Thermal properties of amine hydrochlorides. Part I. Thermolysis of primary n-alkylammonium chlorides

Abstract

Thermogravimetry and differential thermal analysis have been applied to the investigation of the thermal properties of primary n-alkylammonium chlorides of general formula (C n H 2 n+1 NH 3)Cl, with n = 0–8. Irrespective of the chain-length, the thermolysis of amine hydrochlorides occurs in one step and leads to the total volatilization of the salts. The experimental TG and DTG curves were used for examination of the thermodynamics and kinetics of this process. The values evaluated for the enthalpy of vaporization enable the estimation of some parameters characterizing this group of compounds, namely, the enthalpy of formation and the energy of the crystal lattice of the salts, as well as the enthalpy of formation of the C n H 2 n+1 NH + 3 ions. The Jacobs and Russell-Jones equation, describing the kinetics of sublimation, has been adapted to the dynamic conditions. It was found that this equation approximates very well with the experimental TG data and evaluated values of the apparent activation energy are very close to the values of the enthalpy of volatilization. On the other hand, the standard kinetic treatment of the data indicated that two-dimensional diffusion (D2 mechanism) may govern the volatilization process. The values of characteristic parameters describing the thermal properties of amine hydrochlorides, namely, temperature limits, enthalpy and kinetic constants of thermolysis, depend notably on the length of the aliphatic chain of the amine.