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Experiment 7: Limonene Steam Distillation and Optical
Rotation
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Limonene Found in citrus fruits (most abundant in
oranges).
Limonenebp 176 oC
d = 0.840 g/mL
How can we separate limonene from other components?
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Steam Distillation Steam Distillation (Co-distillation with
water): allows distillation of relatively non-volatile organic compounds without decreasing pressure (vacuum)
Relies on mutual immiscibility of water and organic compound
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Vapor Pressures Comparison
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Steam Distillation Setup
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Setup Picture
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Extraction Take organic layer and ~10 mL of
aqueous layer from distillate. Add NaCl and separate using sep
funnel, leaving small amount of aq layer in sep funnel.
Transfer contents of funnel to centrifuge tube and use miscroscale technique to separate.
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Optical Activity Limonene exists as two enantiomers.
Your sample should be optically active!
H
(R)-(+)-Limonenebp 176oCdensity 0.840 g/mL[!]D +125.6o
H
(S)-(-)-Limonenebp 176oCdensity 0.840 g/mL[!]D -122.1o
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Rotation of Plane-polarized Light
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Polarimeter
4 samples: – Ethanol blank – (+)-Limonene – (-)-Limonene – Class sample
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Specific Rotation & Enantiomeric Excess
You will need to calculate specific rotation from observed rotation.
Use density of limonene for concentration. Measure length in dm. Compare your experimental specific rotation
to the literature value to calculate %ee.
€
[α]λt =
αobsc × l
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Experiment Notes
This is experiment is long! Be prepared!
Read optical activity of blank (ethanol) and limonene standards while steam distillation is in progress!
Don’t forget oranges!