Thermodynamics of amide + ketone mixtures. 2. Volumetric, speed of sound and refractive index data for N,N-dimethylacetamide + 2-alkanone systems at several temperatures. Application of Flory's model to tertiary amide +n-alkanone systems

Abstract

of amide+ketone mixtures. 2. Volumetric, speed of sound and refractive index data for N,N-dimethylacetamide+2-alkanone systems at several temperatures. Application of Flory's model to tertiary amide+n-alkanone systems. AbstractData on density,  , speed of sound, c, and refractive index, D n , have been reported at (293-303.15) K for the N,N-dimethylacetamide (DMA)+ CH 3 CO(CH 2 ) u-1 CH 3 (u = 1,2,3) systems, and at 298.15 K for the mixture with u = 5. These data have been used to compute excess molar volumes, E m V , excess adiabatic compressibilities, E S  , and excess speeds of sound E c . Negative E m V values indicate the existence of structural effects and interactions between unlike molecules. From molar excess enthalpies, E m H , available in the literature for N,Ndimethylformamide (DMF), or N-methylpyrrolidone (NMP) + n-alkanone systems, it is shown: (i) amide-ketone interactions are stronger in DMF systems than in those with NMP; (ii) they become weaker when u increases in mixtures with a given amide. Structural effects largely contribute to E m H and are more relevant in mixtures containing NMP. The application of the Flory's model reveals that the random mixing hypothesis is valid in large extent for DMF solutions, while NMP systems are characterized by rather strong orientational effects. From values of molar refraction and of the product int P m V (where int P is the internal pressure and mV the molar volume), it is concluded that dispersive interactions increase with u, or when DMF is replaced by DMA in mixtures with a fixed ketone. 1.amides makes also very interesting their theoretical study [11]. In the case of N,Ndialkylamides, due to the lack of hydrogen-bonds, this has been attributed to the existence of strong dipolar interactions [10,12].2-Alkanones, (CH 3 CO(CH 2 ) u-1 CH 3 ) are polar, aprotic compounds and hydrogen bonds acceptors, used as solvents for plastics and some synthetic fibers or as intermediates in the obtention of very important compounds (e.g., methyl methacrylate). They have also an essential role in biochemistry, as many sugars are ketones, and fatty acid synthesis proceeds via these compounds. These features make suitable the study of amide + alkanone mixtures, which must be taken into account within a general experimental and theoretical research of liquid mixtures containing the functional groups carbonyl, amine or amide. In a previous work, we have provided data on density,  , speeds of sound, c, and refractive indices, D n , at (293.15-303.15) K for DMF systems with u = 1,2,3 and at 298.15 K for the solution with u = 5 [13]. As a continuation of this research, we report now similar data for binary mixtures containing N,Ndimethylacetamide (DMA) and the same 2-alkanones over the same temperature range. In order to complete our study, data available in the literature on N-methylpyrrolidone (NMP) + nalkanone systems are also considered [14][15][16][17]. This allows examine the dependence of thermophysical properties on the size and shape of the amide in systems with a...