Spectrophotometric Determination of the Stability Constant of the Inclusion Complexes of Some Catechol Derivatives with β‐Cyclodextrin Based on Their Reaction with Iodate

The effects of β‐cyclodextrin (β‐CD) inclusion on the kinetics of the oxidation of several cathechol derivatives, including 4‐tert‐butylcatechol, 3‐methylcatechol and 3‐methoxycatechol, with iodate was studied spectrophotometrically. The rate of the oxidation reactions decreased by increasing β‐CD concentration as a result of inclusion. The stability constants for the inclusion complexes of the investigated compounds were determined based on the changes in the rate constants as a function of β‐CD concentration at pH 3.0. The rate constants for the free and complexed forms and also the stability constants for the inclusion complexes were calculated. The role of the hydrophobic effect was evaluated by studying the influence of the presence of different amounts of ethanol on the β‐CD: guest interaction. In a given H₂O‐EtOH mixture the stability of β‐CD complexes shows the order of 4‐tert‐butylcatechol ≈ 3‐methylcatechol ≈ 3‐methoxycatechol. Increasing ethanol content caused a decrease in the stability constant of the inclusion complexes and an increase in observed rate constants.