The oxidation of n-Bu2S by t-BuOOH in the presence of the catalysts [Mn2L2(MeCO2)2 (μ-O)] (ClO4)2 (L= Me3tacn=1,4,7-trimethyl-1,4,7-triazacyclononane) and VO(acac)2 has been studied using microemulsion media (BRIJ 97 and SD2 microemulsions). In the presence of the MnIII complex oxidation to the sulfone occurs, while in the presence of the VIV complex the sulfide is oxidised to the sulfoxide. The oxidation of mustard gas, (ClCH2CH2)2S, has also been studied. The reactions have been monitored by total internal reflectance i.r. spectroscopy. The use of optically transparent microemulsions provides a useful method for carrying out oxidations involving inorganic reagents and water-insoluble substrates.