Thermal properties, thermolysis and thermochemistry of alkanaminium iodides

The thermal features of unbranched compounds of general formula [(CnH2n+1)pNH4−p]I, with n = 0–4 and p =1–4, were studied by thermoanalytical methods (DTA, TG, DTG and Q-TG). All the compounds studied undergo decomposition upon heating, leading to their total volatilisation. In the primary step of the thermal dissociation of these derivatives, HI or RI, in the case of quaternary salts, and the appropriate amines are released in the gaseous phase. This simple thermal decomposition pattern is usually complicated by secondary reactions of an oxidative nature. The latter processes most probably originate from the thermal instability of HI, which can spontaneously decompose to H2 and I2 giving iodine molecules of high oxidative potential. The enthalpies of the thermal dissociation were estimated on the basis of the van't Hoff equation using dynamic thermogravimetric curves. Values derived in this way were used together with available literature data to evaluate the enthalpies of formation and the crystal lattice energies of the hydriodides studied. The crystal lattice energy problems were also examined within the Kapustinskii-Yatsimirskii approach. An attempt was made to describe the kinetics of the thermal decomposition by adopting an Arrhenius model. The influence of the structure of the amines on the thermal behaviour of their iodide salts is reviewed and thoroughly discussed.