AbstractThe protonation rate constants of the mononegative ions of the di‐aza aromatics with water are obtained from the increase in the diffusion current of the first reduction wave on addition of water to the dimethylformamide (DMF) solution. The rate constant is obtained from an approximate derivation given byHoijtinket al. and from an exact solution given byNicholsonet al. From the dependence of the half‐wave potential on the water concentration, it is shown that the difference between the solvation of the neutral molecules and the mononegative ions is highest for the smallest molecules. Quantumchemical calculations predict a high protonation rate constant for pyrimidine and quinazol