Sodium azide is an inorganic compound with the formulaNaN3. This colorless salt is the gas-forming component in some 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 acutely poisonous.[5]
Structure
Sodium azide is an ionic solid. Two crystalline forms are known, rhombohedral and hexagonal.[1][6] Both adopt layered structures. The azide anion is very similar in each form, being centrosymmetric with N–N distances of 1.18 Å. The Na+ ion has an octahedral geometry. Each azide is linked to six Na+ centers, with three Na–N bonds to each terminal nitrogen center.[7]
Preparation
The common synthesis method is the "Wislicenus process", which proceeds in two steps in liquid ammonia. In the first step, ammonia is converted to sodium amide by metallic sodium:
2 Na + 2 NH3 → 2 NaNH2 + H2
It is a redox reaction in which metallic sodium gives an electron to a proton of ammonia which is reduced in hydrogen gas. Sodium easily dissolves in liquid ammonia to produce solvated electrons responsible for the blue color of the resulting liquid. The Na+ and NH−2 ions are produced by this reaction.
The sodium amide is subsequently combined with nitrous oxide:
2 NaNH2 + N2O → NaN3 + NaOH + NH3
These reactions are the basis of the industrial route, which produced about 250 tons per year in 2004, with production increasing due to the increased use of airbags.[5]
Laboratory methods
Curtius and Thiele developed another production process, where a nitrite ester is converted to sodium azide using hydrazine. This method is suited for laboratory preparation of sodium azide:
Alternatively the salt can be obtained by the reaction of sodium nitrate with sodium amide.[8]
3 NaNH2 + NaNO3 → NaN3 + 3 NaOH + NH3
Chemical reactions
Acid formation of hydrazoic acid
Treatment of sodium azide with strong acids gives gaseous hydrazoic acid (hydrogen azide; HN3), which is also extremely toxic:
H+ + N−3 → HN3
Hydrazoic acid equilibrium
Aqueous solutions contain minute amounts of hydrazoic acid, the formation of which is described by the following equilibrium:
N−3 + H2O ⇌ HN3 + OH−, K = 10−4.6
Destruction
Sodium azide can be destroyed by treatment with in situ prepared nitrous acid (HNO2; not HNO3).[9][10]In situ preparation is necessary as HNO2 is unstable and decomposes rapidly in aqueous solutions. This destruction must be done with great caution and within a chemical fume hood as the formed gaseous nitric oxide (NO) is also toxic, and an incorrect order of acid addition for in situ formation of HNO2 will instead produce gaseous highly toxic hydrazoic acid (HN3).[9]
2 NaN3 + 2 HNO2 → 3 N2 + 2 NO + 2 NaOH
Applications
Automobile airbags and aircraft evacuation slides
Older airbag formulations contained mixtures of oxidizers, sodium azide and other agents including ignitors and accelerants. An electronic controller detonates this mixture during an automobile crash:
2 NaN3 → 2 Na + 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.[11] While sodium azide is still used in evacuation slides on modern aircraft, newer-generation automotive air bags contain less sensitive explosives such as nitroguanidine or guanidine nitrate.[12]
Sodium azide is a useful probe reagent, and an antibacterial preservative for biochemical solutions. In the past merthiolate and chlorobutanol were also used as an alternative to azide for preservation of biochemical solutions.[14]
Sodium azide is an instantaneous inhibitor of lactoperoxidase, which can be useful to stop lactroperoxidase catalyzed 125I protein radiolabeling experiments.[15]
It is also used as a mutagen for crop selection of plants such as rice,[18] barley[19] or oats.[20]
Safety considerations
Sodium azide can be fatally toxic,[21] and even minute amounts can cause symptoms. The toxicity of this compound is comparable to that of soluble alkali cyanides,[22] although no toxicity has been reported from spent airbags.[23]
Sodium azide solutions react with metallic ions to precipitate metal azides, which can be shock sensitive and explosive. This should be considered for choosing a non-metallic transport container for sodium azide solutions in the laboratory. This can also create potentially dangerous situations if azide solutions should be directly disposed down the drain into a sanitary sewer system. Metal in the plumbing system could react, forming highly sensitive metal azide crystals which could accumulate over years. Adequate precautions are necessary for the safe and environmentally responsible disposal of azide solution residues.[26]
Intentional consumption
Sodium azide has gained attention in the Netherlands[27] and abroad[28] as a chemical used for homicidal and suicidal purposes.
Sodium azide has been attributed to at least 172 deaths in the period from 2015 to 2022 as part of an illicit substance used as a suicide aid commonly called drug X (Dutch: middel X)[29] In 2021, a review of all case reports of sodium azide intoxication indicated that 37% of cases were suicide attempts.[30] An increase in the usage of sodium azide as a suicide drug has been attributed to its availability through pyrotechnics-focused online stores.[31]
^Pringle, G. E.; Noakes, D. E. (1968-02-15). "The crystal structures of lithium, sodium and strontium azides". Acta Crystallographica Section B. 24 (2): 262–269. Bibcode:1968AcCrB..24..262P. doi:10.1107/s0567740868002062.
^Holleman, Arnold Frederik; Wiberg, Egon (2001), Wiberg, Nils (ed.), Inorganic Chemistry, translated by Eagleson, Mary; Brewer, William, San Diego/Berlin: Academic Press/De Gruyter, ISBN0-12-352651-5.
^ abCommittee 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. ISBN978-0-309-05229-0.{{cite book}}: CS1 maint: multiple names: authors list (link)
^ abTurnbull, Kenneth; Narsaiah, B.; Yadav, J. S.; Yakaiah, T.; Lingaiah, B. P. V. (2008-03-14), "Sodium Azide", Encyclopedia of Reagents for Organic Synthesis, Chichester, UK: John Wiley & Sons, Ltd, doi:10.1002/047084289x.rs045.pub2, ISBN978-0471936237
^Rohloff John C.; Kent Kenneth M.; Postich Michael J.; Becker Mark W.; Chapman Harlan H.; Kelly Daphne E.; Lew Willard; Louie Michael S.; McGee Lawrence R.; et al. (1998). "Practical Total Synthesis of the Anti-Influenza Drug GS-4104". J. Org. Chem.63 (13): 4545–4550. doi:10.1021/jo980330q.
^Applications of sodium azide for control of soilborne pathogens in potatoes. Rodriguez-Kabana, R., Backman, P. A. and King, P.S., Plant Disease Reporter, 1975, Vol. 59, No. 6, pp. 528-532 (link)
^Awan, M. Afsar; Konzak, C. F.; Rutger, J. N.; Nilan, R. A. (2000-01-01). "Mutagenic Effects of Sodium Azide in Rice1". Crop Science. 20 (5): 663–668. doi:10.2135/cropsci1980.0011183x002000050030x.
^Cheng, Xiongying; Gao, Mingwei (1988). "Biological and genetic effects of combined treatments of sodium azide, gamma rays and EMS in barley". Environmental and Experimental Botany. 28 (4): 281–288. Bibcode:1988EnvEB..28..281C. doi:10.1016/0098-8472(88)90051-2.
^Rines, H. W. (1985-02-01). "Sodium azide mutagenesis in diploid and hexaploid oats and comparison with ethyl methanesulfonate treatments". Environmental and Experimental Botany. 25 (1): 7–16. Bibcode:1985EnvEB..25....7R. doi:10.1016/0098-8472(85)90043-7.
