Mechanism of the hydroxyiodination of 2‐butenoic acid

Aqueous iodination of trans ‐2‐butenoic acid proceeds via hydrolysis of I 2 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\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm HOI + CH}_{\rm 3} {\rm CH=\!=CHCOOH} \to {\rm CH}_{\rm 3} {\rm CH(OH)CHICOOH}$$ \end{document}is − d [C 4 H 6 O 2 ]/ dt = 5900 [H + ][C 4 H 6 O 2 ][HOI] M /s at 25.0°C when [IO   3 − ] = 0.025 M and ionic strength = 0.3. The overall rate law in the presence of iodate is\documentclass{article}\pagestyle{empty}\begin{document}$$ -d[{\rm I}_{\rm 2}]/dt = 3.2 \times 10^{ - 3} \times 10^{ - 3} [{\rm H}^{\rm + }][{\rm IO}_{\rm 3}^ -]^{0.65} [{\rm C}_{\rm 4} {\rm H}_{\rm 6} {\rm O}_{\rm 2}]^{1/2} [{\rm I}_{\rm 2}]^{1/2} M/{\rm s}$$ \end{document}where [H + ] and [IO   3 − ] are total concentrations used to prepare the solution.