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:

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.^[8]

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

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]

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 halides.^[10] 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. Oseltamivir, an antiviral medication, is currently produced in commercial scale by a method which utilizes sodium azide.^[13]

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

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; however, some gram-positive bacteria (streptococci, pneumococci, lactobacilli) are intrinsically resistant.^[16]

Agricultural uses

It is used in agriculture for pest control of soil-borne pathogens such as Meloidogyne incognita or Helicotylenchus dihystera.^[17]

It is also used as a mutagen for crop selection of plants such as rice,^[18] barley^[19] or oats.^[20]

As a suicide drug

Sodium azide has gained attention in the Netherlands^[27] and surrounding countries, having been attributed to at least 172 deaths in the period from 2015 to 2022 as part of a suicide drug commonly termed drug X.^[28] In 2021, a review of all case reports of sodium azide intoxication indicated that 37% of cases were suicide attempts.^[29] An increase in the usage of sodium azide as a suicide drug has been attributed to its availability through online retailers.^[30]