Polysulfide 1549715 213381708 2008-05-19T02:06:16Z DumZiBoT 6085301 robot Adding: [[pl:Wielosiarczki]] '''Polysulfides''' are a class of [[chemical compound]]s containing chains of [[sulfur]] atoms. In their simplest form, polysulfides are [[anion]]s with the general formula S<sub>''n''</sub><sup>2−</sup> and the structure <sup>−</sup>SS<sub>n-2</sub>S<sup>−</sup>. These anions are the conjugate bases of the hypothetical acids H<sub>2</sub>S<sub>n</sub>. ==Polysulfide salts== Although elemental sulfur is completely insoluble in water, a solution results upon addition [[sodium sulfide]]: :Na<sub>2</sub>S + 4 S → Na<sub>2</sub>S<sub>5</sub> :Na<sub>2</sub>S + 5 S → Na<sub>2</sub>S<sub>6</sub> :Na<sub>2</sub>S + 6 S → Na<sub>2</sub>S<sub>7</sub> :Na<sub>2</sub>S + 7 S → Na<sub>2</sub>S<sub>8</sub> Alkali metals other than Na<sup>+</sup> can be used. In some cases, these anions have been obtained as organic, which are soluble in organic solvents<ref>{{cite journal | author = Dev, S.; Ramli, E.; Rauchfuss, T. B.; Wilson, S. R. | title = Synthesis and Structure of [M(''N''-Methylimidazole)<sub>6</sub>]S<sub>8</sub>: Polysulfide Salts Prepared by the Reaction N-Methylimidazole + Metal Powder + Sulfur | journal = [[Inorg. Chem.]] | year = 1991 | volume = 30 | pages = 2514 | doi=10.1021/ic00011a011}}</ref> A useful polysulfide is [[lime sulfur]] CaS<sub>n</sub>, which is used as a pesticide in agriculture. ==Applications== ===Polysulfide polymers=== In the commercial world polysulfide usually refers to a class of polymers with alternating chains of several sulfur atoms and hydrocarbons. The general formula for the repeat unit is –[(CH<sub>2</sub>)<sub>m</sub>-S<sub>x</sub>]<sub>n</sub>– , where x indicates the number of sulfur atoms (or rank), and n indicates the number of repeat units. Polymers containing sulfur atoms separated by hydrocarbon sequences are not polysulfides, e.g. [[Poly(p-phenylene sulfide)|polyphenylene sulfide]] (C<sub>6</sub>H<sub>4</sub>S)<sub>n</sub>. Polysulfide polymers can be synthesized by [[condensation polymerization]] reactions between organic dihalides and alkal metal salts of polysulfide anions: :n Na<sub>2</sub>S<sub>5</sub> + n ClCH<sub>2</sub>CH<sub>2</sub>Cl → [CH<sub>2</sub>CH<sub>2</sub>S<sub>5</sub>]<sub>n</sub> + 2n [[Sodium chloride|NaCl]] Dihalides used in this condensation polymerization are dichloroalkanes (such as [[1,2-dichloroethane]], bis-(2-chloroethyl)formal (ClCH<sub>2</sub>CH<sub>2</sub>OCH<sub>2</sub>OCH<sub>2</sub>CH<sub>2</sub>Cl), and 1,3-dichloropropane. In some cases, polysulfide polymers can be formed by [[ring-opening polymerization]] reactions. Polysulfide polymers are insoluble in water, oils, and many other organic solvents. Because of their solvent resistance, these materials find use as [[sealant]]s to fill the joints in pavement, automotive window glass, and aircraft structures. ===Polysulfides in vulcanized rubber=== Many commercial [[elastomers]] contain polysulfides as [[crosslinks (chemistry)|crosslinks]]. These crosslinks interconnect neighboring polymer chains, thereby conferring rigidity. The degree of rigidity is related to the number of crosslinks. Elastomers therefore have a characteristic ability to "snap back" to their original shape after being stretched or compressed. Because of this memory for their original [[cured]] shape, elastomers are commonly referred to as [[rubber]]s. The process of crosslinking the polymer chains in these polymers with sulfur is called [[vulcanization]]. The sulfur chains attach themselves to the "allylic" carbon atoms, which adjacent to C=C linkages. Vulcanization is applied to the processing of several classes of rubbers, including poly[[chloroprene]] ([[Neoprene]]<sup>TM</sup>), styrene-butadiene, and poly[[isoprene]], which is natural rubber. [[Charles Goodyear]]'s discovery of vulcanization, involving the heating of polyisoprene with sulfur, was revolutionary because it converted a sticky and almost useless material into an elastomer which could be fabricated into useful products. ===Energy storage=== {{Main|Sodium-sulfur battery}} The energy released in the reaction of sodium and elemental sulfur is the basis of a battery. Sodium-sulfur batteries require high temperatures to maintain liquid polysulfide and Na<sup>+</sup>-conductive membranes that are unreactive toward sodium, sulfur, and sodium sulfide. ==Polysulfido complexes== Polysulfides are common [[ligand]]s in [[coordination chemistry]]. Example of transition metal polysulfido complexes include (C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>TiS<sub>5</sub>, [Ni(S<sub>4</sub>)<sub>2</sub>]<sup>2−</sup>, and [Pt(S<sub>5</sub>)<sub>3</sub>]<sup>2−</sup>.<ref>Draganjac, M. E.; Rauchfuss, T. B., "Transition Metal Polysulfides: Coordination Compounds with Purely Inorganic Chelate Ligands", Angewandte Chemie International, Edition in English, 1985, vol. 24, 742.</ref> Main group elements also form polysulfides.<ref>Takeda, N.; Tokitoh, N. and Okazaki, R., "Polysulfido Complexes of Main Group and Transition Metals", Topics in Current Chemistry, 2003, vol. 231, 153-202. ISBN 3540403787.</ref> ==References== <references/> [[Category:Sulfur compounds]] [[Category:Inorganic polymers]] {{chem-stub}} [[de:Polysulfide]] [[es:Polisulfuro]] [[ja:多硫化物]] [[pl:Wielosiarczki]] [[ru:Полисульфиды]]