| This work accomplishes three major goals: the novel synthesis of acidic ionic liquids, the design of an acidity scale in non-aqueous medium for these ionic liquids and the elucidation of the structure property relationships of these acidic ionic liquids. Acidity measurements are done by pKa in aqueous media and by relative reactivity of the acidic ionic liquids with diazodiphenylmethane in non-aqueous media. For non-aqueous media the rate of reaction is controlled by the acid strength because the rate limiting step is the proton transfer from the acid to diazodiphenylmethane; this rate is measured via UV-Vis spectroscopy. With increasing electron withdrawing effect, electron density is removed from the nitrogen making the bond between N-H weaker, which increases the acidity in non-aqueous media; however, the opposite is true in aqueous media. For this case the conjugate base is stabilized by intermolecular interactions which are weakened as the electron withdrawing effect increases, decreasing the acidity. Quantum chemistry calculations are used to support this explanation on the substituents effects on the acidity of ionic liquids in aqueous media. Further laboratory experiments are needed to generalize the acidity scale. |
