Steam Distillation of Monoterpenes (
)-(+)-Carvone and (
Caraway Seeds/Analysis of Products by Infrared Spectroscopy and TLC
October 11, 2007
Methods and Background
The purpose of this lab is to successfully isolate carvone, an essential oil, from
caraway seeds by means of steam distillation.
After getting the essential oil from the
seeds, a thin layer chromatography and infrared spectroscopy will be performed to verify
the results of our experiment.
Carvone is most abundant in 2 enantiomers.
It is found in (
smells like caraway, and (
)-(-)-Carvone, which smells like spearmint.
For the purpose
of this class, the enantiomers of carvone are known as terpenoids.
These two specific
enantiomers are monoterpenes.
Enantiomers have identical physical properties (BP, FP,
MP, etc…), an asymmetric carbon (chiral center), and are nonsuperimposable chiral
images, but they have opposite optical rotation, and one enantiomer undergoes a chemical
change at a rate different from its mirror image.
As stated, the biggest difference
between the two enantiomers is their smell.
Due to their differences in stereochemistry,
the receptors on the cells in our nose are chiral because we can distinguish the difference
between the two.
The main experiment of this lab is to successfully perform a steam distillation.
The steam distillation is used as a mild method for separating and purifying a volatile
liquid that is immiscible or insoluble in water.
When this is the case, a codistillation of
the water and volatile substance is necessary to separate them.
Slightly different from
previous labs where we would boil our solution, the caraway seeds will be placed with
water and boiled together.
The main difference between this distillation and simple and
fractional distillations, is the setup of the apparatus.
An additional piece is added to the
stillpot to prevent the mixture of water and caraway from splashing into the condenser.
Also in this lab, thin layer chromatography (TLC) was used to verify our results
of our distillation.
In organic chemistry, TLC is a quick way of analyzing the progress of
In TLC, unlike column, the mobile phase is not flowed over the compound
and stationary phase, but instead placed below the stationary phase and allowed to rise
via capillary action.
In TLC, the stationary phase is a thin layer of absorbent material,
and a small amount of the solution to be separated is put on the absorbent.