Löslichkeitsgleichgewichte von Stereoisomeren : Bedeutung, experimentelle Ermittlung und Anwendung

Autor :Dragomir Sapoundjiev
Herkunft :OvGU Magdeburg, Fakultät für Verfahrens- und Systemtechnik
Datum :14.05.2007
Dokumente :
Dataobject from HALCoRe_document_00006298
Typ :Dissertation
Format :Text
Kurzfassung :Nowadays resolution of mixtures of stereoisomers (especially enantiomers) has become increasingly important for the pharmaceutical, agricultural and food industry. Usually, only one of the stereoisomers can be used as an active pharmaceutical ingredient since the physiological effect on humans varies considerably with the type of stereoisomer. Because of the strong pronounced similarity in their physical and chemical properties, the production of optically pure substances is a difficult task. Crystallization processes are preferably applied for separation of stereoisomers due to their comparably low costs and high selectivity. The knowledge of the corresponding solid-liquid-equilibria (SLE) belongs to the fundamentals necessary for designing crystallization processes in solution. Its experimental study requires significant time and material consumption as well as the development of appropriate analytical techniques. Reliable theoretical methods for prediction of SLE of stereoisomers are still not available. Therefore the data of such equilibria present in the literature are mostly marginal and inconsistent. The objective of the work is the systematical study, interpretation and description of solid-liquid-equilibria of selected systems of stereoisomers. The main focus is concentrated on the determination of ternary phase equilibria of two stereoisomers and a solvent. An important prerequisite is the knowledge of the binary melting equilibria of the two stereoisomers. A detailed analysis of the obtained data is performed. Special attention is drawn to the investigation of the nature of the solid equilibrium phases, normally using a combination of analytical methods. The character of the solid phases can significantly influence the purification of stereoisomers. The ternary phase diagrams measured are extensively discussed regarding a crystallization based separation. Calculations by means of thermodynamic models support the interpretation of the determined phase equilibria. In the frame of the work an innovative calorimetry based method for solubility measurement is developed. Compared to other methods it enables reduction of time and substance input. Applying this technique solubility curves are obtained in relatively large temperature ranges performing single optimized experiments. The measurement of the heat released when solids dissolve, forms the basis of the method. The solubility study is performed in a heating run. The mathematical description of the dynamic experiment plays a key role for the development and quantification of the method. It enables on the one hand an estimation of the influence of different quantities on the solubility results, like dissolution enthalpy, heat capacities and temperature gradients of solubility and, on the other hand, it provides a correlation between the measured heat effects and the solubility curves to be determined. Finally, different separation concepts for gaining pure stereoisomers are explained using solubility diagrams. With a relevant example a realization of a separation and purification process for a stereoisomeric mixture is demonstrated considering its solubility diagram.
Schlagwörter :solubility equilibria, stereoisomers, chiral systems, phase diagrams, calorimetry
Rechte :Dieses Dokument ist urheberrechtlich geschützt.
Größe :174 S.
Erstellt am :23.03.2009 - 13:43:32
Letzte Änderung :22.04.2010 - 09:07:20
MyCoRe ID :HALCoRe_document_00006298
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