A study on the electrochemical reduction mechanism of rotenone

Abstract

In aqueous alkaline medium the reduction of rotenone leads, by a two electron process, to the almost quantitative formation of rotenol; the electrochemical method is therefore an alternative to the chemical preparation of this compound. In DMF rotenone shows two reduction waves. At the potential of the first rotenone is directly reduced, via an e.c.e.c. mechanism; the primary radical anion undergoes a first-order isomerization reaction allowing the cleavage of the 6a,7 ether bond and the formation of a further reducible species. The isomerization reaction is the rate-determining step of the overall process; the value of the rate constant has been evaluated by voltammetric measurements. The final step is a protonation reaction by the depolarizer itself leading to the formation of rotenol anion and 6a,12a-didehydrorotenol anion. The latter gives rise to the second polarographic wave via an e.c.e. mechanism.