Sulfide 292444 220990446 2008-06-22T15:24:28Z RekishiEJ 983723 Interwiki:-ja {{Cleanup|date=May 2007}} The term '''sulfide''' (also spelled '''sulphide''' in [[British English]]) refers to several types of [[chemical compounds]] containing [[sulfur]] in its lowest [[oxidation number]] of &minus;2. Formally, "sulfide" is the di[[anion]], S<sup>2&minus;</sup>, which exists in strongly [[alkaline]] aqueous solutions formed from H<sub>2</sub>S or alkali metal salts such as Li<sub>2</sub>S, Na<sub>2</sub>S, and K<sub>2</sub>S. Sulfide is exceptionally basic and, with a pK<sub>a</sub> > 14, it does not exist in appreciable concentrations even in highly alkaline water, being undetectable at pH < ~15 (8 M [[Sodium hydroxide|NaOH]]). Instead, sulfide combines with electrons in hydrogen to form HS<sup>&minus;</sup>, which is variously called '''hydrogen sulfide''' ion, '''hydrosulfide''' ion, '''sulfhydryl''' ion, or '''bisulfide''' ion. At still lower pH's (<7), HS<sup>&minus;</sup> converts to H<sub>2</sub>S, [[hydrogen sulfide]]. Thus, the exact sulfur species obtained upon dissolving sulfide salts depends on the pH of the final solution. Aqueous solutions of [[transition metals]] [[cations]] react with sulfide sources (H<sub>2</sub>S, NaSH, Na<sub>2</sub>S) to precipitate solid sulfides. Such [[inorganic]] sulfides typically have very low solubility in water and many are related to minerals. One famous example is the bright yellow species CdS or "[[cadmium yellow]]". The black tarnish formed on sterling silver is Ag<sub>2</sub>S. Such species are sometimes referred to as salts. In fact the bonding in transition metal sulfides is highly covalent, which gives rise to their [[semiconductor]] properties, which in turn is related to the practical applications of many sulfide materials. In [[organic chemistry]], "sulfide" usually refers to the linkage C-S-C, although the term [[thioether]] is less ambiguous. For example, the thioether [[dimethyl sulfide]] is CH<sub>3</sub>-S-CH<sub>3</sub>. [[Polyphenylene sulfide]] (see below) has the empirical formula C<sub>6</sub>H<sub>4</sub>S. Occasionally, the term sulfide refers to molecules containing the -SH [[functional group]]. For example, methyl sulfide can mean CH<sub>3</sub>-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 S<sub>2</sub><sup>2&minus;</sup>, or S<sup>&minus;</sup>-S<sup>&minus;</sup>, in association with iron in the formal 2+ oxidation state. Dimethyldisulfide has the connectivity CH<sub>3</sub>-S-S-CH<sub>3</sub>, whereas [[carbon disulfide]] has no S-S linkages, being S=C=S. ==Examples== * [[hydrogen sulfide]] (H<sub>2</sub>S) ==Uses== *[[Cadmium]] sulfide (CdS) can be used in [[photocell]]s. *[[Calcium]] polysulfide ("[[lime sulfur]]") is a traditional [[fungicide]] in [[gardening]]. *[[Carbon disulfide]] (CS<sub>2</sub>) is sometimes used as a [[solvent]] in industrial chemistry. *[[Lead sulfide]] (PbS) is used in [[infra-red]] sensors. *[[Molybdenum disulfide]] (MoS<sub>2</sub>), the mineral [[molybdenite]], is used as a catalyst to remove sulfur from fossil fuels. * [[Mustard Gas]] (Cl-CH<sub>2</sub>CH<sub>2</sub>-S-CH<sub>2</sub>CH<sub>2</sub>-Cl), is a sulfide that has been used as a chemical weapon, the chloride on the molecule acts as a leaving group when in the presence of water and forms a sulfide-alcohol and HCl. *[[Silver sulfide]] (Ag<sub>2</sub>S) is formed on [[silver]] [[electrical contacts]] operating in an atmosphere rich in [[hydrogen sulfide]]. * [[Sodium]] sulfide (Na<sub>2</sub>S) is an important industrial chemical, used in manufacture of [[Kraft process|kraft]] [[paper]], [[dye]]s, [[leather tanning]], [[crude petroleum]] processing, treatment of [[heavy metals|heavy metal]] [[pollution]], and others. *[[Zinc]] sulfide (ZnS) is used for [[lens (optics)|lenses]] and other [[optics|optical]] devices in the [[infrared]] part of the [[Electromagnetic spectrum|spectrum]]. *[[Zinc]] sulfide with a trace of copper is used for [[photoluminescence|photoluminescent]] strips for emergency lighting and luminous watch dials. *Several metal sulfides are used as [[pigment]]s in art, although their use has declined somewhat due to their toxicity. Sulfide pigments include cadmium, mercury, and arsenic. *[[Polyphenylene sulfide]] is a polymer commonly called "Sulfar". Its repeating units are bonded together by sulfide (thioether) linkages. ==Natural occurrence== Many important [[metal]] [[ore]]s are sulfides. Significant [[sulfide mineral]]s include: * [[arsenopyrite]] ([[arsenic]] and [[iron]]) * [[argentite]] ([[silver]]) * [[chalcopyrite]] ([[iron]] and [[copper]]) * [[cinnabar]] ([[mercury (element)|mercury]]) * [[galena]] ([[lead]]) * [[molybdenite]] ([[molybdenum]]) * [[pentlandite]] ([[nickel]]) * [[pyrite]] ([[iron]]) * [[realgar]] ([[arsenic]]) * [[sphalerite]] ([[zinc]]) and * [[stibnite]] ([[antimony]]). ==Safety== Many metal sulfides are so insoluble in water that they are probably not very toxic. Some metal sulfides, when exposed to a strong mineral [[acid]], including [[gastric acid]]s, will release toxic hydrogen sulfide. Organic sulfides are highly flammable. When a sulfide burns, the fumes usually include toxic [[sulfur dioxide]] (SO<sub>2</sub>) gas. Hydrogen sulfide, some of its salts, and almost all organic sulfides have a strong and putrid stench; rotting biomass releases these. [[Thiol|Mercaptans]], in particular, are the strongest-smelling substances known. ==Corrosion induced by sulfide== Dissolved free sulfides (H<sub>2</sub>S, HS<sup>-</sup> and S<sup>2-</sup>) are very aggressive species for the corrosion of many metals such as, ''e.g.'', steel, stainless steel, and copper. Sulfides present in aqueous solution are responsible for [[stress corrosion cracking]] (SCC) of steel, and is also known as [[sulfide stress cracking]]. Corrosion is a major concern in many industrial installations processing sulfides: sulfide ore mills, deep [[oil well]]s, pipeline transporting soured [[oil]], [[Kraft paper]] factories. [[Microbial corrosion|Microbially-induced corrosion]] ([[MIC]]) or [[biogenic sulfide corrosion]] are also caused by [[sulfate reducing bacteria]] producing sulfide. Oxidation of sulfide can also form [[thiosulfate]] (S<sub>2</sub>O<sub>3</sub><sup>2-</sup>) an intermediate species responsible for severe problems of [[pitting corrosion]] of steel and stainless steel while the medium is also acidified by the production of sulfuric acid when oxidation is more advanced. ==References== * Meyer B, Ward K, Koshlap K, Peter L (1983). Second dissociation constant of hydrogen sulfide. ''Inorg Chem, 22:2345''. == See also == *[[Biogenic sulfide corrosion]] *[[Sulfide stress cracking]] *[[Sulfate]] *[[Sulfidation]] *[[Sulfite]] *[[Thioether]] *[[Thiosulfate]] *[[Dithionite]] [[Category:Anions]] [[Category:Corrosion]] [[Category:Sulfides|*]] [[Category:Functional groups]] [[bg:Сулфид]] [[ca:Sulfur]] [[cs:Sulfid]] [[da:Sulfid]] [[de:Sulfide]] [[et:Sulfiidid]] [[es:Sulfuro]] [[eo:Sulfido]] [[fr:Sulfure]] [[he:סולפיד]] [[it:Solfuro]] [[ja:硫化物]] [[nl:Sulfide]] [[no:Sulfid]] [[pl:Siarczki]] [[pt:Sulfeto]] [[ru:Сульфиды]] [[sr:Сулфид]] [[fi:Sulfidi]] [[sv:Sulfider]] [[zh:硫化物]]