The Influence of Halide on the Silver-Catalysed Oxidation of N,N-Dimethyl-p-phenylenediamine by [CoIII(NH3)5Cl]2+

AbstractThe mechanism of the silver colloid catalysed oxidation of N,N-dimethyl-p-phenylenediamine by CoIII(NH3)5Cl2+ was studied in the presence of halides in aqueous solution at a pH of about 5. The silver colloids were prepared by reduction of silver nitrate with ascorbic acid or with sodium boranate in the absence of a special stabilizing agent. The course of the reaction could easily be followed in a double wavelength photometer because of the strong absorbance of p- semiquinonediimine, the first oxidation product of p-phenylenediamine. Both the reaction rate and the irreversible course of the reaction depend on the kind and the concentration of halide present in the solution. Apart from the electrocatalytic redox reaction, the oxidative formation of silver halide by cobalt (III) and the reduction of this silver halide by p-phenylenediamine occur simultaneously. Therefore, the mechanism of at least three important photographic processes can be studied at the same time in this redox system.