Polysulfide Radical Cations

Abstract Inorganic polysulfide anions and the related radical anions S play an important role in the redox reactions of elemental sulfur and therefore also in the geobio chemical sulfur cycle. This chapter describes the preparation of the solid polysulfides with up to eight sulfur atoms and univalent cations, as well as their solid state structures, vibrational spectra and their behavior in aqueous and non-aqueous solutions. In addition, the highly colored and reactive radical anions S with n = 2, 3, and 6 are discussed, some of which exist in equilibrium with the corresponding diamagnetic dianions. 

The rate at which sulfur will react with the unsaturated polymer chains can be increased by the addition of activators a metal oxide plus fatty acid. The most common combination is zinc oxide and stearic acid, with the primary fimction of the fatty acid being to solubilize the zinc in the elastomer. In the presence of the metal, it is believed that the sulfur reacts as a cation at the double bond which results in charged and uncharged polysulfides, the latter of which could in turn form free radicals. Metal activated sulfur vulcanization will proceed more rapidly than crosslinking by sulfur alone, but still too slow for most production purposes. The metal oxide/fatty acid is, in practice, used not to activate the sulfur itself, but to activate the organic compounds used as vulcanization accelerators. 

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