Temperature Dependence of Air-Water Partitioning of N-Methylated (C1 and C2) Fatty Acid Amides

Air-water partitioning of lower N-methylated fatty acid amides (N-methylformamide, N-methylacetamide, N,N-dimethylformamide, and N,N-dimethylacetamide) was examined at several temperatures in the range from (333 to 373) K employing comparative ebulliometry, differential distillation, and the method of circulation still as suitable experimental techniques. Results are reported in the form of limiting (infinite dilution) relative volatility, limiting activity coefficient, Henry's law constant, and air-water partition coefficient. For each amide, the present air-water partitioning data and some other relevant VLE measurements from the literature were combined with existing calorimetric data on respective derivative thermal properties and correlated simultaneously by a suitable model equation. In the entire treatment, precautions were taken to minimize the effect of uncertain vapor pressures of pure amides at lower temperatures. Recommended thermodynamically consistent temperature dependences of the air-water partitioning characteristics were established allowing their reliable extrapolation to lower (ambient) temperatures where low volatility of aqueous amides hinders direct measurements. Furthermore, the performance of three predictive approaches, namely, the modified UNIFAC, the method of Cabani et al. (J. Solution Chem. 1981, 10, 563-595). and the LFER correlation of Abraham (Fluid Phase Equilib. 2007, 262, 97-110), to estimate the air-water partitioning of the amides was tested.