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2005
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In the Laboratory
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Enantiomeric Resolution of (±)-Mandelic Acid by (1R,2S)-(–)-Ephedrine. An Organic Chemistry Laboratory Experiment Illustrating Stereoisomerism
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Marsha R. Baar and Andrea L. Cerrone-Szakal
Department of Chemistry, Muhlenberg College, Allentown, PA 18104
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July 2005
Vol. 82 No. 7
p. 1040
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| Abstract |
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There has been an increasing need, particularly in the pharmaceutical industry,
to prepare chiral substances in single-isomer form. A chiral technique that
makes an excellent introductory organic chemistry experiment is enantiomeric
resolution. The classical resolution of (±)-mandelic acid using the
chiral amine, (1R,2S)-(–)-ephedrine, was adapted for
use in introductory organic chemistry lab curricula. (–)-Ephedrine and
(±)-mandelic acid were reacted to produce diasteromeric ephedrinemandelate
salts. The [(1R,2S)-(–)-ephedrine][(R)-(–)-mandelate]
preferentially precipitated, was recrystallized, and analyzed by melting point,
168–170 °C (lit. 170 °C), 52% yield. The [(–)-ephedrine-][(–)-mandelate]
was neutralized with 6 M HCl, extracted and rotary evaporated to produce a
white solid in 32% yield whose melting point, 132–134 °C (lit. 133–134 °C),
confirmed its identity as (R)-(–)-mandelic acid with a specific
rotation of -135°, which corresponds to 85% optical purity.
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| Supplement |
Instructions for the students and notes for the instructor are available.
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 Contents |
JCE2005p1040W.doc (Microsoft Word)
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| Download |
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| More Information |
Citation |
Baar, Marsha R.; Cerrone-Szakal, Andrea L. J. Chem. Educ. 2005 82 1040.
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Keywords |
Acids / Bases; Chirality / Optical Activity; Diastereomers; Enantiomers; Hands-On Learning / Manipulatives; Laboratory Instruction; Organic Chemistry; Second-Year Undergraduate; Separation Science; Stereochemistry
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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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1040
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