Sodium azide is an inorganic compound with the chemical formula . 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 highly soluble in water and is acutely poisonous.[
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Structure
Sodium azide is an ionic solid. Two crystalline forms are known, rhombohedral and hexagonal.
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:
The sodium amide is subsequently combined with nitrous oxide:
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 .
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.[.]
Chemical reactions
Acid formation of hydrazoic acid
Treatment of sodium azide with strong acids gives hydrazoic acid (hydrogen azide; HN3):
Hydrazoic acid, also extremely toxic, is especially dangerous because it is a volatile liquid at room temperature. Otherwise, aqueous solutions contain only minute amounts of hydrazoic acid, as described by the following equilibrium:
- , K = 10−4.6
Destruction
Sodium azide can be destroyed by treatment with nitrous acid () generated in situ from a solution of with a metal nitrite by acidification with a mineral acid.
A safer modification to the above method that avoids the potential production of hydrazoic acid or nitrogen oxide fumes is that of W. F. Rinkenbach. A solution of sodium nitrite in of water is added to a stirring dispersion of sodium azide in 10% ammonium acetate, followed by addition of of glacial acetic acid. The solution is allowed to stand in a warm place for an hour and disposed of.
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:
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.[ ]
Organic and inorganic synthesis
Due to its explosion hazard, sodium azide is of only limited value in industrial-scale organic synthesis. In the laboratory, it is used to introduce the azide functional group by displacement of .
Sodium azide is a versatile precursor to other inorganic azide compounds, e.g., lead azide and silver azide, which are used in as primary explosives. These azides are significantly more sensitive to premature detonation than sodium azide and thus have limited applications. Lead and silver azide can be made via double displacement reaction with sodium azide and their respective nitrate (most commonly) or acetate salts. Sodium azide can also react with the chloride of certain alkaline earth metals in aqueous solution, such as barium chloride or strontium chloride to respectively produce barium azide and strontium azide, which are also relatively sensitive primarily explosive materials. These azides can be recovered from solution through careful desiccation.
Biochemistry and biomedical uses
Sodium azide is a useful probe reagent, and an antibacterial preservative for biochemical solutions. In the past thiomersal and chlorobutanol were also used as an alternative to azide for preservation of biochemical solutions.
Sodium azide is an instantaneous inhibitor of lactoperoxidase, which can be useful to stop lactroperoxidase catalyzed 125I protein radiolabeling experiments.
In hospitals and laboratories, it is a biocide; it is especially important in bulk reagents and which may otherwise support bacterium growth where the sodium azide acts as a bacteriostatic by inhibiting cytochrome oxidase in gram-negative bacteria; however, some gram-positive bacteria (streptococci, pneumococci, bacillus) are intrinsically resistant.
Agricultural uses
It is used in agriculture for pest control of soil-borne pathogens such as Meloidogyne incognita or Helicotylenchus dihystera.[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)]
It is also used as a mutagen for crop selection of plants such as rice,
Safety considerations
Sodium azide can be fatally toxic,
It produces extrapyramidal symptoms with necrosis of the cerebral cortex, cerebellum, and basal ganglia. Toxicity may also include hypotension,
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.
Intentional consumption
Sodium azide has gained attention in the Netherlands[ Конец скорпиона // Аргументы и факты] 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)
Treatment
The US CDC reports no specific antidote for azide poisoning.
External links
