HSO3

HSO3 is a chemical shorthand associated with the bisulfite moiety, most commonly referring to the bisulfite ion HSO3−. It is derived from sulfurous acid, H2SO3, the conjugate acid of HSO3−. In aqueous solution, sulfurous acid dissociates as H2SO3 ⇌ HSO3− + H+. The bisulfite ion can further lose a proton to form sulfite, SO3^2−, via HSO3− ⇌ SO3^2− + H+. The acid–base behavior depends on pH, with pKa1 of H2SO3 about 1.8–2.0 and pKa2 of HSO3− around 7.0, reflecting its role as both an acid and a base in solution.

Common forms and occurrence: The bisulfite concept encompasses salts such as sodium bisulfite (NaHSO3) and potassium bisulfite (KHSO3), which are water-soluble and widely used in industrial applications. In nature, sulfite/bisulfite species can arise from the dissolution of sulfur dioxide in water or from oxidation-reduction processes in minerals and environmental waters.

Applications and reactions: Bisulfite ions act as reducing agents and as nucleophiles toward carbonyl compounds. In organic chemistry, aldehydes and some ketones form stable bisulfite adducts (RCHO + HSO3− → RCH(OH)SO3−), a property exploited for qualitative analysis and purification. In the food and beverage industry, bisulfite and sulfite salts serve as antioxidants and preservatives, notably in wine and fruit products; they can release sulfur dioxide under acidic conditions, contributing to antimicrobial and anti-oxidant effects.

Safety: Bisulfite salts can be irritants and may trigger hypersensitivity reactions in sensitive individuals. Proper handling and labeling are important, particularly in food processing and consumer products.