Sodium sulfide is a
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
with the
formula
In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwee ...
Na2 S, or more commonly its
hydrate
In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...
Na
2S·9
H2O. Both the anhydrous and the hydrated salts in pure crystalline form are colorless solids, although technical grades of sodium sulfide are generally yellow to brick red owing to the presence of
polysulfide
Polysulfides are a class of chemical compounds containing chains of sulfur atoms. There are two main classes of polysulfides: inorganic and organic. Among the inorganic polysulfides, there are ones which contain anions, which have the general formu ...
s and commonly supplied as a crystalline mass, in flake form, or as a fused solid. They are water-soluble, giving strongly
alkaline
In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a base (chemistry), basic, ionic compound, ionic salt (chemistry), salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as ...
solutions. When exposed to moist air, Na
2S and its hydrates emit
hydrogen sulfide
Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...
, an extremely toxic, flammable and corrosive gas which smells like rotten eggs.
Some commercial samples are specified as Na
2S·''x''H
2O, where a weight percentage of Na
2S is specified. Commonly available grades have around 60% Na
2S by weight, which means that ''x'' is around 3. These grades of sodium sulfide are often marketed as 'sodium sulfide flakes'.
Structure
Na
2S adopts the
antifluorite In solid state chemistry, the fluorite structure refers to a common motif for compounds with the formula MX2. The X ions occupy the eight tetrahedral interstitial sites whereas M ions occupy the regular sites of a face-centered cubic (FCC) structure ...
structure, which means that the Na
+ centers occupy sites of the fluoride in the CaF
2 framework, and the larger S
2− occupy the sites for Ca
2+.
Production
Industrially Na
2S is produced by
carbothermic reduction
Carbothermic reactions involve the reduction of substances, often metal oxides (O^2-), using carbon as the reducing agent. These chemical reactions are usually conducted at temperatures of several hundred degrees Celsius. Such processes are applie ...
of
sodium sulfate
Sodium sulfate (also known as sodium sulphate or sulfate of soda) is the inorganic compound with formula Na2SO4 as well as several related hydrates. All forms are white solids that are highly soluble in water. With an annual production of 6 milli ...
often using coal:
:Na
2SO
4 + 2 C → Na
2S + 2 CO
2
In the laboratory, the salt can be prepared by reduction 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 formula ...
with
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
in anhydrous
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...
, or by sodium in dry
THF
Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water- miscible organic liquid with low viscosity. It is ...
with a catalytic amount of
naphthalene
Naphthalene is an organic compound with formula . It is the simplest polycyclic aromatic hydrocarbon, and is a white crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass. As an aromati ...
(forming
sodium naphthalenide
Sodium naphthalene is an organic salt with the chemical formula Na+. In the research laboratory, it is used as a reductant in the synthesis of organic, organometallic, and inorganic chemistry. It is usually generated in situ. When isolated, it ...
):
:2 Na + S → Na
2S
Reactions with inorganic reagents
The sulfide ion in sulfide salts such as sodium sulfide can incorporate a proton into the salt by protonation:
: + →
Because of this capture of the
proton
A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...
(), sodium sulfide has basic character. Sodium sulfide is strongly basic, able to absorb two protons. Its
conjugate acid
A conjugate acid, within the Brønsted–Lowry acid–base theory, is a chemical compound formed when an acid donates a proton () to a base—in other words, it is a base with a hydrogen ion added to it, as in the reverse reaction it loses a ...
is
sodium hydrosulfide
Sodium hydrosulfide is the chemical compound with the formula NaHS. This compound is the product of the half-neutralization of hydrogen sulfide () with sodium hydroxide (NaOH). NaSH and sodium sulfide are used industrially, often for similar purpos ...
(). An aqueous solution contains a significant portion of sulfide ions that are singly protonated.
: + +
: + +
Sodium sulfide is unstable in the presence of water due to the gradual loss of
hydrogen sulfide
Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...
into the atmosphere.
When heated with
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
and
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
, sodium sulfide can oxidize to
sodium carbonate
Sodium carbonate, , (also known as washing soda, soda ash and soda crystals) is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, odourless, water-soluble salts that yield moderately alkaline solutions ...
and
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 activ ...
:
:2 Na
2S + 3 O
2 + 2 → 2 Na
2CO
3 + 2 SO
2
Oxidation with
hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%†...
gives
sodium sulfate
Sodium sulfate (also known as sodium sulphate or sulfate of soda) is the inorganic compound with formula Na2SO4 as well as several related hydrates. All forms are white solids that are highly soluble in water. With an annual production of 6 milli ...
:
:Na
2S + 4 H
2O
2 → 4 + Na
2SO
4
Upon treatment with
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 formula ...
, polysulfides are formed:
:2 Na
2S + S
8 → 2 Na
2S
5
Uses
Sodium sulfide is primarily used in the
kraft process
The kraft process (also known as kraft pulping or sulfate process) is a process for conversion of wood into wood pulp, which consists of almost pure cellulose fibres, the main component of paper. The kraft process involves treatment of wood chip ...
in the
pulp and paper industry
The pulp and paper industry comprises companies that use wood as raw material and produce pulp, paper, paperboard and other cellulose-based products.
Manufacturing process
The pulp is fed to a paper machine where it is formed as a paper web an ...
.
It is used in water treatment as an oxygen scavenger agent and also as a metals precipitant; in chemical photography for toning black and white photographs; in the textile industry as a bleaching agent, for desulfurising and as a dechlorinating agent; and in the leather trade for the sulfitisation of tanning extracts. It is used in chemical manufacturing as a sulfonation and sulfomethylation agent. It is used in the production of rubber chemicals, sulfur dyes and other chemical compounds. It is used in other applications including ore flotation,
oil recovery, making dyes, and detergent. It is also used during leather processing, as an unhairing agent in the liming operation.
Reagent in organic chemistry
Alkylation of sodium sulfide give
thioether
In organic chemistry, an organic sulfide (British English sulphide) or thioether is an organosulfur functional group with the connectivity as shown on right. Like many other sulfur-containing compounds, volatile sulfides have foul odors. A sul ...
s:
:Na
2S + 2 RX → R
2S + 2 NaX
Even
aryl
In organic chemistry, an aryl is any functional group or substituent derived from an aromatic ring, usually an aromatic hydrocarbon, such as phenyl and naphthyl. "Aryl" is used for the sake of abbreviation or generalization, and "Ar" is used as ...
halides participate in this reaction. By a broadly similar process sodium sulfide can react with alkenes in the
thiol-ene reaction
In organosulfur chemistry, the thiol-ene reaction (also alkene hydrothiolation) is an organic reaction between a thiol () and an alkene () to form a thioether (). This reaction was first reported in 1905, but it gained prominence in the late 1990s ...
to give thioethers.
Sodium sulfide can be used as
nucleophile
In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...
in
Sandmeyer type reactions. Sodium sulfide reduces
1,3-dinitrobenzene derivatives to the
3-nitroanilines. Aqueous solution of sodium sulfide can be refluxed with nitro carrying azo dyes dissolved in
dioxane
1,4-Dioxane () is a heterocyclic organic compound, classified as an ether. It is a colorless liquid with a faint sweet odor similar to that of diethyl ether. The compound is often called simply dioxane because the other dioxane isomers ( 1,2- ...
and
ethanol
Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
to selectively reduce the
nitro groups to
amine
In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituen ...
; while other reducible groups, e.g.
azo group
Azo compounds are organic compounds bearing the functional group diazenyl (, in which R and R′ can be either aryl or alkyl groups).
IUPAC defines azo compounds as: "Derivatives of diazene (diimide), , wherein both hydrogens are substituted ...
, remain intact. Sulfide has also been employed in
photocatalytic
In chemistry, photocatalysis is the acceleration of a photoreaction in the presence of a catalyst. In catalyzed photolysis, light is absorbed by an adsorbed substrate. In photogenerated catalysis, the photocatalytic activity depends on the abi ...
applications.
Sodium sulfide is the active ingredient in
Dr. Scholl's
Dr. Scholl's is a footwear and orthopedic foot care brand originating in the United States, marketed in some countries as simply Scholl. Since 2021, global rights to the brand have been owned by investment firm Yellow Wood Partners through su ...
ingrown toenail
An ingrown nail, also known as onychocryptosis from el, ὄνυξ () 'nail' and () 'hidden', is a common form of nail disease. It is an often painful condition in which the nail grows so that it cuts into one or both sides of the paronychium ...
pain treatment.
Safety
Like
sodium hydroxide
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly caustic base and alkali ...
, sodium sulfide is strongly alkaline and can cause
chemical burns
A chemical burn occurs when living tissue is exposed to a corrosive substance (such as a strong acid, base or oxidizer) or a cytotoxic agent (such as mustard gas, lewisite or arsine). Chemical burns follow standard burn classification and may cau ...
. Acids react with it to rapidly produce
hydrogen sulfide
Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...
, which is highly toxic.
References
{{Sulfides
Sulfides
Sodium compounds
Photographic chemicals
Fluorite crystal structure