AbstractThe reactions of styrene derivatives1a‐14awith sulfur trioxide were studied in the temperature range −60 to 25°C using dichloromethane as solvent and 1.5 mol equiv. of dioxane as reactivity moderator. Reaction of styrene (1a) at low temperature yields the carbyl sulfate1cas the only observable intermediate in the ultimate formation of (E)‐2‐phenylethene‐1‐sulfonic acid (1d). The (phenyl) substituted styrenes3a‐5aclearly demonstrate the presence of the β‐sultones3b‐5bas the sole initial products leading to the corresponding carbyl sulfates3c‐5c. The initially formed β‐sultonebin the reaction of styrene derivatives3a‐5a, 9aand10awith 1.0 mol equiv. of SO3disproportionates to yield equal amounts of the corresponding carbyl sulfate and the starting styrene. This is thought to indicate that there is an equilibrium between the β‐sultone and the starting styrene. The group of the 1‐methyl‐substituted styrenes11a‐13aare an exception to the generally observed eventual conversion of the initial intermediates into the 2‐sulfonic acidsd, since they give the corresponding 3‐sulfonic acidsf.Mechanisms for the formati