Kinetics of the hydrolysis of diaryl (acylamino)(acyloxy) spiro-λ4-sulfanes (2a–e, 3–5) leading to sulfoxides have been studied under pseudo-first-order conditions in dioxane– water mixtures or aqueous buffer solutions. A sulfonium-carboxylate-type dipolar structure of the starting spiro-λ4-sulfanes is supported by IR spectroscopic data. Solvent polarity and ionic strength have no significant influence on the rate of hydrolysis of compounds 2a and ...