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, n D , 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  = 298.15 K for the DMF + 2-heptanone mixture. Due to the high volatility of acetone, the corresponding n D measurements were developed at T  = (293.15 and 298.15) K. The direct experimental data were used to determine the excess molar volumes, V m E , and the excess refractive indices, n D E , at the working temperatures. Values of the excess functions at T  = 298.15 K, for the speed of sound, c E , the isentropic compressibility, κ S E and for the excess thermal expansion coefficient, α p E , 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 V m E values; by the dependence on temperature and pressure of V m E , and by positive P int E (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 V m E values also reveal the existence of structural effects, which largely contribute to the excess molar enthalpy, H m E . V m E and H m E values increase with the chain length of the 2-alkanone. It allows conclude that the relative V m E variation with the ketone size is closely related to that of the interactional contribution to this excess function. Molar refraction values, R m , show that dispersive interactions become more relevant for the systems including longer 2-alkanones.