cleavage. Since inductive cleavage does not require unpairing and re-pairing electrons it can occur at both radical cationic and cationic sites. | 0 | Organic Reactions |
In the Hooker reaction (1936) an alkyl chain in a certain naphthoquinone (phenomenon first observed in the compound lapachol) is reduced by one methylene unit as carbon dioxide in each potassium permanganate oxidation.
:Mechanistically oxidation causes ring-cleavage at the alkene group, extrusion of carbon dioxide in decarboxylation with subsequent ring-closure. | 0 | Organic Reactions |
Donovan's solution can be prepared by mixing arsenic triiodide, mercuric iodide, and sodium bicarbonate in aqueous solution.
Cooleys cyclopædia of practical receipts and ... information on the arts, manufactures, and trades' gives a more complex method. | 1 | Inorganic Reactions + Inorganic Compounds |
Calcium hydroxide is poorly soluble in water, with a retrograde solubility increasing from 0.66 g/L at 100 °C to 1.89 g/L at 0 °C. With a solubility product K of 5.02 at 25 °C, its dissociation in water is large enough that its solutions are basic according to the following dissolution reaction:
: Ca(OH) → Ca + 2 OH
At ambient temperature, calcium hydroxide (portlandite) dissolves in water to produce an alkaline solution with a pH of about 12.5. Calcium hydroxide solutions can cause chemical burns. At high pH values due to a common-ion effect with the hydroxide anion, its solubility drastically decreases. This behavior is relevant to cement pastes. Aqueous solutions of calcium hydroxide are called limewater and are medium-strength bases, which react with acids and can attack some metals such as aluminium (amphoteric hydroxide dissolving at high pH), while protecting other metals, such as iron and steel, from corrosion by passivation of their surface. Limewater turns milky in the presence of carbon dioxide due to the formation of insoluble calcium carbonate, a process called carbonatation:
: Ca(OH) + CO → CaCO + HO
When heated to 512 °C, the partial pressure of water in equilibrium with calcium hydroxide reaches 101kPa (normal atmospheric pressure), which decomposes calcium hydroxide into calcium oxide and water:
: Ca(OH) → CaO + HO
Calcium hydroxide reacts with hydrogen chloride to first give calcium hydroxychloride and then calcium chloride. | 1 | Inorganic Reactions + Inorganic Compounds |
Uranium tetrafluoride reacts with fluorine, first to give uranium pentafluoride and then volatile UF:
:2UF + F → 2UF
:2UF + F → 2UF
UF is reduced by magnesium to give the metal:
:UF + 2Mg → U + 2MgF
It is oxidized to UF at room temperature and then, at 100°C, to the hexafluoride. | 1 | Inorganic Reactions + Inorganic Compounds |
GaAs has been used to produce near-infrared laser diodes since 1962. It is often used in alloys with other semiconductor compounds for these applications.
N-type GaAs doped with silicon donor atoms (on Ga sites) and boron acceptor atoms (on As sites) responds to ionizing radiation by emitting scintillation photons. At cryogenic temperatures it is among the brightest scintillators known and is a promising candidate for detecting rare electronic excitations from interacting dark matter, due to the following six essential factors:
# Silicon donor electrons in GaAs have a binding energy that is among the lowest of all known n-type semiconductors. Free electrons above per cm are not “frozen out" and remain delocalized at cryogenic temperatures.
# Boron and gallium are group III elements, so boron as an impurity primarily occupies the gallium site. However, a sufficient number occupy the arsenic site and act as acceptors that efficiently trap ionization event holes from the valence band.
# After trapping an ionization event hole from the valence band, the boron acceptors can combine radiatively with delocalized donor electrons to produce photons 0.2 eV below the cryogenic band-gap energy (1.52 eV). This is an efficient radiative process that produces scintillation photons that are not absorbed by the GaAs crystal.
# There is no afterglow, because metastable radiative centers are quickly annihilated by the delocalized electrons. This is evidenced by the lack of thermally induced luminescence.
# N-type GaAs has a high refractive index (~3.5) and the narrow-beam absorption coefficient is proportional to the free electron density and typically several per cm. One would expect that almost all of the scintillation photons should be trapped and absorbed in the crystal, but this is not the case. Recent Monte Carlo and Feynman path integral calculations have shown that the high luminosity could be explained if most of the narrow beam absorption is not absolute absorption but a novel type of optical scattering from the conduction electrons with a cross section of about 5 x 10 cm that allows scintillation photons to escape total internal reflection. This cross section is about 10 times larger than Thomson scattering but comparable to the optical cross section of the conduction electrons in a metal mirror.
# N-type GaAs(Si,B) is commercially grown as 10 kg crystal ingots and sliced into thin wafers as substrates for electronic circuits. Boron oxide is used as an encapsulant to prevent the loss of arsenic during crystal growth, but also has the benefit of providing boron acceptors for scintillation. | 1 | Inorganic Reactions + Inorganic Compounds |