SELECTIVE CATALYSIS OF THIOETHER OXIDATIONS WITH DIOXYGEN - CRITICAL ROLE OF NITROSONIUM EDA COMPLEXES IN THE THERMAL AND PHOTOCHEMICAL TRANSFER OF OXYGEN-ATOM FROM NITROGEN-OXIDES TO SULFUR CENTERS

Various alkyl and aryl thioethers (R(2)S) are readily converted in high yields to sulfoxides in the presence of dioxygen and catalytic amounts of nitrogen dioxide. Separate experiments with stoichiometric amounts of reagents (under anaerobic conditions) establish the nitrosonium EDA complex [R(2)S, NO+] NO3- as the critical intermediate formed from the thioether-induced disproportionation of NO2. Low-temperature photoactivation by the deliberate irradiation of the charge-transfer absorption band of [R(2)S, NO+] NO3- leads to sulfoxide via the thioether cation radical. Electron transfer is also a viable route to the thermal (stoichiometric) oxidation of thioethers with NO2 via the same nitrosonium EDA complex. As such, Scheme 4 presents the complete sequence of redox changes of the nitrogen oxides in the catalytic conversion of thioether to sulfoxide via the cation radical.