Green and Sustainable Chemistry, 2011, 1, 7-11
doi:10.4236/gsc.2011.11002 Published Online February 2011 (
Copyright © 2011 SciRes. GSC
Resolution of Alcohol Racemate by Oil
Adi Wolfson*, Nadia Komyagina, Christina Dlugy, Janine Blumenfeld
Green Processes Centre, Chemical Engineering Department, Sami Shamoon College of Engineering,
Bialik/Basel Sts. Beer-Sheva, Israel
Received January 7, 2011; revised January 28, 2011; accepted January 30, 2011
Vegetable oil was successfully used as solvent and acyl donor in the kinetic resolution of several secondary
alcohol racemates yielding high enantioselectivities. Using vegetable oil as solvent and acyl donor allowed
easy separation of the pure alcohol enantiomer by extraction with methanol, by distillation under reduced
pressure, or by column chromatography.
Keywords: Oil, Kinetic Resolution, Lipase, Separation
1. Introduction
Optically pure chiral compounds are important building
blocks in the production of fine chemicals for pharma-
ceuticals, agrochemicals, and food ingredients [1,2]. Pure
enantiomers can be produced by using the “chiral pool”
of readily available natural compounds as starting mate-
rials, by resolving a racemic mixture, or by generating
asymmetry through asymmetric synthesis [3,4].
As starting materials, racemates can be obtained from
natural sources or by ‘classical’ chemical synthesis [1,2].
Since enantiomers exhibit different chemical activities in
a chiral environment, when a racemic mixture reacts with
a chiral (bio- or chemo-) catalyst, the different conversion
rates of the two enantiomers lead to the enrichment of
the less active enantiomer in the mixture. Other methods
of enriching enantiomers are preferential crystallization
and separation by chiral HPLC and chiral membrane.
However, these methodologies typically return low
theoretical yields (maximum 50%) of the pure product.
Chiral alcohols are useful intermediates and auxiliaries
in the production of various fine chemicals [5,6]. Pure
alcohol enantiomers can be produced by asymmetric
hydrogenation or transfer hydrogenation of the corres-
ponding carbonyl compounds using bio- and chemo-
catalysts [7-10] or by resolution of alcohol racemate
[1,2]. Lipase catalyzed kinetic resolution of alcohol ra-
cemate is the oldest and most commonly used method of
obtaining pure alcohol enantiomers [11-15]. Several
other methods-such as direct esterification using carbo-
xylic acid, transesterification using an ester as acyl donor,
and acylation by acyl chloride, anhydride, or vinyl alka-
noates-which differ in the type of acyl donor, can be used
for the resolution.
While water is the solvent of choice for most biocata-
lysis synthesis reactions, it cannot be used for alcohol
resolution, as it directs the reverse reaction, ester hy-
drolysis. Yet, as enzymes require no more than a
monolayer or so of water around them to preserve their
conformation and thus their activity, it can also be used
in an organic medium. It was found that the most hydro-
phobic solvents were the best for maintaining active en-
zymes mainly since the non-polar solvent cannot strip
the water from the protein and as such, does not change
its native structure [15]. The kinetic resolution of alco-
hols in an organic medium was previously reported with
several free and immobilized lipases. In those studies,
Candida antarctica lipase B (CAL-B) and its supported
analogues were mostly used [11-15].
As is typical of many organic reactions, in the kinetic
resolution of alcohols, the choice of the solvent is critical.
Besides activity and enantioselectivity, solvent selection
should also consider environmental aspects and product
separation procedure. We recently showed that using
glycerol triacetate (triacetin) as both solvent and acyl
donor in the kinetic resolution of alcohol resulted in high
conversions and enantioselectivities, and that the product
was easily separated by simple extraction with diethyl
ether [15]. Not only is triacetin environmentally friendly
and non-toxic, using it as acyl donor yielded by-products
that remained in the reaction mixture, and thus, only the
converted and unconverted enantiomers were separated.
In this paper we report on our study about the kinetic
resolution of several secondary alcohol racemates with im-
mobilized C. antarctica lipase B (CAL-B) in vegetable oil
(Figure 1). The oil was used not only as solvent, but also
as acyl donor, yielding pure (S)-alcohol enantiomer and
ester of (R)-alcohol enantiomer and fatty acid. The effects
of oil source and reaction condition on resolution activity
and enantioselectivity were studied together with separa-
tion techniques for (S)-alcohol enantiomer purification.
2. Experimental
All chemicals were purchased from Aldrich, except some
of the vegetable oils, which were bought at a supermarket.
2.1. Kinetic Resolution
In a typical reaction, 2.3 mmol of alcohol racemate were
added to 5 mL vegetable oil together with 0.043 g of C.
antarctica lipase B immobilized on acrylic resin. The
reaction mixture was heated in an oil bath to the required
temperature (80˚C) and mixed with stirrer for 5 h. At the
end of the reaction, the reaction mixture was cooled and
analyzed by TLC to determine alcohol conversion. In
addition, the products were extracted with 2 mL of
methanol for GC-analysis.
For the analytical procedure, the reaction mixture was
analyzed by GC using an Astec Chiraldex G-TA chiral
column (30 m × 0.25 mm, 0.25 μm thickness) to deter-
mine the reaction conversion and the enantiomeric ex-
cess. The injector temperature was 220˚C, and the FID
detector temperature was 250˚C. The temperature pro-
gram initialized at 80˚C for 5 min and then increased up
to 180˚C at a rate of 10˚C/min.
2.2. Alcohol Separation
Pure alcohol enantiomer separation was tested by several
techniques. First, kinetic resolution of 2-octanol was
performed by adding 0.305 g immobilized CAL-B and
16.1 mmol 2-octanol to 35 mL canola oil (purchased
from Aldrich). Then the reaction mixture was mixed in
an oil bath at 80˚C for 5 h, and the immobilized lipase
was filtrated from the reaction mixture at the end of the
R1 R2
R1 R2
R1 R2
Immobilized CAL-B
Figure 1. Kinetic resolution of a secondary alcohol race-
mate in oil.
Two methanol-based alcohol enantiomer extraction
procedures were used. In the first procedure, 150 mL of
methanol were added to the reaction mixture in a 250 mL
Erlenmeyer flask and mixed for 30 min, after which
phase separation was performed. The methanol was then
evaporated under reduced pressure in a Rotavapor. The
second procedure entailed a six-step extraction done us-
ing 25 mL of methanol for each step. The extracts from
all the steps were then joined and evaporated under re-
duced pressure in a Rotavapor. For both of the proce-
dures, the resultant crude was weighed and analyzed by
TLC to determine oil and methyl ester contents and by
GC to detect the total amount of (S)-2-octanol in the
crude. The extraction yield was calculated by dividing
the weight of the crude by half of the weight of the
2-octanol, and the purity was calculated by dividing the
total amount of (S)-2-octanol by half the weight of the
Distillation of (S)-2-octanol from the reaction mixture
was tested under reduced pressure at 120˚C or 90˚C. At
the end of each process, the distillate was weighed and
analyzed by TLC and GC, and the total alcohol yield and
content were calculated as detailed above.
Column chromatography was run in a glass column
measuring 1 m long by 6 cm in diameter. A portion of 5 g
glass wood was fixed at the bottom of the column, and
above it was a 0.5 cm layer of sand. The column was filled
with silica gel as the stationery phase while dichloro-
methane was used as the mobile phase. The elution was
collected at the end of the column and analyzed by TLC to
determine when the oil and the methyl ester exited the
column relative to the alcohol enantiomer (the oil and the
methyl ester were eluted out before the alcohol). The frac-
tion of (S)-2-octanol was collected, and dichloromethane
was evaporated under reduced pressure in a Rotavapor. At
the end of the process, the crude was weighed and ana-
lyzed by TLC and GC, and the total alcohol yield and
content were calculated as detailed above.
3. Results and Discussion
The main motivation to perform the kinetic resolution of
alcohol racemate by oil was to test an alternative to the
toxic and expensive petroleum based organic solvents
usually employed for this purpose. Moreover, in addition
to its function as a solvent, the oil also acted as resolu-
tion agent, which resulted in two different enantiomers,
an alcohol and an ester of alcohol, and a fatty acid. As
the two different enantiomers have different molecular
structure and thus have different polarities, solubilities,
and boiling points in oil, the pure alcohol enantiomer can
be separated using techniques in which there is no need
to first separate the alcohol and ester enantiomers from
the reaction mixture before separating between them.
Copyright © 2011 SciRes. GSC
The investigation began by testing the performance of
immobilized CAL-B in the kinetic resolution of racemic
mixtures of 2-octanol as a representative compound us-
ing several different types of oil (e.g., sunflower, corn,
soybean, and canola oils) that were bought from a su-
permarket and some canola oil purchased from Aldrich
(Table 1). The reactions were run at 80˚C for 5 h in two
scales (2.3 mmol 2-alcohol in 5 mL oil and 16.1 mmol
2-alcohol in 35 mL oil). In all cases, full alcohol conver-
sion was achieved.
As illustrated in Table 1, in the kinetic resolution of
2-octanol, the source of the oil slightly affected the enan-
tiomeric excess (%ee) value of the resultant alcohol en-
antiomer (entries 1-4), and the highest %ee was observed
in canola oil. Cooking oil comprises mainly triglycerides,
but it also contains other chemicals, such as odors and
flavors, as well as antioxidants [17]. Therefore, from all
oil types, alcohol extraction also tuned up some unrec-
ognized organic compounds, which were also detected
when canola oil was bought from Aldrich. Replacing 2-
octanol by 2-butanol or 2-phenylethanol resulted in similar
conversions and enantiomeric excess values (entries
8-11). Performing the resolution with larger amounts of
secondary alcohol, oil, and enzyme yielded the same
results (entries 7 and 9).
Tests of the effect of reaction temperature on reaction
progress over time showed that the enantioselectivity of
2-octanol, which also depended on the reaction conver-
sion, increased with both the reaction temperature and
time, as expected. At temperatures below 60˚C, the reac-
tion progressed slowly with time, while at temperatures
above 60˚C, the reaction reached full conversion and
%ee after one hour (Figure 2). This effect may be attrib-
utable to an energy barrier that can be overcome faster at
higher temperatures and to the decrease, as the tempera-
ture increased, in the viscosity of oil, which served to
increase both mass and heat transfer.
The separation of pure alcohol enantiomer was tested
by several techniques after running the kinetic resolution
Table 1. Lipase catalyzed kinetic resolution of 2-alcohola.
Entry Oil Source Alcohol type ee, (S)
-alcohol (%)
1 Sunflower 2-Octanol 95
2 Corn 2-Octanol 97
3 Soybean 2-Octanol 93
4 Canola 2-Octanol 98
5 Canola (Aldrich) 2-Octanol 98
6b Canola (Aldrich) 2-Octanol 98
7 Canola (Aldrich) 2-Butanol 98
8 Canola (Aldrich) 2-Phenylethanol 99
9 b Canola (Aldrich) 2-Phenylethanol 99
aReaction conditions: 5 mL oil, 0.043 g immobilized CAL-B, 2.3 mmol 2-
alcohol, 80˚C, 5 h; bReaction conditions: 35 mL oil, 0.305 g immobilized
CAL-B, 16.1 mmol 2-alcohol, 80˚C, 5 h.
0510 1520 25
Tim e (h)
E nan tio meric e xcess (% )
Figure 2. Reaction progress over time at different temperatures.
Reaction conditions: 35 mL oil, 0.305 g immobilized lipase
CAL-B, 16.1 mmol 2-octanol. () 25˚C; () 40˚C; () 60˚C;
() 80˚C.
of 2-octanol according to the procedure of Table 1 (entry
6) and filtration of the immobilized lipase from the reac-
tion mixture at the end of the reaction (Table 2). First,
extraction of the product was examined. As oil is a hy-
drophobic organic liquid, several hydrophilic extraction
solvents may be considered. Water, an oil immiscible
solvent that forms a biphasic system with oil but that
poorly dissolves most secondary alcohols, cannot be em-
ployed for the extraction. On the other hand, polar sol-
vents like acetonitrile and DMSO were dissolved in the
oil phase. It was found that methanol and vegetable oil
have a low mutual solubility, while methanol efficiently
dissolved secondary alcohols, identifying it as the most
suitable solvent for the extraction.
The extraction of (S)-2-octanol from the reaction
mixture by methanol was tested using two procedures.
In the first procedure, 150 mL of methanol were added
to the reaction mixture in a 250 mL Erlenmeyer flask
and mixed for 30 min followed by phase separation
(Table 2, entry 1). Then the methanol was evaporated
under reduced pressure in a Rotavapor, and the resul-
tant crude was weighed and analyzed in TLC and GC.
It was found that the overall yield, based on
(S)-2-octanol, was above 100%, as the extraction mix-
ture also contained some oil and small amounts of un-
characterized organic molecules. Based on GC analysis,
the percentage of (S)-2-octanol in the extraction mix-
ture was 89.7%, which implies that all the alcohol was
extracted from the reaction mixture. Performing the
extraction in six extraction steps using 25 mL of
methanol in each step resulted in a lower extraction
yield and a slightly higher purity of the crude after-
methanol evaporation, mainly as the oil content in the
extract decreased (entry 2).
Copyright © 2011 SciRes. GSC
Entry yield (%)
purity (%)
Table 2. Separation of (S)-2-octanol from oila.
Separation technique Total
1 Extr
(150 mL methanol)
action-one step 115 89.7
2 Extraction-six step
(6 25 mL methanol)
4 89 95.2
109 92.4
3 Distillation-120˚C 150 67.7
5 Column-dichloromethane 72 99
aReon il, 0.305 g immobi CAL-B,
2-ocol, l.
rom the reaction mixture
as also tested (Table 2, entries 3 and 4). Because the
ons well as solvent and acyl donor in
e kinetic resolution of secondary alcohol racemates.
, “Chirotechnology: Industrial Synthesis of
Optically Active Compounds,” Marcel Dekker, New
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enium(II) and Lipase
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tan 80˚C, 5 h; bBased on 2-octano
Distillation of (S)-2-octanol f
iling point of 2-octanol is relatively high, the distilla-
tions were done under reduced pressure. Performing the
distillation at a high temperature of 120˚C (entry 3) re-
sulted in large amounts of various organic compounds,
probably from the destruction of the oil molecules, and
therefore, the total yield was above 100%. Lowering the
distillation temperature to 90˚C produced lower yield of
(S)-2-octanol and a low organic compounds content.
Finally, column chromatography was also used for the
separation of the alcohol from the oil and the ester (
e 2, entry 5). Several solvents, such as ethyl acetate,
petroleum ether, or dichloromethane, alone or in mix-
tures and with methanol, were tested. It was found that
using dichloromethane produced the best difference be-
tween the retention factors (Rf) of the oil and ester mix-
ture and of (S)-2-octanol. Ethyl acetate had high elution
strength, which resulted in a high level of transport of all
materials through the column. When using petroleum
ether, their transport through the column was very slow.
Performing the column separation with dichloromethane
yielded 72% pure (S)-2-octanol (entry 5).
4. Conclusions
Vegetable oil functi
Various oil types can be used for the transesterification
step, yielding high enantioselectivities. Increasing either
reaction temperature or time increased the reaction rate.
Separation of the pure alcohol enantiomer from the reac-
tion mixture at the end of the reaction can be done by
extraction with methanol, distillation under reduced
pressure, or by column chromatography.
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