Insights into solute–solvent interactions of thiamine HCl in aqueous 1‑butyl‑3-methylimidazolium tetrafluoroborate and 1‑butyl‑3-methylimidazolium chloride systems: A volumetric study

• Evaluation of volumetric behavior of thiamine HCl in [Bmim][BF4]/[Bmim][Cl] + H2O media. • Transfer parameters signify the dominance of hydrophilic-hydrophilic interactions in systems of study. • Molecular interactions increase with temperature/concentration escalation of [Bmim][BF4]/[Bmim][Cl]. • Structure breaking behavior of thiamine HCl was observed in all studied systems. This work reports the density and volumetric properties of thiamine hydrochloride (vitamin B 1 ) in pure water as well as in aqueous solutions of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF 4 ]) and 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) at temperatures ranging from 293.15 to 313.15 K and at atmospheric pressure. The experimental density data were used to estimate various volumetric and thermodynamic properties, including the apparent molar volume ( V ϕ ), limiting apparent molar volume ( V ϕ o ), limiting apparent molar volume of transfer ( Δ t r V ϕ o ), limiting apparent molar expansibility ( E ϕ o ), Hepler’s constant ( ∂ E ϕ o /∂T ) p , and thermal expansion coefficient (α). The Limiting apparent molar volumes of transfer were determined to assess the effect of ionic liquids on the solvation behavior of thiamine hydrochloride. The temperature dependence of the volumetric properties was analyzed to obtain expansibility parameters and Hepler’s constant. The results indicate significant modifications in hydration and solvation behavior of thiamine hydrochloride in the presence of ionic liquids, which are governed by ion–dipole and hydrogen-bonding interactions. The present study provides useful insights into electrolyte–solvent interactions in ionic-liquid-modified aqueous media and may be relevant for pharmaceutical and green solvent applications .