Heat capacities of a series of terminal linear alkyldiamides determined by DSC

Molar heat capacities of twelve linear alkane-,-diamides H2NOC–(CH2)(n–2)–CONH2, (n=2 to 12 and n=14) were measured bydifferential scanning calorimetry at T=183 to 323 K. Heat flow rate calibration of the Mettler DSC 30 calorimeter was carried out byusing benzoic acid as reference material. The calibration was checked by determining the molar heat capacity of urea in the sametemperature range as that of measurements. The molar heat capacities of alkane-,-diamides increased in function of temperatureand fitted into linear equations. Smoothed values of Cp,m at 298.15 K displayed a linear increase with the number of carbon atoms.The Cp,m contribution of CH2 group was (22.6±0.4) J K–1 mol–1, in agreement with our previous results concerning linearalkane-a,-diols and primary alkylamides as well as the literature data on various series of linear alkyl compounds.