Sodium azide

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Sodium azide
Identifiers
CAS number26628-22-8 YesY
PubChem33557
ChemSpider30958 YesY
EC number247-852-1
UN number1687
ChEBICHEBI:278547 YesY
ChEMBLCHEMBL89295 YesY
RTECS numberVY8050000
Jmol-3D imagesImage 1
Properties
Molecular formulaNaN3
Molar mass65.0099 g/mol
Appearancecolorless to white solid
Odorodorless
Density1.846 g/cm3 (20 °C)
Melting point275 °C; 527 °F; 548 K (violent decomposition)
Solubility in water41.0 g/100 mL (15 °C)
Solubilityinsoluble in ether
Solubility in alcohol0.316 g/100 mL (16 °C)[1]
Solubility in ammoniasoluble
Acidity (pKa)4.8
Structure
Crystal structureHexagonal, hR12[2]
Space groupR-3m, No. 166
Hazards
MSDSExternal MSDS
EU Index011-004-00-7
EU classificationHighly toxic (T+)
Very dangerous for the environment (N)
R-phrasesR28, R32, R50/53
S-phrases(S1/2), S28, S45, S60, S61
NFPA 704
NFPA 704.svg
0
4
2
Flash point300 °C; 572 °F; 573 K
LD5027 mg/kg (oral, rats/mice)[2]
Related compounds
Other anionsSodium cyanide
Other cationsPotassium azide
Ammonium azide
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references
 
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Sodium azide
Identifiers
CAS number26628-22-8 YesY
PubChem33557
ChemSpider30958 YesY
EC number247-852-1
UN number1687
ChEBICHEBI:278547 YesY
ChEMBLCHEMBL89295 YesY
RTECS numberVY8050000
Jmol-3D imagesImage 1
Properties
Molecular formulaNaN3
Molar mass65.0099 g/mol
Appearancecolorless to white solid
Odorodorless
Density1.846 g/cm3 (20 °C)
Melting point275 °C; 527 °F; 548 K (violent decomposition)
Solubility in water41.0 g/100 mL (15 °C)
Solubilityinsoluble in ether
Solubility in alcohol0.316 g/100 mL (16 °C)[1]
Solubility in ammoniasoluble
Acidity (pKa)4.8
Structure
Crystal structureHexagonal, hR12[2]
Space groupR-3m, No. 166
Hazards
MSDSExternal MSDS
EU Index011-004-00-7
EU classificationHighly toxic (T+)
Very dangerous for the environment (N)
R-phrasesR28, R32, R50/53
S-phrases(S1/2), S28, S45, S60, S61
NFPA 704
NFPA 704.svg
0
4
2
Flash point300 °C; 572 °F; 573 K
LD5027 mg/kg (oral, rats/mice)[2]
Related compounds
Other anionsSodium cyanide
Other cationsPotassium azide
Ammonium azide
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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.[2][3] 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

Alternatively the salt can be obtained by the reaction of sodium nitrate with sodium amide.[4]

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 itself 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.[5] 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 lithium aluminium hydride or a tertiary phosphine such as triphenylphosphine in the Staudinger reaction, with Raney nickel or with hydrogen sulfide in pyridine.

Iron aziderecursor 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.[6] 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:[7]

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.[8] No toxicity has been reported from spent airbags.[9]

References[edit]

  1. ^ Hála, J. (2004). "IUPAC-NIST Solubility Data Series. 79. Alkali and Alkaline Earth Metal Pseudohalides". Journal of Physical and Chemical Reference Data 33: 1–0. Bibcode:2004JPCRD..33....1H. doi:10.1063/1.1563591.  edit
  2. ^ 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.
     
  3. ^ Wells, A. F. (1984), Structural Inorganic Chemistry (5th ed.), Oxford: Clarendon Press, ISBN 0-19-855370-6 
  4. ^ Holleman, A. F.; Wiberg, E. (2001), Inorganic Chemistry, San Diego: Academic Press, ISBN 0-12-352651-5 
  5. ^ 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. 
  6. ^ 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. 
  7. ^ 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. 
  8. ^ "MSDS: sodium azide". Mallinckrodt Baker. 2008-11-21. MSDS S2906. 
  9. ^ Olson, K. R. (2007). Poisoning and Drug Overdose. McGraw-Hill Professional. p. 123. ISBN 0-07-144333-9. 

External links[edit]