Polarography in initial stages of elucidation of organic electrode processes

Abstract

To develop a reliable electroanalytical method, it is essential to understand – at least in principle – the nature of physical and chemical processes involved. DC polarography is a useful tool in initial stages of elucidation of processes involving reductions and oxidations of organic compounds in aqueous solutions. Main information to be obtained involves: the number of reduction and oxidation steps, the number of electrons transferred in each step, the nature of the transport of electroactive species, the roles of fast, slower and slow chemical reactions (such as proton transfers or hydration–dehydration equilibria), in particular those preceding electron transfer and the structure of the electrolysis product. The used tools are: (i) Measurements of the limiting current and half-wave potentials and their dependence on composition of the supporting electrolyte; (ii) dependences on drop-time and scan-rate; (iii) product identification; (iv) comparison with structurally related compounds, experimentally and from literature. Examples of reductions of the following bonds are given. Single bonds: C–X (X = halides, OR, OH, NH2, SR), N–Y (Y = O, N, S), O–O, N–N, S–S. Double bonds: C=C, C=N, C=S, N=N, and also triple bonds: C≡C, C≡N. Examples of oxidations are those of phenols and of enediols. Anodic waves due to mercury salt formations are observed for thiols, urea and thiourea derivatives (barbiturates, thiobarbiturates), and dithiocarbamates. References are restricted to our work.