Sodium hydrosulfide

Sodium hydrosulfide is the chemical compound with the formula NaSH. Other names include sodium bisulfide, sodium sulfhydrate, sodium hydrogen sulfide and Nash. This species is the product of the half -neutralization of hydrogen sulfide with a sodium-derived base. NaSH 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, NaSH, being a 1:1 electrolyte, is more soluble. Alternatively, in place of NaSH, H₂S can be treated with an organic amine to generate an ammoniumSH salt. Solutions of SH^- are sensitive to oxygen, converting mainly to polysulfides, indicated by the appearance of yellow.

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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. RbHS and KHS 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, and also in the leather industry for the removal of hair from hides.

References

1. ^ Haarmann, F.; Jacobs, H.; Roessler, E.; Senker, J. "Dynamics of Anions and Cations in Hydrogensulfides of Alkali Metals NaHS, KHS, RbHS: A Proton Nuclear Magnetic Resonance Study" Journal of Chemical Physics (2002) Volume 117, pages 1269-1276.
2. ^ Eibeck, R. I. Sodium Hydrogen Sulfide" Inorganic Syntheses, volume 7, p 128-131, 1963. ISBN 978-0-88275-165-8.