Electroreduction of dialkyl peroxides. Activation-driving force relationships and bond dissociation free energies

Abstract

The electrochemical reduction of five dialkyl peroxides in DMF was studied by cyclic voltammetry. The electron transfer (ET) to the selected compounds is concerted with the oxygen-oxygen bond cleavage (dissociative ET) and is independent of the electrode material. Such an electrochemical behavior provided the opportunity to study dissociative ETs by using the mercury electrode and therefore to test the dissociative ET theory by using heterogeneous activation-driving force relationships. The convolution voltammetry analysis coupled to the doublelayer correction led to reasonable estimates of the standard potential (E°) for the dissociative ET to dialkyl peroxides, as supported, whenever possible, by independent estimates. A thermochemical cycle based on the dissociative ET concept was employed to calculate the bond dissociation free energies (BDFEs) of the five peroxides, using the above E°s together with electrochemical or thermochemical data pertaining to the redox properties of the leaving alkoxide ion. The BDFEs were found to be in the 25-32 kcal/mol range, suggesting a small substituent effect. The dissociative ET E°s were also used together with the experimental quadratic free energy relationships to estimate the heterogeneous reorganization energies.