Unique Evolution of the Local Structure of 1-Butyl-3-methylimidazolium Iodide and Alcohol Mixtures: Formation of Triiodide Without the External Addition of Iodine

This study focuses on how the addition of a variety of primary alcohols (methanol to 1-dodecanol) influences the local structure of 1-butyl-3-methylimidazolium iodide (abbreviated [C 4 mim]I). We used Raman and UV–Vis spectroscopies to gain molecular-level information about the conformational change of C 4 mim + cations and the iodide ions, as well as information about the alcohol (ROH) in [C 4 mim]I mixtures. We found that a unique local structure in which I_3^ - is formed without the external addition of iodine is generated on the alcohol-rich mixtures when short alkyl-chain length alcohols are placed in [C 4 mim]I, where the formation reaction is very slow phenomenon. Furthermore, we propose a plausible mechanism for the peculiar behavior of primary alcohols in [C 4 mim]I: specifically, how longer alcohols up to 1-dodecanol can mix with [C 4 mim]I over the entire compositional range but the mixtures become completely insoluble for tridecanol and beyond.