KINETICS OF THE CHLOROSULFONIC ACID PROMOTED ALPHA-IODINATION OF PROPIONIC-ACID

Propionic acid was found to be a iodinated by molecular iodine in the presence of chlorosulfonic acid in 1, 2-dichloroethane as a solvent at 80 °C. In view of the easy oxidation of hydrogen iodide to molecular iodine by chlorosulfonic acid as well as the detection of SO2 during the iodination, the stoichiometry of the reaction may be CH3CH2CO2H + 0.5I2 + ClSO3H → CH3CHICO2H + HCl + 0.5H2SO4 + 0.5SO2. Kinetic study shows that the initial rate is expressed as v = κobsd[CH3CH2CO2H][I2], where κobsd is proportional to the initial concentration of chlorosulfonic acid at an early stage. A mechanism involving addition of molecular iodine to a ketene intermediate and re-formation of molecular iodine by chlorosulfonic acid is discussed. The yield (ca. 80%) of a iodination is comparable to that of the literature (ca. 80%) and the procedure is simpler for synthesis. © 1979, American Chemical Society. All rights reserved.