Potassium cyanide

Potassium cyanide
IUPAC name
Potassium cyanide
Identifiers
CAS number 151-50-8 YesY
EC number 205-792-3
UN number 1680
RTECS number TS8750000
Properties
Molecular formula KCN
Molar mass 65.12 g/mol
Appearance White crystalline solid
deliquescent
Density 1.52 g/cm3
Melting point

634.5 °C
Boiling point

1625 °C
Solubility in water 71.6 g/100 ml (25 °C)
100 g/100 mL (100 °C)
Solubility in methanol 4.9 g/100 mL (20 °C)
Solubility in glycerol soluble
Thermochemistry
Std enthalpy of
formation ΔfHo298		 −131.5 kJ/mol
Standard molar
entropy So298		 127.8 J K−1 mol−1
Hazards
MSDS ICSC 0671
EU Index 006-007-00-5
EU classification Very toxic (T+)
Dangerous for the environment (N)
R-phrases R26/27/28, R32, R50/53
S-phrases (S1/2), S7, S28, S29, S45, S60, S61
NFPA 704
NFPA 704.svg
0
4
0
Flash point Non-flammable
LD50 5–10 mg/kg (oral in rats, mice, rabbits)[1]
Related compounds
Other anions Potassium cyanate
Potassium thiocyanate
Other cations Sodium cyanide
Related compounds Hydrogen cyanide
 YesY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Potassium cyanide is an inorganic compound with the formula KCN. This colorless crystalline compound, similar in appearance to sugar, is highly soluble in water. Most KCN is used in gold mining, organic synthesis, and electroplating. Smaller applications include jewelry for chemical gilding and buffing.[2]

KCN is highly toxic. The moist solid emits small amounts of hydrogen cyanide due to hydrolysis, which smells like bitter almonds. Not everyone, however, can smell this odor: the ability to do so is a genetic trait.[3] It is used by entomologists as a killing agent in collecting jars, as most insects succumb within seconds, minimizing damage of even highly fragile specimens.

Contents

Production

KCN is produced by treating hydrogen cyanide with potassium hydroxide,

HCN + KOH → KCN + H2O

or by treating formamide with potassium hydroxide:

HCONH2 + KOH → KCN + 2H2O

Approximately 50,000 tons are produced yearly.[2]

Structure

In aqueous solution, KCN is dissociated into hydrated K+ ions and CN−. As a solid, the salt crystallizes such that the cations and anions organize like Na+ and Cl− in NaCl. The cations and anions six-coordinate. Each K+ is linked to two pi-bonds of the CN− as well as two links each to C and N each. Since CN− is diatomic, the symmetry of the solid is lower than that in NaCl. The cyanide anions form sheets. The CN− ions rapidly rotate in the solid at ambient temperature such that the time averaged shape of the CN− ions is spherical.[4]

Applications

In gold mining, KCN and NaCN form water-soluble salts from gold metal in the presence of air:

4 Au + 8 KCN + O2 + 2 H2O → 4 K[Au(CN)2] + 4 KOH

Very few alternative methods exist for this extraction process.

KCN and the related NaCN are widely used in organic synthesis for the preparation of nitriles and carboxylic acids; illustrative in the von Richter reaction.

Toxicity

KCN can be detoxified most efficiently with hydrogen peroxide:[2]: KCN + H2O2 → KOCN + H2O

Cyanide is a potent inhibitor of cellular respiration, acting on mitochondrial cytochrome c oxidase and hence blocking oxidative phosphorylation. This prevents the body from oxidizing food to produce useful energy. Lactic acidosis then occurs as a consequence of anaerobic metabolism. Initially, acute cyanide poisoning causes a red or ruddy complexion in the victim because the tissues are not able to use the oxygen in the blood. The effects of potassium and sodium cyanide are identical. The person may die within 45 minutes if not treated medically. During this period, convulsions may occur. Death occurs mainly by cardiac arrest.

A number of prominent persons were killed or committed suicide using potassium cyanide, including members of the Black Hand Gang (unsuccessfully) and members of the Nazi Party, such as Hermann Göring and Heinrich Himmler, WWII era British agents (using purpose-made suicide pills), and various religious cults such as in Jonestown. Potassium cyanide (and other forms of cyanide) is a popular method of murder in fiction, especially in the books written by Agatha Christie.

References

  1. ↑ Bernard Martel. Chemical Risk Analysis: A Practical Handbook. Kogan, 2004, page 361. ISBN 1903996651.
  2. ↑ 2.0 2.1 2.2 Andreas Rubo, Raf Kellens, Jay Reddy, Joshua Wooten, Wolfgang Hasenpusch "Alkali Metal Cyanides" in Ullmann's Encyclopedia of Industrial Chemistry 2006 Wiley-VCH, Weinheim, Germany. doi:10.1002/14356007.i01_i01
  3. ↑ Online 'Mendelian Inheritance in Man' (OMIM) 304300
  4. ↑ H. T. Stokes, D. L. Decker, H. M. Nelson, J. D. Jorgensen (1993). "Structure of potassium cyanide at low temperature and high pressure determined by neutron diffraction". Physical Review B 47 (17): 11082–11092. doi:10.1103/PhysRevB.47.11082. .

External links