Isobutanol → 2-Methylpropyl hydrogen sulfate

609 g sulfur trioxide-dioxane addition product, which contained 143.9 g (1.8 mols) sulfur trioxide and was dissolved in 400 g dichloroethane, was reacted with 137.1 g (1.85 mols) isobutanol, and a solution of sulfuric acid monoisobutylester in dichloroethane was obtained. 66 g of this solution, which contained 49 g (0.32 mol) sulfuric acid monoisobutylester, was added dropwise within 1 hour to 59.5 g (0.33 mol) dichlorophenylphosphane. The whole was initially heated for a short while to 30° C. and then cooled with water to maintain the reaction temperature at 20° C. Next, the reaction mixture was stirred for 4 hours at room temperature, stripped under a vacuum of 1 mm mercury and at a temperature of up to 30° C. 79 g of a brown, medium-viscous crude product was obtained. 31P-NMR-spectroscopy indicated that 41% of the phosphorus used was present in the crude product in the form of benzenephosphonic acid isobutylester chloride.