Heat capacities and enthalpies of solid-solid transitions and fusion of a series of eleven primary alkylamides by differential scanning calorimetry

Molar heat capacities at constant pressure, C-p,C-m, of 11 primary alkylamides (butanamide, 2-methylpropanamide, pentanamide, 2,2-dimethylpropanamide, hexanamide, octanamide, decanamide, dodecanamide, hexadecanamide, octadecanamide, docosanamide) determined by differential scanning calorimetry (DSC) increased as a function of temperature and were fitted into linear equations. Values at 298.15 K obtained by interpolating/extrapolating the smoothed equations displayed a linear increase with the number of carbon atoms. The C-p,C-m, contribution of the CH2 group was (22.5 +/- 0.7) J . K-1 . mol(-1), in agreement with our previous results for linear alkane-alpha,omega-diamides and alkane-alpha,omega-diols as well as with the literature data for various series of linear alkyl compounds. Temperatures, enthalpies, and entropies of the solid-solid transitions and fusion of alkylamides were also determined. They are discussed with reference to the packing patterns described in the literature.