Sodium azide

Structural formula
General
Surname	Sodium azide
Molecular formula	NaN 3
Brief description	colorless and odorless solid
External identifiers / databases
CAS number 26628-22-8 EC number 247-852-1 ECHA InfoCard 100,043,487 PubChem 33557 ChemSpider 30958 Wikidata Q407577
properties
Molar mass	65.01 g · mol -1
Physical state	firmly
density	1.85 g cm −3 (20 ° C)
Melting point	Decomposition from 300 ° C.
solubility	good in water (420 g · l −1 at 17 ° C) and liquid ammonia, insoluble in diethyl ether
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 300 + 310 + 330-373-410 EUH: 032 P: 262-273-280-301 + 310 + 330-302 + 352 + 310-304 + 340 + 310
MAK	DFG / Switzerland: 0.2 mg m −3 (measured as inhalable dust )
Toxicological data	27 mg kg −1 ( LD 50 ,  rat ,  oral )
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Sodium azide is the sodium salt of hydrazoic acid . It has the formula NaN ₃ and belongs to the azide class of substances .

presentation

Sodium azide is formed when nitrous oxide is passed over sodium amide at 180 ° C:

${\displaystyle \mathrm {NaNH_{2}\ +\ N_{2}O\ {\xrightarrow {180^{\circ }C}}\ NaN_{3}\ +\ H_{2}O} }$

Ammonia is produced as a by-product according to the following equation :

${\displaystyle \mathrm {NaNH_{2}\ +\ H_{2}O\longrightarrow \ NaOH\ +\ NH_{3}\ ^{\uparrow }} }$

The end of the reaction can be determined from the lack of evolution of ammonia gas.

Sodium azide is also obtained from sodium amide and sodium nitrate in the melt at 175 ° C. Sodium hydroxide and ammonia are produced as by-products .

${\displaystyle \mathrm {NaNO_{3}+3\ NaNH_{2}\longrightarrow NaN_{3}+3\ NaOH+NH_{3}} }$

Description / characteristics

In acidic solution, the explosive results from sodium hydrogen azide HN ₃ . When heated, it decomposes from a temperature of 275 ° C. The heat of decomposition determined by DSC is −54 kJ · mol ⁻¹ or −835 kJ · kg ⁻¹ .

${\displaystyle \mathrm {2\ NaN_{3}\longrightarrow 2\ Na+3\ N_{2}} }$(pure nitrogen by spectral analysis )

In the presence of air, the sodium is also oxidized.

${\displaystyle \mathrm {2\ NaN_{3}+{1/2}O_{2}\longrightarrow \ Na_{2}O+3\ N_{2}} }$

The azide ion N ₃ ^- belongs to the pseudohalides . It behaves in many reactions similar to the halide ions . The mesomeric stabilized ion is linear and symmetrical, with uniform distances between the nitrogen atoms. Their bond length lies between that of the NN double and triple bonds . This stabilization is missing in the case of the free acid and the heavy metal azides.

application

Sodium azide is used in industrial synthesis to prepare lead azide and hydrazoic acid, as well as tert -alkyl azides and other organic azides such as tosyl azide.

The reaction of carbonyl compounds with hydrazoic acid in a strongly acidic medium yields amides from ketones with migration of an alkyl group . If carboxylic acids are used, the amine obtained is one carbon atom poorer ( Schmidt reaction ). The hydrazoic acid required for this is generated in situ from sodium azide. Another application is the preparation of alkyl isocyanates from carboxylic acid halides ( Curtius reaction ).

Sodium azide was also used in airbag fuels to fill the airbag until 1995 .

analysis

Analytically, one makes use of the property of azides to react with iodine only in the presence of thiols or potential thiol compounds (such as penicillin) ( iodine-azide reaction ). This implementation is very sensitive; nitrogen and hydrogen iodide are produced. The iodine solution and aqueous sodium azide solution are combined for detection. Then the sample solution (mercaptans, thioethers, disulfides, thiones, S-heterocycles) is added. After a short time, the solution becomes discolored with evolution of gas. Nitrogen is produced according to the following equation:

${\displaystyle \mathrm {S^{2-}+\ I_{2}\ \longrightarrow \ S\ +\ 2\ I^{-}} }$

${\displaystyle \mathrm {S\ +\ 2\ N_{3}^{-}\longrightarrow \ S^{2-}+\ 3\ N_{2}} }$

Biological effect

Sodium azide is also widely used in all areas in which the growth of microorganisms is to be prevented. Sodium azide can be used to keep consumables (beakers, etc.) aseptic for longer in laboratories. The chemical is also added to solutions, dispersions, etc. (approx. 0.1% to 0.001%) which, due to their composition, are very susceptible to microbial spoilage (e.g. solutions of biopolymers, protein dispersions).

The biochemical mechanism of action consists in the disruption of the electron transport chain of the respiratory chain . The azide ion - like cyanide and carbon monoxide - irreversibly blocks the oxygen binding site in the active center of the cytochrome c oxidase . As a result, ATP production comes to a standstill and the cell dies. Cytochrome c oxidase is found in most oxygen-breathing organisms, so azide is a fairly universal poison - even for mammals.

safety instructions

Hydrazoic acid is released from acidic sodium azide solutions. This is very poisonous and burns the mucous membranes. Anhydrous hydrazoic acid explodes when heated and when exposed to slight vibration. Concentrated solutions must not be heated, poured into a splash, or put on hard with the container. Sodium azide specifically inhibits enzymes that contain heavy metals and is therefore toxic. The acid ion also has a strong blood pressure lowering effect. Even inhalation or oral ingestion of small amounts (for example 1.5 ml of 10% solution) can cause severe symptoms of intoxication. Hydrazoic acid and its solutions have an unbearably pungent odor and cause dizziness, headache and skin irritation upon exposure.

Individual evidence

1. ↑ ^{a b c d e f g} Entry on sodium azide in the GESTIS substance database of the IFA , accessed on January 8, 2020(JavaScript required) .
2. ↑ ^{a b c} Entry on sodium azide. In: Römpp Online . Georg Thieme Verlag, accessed on June 14, 2014.
3. ↑ Entry on Sodium azide in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can extend the harmonized classification and labeling .
4. ↑ Swiss Accident Insurance Fund (Suva): Limits - Current MAK and BAT values (search for 26628-22-8 or sodium azide ), accessed on November 2, 2015.
5. ↑ Sodium azide data sheet (PDF) from Carl Roth , accessed on December 14, 2010.
6. ↑ Gerhard Jander, Ewald Blasius, Joachim Straehle: Introduction to the inorganic-chemical internship . 14th edition. Hirzel, Stuttgart 1995, ISBN 3-7776-0672-3 , p. 205.
7. ↑ G. Brauer (Ed.): Handbook of Preparative Inorganic Chemistry. 2nd Edition. vol. 1, Academic Press, 1963, pp. 474-475.
8. ↑ Grewer, T .; Klais, O .: Exothermic decomposition - investigations of the characteristic material properties , VDI-Verlag, series Humanisierung des Arbeitsleben , Volume 84, Düsseldorf 1988, ISBN 3-18-400855-X , p. 11.
9. ↑ A. Eslami, SG Hosseini, V. Asadi: The effect of microencapsulation with nitrocellulose on thermal properties of sodium azide particles. In: Prog. Org. Coatings. 65, 2000, pp. 269-274.
10. ↑ IPA Waste Profiles: End-of-Life Vehicles: Pollutants and Hazardous Properties , as of October 25, 2012.
11. ↑ G. Jander, E. Blasius, J. Strähle: Introduction to the inorganic-chemical practical course. 14th edition. Hirzel, Stuttgart 1995, ISBN 3-7776-0672-3 , p. 300.