Selective and efficient catalytic and photocatalytic oxidation of diphenyl sulphide to sulfoxide and sulfone: the role of hydrogen peroxide and TiO polymorph

In this paper, we describe the role of anatase and rutile crystal phases on diphenyl sulphide (Ph 2 S) catalytic and photocatalytic oxidation. The highly selective and efficient synthesis of diphenyl sulfoxide (Ph 2 SO) and diphenyl sulfone (Ph 2 SO 2 ) at titanium dioxide was demonstrated. Ph 2 S oxidation in the presence of hydrogen peroxide at anatase-TiO 2 can take place both as a catalytic and photocatalytic reaction, while at rutile-TiO 2 only photocatalytic oxidation is possible. The reaction at anatase leads mainly to Ph 2 SO 2 , whereas, in the presence of rutile a complete conversion to Ph 2 SO is achieved after only 15 min (nearly 100% selectivity). Studies on the mechanistic details revealed a dual role of H 2 O 2 . It acts as a substrate in the reaction catalysed only by anatase, but it also plays a key role in alternative photocatalytic oxidation pathways. The presented study shows the applicability of photocatalysis in efficient and selective sulfoxide and sulfone production. Selective sulfoxide and sulfone production can be precisely controlled by choosing TiO 2 polymorph and the reaction mode (catalysis versus photocatalysis).