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Morgan Casto
Dr. Hillwig
Chemoselective, Syntheses of Natural Fragrance and Perfume Additives Lab Report
2/26/19
Introduction:
One of the most important concepts within chemistry is the chemoselectivity of
reactions. This concept deals with a how reagent will choose a functional group to react with,
resulting in the formation of the major product. Our lab studied 6 reactions: three oxidation and
three reduction of the three compounds, whose structures are shown below.
Figure 1: Structures of the three starting materials: citral, geraniol, and carvone.
A type of oxidation reactions that was looked at were epoxidation reactions, which
removed a double bond, and replacing it with an oxygen of citral and carvone. Another type of
oxidation reaction is the copper oxidation of geraniol that starts with an already present alcohol
group, which loses its hydrogen and creates a carbon-oxygen double bond. In the reaction carried
out in lab, the alcohol group is attended to a primary carbon, which show a different result. When
the copper bromide reacted with geraniol, the reaction will be like a reaction carried out with
PCC. The reaction schemes for these reactions are shown below:
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Figure 2: Reaction schemes for the oxidation of citral, geraniol, and carvone, showing the
reagents and products for each reaction.
In the second week, the three reactions were reduction and hydrogenation reactions. The
first of these reactions was a sodium borohydride reduction of citral, which reduces an aldehyde
or ketone down to an alcohol. A second reduction reaction performed was the Clemmensen like
reduction of carvone, which uses zinc to reduce an aldehyde or ketone to an alkane. Finally, the
last type of reaction was hydrogenation of carvone using a platinum catalyst, reducing any
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double bonds. The reaction schemes for these three reduction and hydrogenation reactions are
shown below:
Figure 3: Reaction schemes for the reduction and hydrogenation reactions carried with carvone
and citral
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Week One Oxidation Reactions:
Citral and H2O2:
The product of this reaction is formed when NaOH acts as a catalyst, deprotonating the
hydrogen peroxide, and creating an epoxide where the double bond closest to where the aldehyde
was (Cunningham 323). Evidence for this can be found within the IR spectrum of the product
because of the strong peak around 1725 cm-1 that is a C=O stretch, indicative of the aldehyde
group. Also, around 3000 cm-1 that indicate an alkane C-H stretch. The C13-NMR also shows
proof of the aldehyde, with two peaks around 200 ppm.
Copper Oxidation of Geraniol:
The conversion of an alcohol to an aldehyde with the use CuBr is a two-step oxidation
reaction. The IR spectrum of the product shows evidence that the aldehyde was formed because
of the strong peak around 1700 cm-1, which indicated a C=O stretch. Furthermore, a cluster of
peaks around 3000 cm-1 provides evidence for the presence of alkane groups within the product.
According to the Journal of Chemical Education, a similar reaction was carried out with benzyl
alcohol and CuBr, bi-pyridine, methylimidazole, TEMPO, and acetone, which yielded a product
that had an alcohol group that was converted into an aldehyde, like what was seen in the copper
oxidation of geraniol (Hill 103).
Carvone with Peracetic Acid:
The last oxidation reaction performed in lab was the reaction of carvone with peracetic acid,
which is also an epoxidation reaction. The epoxide is formed with the double bond at the bottom
of the ring, since it is more stable. The IR spectrum shows a string peak at around 1670 cm-1,
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which would represent the ketone group that is attached to the ring. In addition, around 3000 cm-
1, there is a group of peals that indicate an alkane group. The proton NMR for this product shows
evidence for ketone between 2 and 3 ppm, shown in the data as a cluster of peaks. A peak around
6.7 ppm indicates the double bond in the ring, and the oxidized double bond is represented by a
peak around 4.5 ppm.
Week Two Reduction Reactions:
Citral and NaBH4:
The reduction of citral using sodium borohydride converts an aldehyde to an alcohol. The IR
spectrum for the product of this reaction shows this alcohol at around 3500 cm-1. The peak for
the C=O bond is around 1700 cm-1, and is small, which shows that it was involved in the reaction
and was reduced. The C13-NMR for product of this reaction is further evidence that the C=O
bond was reduced. In addition, when looking at the C13 for the staring material, citral, there is a
peak at about 200 ppm for an aldehyde, which is no longer present in the product spectrum.
According to the Journal of Organic Chemistry, sodium borohydride has been used in similar
reactions to reduce ketones and aldehydes to alcohol groups (Johnson and Rickborn 1043).
Clemmensen Type Reduction of Carvone:
Carvone can be reduced using methanol, acetic acid, HCl, and zinc converts the ketone on the
ring to an alcohol and reduces the double bond in the ring down to a single bond. This is because
the alkene was the least stable. The IR spectrum of the product has a peak between 3500 cm-1 and
3000 cm-1, which is indicative of the alcohol as it is an O-H stretch. Peaks around 2800 cm-1
represent the alkane groups. The proton NMR spectrum for the product has a peak that represents
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alcohol group formed from the ketone at around 7.5 ppm. Another peak at around 6.8 ppm is the
reduced double bond. According to an article by Kelly and Deeble, the addition reactants had
part in reducing the alkene of the ring (Kelly and Deeble 1107).
Hydrogenation of Carvone using a Palladium Catalyst:
This reaction was the final reduction of carvone with palladium. This reaction reduces the ketone
to an alcohol, and reduces the double bond at the bottom of the structure. However, because we
did not re-pierce the septum of the reaction flask, our H-NMR is inconclusive because it presents
a peak for the alkene portion of ring, which should not be in the product. This is due to an excess
amount of hydrogen. In the H-NMR for the starting material, carvone, there is a peak around 7
ppm that corresponds to the alkene portion of the ring, if the product was correctly formed, this
peak would no be found within the product data. However, looking at our product data, that peak
is still present due to this error. The product that should have been formed in this reaction is
different from that of different hydrogenation of carvone that was carried out in a different
experiment. In that experiment, the alkene at the bottom of the structure is reduced, but the
ketone, however, was not. This contrasting point may have been due to the use of different
catalysts. The reduction for this reaction used a paladdium catalyst, but the experiment outlined
in the academic paper used Wilkson’s catalyst, RhCl(PPh3)3. This resulted in only the least
hindered alkene, the one at the bottom of the structure to be reduced, and the reaction stopped
there (Kelly and Deeble 1107).
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Comparing Reactions:
Two of the oxidation reactions formed epoxides: the oxidations of citral and carvone.
Both molecules are structurally different, but both form epoxides from an alkene within their
structures. The citral oxidation product was due to nucleophilic epoxidation because the sodium
hydroxide acts as a catalyst and deprotonates hydrogen peroxide, increasing it’s nucleophilicity,
leading to formation of the epoxide (Cunningham 323). In the oxidation of carvone, the peracetic
acid attacks the alkene at the bottom of the structure because it is the most stable alkene of all of
them.
Reading and Reflection:
Reading #1: Chemoselective Reactions of Citral: Green Synthesis of Natural Perfumes for
the Undergraduate Organic Laboratory by Anna D. Cunningham, Eun Y. Ham, and David A.
Vosburg
When comparing the results of the exact same reactions shown in the academic paper, the
product of the citral oxidation with hydrogen peroxide is accurate. Both reactants utilize the
same reactants: the catalyst, NaOH, hydrogen peroxide, and methanol. As previously stated
above, the hydrogen peroxide was deprotonated by the sodium hydroxide, which then leads to
the formation of the epoxide. Within the academic paper, the reaction was carried at a set
temperature of 0° C; however, in lab, we did not use a set temperature, rather the solution was
kept on an ice bath to cool the reaction. The reaction within reading also proceeded faster than
reaction in lab.
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Reading #2: Hydrogenation of Citral over Activated Carbon Cloth Catalyst by Jeanette
Aumo, Susanna Oksanen, Jyri-Pekka Mikkola, Tapio Salmi, and Dmitry Yu. Murzin
The experiment performed in this paper was the oxidation of citral and the resulting product was
like one formed in this lab experiment. The citral hydrogenation in the academic paper results in
several products, one of which is geraniol, which is what citral can oxidize to. However, the
catalysts used differ. The reaction presented within the paper used Ni/ACC and Pt catalysts,
while the one performed in lab used sodium borohydride.
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Works Cited:
Cunningham, Anna D, et al. “Chemoselective Reactions of Citral: Green Syntheses of Natural
Perfumes for the Undergraduate Organic Laboratory.” Journal of Chemical Education,
vol. 88, no. 3, 2011
Hill, Nicholas J, et al. “Aerobic Alcohol Oxidation Using a Copper(I)/TEMPO Catalyst System:
A Green, Catalytic Oxidation Reaction for the Undergraduate Organic Chemistry
Laboratory.” Journal of Chemical Education, 2013.
Johnson, M Ross, and Bruce Rickborn. “Sodium Borohydride Reduction of Conjugated
Aldehydes and Ketones.” The Journal of Organic Chemistry, vol. 35, no. 4, Apr. 1970.
Kelly, Lawrence F, and Geoffrey J Deeble. “Selectivity in Organic Synthesis: Chemo- and
Regiospecific Reductions of Carvone.” Journal of Chemical Education, vol. 63, no. 12,
Dec. 1986.
