Kinetic and thermodynamic properties of the aerial oxidation of hydroquinone in developer solutions

The aerial oxidation kinetics of hydroquinone in a freshly prepared developer solution at different temperatures and pHs has been studied. The activation parameters, E_a, ΔG^#, ΔS^#, ΔH^# and enthalpy of formation of activated complex, ΔH⁰_f(X^# ), are determined. The large negative value of free energy of activation ΔG^# proves that hydroquinone extremely tends to be oxidized by air at optimum temperature (20°C and optimum pH (10.5) and converts to the activated complex semiquinone. It was also found that if the pH of the developer solution is increased from 9.3 to 10.5 the reaction rate will increase by a factor of 2.