Nitrite Chemistry (1): General

Nitrite([NO2]-) is a common ion that has multiple modes of coordination. Mainly:

-NO2

-ONO

<O2N

Among these, the -NO2 isomer(nitro) is of course the most interesting.

As is known to all in organic chemistry, nitro is a strong electron-withdrawing or more specifically pi-accepting group. In coordination chemistry it is also so, for example, [Co(NO2)6]4- is a rather rare d7 low-spin while corresponding [Co(bipy)3]2+ is a normal d7 high-spin. However its properties are still different from other strong field ligands like CO or CN- whose complexes can hardly cross the 18e line. It is said to be a weaker sigma-donor and pi-acceptor than CN- at least for Fe2+.

Its sodium salt, NaNO2, is hygroscopic and gradually oxidize into NaNO3 when exposed to air. It is rather hard to prepare, but can be bought. Although online shops has withdrawn it due to an all-known reason, it is in fact still possible to buy if you are careful enough. I bought a pack due to the same reason. It is commonly used as a food additive and preservative. Due to this it is rather less politically incorrect than the nitrate salts.

It is much more kinetically reactive than nitrate, so it can easily oxidize other things especially in acidic solution. If acidity is increased further, HNO2 may predominate and decomposition would appear.

In organic chemistry it is mainly used to convert aromatic amine (Ar-NH2) into diazonium salts (Ar-N2X).