Imidazolium acetate ionic liquids (ILs) are used as electrolytes, solvents, catalysts in the fields of electrochemistry, separation, and synthesis. The nature of the anion-cation intermolecular interactions is important in these applications. In order to understand the influence of water content, temperature, and carbon side-chain length on these interactions, Raman spectroscopy and multiple regression analysis are utilized for this work. The C-C stretching vibration of the acetate ion in Raman spectra is sensitive to the environment of the acetate ion, which make the C-C stretching vibration desirable as a sensor for the anion-cation intermolecular interactions. With the IL water mole fraction increasing from 0.028 to 0.898 at 21 °C, the C-C stretching vibration undergoes a blue shift, indicating a weakening of the anion-cation intermolecular interactions. For ILs with fixed water content, the influence of temperature within the range -195°C to 150 °C is also evaluated. Increasing temperature leads to a red shift of the C-C stretching vibration and strengthens the anion-cation intermolecular interactions. Within the small difference in alkyl side-chain length (2 to 4 carbons) on the imidazolium cations, the chain length has little influence on the interactions. A fitted multiple regression model of the anion-cation intermolecular interactions in imidazolium acetate ILs is constructed, accounting for all three variables simultaneously changing. This model can be used to predict the anion-cation intermolecular interactions and optimize the use of ILs in many applications where these variables may change. The model can also be extended to other types of ILs as well as additional experimental parameters.

Investigating the anion-cation intermolecular interactions in imidazolium acetate ionic liquids by Raman spectroscopy and multiple regression analysis

2019 Fall National Meeting

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