Selectivity in the Iodination of Phenol in the Presence of β-Cyclodextrin

Article abstract of DOI:10.1021/jo00257a014

The ratio of products formed in the iodination of phenol and o-chlorophenol with I2/I^- in water solution depends on the pH and buffer concentration.At high pH and high buffer concentration the para/ortho ratio increases.This ratio also increases in the presence of β-cyclodextrin (CD).The kinetics of the iodination reaction was measured for phenol, o-iodophenol, o-chlorophenol, and p-iodophenol, and in all cases the observed rate decreases with the addition of CD.The decrease in the overall rate is due to consumption of the active iodinating species through complexation of I2, I^-, and I3^- with CD.The iodination occurs in the bound substrates as well as in the free substrates.The equilibrium constants for the association of the phenols with CD were determined, and it is possible to conclude that the reaction of the bound substrates is faster than that of the free substrates not only for the para position but also for the ortho position. The catalysis is attributed mainly to a microsolvent effect which in the case of the ortho position is counterbalanced by a steric effect.