Jacobsen’s Method of Epoxidation of an Alkene

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Jacobsen’s Method of Epoxidation of an Alkene

By | March 2013
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Jacobsen’s Method of Epoxidation of an Alkene|

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Abstract
Various types of reactions were completed to first create and then use Jacobsen’s catalyst in the asymmetric epoxidation of an unknown alkene with bleach in the laboratory. The chiral epoxide synthesized was then characterized with GC/MS and NMR. With this information the unknown alkene was able to be identified as 4-chlorostyrene. Introduction

Organisms have evolved with mechanisms that use specific enantiomers of molecules. If the chirality of the molecules is incorrect, they may not be utilized or may even hurt the organism. For this reason a method to create chiral molecules is very important and for this reason we study asymmetric synthesis. One method in which a chiral epoxide can be synthesized is through the use of a Jacobsen-type catalyst. In order to synthesize Jacobsen’s catalyst, Jacobsen’s ligand must be created first which requires the use of 3,5-di-tert-butyl-salicylaldehyde . There are many methods by which this salicylaldehyde can be synthesized but one method with a relatively high yield starts with 2,4-di-tert-butylphenol. The reaction scheme is shown below in Figure 1.

1 2 3
Figure 1: (1) 2,4-di-tert-butylphenol ,(2) 2,4-di-tert-butyl-6-hydroxymethylphenol, (3) 3,5-di-tert-butyl-salicylaldehyde shown above. In this reaction (1) was reacted with formaldehyde utilizing a Lederer-Mannase reaction giving (2) with a good yield. This compound was then oxidized in order to form (3). One oxidizing agent which could be used is sodium hypochlorite (bleach) with phase transfer catalyst. This method of synthesizing the salicylaldehyde is advantageous because it has a very high yield of 88%.1 It also uses many of the techniques that undergraduate students have already learned such as vacuum filtration, drying over anhydrous sodium sulfate, and recrystallization. An alternative method in which one can synthesize chiral epoxides is through...

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