The influence of transition metal ions on the kinetics of ascorbic acid oxidation by methylene blue in strongly acidic media

The kinetics of the oxidation of L-ascorbic: acid (H-2 A) by methylene blue was investigated in strongly acidic media over the temperature range 22-40 degreesC. The kinetic studies were carried out as a function of different variables like concentration, pH, ionic strength and temperature. The rate was found to be a linear relation with [H-2 A], [M.B.] and [H+]. Ionic stre ngth dependence formation indicated complex formation by monocationic and a nionic species in solution. The reaction rate was greatly catalyzed by the presence of trace amounts of copper (II) ion. Possible mechanisms for the c atalyzed and uncatalyzed reactions are proposed. Kinetic evidence for a spe cific catalytic effect by binding of alkali metal ions to oxidant is also r eported. The derived rate equations are in good agreement with the experime ntal observations.