Base catalyzed hydrolysis and 18O=C exchange of ethyl and isopropyl toluoate in H2O and D2O media. The anionic tetrahedral intermediates are protonically equilibrated

Article abstract of DOI:10.1021/ja00111a009

To answer the question of whether the anionic tetrahedral intermediates produced from base hydrolysis of esters are in protonic equilibrium, ¹⁸O exchange studies of the esters ethyl toluoate (2) and isopropyl toluoate (3) recovered from the basic hydrolysis medium in H₂O and D₂O at 25 °C were undertaken. The observed deuterium solvent kinetic isotope effects on (k_hyd)_H2O/D2O are 0.75 and 0.81 for 2 and 3, respectively. For the ¹⁸O=C exchange process, the DSKIEs are (k_ex)_H2O/D2O = 0.97 and 0.86 for 2 and 3. Overall (k_ex/k_hyd)_H2O = 0.068, (k_ex/k_hyd)_D2O = 0.052 for 2; for 3 these values are (k_ex/k_hyd)_H2O = 0.15, (k_ex/k_hyd)_D2O = 0.14. On the basis of these results there is no compelling evidence for a process limiting the exchange where there is a proton in flight generating a strong primary deuterium kinetic isotope effect.