The production of
sulfonic acids which are required as precursors
for detergents, dyes, and drugs can be performed by the sulfoxidation
of hydrocarbons. In this industrial process, SO2 is electronically
excited by UV light, and a CH-bond activation is initiated. This leads
to a radical reaction mechanism that eventually results in the formation
of sulfonic acid as a product. Recent research has demonstrated that
the sulfoxidation of hydrocarbons on titanium dioxide as a photocatalyst
can be carried out by using visible light (400–420 nm). This
offers new efficient industrial possibilities. However, first studies
have shown that the reaction mechanism on the titanium dioxide surface
may contrast with the known gas phase mechanism. In this work, the
sulfoxidation of hydrocarbons on titanium dioxide (anatase and rutile
modification) is investigated in more detail with regard to the adsorption
of SO2, the CH-bond activation, and other reaction steps
using quantum chemical simulations from first principles. Discrepancies with regard to the up-to-now established reaction
mechanism will be elucidated, and important aspects, such as the poisoning
of the catalyst, will be identified.