Journal of Physical Chemistry B, Vol.112, No.49, 15914-15920, 2008
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 I-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, 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 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.