Thermodynamics of amide + ketone mixtures. 1. Volumetric, speed of sound and refractive index data for N,N-dimethylformamide + 2-alkanone systems at several temperatures

Abstract

Densities, ρ, speeds of sound, c, and refractive indices, nD, have been measured for the systems N,N-dimethylformamide (DMF)+propanone, +2-butanone, or +2-pentanone in the temperature range from (293.15 to 303.15)K and at T=298.15K for the DMF+2-heptanone mixture. Due to the high volatility of acetone, the corresponding nD measurements were developed at T=(293.15 and 298.15)K. The direct experimental data were used to determine the excess molar volumes, VmE, and the excess refractive indices, nDE, at the working temperatures. Values of the excess functions at T=298.15K, for the speed of sound, cE, the isentropic compressibility, κSE and for the excess thermal expansion coefficient, αpE, were also calculated. The investigated systems are characterised by strong (amide+ketone) interactions, which become weaker when the alkanone size is increased. This is supported by negative VmE values; by the dependence on temperature and pressure of VmE, and by positive PintE (excess internal pressure) values. Analysis of the systems in terms of the Rao’s constant indicates that there is no complex formation. In addition, negative VmE values also reveal the existence of structural effects, which largely contribute to the excess molar enthalpy, HmE. VmE and HmE values increase with the chain length of the 2-alkanone. It allows conclude that the relative VmE variation with the ketone size is closely related to that of the interactional contribution to this excess function. Molar refraction values, Rm, show that dispersive interactions become more relevant for the systems including longer 2-alkanones.