Deep eutectic solvents based on ammonium iodide and iodine possessing high electrical conductivity

• Published in: Journal of molecular liquids Vol. 384; p. 122250
• Main Authors: Koyakkat, Maharoof, Moriyama, Katsuhiko, Asakura, Satoshi, Kawamoto, Hiroyuki, Shirota, Hideaki
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.08.2023
• Subjects: Ammonium iodide; Deep eutectic solvent; High electrical conductivity; Polyiodides; Raman spectrum; High electrical conductivity; Deep eutectic solvent; Ammonium iodide; Polyiodides; Raman spectrum
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2023.122250

[Display omitted] •A facile preparation of deep eutectic solvents composed of various ammonium iodides and iodine was demonstrated.•The deep eutectic solvents possess high electrical conductivities (e.g., ∼100 mS cm−1 for methylammonium iodide one).•The molar conductivities of most DESs in this study were much higher than the ideal value based on the Walden rule.•Raman spectra showed polyiodides in DESs of dibutylammonium iodide and iodine.•High electrical conductivity is accounted for by the Grotthuss mechanism. Herein, we have demonstrated the preparation of deep eutectic solvents (DESs) using ammonium iodides and iodine. Binary mixtures of 10 ammonium iodides with iodine were examined, and methylammonium iodide [MeNH3]I, diethylammonium iodide [Et2NH2]I, butylammonium iodide [BuNH3]I, and dibutylammonium iodide [Bu2NH2]I formed liquid DESs when mixed with iodine within specific concentration ranges. The DESs showed high electrical conductivities, which increased with the iodine concentration. Among the DESs studied here, [MeNH3]I/I2 with the molar ratio of 1:2.5 showed a very high electrical conductivity (approximately 100 mS cm−1 at 298 K). Overall, the viscosity of the DES series decreased with increasing iodine concentration. The Walden plot showed that most DESs studied here were good electrical conductors, whereas [Bu2NH2]I/I2 DESs with the molar ratios of 1:0.75 and 1:1.00 were almost ideal electrical conductors. Raman spectra of the DESs [Bu2NH2]I/I2 mixtures showed the presence of polyiodides; thus the high electrical conductivity of the DESs in this study was attributed to the Grotthuss mechanism.