Kinetic study of thermally stimulated dissociation of inclusion complex of 1-methylcyclopropene with alpha-cyclodextrin by thermal analysis.

The thermally stimulated dissociation of the inclusion complex of 1-methylcyclopropene (1-MCP) with alpha-cyclodextrin (alpha-CD) in solid state was studied by means of thermogravimetry (TG) and differential scanning calorimetry (DSC). The mass loss of 1-MCP/alpha-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 degrees 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, k0) 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 alpha-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 alpha-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.