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A polysulfane is a chemical compound of chemical formula , where n > 1 (although disulfane () is sometimes excluded). Compounds containing 2 – 8 sulfur atoms have been isolated, longer chain compounds have been detected, but only in solution.R. Steudel "Inorganic Polysulfanes H2S n with n > 1" in Elemental Sulfur and Sulfur-Rich Compounds II (Topics in Current Chemistry) 2003, Volume 231, pp 99–125. is colourless, higher members are yellow with the colour increasing with the sulfur content. In the chemical literature the term polysulfanes is sometimes used for compounds containing , e.g. organic polysulfanes .
This decomposition reaction is catalyzed by alkali. To suppress this behavior, containers for polysulfanes are often pretreated with acid to remove traces of alkali.Greenwood and Earnshaw, p. 683
In contrast to the thermodynamic instability of polysulfates, polysulfide anions form spontaneously by treatment of with elemental sulfur:
Beyond and , many higher polysulfanes ( n = 3 – 8) are known.R. Steudel "Inorganic Polysulfanes H2S2 with n > 1" in Elemental Sulfur and Sulfur-Rich Compounds II (Topics in Current Chemistry) 2003, Volume 231, pp 99-125. They have unbranched sulfur chains. Starting with disulfane , all known polysulfanes are liquids at room temperature. The density, boiling point and viscosity correlate with chain length. Physical properties of polysulfanes are given in the table below.
They also react with sulfite and cyanide producing thiosulfate and thiocyanate respectively.
Polysulfanes can be made from polysulfides by pouring a solution of a polysulfide salt into cooled concentrated hydrochloric acid. A mixture of metastable polysulfanes separates as a yellow oil, from which individual compounds may be separated by fractional distillation. Other more selective syntheses are:
The reaction of polysulfanes with sulfur dichloride or disulfur dichloride produces long-chain dichloropolysulfanes:
The reaction with a sulfite salt (a base) quantitatively decomposes the polysulfane to produce thiosulfate and hydrogen sulfide:
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