Sodium bisulfite

Sodium bisulfite (or sodium bisulphite, sodium hydrogen sulfite) is a chemical compound with the chemical formula NaHSO3. Sodium bisulfite is a food additive with E number E222. This salt of bisulfite can be prepared by bubbling sulfur dioxide in a solution of sodium carbonate in water. Sodium bisulfite in contact with chlorine bleach (aqueous solution of sodium hypochlorite) will generate heat and form sodium bisulfate and sodium chloride. Sodium bisulfite (or sodium bisulphite, sodium hydrogen sulfite) is a chemical compound with the chemical formula NaHSO3. Sodium bisulfite is a food additive with E number E222. This salt of bisulfite can be prepared by bubbling sulfur dioxide in a solution of sodium carbonate in water. Sodium bisulfite in contact with chlorine bleach (aqueous solution of sodium hypochlorite) will generate heat and form sodium bisulfate and sodium chloride. Sodium bisulfite can be prepared by bubbling excess sulfur dioxide through a solution of suitable base, such as sodium hydroxide or sodium bicarbonate. Sodium bisulfite is a weakly acidic species with a pKa of 6.97. Its conjugate base is the sulfite ion, SO32−: The theoretical fully protonated species is sulfurous acid (H2SO3); however this does not exist in solution and treatment of sodium bisulfite with acids will result in decomposition with telltale effervescence of sulfur dioxide, e.g., In organic chemistry sodium bisulfite has several applications. It forms a bisulfite adduct with aldehyde groups and with certain cyclic ketones to give a sulfonic acid. This reaction is useful for purification procedures. Contaminated aldehydes in a solution precipitate as the bisulfite adduct which can be isolated by filtration. The reverse reaction takes place in presence of a base such as sodium bicarbonate or sodium hydroxide and the bisulfite is liberated as sulfur dioxide. Examples of such procedures are described for benzaldehyde, 2-tetralone, citral, the ethyl ester of pyruvic acid and glyoxal. In the ring-expansion reaction of cyclohexanone with diazald, the bisulfite reaction is reported to be able to differentiate between the primary reaction product cycloheptanone and the main contaminant cyclooctanone. The other main use of sodium bisulfite is as a mild reducing agent in organic synthesis in particular in purification procedures. It can efficiently remove traces or excess amounts of chlorine, bromine, iodine, hypochlorite salts, osmate esters, chromium trioxide and potassium permanganate.