polysulfides

Polysulfides are compounds in which sulfur atoms form one or more sulfur–sulfur linkages in a chain between two terminals. They occur as inorganic polysulfide ions S_n^2−, and as organic polysulfides with the general structure R–S–(S)_m–R', where m ≥ 1. In inorganic polysulfides, reaction of sulfide sources with elemental sulfur yields salts such as Na_2S_x (2 ≤ x ≤ 6 in common samples); in solution the average chain length varies with conditions. Organic polysulfides feature a chain of sulfur atoms sandwiched between two organic groups and are commonly prepared by reaction of organic thiols or thiolate with elemental sulfur or via oxidation of dithiols. The S–S bonds are relatively weak compared with C–S bonds, making polysulfides reactive toward nucleophiles and undergoing chain-shortening or chain-length equilibration.

Applications include inorganic polysulfide salts used in chemical synthesis and battery research, and organic polysulfide polymers and elastomers. Polysulfide polymers, often called polysulfide rubber, are flexible, chemical resistant, and commonly used as sealants, adhesives, and protective coatings, especially for fuel systems and aerospace applications. In energy storage, polysulfide species such as Li_2S_x are intermediates in lithium–sulfur batteries and contribute to the shuttle effect, affecting capacity and cycling stability.

Safety: many polysulfides are corrosive or irritant and release malodorous sulfurous vapors on hydrolysis; handling requires appropriate precautions.