The title compounds I (R = H, R1 = CF3, R2 = R5 = H, R3 = Me, R4 = OMe; R = H, R1 = OMe, R2 = H, R3 = R5 = Me, R4 = OMe) undergo acid-induced transformations into the cyclic sulfenamides II via the putative sulfenic acids III.At high concentrations mixtures of II and thiolsulfinates IV (n = 1) were obtained.In contrast, I (R = CF3, R1 = H, R2 = R3 = Me, R4 = OMe, R5 = H), which cannot form II, is completely transformed under similar conditions into IV (n = 1), the anhydride of III.The temperature-dependent equilibrium between II and IV (n = 1) and the kinetics of the ring opening of II by water provide evidence for the sulfenic acid III as an intermediate involved in the pH-dependent transformations of I.IV (n = 1) decompose mainly to the disulfides IV (n = 0) at a rate depending on the solvent and conditions and are also reduced to disulfides by thiols.