Heat stability of allyl isothiocyanate and phenyl isothiocyanate complexed with randomly methylated β-cyclodextrin

Abstract

Inclusion complexation reactions between isothiocyanates (ITCs), namely, allyl isothiocyanate (AITC) and phenyl isothiocyanate (PITC), and randomly methylated β-cyclodextrin (RM-β-CD) displayed “AP” type solubility isotherms, indicating continuous increases in the stoichiometry of the inclusion complexes. The complex powders were prepared by spray drying and their heat stability was studied by thermal analysis and heat treatment in paraffin. The solid-state dissociation reactions were satisfactorily described by the unimolecular decay law. The apparent activation energy of dissociation, ED, was determined to be 48 and 58kJ/mol, respectively, for the AITC/RM-β-CD and PITC/RM-β-CD complexes, while the apparent activation energies of decrease of ITCs in paraffin, EP for the pure AITC and PITC, and the corresponding inclusion complexes were 26, 48, 44, and 54kJ/mol, respectively, suggesting volatility suppression and physical stabilisation by inclusion complexation as the plausible mode of stabilisation of the ITCs in paraffin. A compensation effect in the kinetics of depletion of the ITCs in paraffin was established.