Glycerol as a cheap, safe and sustainable solvent for the catalytic and regioselective β,β-diarylation of acrylates over palladium nanoparticles

Article abstract of DOI:10.1039/b925021b

Herein we show that glycerol can be considered as a promising cheap and green solvent for the regioselective β,β-diarylation of alkenes. Whereas this reaction is generally catalyzed under an inert atmosphere by expensive phosphine or carbene-palladium complexes, we show here that the diarylation of alkenes can be conveniently achieved in glycerol in the presence of air-stable palladium nanoparticles. These palladium nanoparticles were stabilized over a sugar-based surfactant derived from biomass. By an adjustment of the reaction temperature, we were able to control the mono- and diarylation step of alkenes, thus offering a convenient route to unsymmetrical diarylated alkenes. At the end of the reaction, the diarylated alkenes were cleanly and selectively extracted from the glycerol-palladium catalytic phase using supercritical carbon dioxide, thus affording a convenient purification work-up. Within the framework of green chemistry, this work combines (i) catalysis in a cheap, safe and sustainable medium, (ii) easily made and air-stable palladium nanoparticles as the catalyst, and (iii) a clean and selective extraction of the reaction products with supercritical carbon dioxide.

Full text of DOI:10.1039/b925021b

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Volume 12 | Number 5 | May 2010 | Pages 729–924
ISSN 1463-9262
Jérôme et al.
Ho et al.
Glycerol as a cheap and sustainable
solvent
Environmental considerations in
biologics manufacturing
Gramatica and Papa
QSPR as a support for EU REACH
Anastas et al.
Advances in lactone synthesis

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Glycerol as a cheap, safe and sustainable solvent for the catalytic and
regioselective b,b-diarylation of acrylates over palladium nanoparticles †‡
Mathieu Delample,a,b Nicolas Villandier,a Jean-Paul Douliez,b Se´verine Camy,c Jean-Ste´phane Condoret,c
Yannick Pouilloux,a Joe¨l Barraulta and Franc¸ois Je´roˆme*a
Received 27th November 2009, Accepted 29th January 2010
First published as an Advance Article on the web 5th March 2010
DOI: 10.1039/b925021b
Herein we show that glycerol can be considered as a promising cheap and green solvent for the
regioselective b,b-diarylation of alkenes. Whereas this reaction is generally catalyzed under an
inert atmosphere by expensive phosphine or carbene-palladium complexes, we show here that the
diarylation of alkenes can be conveniently achieved in glycerol in the presence of air-stable
palladium nanoparticles. These palladium nanoparticles were stabilized over a sugar-based
surfactant derived from biomass. By an adjustment of the reaction temperature, we were able to
control the mono- and diarylation step of alkenes, thus offering a convenient route to
unsymmetrical diarylated alkenes. At the end of the reaction, the diarylated alkenes were cleanly
and selectively extracted from the glycerol-palladium catalytic phase using supercritical carbon
dioxide, thus affording a convenient purification work-up. Within the framework of green
chemistry, this work combines (i) catalysis in a cheap, safe and sustainable medium, (ii) easily
made and air-stable palladium nanoparticles as the catalyst, and (iii) a clean and selective
extraction of the reaction products with supercritical carbon dioxide.
Therefore, these reactions are generally carried out in high boil-
Introduction
ing point solvents such as DMF,5b,6e in ionic liquids6a–c or under
The palladium-catalyzed Mizoroki–Heck coupling is a reaction
pressure.6d Within the framework of green chemistry, Botella and
of fundamental importance in organic chemistry and has broad
Najera investigated the b,b-diarylation of acrylate derivatives in
applications from the manufacture of basic chemicals to the
water and in the presence of an oxime-derived palladacycle.7 At
120 ◦C (under pressure of water), they successfully achieved the
preparation of fine pharmaceuticals. In this context, plenty of
work have been focused on this reaction.1 Even if spectacular
results have been reported over the last 30 years, this work was
mainly applicable to the monoarylation of alkenes, and examples
b,b-diarylation of tert-butyl acrylate. If this work indisputably
offered a greener route to the synthesis of disubstituted acrylate
derivatives, this method is only applicable to the tert-butyl
of diarylation remain scarce. Diarylated alkenes are valuable
acrylate. Indeed, in water, the authors pointed out that other
chemical platforms that are used in many processes, and their
acrylate derivatives were partially hydrolyzed, making difficult
one-pot synthesis still represents a challenging task today.
the isolation of the disubstituted alkenes in good yield.7a
In the current literature, phosphine2–5,6d,e and carbene6a–c
Recently, we and the group of Wolfson have reported that
palladium complexes have been reported as efficient catalysts
glycerol may be considered as a promising cheap and green
for the diarylation of various alkenes, such as vinyl silane,2
solvent for catalysis.8,9 Indeed, like water, glycerol is highly
boronate,3 2-pyrimidylsulfide,4 ethers5 and acrylates.6 Although
hydrophilic, non-toxic, cheap (0.5 € Kg-1, sometimes even
these catalysts provided excellent results in many respects, they
cheaper than water!), non-flammable and available on a large
are unfortunately expensive and require an inert atmosphere.
scale from biomass (hydrolysis of vegetable oils, production
The diarylation of acrylate derivatives generally occurs at a
of glycerol = 1.5 Mt in 2008). Moreover, glycerol exhibits a
higher temperature (120–140 ◦C) than the monoarylation step.
high boiling point and a low vapour pressure (<1 mmHg at
50 ◦C), making easier and safer the development of catalytic
processes at a temperatures higher than 100 ◦C. In 2009, the
aLaboratoire de Catalyse en Chimie Organique, Universite´ de
number of publications dealing with the possible use of glycerol
as a sustainable solvent for catalysis significantly increased,
thus showing the interest of the scientific community in this
medium.10
Here, we wish to show that the regioselective b,b-diarylation
of acrylate derivatives can be conveniently achieved in glycerol in
the presence of easily-made palladium nanoparticles stabilized
over a sugar-based surfactant derived from biomass. To the
best of our knowledge, this is the first example of the b,b-
diarylation of alkenes over palladium nanoparticles. This work
Poitiers/CNRS, 40 avenue du recteur Pineau, 86022, Poitiers, France.
E-mail: francois.jerome@univ-poitiers.fr; Fax: +33(0) 5 49 45 33 49;
Tel: +33 (0) 5 49 45 33 49
bUR1268, Biopolyme`res Interactions Assemblages, INRA, rue de la
Ge´raudie`re, 44316, Nantes, France
cLaboratoire Ge´nie Chimique, INPT/ENSIACET, 6 rue Paulin Talabot,
31106, Toulouse, France
† The synthesis and characterization of aminopolysaccharide (AP) has
been already described in a previous paper.8b
‡ Electronic supplementary information (ESI) available: Product char-
acterizations and 1H NMR spectra. See DOI: 10.1039/b925021b
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Table 1 b,b-Diarylation of acrylate derivatives in glycerol
opens access to a wide range of symmetrical and unsymmetrical
trisubstituted alkenes in air and without the assistance of any
phosphine or carbene ligands, like is generally the case. It should
be noted that, at the end of the reaction, the trisubstituted
alkenes were cleanly and selectively extracted from the catalytic
phase with supercritical carbon dioxide (scCO2), thus affording
a very convenient purification work-up. Within the framework
of green chemistry, this work gathers (i) catalysis in a cheap
and sustainable media, (ii) the utilization of air-stable palladium
nanoparticles stabilized over a bio-based surfactant, and (iii)
a clean and selective extraction of the reaction products with
scCO2.
Entry
1b
R
ArI
Product
Yield (%)a
67
Cyclohexyl
1a
2
3
4
5
6
7c
Cyclohexyl
Butyl
1a
1b
1c
1d
1e
1f
92
95
96
70
85
80
Results and discussion
Recently, we reported the synthesis of a new sugar-based
surfactant called aminopolysaccharide (AP), which has been
found particularly efficient for catalysis in glycerol.8b Indeed,
owing to its surfactant properties, we showed that AP was
able to increase the solubility of organic reactants in the
glycerol phase, thus resulting in a significant increase of the
reaction rate. In a continuation of our efforts, we decided to
use AP as a ligand for the coordination of palladium. The
coordination of palladium onto AP was performed by mixing
the AP ligand with a methanolic solution of Pd(OAc)2 (0.3 g L-1).
The mixture was stirred for 4 h and the methanol then gently
removed under reduced pressure. The recovered black solid was
Cyclohexyl
Butyl
Cyclohexyl
Butyl
8c
9
Cyclohexyl
Cyclohexyl
1g
1h
86
93
◦
placed in an oven at 70 C and 10-1 mmHg for 15 h, yielding
the corresponding surfactant-combined catalyst Pd/AP. ICP
analysis revealed a Pd content of 1.5 wt%. Further inspection by
transmission electronic microscopy showed that the amphiphilic
AP was able to stabilize some Pd nanoparticles with an average
size of 6 nm (Scheme 1).
a Isolated yield after 30 h of reaction, 3 equiv. of aryl iodides and
triethylamine were used. b 2 equiv. of iodobenzene was used. c Reaction
performed at 80 ◦C.
inspections revealed that the monoarylated intermediate was
actually strongly retained within the amphiphilic framework
of the Pd/AP catalyst (see the experimental section for more
details§). With the aim of increasing the yield of 1a, 3 equiv. of
§ General procedure for the synthesis of Pd/AP: In a typical procedure,
the AP ligand (DS = 0.5, 1.6 mmol N g-1, 100 mg) was dissolved in
10 mL of methanol. Then, 3.2 mg of Pd(OAc)2 dissolved in 10 mL
of methanol was added dropwise to the methanolic solution of AP. The
resulting mixture was then stirred for 4 h at room temperature. After this
period, the solution was placed in a rotary evaporator and the methanol
gently removed under reduced pressure (15 mmHg). The recovered
Scheme 1 Synthesis of the Pd/AP catalyst.
1. Symmetrical b,b-diarylation of acrylate derivatives
◦
black solid was finally placed in an oven at 70 C (10-1 mmHg) for
24 h, affording the corresponding Pd/AP. ICP measurements revealed a
Pd content of 1.5%. As mentioned in main text, the AP ligand was
able to stabilise some palladium nanoparticles with an average size
of 6 nm. The average particle size was determined on the basis of
500 nanoparticles. General procedure for the b,b-diarylation of acrylate
derivatives (Table 1): In a 15 mL glass autoclave, acrylate (3 mmol),
aryl iodide (9 mmol), triethylamine (18 mmol), glycerol (2.5 mL) and
Pd/AP (200 mg, 0.009 equiv.) were stirred under aerobic conditions
at 120 ◦C for 30 h. The reaction progress was monitored by gas
chromatography. Note: As mentioned in the main text, 3 equiv. of aryl
iodides were necessary due to the side formation of biphenyl (<10%
yield), which is a known side product in palladium-catalyzed Heck
coupling. When stoichiometric amounts of iodobenzene (6 mmol), butyl
acrylate (3 mmol) and triethylamine (6 mmol) were heated in 2.5 mL of
In a first set of experiments, we tested the catalytic activity of
the Pd/AP catalyst, using iodobenzene and cyclohexylacrylate
as model substrates. The reaction was performed in the presence
of 0.9 mol% of palladium nanoparticles stabilized over AP and
triethylamine. To our delight, when the reaction was heated at
120 ◦C in the presence of 2 equiv. of iodobenzene, a double
arylation of cyclohexyl acrylate took place, and 1a was obtained
in 67% yield (Table 1, entry 1). It should be noted that, at 120 ◦C,
biphenyl (<10% yield) was also produced as a side product.
Surprisingly, under stoichiometric conditions, no monoarylated
adduct was detected, despite the formation of biphenyl. Further
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iodobenzene were used. As expected, under these conditions,
the yield of 1a was raised from 67 to 92% yield (Table 1,
entry 2).
to the crude mixture and the temperature raised to 120 ◦C.
To our delight, under these conditions, the unsymmetrical b,b-
diarylated alkenes 2a and 2b were obtained in 60–76% yield,
thus providing a cost-efficient, safe and environmentally friendly
route to more valuable substrates (Scheme 2).
As summarized in Table 1, many aryl iodides were tested
in glycerol and, in all cases, the diarylated alkenes 1b-h were
successfully obtained in air with a yield range of 70–96%.
Interestingly, contrary to what was observed in water, the ester
moiety was found to be highly stable in glycerol and, in all
cases, no transesterification reaction between glycerol and the
ester moiety occurred (triethylamine is not basic enough to
catalyze this reaction at 120 ◦C). Note that, in accordance
with most previous works on the diarylation of alkenes, this
catalytic process was most efficient with aryl iodides. Indeed,
the utilization of aryl bromides or chlorides unfortunately
slowed down the reaction rate to unacceptable levels. It is also
noteworthy that the reaction is highly regioselective, since only
b,b-diarylation occurred in glycerol.
Scheme 2 Unsymmetrical b,b-diarylation of acrylate derivatives in
glycerol.
3
Extraction of the reaction products with scCO2
We also carefully checked the stability of the glycerol under
our conditions (NMR, GC). To this end, glycerol (2.5 mL)
was mixed with triethylamine (9 mmol) and 200 mg of Pd/AP
(Pd: 0.9 mol%), and heated at 120 ◦C for 48 h. No product
resulting from the palladium-catalyzed degradation of glycerol
was detected, indicating the stability of glycerol under our
conditions (see the 1H NMR spectra in the ESI, Scheme S1 and
S2‡). This result is in accordance with previous works described
in the literature.11
Next, we examined the extraction of the reaction products from
the glycerol phase. As is the case for ionic liquids, glycerol
is a high boiling point solvent and its removal by distillation
is not conceivable. Therefore, the extraction of the reaction
products from the glycerol phase is an important issue that
must be addressed. Recently, we found that long alkyl chain
esters can be directly extracted from glycerol by simple phase
decantation, thus avoiding the assistance of volatile organic
solvents.8b However, in the present case, this process is not
applicable, since, in the presence of the amphiphilic Pd/AP
catalyst, the reaction products remain soluble in glycerol.
Therefore, the assistance of an extraction solvent was found to
be necessary to recover the product from the reaction. Among
all of the tested extraction solvents, we found that scCO2 was
by far the most efficient solvent to selectively extract the b,b-
diarylated products from the glycerol-Pd/AP catalytic phase.
Indeed, other tested solvents such as dichloromethane, ethyl
acetate and toluene, among others, led to the concomitant
extraction of the reaction products and the Pd/AP catalyst,
thus involving further purification steps.
In order to get as close as possible to industrial apparatus,
scCO2 extractions were performed on a SEPAREX SF200
pilot, comprising an extraction vessel (200 mL) followed by a
cascade of three separators connected to the extractor outlet
(see the ESI for the apparatus, Fig. S2‡). In these experiments,
the b,b-diarylation of butyl acrylate with iodobenzene was
chosen as the model reaction. Compared to the above-described
experiments, this reaction was scaled-up and stoichiometric
amounts of iodobenzene (96 mmol), butyl acrylate (48 mmol)
and triethylamine (96 mmol) were used (Pd/AP = 0.9 mol%, i.e.
3.1 g) in order to determine the efficiency of the whole process.
Under these conditions, 95% of the iodobenzene was consumed
after 30 h of reaction and 10.1 g of 1b (75% yield) was produced.
The mixture was then introduced into the extractor and scCO2
extractions were performed with a scCO2 flow of 40 g min-1 at
50 ◦C and 250 bar. Samples were collected from the separators
every 30 min and analyzed (Fig. 1). Note that in our apparatus,
the scCO2 was recycled in order to avoid the excessive utilization
of CO2.
2. Unsymmetrical b,b-diarylation of acrylate derivatives
We then moved onto the synthesis of unsymmetrical disubsti-
tuted alkenes, which represent an even more challenging task.
Unfortunately, the addition of two different aryl iodides at
120 ◦C in the same reaction pot afforded a mixture of sym-
metrical and unsymmetrical disubstituted alkenes. Considering
that the monoarylation of alkenes easily takes place at 80 ◦C in
glycerol with commonly used palladium complexes, it occurred
to us that the mono- and diarylation of alkenes could be closely
controlled in glycerol by adjustment of the reaction temperature.
To this end, the catalytic reaction was first performed at 90 ◦C
with iodobenzene. As expected, at 90 ◦C, only the monoarylation
took place. Then, iodonaphthalene (2 equiv.) was directly added
glycerol at 120 ◦C, 0.56 g of 1b (67% yield), 0.05 g of biphenyl (10% yield)
and 0.04 g of unreacted iodobenzene were isolated after extraction with
dichloromethane and purification over silica gel. Surprisingly, despite
biphenyl being produced, no trace of the monoarylated adduct was
detected. Further inspection revealed that the monoarylated adduct
was actually strongly encapsulated by the Pd/AP catalyst. Indeed,
extensive extraction of the glycerol phase with a large excess of hot
toluene (6 ¥ 10 mL) led to the release of the monoarylated adduct
encapsulated by the Pd/AP, and 0.2 g of the monoarylated adduct
(28% yield) was recovered. For the moment, we cannot explain the
selective encapsulation of the monoarylated adduct, as compared to 1b.
It should be noted that the encapsulation of the intermediate mono-Heck
adduct is more pronounced when using butyl acrylate derivatives than
with cyclohexyl acrylate. General procedure for the unsymmetrical b,b-
diarylation of acrylate derivatives (Scheme 2): In a 15 mL glass autoclave,
acrylate derivatives (3 mmol), iodobenzene (3 mmol), triethylamine
(6 mmol), glycerol (2.5 mL) and Pd/AP (200 mg, 0.009 equiv. of
Pd) were stirred under aerobic conditions at 90 ◦C for 24 h. Then,
iodonaphthalene (6 mmol) and triethylamine (12 mmol) were added
to the crude mixture, and the temperature was raised to 120 ◦C. The
reaction progress was monitored by gas chromatography.
To our great delight, after 420 min of continuous extraction
with scCO2, 8.6 g of products were cleanly recovered from the
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glycerol contamination remained similar to that observed above
at 40 g min-1.
Even if the scCO2 allows the convenient and selective extrac-
tion of 1b from the glycerol-Pd/AP phase, the possible recycling
of the catalytic phase remains particularly difficult. Indeed, in
the typical case of palladium Heck couplings, an unavoidable
accumulation of salts occurs cycle after cycle, making more and
more difficult the dissolution of the reactants from the glycerol
phase. Consequently, as previously observed in water or ionic
liquids, a gradual decrease of the reaction rate is observed cycle
after cycle (see the recycling experiments in the ESI, Fig. S1‡).
Note that the stabilization of palladium nanoparticles over a
solid support would provide greater means to recover the catalyst
from the glycerol phase and then to reuse it. This aspect is now
the topic of our investigations and will be reported in due course.
Fig. 1 The extraction of 1b with scCO2 at 40 g min-1, 50 ◦C and
250 bar.
Conclusions
glycerol–Pd/AP catalytic phase and only 0.4 g of contamination
with glycerol occurred. The extraction here was rather long
because the reaction products were strongly retained in the
glycerol phase by the amphiphilic Pd/AP catalyst. Even if the
recovered products were contaminated with 4 wt% of glycerol,
the total removal of glycerol from the extracted products could
be easily performed by simple phase decantation (in the absence
of the Pd/AP catalyst,12 glycerol is not miscible with 1b), thus
considerably increasing the interest in using glycerol as the
solvent (Fig. 2).
We report here that the regioselective symmetrical and un-
symmetrical b,b-diarylation of acrylate derivatives can be
conveniently performed in cheap and safe glycerol. Whereas
expensive and air-sensitive palladium complexes are generally
required to achieve this reaction, we have shown here that
the b,b-diarylation of acrylate derivatives can be catalyzed in
glycerol over air-stable palladium nanoparticles. These palla-
dium nanoparticles were easily prepared using a sugar-based
surfactant derived from biomass. Interestingly, we found that the
produced diarylated alkenes could be selectively extracted from
the catalytic phase using scCO2, thus offering (i) a simple work-
up procedure and (ii) an alternative to the extensive utilization
of volatile organic solvents. We are fully convinced that this
combination of glycerol and scCO2 will provide new tools for
the design of greener catalytic processes, and this aspect is now
under investigation in our group.
Fig. 2 Pictures of the extracted products with scCO2. Note that in
order to clearly show the contamination with glycerol, a few drops of
ethyl acetate were added to the collected vials before taking the pictures.
However, in this work, no organic solvent was used and the glycerol could
be directly removed by simple centrifugation without the assistance of
any organic solvent.
Acknowledgements
The authors are grateful to the CNRS, INRA and the French
Ministry of Research for their financial support. The program
CPDD of the CNRS (RDR-1 action) is also strongly acknowl-
edged for financial support. M. D. is grateful to the CNRS and
INRA for his PhD grant. N. V. acknowledges ADEME and
Re´gion Poitou-Charentes for his PhD grant.
The solubility of glycerol in CO2 under high pressure has been
estimated thanks to the equation of Chrastil,13 which correlates
the solubility of solids and liquids in supercritical gases with
the density of the gas. Under our conditions, we found that the
solubility of glycerol in scCO2 was 40 times lower than that of
water (0.06 Kg m-3 for glycerol vs. 2.39 Kg m-3 for water; see the
ESI for the calculation‡).
The recovered extracted products were then fully analyzed.
The extracted products (8.6 g) contained 7.8 g of 1b (60% isolated
yield), which corresponds to an extraction efficiency of 77%. The
molar purity of the recovered 1b was 86% (contamination of 1b
with 0.4 g of unreacted iodobenzene and 0.4 g of biphenyl).
Note that if the reaction was heated up to totally consume
the iodobenzene, iodobenzene could no longer be co-extracted
with 1b; in this case, the molar purity of 1b reached 93%. As
expected, a decrease of the scCO2 flow from 40 to 15 g min-1
decreased the extraction efficiency from 77 to 55%, while the
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808 | Green Chem., 2010, 12, 804–808
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