Titrimetric methods based on redox reactions constitute at present one of the most extensive and most developed fields of analytical chemistry.1-4Increased attention recently has been paid to redox titrations in nonaqueous or mixed media.5-7Although systematic research of chemical processes in nonaqueous media began in the beginning of this century, it was originally concentrated almost exclusively on acid-base reactions. The theoretical treatment and practical use of redox reactions in nonaqueous media have not yet attained the level common for acid-base reactions. The main reason is that redox reactions are complex processes in which the actual electron transfer is only one of several steps. Especially with organic substances, the overall process involves dissociation and formation of covalent bonds that usually occurs in several steps with formation of variously reactive intermediates. For this reason, it is impossible to use the values of formal redox potentials for prediction of analytical applicability of redox reactions in nonaqueous solutions; moreover, these values are often unknown. The optimum conditions for determinations are found experimentally more often than on the basis of detailed knowledge of the studied systems.