Solubility and thermal stability of some amino-mellitate compounds

By reaction between the anion of mellitic acid (benzenehexacarboxylic acid) and some protonated linear polyamines (diethylenetriamine, triethylenetetramine, tetraethylene-pentamine, pentaethylenehexamine, spermidine, and spermine), fairly insoluble complexes have been obtained, with the general formula (amine)(x)(mellitate)H-6 (diethylenetriamine and spermidine, x = 1; triethylenetetramine and spermine, x = 0.75; tetraethylenepentamine, x = 0.6 and 0.8; pentaethylenehexamine, x=0.5). K-s0 values for these complexes have been determined at I=0 mol dm(-3) and T= 25 degrees C (log K-s0 ranges between - 48.2 and - 56.6). The solubility has been studied as a function of pH and of ionic strength. The thermal analysis, performed using air or argon flow, showed that all the solids behave in a similar way. In the range 20-120 degrees C the loss of hydration water occurs, and in the range 150-350 degrees C the first step of non oxidative decomposition takes place, with complete decomposition at 650 degrees C in air flow, whilst in argon flow the decomposition is still incomplete at 900 degrees C. Preliminary results of a parallel diffractometric study are also reported. (C) 1999 Elsevier Science B.V. All rights reserved.