Study on thermo physical and excess molar properties of binary systems of ionic liquids. I: [Cnmim][PF6] (n = 6, 8) and alkyl acetates

Abstract

The measurements of densities, ρ, speeds of sound, u and refractive indices, nD for binary mixtures containing 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6mim][PF6]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([C8mim][PF6])+ethyl acetate (EA) and butyl acetate (BA) were reported over full range of concentrations. The measurements were performed at atmospheric pressure and seven different temperatures of five degree intervals between (293.15 and 323.15)K. The excess properties on mixing were derived from measured values of these properties. The values of density were utilized to obtain excess molar volumes, VmE, speeds of sound to obtain excess molar isentropic compressibilities, κS,mE and refractive index to get refractive index deviations, ΔφnD. The binary co-efficients of excess properties were obtained by Redlich–Kister polynomial equation. The influences of temperature and addition of –CH2 group in imidazolium cation of ionic liquids as well as acetate on excess properties have been discussed. The VmE and κS,mE are negative and decease with increase in temperature while ΔφnD are positive and increase with increase in temperature. For common acetate, The VmE increases with each increment of –CH2 group in imidazolium cation of IL and similar is true when –CH2 group increases in alkyl acetate for common IL. The deviation in VmEwas investigated by employing Prigogine–Flory–Patterson theory.