Difference between revisions of "Potassium cyanide"
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There are several ways to produce potassium cyanide. | 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]] | + | 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 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. See the [[Sodium_cyanide#Preparation|preparation section of NaCN]] for more information. |
A different route involves treating [[formamide]] with [[potassium hydroxide]]. | A different route involves treating [[formamide]] with [[potassium hydroxide]]. | ||
Revision as of 15:46, 20 March 2019
| 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, methanol 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 | |
| Std molar
entropy (S |
127.8 J·K−1·mol−1 |
| Std enthalpy of
formation (ΔfH |
−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.
Contents
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 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. 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
- 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. 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
- ↑ http://nist.gov/data/PDFfiles/jpcrd643.pdf
- ↑ http://www.cipca.org/presentations/2013/parham_ww-treatment.pdf
