Sodium azide

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Sodium azide
Sodium azide.svg
The sodium cation Ball-and-stick model of the azide anion
Identifiers
CAS number 26628-22-8 YesY
PubChem 33557
ChemSpider 30958 YesY
EC number 247-852-1
UN number 1687
ChEBI CHEBI:278547 YesY
ChEMBL CHEMBL89295 YesY
RTECS number VY8050000
Jmol-3D images Image 1
Properties
Molecular formula NaN3
Molar mass 65.0099 g/mol
Appearance colorless to white solid
Odor odorless
Density 1.846 g/cm3 (20 °C)
Melting point 275 °C (527 °F; 548 K) violent decomposition
Solubility in water 38.9 g/100 mL (0 °C)
40.8 g/100 mL (20 °C)
55.3 g/100 mL (100 °C)
Solubility very soluble in ammonia
slightly soluble in benzene
insoluble in ether, acetone, hexane, chloroform
Solubility in methanol 2.48 g/100 mL (25 °C)
Solubility in ethanol 0.22 g/100 mL (0 °C)
Acidity (pKa) 4.8
Structure
Crystal structure Hexagonal, hR12[1]
Space group R-3m, No. 166
Thermochemistry
Specific
heat capacity
C
76.6 J/mol K
Std molar
entropy
So298
70.5 J/mol K
Std enthalpy of
formation
ΔfHo298
21.3 kJ/mol
Gibbs free energy ΔG 99.4 kJ/mol
Hazards
MSDS External MSDS
EU Index 011-004-00-7
EU classification Highly toxic (T+)
Very dangerous for the environment (N)
R-phrases R28, R32, R50/53
S-phrases (S1/2), S28, S45, S60, S61
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 4: Very short exposure could cause death or major residual injury. E.g., VX gas Reactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorus Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point 300 °C (572 °F; 573 K)
LD50 27 mg/kg (oral, rats/mice)[1]
Related compounds
Other anions Sodium cyanide
Other cations Potassium azide
Ammonium azide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

Sodium azide is the inorganic compound with the formula NaN3. This colorless salt is the gas-forming component in many car airbag systems. It is used for the preparation of other azide compounds. It is an ionic substance, is highly soluble in water, and is very acutely toxic.

Structure and preparation[edit]

Sodium azide is an ionic solid. Two crystalline forms are known, rhombohedral and hexagonal.[1][2] The azide anion is very similar in each, being centrosymmetric with N–N distances of 1.18 Å. The Na+
ion is pentacoordinated.

The common synthesis method is the "Wislicenus process," which proceeds in two steps from ammonia. In the first step, ammonia is converted to sodium amide:

2 Na + 2 NH3 → 2 NaNH2 + H2

The sodium amine is subsequently combined with nitrous oxide:

2 NaNH2 + N2O → NaN3 + NaOH + NH3

Curtius and Thiele developed another production process where a nitrite ester is converted to sodium azide using hydrazine. This method is well suited for laboratory preparation of sodium azide:

2 NaNO2 + 2 C2H5OH +H2SO4 → 2 C2H5ONO + Na2SO4 + 2 H2O
C2H5ONO + N2H4-H2O + NaOH → NaN3 + C2H5OH + 3 H2O

Alternatively the salt can be obtained by the reaction of sodium nitrate with sodium amide.[3]

Applications[edit]

Automobile airbags and airplane escape chutes[edit]

Older airbag formulations contained mixtures of oxidizers and sodium azide and other agents including ignitors and accelerants. An electronic controller detonates this mixture during an automobile crash:

2 NaN3 → 2Na + 3 N2

The same reaction occurs upon heating the salt to approximately 300 °C. The sodium that is formed is a potential hazard alone and, in automobile airbags, it is converted by reaction with other ingredients, such as potassium nitrate and silica. In the latter case, innocuous sodium silicates are generated.[4] Sodium azide is also used in airplane escape chutes. Newer generation air bags contain nitroguanidine or similar less sensitive explosives.

Organic and inorganic synthesis[edit]

Due to its explosion hazard, sodium azide is of only limited value in industrial scale organic chemistry. In the laboratory, it is used in organic synthesis to introduce the azide functional group by displacement of halides. The azide functional group can thereafter be converted to an amine by reduction with either SnCl2 in ethanol or lithium aluminium hydride or a tertiary phosphine, such as triphenylphosphine in the Staudinger reaction, with Raney nickel or with hydrogen sulfide in pyridine.

Sodium azide is a versatile precursor to other inorganic azide compounds, e.g., lead azide and silver azide, which are used in explosives.

Biochemistry and biomedical uses[edit]

Sodium azide is a useful probe reagent, mutagen, and preservative. In hospitals and laboratories, it is a biocide; it is especially important in bulk reagents and stock solutions which may otherwise support bacterial growth where the sodium azide acts as a bacteriostatic by inhibiting cytochrome oxidase in gram-negative bacteria; gram-positive (streptococci, pneumococci, lactobacilli) are intrinsically resistant.[5] It is also used in agriculture for pest control.

Azide inhibits cytochrome oxidase by binding irreversibly to the heme cofactor in a process similar to the action of carbon monoxide. Sodium azide particularly affects organs that undergo high rates of respiration, such as the heart and the brain.[citation needed]

Reactions[edit]

Treatment of sodium azide with strong acids gives hydrazoic acid, which is also extremely toxic:

H+
+ N
3
HN
3

Aqueous solutions contain minute amounts of hydrogen azide, as described by the following equilibrium:

N
3
+ H
2
O
is in equilibrium with HN
3
+ OH
(K = 10−4.6
)

Sodium azide can be destroyed by treatment with nitrous acid solution:[6]

2 NaN3 + 2 HNO2 → 3 N2 + 2 NO + 2 NaOH

Safety considerations[edit]

Sodium azide is a severe poison. It may be fatal in contact with skin or if swallowed. Even minute amounts can cause symptoms. The toxicity of this compound is comparable to that of soluble alkali cyanides and the lethal dose for an adult human is about 0.7 grams.[7] No toxicity has been reported from spent airbags.[8]

References[edit]

  1. ^ a b c Stevens E. D., Hope H. (1977). "A Study of the Electron-Density Distribution in Sodium Azide, NaN
    3
    ". Acta Crystallographica A 33 (5): 723–729. doi:10.1107/S0567739477001855.
     
  2. ^ Wells, A. F. (1984), Structural Inorganic Chemistry (5th ed.), Oxford: Clarendon Press, ISBN 0-19-855370-6 
  3. ^ Holleman, A. F.; Wiberg, E. (2001), Inorganic Chemistry, San Diego: Academic Press, ISBN 0-12-352651-5 
  4. ^ Betterton, E. A. (2003). "Environmental Fate of Sodium Azide Derived from Automobile Airbags". Critical Reviews in Environmental Science and Technology 33 (4): 423–458. doi:10.1080/10643380390245002. 
  5. ^ Lichstein, H. C.; Soule, M. H. (1943). "Studies of the Effect of Sodium Azide on Microbic Growth and Respiration: I. The Action of Sodium Azide on Microbic Growth". Journal of Bacteriology 47 (3): 221–230. PMC 373901. PMID 16560767. 
  6. ^ Committee on Prudent Practices for Handling, Storage, and Disposal of Chemicals in Laboratories, Board on Chemical Sciences and Technology, Commission on Physical Sciences, Mathematics, and Applications, National Research Council (1995). "Disposal of Waste". Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: National Academy Press. p. 165. ISBN 0-309-05229-7. 
  7. ^ "MSDS: sodium azide". Mallinckrodt Baker. 2008-11-21. MSDS S2906. 
  8. ^ Olson, K. R. (2007). Poisoning and Drug Overdose. McGraw-Hill Professional. p. 123. ISBN 0-07-144333-9. 

External links[edit]