Protonated/deprotonated properties of a room temperature ionic liquid–water system: N, N-Diethyl-N-methyl-N-2-methoxyethyl ammonium tetrafluoroborate

The pH oscillations related to the protonation/deprotonation process in a room temperature ionic liquid (RTIL)–water system were observed at fixed temperatures. The RTIL was hydrophilic N, N-diethyl-N-methyl-N-2-methoxyethyl ammonium tetrafluoroborate ([DEME][BF4]). The rhythmic oscillations of pH were observed only at a water concentration of approximately 90 mol%, where the equilibrated pH value was approximately 3. In contrast, in the water-poor region from 6 to 10 mol% H2O, the pH was almost constant at approximately 8 within the investigated timeframe. The acid–base properties of the [DEME][BF4]–water mixture are related to particular aggregations in the liquid phase.