Selective and efficient catalytic and photocatalytic oxidation of diphenyl sulphide to sulfoxide and sulfone: the role of hydrogen peroxide and TiO2 polymorph

Abstract

In this paper, we describe the role of anatase and rutile crystal phases on diphenyl sulphide (Ph₂S) catalytic and photocatalytic oxidation. The highly selective and efficient synthesis of diphenyl sulfoxide (Ph₂SO) and diphenyl sulfone (Ph₂SO₂) at titanium dioxide was demonstrated. Ph₂S oxidation in the presence of hydrogen peroxide at anatase-TiO₂ can take place both as a catalytic and photocatalytic reaction, while at rutile-TiO₂ only photocatalytic oxidation is possible. The reaction at anatase leads mainly to Ph₂SO₂, whereas, in the presence of rutile a complete conversion to Ph₂SO is achieved after only 15 min (nearly 100% selectivity). Studies on the mechanistic details revealed a dual role of H₂O₂. 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.