Preparation of selenoxides from the catalytic autoxidation of organoselenides with nitrogen oxides

Abstract

Various alkyl, aryl and benzyl selenides (RSeR') are readily converted in high yields to the corresponding selenoxide in the presence of dioxygen and catalytic amounts of either nitrogen dioxide, nitrosonium cation or nitric oxide in acetic acid. The selenoxides are initially isolated as the acetic acid adducts (from which the free selenoxides are readily liberated by treatment with base). Nitrogen dioxide is also capable of the stoichiometric oxidation of the selenoethers; and the electron donor-acceptor or EDA complex with nitrosonium, i.e. [R(2)Se . NO+]NO3- is formed as the first intermediate by the selenoether-induced disproportionation of NO2. The critical role of the nitrosonium EDA complex is further demonstrated by the production of selenoxide by an alternative (low-temperature) photochemical procedure involving the deliberate irradiation of the charge-transfer absorption band of [PhSeMe . NO+]NO3-. A scheme is shown that presents the sequence of redox changes of the nitrogen oxides involved in the catalytic conversion of selenoethers to their selenoxides.