Potassium cyanide

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Potassium cyanide
Names
IUPAC name
Potassium cyanide
Properties
KCN
Molar mass 65.12 g/mol
Appearance White solid
Odor Faint almond-like
Density 1.52 g/cm3
Melting point 634.5 °C (1,174.1 °F; 907.6 K)
Boiling point 1,625 °C (2,957 °F; 1,898 K)
71.6 g/100 ml (25 °C)
100 g/100 ml (100 °C)
Solubility Soluble in ethylene glycol, glycerol
Slightly soluble in acetonitrile, DMF
Almost insoluble in acetone, dioxane, tert-butanol
Solubility in ammonia 4.55 g/100 g (-33.9 °C)[1]
Solubility in ethanol 0.57 g/100 ml
1.21 g/100 ml (20 °C)
Solubility in formamide 14.6 g/100 ml
Solubility in glycerol 31.84 g/100 ml (15 °C)
Solubility in hydroxylamine 41 g/100 ml
Acidity (pKa) 11.0
Thermochemistry
127.8 J·K−1·mol−1
−131.5 kJ/mol
Hazards
Safety data sheet Sigma-Aldrich
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
5 mg/kg (oral, rabbit)
10 mg/kg (oral, rat)
5 mg/kg (oral, rat)
8.5 mg/kg (oral, mouse)
Related compounds
Related compounds
Sodium cyanide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Potassium cyanide is a compound with the formula KCN, a very toxic cyanide salt, similar to sodium cyanide, with a variety of uses in chemistry and industry.

Properties

Chemical

Potassium cyanide can be oxidized to potassium cyanate using hydrogen peroxide or bleach.

Physical

Potassium cyanide is a white solid soluble in water. It has a weak almond-like odor.

Availability

Chemical suppliers may sell potassium cyanide, however, due to its high toxicity it's almost impossible to get hold of.

Preparation

There are several ways to produce potassium cyanide.

One route involves melting urea with potassium hydroxide. This gives potassium cyanate. Crush the resulting solid and grind it. Mix it with a reducing agent, such as carbon or magnesium to make a thermite-like mixture. Ignite it to reduce the potassium cyanate to potassium cyanide and magnesium or carbon oxides. This route gives impure potassium cyanide which needs to be purified. See the preparation section of NaCN for more information.

A different route involves treating formamide with potassium hydroxide.

Decomposition of potassium ferrocyanide also gives potassium cyanide.

Another more dangerous route involves the acidification of Prussian blue to give hydrogen cyanide which is bubbled to a cooled solution of potassium hydroxide. This gives crude potassium cyanide which can be purified by recrystallization.

Projects

  • Make organic nitriles
  • Extract and dissolve gold, silver metal

Handling

Safety

Potassium cyanide is highly toxic. Ingestion can lead to death. Lethal dose for an average weight person is considered to be between 200–300 mg.

Storage

Potassium cyanide should be stored in closed bottles, away from any acids, in a locked cabinet with a clear hazard label on the storage bottle.

Disposal

Potassium cyanide can be destroyed by oxidizing it with excess bleach or hydrogen peroxide to the less harmful sodium cyanate.

KCN + NaClO → KCNO + NaCl
KCN + H2O2 → KCNO + H2O

Decreasing the pH of the potassium cyanate in the presence of bleach, by adding an acid, will cause it to convert to potassium chloride.[2]

2 NaClO + 2 H+ → Cl2 + 2 Na+ + H2O
2 KCN + 4 NaCNO + 3 Cl2 → 2 KCl + 4 NaCl + 2 CO2 + N2 + 2 H2O

Potassium cyanate will also slowly hydrolyzes in water to harmless potassium carbonate and ammonium carbonate.

2 KCNO + 4 H2O → K2CO3 + (NH4)2CO3

References

  1. http://nist.gov/data/PDFfiles/jpcrd643.pdf
  2. http://www.cipca.org/presentations/2013/parham_ww-treatment.pdf

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