Polysulfide

Polysulfides are a class of chemical compounds containing chains of sulfur atoms. There are two main classes of polysulfides: anions and organic polysulfides. Anions have the general formula S2−n. These anions are the conjugate bases of the hydrogen polysulfides H2Sn. Organic polysulfides generally have the formulae RSnR, where R = alkyl or aryl.The alkali metal polysulfides arise by treatment of a solution of sulfide, e.g. sodium sulfide, with elemental sulfur:In commerce, the term 'polysulfide' usually refers to a class of polymers with alternating chains of several sulfur atoms and hydrocarbons. They have the formula R2Sx. In this formula x indicates the number of sulfur atoms (or 'rank'). Polysulfide polymers can be synthesized by condensation polymerization reactions between organic dihalides and alkali metal salts of polysulfide anions:In addition to water and ammonia, the clouds in the atmospheres of the gas giant planets contain ammonium sulfides. The reddish-brownish clouds are attributed to polysulfides, arising from the exposure of the ammonium sulfides to light.Polysulfides, as sulfides, can induce stress corrosion cracking in carbon steel and stainless steel.