aldol reaction Essay

795 WordsFeb 22, 20154 Pages
Aldol In this preparative lab, an aldol (trans-p-anisalacetophenone) was produced from the reaction between p-anisaldehyde and acetophenone with the presence sodium hydroxide. The reaction also showed the importance of an enolate and the role it played in the mechanism. Sodium hydroxide acts as a catalyst in this experiment and is chosen because of its basic conditions and pH. The acetophenone carries an alpha hydrogen that has a pKa between 18 and 20. This alpha hydrogen is acidic because of its location near the carbonyl on acetophenone. When the sodium hydroxide is added, it deprotonates the hydrogen and creates an enolate ion. This deprotonation creates a nucleophilic carbon that can attack an electrophilic carbon (like a parent…show more content…
The initial product is the beta-hydroxyketone, which rapidly undergoes dehydration and creates the final product, trans-p-anisalacetophenone. Technically, both the carbonyls cannot be mixed together with sodium hydroxide to get one product. We will get a dominant product of trans-p-anisalacetophenone. This reaction is an exception and we get away with it. P-anisaldehyde and acetophenone together only make one enolate. This helps our exception, but there are still two carbonyls. With our weak base, we should be worried about acetophenone reacting with itself but we are not. This is due to steric hindrance, like I stated earlier. Aldehydes are better electrophilic carbons and therefore the ketone will react with the aldehyde faster than reacting with itself. It will quickly form the product trans-p-anisalacetophenone because it is the favored product. We do not have to use expensive LDA, we can use the weaker base and get away with it. The reaction took place in a conical vial and .2mL of each of the reactant samples were added to it along with some 95% ethanol. Two drops of NaOH were added shortly after and stirred at room temperature for fifteen minutes. The vial was cooled in and ice bath and crystallized. Vacuum filtration was performed to filter the crude product. The crude product was recrystallized using methanol and filtered again. We made one change to the procedure and instead of using .7mL of ethanol we
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