Sulfide (
British English
British English (BrE, en-GB, or BE) is, according to Oxford Dictionaries, "English as used in Great Britain, as distinct from that used elsewhere". More narrowly, it can refer specifically to the English language in England, or, more broadl ...
also sulphide) is an
inorganic anion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
of
sulfur
Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...
with the chemical formula S
2− or a compound containing one or more S
2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds large families of inorganic and
organic compounds, e.g. lead sulfide and
dimethyl sulfide.
Hydrogen sulfide (H
2S) and
bisulfide (SH
−) are the conjugate acids of sulfide.
Chemical properties
The sulfide ion, S
2−, does not exist in aqueous alkaline solutions of Na
2S. Instead sulfide converts to hydrosulfide:
:S
2− + H
2O → SH
− + OH
−
Upon treatment with an acid, sulfide salts convert to
hydrogen sulfide:
:S
2− + H
+ → SH
−
:SH
− + H
+ → H
2S
Oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...
of sulfide is a complicated process. Depending on the conditions, the oxidation can produce elemental sulfur,
polysulfides,
polythionates,
sulfite
Sulfites or sulphites are compounds that contain the sulfite ion (or the sulfate(IV) ion, from its correct systematic name), . The sulfite ion is the conjugate base of bisulfite. Although its acid ( sulfurous acid) is elusive, its salts are w ...
, or
sulfate. Metal sulfides react with
halogens, forming
sulfur
Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...
and metal salts.
:8 MgS + 8 I
2 → S
8 + 8 MgI
2
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
Cadmium pigments are a class of pigments that contain cadmium. Most of the cadmium produced worldwide has been for use in rechargeable nickel–cadmium batteries, which have been replaced by other rechargeable nickel-chemistry cell varieties ...
". 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
A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way ...
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
A metal (from ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, e ...
ores are sulfides. Significant examples include:
argentite
In mineralogy, argentite (from the Latin ''argentum'', silver) is cubic silver sulfide (Ag2S), which can only exist at temperatures above 173 °C, 177 °C or 179 °C. When it cools to ordinary temperatures it turns into its monocli ...
(
silver
Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...
sulfide),
cinnabar (
mercury sulfide),
galena (
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, ...
sulfide),
molybdenite (
molybdenum sulfide),
pentlandite (
nickel
Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow t ...
sulfide),
realgar (
arsenic
Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, b ...
sulfide), and
stibnite (
antimony
Antimony is a chemical element with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient ti ...
),
sphalerite (
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
sulfide), and
pyrite
The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral.
Pyrite's metallic Luster (mineralogy), lust ...
(
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
disulfide), and
chalcopyrite (
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
-
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pink ...
sulfide).
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
oil wells, pipelines transporting soured
oil,
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
Thiosulfate ( IUPAC-recommended spelling; sometimes thiosulphate in British English) is an oxyanion of sulfur with the chemical formula . Thiosulfate also refers to the compounds containing this anion, which are the salts of thiosulfuric acid, e ...
() an intermediate species responsible for severe problems of
pitting corrosion
Pitting corrosion, or pitting, is a form of extremely localized corrosion that leads to the random creation of small holes in metal. The driving power for pitting corrosion is the depassivation of a small area, which becomes anodic (oxidation re ...
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
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J ...
, "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
Polyphenylene sulfide (PPS) is an organic polymer consisting of aromatic rings linked by sulfides. Synthetic fiber and textiles derived from this polymer resist chemical and thermal attack. PPS is used in filter fabric for coal boilers, p ...
(see below) has the empirical formula C
6H
4S. Occasionally, the term sulfide refers to molecules containing the –SH
functional group
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the r ...
. 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
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...
(that is, Mo
4+ and two S
2−). Iron disulfide (
pyrite
The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral.
Pyrite's metallic Luster (mineralogy), lust ...
, 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
In chemistry, peroxides are a group of compounds with the structure , where R = any element. The group in a peroxide is called the peroxide group or peroxo group. The nomenclature is somewhat variable.
The most common peroxide is hydrogen p ...
–O–O– bond. The
disulfide bond (–S–S–) plays a major role in the conformation of
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s and in the catalytic activity of
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...
s.
Examples
Preparation
Sulfide compounds can be prepared in several different ways:
#Direct combination of elements:
#:Example: Fe
() + S
() → FeS
()
#Reduction of a sulfate:
#:Example: MgSO
4() + 4C
() → MgS
() + 4CO
()
#Precipitation of an insoluble sulfide:
#:Example: M
2+ + H
2S
() → 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
gastric acids, will release toxic
hydrogen sulfide.
Organic sulfides are highly flammable. When a sulfide burns it produces
sulfur dioxide
Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic a ...
(SO
2) 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
The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
names, are determined according to the substitutive and additive nomenclatures, respectively. However, 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.
References
External links
*
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Anions
Corrosion
Functional groups
Sulfur ions