Conductivity and dissociation behavior of l(+)-lactic acid in the aqueous solutions of (1-butyl-4-methylpyridinium halide, 1-butyl-3-methylimidazolium halide + polyethylene glycol) at different temperatures

Abstract

In this paper, the effect of some ionic liquids on the conductivity behavior of l(+)–lactic acid was studied in polyethylene glycol aqueous solutions. The molar conductivities of l(+)–lactic acid in the aqueous solutions of polyethylene glycol, polyethylene glycol+1–butyl–3–methylimidazolium bromide, polyethylene glycol+1–butyl–3–methylimidazolium chloride, polyethylene glycol+1–butyl–4–methylpyridinium bromide, and polyethylene glycol+1–butyl–4–methylpyridinium chloride were measured at the temperature ranges of (288.15–318.15)K. The molar conductivity data were correlated using Quint–Viallard (QV) conductivity equation to calculate the limiting molar conductivities (Λ0) and dissociation constants (KD). The results show that limiting molar conductivity increase by increasing both of the anion size and acidic power of ILs cation. The KD values were also used to calculate the dissociation standard thermodynamic functions (ΔGD0, ΔSD0, and ΔHD0). The values of ΔGD0 are positive and become more positive at higher temperatures. This implies that the dissociation of the acid is controlled by entropy term.