Azides

Key points: Azides are toxic and unstable; they are used as detonators in explosives. Azides, in which nitrogen is present as N₃, may be synthesized by the oxidation of sodium amide with either NO₃⁻ ions or N₂O at elevated temperatures:

The average oxidation number of N in the azide ion is –. The ion is isoelectronic with both dinitrogen oxide, N₂O, and CO₂ and, like these two molecules, is linear. It is a reasonably strong Brønsted base, the pKa of its conjugate acid, hydrazoic acid, HN₃, being 4.77. It is also a good ligand towards d-block ions. However, heavy-metal complexes or salts, such as Pb(N₃)₂ and Hg(N₃)₂, are shock-sensitive detonators and decompose to pro duce the metal and nitrogen:

Ionic azides such as NaN3 are thermodynamically unstable but kinetically inert; they can be handled at room temperature. Sodium azide is toxic and is used as a chemical preservative and in pest control. When alkali metal azides are heated or detonated by impact they explode, liberating N₂; this reaction is used in the inflation of air bags in cars, in which the heating of the azide is electrical. A brief illustration. A typical airbag contains approximately 50 g of NaN₃. To estimate the volume of nitrogen produced when the azide is detonated at room temperature and pressure (20C and 1.0 atm) we need to consider the amount (in moles) of N₂ molecules produced in the decomposition reaction 2NaN₃(s) → 2Na(s)+3N₂ (g). Because 50 g of NaN3 contains 0.77 mol NaN3, it liberates 1.2 mol N₂. This amount occupies 26 dm3 at 20C and 1.0 atm. As the airbag is restricted in volume, the pressure of nitrogen in the airbag will be high, so providing protection to the driver.

Compounds containing the polynitrogen cation, N₅⁺ (11), have been synthesized from species containing N₃⁻ and N2 F ions. For example, N5 AsF₆ is prepared from N₂FAsF₆ and HN₃ in anhydrous HF solvent:

The compound is a white solid that decomposes explosively above 250ºC. It is a powerful oxidizing agent and ignites organic material even at low temperatures. Salts of dipositive anions can be prepared from metathesis with the salts of monopositive anions in anhydrous HF:

The product is a white solid that is friction-sensitive and decomposes to N5 SnF₆ above 250^ºC. This product, N5 SnF₆, is stable up to 500^ºC.

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مواضيع ذات صلة

Phosphine, arsane, and stibine

Hydrazine and hydroxylamine

Ammonia

Phosphides

Nitrides

Nitrogen activation

Microporous solids

Aluminosilicates

Compounds with nitrogen

Oxides of germanium, tin, and lead

Compounds of carbon with oxygen and sulfur

Tin and lead halides