Molecular Interactions of Diphenhydramine-hydrochloride with Some Imidazolium-Based Ionic Liquids in Aqueous Media at T = 293.15–313.15 K: Volumetric, Acoustic, and UV Absorption Studies

[Image: see text] From the density (ρ) and speed-of-sound (u) measurements, the interactions of the drug diphenhydramine-hydrochloride (DPH) with three imidazolium-based ionic liquids (ILs) (1-butyl-3-methylimidazolium chloride, [C(4)mim][Cl], 1-hexyl-3-methylimidazolium chloride1, [C(6)mim][Cl], and 1-methyl-3-octylimidazolium chloride, [C(8)mim][Cl]) have been investigated in aqueous medium at T = 293.15–313.15 K and experimental pressure p = 0.1 MPa. From the density calculations, the apparent molar volume (V(ϕ)) and the apparent partial molar volumes of transfer (Δ(t)V(ϕ)(o)) have been determined for various solutions of DPH in aqueous solutions of different ILs. In addition, from the speed-of-sound data, the apparent molar isentropic compressibility (K(ϕ)), apparent partial molar isentropic compressibility (K(ϕ)(o)), and apparent partial molar isentropic compressibility of transfer (Δ(t)K(ϕ)(ο)) have been calculated. The pair and triplet interaction coefficients are derived from apparent partial molar volumes of transfer. For the present mixtures, the absorption spectra have been also recorded using a UV–visible spectrophotometer. Using Hepler’s constant, the structure-making nature of the solute has been confirmed. All these calculated parameters provide detailed insights into various physicochemical interactions prevailing in the ternary system and confirm the presence of a strong attractive interaction between DPH and ILs.