Spectroelectrochemical Measurement of the Anodic Oxidation Rate of Phenidone in Physical Developers

Abstract

It was attempted to obtain the standard rate constant (k⁰)for the anodic oxidation of Phenidone (P) in pliysical developers using a spectroelectrochemical measurement in which P was oxidized to Phenidone radical (P^•) on a reflective silver electrode and in which the absorbance change owing to the formation and disappearance of P^• was monitored spectrophotometrically. The k⁰ obtained in a silver thiocyanate developer loas nearly equal to that in the absence of the silver complex (k⁰*) and remained almost constant with time after addition of P, while that obtained in the silver thiosulphate developer was much smaller than k^0* and increased with time. These results suggested an inhibition of the charge transfer by the adsorption of thiosulphate at the silver surface and a displacement of the inhibiting thiosulphate by a species produced from the P oxidation, for which the inhibiting effect is smaller than that of thiosulphate.