Experiment 7: Limonene
Steam Distillation and Optical
Rotation
Limonene
  Found
in citrus fruits (most abundant in
oranges).
  How
Limonene
bp 176 oC
d = 0.840 g/mL
can we separate
limonene from other
components?
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
Vapor Pressures Comparison
Steam Distillation Setup
Setup Picture
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.
 
Optical Activity
  Limonene
exists as two enantiomers.
H
H
(R)-(+)-Limonene
bp 176oC
density 0.840 g/mL
[!]D +125.6o
  Your
(S)-(-)-Limonene
bp 176oC
density 0.840 g/mL
[!]D -122.1o
sample should be optically active!
Rotation of Plane-polarized Light
Polarimeter
 
4 samples:
–  Ethanol blank
–  (+)-Limonene
–  (-)-Limonene
–  Class sample
Specific Rotation & Enantiomeric
Excess
α obs
[α ] =
c×l
t
λ
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.
 
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!