A KINETIC AND MECHANISTIC STUDY OF THE ISOTHERMAL DECOMPOSITION OF CALCIUM MALEATE DIHYDRATE AND CALCIUM FUMARATE TRIHYDRATE

The kinetics of the isothermal decomposition of calcium maleate dihydr ate (between 460 and 490 degrees C) and calcium fumarate trihydrate (b etween 460 and 530 degrees C) were studied. Kinetic measurements were carried out using the accumulatory method for the evolution of permane nt product gases in a calibrated pre-evacuated glass apparatus. The pr oduct gases, from both reactants, were shown by mass spectrometry to b e dominated by CO2 with relatively smaller amounts of CO, C2H2 and C2H 4. The solid decomposition products, from both reactants, were identif ied using X-ray powder diffraction and IR spectroscopy as a mixture of CaCO3 and Ca(OH)(2) together with carbonaceous residue. Due to the un certainity of the composition of the solid residue, approximate reacti on stoichiometry for the decomposition of both reactants is given. Ana lysis of kinetic data was somewhat complicated by the intervention of a secondary reaction possibly involving gaseous species. Kinetic data of both reactants were found to fit the zero-order equation in the ran ge 0.05 < alpha < 0.47. Afterwards, data were best fitted to the secon d-order rate equation in the range 0.47 < alpha < 0.78. NMR analysis o f partially decomposed calcium maleate showed no isomerization to the more stable fumarate anion. Scanning electron microscopy (SEM) reveale d that neither of these two reactants underwent comprehensive melting during the decomposition reaction.