UNCATALYZED OXIDATION OF L(-)ARABINOSE BY ACIDIC MANGANESE (VII). OPTIMIZATION, STOICHIOMETRY, ACTIVATION FUNCTIONS AND MECHANISM

Abstract

The uncatalyzed oxidation of L(-)arabinose by manganese (VII) in acidic medium of H2SO4 and constant ionic strength (using potassium nitrate) were investigated kinetically. The change in concentration of manganese (VII) was followed using spectrophotometric method. The study showed that the reaction rate increases by raising the concentration of L(-)arabinose, manganese (VII) and H+ and is independent of salt concentration. The optimum condition of the reaction (highest rate value) found at 0.02 M of L(-)arabinose, 0.0003 M of manganese (VII), 0.5 M of H+ and 0.5 M of KNO3. Findings from stoichiometry measurements revealed that one mol of arabinose consumed two mol of manganese (VII). The temperature influence on the reaction was carried under constant experimental conditions, it was found that the rate of the reaction enhanced by raising the temperature. The activation energy of the reaction was evaluated and found to be 22.74 kJ·mol-1. Activation functions namely, frequency factor, free energy change and the entropy change of the uncatalyzed oxidation were also evaluated at various temperatures. Spot test analysis of the uncatalyzed reaction products revealed the presence of formic acid supporting the proposed mechanism. Reaction rate law was established and it was in strong agreement with the experimental results.

Keywords

• activation energy
• ionic strength
• pseudo-first order
• spectrophotometric method
• spot analysis