Steam Distillation – Oil of Cloves
ORG I LABORATORY
PRE LAB LECURE
Distillations:
Steam Distillation
1. Steam distillation arises from an interesting curiosity of
immiscible systems
2. The distillation of liquids that are fully miscible is governed by
Raoult’s Law
PT = NAP˚A +NBP˚B + NCP˚C + …
(1)
•
•
The mixture will have its own unique boiling point
The contribution of each component to the vapor phase is
related to its partial vapor pressure and mole fraction
3. In the distillation of immiscible liquids, the two act as two
separate liquids
A
B
Distillations:
Steam Distillation
4. The total vapor pressure above an immiscible system is equal
to the sum of the vapor pressures independent of their
relative amounts
PT = P˚A + P˚B + P˚C + … (2)
5. The mixture will boil at a temperature
typically lower than either liquid
6. Consider a mixture of iodobenzene and water:
At 98 oC the value of each vapor pressure is:
I
H
H
O
46 torr + 714 torr
= 760 torr Mixture boils!
Distillations:
Steam Distillation
7. The mole fraction of each component (nA and nB) in the vapor
phase is given by the ratio of its partial pressure over the total
pressure: nA = P˚A/PT (3) and nB = P˚B/PT (4)
8. If the vapor is condensed, the resulting distillate has the same
composition. The ratio of the mole fractions for A and B in the
distillate is then given by Equation 5, which results from dividing
equation 3 by equation 4:
nA/nB = P˚A/P˚B (5)
• Thus in the case of the steam distillation of iodobenzene and
water, the vapor phase, iodobenzene would only have a mole
fraction of 0.064 (46 torr/714 torr)
•
But because it has a larger molecular weight (204 vs. 18
grams per mole) about 0.7 grams of iodobenzene are
collected for every gram of water
•
In the gas phase the two are fully miscible, but once the vapor
condenses – the two are no longer miscible – and can be
physically separated
Distillations:
Steam Distillation
B. Uses/Apparatus
•
This method is typically
used to extract the volatile
components of plants for
use in perfumery, flavors or
aromatherapy products.
•
Steam distillation is used in
the industries that produce
these products as well as
amateur set-ups like this
one
Isolation of Natural Products
• This isolation of a “natural product” from its native matrix is one of the
oldest examples of applied organic chemistry – medicines and herbal
remedies prepared by early human civilizations are good examples of this
• This field undergoing explosive growth as we attempt to find interesting
molecules in nature that can be used for medicinal purposes as well as for
flavorings, dyes and cosmetics from a natural rather than synthetic source
• The American Chemical Society (ACS) publishes
a Journal that covers recent developments in this
highly interesting and important field
• Papers start with the isolation of the
animal or plant from it’s native environment
followed by the various separation and identification
techniques used to identify each component
• Recently, the initial assays of the anti-microbial,
anti-carcinogenic and toxicity behavior of each
component are also reported
When these isolations are for medicinal purposes, the field is known as
Pharmacognosy
"Pharmacognosy" derives from two Greek words, "pharmakon" or drug, and
"gnosis" or knowledge. Like many contemporary fields of science, pharmacognosy has undergone significant change in recent years and today
represents a highly interdisciplinary science which is one of five major
areas of pharmaceutical education.
Its scope includes the study of the physical, chemical, biochemical and
biological properties of drugs, drug substances, or potential drugs or drug
substances of natural origin as well as the search for new drugs from
natural sources.
Research problems in pharmacognosy include studies in the areas of
phytochemistry, microbial chemistry, biosynthesis, biotransformation,
chemotaxonomy, and other biological and chemical sciences.
In today's experiment we will isolate oil of cloves from cloves (Eugenia
caryophyllata). Cloves have been used as a flavoring agent for food for
thousands of years.
In addition, oil of cloves was one of the first know dental pain killers...a few
drops of oil of cloves will numb the pain of a tooth ache. One formulation
sold on the market for tooth pain relief still contains oil of cloves. Oil of
cloves is rich in eugenol (4-allyl-2-methoxyphenol) and contains a trace
amount of caryophphyllene.
OH
OCH3
H2C
CH CH2
Eugenol
CH3
CH3
H3C
H2C
Caryophyllene
Steam Distillation of an Essential Oil
We will be using
a modification of
the distillation
apparatus in the
text
Steam Distillation of an Essential Oil
The liquid will be
transferred to a
large separatory
funnel and
extracted with
methlyene
chloride CH2Cl2
H2O
CH2Cl2
The essential oil extract is soluble in
methlyene chloride, not water – So
draining the lower methylene chloride
layer, and evaporating the methylene
chloride, will afford the extracted oil –
Steam Distillation of an Essential Oil
The methylene
chloride extract will
be dried by passing it
through a disposable
pipette filled with
anhydrous Na2SO4
drying agent
about
1.5 in. of Na SO
2
4
cotton plug
Inverted funnel acts
as disposable pipet
holder
– you will obtain a weight of
the material (it won’t be much)
and calculate a % recovery
based on the original mass of
plant material
Apparatus for drying
ether solution
Steam Distillation of an Essential Oil
We will analyze the
essential oil by gas
chromatography…
qualitatively – to determine
which components are in the oil
and quantitatively to determine the
relative amounts of each component