Liquid phase acetoxylation of α-pinene over Amberlyst-70 ion-exchange resin

Article abstract of DOI:10.1016/j.apcata.2012.05.034

Heterogeneously-catalyzed and solvent-catalyzed liquid phase acetoxylation of α-pinene with acetic acid acting as both a solvent and a reagent was studied. Both solvent-catalyzed and catalytic experiments were carried out and various reaction conditions were studied. The influence of temperature, pressure, solvent and gas milieu were taken into account. Bornyl, fenchyl, verbenyl as well as α-terpinyl acetates, limonene, camphene and γ-terpinene were found among reaction products. The addition of the catalyst allowed for maximization of the yield of bornyl acetate. The predominant products obtained were α-terpinyl, verbenyl and bornyl acetates. The reaction pathways were identified and evaluated. The aim of this work was to study the feasibility of batch acetoxylation of α-pinene. The analysis of the complex product distribution is not trivial and, consequently, resolving the reaction network was important. The optimized reaction conditions were searched for aiming at an efficient conversion of α-pinene to a mixture of valuable products.

Full text of DOI:10.1016/j.apcata.2012.05.034

Applied Catalysis A: General 435–436 (2012) 43–50
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Liquid phase acetoxylation of ␣-pinene over Amberlyst-70 ion-exchange resin
M. Goletsa,∗, S. Ajaikumara, D. Blombergb, H. Grundbergc, J. Wärnåd, T. Salmid, J.-P. Mikkolaa,d,∗∗
a Technical Chemistry, Department of Chemistry, Chemical-Biological Center, Umeå University, SE-90187, Umeå, Sweden
b Processum Biorefinery Initiative AB, SE-89186, Örnsköldsvik, Sweden
c Aditya Birla Domsjö Fabriker AB, SE-89186, Örnsköldsvik, Sweden
d Laboratory of Industrial Chemistry and Reaction Engineering, Process Chemistry Centre, Åbo Akademi University, Biskopsgatan 8, FI-20500, Åbo-Turku, Finland
a r t i c l e i n f o
a b s t r a c t
Article history:
Heterogeneously-catalyzed and solvent-catalyzed liquid phase acetoxylation of ␣-pinene with acetic acid
acting as both a solvent and a reagent was studied. Both solvent-catalyzed and catalytic experiments were
carried out and various reaction conditions were studied. The influence of temperature, pressure, solvent
and gas milieu were taken into account. Bornyl, fenchyl, verbenyl as well as ␣-terpinyl acetates, limonene,
camphene and ␥-terpinene were found among reaction products. The addition of the catalyst allowed
for maximization of the yield of bornyl acetate. The predominant products obtained were ␣-terpinyl,
verbenyl and bornyl acetates. The reaction pathways were identified and evaluated.
The aim of this work was to study the feasibility of batch acetoxylation of ␣-pinene. The analysis of
the complex product distribution is not trivial and, consequently, resolving the reaction network was
important. The optimized reaction conditions were searched for aiming at an efficient conversion of
␣-pinene to a mixture of valuable products.
Received 19 January 2012
Received in revised form 22 May 2012
Accepted 24 May 2012
Available online 1 June 2012
Keywords:
Heterogeneous catalyst
Amberlyst 70
␣-Pinene acetoxylation
␣-Terpinyl acetate
Biorefinery
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
␣-terpineol. The equipment corrosion, environmental pollution,
large consumption and non-recyclability of the mineral acid are
Nowadays, many research groups are involved in the produc-
tion of value-added chemicals from renewable feed-stocks due to
imminent future threat of lack of fossil resources. Various streams
available from chemical pulping and biorefinery process streams
contain substantial amounts of terpenes and of those ␣-pinene is
often predominant [1]. ␣-Pinene is a comparably cheap terpene
that can be upgraded to numerous valuable products [2].
In recent years, the demand for alternative flavoring agents for
food, other alimentary products and perfumes has increased. The
industry evidently desires to reach maximally favorable flavor and
aroma characteristics. The same time, it is important to improve
the production and purification processes of terpene esters. Also,
to counter-effect the products tendency to spoil is of high impor-
tance [3]. ␣-Terpinyl acetate is a valuable monoterpene ester and
is widely used as a fragrance in soaps and perfumes because of
its excellent alkali stability [4]. The mentioned acetylated product
is conventionally produced via ␣-pinene treatment with min-
eral acids, followed by an etherification step of the intermediate
some of the severe drawbacks of the conventional process [5,6].
The related product, bornyl acetate, is an important component for
fragrance industry. It is used for soaps, bath products and air fresh-
eners. Alternatively, this chemical is an intermediate for camphor
production [7].
Earlier studies have been conducted in zeolite-catalyzed trans-
formations of ␣-pinene and limonene to acetylated products in
alcoholic solvents [4,8–12]. In addition, liquid phase acetoxyla-
tion of ␣-pinene and limonene in acetic acid was investigated
over various zeolites and acidic ionic liquids by a few research
groups [4,5,7,13], whereas Robles-Dutenhefner et al. [14] studied
the same reaction over silica-supported heteropoly-acid (PW). Also,
hydration and bio-conversion of limonene to ␣-terpineol – which
could be used for ␣-terpinyl acetate production – has been studied
[15–17]. Except via limonene hydration, ␣-terpinyl acetate could
also be produced from limonene and acetic acid with the help of
e.g. Fe2(SO4)3 [18]. The reaction of ␣-terpineol with acetic anhy-
dride, in the presence of this catalyst, also gave rise to ␣-terpinyl
acetate. Furthermore, quite good results in ␣-pinene oxidation
were obtained over palladium acetate catalysts, with hydrogen
peroxide in acetic acid solutions [19].
∗
Corresponding author. Tel.: +46 0 76 104 3381.
Corresponding author at: Technical Chemistry, Department of Chemistry,
In this paper, we report ␣-pinene acetoxylation to the valuable
mixture of terpene acetates. Both the acetic-acid (solvent-catalyzed
mode) and the heterogeneously catalyzed reaction networks (over
an ion-exchange resin, mesoporous Amberlyst 70 catalyst) were
resolved. Also, an analysis of the reaction kinetics was conducted.
∗∗
Chemical-Biological Center, Umeå University. SE-90187, Umeå, Sweden.
Tel.: +46 0 70 620 0371.
E-mail addresses: Mikhail.Golets@chem.umu.se (M. Golets),
Jyri-Pekka.Mikkola@chem.umu.se (J.-P. Mikkola).
0926-860X/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2012.05.034

44
M. Golets et al. / Applied Catalysis A: General 435–436 (2012) 43–50
SY
Yield (%) = X(%) ×
100
2. Experimental
2.1. Materials
(3)
A tailor-made mixture cocktail of high purity standards (95 wt%) of
containing the main predominant reaction products, including both
acetates, was analyzed by means of GC. The mixture also included
␣-pinene. The concentration of each species in the amount of each
mixture was similar (0.2 g) compound was equal to the amount
of other compounds and was 0.2 g. Also, the calibration of each
compound was performed on individual bases analyzed with GC
separately for comparison. It was shown by the analysis that the
peak area was not influenced by the rather small variations in
molecular mass or density and was equal for all terpene and terpene
acetate species.
The reagents, glacial acetic acid and acetone were used as
received from Sigma–Aldrich AB. The gases, oxygen, nitrogen and
hydrogen were purchased from commercial sources (AGA AB)
and had a purity of 99.999%. The terpenes and their derivatives,
␣-pinene, ␤-pinene, ␣-terpineol, limonene, ␥-terpinene, borneol,
bornyland␣-terpinylacetateswerepurchasedfromSigma–Aldrich
AB at a purity level of 95%. Amberlyst 70 catalyst was obtained as
a gift from Rohm and Haas AB and used as received.
2.2. Apparatus and general reaction procedure
2.4. Preliminary catalyst characterization
A laboratory scale high-pressure reactor (PARR), equipped with
a stirrer and a heating jacket, was used to carry out ␣-pinene ace-
toxylation tests. First, the catalyst in a quantity of 0.1 g was loaded
in the reactor vessel. Then 5.5 g of ␣-pinene (measured to 0.1 g accu-
racy) and 120 ml of acetic acid were introduced as a mixture in the
reaction zone. The reactor temperature was maintained by heat-
ing jacket and cooler system controlled by a PC. The influence of
different gas pressures on the reaction was studied. The stirring
speed of 1000 min−1 was applied in order to eliminate any external
mass-transfer limitations.
The acid site concentration of the catalyst was measured by
means of a titration method described elsewhere [20]. Further,
fresh and spent catalyst samples were analyzed by means of nitro-
gen physisorption measurements. Samples of the Amberlyst 70
catalyst exposed to the reaction conditions at 100 ◦C were analyzed.
The analysis of surface area, pore diameter and volume were car-
ried out by a Micromeritics Tristar 3000 analyzer in accordance
to the Brunauer–Emmett–Teller (B.E.T.) method. A sample of 0.1 g
was degassed at 120 ◦C for 1 h in vacuum (10−5 torr) in order to
remove the moisture from the pores of the material. By applying
the B.E.T. method, the pore diameter and volume were calculated
from the adsorption isotherms. The adsorption data was used to
calculate the surface area up to a relative pressure of 0.2 bar. The
SEM (scanning electron microscopy) images of fresh and spent cat-
alyst particles were visualized with a Cambridge Stereoscan 360iXP
electron microscope.
2.3. Product analysis
The progress of the reaction was monitored by withdrawing
samples at different time intervals during the course of the reaction.
The reaction products were analyzed by means of a gas chromato-
graph (GC) (Agilent Technologies, Model no. 7820A), equipped with
a HP-5 capillary column (30 m long, 0.32 mm internal diameter and
0.25 ␮m film thickness)and a FIDdetector. Nitrogenwas used as the
carrier gas in the GC (flow 1.0 mL/min) with the following temper-
ature programming: the detector and injection port temperature
of 250 ◦C, column temperature ranging from 70 to 220 ◦C with the
holding time of 0.5 min at the initial temperature and the heating
ramp of 20 ◦C/min. The reaction products and substrate have had
the following retention times (min): ␣-pinene (1.920); camphene
(2.120); verbenyl acetate (2.400); limonene (2.510); ␥-terpinene
(2.770); fenchyl acetate (3.620); bornyl acetate (4.070); ␣-terpinyl
acetate (4.490); by-products (from 6.500 to 8.000). ␣-Pinene con-
version was defined as the concentration ratio of converted species
(products) to the initial concentration of ␣-pinene. GC–MS analysis
(gas chromatography coupled to mass spectrometry) was utilized
in the detailed product analysis and identification. For the GC–MS
analysis, a device by Thermo Trace DSQ was used. The column
parameters were: VF-5MS, 30 m, 0.25 mm I.D., phase 0.25 ␮m and
a constant nitrogen flow rate of 1.5 ml/min was applied. The injec-
tion temperature was 230 ◦C and the initial temperature of the oven
was 50 ◦C, maintained for 1 min, where after a temperature ramp
(20 ◦C/min) was commenced up to 300 ◦C. For the precise prod-
uct analysis by means of GC, several terpene standard solutions
were applied. The standards of anticipated reaction products were
diluted in acetone (0.3 ml) before injection to the GC. The concen-
tration of the products was expressed in terms of wt% to the whole
amount of the reacted ␣-pinene in the product mixture. The ␣-
pinene conversion, product selectivities and yields were calculated
as follows:
3. Results
3.1. Acetoxylation of ˛-pinene
For the studied reaction, ␣-terpinyl, fenchyl, verbenyl and
bornyl acetates as well as limonene, camphene and ␥-terpinene
were all found in the product mixture. The other products were
found in amounts less than 1 wt% and were considered negligible.
The formation of by-products was not uniform in case of all pro-
longed reactions. A temperature range of 25–125 ◦C and a pressure
range from atmospheric to 20 bar were considered. The influence of
the gas atmosphere, i.e. nitrogen, oxygen or hydrogen atmosphere
was also investigated. A pressurizing gas was needed to suppress
the evaporation of the reactants involved. Glacial as well as aque-
ous acetic acid (2.5 wt% and 5 wt%, respectively) and also a blend
of acetic acid and toluene or ethyl acetate (5 wt%) were tried as
co-solvents. The influence of each factor was studied in catalytic
(Amberlyst 70) and the solvent-catalyzed mode. Fig. 1 (Symbols:
(•) 100◦C, 10 bars, N2, cat; (−) 100◦C, 10 bars, N2, no cat; (+) 75◦C,
10 bars, N2, cat; (ꢀ) 125◦C, 10 bars, N2, cat; (ꢁ) 100◦C, 20 bars,
H2, cat; (ꢂ) 100◦C, 20 bars, O2, cat; (ꢃ)100◦C, 20 bars, O2, no cat;
( ) 100◦C, 20 bars, O2, no cat, 5 wt % ethyl acetate/95 wt % acetic
acid; (ꢀ)100◦C, 20 bars, O2, cat, 5 wt % toluene/95 wt % acetic
acid; (×) 100◦C, 20 bars, O2, cat, 95% aqueous acetic acid.) describes
the conversion of ␣-pinene. Figs. 2 and 3 refer to the evolution of
corresponding products under various reaction conditions.
initial ␣-pinene GC peak area − final ˛-pinene GC peak area
X (%) =
× 100
× 100
(1)
initial ˛-pinene GC peak area
GC peak area of the product Y
SY (%) =
(2)
(GC peak area of ␣-pinene)initial − (GC peak area of ␣-pinene)final

M. Golets et al. / Applied Catalysis A: General 435–436 (2012) 43–50
45
Fig. 1. ␣-Pinene conversion.
It was evident that camphene and fenchyl acetates were formed
as parallel reaction products. The maximum yields of these prod-
ucts were reached at 100 ◦C and 20 bar, in the solvent-catalyzed
reaction system when the solvent was a blend of acetic acid and
ethyl acetate and oxygen was used to pressurize the reaction vessel.
The yield of ␥-terpinene was in the range of 15 wt% in several cases.
Under the solvent-catalyzed reaction conditions, in glacial acetic
50
α-terpinyl acetate
40
30
20
10
0
Fig. 3. The evolution of reaction products under oxygen atmosphere.
0
0
0
2
4
4
4
6
6
6
8
8
8
10
10
10
acid, verbenyl acetate formation could be maximized (16 wt%).
After prolonged reaction times (10–18 h), by-products started to
emerge. As a result of very long batch times, more than 30 wt% of by-
products could be found. By-products were observed eluted in the
GC chromatogram after the main reaction products. Under the opti-
mized reaction conditions there were fewer by-products formed
while the conversion was always high throughout the experimen-
tal matrix. The formation of the undesired by-products was favored
by nitrogen atmosphere, in combination with harsh reaction condi-
tions (up to 20 wt% of the final product mix, in 10 h), while oxygen
atmosphere counter-effected the formation of by-products even
during prolonged experimental runs (up to 18 h of batch time) in
case of the solvent-catalyzed reaction. The reason of this observa-
tion will be discussed later.
Time, h
Time, h
Time, h
50
40
30
20
10
0
bornyl acetate
2
Optimal reaction conditions were determined for the catalytic
and solvent-catalyzed modes, respectively. The optimal reaction
time and solvent type were chosen accordingly for each case. On
the basis of earlier results, it was determined that around 10 h batch
time is appropriate (Tables 1 and 2).
50
40
30
20
10
0
limonene
3.2. Catalyst characterization
Conventional titration (glass buret) method revealed that the
number of acid sites in the Amberlyst 70 resin was reduced from
2.48 to 1.61 eq/kg upon exposure to the reaction solution. The ini-
tial value determined was in line with the manufacturer’s data.
The results of nitrogen physisorption for Amberlyst 70 are given
in Table 3.
2
Fig. 2. The evolution of reaction products under nitrogen and hydrogen atmo-
spheres.

46
M. Golets et al. / Applied Catalysis A: General 435–436 (2012) 43–50
Table 1
Sample concentration data showing the evolution of products in catalytic reactiona
Reaction time (h)
␣-Pinene
Products concentration (wt%)b
conversion (%)
Limonene
␥-Terpinene
Camphene
Fenchyl acetate
Bornyl acetate
␣-Terpinyl
acetate
0.5
1
2
4
6
12.3
21.8
95.1
98.4
99.1
99.2
3.0
6.8
32.1
34.3
31.7
31.1
1.8
4.8
10.8
1.7
2.4
2.4
0.6
1.4
6.4
2.9
2.6
2.6
0
0
2.4
5.8
5.8
7.4
0
1.2
13.4
19.7
23.6
29.9
4.7
8.7
2.4
0
0
0
10
a
100 ◦C, 20 bar, O2, 95% aqueous acetic acid, 10 h.
Proportionally to the whole amount of ␣-pinene.
b
Table 2
Sample concentration data showing the evolution of products in solvent-catalyzed reactiona
Reaction time (h)
␣-Pinene
Products concentration (wt%)b
conversion (%)
Limonene
␥-Terpinene
Camphene
Fenchyl
acetate
Bornyl
acetate
␣-Terpinyl
acetate
Verbenyl
acetate
0.5
1
2
4
6
1.4
8.8
19.8
31.0
47.7
90.1
0
0
0
1.3
1.9
3.1
5.0
0
0
0
0
0
3.0
5.0
0
1.3
3.8
8.8
12.6
18.8
28.3
0
1.4
1.7
2.8
4.4
7.2
0.7
0.8
1.3
2.0
3.4
1.0
2.4
3.5
5.8
9.4
4.7
5.6
6.3
9.8
16.0
10
a
100 ◦C, 20 bars, O2, glacial acetic acid, 10 h.
Proportionally to the whole amount of ␣-pinene.
b
Table 3
BET surface area, pore size and pore volume data for Amberlyst 70.
Catalyst
SBET (m2/g)
Pore size (nm)
Pore volume (cm3/g)
Concentration of
acid sites (eq/kg)
Fresh
Spent
40.2
3.6
25.3
23.0
0.3
0.02
2.48
1.61
According to the results, the specific surface area and pore
volume were significantly reduced, thus indicating catalyst deacti-
vation. The average pore size of the catalyst was slightly reduced
under the reaction conditions.
The SEM images scaled at 2.00 ␮m for Amberlyst 70, before and
after the reaction, are presented in Fig. 4. It is evident that the
surface has undergone morphology changes. The fresh resin had
a sphere diameter of around 350–600 ␮m, while the spent cata-
lyst contained spheres of around 400–800 ␮m, thus demonstrating
swelling of the resin particles.
three times after each and every reaction cycle. The conversion of ␣-
pinene obtained during the first batch was 96%, whereas the second
and third batch resulted in 68% and 60% conversion, respectively.
No abrasion of catalyst particles was observed at this temperature.
Rather severe catalyst decomposition (about 30%) was observed at
higher temperatures.
4. Discussion
It was evident that the role of the temperature was the decisive
one: the overall trend was rapid ␣-pinene conversion at elevated
temperatures. Within the temperature interval of 25–75 ◦C, the
selectivity toward main products remained almost unchanged.
Temperatures below 75 ◦C were found to be too low and resulted
in a significant drop in conversion over time and, consequently, a
reaction time exceeding 24 h was required. The ␣-terpinyl acetate
formed during the course of the reaction was consumed to form
3.3. Recovery and reusability of the catalyst
The catalyst reusability was studied in a temperature range of
75–100 ◦C (Fig. 1). The catalyst was recovered by means of filtration
and washed with acetone. Thereafter the catalyst was washed with
0.1 N HCl solution and dried. The same procedure was repeated
Fig. 4. Amberlyst 70 SEM images – fresh and spent catalyst samples.

M. Golets et al. / Applied Catalysis A: General 435–436 (2012) 43–50
47
Fig. 5. The overall reaction network.
limonene in case of prolonged reaction time and high temperatures.
Furthermore, bornyl and fenchyl acetates, as well as camphene and
limonene were rapidly formed at 100–125 ◦C, although also some
by-products started to form, thus resulting in decreased selectiv-
ity. In fact, toward the end of a batch, the reaction mixture turned
at first yellow and then brown. Elevated temperatures were more
beneficial in terms of ␥-terpinene formation. Still, under optimized
reaction conditions, ␣-terpinyl acetate yield was nearly 30 wt%. Our
observations about the influence of temperature were in line with
the literature results [9,14].
Interestingly, Hensen et al. [9] reported that pressure does
not significantly influence the conversion and selectivity profiles.
However, our results were quite the opposite. As can be seen
(Figs. 2 and 3), the selectivity toward ␣-terpinyl acetate, limonene
and ␥-terpinene was significantly influenced when 10 respective
20 bar of gas pressure was applied. The optimal yield was always
coupled to the optimal combination of several reaction parameters.
A pressure lower than 10 bar led to poor conversion, whereas higher
pressure accelerated the conversion and influenced the selectivity
profiles. This phenomenon could be explained by the partial evap-
oration of the reaction mixture. Elevated pressure levels should
reduce the products that evolve to the gas (vapor) phase and thus
increase their interaction with the solvent and the catalyst.
The aggressive reaction environment used caused serious cat-
alyst deterioration and deactivation. As mentioned in Section 3.2,
the pore volume and the concentration of acid sites of the catalyst
were reduced under the high temperature and pressure conditions.
As already mentioned (Section 3.1), aqueous and glacial acetic
acid milieus gave the best results both during the catalytic and
solvent-catalyzed reaction experiments, respectively. Beneficial ␣-
pinene conversion obtained in the presence of water could be
explained by the stronger nucleophilic properties of water than
that of acetic acid due to faster hydration. Williams and Whittaker
[21] showed that water addition increases the ␣-terpinyl acetate
yield and, at the same time, has an insignificant effect on bornyl
acetate formation. At increased water concentrations, a significant
drop in the conversion albeit rise in selectivity due to prevention
of by-products formation has been observed [14]. In our case, in
aqueous acetic acid, about 50 wt% less by-products were formed,
even during prolonged batch times. Similar effect was observed
even when more than 10 wt% of water was added. The conversion
decreased significantly since water addition inhibits the acetoxyla-
tion reaction [14]. In our case, the use of 2.5 wt% aqueous acetic acid
solution resulted in less ␣-terpinyl acetate and more bornyl acetate,
compared to the case when glacial acetic acid was applied as the
solvent. The aggressive reaction conditions and the influence of
the gas atmosphere used contributed to this behavior. Toluene and
ethyl acetate blends with acetic acid resulted in average behavior
in terms of conversion and selectivity.
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
The influence of nitrogen, oxygen and hydrogen gas atmo-
spheres was studied. Nitrogen was assumed as a ‘neutral’ gas, which
provided the pressure only, although by-products formation was
observed in several cases. The plausible reason for this is the high
temperature applied. The use of hydrogen led to average conver-
sion and selectivity in all cases. Accelerated limonene degradation
0
5
10
15
20
25
30
35
40
time h
Fig. 6. Simulation of a CSTR reactor with the concentration of reactant as function
of residence time (for temperatures 75, 100, 125 ◦C, respectively).

48
M. Golets et al. / Applied Catalysis A: General 435–436 (2012) 43–50
Fig. A.1. Description of the reaction network used in the kinetic modeling (B–acetoxylation agent, I+1–pinyl ion, I+2–terpinyl ion).
due to fast hydration was a serious drawback, promoted by the
presence of hydrogen molecules. The best yields under otherwise
optimized combination of reaction parameters were obtained in
oxygen atmosphere.
The effect of the temperature on the initial rate of ␣-pinene
acetoxylation according to the optimized experimental data was
described by the Arrhenius plot. The data set was modeled with
the help of the following set of equations:
Fig. 5 represents the reaction network. The pinyl ion is rapidly
formed from ␣-pinene, followed by a rearrangement taking place
without a capture by nucleophiles [21]. As shown already earlier
that, in addition to the ring-opening reaction, two ring-enlarging
reactions are also possible [4,5]. The observed high selectivity
toward bornyl acetate versus fenchyl acetate could be explained
by the fact that the ring-enlargement reaction with an isopropyl
group proceeds easier than with a methyl group. Further, the ring-
enlarging reaction (1) is preferred in comparison to the reaction
(2). With increasing ␣-pinene conversion, the terpinyl ion attacks
on the olefinic compounds present in the system and can result in
the formation of by-products [14].
In general, both heterogeneously- and solvent-catalyzed reac-
tions were successful when the optimized reaction conditions were
applied. Both reaction modes allowed obtaining valuable prod-
ucts. As mentioned (Figs. 2 and 3), the additional acidity, provided
by the Amberlyst 70, stimulated the bornyl acetate formation
without cleavage of the internal pinyl ring, whereas, the forma-
tion of ␣-terpinyl acetate was solvent-catalyzed. Verbenyl acetate
was only formed in under the solvent-catalyzed mode. Plausibly,
this product is formed directly from ␣-pinene due to its allylic
oxidation by O2 followed by the acetoxylation without any ring
rearrangements.
d[n]
d[t]
r =
= k[n]
(4)
[n]t = [n]0e−kt
In[n]t = In[n]0 − kt
(5)
(6)
A strong Arrhenius-type temperature dependence was demon-
strated with glacial acetic acid for bornyl acetate, also supported
by the experimental observations. However, less obvious correla-
tion can be seen in terms of limonene and ␣-terpinyl acetate. When
observing the Arrhenius plots, the activation energies for the three
main reaction products were as follows: 106, 29.1 and 16.6 kJ/mol
for bornyl acetate, limonene and ␣-terpinyl acetate, respectively.
The experimental data was fitted with a kinetic model imple-
mented in the ModEst (Profmath Oy) software. The simulation of
the Continuous Stirred-Tank Reactor (CSTR) reactor with the con-
centration of reactant as function of residence time was included
(Fig. 6) [23]. The details of kinetic modeling are described in
Appendix A.
5. Conclusions
In this paper we investigated a one-stage process for ␣-pinene
liquid-phase acetoxylated transformation to value-added products,
both under catalytic and solvent-catalyzed modes. The catalyst
used was Amberlyst 70 ion-exchange resin. A wide range of
process parameters was studied. The importance of various pro-
cess parameters can be summarized as follows: temperature,
catalytic/solvent-catalyzed process, gas type, solvent composition
and pressure. Serious catalyst deactivation was observed when
Under oxygen atmosphere, a portion of ␣-pinene was oxidized
to ␣-pinene oxide. As the next step, this compound further reacted
with acetic acid and dehydrated leading to additional formation
of the verbenyl acetate. The amount of terpinyl ions found in the
reaction mixture can thus be considered directly proportional to
the lower yield of by-products. Our observation was supported by
the literature [22].

M. Golets et al. / Applied Catalysis A: General 435–436 (2012) 43–50
49
Table A.1
The numerical values of parameters and their errorsa.
Estimated
Estimated
Est. relative error of parameters
Std. error (%)
Std error (%)
k10
k3
k5
0.295E−01
0.881E−01
0.281E−01
0.458E−01
0.534E+05
0.533E+05
0.538E+05
0.537E+05
0.427E−02
0.910E−02
0.439E−02
0.432E−02
0.850E+04
0.603E+04
0.916E+04
0.558E+04
14.5
10.3
15.6
9.4
15.9
11.3
17.0
10.4
6.9
9.7
6.4
10.6
6.3
8.8
k9
Ea10
Ea3
Ea5
Ea9
5.9
9.6
a
Units: k3, k9 and k10 – 1/h; k5 – dm3/(mol h); Ea – J/mol.
Table A.2
Parameter correlation matrix.
The reaction rates were expressed by meant the following set of
equations:
ꢂ
ꢂ
ꢂ
ꢂ
ꢀ
ꢃ
1
CP
1
r3 = A3
r4 = A4
r5 = A5
×
×
×
CA
CA
−
−
× CH
(A.2)
(A.3)
(A.4)
−0.390
0.016
0.027
−0.651
0.312
0.010
0.017
1
Keq3
−0.395
1
−0.345 0.025
0.316 0.010
−0.589 0.311
0.315 −0.651
0.313 0.016
1
ꢃ
CP
0.017
1
2
× CH
0.308 −0.370
0.015 0.026 −0.379
−0.618 0.044 −0.314 0.040
1
Keq4
1
ꢃ
1
CP
3
CA × CB
CA × CB
−
−
× CH
Keq4
ꢃ
CP
4
r6 = A6
r7 = A7
r8 = A8
×
×
×
× CH
(A.5)
(A.6)
(A.7)
harsh experimental conditions were applied; still, the optimal
product yield was rapidly reached. As a summary: a typical prod-
uct mixture in the solvent-catalyzed reaction contained 28 wt% of
␣-terpinyl acetate, 9 wt% of bornyl acetate, 5 wt% of ␥-terpinene,
5 wt% of fenchyl acetate, 7 wt% of limonene and 16 wt% of verbenyl
acetate, whereas 30 wt% of bornyl acetate and 31 wt% of limonene,
respectively, were obtained in the catalytic process. Thus, the
catalytic reaction mode resulted in a significantly higher yield
of the valuable bornyl acetate. Increased temperatures or hydro-
gen atmosphere resulted in extensive formation of by-products
whereas verbenyl acetate was formed only upon solvent-catalyzed
reaction. Moreover, oxygen atmosphere is beneficial since the use
of it prevents the by-products formation to a large extent upon
the solvent-catalyzed reaction. According to the kinetic model, the
reaction pathways in line with the routes toward limonene and
bornyl acetate formation are the predominant ones. The modeling
results are in strong correlation with the experimental observa-
tions. Industrially feasible operations and scale-up of the studied
process requires the evaluation of several aspects and more studies
taking into account the separation aspects are needed.
Keq6
ꢁ
CP × CB − CP
1
5
ꢂ
ꢃ
CP
6
CA × CB
−
× CH
Keq8
ꢂ
ꢃ
CP
7
r9 = A9
×
CA
−
× CH
(A.8)
Keq9
ꢂ
ꢃ
CP
8,9
r10 = A10
r11 = A11
×
×
CA
−
× CH
(A.9)
Keq10
ꢀ
ꢁ
CP − CP
(A.10)
8
9
The batch reactor model is expressed as following:
dCA
= −r3 − r4 − r5 − r6 − r8 − r9 − r10
(A.11)
(A.12)
(A.13)
(A.14)
(A.15)
(A.16)
(A.17)
(A.18)
(A.19)
dt
dCB
dt
= −r5 − r6 − r7 − r8
dCP
1
= r3 − r7
= r4
Acknowledgments
dt
dCP
dt
2
3
4
5
6
7
Umeå University Business Graduate School, Processum Biore-
finery Initiative AB, Aditya Birla Domsjö Fabriker AB, Holmen
Energi AB, MoRe Research AB and Metsä Group Husum AB are
gratefully acknowledged for the financial support. The Bio4Energy
programme is acknowledged. Rohm and Haas Nordic representa-
tive is gratefully acknowledged for providing the catalyst samples.
dCP
dt
= r5
dCP
dt
= r6
dCP
dt
= r7
Appendix A.
dCP
dt
Reaction network was organized in line with Fig. A.1 and the
actual reaction network (Fig. 5).
The temperature dependency was expressed with the Arrhenius
equation as:
= r8
dCP
dt
= r9
ꢀ
ꢁ
dCP
E
a
8,9
j
1.odo
1.odo
T
mean
−
= r10 − r11
(A.20)
temp
R
Aj = kj × e
(A.1)
dt

50
M. Golets et al. / Applied Catalysis A: General 435–436 (2012) 43–50
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