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Potassium hydride

| NFPA-H = 3 | NFPA-F = 3 | NFPA-R = 2 | NFPA-S = W Sodium hydride Rubidium hydride Caesium hydride

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.

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.

Potassium hydride is soluble in fused hydroxides (such as molten sodium hydroxide) and salt mixtures, but not in organic solvents.

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 .

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.

References

References

  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. (12 August 2002). "Metals and chemical change". Royal Society of Chemistry.
  3. Douglass F. Taber, Christopher G. Nelson. (2006). "Potassium Hydride in Paraffin: A Useful Base for Organic Synthesis". J. Org. Chem..
  4. E. Dönges. (1963). "Handbook of Preparative Inorganic Chemistry, 2nd Ed.". Academic Press.
  5. 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.
  6. Pradyot Patnaik. (1 July 2007). "A Comprehensive Guide to the Hazardous Properties of Chemical Substances". John Wiley and Sons.
  7. Charles A. Brown, Prabhakav K. Jadhav. (1925). "(−)-α-Pinene by Isomerization of (−)-β-Pinene".
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metal-hydrides potassium-compounds superbases rock-salt-crystal-structure
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