REDOX PROCESSES IN MICRODROPLETS STUDIED BY VOLTAMMETRY, MICROSCOPY, AND ESR SPECTROSCOPY - OXIDATION OF N,N,N',N'-TETRAHEXYLPHENYLENE DIAMINE DEPOSITED ON SOLID ELECTRODE SURFACES AND IMMERSED IN AQUEOUS-ELECTROLYTE SOLUTION

Electrochemical processes in nonhomogeneous media such as emulsions al low the electrolysis of materials of low solubility, which gives rise to new ways of controlling reaction environments, and/or simpler separ ation of products. However, the mechanistic details of these redox pro cesses are not well understood. Two types of processes may be consider ed: (i) reactions in the two-phase solution environment coupled by sim ple mass transport in one phase to the interfacial electron transfer, and(ii) reactions involving both liquids in direct contact to the elec trode surface (wetting). The latter type of process can be studied sep arately and is analyzed in this work for the one electron oxidation of the oil N,N,N',N'-tetrahexylphenylene diamine deposited in the form o f microdroplets on basal plane pyrolytic graphite, gold, or siliconize d indium tin oxide (ITO) electrodes and immersed in aqueous electrolyt e. The bulk conversion of the nonconducting oily material proceeds via the uptake of anions from the aqueous phase and the formation of a da rk blue product monitored by voltammetry, optical microscopy, and ESR spectroscopy. The process is extremely sensitive to the type of anion which is electroinserted into the organic phase as is shown for ClO4-, PF6-, Cl-, I-, and OH-. In the case of electroinsertion of hydroxide, a coupled chemical process occurs that can be monitored voltammetrica lly. (C) 1997 Elsevier Science S.A.