Azide

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An azide is the N₃^- anion, the anion of hydrazoic acid or a reactive group in organic chemistry where a carbon substituent is attached as RN₃. The azido group is the corresponding N_{3 organic functional group Review: S. Bräse, C. Gil, K. Knepper, V. Zimmermann, Angew. Chem. 2005, 117, 5320-5374; Angew. Chem. Int. Ed. 2005, 44, 5188-5240..}

Contents

1 Azide anion
2 Organic azides
3 Safety
4 External links
5 References

Azide anion

The anion's structure is:

N^-=N⁺=N^-

with a net charge of -1. Heavy metal azides, such as lead azide are very explosive when heated or shaken. Sodium azide (NaN₃) is used in airbags. The azide anion is toxic, inhibiting the function of cytochrome c oxidase by binding irreversibly to the heme cofactor, in a process similar to that of carbon monoxide. Lead azide is another explosive inorganic azide compound.

Organic azides

Organic azides engage in useful organic reactions. They are relatively stable substituents, and act as nucleophiles on the terminal nitrogen (usually liberating nitrogen after cycloreversion reactions), and have electron-donating character for the neighboring carbon. An Azide can easily expulse diatomic nitrogen, a property which is exploited in many reactions such as the Staudinger Ligation or the Curtius rearrangement or for example in the synthesis of γ-imino-β-enamino esters An efficient synthesis of γ-imino- and γ-amino-β-enamino esters Sven Mangelinckx, Pieter Van Vooren, David De Clerck, Ferenc Fülöp, and Norbert De Kimpea Arkivoc JC-1560E 2005 [Online Article]. In the Azide alkyne Huisgen cycloaddition azides react as 1,3-dipoles.

γ-imino-β-enamino esters: Reaction conditions: a) sodium azide 4 eq., acetone, 18 hrs reflux 92% chemical yield b) isopropyl amine, Titanium tetrachloride, diethyl ether 14 hrs. reflux 83% yield. Azide 2 is formed in a nucleophilic aliphatic substitution reaction displacing chlorine in 1 by the azide anion. The ketone reacts with the amine to an imine which tautomerizes to the enamine in 4. In the next rearrangement reaction nitrogen is expulsed and a proton transferred to 6. The last step is another tautomerization with the formation of the enamine 7 as a mixture of cis and trans isomers

Examples of organic azides:

trimethylsilylazide, organic reagent see:trimethylsilyl

Safety

Sodium azide is toxic (LD₅₀ oral (rats) = 27 mg/kg) and can be absorbed through the skin.
Sodium azide decomposes explosively upon heating to above 275 °C (hence its use in airbags in the automotive industry).
Sodium azide reacts vigorously with CS₂, bromine, nitric acid, dimethyl sulfate, and a series of heavy metals, including copper and lead.
In reaction with water or Brønsted acids the highly toxic and explosive hydrogen azide is released.
It has been reported that sodium azide and polymer-bound azide reagents react with dichloromethane and chloroform to form di- and triazidomethane resp., which are both unstable in high concentrations in solution. Various devastating explosions were reported while reaction mixtures were being concentrated on a rotary evaporator. The hazards of diazidomethane (and triazidomethane) have been well documented by A. Hassner et al. A. Hassner et al., Angew. Chem. Int. Ed. Engl., 25, 479 (1986), J. Org. Chem., 55, 2304 (1990)..
Heavy-metal azides that are highly explosive under pressure or shock are formed when solutions of sodium azide or HN₃ vapors come into contact with heavy metals or their salts. Heavy-metal azides can accumulate under certain circumstances, for example, in metal pipelines and on the metal components of diverse equipment (rotary evaporators, freezedrying equipment, cooling traps, water baths, waste pipes), and thus lead to violent explosions. Some organic and other covalent azides are classified as highly explosive and toxic (inorganic azides as neurotoxins; azide ions as cytochrome c oxidase (COX) inhibitors).
Solid iodoazide is explosive and should not be prepared in the absence of solvent. L. Marinescu, J. Thinggaard, I. B. Thomsen, M. Bols, J. Org. Chem. 2003, 68, 9453 – 9455..

External links

http://www.azides.org
[Synthesis of organic azides - Recent methods]

References

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