THERMAL-DECOMPOSITION OF CALCIUM MALONATE DIHYDRATE

A kinetic and microscopic study has been undertaken of the thermal decomposition of calcium malonate. Reaction in the temperature range 612-653 K proceeds without any evidence of detectable melting. From analytical measurements the stoichiometry of the overall reaction was found to be: CH2 (COO)2Ca→0.15 (CH3COO)2Ca+0.85 CaCO3[+0.67C]+0.32 CO2+ 0.01 CO+0.17 (CH3)2CO+0.02 HCOOCH3. Kinetic data showed that reaction initially proceeded at constant rate to fractional reaction, α=0.15. Following a brief accelatory process (0.15<α<0.20) reaction became deceleratory thereafter and the activation energy for the medium region was relatively large, 465 kJ mol-1. None of the rate equations characteristic of solid state reactions was obeyed. A reaction mechanism is proposed, in which the participation of the monobasic acetate interrupts an extended chain structure resulting from links between the dibasic malonate ion and divalent calcium ion, thus enhancing reactivity. © 1990.