Puneet Varma (Editor)

Potassium hydride

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Formula
  
KH

Boiling point
  
316 °C

Appearance
  
colourless crystals

Molar mass
  
40.1062 g/mol

Density
  
1.47 g/cm³

Potassium hydride wwworganicchemistryorgabstractslit1498mgif

Potassium hydride, KH, is the inorganic compound of potassium and hydride, and is therefore classed as an alkali metal 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.

Contents

Preparation

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.

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:

KH + H2O → KOH + H2

Potassium hydride is a superbase that is stronger than sodium hydride. It is used to deprotonate certain carbonyl compounds to give enolates. It also deprotonated amines to give the corresponding amides of the type KNHR and KNR2.

Safety

KH is pyrophoric in air, reacts violently with acids and ignites upon contact with oxidants, including oxygen and other gases. This is why the commercial product is a suspension in mineral oil.

References

Potassium hydride Wikipedia


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