Sodium bisulfide

Sodium hydrosulfide
CAS number 16721-80-5 YesY
207683-19-0 (hydrate)
PubChem 28015
ChemSpider 26058 YesY
EC number 240-778-0
RTECS number WE1900000
Jmol-3D images Image 1
Molecular formula NaHS
Molar mass 56.063 g/mol
Appearance off-white solid, deliquescent
Density 1.79 g/cm3
Melting point

350 ºC (anhydrous)
55 °C (dihydrate)
22 °C (trihydrate)

Solubility in water 50 g/100 mL (22 °C)
Solubility soluble in alcohol, ether
Crystal structure rhombohedral
EU Index Toxic
R-phrases R17 R23 R24 R25
Main hazards Flammable solid, stench, releases hydrogen sulfide
NFPA 704
Flash point 90 ºC
Related compounds
Other anions Sodium hydroxide
Sodium amide
Other cations Ammonium hydrosulfide
Related compounds Sodium sulfide
 N (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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. NaHS is a useful reagent for the synthesis of organic and inorganic sulfur compounds, sometimes as a solid reagent, and more often as an aqueous solution. Solid NaHS is colorless and typically smells like H2S due to hydrolysis by atmospheric moisture. In contrast with sodium sulfide, 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 salt. Solutions of HS are sensitive to oxygen, converting mainly to polysulfides, indicated by the appearance of yellow.

Structure and properties

Crystalline NaHS undergoes two phase transitions. 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.[1]

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, NaOMe, with hydrogen sulfide:[2]

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, as a flotation agent in copper mining where it is used to activate oxide mineral species, and in the leather industry for the removal of hair from hides.


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