Sodium cyanide

Sodium cyanide
Sodium cyanide bonding
Identifiers
3D model (JSmol)
ChEMBL
ChemSpider
ECHA InfoCard 100.005.091 Edit this at Wikidata
EC Number
  • 205-599-4
RTECS number
  • VZ7525000
UNII
UN number 1689
  • InChI=1S/CN.Na/c1-2;/q-1;+1 checkY
    Key: MNWBNISUBARLIT-UHFFFAOYSA-N checkY
  • InChI=1S/CN.Na/c1-2;/q-1;+1
    Key: MNWBNISUBARLIT-UHFFFAOYAG
  • [C-]#N.[Na+]
Properties
NaCN
Molar mass 49.0072 g/mol
Appearance white solid
Odor faint bitter almond-like
Density 1.5955 g/cm3
Melting point 563.7 °C (1,046.7 °F; 836.9 K)
Boiling point 1,496 °C (2,725 °F; 1,769 K)
48.15 g/100 mL (10 °C)
63.7 g/100 mL (25 °C)
Solubility soluble in ammonia, methanol, ethanol
very slightly soluble in dimethylformamide, SO2
insoluble in dimethyl sulfoxide
1.452
Thermochemistry[1]
70.4 J·mol−1·K−1
115.6 J·mol−1·K−1
−87.5 kJ·mol−1
−76.4 kJ·mol−1
Enthalpy of fusion (ΔfH⦵fus)
 8.79 kJ·mol−1
Hazards
GHS labelling:
GHS06: Toxic GHS09: Environmental hazard
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
4
0
0
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
6.44 mg/kg (rat, oral)
4 mg/kg (sheep, oral)
15 mg/kg (mammal, oral)
8 mg/kg (rat, oral)[3]
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 5 mg/m3[2]
REL (Recommended)
 C 5 mg/m3 (4.7 ppm) [10-minute][2]
IDLH (Immediate danger)
 25 mg/m3 (as CN)[2]
Safety data sheet (SDS) ICSC 1118
Related compounds
Other cations
 Potassium cyanide
Related compounds
 Hydrogen cyanide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Sodium cyanide is a compound with the formula NaCN and the structure Na+ −C≡N. It is a white, water-soluble solid. Cyanide has a high affinity for metals, which leads to the high toxicity of this salt. Its main application, in gold mining, also exploits its high reactivity toward metals. It is a moderately strong base.

Production and chemical properties

Sodium cyanide is produced by treating hydrogen cyanide with sodium hydroxide:[4]

HCN + NaOH → NaCN + H2O

Worldwide production was estimated at 500,000 tons in the year 2006. Formerly it was prepared by the Castner 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.[5] The anions and cations are each six-coordinate. Potassium cyanide (KCN) adopts a similar structure. [6]

When treated with acid, it forms the toxic gas hydrogen cyanide:

NaCN + H+ → HCN + Na+

Because the salt is derived from a weak acid, sodium cyanide readily reverts to HCN by hydrolysis; the moist solid emits small amounts of hydrogen cyanide, which is thought to smell like bitter almonds (not everyone can smell it—the ability thereof is due to a genetic trait[7]). 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 (H2O2) to produce sodium cyanate (NaOCN) and water:[4]

NaCN + H2O2 → NaOCN + H2O

Applications

Cyanide mining

Gold cyanidation (also known as the cyanide process) is the dominant technique for extracting gold, much of which is obtained from low-grade ore. More than 70% of cyanide consumption globally is used for this purpose. The application exploits the high affinity of gold(I) for cyanide, which induces gold metal to oxidize and dissolve in the presence of air (oxygen) and water, producing the salt sodium dicyanoaurate (or sodium gold cyanide) (NaAu(CN)2):[4]

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

A similar process uses potassium cyanide (KCN, a close relative of sodium cyanide) to produce potassium dicyanoaurate (KAu(CN)2).

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 chemicals, including pharmaceuticals. Illustrative is the synthesis of benzyl cyanide by the reaction of benzyl chloride and sodium cyanide.[8]

Niche uses

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

It was used as an insecticide, rodenticide and antibacterial, but these uses were cancelled by the EPA in 1987.[9]

Toxicity

Main article: Cyanide poisoning

Sodium cyanide, like other soluble cyanide salts, is among the most rapidly acting of all known poisons. NaCN 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. An oral dosage as small as 200–300 mg can be fatal.

References

  1. ^ CRC handbook of chemistry and physics : a ready-reference book of chemical and physical data. William M. Haynes, David R. Lide, Thomas J. Bruno (2016-2017, 97th ed.). Boca Raton, Florida. 2016. ISBN 978-1-4987-5428-6. OCLC 930681942.{{cite book}}: CS1 maint: location missing publisher (link) CS1 maint: others (link)
  2. ^ a b c NIOSH Pocket Guide to Chemical Hazards. "#0562". National Institute for Occupational Safety and Health (NIOSH).
  3. ^ "Cyanides (as CN)". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  4. ^ a b c Rubo, Andreas; Kellens, Raf; Reddy, Jay; Steier, Norbert; Hasenpusch, Wolfgang (2006). "Alkali Metal Cyanides". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.i01_i01. ISBN 978-3527306732.
  5. ^ Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.
  6. ^ 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 (Submitted manuscript). 47 (17): 11082–11092. Bibcode:1993PhRvB..4711082S. doi:10.1103/PhysRevB.47.11082. PMID 10005242.
  7. ^ Online Mendelian Inheritance in Man (OMIM): 304300
  8. ^ Adams, Roger; Thal, A. F. (1922). "Benzyl cyanide". Organic Syntheses. 2: 9. doi:10.15227/orgsyn.002.0009.
  9. ^ "Reregistration Eligibility Decision (R.E.D. Facts) Sodium cyanide" (PDF). United Stated Environmental Protection Agency. September 1994.