Study of the intermolecular interaction in hydrophobic deep eutectic solvent of (2-n-octyl-4-isothiazolin-3-one + 1-decanol) from the density, viscosity, thermodynamic, spectroscopic and quantum chemical calculations

Hydrophobic deep eutectic solvents (HDESs) are considered as green solvents and have been developed rapidly in recent years, which are widely used in diverse applications. In this study, we introduce a binary system composed of 2-n-octyl-4-isothiazolin-3-one (OIT) as a novel hydrogen bond acceptor (HBA) and 1-decanol as a hydrogen bond donor (HBD) under atmospheric pressure. The fundamental physicochemical properties, including density and dynamic viscosity, of the binary systems with various mole ratios were measured at temperatures of 293.15 K, 303.15 K, 313.15 K, 323.15 K, and 333.15 K. The excess molar volume ($V_m^E$), viscosity deviation ($\Delta \eta$) and excess Gibbs free energy (${\Delta G}^{\ast E}$) for activation of viscous flow were calculated and fitted according to the Redlich-Kister type polynomial equation. Furthermore, the spectral analysis (FTIR, UV–vis and ¹H NMR) confirmed the presence of intermolecular hydrogen bonding in the binary systems. In addition, quantum chemical calculations revealed that there may be multiple modes of hydrogen bond formation between OIT molecule and 1-decanol molecule. However, selecting the most energetically favorable point, the most prominent hydrogen bond was found to be between the amide O atom of OIT and the hydroxyl H atom of 1-decanol.