sodium cyanide

Sodium cyanide
Identifiers
CAS number	143-33-9
PubChem	8929
UN number	1689
RTECS number	VZ7525000
Properties
Molecular formula	NaCN
Molar mass	49.0072 g/mol
Appearance	white solid
Density	1.595 g/cm3
Melting point	563.7 °C
Boiling point	1496 °C
Solubility in water	58 g/100 ml (20 °C) (hydrate solubility), 82 g/100 ml (34.7 °C)
Refractive index (nD)	1.45
Hazards
MSDS	ICSC 1118
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	0 3 0
Flash point	Non-flammable
LD50	5.8–15 mg/kg (oral in rats, mice)[1]
Related compounds
Other cations	Potassium cyanide
Related compounds	Hydrogen cyanide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Sodium cyanide is an inorganic compound with the formula NaCN. This highly toxic colourless salt is used mainly in gold mining but has other niche applications. It is an inorganic salt derived from neutralisation reactions involving the weak acid hydrogen cyanide.

Production and chemical properties

Sodium cyanide is produced by treating hydrogen cyanide with sodium hydroxide:^[2]

HCN + NaOH → NaCN + H₂O

Worldwide production was estimated at 500,000 tons in the year 2006. In former times, it was prepared by the Castner-Kellner process involving the reaction of sodium amide with carbon at elevated temperatures.

NaNH₂ + C → NaCN + H₂

The structure of solid NaCN is related to that of sodium chloride.^[3] The anions and cations are each six-coordinate (KCN has a similar structure). Each Na⁺ forms pi-bonds to two CN^- groups as well as two "bent" K---CN and two "bent "K---NC links.^[4]

Because the salt is derived from a weak acid, NaCN readily reverts back to HCN by hydrolysis: the moist solid emits small amounts of hydrogen cyanide, which smells like bitter almonds (not everyone can smell it—the ability thereof is due to a genetic trait^[5]). Sodium cyanide reacts rapidly with strong acids to release hydrogen cyanide. This dangerous process represents a significant risk associated with cyanide salts. It is detoxified most efficiently with hydrogen peroxide:^[2]

NaCN + H₂O₂ → NaOCN + H₂O

Sodium cyanide can be produced by treating formamide with sodium hydroxide. HCONH₂ + NaOH → NaCN + 2H₂O

Applications

Cyanide mining

Sodium cyanide is mainly used to extract gold and other precious metals in mining. This application exploits the high affinity of gold(I) for cyanide, which induces gold metal to oxidize and dissolve in the presence of air and water.

4 Au + 8 NaCN + O₂ + 2 H₂O → 4 Na[Au(CN)₂] + 4 NaOH

Few alternative methods exist for this extraction process.

Chemical feedstock

Several commercially significant chemical compounds are derived from cyanide, including cyanuric chloride, cyanogen chloride, and many nitriles. In organic synthesis, cyanide, which is classified as a strong nucleophile, is used to prepare nitriles, which occur widely in many specialty chemicals, including pharmaceuticals.

Niche uses

Being highly toxic, sodium cyanide is used to kill or stun rapidly such as in illegal cyanide fishing and in collecting jars used by entomologists.

Toxicity

Cyanide salts are among the most rapidly acting of all known poisons. Cyanide is a potent inhibitor of respiration, acting on mitochondrial cytochrome oxidase and hence blocking electron transport. This results in decreased oxidative metabolism and oxygen utilization. Lactic acidosis then occurs as a consequence of anaerobic metabolism.

References

1. ^ Martel, B.; Cassidy, K. (2004). Chemical Risk Analysis: A Practical Handbook. Butterworth–Heinemann. pp. 361. ISBN 1903996651. 
2. ^ ^{a b} Andreas Rubo, Raf Kellens, Jay Reddy, Norbert Steier, Wolfgang Hasenpusch "Alkali Metal Cyanides" in Ullmann's Encyclopedia of Industrial Chemistry 2006 Wiley-VCH, Weinheim, Germany.ISBN 10.1002/14356007.i01 i01
3. ^ Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.
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". Phys. Rev. B 47 (17): 11082-11092. doi:10.1103/PhysRevB.47.11082. 
5. ^ Online 'Mendelian Inheritance in Man' (OMIM) 304300

See also

• Cyanide

External links

• Institut national de recherche et de sécurité (1997). "Cyanure de sodium. Cyanure de potassium". Fiche toxicologique n° 111, Paris:INRS, 6pp. (PDF file, in French)
• International Chemical Safety Card 1118
• Hydrogen cyanide and cyanides (CICAD 61)
• National Pollutant Inventory - Cyanide compounds fact sheet
• NIOSH Pocket Guide to Chemical Hazards
• EINECS number 205-599-4
• CID 8929 from PubChem
• CSST (Canada)
• Sodium cyanide hazards to fish and other wildlife from gold