Oxygenation of sulfides to the corresponding sulfoxides by a distinct bis(mu-oxo)dicopper(III) complex has been accomplished for the first time using 2-(2-pyridyl)ethylamine derivative L-Py1Bz (N-ethyl-N-[2-(2-pyridyl)ethyl]-alpha,alpha-dideuteriobenzylamine) as the supporting ligand, Detailed kinetic analysis has indicated that the reaction consists of two distinct steps, where the first quick process is association of the substrate to the bis(mu-oxo)dicopper(III) complex (k(1)) and the second slow process is intramolecular oxygen atom transfer from the copper-oxo species to the substrate in the associated complex (k(2)). The rate constant k(2) of the second process is rather insensitive to the oxidation potential of the substrates, suggesting that the oxo-transfer reaction proceeds via a mechanism involving direct oxygen atom transfer rather than a mechanism involving electron transfer.