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2001
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In the Laboratory
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Synthesis and Spectroscopic Analysis of a Cyclic Acetal: A Dehydration Performed in Aqueous Solution
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David M. Collard, Adolphus G. Jones, and Robert M. Kriegel
School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332-0400
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January 2001
Vol. 78 No. 1
p. 70
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| Abstract |
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The treatment of aldehydes (and ketones) with diols in the presence of acid gives acetals (and ketals) in an equilibrium reaction. Treatment of pentaerythritol with benzaldehyde in aqueous acid gives the monoacetal, 5,5-bis(hydroxymethyl)-2-phenyl-1,3-dioxane. The reaction has a number of interesting features. The isolated product is the monobenzal not the dibenzal, and the reaction, a dehydration, is performed in water. The reaction proceeds to provide the acetal owing to the insolubility of the product in the aqueous reaction medium, thus removing the product from the equilibrium. This experiment is suitable for incorporation into the undergraduate organic laboratory as the synthesis of a product for characterization by melting point, solubility, and proton nuclear magnetic resonance. Only through recognition of the three-dimensional structure of the dioxane ring can students explain the appearance of the 1H NMR spectrum of the product. The hydroxymethyl groups of the product are inequivalent, as are the hydrogens of the methylenes in the ring. The experiment may also be presented as a group exercise to optimize the conditions of a reaction to maximize the yield of the desired product.
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The written material given to students, notes for the instructor, and CAS registry numbers for all chemicals are available.
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JCE2001p0070W.doc (MS Word 98, Windows)
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| More Information |
Citation |
Collard, David M.; Jones, Adolphus G.; Kriegel, Robert M. J. Chem. Educ. 2001 78 70.
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Keywords |
Laboratory Instruction; NMR Spectrometry; Organic Chemistry; Organic Synthesis
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History |
Created:
Last Updated: |
November 30, 2000
August 31, 2005
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| Home > JCE Print > Journal of Chemical Education > Issues >
2001
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January
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70
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