Bisulfite

Its conjugate base is sulfite, SO2−3: Attempted isolation of the common salts of bisulfite results in dehydration of the anion with formation of metabisulfite (S2O2−5), also known as disulfite: Because of this equilibrium, anhydrous sodium and potassium salts of bisulfite cannot be obtained.

In water chlorination, sodium bisulfite is used to reduce the residual 'chlorine' which can have a negative impact on aquatic life.

In organic chemistry, sodium bisulfite is used to form adducts with aldehyde and with certain cyclic ketones.

[8] Examples of such procedures are described for benzaldehyde,[9] 2-tetralone,[10] citral,[11] the ethyl ester of pyruvic acid[12] and glyoxal.

[14] Another use of bisulfite in organic chemistry is as a mild reducing agent, for example to remove traces or excess amounts of chlorine, bromine, iodine, hypochlorite salts, osmate esters, chromium trioxide and potassium permanganate.

The Bucherer carbazole synthesis is a related organic reaction that uses sodium bisulfite as a reagent.

Sodium bisulfite is used in the analysis of the methylation status of cytosines in DNA.