Experiment II: Steam Distillation: Isolation of Limonene from Orange Peels
Purpose. To extract out and characterize a simple organic compound (a terpene) from oranges via
steam distillation.
Discussion. The distillation of a homogeneous binary mixture produces a vapor to which each
component in the mixture contributes a part. The distillation of a heterogeneous binary mixture, on
the other hand, produces a vapor mixture that is only dependent upon the temperature. Thus, if a
mixture is composed of water and a high-boiling, water-immiscible substance, the mixture will boil
near but somewhat below 100oC. Most of the distillate will be water, but a separable portion of it
will be the immiscible component, usually in a high state of purity. The process just described,
called steam distillation, is an excellent technique for the isolation of many water-insoluble
compounds that are unstable at temperatures near their boiling points, or compounds difficult to
isolate or purify in any other way.
Steam distillations may be carried out in the following ways. The compound to be separated
and water are simply placed in a conventional distillation apparatus and the distillation collected.
This is called direct steam distillation. The distillate, which appears as a heterogeneous mixture,
may be either two liquid layers or a solid and water. A separation is easily effected by way of the
separatory funnel or by simple separation.
In the present experiment we will isolate by way of direct steam distillation a sample of
limonene from a few oranges. Limonene (see IR spectrum below for structure) is an essential oil
made up of two isoprene units,
, to form one of a class of compounds known as terpenes.
Experimental Procedure. Estimated time of experiment: 1.5 h. While it is always good
experimental practice to use a chemical fume hood, this experiment may be done outside of
the hood.
Physical Properties of
Components*
Compound
Literature Density
value
Literature Refractive
index (RI)
Water
Limonene
*Note: See question #2 (below) for filling in this chart.
The apparatus for this experiment has been assembled for you and will be placed at your laboratory
station. With the help of a high-speed food blender, prepare a puree from the parings of four large
navel oranges (see note 1). Use sufficient distilled water to produce approximately 300 mL of
slurry (add a bit of water at a time; it is easier to add water to dilute than to peel more oranges to
add more orange parings). Place all of the orange peel slurry in the distillation flask and bring
mixture to a steady boil with a properly adjusted heater setting. Avoid violent boiling, for excessive
frothing results and may carry small amounts of slurry directly into the condenser. Should this
occur, the contents of the receiver must be returned to the distillation flask, the condenser flushed
with fresh distilled water, and the distillation resumed more judiciously. Periodically add 5-10 mL
distilled water to the distillation flask from the separatory funnel to maintain a constant volume.
Continue the distillation until about 25 mL of condensate has been collected. By this time and oily
layer may be seen on the surface of the collected distillate and about 1 mL of the top oily layer
should be present. If no oily layer appears, it may be necessary to collect a larger volume of
condensate or to recollect some limonene, the distillation may be stopped and any water remaining
in the separatory funnel discarded. Collect the top layer via a Pasteur pipet. If the limonene does
not separate out in the graduated cylinder, transfer the distillate to the separatory funnel and
separate the organic layer from the water. Store the limonene collected in a clean test tube or vial
for IR analysis.
Note 1. A citrus grater or sharp knife can be used to remove only the outer portion of orange peel.
The heavy white pulp which constitutes the bulk of the orange peel is not to bee used. The citrus
grater generally gives excellent yields.
Characterization.
1. Obtain an IR spectrum of your sample of limonene and compare it to that shown in Figure (1).
Attach the IR spectrum to your notebook pages on this lab.
2. Obtain the RI of your sample of limonene and compare it to the literature. Record the number in
your notebook pages on this lab.
Figure 1
Sample: limonene
%T _X_
ABS ___
Sample: _liquid_
16 scans
Matrix material: _neat_
limonene
Questions: (to be answered neatly in your laboratory notebook)
1. The terpene, squalene, is a natural organic compound originally obtained for commercial
purposes primarily from shark liver oil. How many isoprene units make up this
compound? The structure of squalene is:
2. During the lab, fill in the densities of water and limonene as well as the RI’s of these
compounds using the Aldrich catalog. (If this catalog hasn’t been shown to you yet, see
your instructor). You will use this reference book throughout the lab course.