Kinetic Study of Thermally Stimulated Dissociation of Inclusion Complex of 1-Methylcyclopropene with α-Cyclodextrin by Thermal Analysis

The thermally stimulated dissociation of the inclusion complex of 1-methylcyclopropene (1-MCP) with α-cyclodextrin (α-CD) in solid state was studied by means of thermogravimetry (TG) and differential scanning calorimetry (DSC). The mass loss of 1-MCP/α-CD inclusion complex occurs in four separated phases with the thermal dissociation of the inclusion complex and release of 1-MCP taking place in the second phase between 90 and 230 °C. The kinetic parameters of the dissociation reaction (the apparent activation energy of dissociation, E D, the reaction order of thermal dissociation, n, and the pre-exponential factor, k 0) were evaluated. The dissociation reaction was satisfactorily described by the unimolecular decay law, where the reaction order, n = 1. The effect of the molar ratio of 1-MCP to α-CD (inclusion ratio) in the inclusion complex on the temperature dependence of the dissociation reaction was also studied. The E D decreased with increasing inclusion ratio indicating higher complex stability at lower inclusion ratios. The extrapolation of the E D of the inclusion complexes with different inclusion ratios to 1 mol 1-MCP/mol α-CD yielded the “true” E D of 20.9 ± 2.8 and 18.1 ± 0.2 kJ/mol for TG and DSC, respectively. The “true” ln k 0TG and the “true” ln k 0DSC were also determined by extrapolation, yielding values of +4.5 ± 1.0 and −0.3 ± 0.3, respectively.