Experiment 7: Limonene Steam Distillation and Optical

Rotation

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?

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.

 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

Rotation of Plane-polarized Light

Polarimeter

  4 samples: –  Ethanol blank –  (+)-Limonene –  (-)-Limonene –  Class sample

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

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!