Kinetic deuterium solvent isotope effects in the pyridine-catalysed iodination of 2-nitropropane in aqueous and methanolic solutions

Abstract

The rate of proton transfer from 2-nitropropane to pyridine was measured in the solvents H₂O, D₂O, CH₃OH, and CH₃OD by the observation of the rate of disappearance of added iodine at 25 °C. The reaction is ca. 150 times slower in methanol than in water, but the factor by which the rate constant is changed when hydroxylic protium is replaced by deuterium is slight and practically the same in both media (k_H/k_Dca. 1.05 ± 0.02). The result rules out from further consideration the idea that the marked difference in solvent isotope effects for the corresponding reactions of the same substrate with lyate ions in these two solvents is due to some general and unexplained solvent effect rather than to an effect specifically associated with the chemical differences between lyate ions in water and alcoholic media.