SUMMARY / RELATED TOPICS

Sulfide

Sulfide is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. Sulfide refers to chemical compounds large families of inorganic and organic compounds, e.g. lead sulfide and dimethyl sulfide. Hydrogen sulfide and bisulfide are the conjugate acids of sulfide; the sulfide ion, S2−, does not exist in aqueous alkaline solutions of Na2S. Instead sulfide converts to hydrosulfide: S2− + H2O → SH− + OH−Upon treatment with an acid, sulfide salts convert to hydrogen sulfide: S2− + H+ → SH− SH− + H+ → H2SOxidation of sulfide is a complicated process. Depending on the conditions, the oxidation can produce elemental sulfur, polythionates, sulfite, or sulfate. Metal sulfides react with halogens, forming metal salts. 8 MgS + 8 I2 → S8 + 8 MgI2 Aqueous solutions of transition metals cations react with sulfide sources to precipitate solid sulfides. Such inorganic sulfides have low solubility in water, many are related to minerals with the same composition.

One famous example is the bright yellow species CdS or "cadmium yellow". The black tarnish formed on sterling silver is Ag2S; such species are sometimes referred to as salts. In fact, the bonding in transition metal sulfides is covalent, which gives rise to their semiconductor properties, which in turn is related to the deep colors. Several have practical applications as pigments, in solar cells, as catalysts; the fungus Aspergillus niger plays a role in the solubilization of heavy metal sulfides. Many important metal ores are sulfides. Significant examples include: argentite, galena, pentlandite and stibnite, pyrite, chalcopyrite. Dissolved free sulfides are aggressive species for the corrosion of many metals such as steel, stainless steel, copper. Sulfides present in aqueous solution are responsible for stress corrosion cracking of steel, is known as sulfide stress cracking. Corrosion is a major concern in many industrial installations processing sulfides: sulfide ore mills, deep oil wells, pipelines transporting soured oil, Kraft paper factories.

Microbially-induced corrosion or biogenic sulfide corrosion are caused by sulfate reducing bacteria producing sulfide, emitted in the air and oxidized in sulfuric acid by sulfur oxidizing bacteria. Biogenic sulfuric acid reacts with sewerage materials and most causes mass loss, cracking of the sewer pipes and structural collapse; this kind of deterioration is a major process affecting sewer systems worldwide and leading to high rehabilitation costs. Oxidation of sulfide can form thiosulfate an intermediate species responsible for severe problems of pitting corrosion of steel and stainless steel while the medium is acidified by the production of sulfuric acid when oxidation is more advanced. In organic chemistry, "sulfide" refers to the linkage C–S–C, although the term thioether is less ambiguous. For example, the thioether dimethyl sulfide is CH3–S–CH3. Polyphenylene sulfide has the empirical formula C6H4S; the term sulfide refers to molecules containing the –SH functional group. For example, methyl sulfide can mean CH3–SH.

The preferred descriptor for such SH-containing compounds is thiol or mercaptan, i.e. methanethiol, or methyl mercaptan. Confusion arises from the different meanings of the term "disulfide". Molybdenum disulfide consists of separated sulfide centers, in association with molybdenum in the formal +4 oxidation state. Iron disulfide on the other hand consists of S2−2, or −S–S− dianion, in association with divalent iron in the formal +2 oxidation state. Dimethyldisulfide has the chemical binding CH3–S–S–CH3, whereas carbon disulfide has no S–S bond, being S=C=S. Most in sulfur chemistry and in biochemistry, the disulfide term is ascribed to the sulfur analogue of the peroxide –O–O– bond; the disulfide bond plays a major role in the conformation of proteins and in the catalytic activity of enzymes. Sulfide compounds can be prepared in several different ways: Direct combination of elements: Example: Fe + S → FeS Reduction of a sulfate: Example: MgSO4 + 4C → MgS + 4CO Precipitation of an insoluble sulfide: Example: M2+ + H2S → MS + 2H+ Many metal sulfides are so insoluble in water that they are not toxic.

Some metal sulfides, when exposed to a strong mineral acid, including gastric acids, will release toxic hydrogen sulfide. Organic sulfides are flammable; when a sulfide burns it produces sulfur dioxide gas. Hydrogen sulfide, some of its salts, all organic sulfides have a strong and putrid stench; the systematic names sulfanediide and sulfide, valid IUPAC names, are determined according to the substitutive and additive nomenclatures, respectively. However, the name sulfide is used in compositional IUPAC nomenclature which does not take the nature of bonding involved. Examples of such naming are selenium disulfide and titanium sulfide, which contains no sulfide ions whatsoever

St. Leger Italiano

The St. Leger Italiano is a Group 3 flat horse race in Italy open to thoroughbreds aged three years or older, it is run at Milan over a distance of 2,800 metres, it is scheduled to take place each year in October. It is Italy's equivalent of a famous race in England; the St. Leger Italiano was established in the late 19th century, it was restricted to three-year-olds; the first winner to complete a Triple Crown was Niccolo dell'Arca in 1941. The feat was subsequently achieved by Gladiolo in 1946 and Botticelli in 1954; the present system of race grading was introduced in the early 1970s, for a period the St. Leger Italiano held Group 2 status, it was relegated to Group 3 level in 1988, from this point it was contested over 2,900 metres at Turin. For several years it was held in July; the race was opened to older horses and rescheduled for the autumn in 1994. It was downgraded to Listed level, it began its current spell at Milan in 2002, it regained Group 3 status in 2010. A The 2008 running was cancelled because of a strike.

List of Italian flat horse races Racing Post / irishracing.com / siegerlisten.com: 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2009 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017

Meda Nunatak

Meda Nunatak is the rocky ridge extending 2.65 km in west-northwest to east-southeast direction, 700 m wide and rising to 770 m in Attlee Glacier on Foyn Coast, Antarctic Peninsula. The feature is named after Meda of a Thracian princess and wife of Philip II of Macedon. Meda Nunatak is located at 66°13′19″S 63°53′28″W, 15.35 km southwest of Bastion Peak, 8.8 km west-northwest of Fitzmaurice Point and 6.52 km northeast of Gluhar Hill. British mapping in 1974. British Antarctic Territory: Graham Land. Scale 1:250000 topographic map. BAS 250 Series, Sheet SQ 19-20. London, 1974. Antarctic Digital Database. Scale 1:250000 topographic map of Antarctica. Scientific Committee on Antarctic Research. Since 1993 upgraded and updated. Meda Nunatak. SCAR Composite Antarctic Gazetteer. Bulgarian Antarctic Gazetteer. Antarctic Place-names Commission. Meda Nunatak. Copernix satellite imageThis article includes information from the Antarctic Place-names Commission of Bulgaria, used with permission