Individual Project - Redo

Individual Project - Redo - Amy Linkous 11/16/09 CHEM 2556,...

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Amy Linkous 11/16/09 CHEM 2556, CRN: 91653 Individual Project: Experiment 1: Tetraphenylcyclopentadienone from Benzaldehyde and Phenylacetic Acid Abstract The purpose of this experiment was to explore the three-step synthesis of tetraphenylcyclopentadienone, beginning with benzaldehyde, as an interesting example of ring formation. Benzoin was formed from benzaldehyde in the presence of thiamine as a catalyst, after which benzil was formed from benzoin in the presence of concentrated nitric acid. Finally, tetraphenylcyclopentadienone was formed from benzil and dibenzylketone. The resultant data from each step indicated that each intended product was indeed formed. Introduction Step One: Benzoin from Benzaldehyde This step is a condensation reaction. Cyanide was used as the original catalyst when the reaction was first being studied due to its “remarkably specific” catalytic capabilities (Fieser 297). It made a good catalyst for this reaction because it “acts as a nucleophile…, increases the acidity of the aldehydic proton,” and it is a very good leaving group (Fieser 297). The main problem with using cyanide was that potassium and hydrogen cyanide are poisons that can easily be fatal with mere minutes of exposure. Thiamine is far less dangerous and is able to perform the
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same three key functions, and so it is used as the catalyst of choice at present. In the presence of base, thiamine loses its most acidic proton and attacks the aldehydic carbon, pushing electrons onto oxygen (which then picks up the lost proton). Because of the combined power of the electron withdrawing groups in close proximity to the aldehydic proton, it is now very acidic and is easily removed, creating a carbanion. This new carbanion reacts with an additional benzaldehyde molecule, making a carbon-carbon bond with the aldehydic carbon. At this point, the oxygen on the original molecule pushes its electrons back down to reform the double bond
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Individual Project - Redo - Amy Linkous 11/16/09 CHEM 2556,...

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