Sodium hydrosulfide

Sodium hydrosulfide
IUPAC name	Sodium hydrosulfide
Other names	Sodium bisulfide Sodium sulfhydrate Sodium hydrogen sulfide
Identifiers
CAS number	16721-80-5 Y, 207683-19-0 (hydrate)
PubChem	28015
EC number	240-778-0
RTECS number	WE1900000
InChI	1/Na.H2S/h;1H2/q+1;/p-1
InChI key	HYHCSLBZRBJJCH-REWHXWOFAV
ChemSpider ID	26058
Properties
Molecular formula	NaHS
Molar mass	56.063 g/mol
Appearance	off-white solid, deliquescent
Density	1.79 g/cm3
Melting point	52–54 ºC (hydrate) 350 ºC (anhydrous)
Hazards
MSDS	TDC MSDS
EU Index	Not listed
Main hazards	Flammable solid, stench, releases hydrogen sulfide
NFPA 704	2 3 0
Flash point	90 ºC
Related compounds
Other anions	Sodium hydroxide Sodium amide
Other cations	Ammonium hydrosulfide
Related compounds	Sodium sulfide
Y (what is this?)  (verify) 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 a sodium-derived base. 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 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 SH^- 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 360K, 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 360K, a rhombohedral structure forms, and the HS^- sweeps out a discoidal shape. Below 114K, 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.

Preparation

The usual laboratory synthesis entails treatment of 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.

Applications

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.

References

1. ^ Haarmann, F.; Jacobs, H.; Roessler, E.; Senker, J. (2002). "Dynamics of anions and cations in hydrogensulfides of alkali metals (NaHS, KHS, RbHS): A proton nuclear magnetic resonance study". J. Chem. Phys. 117: 1269–1276. doi:10.1063/1.1483860. 
2. ^ Eibeck, R. I. (1963), "Sodium Hydrogen Sulfide", Inorg. Synth. 7: 128–31, doi:10.1002/9780470132388.ch35