Preparation of ecological catalysts derived from Zn hyperaccumulating plants and their catalytic activity in Diels-Alder reaction

Article abstract of DOI:10.1016/j.crci.2013.09.009

Zn hyperaccumulating plants Noccaea caerulescens and Anthyllis vulneraria were used as the starting material for preparation of novel Lewis ecological catalysts. Those catalysts efficiently mediate the Diels-Alder reaction. High yields, very good regio- a

Full text of DOI:10.1016/j.crci.2013.09.009

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CRAS2C-3824; No. of Pages 7
C. R. Chimie xxx (2013) xxx–xxx
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Comptes Rendus Chimie
www.sciencedirect.com
Preliminary communication/Communication
Preparation of ecological catalysts derived from Zn
hyperaccumulating plants and their catalytic activity
in Diels–Alder reaction§
Vincent Escande a,b, Tomasz K. Olszewski c, Claude Grison a,
*
a
´
´
Centre d’ecologie fonctionnelle et evolutive, UMR CNRS-UM2 5175, 1919, route de Mende, 34293 Montpellier cedex 5, France
b
ˆ
´
´
´
Agence de l’environnement et de la maıtrise de l’energie (ADEME), 20, avenue du Gresille, BP 90406, 49004 Angers cedex 01, France
c Faculty of Chemistry, Department of Organic Chemistry, Wrocław University of Technology, Wybrzez˙e Wyspian´skiego 27, 50-370,
Wroclaw, Poland
A R T I C L E I N F O
A B S T R A C T
Article history:
Zn hyperaccumulating plants Noccaea caerulescens and Anthyllis vulneraria were used as
the starting material for preparation of novel Lewis ecological catalysts. Those catalysts
efficiently mediate the Diels–Alder reaction. High yields, very good regio- and
diastereoselectivity, low catalyst loading and the possibly of its recovery and reuse,
along with mild reaction conditions, eco-friendly treatment and short reaction time, are
the key advantages of the presented approach.
Received 27 May 2013
Accepted after revision 18 September 2013
Available online xxx
Keywords:
Heterogeneous catalysis
Ecological catalysis
Cycloaddition
ß 2013 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Lewis acids
´ ´
R E S U M E
Sustainable chemistry
Mots cle´s:
´ ´
Les plantes hyperaccumulatrices de Zn Noccaea caerulescens et Anthyllis vulneraria ont ete
Catalyse he´te´roge`ne
´
`
`
´
utilisees comme matieres premieres pour la preparation de nouveaux catalyseurs
e´cologiques de type acides de Lewis. Ces catalyseurs ont montre´ une haute efficacite´ dans
la re´action de Diels–Alder. Les avantages cle´s de l’approche pre´sente´e sont les suivants :
´
Catalyse ecologique
Cycloaddition
Acides de Lewis
Chimie durable
´
´
`
´
´
´
´
´
rendements eleves, tres bonnes regio- et diastereoselectivites, faibles charges catalytiques,
´
´
´
´
´
possibilite de recyclage du catalyseur, conditions reactionnelles moderees, traitement eco-
compatible et courtes dure´es de re´action.
´
´
´
´
ß 2013 Academie des sciences. Publie par Elsevier Masson SAS. Tous droits reserves.
1. Introduction
Lewis acid catalysts. The potential of such systems brings
numerous advantages, such as protection of moisture-
Catalysis was established as the 9th of the twelve
principles of green chemistry and is sometimes referred to
as the ‘‘foundational pillar’’ of green chemistry [1]. Among
many catalysts, Lewis acids play a central role. Current
interest in green chemistry promotes the development of
heterogeneous catalysis, including the use of supported
sensitive Lewis acids from hydrolysis through their
dispersion on support, easier manipulation, and
a
avoidance of deactivation by hydrolysis. Furthermore,
chemo-, regio-, and stereoselectivity can be optimized,
work-up is based on simple filtration, wastes are
minimized and Lewis acid catalyst recycling becomes
possible [2]. Additionally, modern chemistry requires
chemical processes designed to reduce waste production,
facilitate efficient reuse and recycling, and use of starting
material derived from renewable resources or from
abundant wastes [3,4].
§
Thematic issue devoted to Franc¸ois Garin.
*
Corresponding author.
E-mail address: claude.grison@cefe.cnrs.fr (C. Grison).
1631-0748/$ – see front matter ß 2013 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.crci.2013.09.009
Please cite this article in press as: Escande V, et al. Preparation of ecological catalysts derived from Zn
hyperaccumulating plants and their catalytic activity in Diels–Alder reaction. C. R. Chimie (2013), http://dx.doi.org/
10.1016/j.crci.2013.09.009

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Table 1
Composition of the obtained plant extract.
Mass percent composition
Na
K
Mg
Ca
Fe
Zn
Cd
Al
Pb
O
Cl
A. vulneraria and N. caerulescens crude extracts
1.72
5.72
1.60
10.30
2.75
6.75
0.19
1.50
0.44
15.97
42.27
In line with the aforementioned new trends in organic
chemistry, here we report on the preparation and usage of
supported Lewis acid catalyst derived from non-conven-
tional biomass, i.e. metal-hyperaccumulating species, that
we named ‘‘ecological catalysts’’. Metal-hyperaccumulat-
ing plants, or metallophytes, extract trace metals (TM)
from soil and concentrate them in their shoots. Exploring
the utility of these plants led to the development of
phytoextraction techniques that represent an opportunity
to remove TM from contaminated soils, e.g., contaminated
mine sites, which in turn represent a major environmental
problem worldwide. Nowadays, the approach using plants
to clean up the environment is cost-effective, achievable
on a large-scale, and has a good public acceptance. The
main disadvantage, however, is the lack of real economic
opportunities [5–8]. Herein, we demonstrated that metal-
lophytes could be the basis of a novel, plant-inspired,
metallo-catalytic platform with synthetic potential in one
of the most important processes in organic chemistry,
namely the Diels–Alder reaction. In the presented study we
used the two best zinc hyperaccumulating plants, Noccaea
caerulescens and Anthyllis vulneraria. Both are able to
concentrate about 120,000 ppm of ZnII in calcined shoots
[9].
of HCl (1 M) and the concentration of the solution, which
led to an unusual mixture of metallic chlorides and oxides
[9–14]. The potential of zinc hyperaccumulating plants for
ecological catalysis was based on the total mineral
composition of contaminated biomass. The presence of
ZnII, CdII and PbII results from the trace metals (TM)
hyperaccumulation ability of metallophyte plants. Addi-
tionally, NaI, KI, CaII, MgII, FeIII were also present as they are
essential for plant growth. X-ray fluorescence (XRF) was
used to determine the exact chemical composition of the
obtained plant extract (Table 1).
XRF data were additionally confirmed by inductively
coupled plasma mass spectroscopy (ICP–MS). The extract
contained high amounts of transition metals: 6.75% of ZnII
and 2.75% of FeIII, known to be powerful Lewis acids. A
significant amount of CaII (10.30%) was also noted. The
results presented in Table 1 confirmed the exceptional
capacity of Noccaea caerulescens and Anthyllis vulneraria for
the hyperaccumulation of Zn. It has to be noted that, using
ion-exchange resin Amberlite IRA 400, it was possible to
separate the metallic species and obtain fractions enriched
in ZnII and CaII [15]. In this study, however, only crude
extracts were employed.
Subsequently, the resulting plant extract was deposited
on montmorillonite K10 as a conventional support. The
methodology was based on a co-grinding; montmorillonite
K10 was placed in a porcelain mortar and air-dried crude
extract was then added and mixed with montmorillonite
K10 using a pestle to obtain a homogeneous powder [16].
The supported ecological catalyst was characterized by
XRD (Fig. 1). As shown in Table 2, K2ZnCl4 was the sole
observed zinc chloride; it is a masked form of ZnCl2 [15].
2. Results and discussion
2.1. Preparation and characterisation of the ecological
catalysts
The ecological catalysts were prepared by thermal
treatment of leaves at 400 8C, followed by the addition
Fig. 1. X-ray diffraction (XRD) pattern of our supported ecological catalyst (colour online).
Please cite this article in press as: Escande V, et al. Preparation of ecological catalysts derived from Zn
hyperaccumulating plants and their catalytic activity in Diels–Alder reaction. C. R. Chimie (2013), http://dx.doi.org/
10.1016/j.crci.2013.09.009

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3
Table 2
X-ray diffraction (XRD) pattern of our supported ecological catalyst.
Fraction
Mineral
Formula (simplified)
Supported ecological catalyst on montmorillonite K 10
Chlorocalcite, syn
KCaCl3
Potassium zinc tetrachloride
Potassium perchlorate
Calcium chloride hydrate
Calcium magnesium silicate
Quartz
K2ZnCl4
KClO4
CaCl2(H2O)2
Ca2MgSi2O7
SiO2
Tridymite
SiO2
2.2. Determination of the Lewis acidity of the crude ecological
catalyst
indicates the presence of strongly bonded pyridine. In
previous studies, these bands were attributed to pyridine
coordinated to Lewis acid sites. The occurrence of these
bands at different frequencies in this range may account
for the involvement of different types of Lewis acid sites
[18].
In order to determine the Lewis acidity of the ecological
catalyst, infrared spectra of pyridine adsorbed on crude
fraction were recorded at 25 8C and 150 8C in order to
distinguish frequencies of physisorbed pyridine from
frequencies of pyridine coordinated to Lewis sites
(Fig. 2). Pyridine is widely used as a probe molecule for
the determination of the Lewis acidity of solid acids, by
monitoring the bands in the range of 1400–1650 cmÀ1
arising from its ring vibration modes [17,18].
As shown in Fig. 2, a band at 1440 cmÀ1 observed at
25 8C disappeared after outgassing at 150 8C, and thus
could be attributed to physisorbed, weakly bonded,
pyridine [17]. In the same range, a band at 1450 cmÀ1
was observed at 150 8C. This band is characteristic of
pyridine, which is still strongly bonded at this temperature
by coordination to Lewis acid sites [17]. This was the first
indication of the extract Lewis acidity. In turn, the band
intensity at 1486–1487 cmÀ1 could be attributed to
physisorbed pyridine, as the intensity was strongly
reduced after heating.
Furthermore, the band at 1599 cmÀ1 observed at 25 8C,
which disappeared at 150 8C, is characteristic of hydrogen-
bonded pyridine [17]. Additionally, several bands were
observed in the range of 1600–1640 cmÀ1 with small
frequency variations, depending on outgassing tempera-
ture (1608 and 1631 cmÀ1 at 25 8C; 1609, 1628 and
1639 cmÀ1 at 150 8C). The continued existence of bands in
this range, in spite of heating at elevated temperature,
2.3. Application of the supported ecological catalyst in the
Diels–Alder reaction
The Diels–Alder reaction is one of the most popular
transformations for organic chemists to efficiently gen-
erate molecular complexity. Since its discovery in 1928 by
Diels and Alder [19], this pericyclic reaction involving a
conjugated diene and a dienophile has been used for the
diastereo- and regioselective generation of six-membered
rings with up to four stereogenic centres in a single step.
The Diels–Alder reaction has opened the way to the
synthesis of
a plethora of organic substances with
elaborated structures, thus underlining its power for the
rapid generation of molecular complexity [20–22]. This
transformation is universally acknowledged for the rapid,
atom-economical build-up of complex structures of
defined geometry with minimal waste. These criteria fulfil
the requirements of a scalable chemical process; thus
application of this transformation in chemical industry is a
feasible enterprise [23–25].
Inspired by the previous works on the successful
application of clays [26–28] and zeolites [29] as catalysts
for the Diels–Alder reaction, we decided to use our K10-
supported ecological catalyst for that transformation.
Fig. 2. IR spectra of adsorbed pyridine on a crude extract taken following brief outgassing at the indicated temperatures.
Please cite this article in press as: Escande V, et al. Preparation of ecological catalysts derived from Zn
hyperaccumulating plants and their catalytic activity in Diels–Alder reaction. C. R. Chimie (2013), http://dx.doi.org/
10.1016/j.crci.2013.09.009

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Table 3
Effect of the nature of the Lewis acid catalyst on the model Diels–Alder reaction of 3-buten-2-one with 2,3-dimethyl-1,3-butadiene.
O
O
catalyst
+
toluene
110°C, 4 h
Entry
Catalysta
Yield [%]b
1
2
3
4
5
K10-supported ecological catalyst (0.1 equiv. Zn)
100
44
67
98
6
K10
ZnCl2 (0.1 equiv. Zn)
Recycled K10-supported ecological catalyst (0.1 equiv. Zn)c
No catalyst
a
Reaction conditions: toluene, 110 8C, 4 h.
Yield determined by GC-MS.
b
c
Catalyst recycled one time.
Table 4
Scope of the Diels–Alder reaction catalysed by the K10-supported ecological catalyst.
Entry
1
Diene
Dienophile
Product
Catalyst
Solvent
Toluene
T [8C]
t [h]
Yield [%]a
100
endo/exo
K10-supported ecological
catalyst (0.1 equiv Zn)
110
4
–
O
O
H
H
2
3
K10-supported ecological
catalyst (0.1 equiv Zn)
Toluene
Toluene
5
5
1
1
93
34
–
–
COOEt
COOEt
COOEt
EtOOC
K10 only
COOEt
COOEt
COOEt
EtOOC
4
5
6
K10-supported ecological
catalyst (0.1 equiv Zn)
Toluene
Toluene
CH2Cl2
25
25
5
0.25
0.25
4
91
33
98
95/5
95/5
91/9
COOEt
COOEt
COOEt
COOEt
COOEt
K10 only
COOEt
COOEt
COOEt
K10-supported ecological
catalyst (0.1 equiv Zn)
COOMe
COOMe
7
K10-supported ecological
catalyst (0.1 equiv Zn)
Toluene
110
4
99
–
COOMe
COOMe
‘‘1,4 adduct’’+
+
COOMe
‘‘1,3 adduct’’
(1,4/1,3: 80/20)
Please cite this article in press as: Escande V, et al. Preparation of ecological catalysts derived from Zn
hyperaccumulating plants and their catalytic activity in Diels–Alder reaction. C. R. Chimie (2013), http://dx.doi.org/
10.1016/j.crci.2013.09.009

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5
Table 4 (Continued )
Entry
8
Diene
Dienophile
Product
Catalyst
Solvent
Water
T [8C]
t [h]
Yield [%]a
92
endo/exo
K10-supported ecological
60
1.5
–
O
H
HO
H
catalyst (0.1 equiv Zn)
O
OH
O
O
H
de: 71%b
9
K10-supported ecological
catalyst (0.1 equiv Zn)
Water
25
6
84
–
NH
c
d
N
H
H
H
a
Yield determined by GC-MS.
Determined by 1H NMR.
b
c
Dienophile generated in situ, by mixing formaldehyde and ammonia.
d
Isolated as hydrochloride.
Initially, the reaction of 3-buten-2-one with 2,3-dimethyl-
1,3-butadiene, as model substrates, was investigated.
Reactions were carried out in toluene at 110 8C for 4 h
(Table 3).
selectivity of the Diels–Alder reaction was observed (Table
4, entry 7). Importantly, under the same reaction condi-
tions experiments performed with the use of montmor-
illonite K10 resulted in the formation of the desired
products in much lower yields (Table 4, entries 3, 5).
Additionally, we discovered that the K10-supported
ecological catalyst also catalyses the hetero Diels–Alder
reaction (Table 4, entries 8, 9). Environmentally benign
conditions of that reaction are worth mentioning; use of
water as solvent and moderate reaction temperature and
time. Importantly, very good diastereomeric excess (de) in
the lactone, formed by rearrangement of the endo transient
cycloadduct, has to be noted (Table 4, entry 8). Similar
reaction catalysed by Cu(II) reported in the literature gave
the lactone with de = 30% [30].
We have also performed the Diels–Alder reaction in an
asymmetric fashion. The reaction of cyclopentadiene and
dimenthyl fumarate is known to proceed with high
stereoselectivity when strong Lewis acids are used at –
78 8C, affording 6 in 99% de [31].
However, the search for efficient catalysts that can be
used under softer conditions is still needed [32]. Encoura-
ging results were obtained in asymmetric cycloaddition
when our Zn-ecological catalyst was used (Scheme 1).
When coordinated to Lewis acids, the dimenthyl
fumarate exists in the s-trans form predominantly, thus
the two (–)-menthyl groups cover the re face of the
molecule [31]. Therefore, the addition of cyclopentadiene
affords mainly the product 6, obtained in 63/38 (S,S)/(R,R)
ratio with the use of our Zn-ecological catalyst. It should be
noted that this value is much higher than that obtained
with commercial ZnCl2, reported to be only 52/48 [32].
The screening of the nature of the Lewis acid catalyst
used revealed a pronounced effect on the reaction yield. To
our satisfaction, it was found that the use of our K10-
supported ecological catalyst leads to the desired product
in quantitative yield (Table 3, entry 1), whereas the
application of commercially available ZnCl2 gives only 67%
of the desired product (Table 3, entry 3). Knowing that the
montmorillonite K10 can catalyse the Diels–Alder reaction
[28], we have performed the model reaction only in the
presence of this catalyst; however, a yield of 44% only of
the desired product was obtained (Table 3, entry 2). The
reaction carried out in the absence of any catalyst resulted
in the formation of only trace amounts of the desired
product (Table 3, entry 5). Importantly, we were able to
recycle and reuse our ecological catalyst (Table 3, entry 4).
After filtration of the K10-supported ecological catalyst,
washing with toluene (3 Â 20 mL) and Et2O (3 Â 20 mL),
drying at 150 8C for 5 h, the catalyst was reused and did not
show significant loss in activity (Table 3, entry 4).
Subsequently,
a selected spectrum of dienes and
dienophiles was examined to test the scope and limitations
of the K10-supported ecological catalyst (Table 4). When
cyclopentadiene was used as a substrate, the reaction
proceeded well already at low temperatures and furnished
the desired products with very good yields in short times
(Table 4, entries 2, 4, 6). It has to be noted that very good
endo/exo reports were obtained (Table 4, entries 4, 6).
When myrcene was used as a dienophile, very good
Scheme 1. Asymmetric Diels–Alder reaction catalysed by our K10-supported ecological catalyst.
Please cite this article in press as: Escande V, et al. Preparation of ecological catalysts derived from Zn
hyperaccumulating plants and their catalytic activity in Diels–Alder reaction. C. R. Chimie (2013), http://dx.doi.org/
10.1016/j.crci.2013.09.009

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3. Conclusions
X-ray diffraction (XRD) data measurements on the
samples dried at 110 8C for 2 h were performed by using a
In conclusion, we have prepared and characterised a
novel supported Lewis acid catalyst issued from biomass of
Zn hyperaccumulating plants Noccaea caerulescens and
Anthyllis vulneraria. The catalytic activity of the catalyst
was tested in the Diels–Alder reaction. The use of this eco-
catalyst is featured with mild reaction conditions, simple
operation, low catalyst loading, good substrate scope,
excellent selectivity, and the possibility of its recovery and
reuse. Further experimentation would be required in order
to fully determine the potential of the new plant-based
catalysts, but there is no doubt that they will continue to
display very interesting properties for cutting-edge green
chemistry. Additionally, the use of metal-hyperaccumu-
lating plants as a source of metals for applications as
catalysts in chemical processes presents an interest for the
phytoremediation of mine sites contaminated with heavy
metals.
Bruker diffractometer (D8 advance, with a Cu K
˚
a radiation
l
= 1.54086 A) equipped with a Lynxeyes detector.
FT-IR measurements were carried out using pyridine as
a probe molecule. The samples were pressed into wafers
(8 mg.cmÀ2) and activated in the IR cell under flowing air
(1 cm3.sÀ1) at 400 8C for 10 h and then under vacuum
(10À3 Pa) for 1 h. A PerkinElmer Spectrum 100 FT-IR
spectrometer was used for recording the spectra. Excess
gaseous pyridine was adsorbed, then the samples were
degassed for 15 min at 25 8C (10À3 Pa), and a first spectrum
was recorded. The samples were then degassed for 15 min
at 150 8C (10À3 Pa) to eliminate the physisorbed pyridine,
and a second spectrum was recorded.
4.3. Representative procedure for the Diels–Alder reaction
A round-bottom flask equipped with a condenser was
charged with the catalyst derived from biomass (32 mg,
quantity corresponding to 0,01 mmol of Zn, 0,10 equiv,
according to ICP–MS and XRF analysis), 3-buten-2-one
(7 mg, 0.1 mmol) and 2,3-dimethyl-1,3-butadiene (8.2 mg,
0.1 mmol) and 2 mL of toluene. The flask was placed in an
oil bath and heated at 110 8C for 4 h. After that time, GC
analysis was performed using tridecane as an internal
standard.
4. Experimental part
4.1. Preparation of catalytic extracts from metallophyte
species
Leaves were harvested before flowering, air-dried and
crushed. The obtained solid (150 g) was calcinated at
400 8C for 5 h and the resulting powder (24 g) was added to
1-L of a solution of a 1 M HCl solution. The solution was
heated at 60 8C and stirred for 2 h. The reaction mixture
was filtered on celite. The resulting solutions, composed
of different metal chlorides, were concentrated under
vacuum. Dry residue was supported on montmorillonite
K10 by co-grinding with mortar and pestle, at room
temperature. The 2.0 g of montmorillonite K10 were mixed
with the plant-derived Lewis acids (amount corresponding
to 1.1 mmol of metal of interest/g of support). This mixture
was activated at 100 8C for 15 min before use.
Acknowledgments
The authors would like to thank ANR (11ECOT 011 01),
ADEME, FEDER programme for financial supports.
Mr. Robert Feldman is acknowledged for the text proof-
reading.
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10.1016/j.crci.2013.09.009

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Please cite this article in press as: Escande V, et al. Preparation of ecological catalysts derived from Zn
hyperaccumulating plants and their catalytic activity in Diels–Alder reaction. C. R. Chimie (2013), http://dx.doi.org/
10.1016/j.crci.2013.09.009