Potassium hydride
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| Template:Longitem | KH |
| Molar mass | 40.1062 g/mol |
| Appearance | white to gray crystalline powder |
| Density | 1.43 g/cm3[1] |
| Melting point | Template:Chembox CalcTemperatures |
| Solubility | insoluble in benzene, diethyl ether, carbon disulfide |
| Template:Longitem | cubic, cF8 |
| Template:Longitem | Fm3m, No. 225 |
| Template:Longitem | 37.91 J/(mol⋅K) |
| Template:Longitem | −57.82 kJ/mol |
| NFPA 704 (fire diamond) | Template:NFPA 704 diamond |
| Template:Longitem | Lithium hydride Sodium hydride Rubidium hydride Caesium hydride |
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Potassium hydride, KH, is the inorganic compound of potassium and hydrogen. It is an alkali metal hydride. It is a white solid, although commercial samples appear gray. It is a powerful superbase that is useful in organic synthesis. It is sold commercially as a slurry (~35%) in mineral oil or sometimes paraffin wax to facilitate dispensing.[3]
Preparation
Potassium hydride is produced by direct combination of the metal and hydrogen at temperatures between 200 and 350 °C:
This reaction was discovered by Humphry Davy soon after his 1807 discovery of potassium, when he noted that the metal would vaporize in a current of hydrogen when heated just below its boiling point.[4]Template:Rp
Potassium hydride is soluble in fused hydroxides (such as molten sodium hydroxide) and salt mixtures, but not in organic solvents.[5]
Reactions
KH reacts with water according to the reaction:
As a superbase, potassium hydride is more basic than sodium hydride. It is used to deprotonate certain carbonyl compounds to give enolates. It also deprotonates amines to give the corresponding amides of the type KNHR and Template:Chem2.[6]
Safety
KH can be pyrophoric in air, react violently with acids, and can ignite upon contact with oxidants. As a suspension in mineral oil, KH is less dangerous.
See also
References
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- ↑ Robert E. Gawley, Xiaojie Zhang, Qunzhao Wang, "Potassium Hydride" Encyclopedia of Reagents for Organic Synthesis 2007 John Wiley & Sons. Script error: No such module "CS1 identifiers".
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- ↑ Humphry Davy (1808), The Bakerian Lecture on some new phenomena of chemical changes produced by electricity, particularly the decomposition of fixed alkalies, and the exhibition of the new substances which constitute their bases; and on the general nature of alkaline bodies. Philosophical Transactions of the Royal Society, volume 88, pages 1–44. In The Development of Chemistry, 1789–1914: Selected essays, edited by D. Knight, pp. 17–47.
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