Kinetics of Ascorbic Acid Autoxidation as a Function of Dissolved Oxygen Concentration and Temperature

The kinetics of ascorbic acid autoxidation was studied at pH 6.1 (μ= 0.08) using a buffered model system. Oxygen replenishment in the solution was accomplished by shaking the reaction vessel in a shaker water bath or by bubbling oxygen-nitrogen gas mixtures through the solution. Using the former system, a second order rate constant of 58.19 ± 11.92 min^?1 M^?1 was calculated (45°C), Since the shaker bath did not assure oxygen replenishment and dissolved oxygen levels could not be varied, the latter system was developed. The second order rate constants in the gas mixture experiments ranged from 20.80 ± 2.28 min^?1 M^?1 (30°C) to 176 ± 6.93 min^?1 M^?1 (55°C). Activation energies measured under different conditions ranged from 9.47 to 16.43 kcal mole^?1.