The cobalt(II) acetylacetonate/aldehyde-promoted aerobic oxidation of three bis-sulfides of general formula R-1-SCH2CH2S-R-2, where R-1 is a heterocycle and R-2 is p-tolyl, provides a method to functionalise selectively the sulfur atom bonded to the p-tolyl moiety leading to the corresponding monosulfoxides. The same chemoselectivity and Little diastereoisomeric excess (10%) was achieved by submitting to oxidative conditions the chiral bis-sulfide (S)-R-3- SCH2CH(CH3)CH2-SR4 (R-3 = benzothiazolyl, R-4 = p-tolyl).