THERMAL ISOMERIZATION OF MALEATE ION IN POTASSIUM HALIDE MATRICES

The thermal isomerization of the maleate ion to the fumarate has been studied in KCl, KBr, and KI matrices by infrared spectroscopy. In the temperature range of 240-300°, the reaction proceeds essentially quantitatively by first-order kinetics with a negligible decomposition of the maleate or the fumarate ion. When crystalline, hydrated, disodium maleate was used as the solute, the same rate constant of 2.6 × 1015 exp[(-47,000 ± 5000)/RT] sec-1 was obtained from KCl and KBr matrices while the rate constants were lower in the KI matrix by a factor of about 3 but with the same activation energy. With anhydrous disodium maleate as the solute, the rate constant was 5.3 × 108 exp[(-30,000 ± 5000)/RT] sec-1 in KCl while those from KBr and KI matrices had the same activation energy but were both lower by a factor of about 3. It is suggested that this variation in the reaction activation energy arises from the changes in the structure of the maleate ion according to the method of dehydration of the crystalline hydrated disodium maleate.