Mechanistic Study on the Disproportionation of Alcohols Catalyzed by Molecular Iodine

Disproportionation of alcohols to the corresponding alkanes and aldehydes/ketones is an important reaction, especially for biomass valorisation. Previously, we reported for the first time that hydroiodic acid can be used as an efficient catalyst for the alcohol disproportionation reaction, and the interconversion between hydroiodic acid and iodine is the key step for hydrogen transfer. As a continuation of our previous work, this work mainly focused on the mechanistic study involved and studied the difference between hydroiodic acid or molecular iodine as the catalyst for the disproportionation of alcohols. Density Functional Theoretical calculation indicated the oxidation step was a synergistic reaction process through the iodine effect on oxygen-hydrogen bond, which was proved by the characteristic oxygen-iodine bond captured by in-situ Attenuated Total Reflectance Fourier Transform Infrared. A non-polar solvent was preferable for the reaction with iodine. Addition of small amount of water was shown to be beneficial for the reaction, because water promoted Brønsted acidity of hydroiodic acid and accelerated the rate-determining step. Finally, we showed that the system was also applicable to various benzyl, allyl alcohols, and some heterocyclic alcohols. Graphical Abstract