Mechanism of the hydroxyiodination of 2-butenoic acid

Aqueous iodination of trans-2-butenoic acid proceeds via hydrolysis of I₂ to form HOI and I^?, then rapid addition of HOI across the double bond to form the iodohydrin product. In the presence of iodate to keep iodide concentration low, the reaction proceeds at a conveniently measurable rate. The rate for the addition reaction is ?dC₄H₆O₂]/dt = 5900 H⁺]C₄H₆O₂]HOI]M/s at 25.0°C when IO] = 0.025M and ionic strength = 0.3. The overall rate law in the presence of iodate is where H⁺] and IO] are total concentrations used to prepare the solution.