Density functional theory suggests that the formal 2-electron oxidation of sulfides, RR′S, to sulfoxides, RR2′ S {double bond, long} O by the model MnV{double bond, long}O catalyst, [(TACN)MnV O(OH)2]+, proceeds in two quite distinct 1-electron steps. Transfer of the first electron is barrierless and generates a sulfur radical cation, antiferromagnetically coupled to a MnIV centre via a covalent μ-oxo bridge. The second electron-transfer step is accompanied by migration of the oxygen atom to the sulfur centre, and is rate-determining. The absence of a barrier in the first step, where a sulfur radical is formed, means that the presence of electron-donating or withdrawing substituents on the sulfide has only a minor impact on the rate of reaction. © 2007 Elsevier B.V. All rights reserved.