Potassium cyanide

Potassium cyanide

Names
IUPAC name Potassium cyanide
Identifiers
Jmol-3D images	Image
SMILES [C-]#N.[K+]
Properties
Chemical formula	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)
Solubility in water	71.6 g/100 ml (25 °C) 100 g/100 ml (100 °C)
Solubility	Soluble in ethylene glycol, glycerol, methanol Slightly soluble in acetonitrile, DMF Almost insoluble in acetone, dioxane, tert-butanol
Solubility in ammonia	4.55 g/100 g (-33.9 °C)
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
Std molar entropy (So298)	127.8 J·K−1·mol−1
Std enthalpy of formation (ΔfHo298)	−131.5 kJ/mol
Hazards
Safety data sheet	Sigma-Aldrich
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (Median dose)	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 cyanuric acid or urea with potassium hydroxide. This gives potassium cyanate. Crush the resulting solid and grind it. Mix it with a reducing agent, such as carbon and heat it until no more gases are released. Or use magnesium as a reducing agent to make a thermite-like mixture, which is ignited to reduce the potassium cyanate to potassium cyanide, though the yield of this route is bad. Both routes give impure potassium cyanide, which needs to be purified to be of any use in chemical reactions. See the preparation section of NaCN for more information.

A different route involves treating formamide with potassium hydroxide.

The 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
• Make cyanogen and cyanuric chloride
• Extract and dissolve gold, silver metal
• Make Prussian blue
• Make glycolic acid
• Von Richter reaction

Handling

Safety

Potassium cyanide is highly toxic. Ingestion can lead to death. The 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 → KOCN + NaCl

KCN + H₂O₂ → KOCN + 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 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 KOCN + 4 H₂O → K₂CO₃ + (NH₄)₂CO₃

References

Relevant Sciencemadness threads

• Purer KCN
• Test Potassium Cyanide