Investigation on Phase Transitions and Thermodynamic Properties of 1-Dodecylamine Hydrochloride (C₁₂H₂₅NH₃Cl)(s) by an Improved Adiabatic Calorimeter

Abstract

1-Dodecylamine hydrochloride was synthesized by the solvent-thermal method. The structure and composition of the compound were characterized by chemical and elemental analyses, the X-ray powder diffraction technique, and X-ray crystallography. The main structure and performance of an improved automated adiabatic calorimeter are described. Low-temperature heat capacities of the title compound are measured by the new adiabatic calorimeter over the temperature range from 78 K to 397 K. Two solid-to-solid phase transitions have been observed at the peak temperatures of (330.78 ± 0.43) K and (345.09 ± 0.16) K. The molar enthalpies of the two phase transitions of the substance were determined to be (25.718 ± 0.082) kJ · mol⁻¹ and (5.049 ± 0.055) kJ · mol⁻¹, and their corresponding molar entropies were calculated as (77.752 ± 0.250) J · mol⁻¹ · K⁻¹ and (14.632 ± 0.159) J · mol⁻¹ · K⁻¹, respectively, based on the analysis of heat–capacity curves. Experimental values of heat capacities for the title compound have been fitted to two polynomial equations. In addition, two solid-to-solid phase transitions and a melting process of C₁₂H₂₅NH₃Cl(s) have been verified by differential scanning calorimetry.