ELECTROOXIDATION OF ASCORBIC-ACID IN AN AQUEOUS CITRATE SUFFER SOLUTION

Ascorbic acid is a non-toxic reducing agent with potential application s in the electroless deposition of metals. Reducing agents can be cons umed through (i) homogeneous reactions in solution (e.g., reaction wit h gold thiosulfate, oxygen or peroxide) and (ii) heterogeneous surface reactions, leading either to the deposition of metal or nonmetal depo siting reactions, The chemical and electrochemical oxidation of ascorb ic acid has been investigated in an aqueous citrate solution at pH 6.4 and 25 degrees C to quantify its consumption rate in electroless proc esses. Ascorbic acid undergoes a homogeneous reaction with dissolved o xygen in a pseudo first-order reaction having a rate constant of (1.75 x 10(-3))/min, This is equivalent to consuming five percent of the in itial ascorbic acid concentration in 30 min. Hydrogen peroxide is one of the possible side products of ascorbic acid oxidation, The addition of hydrogen peroxide on gold surfaces does not significantly accelera te the reaction between dissolved oxygen and ascorbic acid. The diffus ion coefficient was found to be 6.46 x 10(-6) cm(2)/sec.