The Benzoin Condensation
The Benzoin Condensation
The Benzoin Condensation
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Post-Lab Questions<br />
1. A procedure is provided to remove benzoic acid, if present, from the benzaldehyde.<br />
a. Why might the presence of benzoic acid be deleterious to the reaction? Fully explain<br />
your answer – be specific!<br />
b. How does treatment with sodium carbonate remove the benzoic acid? Show the<br />
balanced reaction which would occur in that step.<br />
2. Calculate the theoretical yield and % yield of your crude benzoin product. To receive credit,<br />
you must show your work for both calculations; the density of benzaldehyde is 1.045 g/mL.<br />
3. How many π-electrons are in the thiazoline ring (the 5-membered ring) of thiamine<br />
hydrochloride? of thiamine? Are these rings anti-aromatic, non-aromatic, or aromatic?<br />
4. Show a detailed mechanism for the reaction of the thiamine carbanion with benzaldehyde.<br />
<strong>The</strong> reaction will be similar to nucleophilic attacks at carbonyls that you have previously studied<br />
(ie., a Grignard reaction); you may wish to refer to your textbook. (hint: when thiamine reacts<br />
with benzaldehyde, it forms a carbanion very similar in structure to the carbanion of<br />
mandelonitrile, shown on the first page of this handout).<br />
4
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