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An experiment has been devised that allows a student to prove that nucleophilic addition to a keto group predominates over nucleophilic substitution at an ester group in a case in which both are theoretically possible. The student reacts ethyl 2-acetyl-3-oxobutanoate with hydrazine and with phenylhydrazine and shows, by 1H NMR spectroscopy, that the products are 4-carbethoxypyrazoles and not 4-acetylpyrazolones. Students may also use 1H NMR to show that ethyl 2-acetyl-3-oxobutanoate is 100% enolized in carbon tetrachloride solution.
The experiment asks the student to solve a puzzle, which adds to the student's interest and sense of excitement. It can also be used to teach students how to conduct a literature search. The products obtained are described in the literature, so students can be asked to compare their melting points with those of other workers.
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