Sodium polysulfide

[1][2] The salts are dark red solids that dissolve in water to give highly alkaline and corrosive solutions.

[4] Alternatively they are produced by the redox reaction of aqueous sodium hydroxide with sulfur at elevated temperatures.

[5] Finally they arise by the reduction of elemental sulfur with sodium, a reaction often conducted in anhydrous ammonia.

As exploited in the sodium-sulfur battery, the polysulfides absorb and release reducing equivalents by breaking and making S-S bonds, respectively.

Protonation of these salts gives hydrogen sulfide and elemental sulfur, as illustrated by the reaction of sodium pentasulfide:

NFPA 704 four-colored diamond Health 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gas Flammability 0: Will not burn. E.g. water Instability 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calcium Special hazards (white): no code
S 4 2− from the crystal structure, highlighting its skewed conformation.
S 5 2− from the crystal structure, highlighting its skewed conformation.