Chirality of Ethyl-3-hydroxybutanoate Generated from a Biological Pathway Jake Zimny
Philadelphia, PA 19141
Submitted February 10, 2006
Abstract: The reaction being studied is a reduction of a ketone into an alcohol with a chiral center. Because a biological agent, bakers' yeast, is being used to drive this reaction, the optical purity that results in the product is so stereo-selective that the major product, (+), is formed for 89% of the product.
Introduction: This experiment was preformed to study the chiral selectivity of the reduction of the ketone portion of Ethyl acetate to a secondary alcohol. This reaction was enzyme catalyzed with a common batch of baker's yeast. The reaction conditions of this process are therefore much less harsh and therefore more environmentally friendly. The main focus of this experiment will not be on the inherent "greenness" or the energy considerations of this mechanism versus a comparable method, but instead focus on the stereo-selectivity. The stereo-selectivity of the product using a biological catalyst is important when contrasted to other methods of generating the product. The most common reaction that would mimic the reduction taking place in this experiment is hydride addition using sodium borohydride, NaBH4. Normally an alternative to this oxidizing agent would be lithium aluminum hydride, LiAlH4, however this reagent would also react with the ester portion of our starting reagent. The effect of reducing the ketone via hydride addition is that product is entirely a racemic mixture (McMurry 696). After the initial reaction the product was isolated using a series of vacuum filtrations, ether extractions, and rotorary evaporations, before being analyzed via proton NMR spectroscopy.
Results and Discussion: The table listed below as Table 1 lists the starting amounts of each of the chemicals present in the reaction flask, along with their formula mass.
Moleculear Mass (g/ mol)
References: McMurray, John. Organic Chemistry. Sixth Edition. Brooks/ Cole: New York, 2004.
Acknowledgements: The experiment was preformed in concurrence with one fellow student, Kevin Salmon.
Appendicies: The following graphs are listed in ascending page number order: the IR spectrum of the molecule, the NMR spectrum of the molecule and the depiction of the NMR spectrum focusing the geminal hydrogens that are effected by the addition of the LSR.
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