Metal-free oxidation of sulfides by carbon nitride with visible light illumination at room temperature

Mesoporous graphitic carbon nitride (mpg-C3N4) has been developed as a non-metal, heterogeneous photocatalyst for the selective oxidation of sulfides to sulfoxides with O2 at room temperature. Especially, the combination of mpg-C3N4 and aldehydes was a highly active system under visible-light irradiation. For example, mpg-C3N4/isobutyraldehyde catalytic oxidation of methyl phenyl sulfide afforded 97% conversion with 98% selectivity for the methyl phenyl sulfoxide in 4 h. Moreover, the mpg-C3N4 can be easily recovered by filtration and then reused at least four times without losing activity. By exploring the electron spin resonance and some comparative experiments, a catalytic mechanism of this oxidation was provided. Finally, the system also works well in the oxidation of a number of sulfides, including sulfides bearing various groups, and phenyl disulfide. The use of a metal-free heterogeneous catalyst and visible light energy, along with the mild reaction conditions makes this oxidation reaction an environmentally benign and energy-saving chemical process.