Ruthenium borides are compounds of ruthenium and boron. Their most remarkable property is high hardness. Vickers hardness HV = 50 GPa was reported for thin films composed of Ru2B3 phases; this value is higher than those of bulk RuB2 or Ru2B3, but it has to be confirmed independently, as measurements on superhard materials are intrinsically difficult. For example, note that the initial report on extreme hardness of related material rhenium diboride was too optimistic. Ruthenium diboride was first thought to have a hexagonal structure, as in rhenium diboride, but it was tentatively determined to possess an orthorhombic structure
In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies between different classes of hydrates, some of which were so labeled before their chemical structure was understood. In organic chemistry, a hydrate is a compound formed by the addition of water or its elements to another molecule. For example: ethanol, CH3–CH2–OH, is the product of the hydration reaction of ethene, CH2=CH2, formed by the addition of H to one C and OH to the other C, so can be considered as the hydrate of ethene. A molecule of water may be eliminated, for example by the action of sulfuric acid. Another example is chloral hydrate, CCl3–CH2, which can be formed by reaction of water with chloral, CCl3–CH=O. Many organic molecules, as well as inorganic molecules, form crystals that incorporate water into the crystalline structure without chemical alteration of the organic molecule; the sugar trehalose, for example, exists as a dihydrate. Protein crystals have as much as 50% water content.
Molecules are labeled as hydrates for historical reasons not covered above. Glucose, C6H12O6, was thought of as C66 and described as a carbohydrate. Methanol is sold as "methyl hydrate", implying the incorrect formula CH3OH2, while the correct formula is CH3–OH. Hydrates are inorganic salts "containing water molecules combined in a definite ratio as an integral part of the crystal" that are either bound to a metal center or that have crystallized with the metal complex; such hydrates are said to contain water of crystallization or water of hydration. If the water is heavy water, where the hydrogen involved is the isotope deuterium the term deuterate may be used in place of hydrate. A colorful example is cobalt chloride, which turns from blue to red upon hydration, can therefore be used as a water indicator; the notation "hydrated compound⋅nH2O", where n is the number of water molecules per formula unit of the salt, is used to show that a salt is hydrated. The n is a low integer, though it is possible for fractional values to occur.
For example, in a monohydrate n is one, in a hexahydrate n is 6. Numerical prefixes of Greek origin are: A hydrate which has lost water is referred to as an anhydride. A substance that does not contain any water is referred to as anhydrous; some anhydrous compounds are hydrated so that they are said to be hygroscopic and are used as drying agents or desiccants. Clathrate hydrates are water ice with gas molecules trapped within. An important example is methane hydrate. Nonpolar molecules such as methane can form clathrate hydrates with water under high pressure. Although there is no hydrogen bonding between water and guest molecules when methane is the guest molecule of the clathrate, guest-host hydrogen bonding forms when the guest is a larger organic molecule such as tetrahydrofuran. In such cases the guest-host hydrogen bonds result in the formation of L-type Bjerrum defects in the clathrate lattice; the stability of hydrates is determined by the nature of the compounds, their temperature, the relative humidity
European Chemicals Agency
The European Chemicals Agency is an agency of the European Union which manages the technical and administrative aspects of the implementation of the European Union regulation called Registration, Evaluation and Restriction of Chemicals. ECHA is the driving force among regulatory authorities in implementing the EU's chemicals legislation. ECHA helps companies to comply with the legislation, advances the safe use of chemicals, provides information on chemicals and addresses chemicals of concern, it is located in Finland. The agency headed by Executive Director Bjorn Hansen, started working on 1 June 2007; the REACH Regulation requires companies to provide information on the hazards and safe use of chemical substances that they manufacture or import. Companies register this information with ECHA and it is freely available on their website. So far, thousands of the most hazardous and the most used substances have been registered; the information is technical but gives detail on the impact of each chemical on people and the environment.
This gives European consumers the right to ask retailers whether the goods they buy contain dangerous substances. The Classification and Packaging Regulation introduces a globally harmonised system for classifying and labelling chemicals into the EU; this worldwide system makes it easier for workers and consumers to know the effects of chemicals and how to use products safely because the labels on products are now the same throughout the world. Companies need to notify ECHA of the labelling of their chemicals. So far, ECHA has received over 5 million notifications for more than 100 000 substances; the information is available on their website. Consumers can check chemicals in the products. Biocidal products include, for example, insect disinfectants used in hospitals; the Biocidal Products Regulation ensures that there is enough information about these products so that consumers can use them safely. ECHA is responsible for implementing the regulation; the law on Prior Informed Consent sets guidelines for the import of hazardous chemicals.
Through this mechanism, countries due to receive hazardous chemicals are informed in advance and have the possibility of rejecting their import. Substances that may have serious effects on human health and the environment are identified as Substances of Very High Concern 1; these are substances which cause cancer, mutation or are toxic to reproduction as well as substances which persist in the body or the environment and do not break down. Other substances considered. Companies manufacturing or importing articles containing these substances in a concentration above 0,1% weight of the article, have legal obligations, they are required to inform users about the presence of the substance and therefore how to use it safely. Consumers have the right to ask the retailer whether these substances are present in the products they buy. Once a substance has been identified in the EU as being of high concern, it will be added to a list; this list is available on ECHA's website and shows consumers and industry which chemicals are identified as SVHCs.
Substances placed on the Candidate List can move to another list. This means that, after a given date, companies will not be allowed to place the substance on the market or to use it, unless they have been given prior authorisation to do so by ECHA. One of the main aims of this listing process is to phase out SVHCs where possible. In its 2018 substance evaluation progress report, ECHA said chemical companies failed to provide “important safety information” in nearly three quarters of cases checked that year. "The numbers show a similar picture to previous years" the report said. The agency noted that member states need to develop risk management measures to control unsafe commercial use of chemicals in 71% of the substances checked. Executive Director Bjorn Hansen called non-compliance with REACH a "worry". Industry group CEFIC acknowledged the problem; the European Environmental Bureau called for faster enforcement to minimise chemical exposure. European Chemicals Bureau Official website
In chemistry, a salt is an ionic compound that can be formed by the neutralization reaction of an acid and a base. Salts are composed of related numbers of cations and anions so that the product is electrically neutral; these component ions can be inorganic, such as organic, such as acetate. Salts can be classified in a variety of ways. Salts that produce hydroxide ions when dissolved in water are called alkali salts. Salts that produce acidic solutions are acidic salts. Neutral salts are those salts that are neither basic. Zwitterions contain an anionic and a cationic centres in the same molecule, but are not considered to be salts. Examples of zwitterions include amino acids, many metabolites and proteins. Solid salts tend to be transparent. In many cases, the apparent opacity or transparency are only related to the difference in size of the individual monocrystals. Since light reflects from the grain boundaries, larger crystals tend to be transparent, while the polycrystalline aggregates look like white powders.
Salts exist in many different colors, which arise either from the cations. For example: sodium chromate is yellow by virtue of the chromate ion potassium dichromate is orange by virtue of the dichromate ion cobalt nitrate is red owing to the chromophore of hydrated cobalt. copper sulfate is blue because of the copper chromophore potassium permanganate has the violet color of permanganate anion. Nickel chloride is green of sodium chloride, magnesium sulfate heptahydrate are colorless or white because the constituent cations and anions do not absorb in the visible part of the spectrumFew minerals are salts because they would be solubilized by water. Inorganic pigments tend not to be salts, because insolubility is required for fastness; some organic dyes are salts, but they are insoluble in water. Different salts can elicit all five basic tastes, e.g. salty, sour and umami or savory. Salts of strong acids and strong bases are non-volatile and odorless, whereas salts of either weak acids or weak bases may smell like the conjugate acid or the conjugate base of the component ions.
That slow, partial decomposition is accelerated by the presence of water, since hydrolysis is the other half of the reversible reaction equation of formation of weak salts. Many ionic compounds exhibit significant solubility in water or other polar solvents. Unlike molecular compounds, salts dissociate in solution into cationic components; the lattice energy, the cohesive forces between these ions within a solid, determines the solubility. The solubility is dependent on how well each ion interacts with the solvent, so certain patterns become apparent. For example, salts of sodium and ammonium are soluble in water. Notable exceptions include potassium cobaltinitrite. Most nitrates and many sulfates are water-soluble. Exceptions include barium sulfate, calcium sulfate, lead sulfate, where the 2+/2− pairing leads to high lattice energies. For similar reasons, most alkali metal carbonates are not soluble in water; some soluble carbonate salts are: potassium carbonate and ammonium carbonate. Salts are characteristically insulators.
Molten salts or solutions of salts conduct electricity. For this reason, liquified salts and solutions containing dissolved salts are called electrolytes. Salts characteristically have high melting points. For example, sodium chloride melts at 801 °C; some salts with low lattice energies are liquid near room temperature. These include molten salts, which are mixtures of salts, ionic liquids, which contain organic cations; these liquids exhibit unusual properties as solvents. The name of a salt starts with the name of the cation followed by the name of the anion. Salts are referred to only by the name of the cation or by the name of the anion. Common salt-forming cations include: Ammonium NH+4 Calcium Ca2+ Iron Fe2+ and Fe3+ Magnesium Mg2+ Potassium K+ Pyridinium C5H5NH+ Quaternary ammonium NR+4, R being an alkyl group or an aryl group Sodium Na+ Copper Cu2+Common salt-forming anions include: Acetate CH3COO− Carbonate CO2−3 Chloride Cl− Citrate HOC2 Cyanide C≡N− Fluoride F− Nitrate NO−3 Nitrite NO−2 Oxide O2− Phosphate PO3−4 Sulfate SO2−4 Salts with varying number of hydrogen atoms, with respect to the parent acid, replaced by cations can be referred to as monobasic, dibasic or tribasic salts: Sodium phosphate monobasic Sodium phosphate dibasic Sodium phosphate tribasic Salts are formed by a chemical reaction between: A base and an acid, e.g. NH3 + HCl → NH4Cl A metal and an acid, e.g. Mg + H2SO4 → MgSO4 + H2 A metal and a non-metal, e.g. Ca + Cl2 → CaCl2 A base and an a
The Shvo catalyst, named after Youval Shvo, is an organoruthenium compound, used for transfer hydrogenation. Related derivatives are known; the compound is of academic interest as an early example of a catalyst for transfer hydrogenation that operates by an "outer sphere mechanism." Shvo's catalyst represents a subset of homogeneous hydrogenation catalysts that involves both metal and ligand in its mechanism. The complex was prepared by the reaction of diphenylacetylene and triruthenium dodecacarbonyl; this synthetic route is efficient, despite the complicated pathway, which includes formation of cyclopentadienone-like ligands. Related syntheses use the preformed cyclopentadienone. A related iron analogue is known, see Knölker complex; the compound contains a pair of equivalent Ru centres that are bridged by a strong hydrogen bond and a bridging hydride. In solution, the complex dissociates unsymmetrically: 2HRu2H4 → RuH2 + Ru2The hydride RuH2 transfers H2 to polar substrates such as ketones and iminium cations.
The cyclopentadienone species Ru2 abstracts H2 from substrates. In the early 1980s, while studying transfer dehydrogenation reactions catalyzed by triruthenium dodecacarbonyl, it was noted by Youval Shvo that both rate of reaction and catalytic turnover were drastically improved through the use of diphenylacetylene as hydrogen acceptor. A series of judicious experiments demonstrated that under the reaction conditions, diphenylacetylene was reacting with the complex to form cyclopentadienone ligands in situ; the complexes with cyclopentadienone were shown to be the source of the improved outcomes. In 1986, Shvo and others reported that they had characterized this new class of ruthenium complexes which were catalytically active in the hydrogenation and dehydrogenation of numerous functional groups. Shvo's catalyst is synthesized using tetracyclone and triruthenium dodecacarbonyl, which are refluxed together in a dry aromatic solvent such as toluene for at least 2 days. After forming the monomeric species, the bridged hydrogen dimer is formed by refluxing in the presence of a hydrogen donor, such as isopropanol.
When in solution, Shvo's catalyst dissociates into two unequal halves: one contains both hydrogen atoms from the dimer, the other becomes coordinatively unsaturated. The hydrogen-containing complex performs hydrogenation through addition of both H+ and H- to the double bond, while the unsaturated complex abstracts hydrogen from a suitable donor or from H2 gas itself. Together, the components work in tandem to efficiently transfer H2 from one molecule to another, bringing about the redox reaction. In the presence of a suitable hydrogen donor or hydrogen gas, Shvo's catalyst is useful for the reduction of several polar functional groups. In 2011 this catalyst was demonstrated to be effective at hydrogenating bio-oil in order to improve its quality as a fuel and promoting the hydrolysis of complex carbohydrates into monomeric sugars. While the catalyst was studied in the context of reduction of aldehydes and ketones, further examination in the area has revealed ways to tailor reactivity of the complex to achieve desired outcomes.
The most notable example is the use of chiral ligands to achieve enantioselective reduction with ratios up to 99:1. Catalytic reductions of alkenes with different degrees of substitution have been reported, many of which give quantitative yields. One obstacle to the use of Shvo's catalyst in the hydrogenation of alkynes is its propensity to bind the alkyne quite forming a stable complex that poisons the catalyst. A comparative study analyzing the rate of hydrogenation among substrates determined that imines reacted more than their corresponding aldehyde counterparts by a factor of 26; when a hydrogen donor other than H2 gas is used for a hydrogenation reaction, it becomes dehydrogenated by the catalyst as a result. The catalytic process can thus be seen as a dehydrogenation if the hydrogen donor is the target of the method, using an auxiliary hydrogen acceptor instead. For example, "Isopropanol is used with Shvo's catalyst to reduce 2-butene to butane," and "2-butene is used with Shvo's catalyst to oxidize isopropanol to acetone," are describing the same process.
It is worth noting that a suitable hydrogen acceptor/donor for a given reaction must be chosen to provide sufficient thermodynamic incentive for the desired hydrogen transfer. It is possible to transfer hydrogen in an intramolecular fashion, for example when converting allylic alcohols to ketones; when used with certain reactants, the catalyst facilitates an addition reaction through oxidation and/or traps the product through reduction. After primary alcohols are oxidized to aldehydes via the catalyst, the aldehydes formed undergo a Tishchenko reaction to form the corresponding ester. Addition of the amine is facilitated through oxidation to the ynone, followed by reduction of the product. Multiple products are possible due to amine additions at different sites. Another case of "hydrogen borrowing", the alkylation of amines using other amines is promoted by Shvo's catalyst; the reaction proceeds through oxidation to an imine, which allows nucleophilic attack, followed by an elimination step and reduction of the double bond.
The exact mechanism of hydrogenation reactions performed using Shvo's catalyst has been a matter of debate, broadly between two alternative descriptions of the double bond's interaction with the complex at the rate-determining step. The proposed alternatives are an inner-sphere me
Dichlorotetrakis ruthenium describes coordination compounds with the formula RuCl24, where DMSO is dimethylsulfoxide. Both cis and trans isomers are known; the cis isomer is a yellow, air-stable solid, soluble in some organic solvents. These compounds have attracted attention as possible anti-cancer drugs; the cis isomer illustrates linkage isomerism for the DMSO ligand. One of the two dmso ligands that are cis to both chloride ligands is O-bonded while the other three dmso ligands are S-bonded. In the trans isomer, yellow, all four dmso ligands are S-bonded; the cis isomer is formed thermally, the trans isomer is obtained by UV-irradiation of the cis isomer. The complexes were first prepared by heating DMSO solutions of ruthenium trichloride under hydrogen atmosphere. An alternative procedure has been developed. RuCl24 was identified as a potential anticancer agent in the early 1980s. Continued research has led to the development of several related dmso-containing ruthenium compounds, some of which have undergone early-stage clinical trials