Sodium hydrosulfide
Sodium hydrosulfide is the chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

  with the formula NaHS. This compound is the product of the half neutralization of hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

 with sodium hydroxide. NaHS is a useful reagent for the synthesis of organic and inorganic sulfur compounds. It is a colorless solid that typically smells like H2S due to hydrolysis by atmospheric moisture. In contrast with sodium sulfide
Sodium sulfide
Sodium sulfide is the name used to refer to the chemical compound Na2S, but more commonly it refers to the hydrate Na2S·9H2O. Both are colorless water-soluble salts that give strongly alkaline solutions...

, Na2S, which is insoluble in organic solvents, NaHS, being a 1:1 electrolyte, is more soluble. Alternatively, in place of NaHS, H2S can be treated with an organic amine to generate an ammonium
The ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...

 salt. Solutions of HS are sensitive to oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

, converting mainly to polysulfide
Polysulfides are a class of chemical compounds containing chains of sulfur atoms. There are two main classes of polysulfides: anions and organic polysulfides. Anions have the general formula Sn2−. These anions are the conjugate bases of the hydrogen polysulfides H2nSn...

s, indicated by the appearance of yellow.

Structure and properties

Crystalline NaHS undergoes two phase transition
Phase transition
A phase transition is the transformation of a thermodynamic system from one phase or state of matter to another.A phase of a thermodynamic system and the states of matter have uniform physical properties....

s. At temperatures above 360 K, NaHS adopts the NaCl structure, which implies that the HS behaves as a spherical anion due to its rapid rotation leading to equal occupancy of eight equivalent positions. Below 360 K, a rhombohedral structure forms, and the HS sweeps out a discoidal shape. Below 114 K, the structure becomes monoclinic. The analogous rubidium and potassium compounds behave similarly.

NaHS has a relatively low melting point of 350 °C. In addition to the aforementioned anhydrous forms, it can be obtained as two different hydrates, NaHS·2H2O and NaHS·3H2O. These three species are all colorless and behave similarly, but not identically.


The usual laboratory synthesis entails treatment of sodium methoxide
Sodium methoxide
Sodium methoxide is a chemical compound, with formula CH3ONa. This colourless solid, which is formed by the deprotonation of methanol, is a widely used reagent in industry and the laboratory...

, NaOMe, with hydrogen sulfide:
NaOMe + H2S → NaHS + MeOH

Industrially, NaOH is employed as the base. The quality of the NaHS can be assayed by iodometric titration, exploiting the ability of HS to reduce I2.


Thousands of tons of NaHS are produced annually. Its main uses are in paper manufacture as a makeup chemical for sulfur used in the Kraft process
Kraft process
The kraft process describes a technology for conversion of wood into wood pulp consisting of almost pure cellulose fibers...

, as a flotation
Froth flotation
Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is used in several processing industries...

 agent in copper mining
Copper extraction
Copper extraction techniques refers to the methods for obtaining copper from its ores. This conversion consists of a series of chemical, physical, and electrochemical processes. Methods have evolved and vary with country depending on the ore source, local environmental regulations, and other...

 where it is used to activate oxide mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

species, and in the leather industry for the removal of hair from hides.
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