Microsoft Word - WaterChemistry

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Organosulfur compounds, undesirable impurities in petroleum, may be upgraded by
subjecting them to hydrodesulfurization, which cleaves the C–S bonds:

R-S-R + 2 H 2 → 2 RH + H 2 S

The resulting hydrogen sulfide from this process, and also as it occurs in natural gas, is
converted into elemental sulfur by the Claus process. This process entails oxidation of
some hydrogen sulfide to sulfur dioxide and then the comproportionation of the two:

3 O 2 + 2 H 2 S → 2 SO 2 + 2 H 2 O

SO 2 + 2 H 2 S → 3 S + 2 H 2 O

Compounds
Common oxidation states of sulfur range from −2 to +6. Sulfur forms stable compounds
with all elements except the noble gases.

Sulfides
Treatment of sulfur with hydrogen gives hydrogen sulfide. When dissolved in water,
hydrogen sulfide is mildly acidic:

H 2 S HS– + H+

Hydrogen sulfide gas and the hydrosulfide anion are extremely toxic to mammals, due to
their inhibition of the oxygen-carrying capacity of hemoglobin and certain cytochromes in
a manner analogous to cyanide and azide.

Reduction of elemental sulfur gives polysulfides, which consist of chains of sulfur atoms
terminated with S– centers:

2 Na + S 8 → Na 2 S 8

This reaction highlights arguably the single most distinctive property of sulfur: its ability to
catenate (bind to itself by formation of chains). Protonation of these polysulfide anions
gives the polysulfanes, H 2 Sx where x = 2, 3, and 4. Ultimately reduction of sulfur gives
sulfide salts:

16 Na + S 8 → 8 Na 2 S

The interconversion of these species is exploited in the sodium-sulfur battery. The radical
anion S 3 – gives the blue color of the mineral lapis lazuli.

With very strong oxidants, S 8 can be oxidized, for example, to give bicyclic S 8 2+.