Simultaneous production of biobased styrene and acrylates using ethenolysis

Article abstract of DOI:10.1039/c2gc35498e

Phenylalanine (1), which could be potentially obtained from biofuel waste streams, is a precursor of cinnamic acid (2) that can be converted into two bulk chemicals, styrene (3) and acrylic acid (4), via an atom efficient pathway. With 5 mol% of Hoveyda-Grubbs 2nd generation catalyst, 1 bar of ethylene, and using dichloromethane as solvent, cinnamic acid (2) can be converted to acrylic acid and styrene at 40 °C in 24 h with 13% conversion and 100% selectivity. Similar results are obtained using cinnamic acid esters (methyl, ethyl and n-butyl) as substrates and optimisation leads to higher conversions (up to 38%). For the first time, cross-metathesis of these types of electron deficient substrates was achieved.

Full text of DOI:10.1039/c2gc35498e

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PAPER
Simultaneous production of biobased styrene and acrylates using ethenolysis†
a
a
b
a
a
Jurjen Spekreijse, Jérôme Le Nôtre, Jacco van Haveren, Elinor L. Scott* and Johan P. M. Sanders
Received 3rd April 2012, Accepted 10th July 2012
DOI: 10.1039/c2gc35498e
Phenylalanine (1), which could be potentially obtained from biofuel waste streams, is a precursor of
cinnamic acid (2) that can be converted into two bulk chemicals, styrene (3) and acrylic acid (4), via an
atom efficient pathway. With 5 mol% of Hoveyda–Grubbs 2nd generation catalyst, 1 bar of ethylene, and
using dichloromethane as solvent, cinnamic acid (2) can be converted to acrylic acid and styrene at 40 °C
in 24 h with 13% conversion and 100% selectivity. Similar results are obtained using cinnamic acid esters
(methyl, ethyl and n-butyl) as substrates and optimisation leads to higher conversions (up to 38%). For
the first time, cross-metathesis of these types of electron deficient substrates was achieved.
5
for food applications. This means that substantial amounts of
phenylalanine (1) could be available as a feedstock for the pro-
duction of bulk chemicals without competing with the food and
feed market.
Introduction
A search for a green and sustainable alternative for fossil based
chemistry is needed due to depleting fossil resources, geopoliti-
cal instability and global warming. Biomass as a feedstock offers
an alternative with a closed carbon cycle. Amino acids are abun-
dant in biomass and they are highly functionalized. These prop-
erties make efficient routes towards bulk chemicals possible,
which saves energy and reagents. The amino acid content of
There are already several examples of synthetic routes from
amino acids to bulk chemicals. The syntheses of N-methylpyrrol-
idone, acrylonitrile and succinonitrile from glutamic acid and
,4-diaminobutane from arginine have been reported in recent
years. Styrene (3) (17 million tons produced worldwide per
6
7
8
9
1
1
10
several sources of biomass was recently reviewed by Lammens.
year) and acrylic acid (4) (2.5 million tons produced world-
10
Examples include wheat DDGS, vinasses and leaves from differ-
ent crops with, depending on the waste stream, a protein content
ranging from 20 to 40%. These proteins can be isolated from the
biomass followed by hydrolysis. Next, the formed amino acids
need to be separated from each other. Several examples have
been reported on the isolation of the protein content from differ-
wide per year) are important bulk chemicals for the plastic
industries, yet there are only a few examples of the production of
these chemicals from biomass. OPX Biotechnologies together
with DOW Chemicals are developing the synthesis of acrylic
11
acid (4) from biomass via 3-hydroxy propionic acid. McKenna
12
and Nielsen
proposed a biosynthetic decarboxylation of
1
ent biomass sources. Hydrolysis and further separation to pure
cinnamic acid (2) from sugars to styrene (3) with the loss of CO2,
but the toxicity of styrene (3) limits the scale of the production.
An enzymatic conversion of phenylalanine is well known in
Herein we propose a highly atom efficient syn-
thesis of styrene and acrylates from cinnamic acid, simul-
taneously producing two major bulk chemicals from a waste
amino acids are still developing fields that are progressing fast
and will become economically feasible in the near future, for
example, by modifying specific amino acids enzymatically in
combination with electrodialysis.
In 2020, European guidelines aim for 10% of all transpor-
13–15
literature.
2
3
16
tation fuels to be originated from biomass, resulting in waste
stream in only two synthetic steps (Scheme 1).
streams containing proteins from 20 to 40% of the dry matter
weight. Combined with the estimated worldwide biofuel pro-
4
duction, this will lead to the production of ca. 100 million
Experimental
tons of protein per year, corresponding on average to 5%
(
(
ca. 5 million tons) of each amino acid, including phenylalanine
1). In 2000 only 13 000 tons of phenylalanine (1) was produced
All experiments carried out at elevated pressures were performed
in 6 individual 75 mL Parr pressure reactors (Parr multiple
reactor system series 5000). Reaction mixtures were prepared in
Schlenk tube glassware under a positive pressure of nitrogen
and transferred to the reactors via syringe. Ethylene 3.5 (purity
1
a
Chair of Biobased Commodity Chemicals, Wageningen University and
≥
99.95%) was supplied by Linde Gas Benelux and used as
Research Centre, P.O. Box 17, 6700 AA, Wageningen, The Netherlands.
E-mail: elinor.scott@wur.nl; Fax: +31 3174 83011;
Tel: +31 31748 1172
received. Dichloromethane was dried over CaCl and distilled
2
under nitrogen before use. Other anhydrous solvents (purchased
from Sigma-Aldrich) and Milli-Q water were degassed with
nitrogen before use. Cinnamic acid (2) was supplied by Sigma-
Aldrich and used without additional purification. Methyl (5) and
b
Food & Biobased Research, Wageningen University and Research
Centre, Wageningen, The Netherlands
†
1
Electronic supplementary information (ESI) available. See DOI:
0.1039/c2gc35498e
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Scheme 1 Two step conversion of phenylalanine (1) into styrene (3) and acrylic acid (4).
ethyl (6) cinnamate (Sigma-Aldrich) and n-butyl cinnamate (7)
prepared following a standard esterification procedure) were
For the catalyst screening the stock solution consisted of
solvent and substrate. The catalyst was introduced in the reactor
immediately followed by the stock solution. The rest of the pro-
cedure was followed as described above.
For the solvent and substrate screening, no stock solution was
used. The catalyst, substrate and solvent were directly added into
(
filtered through a plug of neutral alumina and degassed with
nitrogen before use. All ruthenium catalysts were obtained from
Sigma-Aldrich. Concentration of solutions was carried out by
using a rotary evaporator. Purification by filtration over a silica
plug was undertaken on silica gel (400–630 mesh). Proton
the reactor, which was directly purged with N . The rest of the
2
1
nuclear magnetic resonance spectra ( H NMR) were recorded on
procedure was followed as described above.
a Bruker AM-400 (400 MHz). GC-MS analyses were performed
on a CE Instrument GC 8000 Top (capillary column SGE-Forte,
3
0 m × 0.25 mm, 0.25 μm) chromatograph linked to an Auto-
mass II Finnigan MAT (70 eV) apparatus. The temperature
Results
profile was held at 50 °C for 2 min, then increased to 300 °C
1
(
10 °C min− ), and held at 300 °C for 2 min.
Phenylalanine (1) can be converted to cinnamic acid (2) using
the enzyme phenylalanine ammonia lyase (PAL). This enzyme
has been studied in detail and conversions to cinnamic acid (2)
Esterification
13–15
are in the range of 58 to 93%.
Here we report the conversion of cinnamic acid (2) to styrene
3) and acrylic acid (4), which follows a metathesis reaction
See ESI† for detailed typical procedures.
(
using ethylene, also called ethenolysis. Ethylene can be pro-
17
duced from ethanol, which can be obtained from biomass.
Self-metathesis tests
18
Even though ethenolysis is well understood, it has been gener-
ally applied to fatty acids or comparable substrates with non-
functionalized double bonds. The substrate for the ethenolysis
proposed here possesses an acid functionality and a conjugated
π-system. This makes the double bond electron deficient and a
challenging metathesis substrate. To the best of our knowledge
the only previous example of an ethenolysis of a similar
compound is the ethenolysis on diethyl fumarate patented by
0
.34 mL (2 mmol) ethyl cinnamate (6) was added to 10 mL
dichloromethane (DCM) in a Schlenk tube under a nitrogen
atmosphere. 5 mol% catalyst was added and the reaction was
heated to 40 °C and stirred for 24 h. The DCM was evaporated
under atmospheric pressure and the crude product was analysed
1
by H NMR spectroscopy.
19
Genomatica. However, the highest yield reported was 7% of
ethyl acrylate (9).
Ethenolysis
To obtain acrylic esters (8–10), cinnamic acid (2) was ester-
ified to its methyl (5), ethyl (6) and n-butyl (7) esters
A stock solution was prepared in a Schlenk tube containing
DCM with the substrate (0.02–0.50 M) and the catalyst (I) to
(Scheme 2). Several catalysts have been tested under which the
(
V) (5–12.5 mol%). The solution was divided over the reactors
Brønsted acids sulphuric acid, Amberlyst 15 and 36, the Lewis
using a syringe (10 mL per reactor) and the reactors were purged
20
acid iron trichloride and the enzyme CAL-B (see ESI†).
Sulphuric acid in combination with a drying agent gave the
highest yield (91%).
three times with N . The reactors were placed in the control
2
system and purged three times with ethylene. The pressure of
ethylene was applied and the reactions were heated and stirred
during the reaction time. (For reaction pressure depicted as being
less than 1 bar of ethylene, mixtures of ethylene and nitrogen
were prepared and reactions were performed under 1 bar of the
gas mixture atmosphere. For instance, a reaction performed with
0
.5 bar of ethylene was performed with 1 bar of a 50/50 ethyl-
ene/nitrogen gas mixture). After the reaction, the reactors were
opened and an aliquot was filtered over a plug of silica, washed
with the used solvent once and injected into the GC-MS. The
crude mixture was concentrated by heating to 50 °C for a couple
of minutes under atmospheric pressure. The conversion of the
1
cinnamic acid (2) or its esters (5–7) was measured by H NMR.
Scheme 2 Esterification of cinnamic acid (2).
2748 | Green Chem., 2012, 14, 2747–2751
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Scheme 3 Ethenolysis of cinnamic acid (2) and cinnamic esters (5–7) to styrene (3) and acrylic acid (4) and esters (8–10).
Fig. 2 Commercially available catalysts used in this work.
Fig. 1 Pressure screening for the conversion of cinnamic acid (2) and
ethyl cinnamate (6): 0.02 M substrate, 24 h, 40 °C, 5 mol% (I). (Press-
ures of ethylene below 1 bar represent a pressure of 1 bar of nitrogen
and ethylene, where the partial pressure of ethylene is shown.)
a
Table 1 Ethenolysis of ethyl cinnamate (6) – catalyst screening
b,c
Entry
Catalyst
Conversion (%)
1
2
3
4
5
I
16
<1
<1
5
II
III
IV
V
For the ethenolysis of ethyl cinnamate (6) the Hoveyda–
Grubbs 2nd generation catalyst (I) was used at an ethylene
pressure of 2 bar, which resulted in a conversion of 4%
3
a
Reaction conditions: Pethylene = 1 bar, 40 °C, 22–24 h, 0.05 M (6),
b
1
c
(Scheme 3). From the literature, it is generally considered that an
5.0 mol% cat., 10 mL DCM. Conversion measured by H NMR. All
reactions proceed with 100% selectivity.
increase in the pressure of ethylene will lead to an increase in
18,21
conversion.
However, it was observed from our own exper-
iments that increasing the pressure led to a decrease in conver-
sion (Fig. 1). Interestingly, we found that a low pressure of
ethylene was beneficial and led to a more optimum conversion.
It is proposed that the difference is caused by the electron
deficient nature of the substrate. The low reactivity of the elec-
tron deficient double bond causes ethylene to predominantly
undergo self-metathesis. This non-productive part of the catalytic
cycle has been reported by Scholz et al. At lower pressures,
there is less ethylene available and the equilibrium is shifted
towards the active part of the catalytic cycle.
self-metathesis reaction into stilbene. This is supported by the
fact that no self-metathesis of the starting material is observed
under similar conditions and that styrene (3) undergoes self-
metathesis in control experiments, where ethyl acrylate (6) does
not (see ESI†). Thus, stilbene originates from styrene (3). The
group of Prof. R. H. Grubbs found similar results regarding
selectivity, where an excess of the more reactive metathesis
2
2
23
partner increases selectivity.
Ethenolysis on cinnamic acid (2) gave 7% conversion at 2 bar,
which is similar to the result of ethyl cinnamate (6). The same
optimum at lower pressures was observed for cinnamic acid (2)
A screening of several commercially available catalysts was
performed on ethyl cinnamate (6) (Fig. 2, Table 1). Both phos-
phine-based catalysts showed no conversion (Table 1, entries 2
and 3), where catalysts (IV) and (V) showed slightly higher
activity (Table 1, entries 4 and 5). The Hoveyda–Grubbs 2nd
generation catalyst (I) proved to be the most suitable and active
catalyst for the substrate (Table 1, entry 1). The higher activity of
(I) can be explained by the electron donating carbene ligand,
(Fig. 1).
A disadvantage of using low ethylene pressures is the loss of
selectivity. At a partial ethylene pressure below 0.5 bar (com-
bined with 0.5 bar nitrogen), lower amounts of styrene (3) com-
pared to acrylate (4, 9) were observed and a correlating amount
of stilbene was formed. This implies that styrene (3) undergoes a
24
which stabilizes the electron poor substrate.
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A catalyst screening was also performed on cinnamic acid (2)
Table 2). The results were similar to the experiments on ethyl
in toluene at 110 °C (Table 3, entries 2, 3 and 7, 8). Varying the
reaction time showed that the catalyst is still active after 24 h and
that a conversion of 29% can be obtained after 48 h (Table 3,
entries 11–14).
Based on these data the reaction was optimized using higher
concentrations of butyl cinnamate (7) and the ethylene pressure
was tuned in order to enhance selectivity (Table 4).
(
cinnamate (6) (Table 1), and again the highest conversion (23%)
was obtained with the Hoveyda–Grubbs 2nd generation
catalyst (I).
Under the conditions presented in Fig. 1 at 1 bar, using the
same concentration of substrates, we found that cinnamic acid
(
2), methyl cinnamate (5) and ethyl cinnamate (6) resulted in
Increasing the pressure of ethylene and the concentration of
the starting material decreased the conversion, but increased the
selectivity to the desired products (Table 4, entries 1–4). This
resulted in a fully selective conversion of n-butyl cinnamate (7)
towards styrene (3) and n-butyl acrylate (10) of 14% (Table 4,
entry 4). A higher pressure decreased the conversion, even when
the concentration of n-butyl cinnamate (7) was increased as well,
however, no side products were observed in any of these reac-
tions (Table 4, entries 5–11). At pressures of 20 bar and above,
the best result was 11% conversion (Table 4, entry 6). An exper-
iment performed using neat substrate, which can be seen as the
highest concentration, gave a low conversion, however, with a
very low catalyst loading (Table 4, entry 11).
similar conversions with 13%, 12% and 15%, respectively. We
therefore concluded that there is no significant difference in reac-
tivity between the acid and esters.
For the reaction media several solvents were tested, among
which was dimethylcarbonate (DMC), an eco-friendly solvent
2
5
for metathesis reactions. The highest conversion (23%) was
obtained when using dichloromethane (DCM) (Table 3, entry 1).
Toluene as a solvent resulted in a conversion of 10% (Table 3,
entry 3), while DMC proved a viable alternative with a conver-
sion of 15% (Table 3, entry 2). Hexane is also a common solvent
for metathesis reactions, but only resulted in a conversion of 5%
in this reaction (Table 3, entry 6). Protic solvents showed no con-
version (Table 3, entries 4 and 5). Decreasing the catalyst
loading from 12.5 mol% to 5.0 mol% lowered the conversion
from 23% to 13% (Table 3, entries 1 and 9). Increasing the reac-
tion temperature resulted in a moderate increase in the conver-
sion to the desired products with a 21% conversion for the
reaction in DMC at 90 °C and 13% conversion for the reaction
a
Table 4 Optimization of the ethenolysis of n-butyl cinnamate (7)
b
c
[
7]
(I)
(mol%)
P
(bar)
ethylene
Conv.
(%)
Selectivity
(%)
Entry (M)
1
2
3
4
5
6
7
8
9
0.05
0.05
0.10
0.10
0.10
0.10
0.10
0.25
0.25
0.50
Neat
12.5
12.5
5.0
5.0
5.0
5.0
5.0
5.0
5.0
1
1
1
38
19
29
14
9
11
3
2
4
2
3
60
70
90
d
a
Table 2 Ethenolysis of cinnamic acid (2) – catalyst screening
5
100
100
100
100
100
100
100
100
b,c
Entry
Catalyst
Conversion (%)
10
20
33
35
20
20
35
1
2
3
4
5
I
23
<1
<1
<1
10
II
III
IV
V
10
11
5.0
0.25
a
a
Reaction conditions: Pethylene = 1 bar, 40 °C, 22–24 h, 0.02 M (2),
2.5 mol% cat., 10 mL DCM. Conversion measured by H NMR. All
Reaction conditions: DCM, T = 40 °C, reaction time = 24 h.
1 c
b
1
c
b
d
1
Conversion measured by H NMR. Stilbene appears as by-product.
Reaction time = 4 h.
reactions proceed with 100% selectivity.
a
Table 3 Ethenolysis of cinnamic acid (2)
b
c,d
Entry
Loading (I) (mol%)
Solvent
Pethylene (bar)
Temp. (°C)
Time (h)
Conv. (%)
1
2
3
4
5
12.5
12.5
12.5
12.5
12.5
12.5
12.5
12.5
5.0
5.0
5.0
5.0
5.0
DCM
DMC
Toluene
MeOH
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.5
0.5
0.5
0.5
40
40
40
40
40
70
90
110
40
RT
40
40
40
40
24
24
24
24
24
24
24
24
24
24
2
23
15
10
0
0
5
21
13
13
6
H
2
O
e
6
Hexane
DMC
Toluene
DCM
DCM
DCM
DCM
DCM
DCM
7
8
9
1
0
1
1
6
1
1
1
2
3
4
4
24
48
13
19
29
5.0
a
b
Reaction conditions: [cinnamic acid (2)] = 0.02 M. Pressures of ethylene below 1 bar represents a pressure of 1 bar of nitrogen and ethylene, where
c
1
d
e
the partial pressure of ethylene is shown. Conversion measured by H NMR. All reactions proceed with 100% selectivity. 0.05 M of cinnamic acid
2) used.
(
2750 | Green Chem., 2012, 14, 2747–2751
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3
4
The European Parliament and the Council of the European Union, Direc-
tive 2009/28/EC of the European Parliament and the Council of 23 April
Conclusions
2009, Off. J. Eur. Union, 2009, L140/16.
We have shown for the first time that styrene, and acrylic acid
and esters, can be obtained from cinnamate derivatives using an
atom-efficient ethenolysis reaction. The substrates possess elec-
tron poor double bonds, making them very challenging for
metathesis catalysts. However, with careful selection of the reac-
tion conditions, especially a low ethylene pressure, and the use
of a Hoveyda–Grubbs 2nd generation catalyst (I), conversions
reached 15 to 30% with high selectivity. Cinnamic acid could be
obtained from plant residue rest streams, making the strategy a
potential route to bio-styrene and bio-acrylate compounds,
important monomers for the plastic industry. Efforts to
improve both the efficiency and the sustainability of this
process are currently under investigation in our laboratory,
especially on the production of cinnamic acid from protein waste
streams, design of new catalysts and their immobilisation for
recycling.
International Energy Agency,http://www.iea.org/press/pressdetail.asp?
PRESS_REL_ID=411 and related report: Technology Roadmap, Biofuels
for Transport,http://www.iea.org/papers/2011/biofuels_roadmap.pdf Date
accessed: March 2012.
A. L. Demain, Biotechnol. Adv., 2000, 18, 499–514.
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We would like to thank Daan van Es for useful discussions,
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ments. This work is part of the Biobased Performance Materials
research programme, project no. BPM-060 “ACTION”, and is
financially supported by the Netherlands Ministry of Economic
Affairs, Agriculture and Innovation.
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This journal is © The Royal Society of Chemistry 2012
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