AbstractThe oxidation of dithiocarboxylic esters with peracids is described. Methyl dithio‐l‐naphthoate (I) produces the trans‐ and cis‐(methylthio)sulfines I la and IIb. The trans‐isomer IIa gives on oxidation the trans‐(methylsulfinyl)sulfine IIIa, which is then converted to the trans‐(methylsulfonyl)sulfine IVa by further treatment with a peracid (Scheme I). Similarly phenyl dithiobenzoate (V) gives trans‐ and cis‐phenyl(phenylthio)sulfine (VIa and VIb). Each of these isomers was subjected to further oxidation giving the trans‐ and cis‐phenyl(phenylsulfinyl) sulfines VIIa and VIIb, and the trans‐ and cis‐phenyl(phenylsulfonyl)sulfines, VIIIa and VIIIb (Scheme II). Similarly, phenyl 2,4,6‐trimethyldithiobenzoate (IX) is oxidized to the corresponding trans‐ and cis‐mesityl(phenylthio)‐, mesityl (phenylsulfinyl) and mesityl(phenylsulfonyl)sulfines, Xa,b, XIa,b and XIIa,b, respectively. (Scheme III).The spectra, particularly the PMR spectra, are discussed in conjunction with the structural assignment of the sulfines. The deshielding effect of the > CSO group and also intramolecular shielding effects are invoked. Interestingly, the ortho‐methyl groups in both mesityl(phenylsulfinyl)sulfines (XIa,b) are magnetically non‐equivalent. This results from the asymmetric sulfoxide function in these sulfines which makes the two ortho methyl groups in XI diastereotopic.