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Formation Mechanism and Pseudopolymorph Studies of Racemic Tartaric Acid

Author: WangXiaoFang
Tutor: WeiHongYuan
School: Tianjin University
Course: Chemical Engineering
Keywords: Racemic tartaric acid Formation mechanism Pseudopolym-orphs Water activity Thermal kinetic Thermal dynamics
CLC: TQ460.1
Type: PhD thesis
Year: 2012
Downloads: 117
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Abstract


Pseudopolymorph has a certain impact on characterization, bioavailability andformulation of drug, it has been an important issue in the chemical industry for a fewyears, and the study of pseudopolymorph has become an important and essential partin drug research and development.Tartaric acid is an important and versatile organic acid which is widely used inmedicine and food fields. There are three optical isomerism, levotartaric acid (D-TA),dextrotartaric acid (L-TA) and meso-tartaric acid (meso-TA). Racemic tartaric acid(race-or DL-TA) is a1:1mixture of the L-and D-TA forms. In this work, theformation mechanism and pseudopolymorph of DL-TA was investigated as follows.The solubilities of L-and DL-TA in pure solvents were determined by staticmethod, and the results were correlated using semi-empirical equation. Based on thesolubility data, the dissolution enthalpy and entropy of the L-and DL-TA werecalculated using van’t Hoff plots. The metastable zone of L-and DL-TA in water wasalso determined. The thermal stability of L-and DL-TA was investigated.With DSC and HPLC, the influence of L-TA on the solubility and meltingtemperature of D-TA was studied. The binary and ternary phase diagrams of theenantiomers were determined to identify the type of DL-TA, and the formationmechanism was discussed.The influence of temperature and water activity on the stability of monohydrateand anhydrous DL-TA was investigated using XRD, TG and DSC. The equilibriumwater activity at different temperature was obtained, and the variation of equilibriumwater activity as a function of temperature was fitted to an equation. This sectionproposed an approach to crystallize anhydrous DL-TA at lower temperature. Theapproach can be applied for other anhydrate and hydrate systems.The transformation process from monohydrate to anhydrous DL-TA inethanol-water mixed solvent was investigated using on-line ART-FTIR and off-linemicroscope. The composition of solid phase during the transformation process wasanalyzed by DSC to investigate the effect of water activity on the conversion ratefrom monohydrate to anhydrous DL-TA in water-ethanol mixed solvent.The thermal kinetics and the dynamics of dehydration, melt and decompositionof monohydrate DL-TA were investigated using DSC and TG. The activation energyand pre-exponential factor was calculated by model-fitting method and model-free method. And the dynamics equation of the dehydration of monohydrate DL-TA wasobtained. Furthermore, the mechanism of dehydration of monohydrate DL-TA wasdiscussed at a molecular level.

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