Wyniki wyszukiwania - BazTech

1

Rozdzielenie mieszanin racemicznych za pomocą krystalizacji. Część 1, Optymalizacja warunków rozdziału

Kołodziejska R., Kopkowska E., Studzińska R., Karczmarska-Wódzka A., Augustyńska B.

Wiadomości Chemiczne

|

2015

|

[Z] 69, 1-2

65--88

EN

Methods for obtaining optically active compounds in enantiopure form are commonly classified into three categories: utilization of chiral pool starting materials (stereoselective multistep synthesis), creation of chirality from achiral precursors (asymmetric synthesis) and separation of racemates into their enantiomer constituents (crystallization, chromatography on chiral phases, kinetic resolution). The most important method for the separation of enantiomers is the crystallization. The crystallization can be carried out in the variants: direct crystallization of enantiomer mixtures (homo- and heterochiral aggregates – Scheme 2, 3) and separation of diastereoisomer mixtures (classical resolution) (Scheme 1) [1–5]. The most widely used method for the separation of enantiomers rests on the crystallization of diastereoisomers formed from a racemate and an enantiopure reagent – resolving agent (resolution via salt-formation and complex-formation). The pair of diastereoisomers exhibit different physicochemical properties (e.g., solubility, melting point, boiling point, adsorbtion, phase distribution). For this reason, the crystalline material can be separated from the residue by filtration (Scheme 22) [4, 27], distillation (Scheme 23, 24) [28, 29], sublimation (Scheme 25) [4, 30], or extraction (Scheme 26) [2, 31]. The composition of crystalline diastereoisomers is influenced by resolving agent (structure (Scheme 4) [4] and amount of resolving agent (Scheme 5) [4]), structure of racemates (Scheme 10) [2, 15], the character and amount of supplementary additives (Scheme 6–9) [4, 12–15], nature of the solvent (crystallization with solvent) – Scheme 11–18 [2, 4, 16–23] and time of crystaillzation (Scheme 19–21) [4, 14, 25, 26].

2

Rozdzielenie mieszanin racemicznych za pomocą krystalizacji. Część 2, Rozdzielenie racematów z utworzeniem diastereoizomerycznych soli

Kołodziejska R., Studzińska R., Kopkowska E., Karczmarska-Wódzka A., Augustyńska B.

Wiadomości Chemiczne

|

2015

|

[Z] 69, 1-2

89--110

EN

The enantioseparation of a racemate through diastereomeric salt formation with a resolving agent is one of the most attractive methods for obtaining an enantiopure compound, with advantages such as its simplicity in operation, recyclability of the chiral source, and applicability on an industrial scale. In this method the enantiomers are converted into a diastereomeric salt pair by reaction with a single enantiomer of resolving agent. The diastereomers are then separated by crystallization taking advantage of the different solubility of the two compounds [1–3]. The formation of diastereomers, to be separated afterward, usually consists of salt formation with a resolving agent of opposite acide-base character (Scheme 1, 9). In this process, the molecules of opposite character (amine and acid) recognize each other by various interactions on the basis of their molecular structures and functional groups [3]. Using this method can be obtained a series of enantiomerically pure amines (Scheme 2–8) [4–26] and acids (Scheme 10–17) [27–41] which may be valuable substrates for asymmetric synthesis. The conditions for enantioseparation play an important role. On the efficiency of the enantioseparation has an effect the resolving agent, nature of the solvent or just its dielectric constant and the character and amount of some supplementary additives.

3

Separation of racemic mixtures by membrane methods

Ceynowa J.

Chemia Analityczna

|

1998

|

Vol. 43, No. 6

917-933

EN

The recent approaches in getting separation of enantiomers from the racemic mixtures in different membrane systems are presented. The following membrane systems for the separation are described: a) typical two-phase extraction as well as three-phase extraction in systems with supported liquid membranes taking place by a participation of a selected chiral additive; b) separation in the systems with solid, modified microporous membranes. In the membranes specific recognition sites must be introduced, which are able to discriminate optically active substances in terms of their permeation behaviour, c) kinetic resolution by asymmetric, enzyme catalyzed reactions, especially those catalyzed by lipases. The catalysis is being provided in both aqueous (hydrolysis) and lipophilic media (esterification and transesterification). These processes are used for the preparation of pure enantiomers of chiral alcohols and /or acids.

PL

Przedstawiono metody separacji enancjomerów optycznych z mieszanin racemicznych za pomocą układów membranowych: a) w typowych procesach ekstrakcji z zastosowaniem unieruchomionych membran ciekłych z chiralnymi przenośnikami; b) w układach ze stałą, zmodyfikowaną membraną ultrafiltracyjną. Istota modyfikacji takich membran polega na wprowadzeniu specyficznych substancji chiralnych wywołujących różnice w szybkości przepływu obydwu enancjomerów; c) w reaktorach membranowych, z wykorzystaniem separacji kinetycznej w czasie enzymatycznej reakcji katalitycznej. Bardziej szczegółowo zostały przedstawione procesy z zastosowaniem lipaz, zachodzące zarówno w środowisku wodnym (hydroliza), jak i lipofilowym (estryfikacja i transestryfikacja), stosowane do otrzymywania enancjomerów chiralnych alkoholi i/albo kwasów. Zwrócono uwagę na układy z enzymem immobilizowanym bezpośrednio w membranie polimerowej.