nitrite, any member of either of two classes of compounds derived from nitrous acid. Salts of nitrous acid are ionic compounds containing the nitrite ion, NO-2, and a positive ion such as Na+ in sodium nitrite (NaNO2). Esters of nitrous acid are covalent compounds having the structure R―O―N―O, in which R represents a carbon-containing combining group such as ethyl (C2H5) in ethyl nitrite. These covalent nitrites are isomers of the nitro compounds—e.g., nitroethane—which are considered to be derivatives of nitric acid rather than of nitrous acid.
Nitrites usually are prepared by absorption of nitric oxide and nitrogen dioxide in an alkaline solution. In an older method, sodium nitrate was fused with lead, and the resulting sodium nitrite was dissolved in water and separated from the by-product, lead oxide, by filtration. Nitrites are used as food preservatives and in medicine as vasodilators to relieve cardiac pain. See also nitroso compound.