[1310-61-8] · HKS · Potassium Hydrogen Sulfide · (MW 72.18)
Physical Data: mp 455 °C; d 1.68-1.70 g cm-3.
Solubility: very sol H2O; sol EtOH.
Form Supplied in: commercially available as a crystalline solid; colorless when pure. May be contaminated with K2S2O3 and K2CO3.
Preparative Methods: saturation of ethanolic KOH by H2S.4
Handling, Storage, and Precautions: extremely hygroscopic. Darkens on heating to yellow, then deep red at mp. Aqueous solutions evolve H2S on heating (KSH + H2O &ibond; KOH + H2S), and decompose in air to polysulfides and H2S. Oxygen also yields K2S2O3 and traces of K2SO3. Carbon dioxide yields H2S and K2CO3. For other precautions and toxicity see Sodium Hydrogen Sulfide.
Yields from organic halides may be less satisfactory than with NaSH because of formation of greater amounts of thioether with KSH.5 The amount of thiol may be increased at the expense of the thioether by addition of Hydrogen Sulfide or Sulfuric Acid. Phase transfer catalysis is useful (eq 1).6
Thiobenzoic acid (PhCOSH) is obtained in 61-76% yield by addition of Benzoyl Chloride to ethanolic KSH;4b it is an intermediate in the preparation of benzoyl disulfide.4c Anhydrides (eq 2)8 and esters also are suitable.
As noted above, thioether formation from organic halides occurs to a greater extent with KSH than with NaSH. Modest yields (15-50%) of sulfides are obtained, along with polymers, by Michael addition of KSH to a,b-unsaturated ketones or sulfones generated in situ from ketone or sulfone and formaldehyde (eq 3).9
In general, KSH and NaSH are interchangeable with respect to their use in the generation of the thiocarbonyl functional group. The thiolysis of benzotrichloride yields the potassium salt of dithiobenzoic acid, an intermediate in the preparation of thiobenzoylthioglycolic acid, a useful thiobenzoylating agent (eq 4).4a Other trichlorides behave similarly.
Treatment of 2-alkoxy-2-oxo-1,3,2-dioxaphospholanes with KSH gives a phosphodiester with a b-mercaptoethyl group that functions as a protective group easily removed by treatment with base (eq 5).10 The S-substituted derivatives are more useful as protective groups since they are stable to bases as well as acids.
Donald C. Dittmer
Syracuse University, NY, USA