Dehydrogenative coupling of silanes

The dehydrogenative coupling of silanes is a reaction type for the formation of Si-Si bonds. Although never commercialized, the reaction has been demonstrated for the synthesis of certain disilanes as well as polysilanes. These reactions generally require catalysts.
Metallocene-based catalysts.
Titanocene and related their complexes are typical catalysts. A typical reaction involves phenylsilane:
Para- and meta-substituted phenylsilanes polymerize readily but ortho-substituted polymers were failed to form. Polymers white/colorless, tacky and soluble in organic solvents. Crosslinking was not observed.
Using Cp2Ti(OPh)2 as a catalyst, the dehydrogenative coupling of phenylsilane in the presence of vinyltriethoxysilane produces a polysilane terminated with a triethoxysilylvinyl group.
Other catalysts.
Nickel-based catalysts.
The nickel(I) complex [(dippe)Ni(µ-H)]2 promotes the dehydrogenative coupling of some silanes.
Oxide-based catalysts.
While catalysts for dehydrogenative coupling reactions generally tend to be transition metal complexes, magnesium oxide and calcium oxide for the conversion of phenylsilane. Being a heterogeneous process, the products are easily separated from the catalyst.
Wilkinson's Catalyst.
Dehydrogenative coupling of primary silane using Wilkinson's catalyst is slow and dependent on the removal of H2 product. This conversion proceeds by oxidative addition of the Si-H bond and elimination of dihydrogen.
Borane catalysts.
Tris(pentafluorophenyl)borane (B(C6F5)3)) is another catalyst for the dehydrogenative coupling of tertiary silanes. This system has the useful characteristic of being selective for Si-H bonds vs Si-Si bonds, leading to fewer branches and more linear polymers. This catalyst is particularly useful in reactions involving thiols and tertiary silanes or disilanes.
Related reactions of hydrosilanes.
Dehydrodimerization of tertiary silanes.
Due to steric factors, dehydrogenative coupling of tertiary silanes is slow. Disilane formation has been demonstrated in the presence of CpFe(CO)2CH3 combined with UV-irradiation. The mechanism is proposed to involve dissociation of CO ligand, oxidative addition of the Si-H center, followed by reductive elimination of methane. From there, the disilane R3Si-SiR3 is reductively eliminated from the complex.
In addition, this same iron catalyst can be used to build polymers with a Si-R-Si backbone. When R = phenylene, NH, or (C5H4)Fe(C5H4), this reaction works particularly well, and yields of over 95% are obtained.
Cross-coupling.
As well as being coupled to each other, tertiary silanes can be coupled with carboxylic acids to form silyl esters. Ru3(CO)12/EtI is a good catalyst for this. This reaction applies to a wide range of silanes and acids. The complex [Cu(PPh3)3Cl] can also be used to produce silyl esters.
Tertiary silanes may also be dehydrogenatively coupled to aromatic rings with the use of the catalyst TpMe2Pt(Me)2H (TpMe2 = hydrido tris(3,5-dimethylpyrazolyl)borate). For example, this platinum catalyst can be used to react triethyl silane with benzene to produce phenyltriethylsilane, with the elimination of hydrogen gas. This is a terrific catalyst because it eliminates the need for a hydrogen acceptor, something which is normally required for the silation of a C-H bond. This reaction may also be done intramolecularly to produce five- or six-membered silicon-containing rings fused to a phenyl ring. In addition, tributylsilane can be converted into the corresponding cyclic organosilane via the same process. A drawback to this catalyst, however, is that it requires rather harsh reaction conditions (typically 200 °C for 24 hours for the intermolecular reaction, 48 – 72 hours for the intramolecular ones). It is also not particularly regioselective, so starting materials containing substituted benzene would result in a mixture of products.
Polymerization of silane.
Some methods used to produce polysilanes are polymerization of masked dislenes,
electroreduction of dichlorosilanes,
Polymer characterization.
1H and 29Si NMR spectroscopy can sometimes be used to help identify and characterize products from these reactions.
Infrared spectroscopy may also be useful as it can indicate whether or not the product is a tertiary silane. The stretch for Si-H is seen at around 2100 and 910 cm−1. In the case of tertiary silanes however, the peak at 910 cm−1 is not seen. The shift or change in these peaks will be affected by the size of the polymer.


Lanthanite

Lanthanites are a group of isostructural rare earth element (REE) carbonate minerals. This group comprises the minerals lanthanite-(La), lanthanite-(Ce), and lanthanite-(Nd). This mineral group has the general chemical formula of ("REE")2(CO3)3·8(H2O). Lanthanites include La, Ce, and Nd as major elements and often contain subordinate amounts of other REEs including praseodymium (Pr), samarium (Sm), europium (Eu) and dysprosium (Dy). The lanthanite crystal structure consists of layers of 10-fold coordinated REE-oxygen (O) polyhedra and carbonate (CO32−) groups connected by hydrogen bonds to interlayer water molecules, forming a highly hydrated structure.
Origin and formation.
Lanthanites are frequently found as secondary minerals formed by the weathering of other minerals and occur as scales or tabular crystals. Originally identified at Bastnäs, Sweden, they have subsequently been found in New Zealand, Japan, Madagascar, Wales, China, France, Germany, Greenland, Finland, Canada, Austria, Romania, Norway, Brazil, and the United States.
Recently, a different mechanism of formation of lanthanites was discovered: Lanthanites also can form via a highly hydrated, nanoparticulate and poorly ordered carbonate precursor. The lifetime of this rare-earth bearing precursor as well as the kinetics of crystallization of the various REE-lanthanites are dependent on the specific trivalent rare-earth ion involved in the reaction. The times needed for lanthanites to fully crystallize increase linearly with the ionic potential of the trivalent rare-earth ion (La3+, Ce3+, Pr3+, Nd3+) present in their structure. The differences in these ion sizes and ionic potential as well as differences in dehydration energy of the trivalent rare-earth ions control the lifetime of the poorly ordered precursor and thus also the crystallization kinetics of the lanthanites. Furthermore, they also affect the structural characteristics (e.g. unit-cell dimensions and standard shape) of the crystals.


Carbon nanotube chemistry

Carbon nanotube chemistry involves chemical reactions, which are used to modify the properties of carbon nanotubes (CNTs). CNTs can be functionalized to attain desired properties that can be used in a wide variety of applications. The two main methods of CNT functionalization are covalent and non-covalent modifications.
Because of their hydrophobic nature, CNTs tend to agglomerate hindering their dispersion in solvents or viscous polymer melts. The resulting nanotube bundles or aggregates reduce the mechanical performance of the final composite. The surface of CNTs can be modified to reduce the hydrophobicity and improve interfacial adhesion to a bulk polymer through chemical attachment.
Covalent modification.
Covalent modification attaches a functional group onto the carbon nanotube. The functional groups can be attached onto the side wall or ends of the carbon nanotube. The end caps of the carbon nanotubes have the highest reactivity
due to its higher pyrimidization angle and the walls of the carbon nanotubes have lower pyrimidization angles which has lower reactivity. Although covalent modifications are very stable, the bonding process disrupts the sp2
hybridization of the carbon atoms because a σ-bond is formed. The disruption of the
extended sp2 hybridization typically decreases the conductance of the carbon nanotubes.
Oxidation.
The purification and oxidation of carbon nanotubes (CNTs) has been well represented in literature. These processes were essential for low yield production of carbon nanotubes where carbon particles, amorphous carbon particles and coatings comprised a significant percentage of the overall material and are still important for the introduction of surface functional groups. During acid oxidation, the carbon-carbon bonded network of the graphitic layers is broken allowing the introduction of oxygen units in the form of carboxyl, phenolic and lactone groups, which have been extensively exploited for further chemical functionalisation.
First studies on oxidation of carbon nanotubes involved a gas-phase reactions with nitric acid vapor in air, which indiscriminately functionalized the carbon nanotubes with carboxylic, carbonyl or hydroxyl groups. In liquid-phase reactions, carbon nanotubes were treated with oxidizing solutions of nitric acid or a combination of nitric and sulfuric acid to the same effect. However, overoxidation may occur causing the carbon nanotube to break up into fragments, which are known as carbonaceous fragments. Xing et al. revealed sonication assisted oxidation, with sulfuric and nitric acid, of carbon nanotubes and produced carbonyl and carboxyl groups. After the oxidation reaction in acidic solution, treatment with hydrogen peroxide limited the damage on the carbon nanotube network. Single-walled carbon nanotubes can be shortened in a scalable manner using oleum (100% H2SO4 with 3% SO3) and nitric acid. The nitric acid cuts carbon nanotubes while the oleum creates a channel.
In one type of chemical modification, aniline is oxidized to a diazonium intermediate. After expulsion of nitrogen, it forms a covalent bond as an aryl radical:
Esterification/Amidation.
Carboxylic groups are used as the precursor for most esterification and amidation reactions. The carboxylic group is converted into an acyl chloride with the use of thionyl or oxalyl chloride which is then reacted with the
desired amide, amine, or alcohol. Carbon nanotubes have been deposited on with silver nanoparticles with the aid of amination reactions. Amide functionalized carbon nanotubes have been shown to chelate silver nanoparticles. Carbon nanotubes modified with acyl chloride react readily with highly branched molecules such as poly(amidoamine), which acts as a template for silver ion and later being reduced by formaldehyde. Amino-modified carbon nanotubes can be prepared by reacting ethylenediamine with an acyl chloride functionalized carbon nanotubes.
Halogenation reactions.
Carbon nanotubes can be treated with peroxytrifluroacetic acid to give mainly carboxylic acid and trifluroacetic functional groups. The fluorinated carbon nanotubes, through substitution, can be further functionalized with urea, guanidine, thiourea and aminosilane. Using the Hunsdiecker
reaction, carbon nanotubes treated with nitric acid can react with iodosobenzenediacetate to iodate carbon nanotubes.
Cycloaddition.
Also known are protocols for cycloadditions such as Diels-Alder reactions, 1,3-dipolar cycloadditions of azomethine ylides and azide–alkyne cycloaddition reactions. One example is a DA reaction assisted by chromium hexacarbonyl and high pressure. The ID/IG ratio for reaction with Danishefsky's diene is 2.6.
The most well-known 1,3 cycloaddition reaction involves azomethine ylides reacting with carbon nanotubes, which are of great interest. The addition of a pyrrolidine ring can lead to a variety of functional groups such as second-generation
poly(amidoamine) dendrimers, phthalocyanine addends, perfluoroalkylsilane groups, and amino ethyleneglycol groups. The Diels-cycloaddition reaction can occur, especially on fluorinated carbon nanotubes. They are known to undergo Diels–Alder reactions with dienes such as 2,3-dimethyl-1,3-butadiene, anthracene, and 2-trimethylsiloxyl-1,3-butadiene.
Radical addition.
The modification of carbon nanotubes with aryl diazonium salts was studied first by Tour et al. Due to the harsh conditions needed for the "in situ" generated diazonium compound, other methods have been explored. Stephenson et al. reported using aniline derivatives with sodium nitrite in 96% sulfuric acid and ammonium persulfate. Price et al. demonstrated that stirring carbon nanotubes in water and treating with anilines and oxidizing agents proved to be a milder reaction. The diazonium chemistry functionalized carbon nanotubes which was used as a precursor to further modifications. Suzuki and Heck coupling reactions were performed on iodophenyl-functionalized carbon nanotubes. Wong et al. demonstrated mild photochemical reactions to silylate the carbon nanotubes with trimethoxysilane and hexaphenyldisilane.
Nucleophilic addition.
Hirsch et al. conducted nucleophilic additions with organolithium and organomagnesium
compounds onto carbon nanotubes. With further oxidation in air, they were able to create alkyl-modified carbon nanotubes. Hirsch was also able to show the nucleophilic addition of amines by generating lithium amides, leading to
amino-modified carbon nanotubes.
Electrophilic addition.
Nanotubes can also be alkylated with alkyl halides using lithium or sodium metal and liquid ammonia (Birch reduction conditions). The initial nanotube salt can function as a polymerization initiator and can react with peroxides to form alkoxy functionalized nanotubes
The alkyl and hydroxyl modification of carbon nanotubes was demonstrated with the electrophilic addition of
alkylhalides by microwave irradiation. Tessonnier et al. modified carbon nanotubes with amino groups by deprotonating with butyl lithium and reacting with amino substitution. Balaban et al. applied Friedel-Crafts acylation to carbon nanotubes with nitrobenzene at 180 °C along with aluminum chloride.
Non-covalent modifications.
Non-covalent modifications utilize van der Waals forces and π-π interactions by adsorption of polynuclear aromatic
compounds, surfactants, polymers or biomolecules. Non-covalent modifications do not disrupt the natural configuration of carbon nanotubes with the cost of chemical stability, and is prone to phase separation, dissociation in between two phases, in the solid state.
Polynuclear aromatic compounds.
Some common polynuclear aromatic compounds that are functionalized with hydrophilic or hydrophobic moieties are used to
solubilize carbon nanotubes into organic or aqueous solvents. Some of these amphiphiles are phenyl, naphthalene, phenanthrene, pyrene and porphyrin systems. The greater π-π stacking of aromatic amphiphiles such as pyrene amphiphiles had the best solubility compared to phenyl amphiphiles with the worse π-π stacking, lead to more solubility in water. These aromatic systems can be modified with amino and carboxylic acid groups prior to
functionalizing the carbon nanotubes.
Biomolecules.
The interaction between carbon nanotubes and biomolecules has been widely studied because of their potential to be used in
biological applications. The modification of the carbon nanotubes with proteins, carbohydrates, and nucleic acids are built with the bottom-up technique. Proteins have high affinity to carbon nanotubes due to their diversity of amino acids being hydrophobic or hydrophilic. Polysaccharides have been successfully been used to modify carbon nanotubes forming stable hybrids. To make carbon nanotubes soluble in water, phospholipids such as lysoglycerophospholipids have been used. The single phospholipid tail wraps around the carbon nanotube, but the double tailed phospholipids did not have the same ability.
π-π stacking and electrostatic interactions.
Molecules that have bifunctionality are used to modify the carbon nanotube. One end of the molecule are polyaromatic compounds that interact with the carbon nanotube through π-π stacking. The other end of the same molecule has a functional group such as amino, carboxyl, or thiol. For example, pyrene derivatives and aryl thiols were used as the linkers for various metal nanobeads such as gold, silver and platinum.
Mechanical interlocking.
A particular case of non-covalent modification is the formation of rotaxane-like mechanically interlocked derivatives of single-walled nanotubes (SWNTs). In this strategy, the SWNTs are encapsulated by molecular macrocycle(s), which are either formed around them by macrocyclization, or pre-formed and threaded at a later stage. In MINTs (Mechanically Interlocked NanoTubes), the SWNT and organic macrocycle are linked by means of their topology, through a mechanical bond, combining the stability of the covalent strategies -at least one covalent bond must be broken to separate SWNT and macrocycle(s)- with the structural integrity of the classic noncovalent strategies -the C-sp2 network of the SWNT remains intact.
Characterization.
A useful tool for the analysis of derivatised nanotubes is Raman spectroscopy which shows a G-band (G for graphite) for the native nanotubes at 1580 cm−1 and a D-band (D for defect) at 1350  cm−1 when the graphite lattice is disrupted with conversion of sp² to sp³ hybridized carbon. The ratio of both peaks ID/IG is taken as a measure of functionalization. Other tools are UV spectroscopy where pristine nanotubes show distinct Van Hove singularities where functionalized tubes do not, and simple TGA analysis.


Graphene lens

A graphene lens is an optical refraction device. Graphene's unique 2-D honeycomb contributes to its unique optical properties.
Graphene.
The honeycomb structure allows electrons to behave as massless quasiparticles known as Dirac fermions. Graphene's optical conductivity properties are thus unobstructed by any material parameters, as represented by equation 1, where is the electron charge, is Planck's constant and represents the universal conductance.
This behavior is the result of an undoped graphene material at zero temperature (figure 1a). In contrast to traditional semiconductors or metals (figure 1b); graphene's band gap is nearly nonexistent because the conducting and valence bands make contact (Figure 1a). However, the band gap is tunable via doping and electrical gating, changing optical properties. As a result of its tunable conductivity, graphene is suitable for various optical applications.
Applications.
Photodetectors.
Electrical gating and doping allows for adjustment of graphene's optical absorptivity. The application of electric fields transverse to staggered graphene bilayers generates a shift in Fermi energy and an artificial, non-zero band gap (equation 2 figure 1).
where
Varying δD above or below zero (δD=0 denotes non-gated, neutral bilayers) allows electrons to pass through the bilayer without altering the gating-induced band gap. As shown in Figure 2, varying the average displacement field, ▁D, alters the bilayer's absorption spectra. The optical tunability resulting from gating and electrostatic doping (also known as charge plasma doping) lends to the application of graphene as an ultra-broadband photodetector in lenses.
Chang-Hua et al. implemented graphene in an infrared photodetector by sandwiching an insulating barrier of between two graphene sheets. The graphene layers became electrically isolated and exhibited an average Fermi difference of 0.12eV when a current was passed through the bottom layer (Figure 3). When the photodetector is exposed to light, excited hot electrons transitioned from the top graphene layer to the bottom, a process promoted by the structural asymmetry of the insulating barrier. As a consequence of the hot electron transition, the top layer accumulates positive charges and induces a photogating effect on the lower graphene layer, which is measured as a change in current correlating with photon detection. Utilizing graphene both as a channel for charge transport and light absorption, the photodetectors ably detects the visible to mid-infrared spectrum. Nanometers thin and functional at room temperature, graphene photodetectors show promise in lens applications.
Fresnel zone plates.
Fresnel zone plates are devices that focus light on a fixed point in space. These devices concentrate light reflected off a lens onto a singular point (Figure 4). Composed of a series of discs centered about an origin, Fresnel zone plates are manufactured using laser pulses, which embed voids into areflective lens.
Despite its weak reflectance (R = 0.25π2 α 2 at T = 1.3 × 10-4 K), graphene has utility as a lens for Fresnel zone plates. Graphene lenses effectively concentrate light of ʎ = 850 nm onto a single point 120 um away from the Fresnel zone plate (figure 5). Further investigation illustrates that the reflected intensity increases linearly with the number of graphene layers within the lens (Figure 6).
Transparent conductors.
Optoelectronic components such as light-emitting diode (LED) displays, solar cells, and touchscreens require highly transparent materials with low sheet resistance, Rs. For a thin film, the sheet resistance is given by Equation 3:
where is the film thickness and is the DC conductivity.
A material with tunable thickness t and conductivity σ is suitable for optoelectronic applications if Rs is reasonably small. Graphene is such a material; the number of graphene layers that comprise the film can tune t and the inherent tunability of graphene's optical properties via doping or grating can tune sigma. Figure 7 shows graphene's potential relative to other known transparent conductors.
The need for alternative transparent conductors is well documented. Semiconductor based transparent conductors such as doped indium oxides, zinc oxides, or tin oxides suffer from practical downfalls including rigorous processing requirements, prohibitive cost, sensitivity toward Ph, and brittle consistency. However, graphene does not suffer from these shortfalls.


Beta-D

Beta-D (3,4,5-trimethoxy-beta-dideuterophenethylamine) is a lesser-known psychedelic drug. It is one of the few phenethylamines used as a recreational drug that is enriched in deuterium. Beta-D can be prepared as a sulfate salt or as a hydrochloride salt. It is the beta-dideutero analog of mescaline. Beta-D was first synthesized by Alexander Shulgin. In his book "PiHKAL", the dosage is listed as approximately 200–400 mg for the sulfate salt, and 178–356 mg for the hydrochloride salt. Its effects last for 12 hours. Beta-D has a very rapid onset. It produces an increased appreciation of music and a strong connection with God. Very little data exists about the pharmacological properties, metabolism, and toxicity of Beta-D.


Potassium perbromate

Potassium perbromate is the chemical compound composed of the potassium ion and the perbromate ion, with the chemical formula KBrO4.
Preparation.
Potassium perbromate can be prepared by reacting perbromic acid with potassium hydroxide:


Triazolate

A triazolate is a salt derived from a triazole by replacement of a proton with a cation. Different isomers exist 1,2,4-triazolate or 1,2,3-triazolate, both of which are unsaturated heterocyclic ring compounds containing three nitrogen atoms. The basic formula is C2N3H2−. It can be abbreviated by "tz".
Known compounds include zinc, and natural copper minerals, chanabayaite and triazolite.
Trizolate is a tridentate ligand, and can form complexes with metals via the three nitrogen atoms. This enables polymers or metal organic framework compounds to be formed. Triazolate can also be substituted on its carbon atoms.


Chrome chalcedony

Chrome chalcedony is a green variety of the mineral chalcedony, colored by small quantities of chromium.
It is most commonly found in Zimbabwe, where it is known as Mtorolite, Mtorodite, or Matorolite.
Chemical composition.
Chrome chalcedony is similar in appearance to the better known chrysoprase, but differs in that whilst chrome chalcedony is colored by chromium (as chromium(III) oxide), chrysoprase is colored by nickel. The two can be distinguished with a Chelsea color filter, as chrome chalcedony will appear red, whilst chrysoprase will appear green. Chrome chalcedony (unlike chrysoprase) may also contain tiny black specks of chromite.
Chrome chalcedony is (together with agate, carnelian, chrysoprase, heliotrope, onyx and others) a variety of chalcedony. This is a cryptocrystalline form of silica, consisting of fine intergrowths of the minerals quartz and moganite.
Locality.
Chrome chalcedony (known as mtorolite, mtorodite or matorolite) occurs in Zimbabwe, principally near to the mining town of Mtoroshanga, located on the Great Dyke geological feature. It has also been discovered in western Australia, the Balkans, Bolivia, Turkey and the Ural mountains.
Ancient history.
Chrome chalcedony was widely used in jewellery and seals throughout the Roman Empire. The source of the mineral is unclear, as whilst Pliny the Elder described it as coming from India, no deposits have been found there. It may have come from Anatolia (in modern-day Turkey), where deposits are known to exist.
Chrome chalcedony disappeared from use sometime in the 2nd century. It was only rediscovered when the Zimbabwean deposits were found in the 1950s.


Stannate

In chemistry the term stannate refers to compounds of tin (Sn). Stannic acid (Sn(OH)4), the formal precursor to stannates, . The term is also used in naming conventions as a suffix for example the hexachlorostannate ion is .
In materials science, two kinds of tin oxyanions are distinguished:
These materials are semiconductors.


Zinc and the common cold

 (frequently zinc acetate or zinc gluconate lozenges) are a group of dietary supplements that are commonly used for the treatment of the . The use of zinc supplements at doses in excess of 75 mg/day within 24 hours of the onset of symptoms has been shown to reduce the duration of cold symptoms by about 1 day in adults. Adverse effects with zinc supplements by mouth include bad taste and nausea. The intranasal use of zinc-containing nasal sprays has been associated with the loss of the sense of smell; consequently, in June 2009, the United States Food and Drug Administration (USFDA) warned consumers to stop using intranasal zinc.
The human rhinovirus – the most common viral pathogen in humans – is the predominant cause of the common cold. The hypothesized mechanism of action by which zinc reduces the severity and/or duration of cold symptoms is the suppression of nasal inflammation and the direct inhibition of rhinoviral receptor binding and rhinoviral replication in the nasal mucosa.
Effectiveness.
A 2016 meta-analysis on zinc acetate-lozenges and the common cold in 199 patients found that colds were 2.7 days shorter by zinc lozenge usage. This estimate is to be compared with the 7 day average duration of colds in the three trials.
A 2015 meta-analysis on zinc lozenges and the common cold found no difference in the effects of zinc acetate lozenges on diverse respiratory symptoms. Although zinc lozenges most probably lead to highest concentration of zinc in the pharyngeal region, a subsequent meta-analysis showed that the effects of high-dose zinc acetate lozenges did not significantly differ in their effects on pharyngeal and nasal symptoms. The duration of nasal discharge was shortened by 34%, nasal congestion by 37%, sneezing by 22%, scratchy throat by 33%, sore throat by 18%, hoarseness by 43%, and cough by 46%. Zinc lozenges shortened the duration of muscle ache by 54%, but there was no significant effect on the duration of headache and fever.
A 2013 review which said that zinc supplementation might be helpful for the common cold was withdrawn by the Cochrane Collaboration over concerns about the data used.
Interactions.
Some lozenge formulations do not contain enough zinc to effectively reduce the lengths of colds; some of them contain ingredients that bind zinc, like citric acid, which prevent the zinc from working.
Safety.
There have been several cases of people using zinc nasal sprays and suffering a loss of sense of smell. In 2009 the US Food and Drug Administration issued a warning that people should not use nasal sprays containing zinc.
Overdose of zinc intake include bad taste and nausea.
Mechanism of action.
The hypothesized mechanism of action by which zinc reduces the severity and/or duration of cold symptoms is the suppression of nasal inflammation and the direct inhibition of rhinoviral receptor binding and rhinoviral replication in the nasal mucosa. Zinc has been known for many years to have an effect on cold viruses in the laboratory. In the arteriviridae and coronaviridae families of virus that also cause the common cold, in vitro studies found that zinc ionophores block the replication of those viruses in cell culture.


Graphene oxide paper

Graphene oxide paper or graphite oxide paper is a material fabricated from graphite oxide. Micrometer thick films of graphene oxide paper are also named as graphite oxide membranes (in the 1960s) or (more recently) graphene oxide membranes. The membranes are typically obtained by slow evaporation of graphene oxide solution or by the filtration method.
The material has exceptional stiffness and strength, due to the intrinsic strength of the two-dimensional graphene backbone and to its interwoven layer structure which distributes loads.
Preparation.
The starting material is water-dispersed graphene oxide flakes. The aqueous dispersion is vacuum filtrated to produce free standing foils. The thickness of these foils is typically in the range of 0.1-50 micrometers. Depending on application the graphene oxide laminates are named either as papers or as membranes. Alternative methods to prepare free standing graphene oxide multilayers/laminates is to use repeated drop casting or spin coating. These flakes may be chemically bonded, leading to the development of additional new materials. Like the starting material, graphene oxide paper is an electrical insulator; however, it may be possible to tune this property, making the paper a conductor or semiconductor, without sacrificing its mechanical properties.
Properties.
Detailed studies of graphite oxide paper by V. Kohlschütter and P. Haenni date back to 1918. Studies of graphite oxide membranes were performed by Hanns-Peter Boehm, the German scientist who invented the term "graphene", in 1960. The paper titled "Graphite Oxide and its membrane properties" reported synthesis of "paper-like foils" with 0.05 mm thickness. The membranes were reported to be not permeable by gases (nitrogen and oxygen) but easily permeable by water vapors and, suggestively, by any other solvents which are able to intercalate graphite oxide. It was also reported that the membranes are not permeable by "substances of lower molecular weight".
Permeation of water through the membrane was attributed to swelling of graphite oxide structure which enables water penetration path between individual graphene oxide layers. The interlayer distance of dried graphite oxide was reported as 6.35 Å, but in liquid water it increased to 11.6 Å. Remarkably, the paper also cited the inter-layer distance in diluted NaOH as infinity thus reporting dispersion of graphite oxide on single-layered graphene oxide sheets in solution. The study also reported permeation rate of membranes for water 0.1 mg per minute per square cm. The diffusion rate of water was evaluated as 1 cm/hour. Boehm's paper also showed that graphite oxide can be used as cation exchange membrane and reports measurements of osmotic pressures, membrane potentials in KCl, HCl, CaCl2, MgCl2, BaCl2 solutions. The membranes were also reported to be permeable by large alkaloid ions as they are able to penetrate between graphene oxide layers.
In 2012 some of the properties of graphite oxide membranes discovered by Boehm were re-discovered: the membranes were reported to be not permeable by helium but permeable by water vapors. This study was later expanded to demonstrate that several salts (for example KCl, MgCl2) diffuse through the graphene oxide membrane if it is immersed in water solution.
Graphene oxide membranes are actively being studied for their applications to water desalination. Retention rates over 90% were reported in a 1960 study for NaCl solutions using stabilized graphene oxide membranes in reverse osmosis setup.


Taehung mine

The Taehung Youth Hero Mine is one of the largest magnesium mines in North Korea and in the world. The mine is located in the center of the country in South Hamgyong Province. The mine has about 2 billion tonnes of Magnesite. However, facilities have become antiquated and an unstable electricity supply limits the full exploitation of the resources.


Buckypaper

Buckypaper is a thin sheet made from an aggregate of carbon nanotubes or carbon nanotube grid paper. The nanotubes are approximately 50,000 times thinner than a human hair. Originally, it was fabricated as a way to handle carbon nanotubes, but it is also being studied and developed into applications by several research groups, showing promise as vehicle armor, personal armor, and next-generation electronics and displays.
Background.
Buckypaper is a macroscopic aggregate of carbon nanotubes (CNT), or "buckytubes". It owes its name to the buckminsterfullerene, the 60 carbon fullerene (an allotrope of carbon with similar bonding that is sometimes referred to as a "Buckyball" in honor of R. Buckminster Fuller).
Synthesis.
The generally accepted methods of making CNT films involves the use of non-ionic surfactants, such as Triton X-100 and sodium lauryl sulfate, which improves their dispersibility in aqueous solution. These suspensions can then be membrane filtered under positive or negative pressure to yield uniform films. The van der Waals force's interaction between the nanotube surface and the surfactant can often be mechanically strong and quite stable and therefore there are no assurances that all the surfactant is removed from the CNT film after formation. Washing with methanol, an effective solvent in the removal of Triton X, was found to cause cracking and deformation of the film. It has also been found that Triton X can lead to cell lysis and in turn tissue inflammatory responses even at low concentrations.
In order to avoid adverse side-effects from the possible presence of surfactants, an alternative casting process can be used involving a frit compression method that did not require the use of surfactants or surface modification. The dimensions can be controlled through the size of the syringe housing and through the mass of carbon nanotubes added. Their thicknesses are typically much larger than surfactant-cast buckypaper and have been synthesized from 120 μm up to 650 μm; whilst no nomenclature system exists to govern thicknesses for samples to be classified as paper, samples with thicknesses greater than 500 μm are referred to as buckydiscs. The frit compression method allows rapid casting of buckypaper and buckydiscs with recovery of the casting solvent and control over the 2D and 3D geometry.
Aligned multi-walled carbon nanotube (MWNT) growth has been used in CNT film synthesis through the domino effect. In this process, "forests" of MWNTs are pushed flat in a single direction, compressing their vertical orientation into the horizontal plane, which results in the formation of high-purity buckypaper with no further purification or treatment required. By comparison, when a buckypaper sample was formed from the 1 ton compression of chemical vapor deposition (CVD) generated MWNT powder, any application of a solvent led to the immediate swelling of the film till it reverted into particulate matter. It appears that for the CNT powder used, compression alone was insufficient to generate robust buckypaper and highlights that the aligned growth methodology generates "in situ" tube-tube interactions not found in CVD CNT powder and are preserved through to the domino pushing formation of buckypaper.
Recently, a new scalable CNT film fabrication method has been developed: Surface-Engineered Tape Casting (SETC) technique. The SETC technique solves the main challenge of tape-casting which is the detachment of the dried and the typically sticky CNT film from the supporting-substrate. To achieve a perfect detached film, the supporting-substrate has to be engineered with micro-pyramid pore structure morphology. SETC produces large area films from any commercially available carbon nanotubes with tunable length, thickness, density and composition.
Properties.
Buckypaper is one tenth the weight yet potentially 500 times stronger than steel when its sheets are stacked to form a composite. It could disperse heat like brass or steel and it could conduct electricity like copper or silicon.
Applications.
Among the possible uses for buckypaper that are being researched:


Ruizite

Ruizite is a sorosilicate mineral with formula Ca2Mn2Si4O11(OH)4·2H2O. It was discovered at the Christmas mine in Christmas, Arizona, and described in 1977. The mineral is named for discoverer Joe Ana Ruiz.
Description and occurrence.
Ruizite is translucent and orange to red-brown in color with an apricot yellow streak. The mineral occurs as euhedral prisms up to or as radial clusters of acicular (needle-like) crystals.
Ruizite is common at the Christmas mine. The mineral is known from Arizona, Pennsylvania, and Northern Cape Province, South Africa. Ruizite occurs in association with apophyllite, bornite, calcite, chalcopyrite, datolite, diopside, grossular, inesite, junitoite, kinoite, orientite, pectolite, quartz, smectite, sphalerite, vesuvianite, and wollastonite. Ruizite is found in veinlets or fracture surfaces of limestone metamorphosed into a calc-silicate assemblage. The mineral formed by retrograde metamorphism during cooling of a calc–silicate skarn assemblage in an oxidizing environment.
Crystal structure and chemistry.
Ruizite crystallizes in the monoclinic crystal system and twinning is common along the {100} plane between exactly two crystals. Ruizite's formula was originally identified as CaMn(SiO3)2(OH)2·2H2O in 1977. In 1984, Frank C. Hawthorne revised the formula to Ca2Mn2Si4O11(OH)4·2H2O. Ruizite's structure consists of edge-sharing Mnφ6 octahedra, connected at corners into sheets and together into a lattice by clusters of Si4O11(OH)2.
Nitric acid, hydrochloric acid, and potassium hydroxide have little effect on ruizite at low temperatures but readily dissolve the mineral at elevated temperatures.
History.
During the investigation of junitoite at the Christmas mine in Christmas, Arizona, Joe Ana Ruiz and Robert Jenkins discovered an unknown brown mineral. Mine geologist Dave Cook located better specimens, and it was determined to be a new mineral species. The mineral was named "ruizite" in honor of Joe Ruiz as discoverer. Ruizite's properties were analyzed using a sample provided by Joseph Urban, and it was described in the journal "Mineralogical Magazine" in December 1977. The International Mineralogical Association approved the mineral as IMA 1977-077. Type specimens are housed in the University of Arizona, Harvard University, the National Museum of Natural History, and The Natural History Museum.


Vulcanite

Vulcanite is a rare copper telluride mineral. The mineral has a metallic luster, and has a green or bronze-yellow tint. It has a hardness between 1 and 2 on the Mohs scale (between talc and gypsum). Its crystal structure is orthorhombic.
Vulcanite is named for the place where it was discovered in 1961, the Mammoth Good Hope Mine in Vulcan (ghost town and district), Gunnison County, Colorado. Small deposits have also been discovered in Japan, Russia, Saudi Arabia, and Norway. It occurs with native tellurium, rickardite, petzite, and sylvanite.


Carbon nanotube computer

A carbon nanotube computer is a computer built entirely using carbon nanotubes (CNT) based transistors. Researchers from Stanford University said that they had successfully built a carbon nanotube computer and their research paper published on 25 September 2013 in the journal "Nature". They named their first carbon nanotube computer Cedric. It has a one-bit processor containing just 178 transistors.
In 2019, a team at the Massachusetts Institute of Technology created the 16-bit processor called RV16X-NANO. With 14 000 transistors (compared to only hundreds in the first CNT computer made in 2013) it is the largest computer chip yet to be made from carbon nanotubes. It was able to execute a "Hello, World!" program with a message: “Hello, world! I am RV16XNano, made from CNTs”. It is based on the RISC-V instruction set and runs standard 32-bit instructions on 16-bit data and addresses.


POCOP

POCOP is a type of pincer ligand. Pincer type ligands are tridentate ligands that bind three sites on one plane of a metal complex. POCOP forms complexes with one M-C(aryl) bond and two phosphinite ligands. The term POCOP is used both for the ligand, with formula C6H4(OPPh2)2, and its complexes, with formula C6H3(OPPh2)2]− (Ph = C6H5)
Synthesis and structure.
Interest in POCOP arises from its easy synthesis, which accommodates many substituents on phosphorus and results in higher yields than other PCP analogues. The parent POCOP ligand is prepared by treating resorcinol with chlorodiphenylphosphine:
Related ligands can be prepared from chlorodiisopropylphosphine.
Representative complexes are of the type Ni(POCOP)X (X = halide, alkyl, thiolate). The halides arise by direct reaction of the ligand and a nickel halide and offer a relatively cheap, nontoxic and readily available option of the ligand for various applications. There can also be variable conformations of POCOP pertaining to the various R groups branching off of the donor atoms.
In most cases the MPOCOP center features a planar MC3O2P2 core. The rigid conformation and square planar geometry of the POCOP ligand allow for systematic changes over the steric and electronic environment at the metal center. The geometry of metal compounds formed with POCOP ligands can be seen through the P-Ni-P (164.01 Å ) and C-Ni-Cl (178.31Å) bond angles found for (POCOP)NiCl. The bond angles of this compound are representative of angles found for several other pocop metal compounds. Because of relatively small P-Ni-P bond angle the otherwise Ni complexes exhibit a slight tetrahedral distortion.
Catalytic reaction.
Pincer ligands participate in a variety of organic transformation, such as the hydrosilylation, and ethylene oligomerizations, and homocoupling of benzyl halides. Ni PCP pincer complexes promote sulfur-carbon forming reactions.


Vinci (rocket engine)

Vinci is a European Space Agency cryogenic liquid rocket engine currently under development. It is designed to power the new upper stage of Ariane 6.
Overview.
Vinci is an expander cycle rocket engine fed with liquid hydrogen and liquid oxygen. Its biggest improvement from its predecessor, the HM7B (which powers the ESC-A), is the capability of restarting up to five times. It is also the first European expander cycle engine, removing the need for a gas generator to drive the fuel and oxidizer pumps. The engine features a carbon ceramic extendable nozzle in order to have a large, 2.15 m diameter nozzle extension with minimum length: the retracted nozzle part is deployed only after the upper stage separates from the rest of the rocket; after extension, the engine's overall length increases from 2.3 m to 4.2 m.
Development.
Although the ESC-B development was put on hold in 2003, the Vinci project has not been cancelled: at a lower pace, the engine is still being developed. On 22 December 2006, Snecma announced a new ESA contract for Vinci rocket engine long-duration and re-ignition testing.
In late April 2010 the German Aerospace Center DLR announced the start of a six-month test campaign for the Vinci engine at its Lampoldshausen facility. The first successful test firing of this campaign took place on 27 May 2010. A video of a test was released in 2016.
In 2014, NASA was interested with the idea of using the Vinci instead of the RL10 for an upper stage of Space Launch System. The Vinci offers the same specific impulse at the same mass but with 64% greater thrust, which would allow for a reduction of one or two of the four second stage engines for the same performance, while the cost would be lower.
, the first flight of the Ariane 6 rocket with Vinci is planned for 2020.
In July 2017, Ariane Group reported that the first flight models of the combustion chamber had entered production.


Lead oxychloride

Lead oxychlorides are halide compounds of lead with the general formula PbClO(H).
Occurrence in nature.
Lead oxychlorides are found naturally in the minerals hereroite as Pb32O212Cl10, in rickturnerite as Pb7O4(OH)Cl3, in vladkrivovichevite as Pb32O18Cl14, in asisite as Pb7SiO4O4Cl2, in damaraite as Pb3Cl(OH)O2, in hereroite as Pb3Cl(OH)O2, in Mendipite as Pb3Cl2O2, and in the dimorph minerals laurionite and paralaurionite, which are PbCl(OH) members of the matlockite group.
Usage.
Historically, the primary use of lead oxychlorides was in a mixture with other lead compounds (e.g. lead carbonate "white lead") as a pigment in lead paints. The lead compounds were first fused, and the product then ground to fine powder. The powder was then suspended in drying oils (e.g. linseed), to produce e.g. Pattinson's white (PbCl2 2Pb(OH)2) or Turner's yellow (PbCl2 5-7PbO). Turner's yellow is also known as Patent yellow, Cassel yellow, Montpelier yellow, Kassler yellow, mineral yellow, and Verona yellow.
In the late 19th century, lead oxychlorides were briefly used in the manufacture of electrodes for lead-acid batteries. Patented by Charles Francis Brush in 1876, the depressions in a ribbed or grooved sheet of lead were filled with pulverized lead oxychloride (later also lead sulfate). In a second step, the grooved sheet was covered with paper and horizontally suspended in a salt or acid solution, to which a zinc plate was then also added. The mixture in the grooved sheet's depressions was then electrolytically reduced to sponge lead, forming a functional lead-acid cell electrode (if subsequently used as a positive electrode, the sponge lead was converted to lead peroxide during the cell's initial "formation" charge). Brush's technique was superseded by the now standard Faure pasting method in 1880.


Strontium chlorate

Strontium chlorate is a chemical compound, with the formula Sr(ClO3)2. It is a strong oxidizing agent.
Preparation.
Strontium chlorate is created by warming a solution of strontium hydroxide, and adding chlorine to it, which subsequent crystallization. Chlorine has no action on dry Sr(OH)2, but it converts the hydrate (Sr(OH)2·8H2O) into the chloride and chlorate, with a small quantity of strontium hypochlorite also being produced.


Magnesium hydride

Magnesium hydride is the chemical compound with the molecular formula MgH2. It contains 7.66% by weight of hydrogen and has been studied as a potential hydrogen storage medium.
Preparation.
In 1951 preparation from the elements was first reported involving direct hydrogenation of Mg metal at high pressure and temperature (200 atmospheres, 500 °C) with MgI2 catalyst:
Lower temperature production from Mg and H2 using nano crystalline Mg produced in ball mills has been investigated. Other preparations include:
Structure and bonding.
The room temperature form α-MgH2 has a rutile structure. There are at least four high pressure forms: γ-MgH2 with α-PbO2 structure, cubic β-MgH2 with Pa-3 space group, orthorhombic HP1 with Pbc21 space group and orthorhombic HP2 with Pnma space group. Additionally a non stoichiometric MgH(2-δ) has been characterised, but this appears to exist only for very small particles (bulk MgH2 is essentially stoichiometric, as it can only accommodate very low concentrations of H vacancies).
The bonding in the rutile form is sometimes described as being partially covalent in nature rather than purely ionic; charge density determination by synchrotron x-ray diffraction indicates that the magnesium atom is fully ionised and spherical in shape and the hydride ion is elongated.
Molecular forms of magnesium hydride, MgH, MgH2, Mg2H, Mg2H2, Mg2H3, and Mg2H4 molecules identified by their vibrational spectra have been found in matrix isolated samples at below 10 K, formed following laser ablation of magnesium in the presence of hydrogen. The Mg2H4 molecule has a bridged structure analogous to dimeric aluminium hydride, Al2H6.
Reactions.
MgH2 readily reacts with water to form hydrogen gas:
At 287 °C it decomposes to produce H2 at 1 bar pressure, the high temperature required is seen as a limitation in the use of MgH2 as a reversible hydrogen storage medium:
Potential use for hydrogen storage.
Its potential as a reversible "storage" medium for hydrogen has led to interest in improving the hydrogenation and dehydrogenation reaction kinetics. This can be partially achieved by doping or by reducing the particle size using ball milling. An alternative approach under investigation is the production of a pumpable slurry of MgH2 which is safe to handle and releases H2 by reaction with water, with reprocessing of the Mg(OH)2 into MgH2. A series of U.S. patents (US9123925B2, US8651268B2, US8651270B2, US9732906B2) and international patents have been granted for a rechargeable low pressure, low temperature hydrogen storage system employing nano-structured magnesium hydride for high density hydrogen absorption and laser-activated desorption. A practical system employs treated polymer substrates in the form a disc or tape for use in long term storage, transportation and grid stabilization. The system has a unique advantage in the ability to passively capture hydrogen from industrial flues and waste treatment plants before it can bond to form greenhouse gases.


Dicobalt silicide

Dicobalt silicide (Co2Si) is an intermetallic compound, a silicide of cobalt.


Colloidal silica

Colloidal silicas are suspensions of fine amorphous, nonporous, and typically spherical silica particles in a liquid phase.
The surface of colloidal silica in contact with water is covered by siloxane bonds (≡Si–O–Si≡) and silanol groups (≡Si–OH). This makes colloidal silica very hydrophilic and capable of forming numerous hydrogen bonds.
Manufacture.
Colloidal silicas are most often prepared in a multi-step process where an alkali-silicate solution is partially neutralized, leading to the formation of silica nuclei. The subunits of colloidal silica particles are typically in the range of 1 to 5 nm. Whether or not these subunits are joined together depends on the conditions of polymerization. Initial acidification of a waterglass (sodium silicate) solution yields Si(OH)4.
If the pH is reduced below 7 or if salt is added, then the units tend to fuse together in chains. These products are often called silica gels. If the pH is kept slightly on the alkaline side of neutral, then the subunits stay separated, and they gradually grow. These products are often called precipitated silica or silica sols. Hydrogen ions from the surface of colloidal silica tend to dissociate in aqueous solution, yielding a high negative charge. Substitution of some of the Si atoms by Al is known to increase the negative colloidal charge, especially when it is evaluated at pH below the neutral point. Because of the very small size, the surface area of colloidal silica is very high.
The colloidal suspension is stabilized by pH adjustment and then concentrated, usually by evaporation. The maximum concentration obtainable depends on the particle size. For example, 50 nm particles can be concentrated to greater than 50 wt% solids while 10 nm particles can only be concentrated to approximately 30 wt% solids before the suspension becomes too unstable.


Unoctbium


Benzeneselenol

Benzeneselenol, also known as selenophenol, is the organoselenium compound with the formula C6H5SeH, often abbreviated PhSeH. It is the selenium analog of phenol. This colourless, intensely malodorous compound is a useful reagent in organic synthesis.
Synthesis.
Benzeneselenol is prepared by the reaction of phenylmagnesium bromide and selenium:
Reactions.
More so than thiophenol, benzeneselenol is easily oxidized by air. The facility of this reaction reflects the weakness of the Se-H bond. The product is diphenyl diselenide as shown in this idealized equation:
The presence of the diselenide in benzeneselenol is indicated by a yellow coloration. The diselenide can be converted back to the selenol by reduction followed by acidification of the resulting PhSe−.
PhSeH is acidic with a pKa of 5.9. Thus at neutral pH, it is mostly ionized:
It is approximately seven times more acidic than the related thiophenol. Both compounds dissolve in water upon the addition of base. The conjugate base is PhSe−, a potent nucleophile.
History.
Benzeneselenol was first reported in 1888 by the reaction of benzene with selenium tetrachloride (SeCl4) in the presence of aluminium trichloride (AlCl3).
Safety.
The compound is intensely malodorous and, like other organoselenium compounds, toxic.


Technetium(IV) chloride

Technetium(IV) chloride is the inorganic compound with the formula TcCl4. It was discovered in 1957 as the first binary halide of technetium. It is the highest oxidation binary chloride of technetium that has been isolated as a solid. It is volatile at elevated temperatures and its volatility has been used for separating technetium from other metal chlorides. Colloidal solutions of technetium(IV) chloride are oxidized to form Tc(VII) ions when exposed to gamma rays.
Technetium tetrachloride can be synthesized from the reaction of Cl2 with technetium metal at elevated temperatures between 300-500 °C:
Technetium tetrachloride has also been prepared from the reaction of technetium(VII) oxide with carbon tetrachloride in a sealed vessel at elevated temperature:
At 450 °C under vacuum, TcCl4 decomposes to TcCl3 and TcCl2.
As verified by X-ray crystallography, the compound is an inorganic polymer consisting of interconnected TcCl6 octahedra.


Cymrite

Cymrite is a silicate mineral with the chemical formula BaAl2Si2(O,OH)8·H2O. The mineral is named for Cymru, which is the Welsh word for Wales.
Cymrite, with perfect cleavage and a monoclinic crystalline system, falls in the silicate group. Silicates are formed of Silicon and Oxygen bonding together to form tetrahedra. The symmetry of Cymrite is classified as having a mirror plane. It has a moderate relief, meaning the contrast between the mineral and the epoxy of a thin section makes cymrite easily visible. The birefringence of the mineral is 0.01. Cymrite, being monoclinic is anisotropic with two optic axes.
Occurrence.
Cymrite was discovered in Wales but is found in other areas throughout the United States, Africa, Greece and other parts of Europe. It occurs in generally high temperature-pressure areas such as the hydrothermal manganese silicate ore that makes up the Benalt Mine in Wales and in manganese rock that has undergone high-pressure metamorphism found in Greece. It is important to geologists because of its limited occurrence, when cymrite is present on a rock it indicates that the rock, at some point, must have experienced high pressure and temperature.


Tetraethylgermanium

Tetraethylgermanium (common name tetraethyl germanium), abbreviated TEG, is an organogermanium compound with the formula (CH3CH2)4Ge. Tetraethylgermanium is an important chemical compound used in vapour deposition of germanium which is in a tetrahedral shape.
Synthesis.
Clemens Winkler first reported the compound in 1887 from diethylzinc and germanium tetrachloride, shortly after germanium was discovered in 1887.


Sulfur (pharmacy)

Sulfur is used in pharmaceutical skin preparations for the treatment of acne and other conditions. it acts as a keratolytic agent and also kills bacteria, fungi, scabies mites and other parasites.
Chemically, it is the naturally occurring octasulfur (S8).
Forms and uses.
Topical uses.
Precipitated sulfur and colloidal sulfur are used, in form of lotions, creams, powders, soaps, and bath additives, for the treatment of acne vulgaris, acne rosacea, and seborrhoeic dermatitis. Other topical uses included the treatment of superficial mycoses (infections with fungi) and scabies, but this is largely obsolete now.
Adverse effects.
Common adverse effects include irritation of the skin at the application site, such as dryness, stinging, itching and peeling. Generalised allergic reactions are rare; they include hives as well as swelling of lips, tongue, and throat, potentially closing up the respiratory tract.
Overdose.
Ingesting more than a few grams can lead to poisoning by hydrogen sulfide (H2S), which the gut flora produces from sulfur. H2S is also generated on the skin, but topical formulations do not induce toxic concentrations except when large quantities are used for small children.
Mechanism of action.
Sulfur is converted to hydrogen sulfide through reduction, partly by bacteria. H2S kills bacteria (possibly including "Propionibacterium acnes" which plays a role in acne), fungi, and parasites such as scabies mites. In the gut, H2S increases motility, acting as a laxative. Sulfur's keratolytic action is also mediated by H2S; in this case, the hydrogen sulfide is produced by direct interaction with the target keratinocytes themselves.


Organolithium reagent

Organolithium reagents are organometallic compounds that contain carbon – lithium bonds. These reagents are important in organic synthesis, and are frequently used to transfer the organic group or the lithium atom to the substrates in synthetic steps, through nucleophilic addition or simple deprotonation. Organolithium reagents are used in industry as an initiator for anionic polymerization, which leads to the production of various elastomers. They have also been applied in asymmetric synthesis in the pharmaceutical industry. Due to the large difference in electronegativity between the carbon atom and the lithium atom, the C-Li bond is highly ionic. Owing to the polar nature of the C-Li bond, organolithium reagents are good nucleophiles and strong bases. For laboratory organic synthesis, many organolithium reagents are commercially available in solution form. These reagents are highly reactive, and are sometimes pyrophoric.
History and development.
Studies of organolithium reagents began in the 1930s and were pioneered by Karl Ziegler, Georg Wittig, and Henry Gilman. In comparison with Grignard (magnesium) reagents, organolithium reagents can often perform the same reactions with increased rates and higher yields, such as in the case of metalation.
Since then, organolithium reagents have overtaken Grignard reagents in common usage.
Structure.
Although simple alkyllithium species are often represented as monomer RLi, they exist as aggregates (oligomers) or polymers.
The degree of aggregation depends on the organic substituent and the presence of other ligands. These structures have been elucidated by a variety of methods, notably 6Li, 7Li, and 13C NMR spectroscopy and X-ray diffraction analysis. Computational chemistry supports these assignments.
Nature of carbon-lithium bond.
The relative electronegativities of carbon and lithium suggest that the C-Li bond will be highly polar.
However, certain organolithium compounds possess properties such as solubility in nonpolar solvents that complicate the issue.
 While most data suggest the C-Li bond to be essentially ionic, there has been debate as to whether a small covalent character exists in the C-Li bond. One estimate puts the percentage of ionic character of alkyllithium compounds at 80 to 88%.
In allyl lithium compounds, the lithium cation coordinates to the face of the carbon π bond in an η3 fashion instead of a localized, carbanionic center, thus, allyllithiums are often less aggregated than alkyllithiums. In aryllithium complexes, the lithium cation coordinates to a single carbanion center through a Li-C σ type bond.
Solid state structure.
Like other species consisting of polar subunits, organolithium species aggregate.
Formation of aggregates is influenced by electrostatic interactions, the coordination between lithium and surrounding solvent molecules or polar additives, and steric effects.
A basic building block toward constructing more complex structures is a carbanionic center interacting with a Li3 triangle in an η- 3 fashion.
In simple alkyllithium reagents, these triangles aggregate to form tetrahedron or octahedron structures. For example, methyllithium, ethyllithium and "tert"-butyllithium all exist in the tetramer [RLi]4. Methyllithium exists as tetramers in a cubane-type cluster in the solid state, with four lithium centers forming a tetrahedron. Each methanide in the tetramer in methyllithium can have agostic interaction with lithium cations in adjacent tetramers.
Ethyllithium and "tert"-butyllithium, on the other hand, do not exhibit this interaction, and are thus soluble in non-polar hydrocarbon solvents. Another class of alkyllithium adopts hexameric structures, such as "n"-butyllithium, isopropyllithium, and cyclohexanyllithium.
Common lithium amides, e.g. lithium bis(trimethylsilyl)amide and lithium diisopropylamide, are also subject to aggregation. Lithium amides adopt polymeric-ladder type structures in non-coordinating solvent in the solid state, and they generally exist as dimers in ethereal solvents. In the presence of strongly donating ligands, tri- or tetrameric lithium centers are formed.
For example, LDA exists primarily as dimers in THF. The structures of common lithium amides, such as lithium diisopropylamide (LDA) and lithium hexamethyldisilazide (LiHMDS) have been extensively studied by Collum and coworkers using NMR spectroscopy.
Another important class of reagents is silyllithiums, extensively used in the synthesis of organometallic complexes and polysilane dendrimers.
In the solid state, in contrast with alkyllithium reagents, most silyllithiums tend to form monomeric structures coordinated with solvent molecules such as THF, and only a few silyllithiums have been characterized as higher aggregates.
This difference can arise from the method of preparation of silyllithiums, the steric hindrance caused by the bulky alkyl substituents on silicon, and the less polarized nature of Si-Li bonds. The addition of strongly donating ligands, such as TMEDA and (-)-sparteine, can displace coordinating solvent molecules in silyllithiums.
Solution structure.
Relying solely on the structural information of organolithium aggregates obtained in the solid state from crystal structures has certain limits, as it is possible for organolithium reagents to adopt different structures in reaction solution environment. Also, in some cases the crystal structure of an organolithium species can be difficult to isolate. Therefore, studying the structures of organolithium reagents, and the lithium-containing intermediates in solution form is extremely useful in understanding the reactivity of these reagents.
 NMR spectroscopy has emerged as a powerful tool for the studies of organolithium aggregates in solution. For alkyllithium species, C-Li "J" coupling can often used to determine the number of lithium interacting with a carbanion center, and whether these interactions are static or dynamic. Separate NMR signals can also differentiate the presence of multiple aggregates from a common monomeric unit.
The structures of organolithium compounds are affected by the presence of Lewis bases such as tetrahydrofuran (THF), diethyl ether (Et2O), tetramethylethylene diamine (TMEDA) or hexamethylphosphoramide (HMPA). Methyllithium is a special case, in which solvation with ether, or polar additive HMPA does not deaggregate the tetrameric structure in the solid state. On the other hand, THF deaggregates hexameric butyl lithium: the tetramer is the main species, and ΔG for interconversion between tetramer and dimer is around 11 kcal/mol. TMEDA can also chelate to the lithium cations in "n"-butyllithium and form solvated dimers such as [(TMEDA) LiBu-n)]2. Phenyllithium has been shown to exist as a distorted tetramer in the crystallized ether solvate, and as a mixture of dimer and tetramer in ether solution.
Structure and reactivity.
As the structures of organolithium reagents change according to their chemical environment, so do their reactivity and selectivity.
One question surrounding the structure-reactivity relationship is whether there exists a correlation between the degree of aggregation and the reactivity of organolithium reagents. It was originally proposed that lower aggregates such as monomers are more reactive in alkyllithiums.
However, reaction pathways in which dimer or other oligomers are the reactive species have also been discovered, and for lithium amides such as LDA, dimer-based reactions are common.
A series of solution kinetics studies of LDA - mediated reactions suggest that lower aggregates of enolates do not necessarily lead to higher reactivity.
Also, some Lewis bases increase reactivity of organolithium compounds.
However, whether these additives function as strong chelating ligands, and how the observed increase in reactivity relates to structural changes in aggregates caused by these additives are not always clear.
For example, TMEDA increases rates and efficiencies in many reactions involving organolithium reagents. Toward alkyllithium reagents, TMEDA functions as a donor ligand, reduces the degree of aggregation, and increases the nucleophilicity of these species.
However, TMEDA does not always function as a donor ligand to lithium cation, especially in the presence of anionic oxygen and nitrogen centers. For example, it only weakly interacts with LDA and LiHMDS even in hydrocarbon solvents with no competing donor ligands.
In imine lithiation, while THF acts as a strong donating ligand to LiHMDS, the weakly coordinating TMEDA readily dissociates from LiHMDS, leading to the formation of LiHMDS dimers that is the more reactive species. Thus, in the case of LiHMDS, TMEDA does not increase reactivity by reducing aggregation state. Also, as opposed to simple alkyllithium compounds, TMEDA does not deaggregate lithio-acetophenolate in THF solution.
The addition of HMPA to lithium amides such as LiHMDS and LDA often results in a mixture of dimer/monomer aggregates in THF. However, the ratio of dimer/monomer species does not change with increased concentration of HMPA, thus, the observed increase in reactivity is not the result of deaggregation. The mechanism of how these additives increase reactivity is still being researched.
Reactivity and applications.
The C-Li bond in organolithium reagents is highly polarized. As a result, the carbon attracts most of the electron density in the bond and resembles a carbanion. Thus, organolithium reagents are strongly basic and nucleophilic. Some of the most common applications of organolithium reagents in synthesis include their use as nucleophiles, strong bases for deprotonation, initiator for polymerization, and starting material for the preparation of other organometallic compounds.
As nucleophile.
Carbolithiation reactions.
As nucleophiles, organolithium reagents undergo carbolithiation reactions, whereby the carbon-lithium bond adds across a carbon-carbon double or triple bond, forming new organolithium species. This reaction is the most widely employed reaction of organolithium compounds. Carbolithiation is key in anionic polymerization processes, and "n"-butyllithium is used as a catalyst to initiate the polymerization of styrene, butadiene, or isoprene or mixtures thereof.
Another application that takes advantage of this reactivity is the formation of carbocyclic and heterocyclic coumpounds by intramolecular carbolithiation. As a form of anionic cyclization, intramolecular carbolithiation reactions offer several advantages over radical cyclization. First, it is possible for the product cyclic organolithium species to react with electrophiles, whereas it is often difficult to trap a radical intermediate of the corresponding structure. Secondly, anionic cyclizations are often more regio- and stereospecific than radical cyclization, particularly in the case of 5-hexenyllithiums. Intramolecular carbolithiation allows addition of the alkyl-, vinyllithium to triple bonds and mono-alkyl substituted double bonds. Aryllithiums can also undergo addition if a 5-membered ring is formed. The limitations of intramolecular carbolithiation include difficulty of forming 3 or 4-membered rings, as the intermediate cyclic organolithium species often tend to undergo ring-openings. Below is an example of intramolecular carbolithiation reaction. The lithium species derived from the lithium-halogen exchange cyclized to form the vinyllithium through 5-exo-trig ring closure. The vinyllithium species further reacts with electrophiles and produce functionalized cyclopentylidene compounds.
Addition to carbonyl compounds.
Nucleophilic organolithium reagents can add to electrophilic carbonyl double bonds to form carbon-carbon bonds. They can react with aldehydes and ketones to produce alcohols. The addition proceeds mainly via polar addition, in which the nucleophilic organolithium species attacks from the equatorial direction, and produces the axial alcohol. Addition of lithium salts such as LiClO4 can improve the stereoselectivity of the reaction.
When the ketone is sterically hindered, using Grignard reagents often leads to reduction of the carbonyl group instead of addition. However, alkyllithium reagents are less likely to reduce the ketone, and may be used to synthesize substituted alcohols. Below is an example of ethyllithium addition to adamantone to produce tertiary alcohol.
Organolithium reagents are also better than Grignard reagents in their ability to react with carboxylic acids to form ketones. This reaction can be optimized by carefully controlling the amount of organolithium reagent addition, or using trimethylsilyl chloride to quench excess lithium reagent. A more common way to synthesize ketones is through the addition of organolithium reagents to Weinreb amides (N-methoxy-N-methyl amides). This reaction provides ketones when the organolithium reagents is used in excess, due to chelation of the lithium ion between the N-methoxy oxygen and the carbonyl oxygen, which forms a tetrahedral intermediate that collapses upon acidic work up.
Organolithium reagents also react with carbon dioxide to form, after workup, carboxylic acids.
In the case of enone substrates, where two sites of nucleophilic addition are possible (1,2 addition to the carbonyl carbon or 1,4 conjugate addition to the β carbon), most highly reactive organolithium species favor the 1,2 addition, however, there are several ways to propel organolithium reagents to undergo conjugate addition. First, since the 1,4 adduct is the likely to be the more thermodynamically favorable species, conjugate addition can be achieved through equilibration (isomerization of the two product), especially when the lithium nucleophile is weak and 1,2 addition is reversible. Secondly, adding donor ligands to the reaction forms heteroatom-stabilized lithium species which favors 1,4 conjugate addition. In one example, addition of low-level of HMPA to the solvent favors the 1,4 addition. In the absence of donor ligand, lithium cation is closely coordinated to the oxygen atom, however, when the lithium cation is solvated by HMPA, the coordination between carbonyl oxygen and lithium ion is weakened. This method generally cannot be used to affect the regioselectivity of alkyl- and aryllithium reagents.
Organolithium reagents can also perform enantioselective nucleophilic addition to carbonyl and its derivatives, often in the presence of chiral ligands. This reactivity is widely applied in the industrial syntheses of pharmaceutical compounds. An example is the Merck and Dupont synthesis of Efavirenz, a potent HIV reverse transcriptase inhibitor. Lithium acetylide is added to a prochiral ketone to yield a chiral alcohol product. The structure of the active reaction intermediate was determined by NMR spectroscopy studies in the solution state and X-ray crystallography of the solid state to be a cubic 2:2 tetramer.
SN2 type reactions.
Organolithium reagents can serve as nucleophiles and carry out SN2 type reactions with alkyl or allylic halides.
Although they are considered more reactive than Grignards reactions in alkylation, their use is still limited due to competing side reactions such as radical reactions or metal-halogen exchange. Most organolithium reagents used in a alkylations are more stabilized, less basic, and less aggregated, such as heteroatom stabilized, aryl- or allyllithium reagents. HMPA has been shown to increase reaction rate and product yields, and the reactivity of aryllithium reagents is often enhanced by the addition of potassium alkoxides. Organolithium reagents can also carry out nucleophilic attacks with epoxides to form alcohols.
As base.
Organolithium reagents provide a wide range of basicity. "tert"-Butyllithium, with three weakly electron donating alkyl groups, is the strongest base commercially available (pKa = 53). As a result, the acidic protons on -OH, -NH and -SH are often protected in the presence of organolithium reagents. Some commonly used lithium bases are alkyllithium species such as "n"-butyllithium and lithium dialkylamides (LiNR2). Reagents with bulky R groups such as lithium diisopropylamide (LDA) and lithium bis(trimethylsilyl)amide (LiHMDS) are often sterically hindered for nucleophilic addition, and are thus more selective toward deprotonation. Lithium dialkylamides (LiNR2) are widely used in enolate formation and aldol reaction. The reactivity and selectivity of these bases are also influenced by solvents and other counter ions.
Metalation.
Metalation with organolithium reagents, also known as lithiation or lithium-hydrogen exchange, is achieved when an organolithium reagent, most commonly an alkyllithium, abstracts a proton and forms a new organolithium species.
Common metalation reagents are the butyllithiums. "tert"-Butyllithium and "sec-"butyllithium are generally more reactive and have better selectivity than "n"-butyllithium, however, they are also more expensive and difficult to handle. Metalation is a common way of preparing versatile organolithium reagents. The position of metalation is mostly controlled by the acidity of the C-H bond. Lithiation often occurs at a position α to electron withdrawing groups, since they are good at stabilizing the electron-density of the anion. Directing groups on aromatic compounds and heterocycles provide regioselective sites of metalation; directed ortho metalation is an important class of metalation reactions. Metalated sulfones, acyl groups and α-metalated amides are important intermediates in chemistry synthesis. Metalation of allyl ether with alkyllithium or LDA forms an anion α to the oxygen, and can proceed to 2,3-Wittig rearrangement. Addition of donor ligands such as TMEDA and HMPA can increase metalation rate and broaden substrate scope. Chiral organolithium reagents can be accessed through asymmetric metalation.
Directed ortho metalation is an important tool in the synthesis of regiospecific substituted aromatic compounds. This approach to lithiation and subsequent quenching of the intermediate lithium species with electrophile is often better than the electrophilic aromatic substitution due to its high regioselectivity. This reaction proceeds through deprotonation by organolithium reagents at the positions α to the direct metalation group (DMG) on the aromatic ring. The DMG is often a functional group containing a heteroatom that is Lewis basic, and can coordinate to the Lewis-acidic lithium cation. This generates a complex-induced proximity effect, which directs deprotonation at the α position to form an aryllithium species that can further react with electrophiles. Some of the most effective DMGs are amides, carbamates, sulfones and sulfonamides. They are strong electron-withdrawing groups that increase the acidity of alpha-protons on the aromatic ring. In the presence of two DMGs, metalation often occurs ortho to the stronger directing group, though mixed products are also observed. A number of heterocycles that contain acidic protons can also undergo ortho-metalation. However, for electron-poor heterocycles, lithium amide bases such as LDA are generally used, since alkyllithium has been observed to perform addition to the electron-poor heterocycles rather than deprotonation. In certain transition metal-arene complexes, such as ferrocene, the transition metal attracts electron-density from the arene, thus rendering the aromatic protons more acidic, and ready for ortho-metalation.
Superbases.
Addition of potassium alkoxide to alkyllithium greatly increases the basicity of organolithium species. The most common "superbase" can be formed by addition of KOtBu to butyllithium, often abbreviated as "LiCKOR" reagents. These "superbases" are highly reactive and often stereoselective reagents. In the example below, the LiCKOR base generates a stereospecific crotylboronate species through metalation and subsequent lithium-metalloid exchange.
Asymmetric metalation.
Enantioenriched organlithium species can be obtained through asymmetric metalation of prochiral substrates. Asymmetric induction requires the presence of a chiral ligand such as (-)-sparteine. The enantiomeric ratio of the chiral lithium species is often influenced by the differences in rates of deprotonation. In the example below, treatment of "N"-Boc-"N"-benzylamine with "n"-butyllithium in the presence of (-)-sparteine affords one enantiomer of the product with high enantiomeric excess. Transmetalation with trimethyltinchloride affords the opposite enantiomer.
Enolate formation.
Lithium enolates are formed through deprotonation of a C-H bond α to the carbonyl group by an organolithium species. Lithium enolates are widely used as nucleophiles in carbon-carbon bond formation reactions such as aldol condensation and alkylation. They are also an important intermediate in the formation of silyl enol ether.
Lithium enolate formation can be generalized as an acid-base reaction, in which the relatively acidic proton α to the carbonyl group (pK =20-28 in DMSO) reacts with organolithium base. Generally, strong, non-nucleophilic bases, especially lithium amides such LDA, LiHMDS and LiTMP are used. THF and DMSO are common solvents in lithium enolate reactions.
The stereochemistry and mechanism of enolate formation have gained much interest in the chemistry community. Many factors influence the outcome of enolate stereochemistry, such as steric effects, solvent, polar additives, and types of organolithium bases. Among the many models used to explain and predict the selectivity in stereochemistry of lithium enolates is the Ireland model.
In this assumption, a monomeric LDA reacts with the carbonyl substrate and form a cyclic Zimmerman-Traxler type transition state. The (E)-enolate is favored due to an unfavorable "syn-pentane" interaction in the (Z)-enolate transition state.
Addition of polar additives such as HMPA or DMPU favors the formation of (Z) enolates. The Ireland model argues that these donor ligands coordinate to the lithium cations, as a result, carbonyl oxygen and lithium interaction is reduced, and the transition state is not as tightly bound as a six-membered chair. The percentage of (Z) enolates also increases when lithium bases with bulkier side chains (such as LiHMDS) are used. However, the mechanism of how these additives reverse stereoselectivity is still being debated.
There have been some challenges to the Ireland model, as it depicts the lithium species as a monomer in the transition state. In reality, a variety of lithium aggregates are often observed in solutions of lithium enolates, and depending on specific substrate, solvent and reaction conditions, it can be difficult to determine which aggregate is the actual reactive species in solution.
Lithium-halogen exchange.
Lithium-halogen exchange involves heteroatom exchange between an organohalide and organolithium species.
Lithium-halogen exchange is very useful in preparing new organolithium reagents. The application of lithium-halogen exchange is illustrated by the Parham cyclization.
Transmetalation.
Organolithium reagents are often used to prepare other organometallic compounds by transmetalation. Organocopper, organotin, organosilicon, organoboron, organophosphorus, organocerium and organosulfur compounds are frequently prepared by reacting organolithium reagents with appropriate electrophiles.
Common types of transmetalation include Li/Sn, Li/Hg, and Li/Te exchange, which are fast at low temperature. The advantage of Li/Sn exchange is that the tri-alkylstannane precursors undergo few side reactions, as the resulting n-Bu3Sn byproducts are unreactive toward alkyllithium reagents. In the following example, vinylstannane, obtained by hydrostannylation of a terminal alkyne, forms vinyllithium through transmetalation with n-BuLi.
Organolithium can also be used in to prepare organozinc compounds through transmetalation with zinc salts.
Lithium diorganocuprates can be formed by reacting alkyl lithium species with copper(I) halide. The resulting organocuprates are generally less reactive toward aldehydes and ketones than organolithium reagents or Grignard reagents.
Preparation.
Most simple alkyllithium reagents, and common lithium amides are commercially available in a variety of solvents and concentrations. Organolithium reagents can also be prepared in the laboratory. Below are some common methods for preparing organolithium reagents.
Reaction with lithium metal.
Reduction of alkyl halide with metallic lithium can afford simple alkyl and aryl organolithium reagents.
Industrial preparation of organolithium reagents is achieved using this method by treating the alkyl chloride with metal lithium containing 0.5-2% sodium. The conversion is highly exothermic. The sodium initiates the radical pathway and increases the rate. The reduction proceeds via a radical pathway. Below is an example of the preparation of a functionalized lithium reagent using reduction with lithium metal. Sometimes, lithium metal in the form of fine powders are used in the reaction with certain catalysts such as naphthalene or 4,4’-di-t-butylbiphenyl (DTBB). Another substrate that can be reduced with lithium metal to generate alkyllithium reagents is sulfides. Reduction of sulfides is useful in the formation of functionalized organolithium reagents such as alpha-lithio ethers, sulfides, and silanes.
Metalation.
A second method of preparing organolithium reagents is a metalation (lithium hydrogen exchange). The relative acidity of hydrogen atoms controls the position of lithiation.
This is the most common method for preparing alkynyllithium reagents, because the terminal hydrogen bound to the "sp" carbon is very acidic and easily deprotonated. For aromatic compounds, the position of lithiation is also determined by the directing effect of substituent groups. Some of the most effective directing substituent groups are alkoxy, amido, sulfoxide, sulfonyl. Metalation often occurs at the position ortho to these substituents. In heteroaromatic compounds, metalation usually occurs at the position ortho to the heteroatom.
Lithium halogen exchange.
See lithium-halogen exchange (under Reactivity and applications)
A third method to prepare organolithium reagents is through lithium halogen exchange.
"tert-"butyllithium or "n-"butyllithium are the most commonly used reagents for generating new organolithium species through lithium halogen exchange. Lithium-halogen exchange is mostly used to convert aryl and alkenyl iodides and bromides with "sp2" carbons to the corresponding organolithium compounds. The reaction is extremely fast, and often proceed at -60 to -120 °C.
Transmetalation.
The fourth method to prepare organolithium reagents is through transmetalation. This method can be used for preparing vinyllithium.
Shapiro reaction.
In the Shapiro reaction, two equivalents of strong alkyllithium base react with p-tosylhydrazone compounds to produce the vinyllithium, or upon quenching, the olefin product.
Handling.
Organolithium compounds are highly reactive species and require specialized handling techniques. They are often corrosive, flammable, and sometimes pyrophoric (spontaneous ignition when exposed to air or moisture). Alkyllithium reagents can also undergo thermal decomposition to form the corresponding alkyl species and lithium hydride. Organolithium reagents are typically stored below 10 °C. Reactions are conducted using air-free techniques. The concentration of alkyllithium reagents is often determined by titration.
Organolithium reagents react, often slowly, with ethers, which nonetheless are often used as solvents.


Bunsenite

Bunsenite is the naturally occurring form of nickel(II) oxide, NiO. It occurs as rare dark green crystal coatings. It crystallizes in the cubic crystal system and occurs as well formed cubic, octahedral and dodecahedral crystals. It is a member of the periclase group.
It was first described in 1868 for a sample from a hydrothermal nickel-uranium vein from Johanngeorgenstadt, Erzgebirge, Saxony, Germany and named for German chemist Robert William Eberhard Bunsen (1811–1899). Other occurrences include west of the Scotia talc mine near Bon Accord, Barberton district, Transvaal, South Africa and from Kambalda south of Kalgoorlie, Western Australia. The South African occurrence has evidence of thermal metamorphism of a nickel-rich meteorite. It occurs associated with native bismuth, annabergite, aerugite, xanthiosite in Germany; and with liebenbergite, trevorite, nickeloan serpentine, nickeloan ludwigite, violarite, millerite, gaspeite, nimite and bonaccordite in the South African occurrence.


Wiklundite

Wiklundite is a rare and complex arsenite-silicate mineral with the formula Pb2(Mn2+,Zn)3(Fe3+,Mn2+)2(Mn2+,Mg)19(As3+O3)2(Si,As5+O4)6(OH)18Cl6. The mineral characterizes in a large "c" unit cell parameter. It was found in Långban, Sweden - a home for many rare and exotic minerals.
Relation to other minerals.
Structure of wiklundite is unique. A slightly chemically similar mineral, although lacking manganese and iron, is hereroite.


Vanadium(II) chloride

Vanadium(II) chloride is the inorganic compound with the formula VCl2, and is the most reduced vanadium chloride. Vanadium(II) chloride is an apple-green solid that dissolves in water to give purple solutions.
Preparation, properties, and related compounds.
Solid VCl2 is prepared by thermal decomposition of VCl3, which leaves a residue of VCl2:
VCl2 dissolves in water to give the purple hexaaquo ion [V(H2O)6]2+. Evaporation of such solutions produces crystals of [V(H2O)6]Cl2.
Structure.
Solid VCl2 adopts the cadmium iodide structure, featuring octahedral coordination geometry. VBr2 and VI2 are structurally and chemically similar to the dichloride. All have the d3 configuration, with a quartet ground state, akin to Cr(III).
Vanadium dichloride is a powerful reducing species, being able to convert sulfoxides to sulfides, organic azides to amines, as well as reductively coupling some alkyl halides.


Calamine (mineral)

Calamine is a historic name for an ore of zinc. The name "calamine" was derived from "lapis calaminaris", a Latin corruption of Greek "cadmia (καδμία)", the old name for zinc ores in general. The name of the Belgian town of Kelmis, "La Calamine" in French, which was home to a zinc mine, comes from this. In the 18th and 19th centuries large ore mines could be found near the German village of Breinigerberg.
During the early 19th century it was discovered that what had been thought to be one ore was actually two distinct minerals:
Although chemically and crystallographically quite distinct, the two minerals exhibit similar massive or botryoidal external form and are not readily distinguished without detailed chemical or physical analysis. The first person to separate the minerals was the British chemist and mineralogist James Smithson in 1803. In the mining industry the term calamine has been historically used to refer to both minerals indiscriminately.
In mineralogy calamine is no longer considered a valid term. It has been replaced by smithsonite and hemimorphite in order to distinguish it from the pinkish mixture of zinc oxide (ZnO) and iron(III) oxide (Fe2O3) used in calamine lotion.
Early history.
In the 16th century demand for latten (brass) in England came from the needs of wool-carding, for which brass-wire combs were preferred, and battery pieces (brassware formed by hammering sheet brass in a battery mill). The only known method for producing the alloy was by heating copper and calamine together in the cementation process and in 1568 a royal charter was granted to the Society of the Mineral and Battery Works to search for the mineral and produce brass, to reduce dependence on imported metal from Germany. Factories to exploit the process were established at Isleworth and Rotherhithe. By the late 17th century enough was known of metallic zinc to make brass solder directly by combining copper and spelter (zinc ingots). In 1738 a patent was granted to William Champion, a Bristol brass founder, for the large-scale reduction of calamine to produce spelter.
In 1684 a paper presented to the Royal Society touched on the medicinal and veterinary properties of the compound when in finely powdered form. Since then no mechanism of action for the powder has been identified, and the only medical effect of the powdered mineral appears to be its ability to absorb moisture secreted from irritated and weeping skin.


Tetramethyltin

Tetramethyltin is an organometallic compound with the formula (CH3)4Sn. This liquid, one of the simplest organotin compounds, is useful for transition-metal mediated conversion of acid chlorides to methyl ketones and aryl halides to aryl methyl ketones. It is volatile and toxic, so care should be taken when using it in the laboratory.
Synthesis and structure.
Tetramethyltin is synthesized by reaction of the Grignard reagent methylmagnesium iodide, with tin tetrachloride, which is synthesized by reacting tin metal with chlorine gas.
In tetramethyltin, the metal surrounded by four methyl groups in a tetrahedral structure is a heavy analogue of neopentane.
Applications.
Precursor to methyltin compounds.
Tetramethyltin is a precursor to trimethyltin chloride (and related methyltin halides), which are precursors to other organotin compounds. These methyltin chlorides are prepared via the so-called Kocheshkov redistribution reaction. Thus, (CH3)4Sn and SnCl4 are allowed to react at temperatures between 100 °C and 200 °C to give (CH3)3SnCl as a product:
A second route to trimethyltin chloride utilizing tetramethyltin involves the reaction of mercury(II) chloride to react with (CH3)4Sn.
A variety of methyltin compounds are used as precursors for stabilizers in PVC. Di- and trimercaptotin compounds are used to inhibit the dehydrochlorination, which is the pathway for photolytic and thermal degradation of PVC.
Surface functionalization.
Tetramethyltin decomposes in the gas phase at about 277 °C; (CH3)4Sn vapor reacts with silica to give a (CH3)3Sn-grafted solid.
This reaction is also possible with other alkyl substituents. In a similar process, tetramethyltin has been used to functionalize certain zeolites at temperatures as low as −90 °C.
Applications in organic synthesis.
In organic synthesis, tetramethyltin undergoes palladium-catalyzed coupling reactions with acid chlorides to give methyl ketones:


Dichloroacetamide

Dichloroacetamide is a chlorinated derivative of acetamide.


Organoneptunium chemistry

Organoneptunium chemistry is the chemical science exploring the properties, structure and reactivity of organoneptunium compounds, which are organometallic compounds containing a carbon to neptunium chemical bond. Several such compounds exist even though the element itself, neptunium, is man-made and highly radioactive: tricyclopentadienylneptunium-chloride, tetrakis(cyclopentadienyl)neptunium(IV) and neptunocene Np(C8H8)2.


YF-77

The YF-77 is China's first cryogenic rocket engine developed for booster applications. It burns liquid hydrogen fuel and liquid oxygen oxidizer using a gas generator cycle. A pair of these engines powers the LM-5 core stage. Each engine can independently gimbal in two planes. Although the YF-77 is ignited prior to liftoff, the LM-5's four strap-on boosters provide most of the initial thrust in an arrangement similar to the European Vulcain on the Ariane 5 or the Japanese LE-7 on the H-II.
Development.
In January 2002, the development of a new cryogenic engines was approved by the Commission for Science, Technology and Industry for National Defense. The development responsibility was assigned to the Beijing Aerospace Propulsion Institute, a division of the Academy of Aerospace Launch Propulsion Technology. The preliminary design was accomplished by mid-2002 and the first set of components was manufactured by early 2003. The same year saw the initial component and subsystem tests, with the gas generator successfully performing its first test on July 30. By December 2003 the whole powerpack successfully passed its first integrated test, and on September 17, 2004 a successful 50-second firing of a complete prototype engine was achieved.
In May 2013 the formal qualification testing campaign began. By the end of 2013 more than 70 tests and 24,000 seconds of firing at steady state conditions had been performed by 12 engines. The concept review confirmed that the performance goal and launcher requirements were met, and the engine was ready for integration for the first launch of the Long March 5 rocket.
Engine development began in the 2000s, with testing directed by the China National Space Administration (CNSA) commencing in 2005. The engine has been successfully tested by mid-2007.
Technical description.
The requirements for an inexpensive, highly reliable, disposable engine are met by using dual (sea level) gas generator engines on a single mounting frame. Each engine has dual turbopumps with separate gas exhaust. Both turbines are fed by a single fuel rich gas generator. The combustion chambers and throat are regeneratively cooled, while the nozzle, of welded pipe construction, uses dump cooling. The turbopumps use solid propellant cartridges for start-up, while the gas generator and combustion chamber use pyrotechnic igniters. The valves and prevalves are helium-actuated ball valves. The thrust and mixture ratio are calibrated with venturis and a propellant utilization valve on ground tests. The engine also has dual heat exchanger to supply hot gaseous hydrogen and oxygen for tank pressurization.
All subsystems are attached to the combustion chamber and gimbal is achieved by rotating the whole engine on two orthogonal planes with two independent actuators. The injector plate uses coaxial injectors, some of which are extended to create baffles that prevent high frequency instabilities. The titanium fuel turbopump uses a two-stage pump with inducer and is actuated by a two-stage axial turbine. It rotates at 35,000 rpm and supplies a discharge pressure of . The oxidizer turbopump uses a single-stage centrifugal pump with a helical inducer driven by a two-stage turbine. It rotates at 18,000 rpm and supplies a discharge pressure of .


Titanyl sulfate

Titanyl sulfate is the inorganic compound with the formula TiOSO4. It is a white solid that forms by treatment of titanium dioxide with fuming sulfuric acid. It hydrolyzes to a gel of hydrated titanium dioxide. The structure consists of dense polymeric network with tetrahedral sulfur and octahedral titanium centers. The six ligands attached to titanium are derived from four different sulfate moieties and a bridging oxide. A monohydrate is also known, being prepared similarly to the anhydrous material. In the hydrate, one Ti–OS bond is replaced by Ti–OH2.


Armilenium

Armilenium is a C11H11 carbocation and was originally proposed as the first entirely organic sandwich compound. Named for its resemblance to an armillary sphere, NMR evidence for the carbocation was first described by Melvin J. Goldstein and Stanley A. Klein at Cornell University in 1973. In subsequent 13C NMR experiments by Goldstein and Joseph P. Dinnocenzo in 1984, the C11H11 carbocation was generated under stable ion conditions at lower temperature and at higher magnetic field than previously possible. These experiments revealed the carbocation to be fluxional. Fitting of the dynamic NMR process ruled out the sandwich species even as an intermediate in the 20-fold degenerate rearrangement of the carbocation.


Brianyoungite

Brianyoungite is a secondary zinc carbonate mineral. The Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association (IMA) classifies it as a carbonate with the formula Zn3(CO3)(OH)4, but sulfate groups SO4 also occupy the carbonate CO3 positions, in the ratio of about one sulfate to three carbonates, so other sources give the formula as Zn3(CO3,SO4)(OH)4, and Gaines et al. classify the mineral as a compound carbonate. It is
similar in appearance to hydrozincite, another zinc carbonate. It was discovered in 1991 and designated IMA1991-053. In 1993 it was named "brianyoungite" after Brian Young (born 1947), a field geologist with the British Geological Survey, who provided the first specimens.
Appearance.
The mineral occurs as tiny rosettes less than 100 µm across, composed of thin blades just one or two micrometers across, elongated parallel to the b crystal axis, and tapering to a sharp point. The crystals are white and transparent to translucent, with a vitreous lustre and a white streak.
Structure.
The mineral belongs in the orthorhombic crystal system, or the monoclinic with β (the angle between the a and c crystal axes) close to 90o. The space group is unknown, but assumed to be either P21/m, P21 or P2221. The structure is similar to that of hydrozincite. There are four formula units per unit cell (Z = 4) and the lengths of the sides of the unit cell are a = 15.724 Å, b = 6.256 Å and c = 5.427 Å.
Physical properties.
Brianyoungite is a soft mineral with Mohs hardness similar to halite, only 2 to according to some sources, but others say that the hardness is not determinable. It is fairly dense, with specific gravity 3.93 to 4.09, similar to that of celestine. Cleavage is perfect perpendicular to the a crystal axis (perfect on {100}) and possible perpendicular to the c crystal axis (possible on {001}). It is readily soluble with effervescence in acids.
Optical properties.
The mineral is biaxial, with refractive indices nω = 1.635 and nε = 1.650 and maximum birefringence δ = 1.635. It exhibits straight extinction. It is not fluorescent.
Occurrence.
The type locality is the Bloomsberry Horse level of the Brownley Hill mine, Nenthead, Alston Moor District, North Pennines, North and Western Region (Cumberland), Cumbria, England. The type material is conserved at the Royal Museum of Scotland, Edinburgh, Scotland, 1992.17.1–8.
Brianyoungite occurs with gypsum on rubbly limestone in the oxidised zone of Brownley Hill Mine, and on specimens from the nearby Smallcleugh mine. It may be a secondary post-mining mineral.
At the type locality it is associated with gypsum, smithsonite, pyrite and goethite.