Abstract
When the asymmetric aldol reactions are catalyzed by amino acids in water, a certain amount of organic solvents such as ethanol, tetrahydrofuran still had to combine with water to dissolve the organic aldehydes and promote the reaction. But to protect the environment our aim is to completely eliminate the use of organic solvent, therefore we have started to investigate a new system for amino acids catalyzed aldol reaction in water without using any organic solvents. Mainly we use organic solvent to form a homogeneous phase for all reactants which is not possible if the solvent is water, as it makes most organic substances spasingly soluble in water. This drawback could be overcome if we use surfactants, which solubilise organic compounds in water. Thereafter, we planned to use cetyl trimethyl ammonium bromide (CTAB) as surfactant to solubilise the substrate p-nitrobenzaldehyde (PNB) and to perform in this aqueous micellar solution a L-proline catalyzed aldol reaction. A quite different mechanism has been proposed in water.
Kurzfassung
Wenn asymmetrische Aldolreaktionen von Aminosäuren in Wasser katalysiert werden, dann muss eine bestimmte Menge von organischen Lösungsmitteln wie Ethanol, Tetrahydrofuran ebenfalls in Wasser gelöst sein, um die organischen Aldehyde zu lösen und die Reaktion zu beschleunigen. Aber aus Gründen des Umweltschutzes ist es unser Ziel, den Einsatz von organischen Lösungsmitteln vollständig zu eliminieren. Folglich haben wir begonnen, ein neues System für die durch Aminosäuren katalysierte Aldolreaktion in Wasser ohne die Verwendung von organischen Lösungsmitteln zu entwickeln. Hauptsächlich verwenden wir organisches Lösungsmittel, um eine homogene Phase für alle Reaktanten zu erzeugen, was nicht möglich ist, wenn das Lösungsmittel Wasser ist und die meisten organischen Substanzen in Wasser nur schwer löslich sind. Dieser Nachteil könnte überwunden werden, wenn wir Tenside verwenden, die organische Verbindungen in Wasser solubilisieren. Deshalb planten wir das Tensid Cetyltrimethylammoniumbromid (CTAB) zu verwenden, um das Substrat p-Nitrobenzaldehyd (PNB) zu solubilisieren, und in dieser wässrigen mizellaren Lösung eine L-Prolin-katalysierte Aldolreaktion durchzuführen. Ein ganz anderer Mechanismus wurde in Wasser vorgeschlagen.
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