Kinetics and Mechanism of the Addition of Sulfite to p-Benzoquinone

Article abstract of DOI:10.1021/jo00361a008

The 1,4-addition of sulfite to p-benzoquinone (BZQ) forming hydroquinone monosulfonate (HQMS) occurs rapidly in neutral solution.From pH 4.5 to 8.0 HQMS is the sole product, and the reaction kinetics are cleanly first order in the quinone.The rapid reversible formation of intermediate carbonyl bisulfite adducts, which precedes irreversible sulfite attack, leads to a complex kinetic dependence on total sulfite concentration and pH (Scheme I and eq. 3).The rate constant for the reaction of sulfite with free benzoquinone to form HQMS is 7.7*10⁴ M^-1 s^-1 (T = 25 deg C, μ = 0.1).The carbonyl bisulfite adduct is also attacked by sulfite to form HQMS with a rate constant of 1.7*10⁴ M^-1 s^-1 (T = 25 deg C, μ = 0.1).