Potassium hydride

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Potassium hydride
NaCl polyhedra.png
Identifiers
CAS number 7693-26-7 YesY
PubChem 82127
ChemSpider 74121 YesY
EC number 232-151-5
Jmol-3D images Image 1
Properties
Molecular formula KH
Molar mass 40.1062 g/mol
Appearance colourless crystals
Density 1.43 g/cm3[1]
Melting point decomposes at ~400 °C[2]
Solubility in water reacts
Solubility insoluble in benzene, diethyl ether, CS2
Structure
Crystal structure cubic, cF8
Space group Fm3m, No. 225
Thermochemistry
Specific
heat capacity
C
37.91 J/(mol K)
Std enthalpy of
formation
ΔfHo298
-57.82 kJ/mol
Related compounds
Other cations Lithium hydride
Sodium hydride
Rubidium hydride
Caesium hydride
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Potassium hydride, KH, is the inorganic compound of potassium and hydride. It is a white solid, although commercial samples appear gray. A powerful base that is useful in organic synthesis, it is also a dangerously reactive compound. For this reason it is sold commercially as a slurry (~35%) in mineral oil or sometimes paraffin wax to facilitate dispensing.[3]

Preparation[edit]

Potassium hydride is produced by direct combination of the metal and hydrogen:

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[edit]

KH reacts with water according to the reaction:

KH + H2O → KOH + H2

Potassium hydride is a superbase that is stronger than sodium hydride. It is used to deprotonate certain carbonyl compounds and amines to give, respectively, enolates and amides.[6]

Safety[edit]

KH is pyrophoric in air, reacts violently with acids and ignites upon contact with oxidants, including oxygen.

See also[edit]

References[edit]

  1. ^ 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
  2. ^ 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. 
  3. ^ Potassium Hydride in Paraffin: A Useful Base for Organic Synthesis Douglass F. Taber and Christopher G. Nelson J. Org. Chem.; 2006; 71(23) pp. 8973–8974 doi:10.1021/jo061420v
  4. ^ 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.
  5. ^ 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. 
  6. ^ Charles A. Brown, Prabhakav K. Jadhav (1925), "(−)-α-Pinene by Isomerization of (−)-β-Pinene", Org. Synth. 65: 224 ; Coll. Vol. 8: 553