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Potassium Hydride

Potassium hydride is an inorganic alkali metal hydride of potassium and hydrogen represented by the chemical formula KH [1]. Since it is an extremely reactive compound, it is commercially available as a suspension of small particles in paraffin wax or mineral oil for easier dispensing [2].

Potassium Hydride Identification

CAS Number 7393-26-7 [1]
PubChem CID 82127 [1]
ChemSpider ID 74121 [3]
EC Number 231-704-8 [1, 4]
RTECS Number N/A [4]
InChI Key OCFVSFVLVRNXFJ-UHFFFAOYSA-N [1]

Potassium Hydride Formula

How is Potassium Hydride Prepared

The synthesis of potassium hydride involves a direct combination of potassium and hydrogen represented by the following equation:

2K + H2 → 2KH

The method of preparation was invented by Sir Humphry Davy after he discovered potassium in 1807 through electrolysis of caustic potash (now called potassium hydroxide) [5].

Reaction with Water

Potassium hydride undergoes a violent reaction with water, producing potassium hydroxide and hydrogen that can burn [6]. It is represented by the following reaction:

KH + H2O → KOH + H2

Properties and Characteristics of Potassium Hydride

General Properties

Molar Mass/Molecular Weight 40.106 g/mol [1, 4]

Physical Properties

Color and Appearance White or colorless crystalline solid, gray (commercial sample) [1, 4]
Melting Point ~ 400 °C, 752 °F (decomposes) [3, 7]
Boiling Point N/A [4]
Density 1.47 g cm-3 [4]
Charge 0 (K+ and H) [1, 3]
State of matter at room temperature Solid [1, 4]
Solubility Insoluble in diethyl ether, benzene, and CS2 [8]
Solubility in Water Decomposes in hot and cold water [8]
Heat Capacity (C) 37.91 J/(mol.K)
Acid Dissociation Constant at Logarithmic Scale (pKa) 35 [9]

Atomic Properties

Crystal Structure Cubic

Potassium Hydride Structure

Uses

  • As a donor of hydride and base to Lewis acids like borates and boranes [8]
  • For deprotonating carbonyl compounds and amines to form enolates and amides respectively [8]
  • In cyclization-condensation, rearrangement, elimination, and reducing reactions [8]

Is it Safe

KH is a pyrophoric compound and thus ignites in contact with air. It also produces flammable gases upon reacting with water [1]. Exposure to potassium hydride may cause eye damage and skin corrosion or burns [1].

References

  1. Potassium Hydride – Pubchem.ncbi.nlm.nih.gov
  2. Potassium Hydride in Paraffin: A Useful Base for Organic Synthesis – Pubs.acs.org
  3. Potassium Hydride – Chemspider.com
  4. Potassium Hydride – Americanelements.com
  5. Science and Celebrity: Humphry Davy’s Rising Star – Sciencehistory.org
  6. Potassium Hydride And Sodium HydrideWeb.stanford.edu
  7. Potassium Hydride – Webelements.com
  8. Potassium Hydride – Onlinelibrary.wiley.com
  9. PKa Values of Common Bases – Uwindsor.ca

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