Nitrite

The nitrite ion, which has the chemical formula NO₂⁻, is a symmetric anion with equal N–O bond lengths and an O–N–O bond angle of approximately 120°. Upon protonation, the unstable weak acid nitrous acid is produced. Nitrite can be oxidized or reduced, with the product somewhat dependent on the oxidizing/reducing agent and its strength. The nitrite ion is an ambidentate ligand, and is known to bond to metal centers in at least five different ways. Nitrite is also important in biochemistry as a source of the potent vasodilator nitric oxide. In organic chemistry the NO₂ group is present in nitrous acid esters and nitro compounds. Nitrites are also used in the food production industry for curing meat.

The nitrite ion

Nitrite salts

Sodium nitrite made industrially by passing "nitrous fumes" into aqueous sodium hydroxide or sodium carbonate solution:

The product is purified by recrystallization. Alkali metal nitrites are thermally stable up to and beyond their melting point (441 °C for KNO₂). Ammonium nitrite can be made from dinitrogen trioxide, N₂O₃, which is formally the anhydride of nitrous acid: