section_path: Compounds/Electron transfer reactions
section_name: Electron transfer reactions
paragraph_text: Electron transfer reactions
  
  Sulfur polycations, S 2+ 8, S 2+ 4 and S 2+ 16 are produced when sulfur is reacted with oxidizing agents in a strongly acidic solution. The colored solutions produced by dissolving sulfur in oleum were first reported as early as 1804 by C. F. Bucholz, but the cause of the color and the structure of the polycations involved was only determined in the late 1960s. S 2+ 8 is deep blue, S 2+ 4 is yellow and S 2+ 16 is red.
  
  Reduction of sulfur gives various polysulfides with the formula S, many of which have been obtained in crystalline form. Illustrative is the production of sodium tetrasulfide:
  
  Some of these dianions dissociate to give radical anions, such as S − 3 gives the blue color of the rock lapis lazuli.
  
  This reaction highlights a distinctive property of sulfur: its ability to catenate (bind to itself by formation of chains). Protonation of these polysulfide anions produces the polysulfanes, H S, where x = 2, 3, and 4. Ultimately, reduction of sulfur produces sulfide salts:
  
  The interconversion of these species is exploited in the sodium–sulfur battery.