Cyclization of citronellal in a supercritical solvent in a flow reactor in the presence of Al2O3

Article abstract of DOI:10.1134/S0036024412120035

The reactivity of citronellal under supercritical solvent conditions in a flow reactor in the presence of Al₂O₃ is examined. It is shown that at 160°C, the main transformation product of citronellal is isopulegol, and when the temperature is increased to 190°C, they are monoterpenes with a para-menthane framework and myrcene. Pleiades Publishing, Ltd., 2012.

Full text of DOI:10.1134/S0036024412120035

ISSN 0036ꢀ0244, Russian Journal of Physical Chemistry A, 2012, Vol. 86, No. 12, pp. 1917–1919. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © V.I. Anikeev, I.V. Il’ina, K.P. Volcho, N.F. Salakhutdinov, 2012, published in Zhurnal Fizicheskoi Khimii, 2012, Vol. 86, No. 12, pp. 2054–2057.
SHORT
COMMUNICATIONS
Cyclization of Citronellal in a Supercritical Solvent
in a Flow Reactor in the Presence of Al O
2
3
a
b
b
b
V. I. Anikeev , I. V. Il’ina , K. P. Volcho , and N. F. Salakhutdinov
a
Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences,
Novosibirsk, 630090 Russia
Vorozhtsov Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences,
Novosibirsk, 630090 Russia
b
Received January 16, 2012
Abstract—The reactivity of citronellal under supercritical solvent conditions in a flow reactor in the presence
of Al O is examined. It is shown that at 160°C, the main transformation product of citronellal is isopulegol,
2
3
and when the temperature is increased to 190°C, they are monoterpenes with a paraꢀmenthane framework
and myrcene.
Keywords: citronellal, isopulegol, cyclization, supercritical solvent, alumina.
DOI: 10.1134/S0036024412120035
The use of flow reactors for the reactions in fine
We showed recently [11, 12] that adding a heteroꢀ
organic synthesis has a number of indisputable advanꢀ geneous catalyst to a supercritical solvent/flow reactor
tages over traditional periodic processes [1–4]. The system enables us to effectively perform different
first of these is accurate control of the contact time, transformations of natural compounds: isomerization,
Meerwein–Ponndorf–Verley reduction [12], and oxiꢀ
dation by atmospheric oxygen [11].
rapid and reproducible alteration of parameters such
as temperature and pressure, effective mixing of
reagents, easy scaling, and so on. The application of
supercritical solvents in flow reactors considerably
expands the possibilities for their employment [5]. For
example, it is known [6–10] that the use of supercritiꢀ
(
ꢀ)ꢀMenthol is an important substances that finds
wide application in the pharmaceutical, perfume, and
food industries. A key stage in the production of synꢀ
thetic menthol is the acidꢀcatalyzed cyclization of citꢀ
cal solvents for the transformations of terpenoids proꢀ ronellal
1
into isopulegol
vides not only a substantial increase in their transforꢀ that cyclization is usually accompanied by the formaꢀ
mation rate, relative to those in gas or liquid phases, tion of other stereoisomers of
, primarily isoꢀisopuleꢀ
(Scheme 1).
2 [13]. It should be noted
2
but also can remarkably affect their selectivity.
gol 3 and neoꢀisopulegol 4
+
OH
+
OH
3 16.3%
OH
2
51.8%
4 6.3%
scCO2/hexane, 160°C
CHO
Al O
2
3
1
+
+
+
O
OH
O
5
0.9%
6 4.4%
7 3.8%
8 1.0%
Scheme 1. Transformation of citronellal
mass spectrometry data).
1 at 160°C (mixture component concentration in %; gasꢀliquid chromatography and
1917

1918
ANIKEEV et al.
Mixture component concentration, %, according to the GLCꢀMS data (selectivity). Transformation of citronellal
curred at 190°C
1
ocꢀ
Flow, mixꢀ
ture/СО2,
ml/min
1
2
7
8
9
10
11
12
13
P
2/5
–
–
–
30.8
5.2
11.9
4.9
15.8
6.2
25.2
3/7.5
31.0
3.2 (4.6) 6.6 (9.6) 21.4 (31.0) 2.3 (3.3) 8.2 (11.9) 6.3 (9.1) 6.9 (10.0) 1.6 (2.3) 12.5 (18.1)
Note: V is flow, and P is other products.
The aim of this work was to study the possibility of
RESULTS AND DISCUSSION
cyclizing
reactor.
1 into 2 in a supercritical solvent in a flow
To perform the transformations of
1, an
scСО2/hexane mixture was chosen as the solvent. The
use of sc CO2 as a component of the complex solvent
considerably reduced the critical temperature, thus
avoiding undesirable secondary transformations of
products formed in the course of the reaction.
EXPERIMENTAL
To conduct our studies, we used citronellal
Fluka), Al O (MachereyꢀNagel, pH 0.5, 50–
1
(
2
7
±
2
3
We used neutral Al O without any preliminary
2
2
3
00
µ
m, BET free surface ~130 m /g).
activation as a catalyst in this reaction. We successfully
used this catalyst earlier for the isomerization of
pinane epoxides in supercritical fluids [12]. Note that
attempts to use nonactivated Al O for the cyclization
The experimental investigation of reactions under
supercritical conditions was performed on the laboraꢀ
tory setup described in detail in [14] with the use of a
2
3
3
tube reactor containing 22.1 cm (20.6 g) of Al O .
2
3
of
1
(16 h, 25
was obtained as the main reaction product,
was not found in the reaction mixture [15]. It
pumped into a mixer at the reactor inlet through a seems that was formed as a result of the disproporꢀ
heatꢀexchanger, where it was heated to the reaction tionation of aldehyde into alcohol and the correꢀ
°С) had also been made earlier, but citꢀ
The reaction mixture was fed into the reactor in two ronellol
flows. The first flow (supercritical СО2) was syringeꢀ while
5
2
5
1
5
temperature. The second flow (1% solution of
hexane) was pistonꢀpumped into the same mixer.
1
in sponding acid by the Cannizzaro reaction.
Our first experiment on the cyclization of
1
in a
The reaction mixture was cooled at the reactor outꢀ flow reactor in complex supercritical solvent was perꢀ
let and transferred for analysis. The composition of formed at 160 and flow rates of the solution of in
°С
1
liquid reaction products was analyzed by chromatoꢀ hexane and CO2 of 2 and 5 mL/min, respectively, and
mass spectrometry on a gas Agilent 6890N chromatoꢀ a contact time of 3.2 min. The obtained product distriꢀ
graph with a quadruple Agilent 5973N mass analyzer bution is shown in Scheme 1. The conversion of aldeꢀ
used as a detector. A quartz HPꢀ5MS column (5%ꢀ hydes
diphenylꢀ95%ꢀdimethylsiloxane copolymer) with a the main products were targeted isopulegols
length of 30 m, internal diameter of 0.25 mm, and a whose fraction in the reaction mixture was 74.4%. The
stationary phase film thickness of 0.25
m was used for selectivity with respect to compound among all of
analysis. The scan range was from 29 to 500
the formed isopulegols was ~70%. Citronellol , puleꢀ
Quality analysis was performed by comparing the gone , menthone , and paraꢀmenthaꢀ3,8ꢀdiene
retention times of components and their total mass were detected as minor products. Compound eviꢀ
spectra with NIST (190825 compounds) and Wiley7 dently forms as a result of the dehydration of isopuleꢀ
375000 mass spectra) data. The percentage composiꢀ gols under reaction conditions.
1 was quantitative under these conditions, and
2–4
µ
2
m/
z
m/z
.
5
6
7
8
8
(
tion of mixtures was calculated from the peak areas in
chromatograms without correcting coefficients.
Our attention was focused on obtaining comꢀ
pounds that can formally be related to the reduction
The contact time of the reaction mixture (
τ) was
(
5) or oxidation (6) products. It is not improbable that
calculated as a ratio between the catalyst volume in the these compounds can be formed from
1
and by the
2
3
reactor VС (cm ) and the total consumption of the Meerwein–Ponndorf–Verley reaction, which (as we
3
mixture at the reactor inlet
Q
(cm
/
s); it was ~3.2 min showed in [12]) can proceed under these conditions.
at a flow of 7 ml/min. The transformation was perꢀ The nonequivalent amount of
5
and observed in the
6
formed in the temperature range
T
= 160–190°C
at reaction mixture can be explained by the different staꢀ
bility of these compounds under reaction conditions
pressure = 190 atm.
p
The temperature and pressure in the reactor that
As the reaction temperature rose to 190°С, isopꢀ
provided supercritical conditions for the reaction mixꢀ ulegols completely disappeared from the reaction
ture were chosen on the basis of thermodynamic calꢀ mixture (table) and the main product turned out to
culations and phase diagrams.
be diene 8. Other paraꢀmenthadienes (limonene 9
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 86
No. 12 2012

CYCLIZATION OF CITRONELLAL IN A SUPERCRITICAL SOLVENT
1919
and
α
ꢀterpinene 10) were identified in noticeable unexpected. We found no examples in the literature
amounts along with paraꢀmenthꢀ3ꢀene 11 (Scheme 2). where compounds 12 and 13 were obtained from
1
,
The formation of acyclic trienes (myrcene 12 and isopulegols, or menthadienes with a paraꢀmenthane
β
ꢀocimene 13) in appreciable amounts was quite framework.
scCO2/hexane, 190°C
1
2
+
7
+
8
+
+
+
+
Al O
2
+
3
9
10
11
at 190°C.
12
13
Scheme 2. Transformation of citronellal
1
In order to reduce the contribution of secondary
transformation products, we shortened the contact
time and raised the flow rates of the citronellal soluꢀ
2. R. L. Hartman, J. P. McMullen, and K. F. Jensen,
Angew. Chem., Int. Ed. Engl. 50, 7502 (2011).
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tion
expected, the reaction mixture contained a considerꢀ
able amount of unreacted compound along with
but the concentration of the latter proved to be minor
table). At 190 , the rate of secondary transformaꢀ
tions of isopulegols evidently exceeds the rate of their
formation considerably. Menthone , which was
1
in hexane and СО2 by a factor of 1.5. As was
mun. (Cambridge, U. K.) 47, 4583 (2011).
4
5
6
. U. Hintermair, G. Francio, and W. Leitner, Chem.
Commun. (Cambridge, U. K.) 47, 3691 (2011).
1
2,
. T. Razzaq, T. N. Glasnov, and C. O. Kappe, Eur. J. Org.
(
°С
Chem.
. K. P. Volcho, I. V. Il`ina, N. F. Salakhutdinov, and
V. I. Anikeev, ARKIVOC (Gainesville, FL, U. S.)
34 (2011).
. V. I. Anikeev, A. Ermakova, I. V. Il’ina, K. P. Volcho,
and N. F. Salakhutdinov, Russ. J. Phys. Chem. A 84
112 (2010).
9, 1321 (2009).
7
8,
absent from the reaction mixture at a longer periods of
contact, was detected in large amounts. The reduced
contact time had virtually no effect on the selectivity
1
7
8
,
of the formation of paraꢀmenthadienes
resulted in a noticeable drop in the concentration of
acyclic trienes 12 and 13
It should be noted that the authors were the first to
study the reactivity of citronellal under supercritical
conditions in a flow reactor in the presence of Al O .
8–10, but
1
. V. I. Anikeev, I. V. Il`ina, K. P. Volcho, et al., J. Superꢀ
.
crit. Fluids 52, 71 (2010).
1
9. V. I. Anikeev, Kinet. Catal. 50, 284 (2009).
2
3
10. A. Yermakova, A. M. Chibiryaev, I. V. Kozhevnikova,
It was shown that at 160
pulegol and when the temperature is elevated to
90 , the main products are myrcene and monoterꢀ
°С, the main product is isoꢀ
and V. I. Anikeev, J. Supercrit. Fluids 48, 139 (2009).
2
1
1. V. I. Anikeev, I. V. Il’ina, S. Yu. Kurbakova, A. A. Nefeꢀ
dov, K. P. Volcho, and N. F. Salakhutdinov, Russ.
J. Phys. Chem. A 86, 190 (2012).
1
°С
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1
1
1
1
2. I. V. Il’ina, S. Yu. Kurbakova, K. P. Volcho, et al.,
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ACKNOWLEDGMENTS
3. C. B. Cortes, V. T. Galvan, S. S. Pedro, and T. V. Garcia,
The work was supported by the Russian Foundaꢀ
tion for Basic Research, grant no. 11ꢀ08ꢀ00171ꢀa.
Catal. Today 172, 21 (2011).
4. V. I. Anikeev, A. Ermakova, A. M. Chibiryaev, and
P. E. Mikenin, Russ. J. Phys. Chem. A 81, 711 (2007).
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Vol. 86
No. 12 2012