Interfacial Self-Assembled Thioxathone Monolayers On The Surfaces Of Silica Nanoparticles As Efficient Heterogeneous Photocatalysts For The Selective Oxidation Of Aromatic Thioethers Under Air Atmosphere

Selective oxidation of organic sulfide under mild conditions has attracted growing attention because of its potential applications for the chemical transformation and degradation of toxic organics. Thioxanthones (TXs) are important photosensitizers for the photocatalytic oxidation of organic sulfides. This paper reports the fabrication of TX-functionalized silica nanocomposites, using a bottom-up self-assembling technique, and their application as heterogeneous photocatalysts for the selective oxidation of sulfides into sulfoxides. Two types of TXs, 3-hydroxy-9H-thioxanthen-9-one (TXOH) and 9-oxo-9H-thioxanthene-2,7-dicarboxylic acid (TXCOOH), were synthesized, and their monolayers were anchored covalently on the surface of silica nanoparticles (nanoSiO(2)) via surface silanization and substitution reactions. The produced nanoSiO(2) TX and nanoSiO(2) TXCOOH composites emitted blue luminescence with an emission wavelength at approximately 430-434 nm; they exhibited a similar to 10 nm red shift compared to TXOH and TXCOOH. Both nanocomposites acted as heterogeneous photocatalysts for the selective oxidation of aromatic thioethers into sulfoxides under mild conditions (radiation, air atmosphere, and room temperature). Good conversion efficiency and selectivity were obtained, particularly for those aromatic thioethers with benzyl- and electron-donating substituents. Since the TX monolayer was anchored covalently on the surface of nanoSiO(2) particles, the nanocomposites displayed good reusability and recyclability, in addition to facile separation of the reagents and photocatalysts from the reaction system.