Spectroscopy and kinetics evidence for the hydrogen-bond activating effect of anion/cation of [Bmim]OAc on the hydrolysis of esters

Experimental and theoretical studies on the hydrolysis of esters catalyzed by different ionic liquids (ILs) have been made. It is found that the rate of the IL catalyzed hydrolysis of an ester depends not only on the structure of the ester but also on the structure of the ions. For the hydrolysis of p-NPB catalyzed by [Bmim]OAc, spectroscopy and kinetics studies complemented by DFT calculations indicate that the hydrogen bonding formed between the cation/anion of [Bmim]OAc and the reactants (both ester and water) is well correlated with the catalytic efficiency of the IL. The anion OAc− of the catalyst contributes more than its cation [Bmim]+ to the hydrolysis of p-NPB. A joined catalytic effect of [Bmim]+ and OAc− was observed especially in neat [Bmim]OAc. The new evidence provided by present studies helps to fully understand the activation mechanism of an IL toward the hydrolysis of an ester.