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 ele ...

with the formula Na₂ S, or more commonly its hydrate Na₂S·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 basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a ...

solutions. When exposed to moist air, Na₂S 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 und ...

, an extremely toxic, flammable and corrosive gas which smells like rotten eggs. Some commercial samples are specified as Na₂S·''x''H₂O, where a weight percentage of Na₂S is specified. Commonly available grades have around 60% Na₂S by weight, which means that ''x'' is around 3. These grades of sodium sulfide are often marketed as 'sodium sulfide flakes'.

Structure

Na₂S 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) structur ...

structure, which means that the Na⁺ centers occupy sites of the fluoride in the CaF₂ framework, and the larger S²⁻ occupy the sites for Ca²⁺.

Production

Industrially Na₂S 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 ...

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 mill ...

often using coal: :Na₂SO₄ + 2 C → Na₂S + 2 CO₂ 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 formul ...

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 ...

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 nitrogeno ...

, or by sodium in dry THF 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 aromat ...

(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 → Na₂S

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 (), 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 ...

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

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 we ...

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 t ...

, sodium sulfide can oxidize to sodium carbonate 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 ...

: :2 Na₂S + 3 O₂ + 2 → 2 Na₂CO₃ + 2 SO₂ 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

: :Na₂S + 4 H₂O₂ → 4 + Na₂SO₄ Upon treatment with

, polysulfides are formed: :2 Na₂S + S₈ → 2 Na₂S₅

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 ...

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 ...

. 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: :Na₂S + 2 RX → R₂S + 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 1 ...

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 a ...

in Sandmeyer type reactions. Sodium sulfide reduces 1,3-dinitrobenzene derivatives to the

3-nitroaniline 3-Nitroaniline, also known as ''meta''-nitroaniline and ''m''-nitroaniline, is a non-volatile stable solid commonly used as a raw material for dyes. 3-Nitroaniline is an aniline carrying a nitro compound, nitro functional group in position 3. It i ...

s. 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 with the chemical formula . Its formula can be also written as or (an ethyl group linked to a h ...

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 substituent su ...

; while other reducible groups, e.g. azo group, 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 ab ...

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 s ...

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 paronychi ...

pain treatment.

Safety

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 alkal ...

, 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 ca ...

. Acids react with it to rapidly produce

, which is highly toxic.

References

{{Sulfides Sulfides Sodium compounds Photographic chemicals Fluorite crystal structure