Kinetic Studies on the Thermal Dissociation of β-Cyclodextrin·Ethyl Benzoate Inclusion Complexes

Abstract

The stability of β-cyclodextrin·ethyl benzoate·6H₂O(β-CD·C₆H₅COOC₂H₅·6H₂O) was investigated by TG and DSC. The mass loss takes place in three stages: the dehydration occurs at 50-120°C; the dissociation of β-CD·C₆H₅COOC₂H₅occurs at 200-260°C; the decomposition of β-CD begins at 280°C. The kinetics of the dissociation of β-CD·C₆H₅COOC₂H₅in a dry nitrogen flow was studied by means of thermogravimetry both at constant temperature and linearly increasing temperature. The results show that the dissociation of β-CD·C₆H₅COOC₂H₅is dominated by a three-dimensional diffusion process (D₃). The activation energy E is 116.19 kJ mol^-1and the pre-exponential factor A 6.5358·10⁹min^-1.

Cyclodextrin is able to form inclusion complexes with a great variety of guest molecules, and the studies focus on the energy of binding between cyclodextrin and the guest molecule. In this paper, the β-cyclodextrin·ethyl benzoate inclusion complex was studied by fluorescence spectrophotometry and infrared absorption spectroscopy, and the results show that the stable energy of inclusion complexes of β-CD with weakly polar guest molecules consists mainly of van der Waals interaction.