Josh Stolz, Chem 213
Synthetic #4 FFR
Steam Distillation of Spice (Spearmint)
Introduction
The use of natural products has been an important subject of interest in organic chemistry
for many years. Specifically, natural products have been largely used to develop pharmaceutical
drugs.1 Drugs derived from natural products have been used to treat a variety of conditions
including inflammations, cancer, bacterial infections, and in the assistance of organ transplants. 2
Natural products or drugs derived from natural products account for 57.7% of all FDA approved
drugs within the last twenty years. 2 Unlike synthetic drugs, one benefit of medicinally valuable
natural products is that many of these drugs usually go straight into production without any
necessary chemical modifications, thus reducing costs for pharmaceutical companies. 3 In
addition, many natural products are used as the building blocks for organic synthesizes or as
blue-prints for synthetic drugs. 3
Natural products or derivatives of natural products are also commonly used in the
chemical manufacturing of flavors. 4 In the current experiment, the natural product spearmint was
steam distilled to obtain spearmint oil. Spearmint oil is commercially used as flavoring, such as
in tooth-paste or chewing gum. 4 The main component of spearmint oil is l-carvone. 4 L-carvone
is responsible for the defined spearmint odor.5 This molecule has also been used in insecticides
and herbal medicine. L-carvone is a ketone composed of a hexene ring and an iso-propenyl
group. The structure for l-carvone can be seen in figure 1.
Figure 1. Structure of l-carvone
In this experiment spearmint oil was isolated from the natural product through steam
distillation. Steam distillation is used when the boiling point of a desired product is too high to
effectively use simple distillation. Steam distillation lowers the boiling point of a compound by
increasing the vapor pressure of the system. If a liquid is immiscible with water, such as the oils
found in spearmint, then the oil may be co-distilled with water in order to lower the boiling point
of that liquid. 6 When two compounds are immiscible, the vapor pressure of the mixture is equal
to the sum of the vapor pressures of each individual liquid; the molar fractions of each compound
is negligible.6 As the vapor pressure exerted by a mixture of liquids equals atmospheric pressure,
the compounds in the liquid phase are able to escape and enter the vapor phase. 6
Since water has a lower boiling point compared to spearmint oil, as water boils it exerts a
much larger vapor pressure than the oil. This allows spearmint oil to only exerting a small vapor
pressure in order to equal atmospheric pressure and enter the vapor phase. It is worth noting that
water will also be affected by the vapor pressure of the oil and will like wise have a lower
boiling point. Steam distillation lowers the boiling point of compounds by decreasing the vapor
pressure needed to enter the gaseous phase. 6
The purpose of this experiment was to steam distill spearmint in order to obtain spearmint
oil and to then determine the components of that oil. By carrying out this experiment it was
possible to learn the fundamentals of steam distillation and the role partial pressure plays in a
compounds boiling point. The components of spearmint oil were characterized and identified by
odor, gas chromatography (GC), and gas chromatography- mass spectrometry (GC-MS).
Experimental
L-carvone. Spearmint leaves (4.01 g) were grinded with a mortar and pestle and added to a
round bottom flask (100 mL) with distilled water (50 mL) and a stir bar. The round bottom flask
(100 mL) was placed in a simple distillation apparatus with a heating mantle. TRN was kept at a
constant 100 C. The distillate was collected at a rate of one drop every 3 seconds in an
Erlenmeyer flask (125 mL) for 1.5 hours. The obtained cloudy liquid was then placed in a
separatory funnel (125 mL) and extracted with dichloromethane (3 x 15 mL). The organic layers
were collected in a beaker (100 mL) and dried with anhydrous sodium sulfate (10 min.) The
liquid was decanted into an Erlenmeyer flask (125 mL) and evaporated with a stream of nitrogen.
A small odorous clear oil drop was produced (0.144 g, 3.59 % recovery); GC (phenyl
methylpolysiloxane, 40 C to 275C at 10 C per min) RT 2.44, 2.46 min.; GC-MS (phenyl
methylpolysiloxane, 40˚C to 275 ˚C at 10˚C per min) RT 12.28 min, m/z 81.95.
Discussion
Through steam distillation, 0.144 g of spearmint oil was isolated from spearmint leaves
for a 3.59 % recovery. Through the analysis of physical observations, GC and GC-MS it is
strongly suggested that l-carvone is the main component of spearmint oil.
From the 4.01 g of spearmint leaves used, only 0.144 g of spearmint oil was obtained.
This is a 3.59 % recovery. This low recovery may be due to the fact that the mass of oil in
spearmint leaves is low compared to the mass of other components such as the cells of the
leaves. It is also possible that some of the oil was left in the original mixture. Running the
distillation for further time would produce more spearmint oil. In addition, due to the differences
in boiling points between l-carvone (230 C), the main component of spearmint oil, and water
(100 C), during distillation a smaller fraction of l-carvone enters the vapor phase compared to
water. 5 This results in less spearmint oil in the distillate compared to water. If additional water
were added during the distillation in conjunction with running the distillation for a longer time,
then more spearmint oil would have been present in the final product. Finally, it is possible that
some of the spearmint oil was lost during extraction. If additional extractions were carried out,
then there could have been a higher % recovery of spearmint oil.
To determine the composition of the spearmint oil GC was used. From the GC data
(Figure 2) two peaks were found at retention times of 2.44 and 2.46 and with a composition of
32.8 % and 67.2 % respectively (Table 1). These peaks are at a retention time that is
characteristic of a solvent therefore it is likely that these peaks are from solvent. Due to the
rounded solvent peak, it is possible that the sample used was too concentrated and this provided
insufficient GC data to correctly analyze the product. In the future a more diluted sample could
be used. The same sample was used for GC-MS as in GC.
Retention Time
2.44
2.46
Area
338
693
Table 1. GC Data
% Composition
32.8 %
67.2 %
The GC-MS data differs from the GC data, therefore the GC data will be disregarded and
only the GC-MS data will be used to identify the compound. From the GC-MS data (Figure 3)
there is one large peak at RT 12.28 with a 100 % composition (Table 3). The m/z value that
corresponds to this abundance is 81.95. From the data library of the GC-MS, the identity of the
only component is 2-cyclohexen-1-one-2-methyl-5-1( 1-methylethenyl)-, (R), which is the
compound carvone. This data suggests that the expected major component of spearmint oil,
carvone, is present. However, this data does not indicate which stereoisomer is present.
Compound
l-carvone
RT
12.28 min
Area
m/z
973316
81.95
Table 2. GC-MS Data
% composition
100 %
The spearmint oil was finally characterized by physical observations. Specifically, the oil
was analyzed by odor. The obtained oil had a minty smell that is similar to commercially found
spearmint products. This property suggests that the present oil contained l-carvone, the
compound responsible for spearmint odor. 5 This observation also suggests that d-carvone, which
has a vastly different odor, is not present. 5
Conclusion
Spearmint oil was successfully isolated from spearmint leaves through steam distillation.
0.144 g of product was obtained for a 3.59 % recovery. While the GC data was inconclusive, the
GC-MS data shows that the only compound present in a significant amount is 2-cyclohexen-1one-2-methyl-5-1(1-methylethenyl)-, (R)- or the compound carvone. From the physical
observation of a minty odor it may be determined that l-carvone is the main component. 5 The
experiment was successful in both isolating and determining the component of spearmint oil, and
demonstrating the relationship between partial pressure and boiling points of immiscible liquids
that is found in steam distillation.
References
(1) Miles, H. W.; Smiley, P. M.; Journal of Chemical Education. 2002. 79, 90.
(2) Ojima, I.; Journal of Medicinal Chemistry. 2008. 51, 25887-25888.
(3) Ortholand, J. Y.; Ganesan, A.; Current Opinion in Chemical Biology. 2004. 8, 271-280
(4) Tsuneya, T.; Ishihara, M.; Shiga, M.; Kawashima, S.; Satoh, H.; Yoshida, F.; Yamagishi, K.;
American Chemical Society. 1993. 11, 137-158.
(5) Murov, S.; Pickering, M.; Journal of Chemical Education. 1973. 50, 74-75.
(6) Rummel, S.; Lab Guide for Chemistry 213; Hayden Mcneil; pp 184-185, 194-195