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]
 Potassium cation, K+ Hydrogen anion, H− | |
| Names | |
|---|---|
| IUPAC name
Potassium hydride
| |
| Identifiers | |
3D model (JSmol)
|
|
| ChemSpider | |
| ECHA InfoCard | 100.028.823 |
| EC Number |
|
PubChem CID
|
|
CompTox Dashboard (EPA)
|
|
| |
| |
| Properties | |
| KH | |
| Molar mass | 40.1062 g/mol |
| Appearance | white to gray crystalline powder |
| Density | 1.43 g/cm3[1] |
| Melting point | decomposes at ~400 °C[2] |
| reacts | |
| Solubility | insoluble in benzene, diethyl ether, carbon disulfide |
| Structure | |
| cubic, cF8 | |
| Fm3m, No. 225 | |
| Thermochemistry | |
Heat capacity (C)
|
37.91 J/(mol⋅K) |
Std enthalpy of
formation (ΔfH⦵298) |
-57.82 kJ/mol |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards
|
corrosive, pyrophoric, reacts violently with acids and water |
| NFPA 704 (fire diamond) | |
| Related compounds | |
Other cations
|
Lithium hydride Sodium hydride Rubidium hydride Caesium hydride |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
| |
Preparation
editPotassium hydride is produced by direct combination of the metal and hydrogen at temperatures between 200 and 350 °C:
- 2 K + H2 → 2 KH
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]: p.25
Potassium hydride is soluble in fused hydroxides (such as molten sodium hydroxide) and salt mixtures, but not in organic solvents.[5]
Reactions
editKH reacts with water according to the reaction:
- KH + H2O → KOH + H2
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 KNR2.[6]
Safety
editKH 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
editReferences
edit- ^ Robert E. Gawley, Xiaojie Zhang, Qunzhao Wang, "Potassium Hydride" Encyclopedia of Reagents for Organic Synthesis 2007 John Wiley & Sons. doi:10.1002/047084289X.rp223.pub2
- ^ David Arthur Johnson; Open University (12 August 2002). Metals and chemical change. Royal Society of Chemistry. pp. 167–. ISBN 978-0-85404-665-2. Retrieved 1 November 2011.
- ^ Douglass F. Taber, Christopher G. Nelson (2006). "Potassium Hydride in Paraffin: A Useful Base for Organic Synthesis". J. Org. Chem. 71 (23): 8973–8974. doi:10.1021/jo061420v. PMC 3248818. PMID 17081034.
- ^ 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.
- ^ Pradyot Patnaik (1 July 2007). A Comprehensive Guide to the Hazardous Properties of Chemical Substances. John Wiley and Sons. pp. 631–. ISBN 978-0-470-13494-8. Retrieved 1 November 2011.
- ^ Charles A. Brown, Prabhakav K. Jadhav (1925). "(−)-α-Pinene by Isomerization of (−)-β-Pinene". Organic Syntheses. 65: 224; Collected Volumes, vol. 8, p. 553.