Thermodynamics and Kinetics of Covalent Addition of Bisulfite Ion to Pyrimidinium Ions

Abstract

Equilibrium and rate constants have been calculated for the reversible covalent addition of bisulfite ion to 2-aminopyrimidinium ion and to its 1-methyl and 4-methyl derivatives. 2-Amino-4,6-dimethylpyrimidinium ion did not appear to add bisulfite ion under the experimental conditions. The 1:1 covalent adducts had very low solubility in aqueous buffers around pH 4. This was consistent with their being zwitterions. Rate-determining steps in adduct formation appeared to involve attack of both bisulfite ion and sulfite ion on the pyrimidinium cation. In the reverse reactions, the zwitterionic adducts appeared to decompose by both nonbase-catalyzed and specific base-catalyzed reactions.