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 betwe ...

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 ...

Na₂S·9 H₂O. Both the anhydrous and the hydrated salts 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 derived from anionic chains of sulfur atoms. There are two main classes of polysulfides: inorganic and organic. The inorganic polysulfides have the general formula . These anions are the conjugate bas ...

s. It is 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 the Arabic word , ) is a basic 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 soluble base has a pH greater than 7.0. The ...

solutions. When exposed to moisture, Na₂S immediately hydrates to give

sodium hydrosulfide Sodium hydrosulfide is the chemical compound with the formula NaSH. 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 purp ...

. Sodium sulfide has an unpleasant rotten egg smell due to the hydrolysis to

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist ...

in moist air. Some commercial samples are described 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'. These samples consist of NaSH, NaOH, and water.

Structure

The structures of sodium sulfides have been determined by

X-ray crystallography X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...

. The nonahydrate features S^2- hydrogen-bonded to 12 water molecules. The pentahydrate consists of S^2- centers bound to Na⁺ and encased by an array of hydrogen bonds. Anhydrous Na₂S, which is rarely encountered, adopts the antifluorite 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 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 mill ...

often using coal: :Na₂SO₄ + 2 C → Na₂S + 2 CO₂ In the laboratory, the salt can be prepared by reduction of

sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...

with

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

in anhydrous

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

, 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 Crystal, crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 Parts-per notation ...

(forming

sodium naphthalenide Sodium naphthalene is an organic salt (chemistry), salt with the chemical formula . 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 is ...

): :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 A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an e ...

(), 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 gives a proton () to a base—in other words, it is a base with a hydrogen ion added to it, as it loses a hydrogen ion in the rever ...

(). 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 a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

and

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

, 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 colorless gas with a pungent smell that is responsible for the odor of burnt matches. It is r ...

: :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 viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...

gives

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

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

Pulp and paper industry

In terms of its dominant use, "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. It aids in the delignification process, affording cellulose, which is the main component of paper. 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

Installation of carbon-sulfur bonds

Alkylation of sodium sulfide give

thioether In organic chemistry, a 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 organic compound, volatile sulfides have ...

s: :Na₂S + 2 RX → R₂S + 2 NaX Even aryl halides participate in this reaction. By a broadly similar process sodium sulfide can react with alkenes in the thiol-ene reaction 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.

Reducing agent

Aqueous solution of sodium sulfide will reduce nitro groups to

amine In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...

. This conversion is applied to production of some azo dyes since other reducible groups, e.g. azo group, remain intact. The reduction of nitro aromatic compounds to amines using sodium sulfide is known as the Zinin reaction in honor of its discoverer. Hydrated sodium sulfide reduces

1,3-dinitrobenzene 1,3-Dinitrobenzene is one of three isomers of dinitrobenzene, with the formula C6H4(NO2)2. It is one of three isomers of dinitrobenzene. The compound is a yellow solid that is soluble in organic solvents. Preparation 1,3-Dinitrobenzene is acc ...

derivatives to the 3-nitroanilines.

Other reactions

Sulfide has also been employed in photocatalytic applications.

Safety

Consisting of the equivalent of

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula . It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly corrosive base (chemistry), ...

, sodium sulfide is strongly alkaline and can cause chemical burns. It reacts rapidly with acids to produce

, a gas which is both highly toxic and potentially explosive. Sodium sulfide hydrolyses in water to form smaller amounts of hydrogen sulfide which also makes it very toxic to aquatic life.

References

{{Sulfides Sulfides Sodium compounds Photographic chemicals Fluorite crystal structure