A kinetic and thermodynamic study of Seratrodast (cas 112665-43-7) polymorphic transition by isothermal microcalorimetry

Add time:07/25/2019    Source:sciencedirect.com

The development of isothermal microcalorimetry to a study of the kinetic and thermodynamics of polymorphic transitions in Seratrodast (cas 112665-43-7) ((±)-7-(3,5,6-trimethyl-1,4-benzoquinon-2-yl)-7-phenylheptanoic acid) Form II is reported. Sieved samples of Form II were allowed to convert to Form I, in a reaction vessel of an isothermal microcalorimeter, under 13, 31, 63 and 93% relative humidity (RH) between 48 and 65 °C. The power (Φ, in Watts) versus time curves from the microcalorimeter were integrated into the heat output (q, in Joules) versus time curves to yield fractional extent of Form I converted versus time curves. The change in enthalpy (−5.70 kJ mol−1) agreed very closely with that obtained by differential scanning calorimetry and solution calorimetry, which indicated that the power measured by the microcalorimeter was due only to the Form II-to-Form I transition. Application of the theoretical kinetic method [J. Am. Ceram. Soc. 55 (1972) 74] revealed that the transition took place via a two-dimensional growth of nuclei mechanism at all the studied relative humidities and temperatures. The rate constant increased with increasing RH and temperature, and with decreasing the particle size of sample. The activation energies obtained from Arrhenius plots were 292, 290, 280 and 284 kJ mol−1, and the extrapolated rate constants at 25 °C were also 3.01×10−10, 3.11×10−10, 9.65×10−10 and 3.84×10−9 s−1 for 13, 31, 63 and 93% RH, respectively.

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