Sulfide (also sulphide in British English)
Chemical properties
The sulfide ion does not exist in aqueous alkaline solutions of Na
2S.
Instead sulfide converts to hydrosulfide:
- S2− + H2O → SH− + OH−
Upon treatment with an acid, sulfide salts convert to hydrogen sulfide:
- S2− + H+ → SH−
- SH− + H+ → H2S
redox of sulfide is a complicated process. Depending on the conditions, the oxidation can produce elemental sulfur, , , sulfite, or sulfate. Metal sulfides react with , forming sulfur and metal salts.
- 8 MgS + 8 I2 → S8 + 8 MgI2
Metal derivatives
Aqueous solutions of transition metals
cations react with sulfide sources (H
2S, NaHS, Na
2S) to precipitate solid sulfides. Such
inorganic sulfides typically have very low solubility in water, and many are related to minerals with the same composition (see below). One famous example is the bright yellow species CdS or "
cadmium yellow". The black tarnish formed on sterling silver is Ag
2S. Such species are sometimes referred to as salts. In fact, the bonding in transition metal sulfides is highly covalent, which gives rise to their
semiconductor properties, which in turn is related to the deep colors. Several have practical applications as pigments, in solar cells, and as catalysts. The fungus
Aspergillus niger plays a role in the solubilization of heavy metal sulfides.
Geology
Many important
metal are sulfides.
[Vaughan, D. J.; Craig, J. R. “Mineral chemistry of metal sulfides" Cambridge University Press, Cambridge: 1978. .] Significant examples include:
argentite (
silver sulfide),
cinnabar (mercury sulfide),
galena (
lead sulfide),
molybdenite (
molybdenum sulfide),
pentlandite (
nickel sulfide),
realgar (
arsenic sulfide), and
stibnite (
antimony sulfide),
sphalerite (
zinc sulfide), and
pyrite (
iron disulfide), and
chalcopyrite (
iron-
copper sulfide). This sulfide
Mineral recorded information (like
Isotope) of their surrounding environment during their formation. Scientists use these minerals to study environments in the deep sea or in the Earth's past.
Corrosion induced by sulfide
Dissolved free sulfides (H
2S, HS
− and S
2−) are very aggressive species for the corrosion of many metals such as steel, stainless steel, and copper. Sulfides present in aqueous solution are responsible for stress corrosion cracking (SCC) of steel, and is also known as sulfide stress cracking. Corrosion is a major concern in many industrial installations processing sulfides: sulfide ore mills, deep
, pipelines transporting soured
oil and
Kraft paper factories.
Microbially-induced corrosion (MIC) or biogenic sulfide corrosion are also caused by sulfate reducing bacteria producing sulfide that is emitted in the air and oxidized in sulfuric acid by sulfur oxidizing bacteria. Biogenic sulfuric acid reacts with sewerage materials and most generally causes mass loss, cracking of the sewer pipes and ultimately, structural collapse. This kind of deterioration is a major process affecting sewer systems worldwide and leading to very high rehabilitation costs.
Oxidation of sulfide can also form thiosulfate (), an intermediate species responsible for severe problems of pitting corrosion of steel and stainless steel while the medium is also acidified by the production of sulfuric acid when oxidation is more advanced.
Organic chemistry
In organic chemistry, "sulfide" usually refers to the linkage C–S–C, although the term
thioether is less ambiguous. For example, the thioether
dimethyl sulfide is CH
3–S–CH
3. Polyphenylene sulfide (see below) has the empirical formula C
6H
4S. Occasionally, the term sulfide refers to molecules containing the –SH
functional group. For example, methyl sulfide can mean CH
3–SH. The preferred descriptor for such SH-containing compounds is
thiol or mercaptan, i.e. methanethiol, or methyl mercaptan.
Disulfides
Confusion arises from the different meanings of the term "
disulfide". Molybdenum disulfide (MoS
2) consists of separated sulfide centers, in association with molybdenum in the formal +4
oxidation state (that is, Mo
4+ and two S
2−). Iron disulfide (
pyrite, FeS
2) on the other hand consists of , or
−S–S
− dianion, in association with divalent iron in the formal +2 oxidation state (ferrous ion: Fe
2+). Dimethyldisulfide has the chemical binding CH
3–S–S–CH
3, whereas
carbon disulfide has no S–S bond, being S=C=S (linear molecule analog to CO
2). Most often in sulfur chemistry and in biochemistry, the disulfide term is commonly ascribed to the sulfur analogue of the
peroxide –O–O– bond. The
disulfide bond (–S–S–) plays a major role in the conformation of
and in the catalytic activity of
.
Examples
Preparation
Sulfide compounds can be prepared in several different ways:
-
Direct combination of elements:
-
:Example: Fe() + S() → FeS()
-
Reduction of a sulfate:
-
:Example: MgSO4() + 4C() → MgS() + 4CO()
-
Precipitation of an insoluble sulfide:
-
:Example: M2+ + H2S() → MS() + 2H+()
Safety
Many metal sulfides are so insoluble in water that they are probably not very toxic. Some metal sulfides, when exposed to a strong mineral
acid, including
, will release toxic
hydrogen sulfide.
Organic sulfides are highly flammable. When a sulfide burns it produces sulfur dioxide (SO2) gas.
Hydrogen sulfide, some of its salts, and almost all organic sulfides have a strong and putrid stench; rotting biomass releases these.
Nomenclature
The systematic names
sulfanediide and
sulfide(2−), valid IUPAC names, are determined according to the substitutive and additive nomenclatures, respectively. The name sulfide is also used in compositional IUPAC nomenclature which does not take the nature of bonding involved. Examples of such naming include selenium disulfide and
titanium sulfide, which contain no sulfide ions.
External links
