Solid state characterization of N (2-propylpentanoyl) urea

Abstract

Solid state chemical properties of N (2-propylpentanoyl) urea (VPU), a newly synthesized anticonvulsant compound, were investigated. Solid state characterization of VPU includes solid phase identification, solid state stability and solubility measurement. Solid phase screening was investigated by treating reference VPU by various methods including recrystallization in several solvents, evaporation crystallization, immediate solidification from melt and thermal treatment. The products obtained were identified for their chemical integrity and purity using thin layer chromatography (TLC) and Fourier transform infrared spectroscopy (FTIR) and phase characterization was done by x-ray powder diffraction (XRPD). Selected products were further determined by differential scanning calorimetry (DSC), thermogravimetry (TGA) and scanning electron microscopy (SEM). There were no differences in the XRPD patterns among the samples, except the product recrystallized from hexane and heptane by rapid solvent evaporation method (method I). DSC and TGA patterns among samples are also similar. As for the methods used to produce various solid phase, no evidence was found to support the existence of polymorph, solvate or hydrate form of VPU. The pure amorphous form cannot be achievable by any methods used in this study. Solid state stability of VPU was studied over a temperature range of 50-80.C as a function of time. The samples obtained were determined by quantitative XRPD analysis with sodium chloride used as internal standard. It was found that the mechanism of the transformation from crystal form to amorphous form of VPU cannot be described by any particular model but the models were needed to calculate the activation energy. Using Arrhenius equation, activation energies obtained from all equations used were not significantly different. Therefore, the major transformation mechanism occurred was not observable. However, it could be summarized that the higher the temperature, the greater rate of transformation. Solubility of VPU was determined. Solubility of the sample which exhibited maximum partialy amorphous phase when collected after 4 weeks at 80.c, was 1.4 times greater than the reference VPU.