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2005
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July
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In the Laboratory
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The Ethylene Ketal Protecting Group Revisited: The Synthesis of 4-Hydroxy-4,4-diphenyl-2-butanone
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Marsha R. Baar, Charles E. Russell, and Kristin L. Wustholz
Department of Chemistry, Muhlenberg College, Allentown, PA 18104
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July 2005
Vol. 82 No. 7
p. 1057
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| Abstract |
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The multistep synthesis of 4-hydroxy-4,4-diphenyl-2-butanone from ethyl acetoacetate illustrates the use of a ketal protecting group. Reaction of ethyl acetoacetate with ethylene glycol with p-TsOH in toluene produced the ketal ester. Reaction of the crude ketal ester with two equivalents of phenyl magnesium bromide followed by an aqueous acid workup generated the tertiary alcohol and simultaneously removed the ketal protecting group to produce the hydroxyketone. Our procedure is a modification of a previously published synthesis whose end product was 4,4-diphenyl-3-buten-2-one, the dehydrated analog. Our modifications involved the exchange of toluene for carcinogenic benzene as the azeotropic solvent in the ketal forming step and the alteration in the Grignard workup from water to one with dilute acid. This shortens the experimental sequence by avoiding the isolation and subsequent deprotection of the hydroxyketal intermediate and avoids the complication of the concurrent dehydration. We engaged the students in a discussion about how minor variations in the Grignard workup procedure can affect which compound is formed and presented the students with the challenge of utilizing spectroscopic analyses to identify the final product.
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| Supplement |
A student handout, report sheets, instructor notes, CAS numbers with specific hazard information, and tabulated spectral data for the ketal ester and hydroxy ketone are available.
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 Contents |
JCE2005p1057W.doc (Microsoft Word)
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| Download |
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| More Information |
Citation |
Baar, Marsha R.; Russell, Charles E.; Wustholz, Kristin L. J. Chem. Educ. 2005 82 1057.
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Keywords |
Grignard Reagents; Hands-On Learning / Manipulatives; IR Spectroscopy; Laboratory Instruction; Mechanisms of Reactions; NMR Spectroscopy; Organic Chemistry; Second-Year Undergraduate; Synthesis
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History |
Created:
Last Updated: |
May 31, 2005
June 8, 2005
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| Home > JCE Print > Journal of Chemical Education > Issues >
2005
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July
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1057
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