Construction and Calibration of a Semi-micro-combustion Calorimeter to Determine the Enthalpies of Combustion of N,N′‑Bis(salicylidene)ethylenediamine and N,N′‑Bis(salicylidene)-1,3-propanediamine

The construction and calibration of a semi-micro-combustion calorimeter for samples of around 35 mg is presented. The calorimeter energy equivalent was determined using benzoic acid as the primary standard, obtaining εcal = (2,338.81 ± 0.22) J·K–1. The operation of the calorimeter was verified by the combustion of 1,2,4-triazole and nicotinic acid as secondary and tertiary standards, respectively, obtaining results similar to data reported in the literature. The calorimeter was used to determine the massic standard energy of combustion of N,N′-bis­(salicylidene)­ethylenediamine and N,N′-bis­(salicylidene)-1,3-propanediamine. In addition to the enthalpies of combustion, the molar standard enthalpies of formation in the crystalline phase were calculated from experimental data. Molar enthalpy of vaporization was determined by thermogravimetry and then used to obtain the molar standard enthalpies of formation in the gas phase. The melting temperatures and enthalpies of fusion of these compounds were also determined by differential scanning calorimetry.