Green reusable Pd nanoparticles embedded in phytochemical resins for mild hydrogenations of nitroarenes

Article abstract of DOI:10.1039/c9nj04474d

A green chemical preparation of Pd nanoparticles (NPs) embedded in phytochemical resins using a plant extract from Pulicaria odora L. and PdCl₂ under ambiant conditions is reported. Two batches of Pd NPs have been prepared: they present homogeneous sizes of respectively 2.2 nm and 3.2 nm depending on the preparation conditions. The Pd NPs were characterized by different techniques (TEM, HRTEM, XRD, XPS and BET) and have been successfully used for the reduction of nitroarenes in EtOH under H₂ at atmospheric pressure at rt in the presence of only 5 mequiv. of Pd. Finally the Pd NPs embedded in resin particles were easily recovered by filtration and used at least seven times without significant loss in efficiency. The residual amount of palladium found in the reaction product is very low (<0.6% of the initial amount). Therefore both preparation of the Pd NPs and their use for hydrogenations of nitroarenes are environmentally benign.

Full text of DOI:10.1039/c9nj04474d

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Green reusable Pd nanoparticles embedded in
phytochemical resins for mild hydrogenations
of nitroarenes†
Cite this: New J. Chem., 2019,
43, 17383
ab
Mohamed Enneiymy,ab Claude Le Drianab and Jean-Michel Becht
*
A green chemical preparation of Pd nanoparticles (NPs) embedded in phytochemical resins using a plant
extract from Pulicaria odora L. and PdCl2 under ambiant conditions is reported. Two batches of Pd NPs
have been prepared: they present homogeneous sizes of respectively 2.2 nm and 3.2 nm depending on the
preparation conditions. The Pd NPs were characterized by different techniques (TEM, HRTEM, XRD, XPS and
BET) and have been successfully used for the reduction of nitroarenes in EtOH under H2 at atmospheric
pressure at rt in the presence of only 5 mequiv. of Pd. Finally the Pd NPs embedded in resin particles were
easily recovered by filtration and used at least seven times without significant loss in efficiency. The residual
amount of palladium found in the reaction product is very low (o0.6% of the initial amount). Therefore both
preparation of the Pd NPs and their use for hydrogenations of nitroarenes are environmentally benign.
Received 29th August 2019,
Accepted 22nd October 2019
DOI: 10.1039/c9nj04474d
rsc.li/njc
use of toxic solvents, expensive and sensitive Pd-catalysts con-
taining ligands constitute other serious drawbacks.3 The use of
1. Introduction
Aromatic primary amines are of crucial importance for the soluble Pd-catalysts is nowadays problematic since no economically-
syntheses of numerous compounds presenting crucial applica- viable Pd ores exist: this precious metal is extracted as a by-product
tions as active pharmaceutical ingredients (API), biologically from nickel, copper or chromium ores. Since palladium has
active molecules, agrochemicals, cosmetics, pigments, dyes or increasing applications, its price is very volatile: 428.000 h kgÀ1
polymers.1 Their preparation has therefore suscited huge in October 2018 and 4 43.000 h kgÀ1 in may 2019. It is therefore
interest.2 Reactions allowing direct introduction of an amino of crucial importance, both economically and environmentally,
group on aromatic rings are scarce and often tedious.3–5 For to use as little palladium as possible.
example the traditional nucleophilic aromatic substitution is
Introduction of a nitro group on arenes via electrophilic
mostly limited to nitro-substituted aryl halides and requires aromatic substitution followed by reduction of the nitro group
often harsh conditions. Recently Cu-catalyzed reactions of aryl is another efficient route to aromatic primary amines.11
iodides4 or areneboronic acids6 with a very large excess of NH3 Reduction of the nitro group could be performed by transition-
have been described. Later, Pd-catalyzed reactions between aryl metal catalyzed reactions using for example sodium borohydride
halides and NH3 have also emerged for the creation of aryl-NH2 (NaBH4) as a reducing agent in the presence of a heterogeneous
bonds. However most of these reactions necessitate also drastic Ru12-, Cu13-, Au14-, Pd15,16-catalyst or even of Fe containing ppm
conditions and hazardous organic solvents.4 Other strategies amounts of Pd.17 However, the major drawbacks of such reduc-
involving aryl halides and nitrogen reagents have also been tions are the lack of chemoselectivity and the formation of large
developed.3 In this respect, Pd-catalyzed couplings between aryl amounts of salts as by-products which are particularly problematic
halides and for example diallylamine,7 the imine derived from on an industrial scale. In addition some heterogeneous catalysts
benzophenone,8,9 or LiHMDS10 have been proposed.3 These efficient for reductions of nitroarenes are difficult to prepare. For
reactions proceed generally in good yields but require a second example, in 2019, Yang et al. have reported a seven-step prepara-
step to liberate the desired NH2 group and therefore suffer in tion of Pd NPs immobilized on a conjugated macrocyclic polymer
most cases from very poor atom economy. Additionnally the for the reduction of a nitroarene using 1.7 mequiv. of supported Pd
and an excess of NaBH4.18 Other methods involve hydrazine11 or
formic acid19 in the presence of a Pd-catalyst. Among all these
a
´
Universite de Haute-Alsace, CNRS, IS2M UMR 7361, F-68100 Mulhouse, France.
reactions, the preparation of aromatic amines by simple transition
metal-catalyzed hydrogenation of nitroarenes which avoids
the formation of by-products seems to be the most interesting
from both a green chemistry and an industrial point of view.
E-mail: jean-michel.becht@uha.fr
b
´
Universite de Strasbourg, France
† Electronic supplementary information (ESI) available: 1H and 13C NMR spectra
of compounds. See DOI: 10.1039/c9nj04474d
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Noteworthily aromatic amines of industrial importance are for fine chemistry40 we have developed herein biosourced Pd NPs
prepared via this route. Besides, nitroarenes represent a very for very mild hydrogenations of nitroarenes.
important environmental problem whether as by-products in
Pulicaria odora L. is a wild species from the Asteraceae
synthesis or as contaminants.20 Hydrogenation to yield useful family. This plant is particularly abundant in the north-west
and more benign aromatic primary amines is therefore impor- of Morocco and grows on sandy grounds. The group of Gadhi
tant both as synthetic method and as promising depollution has shown that the essential oil of Pulicaria odora L. contains
method. However harsh reaction conditions, i.e. high H2 two major constituents: 2-isopropyl-4-methylphenol and isobutyric
pressure and temperature are generally required.21 For example acid 2-isopropyl-4-methylphenylester.41 Some groups have described
the group of Asefa has described a multi-step synthesis of a the antibacterial and antifungal properties of 2-isopropyl-4-
SiO2/Pd/hollow ZrO2 catalyst for hydrogenations of nitroarenes methylphenol.42 Essential oils of Pulicaria odora L. are also
under a 2 MPa H2 pressure.22 Heterogeneous Fe-catalysts have used to treat back-pain and intestinal disorders.41,42 Herein a
also been reported for reductions under H2 pressure.23 The straightforward synthesis of Pd NPs using Pulicaria odora L.
development of mild and ‘‘green’’ conditions is therefore highly aqueous extracts for fast and chemospecific hydrogenations of
desirable and has suscited recently huge interest. In this nitroarenes under ambiant conditions in EtOH at rt is described.
respect some heterogeneous Rh24- or Pt25-catalysts have been Both preparation of Pd NPs and their use for hydrogenations
developed for the reduction of nitroarenes at rt under H2 at of nitroarenes are therefore easy, efficient and, above all,
atmospheric pressure. But Pd-catalysts are certainly the most environment-friendly.
frequently used heterogeneous catalysts for hydrogenations of
nitroarenes. For example the group of Huang has reported a
three-step synthesis of a Pd-containing P-doped porous polymer for
2. Experimental section
hydrogenations of nitroarenes under an atmosphere of H2 at rt.26
A
General
The group of Sadjadi has described a five-step preparation of Pd
NPs immobilized on halloysite bearing melamine based polymer
modified by a cyclodextrin and its use for the hydrogenation of
nitroarenes.27 During the last years several catalysts containing
Pd NPs grafted on various supports, i.e. poly(vinyl)chloride,28 porous
organic polymers (POP),29 hollow magnetic nanocomposites,30
nitrogen-doped carbon nanofibers or silica spheres31 have been
reported for mild hydrogenations of nitroarenes. Some hetero-
geneous bimetallic Pd–Pt32 or Cu–Ni33 catalysts have also been
proposed for such hydrogenations. However, it is important to
note that if various heterogeneous Pd-catalysts allow mild
conditions for the reductions of nitroarenes, generally 410 mequiv.
of palladium are required and, most notably, an important
drawback remains: these catalysts require multi-step syntheses
involving often hazardous substrates and/or solvents making
them not eco-friendly.
Recently simple Pd NPs have suscited huge interest for
various reactions in fine chemistry. They are principally
obtained by chemical or sonochemical reduction methods.34
However, a reducing agent (for example NaBH4), a stabilizer to
prevent the NPs aggregation and a suitable solvent are required
in the reaction. Lately syntheses of Pd NPs simply from a Pd(II)
salt and aqueous extracts of plants have been published.35
Pulicaria odora L. was a gift from the University Chouaib
Doukkali (El Jadida, Morocco). Its roots were dried and ground
to give a fine brown powder. The Pd particle morphology was
evaluated by scanning transmission electron microscopy (STEM)
with a Jeol ARM-200F instrument working at 200 kV. The nano-
particle size distribution was determined using ImageJ software.
Several STEM images were explored and around 500 particles were
counted to ensure a good global assessment of the particles size.
The material structure and crystallinity were investigated by X-ray
powder diffraction (XRD) using a Philips X’Pert MPD diffract-
ometer equipped with Cu Ka1,2 doublet and a flat-plate Bragg–
Brentano theta–theta geometry. All reagents were obtained from
commercial sources (Acros Organics, Sigma-Aldrich and Alfa
Aesar) and were used without further purifications. The Pd/C
and Pd Encat NP30 were obtained respectively from Alfa Aesar
(Ref. A12623) and Sigma Aldrich (Ref. 653667). The silica gel was
purchased from Merck and had a 0.063–0.2 mm granulometry
(70–230 mesh ASTM). The Pd NPs-1 and Pd NPs-2 were recovered
by filtration on a 0.1 mm Durapore membrane filter.
B
Synthetic procedures
Preparation of Pd NPs-1 and Pd NPs-2. The powder from the
Compared to traditional NPs preparations such methods are roots of Pulicaria odora L. (10 g) was refluxed in water (100 mL)
rapid, clean and involve only natural compounds acting both as under vigorous stirring for 1 h. After cooling to rt the reaction
reducing agents and stabilizers for the Pd NPs, avoiding there- mixture was filtered off to afford a solution of the desired
fore the use of additional capping agents and stabilizers. In this phytochemicals. Besides a solution of PdCl2 (0.2 mmol, 35.4 mg
respect some groups have reported such syntheses of Pd NPs for Pd NPs-1 or 0.3 mmol, 53.2 mg for Pd NPs-2) in water
and their applications for Suzuki–Miyaura,36 Stille,37 Hiyama,37 (50 mL) was prepared. The extract from Pulicaria odora L.
and cyanation reactions.38 Recently the group of Veisi has (30 mL) was added to the solution of PdCl2. The reaction
described reusable biosourced Pd NPs for the reduction of mixture was then refluxed for 3 h, cooled to rt, and finally
4-nitrophenol in the presence of NaBH4.39 To the best of our centrifuged at 20 000 rpm for 30 min. The Pd NPs embedded in
knowledge no reusable biosourced Pd NPs of general use for the resin particles were then washed by suspension in EtOH for
‘‘green’’ hydrogenations of nitroarenes have been described. In 5 min, centrifuged at 20 000 rpm for 30 min, isolated and dried
our continuous search for short and efficient green Pd-catalysts under vacuum for 15 h. The Pd NPs-1 (100 mg) and Pd NPs-2
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(130 mg) were obtained and stored without particular precautions. amines can be purified by flash-chromatography on silica with
The Pd-contents of Pd NPs-1 and Pd NPs-2 were determined AcOEt and cyclohexane mixtures.
after complete mineralization of both catalysts followed by
UV-visible spectroscopy.40 The % Pd found was respectively
18 wt% for Pd NPs-1 and 23 wt% for Pd NPs-2. They were
confirmed by XPS.
3. Results and discussion
General procedure for the hydrogenation of nitroarenes. The The Pd NPs were prepared in one-pot by reduction of PdCl2
nitroarene (2 mmol) in EtOH (10 mL) was vigorously stirred in water using phytochemical resins present in extracts of
in the presence of Pd NPs-1 (5 mequiv., 5.9 mg) under H2 at Pulicaria odora L. For this purpose, roots from Pulicaria odora
atmospheric pressure at rt for 1.25 h (for the preparation of L. were ground to give a fine powder which was refluxed in
aromatic amines 1a–b, 1e–l) or 4 h (for the preparation of water. The reaction medium was then filtered and the aqueous
aromatic amines 1c–d). The catalyst was recovered by filtration extract was added respectively to a 4 mmol LÀ1 and a 6 mmol LÀ1
on a membrane (0.1 mm). The Pd NPs-1 were then washed twice solution of PdCl2 in water. After refluxing and centrifugation two
with EtOH (5 mL), filtered and dried under vacuum before batches of Pd NPs-1 and Pd NPs-2 were obtained (Scheme 1). The
reuse. The solvent was evaporated and the aromatic primary Pd-contents of Pd NPs-1 and Pd NPs-2 were measured using a
amines were dried under vacuum. If necessary the aromatic procedure developed previously by our group40 and could be
confirmed by XPS since the distribution of the Pd NPs in the
resin particles is homogeneous. The % of Pd found were
respectively 18 wt% for Pd NPs-1 and 23 wt% for Pd NPs-2. It
is noteworthy that Pd NPs can be stored for several months
without particular precautions.
The Pd NPs-1 and Pd NPs-2 were firstly characterized by
Transmission Electron Microscopy (TEM, Fig. 1). Both Pd NPs-1
(Fig. 1a and c) and Pd NPs-2 (Fig. 1e and g) present narrowly
distributed sizes for the Pd nuclei around 2.2 nm for Pd NPs-1
and 3.2 nm for Pd NPs-2. The high-resolution TEM (HRTEM)
showed for both Pd NPs (Fig. 1b and f) interplanar distance of
0.22 nm, corresponding to the (111) lattice planes of fcc Pd. Finally
the selected area electron diffraction (SAED) pattern (Fig. 1d and h)
Scheme 1 Preparation of Pd NPs-1 and Pd NPs-2.
showed a ring-like diffraction pattern corresponding to interlayer
Fig. 1 (a) TEM image of Pd NPs-1; (b) HRTEM image of Pd NPs-1; (c) size distribution of Pd NPs-1; (d) SAED pattern of Pd NPs-1; (e) TEM image of Pd
NPs-2; (f) HRTEM image of Pd NPs-2; (g) size distribution of the Pd NPs-2; (h) SAED pattern of Pd NPs-2.
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Fig. 2 XRD patterns of Pd NPs-1 and Pd NPs-2.
spacings of 0.22 nm, 0.14 nm and 0.12 nm corresponding to (111),
(022), and (131) planes confirming the presence of crystalline Pd
NPs. Noteworthily, using a 2 mmol LÀ1 PdCl2 solution we also
prepared resins containing a lesser amount of Pd (ca. 10 wt%).
Since TEM images showed mostly the presence of large Pd
aggregates and a heterogeneous distribution of Pd nuclei sizes
(for further details see ESI†), the study was only pursued with
Pd NPs-1 and Pd NPs-2.
The X-ray diffraction (XRD) patterns showed the presence of
several peaks (Fig. 2) attributed to the face-centered-cubic (fcc)
crystalline structure of Pd. Noteworthily a small quantity of PdO
was found in Pd NPs-1.
Fig. 4 XPS patterns of Pd NPs-1 and Pd NPs-2, (a) XPS high resolution
spectrum of Pd NPs-1 and Pd NPs-2, (b) deconvoluted spectrum for C 1s
(Pd NPs-1), (c) deconvoluted spectrum for O 1s (Pd NPs-1), (d) deconvo-
luted spectrum for N 1s (Pd NPs-1), (e) deconvoluted spectrum for Pd 3d of
Pd NPs-1, (f) deconvoluted spectrum for Pd 3d of Pd NPs-2.
whereas Pd is predominant for Pd NPs-2. This observation is not
unexpected since in the literature several examples show that the
ease of oxidation of Pd NPs increases when their size decreases.43
The reaction conditions for the hydrogenation were optimized
using 4-nitroacetophenone at rt in EtOH under 1 atm of H2 in the
presence of Pd NPs-1 or Pd NPs-2 (Table 1). Using 1 mequiv. of Pd,
Pd NPs-1 or Pd NPs-2, afforded the corresponding aromatic
primary amine 1a in respectively 64% and 62% yields (entries 1
and 2). Replacing EtOH with other ‘‘green’’ solvents such as a 1 : 1
EtOH/H2O mixture, iPrOH or propane-1,2-diol was unsuccessful
(entries 3–5). Almost quantitative yields in 1a were obtained
using 2 mequiv. or 5 mequiv. of Pd in respectively 6 h and
1.25 h (entries 6 and 8). Pd NPs-2 are somewhat less efficient
(entries 9 and 10). Under the best conditions (entry 8) the amount
of Pd lost during the reaction was determined: after filtration of
The porosity of Pd NPs-1 and Pd NPs-2 was determined by
nitrogen adsorption (Fig. 3). They possess specific surface area
of respectively 21 m2 gÀ1 and 12 m2 gÀ1, are mesoporous and
the average size of the mesopores is ca. 3.4 nm.
The surface chemistry of Pd NPs-1 and Pd NPs-2 was
characterized by the XPS technique (Fig. 4a). The patterns
showed the presence of several peaks which could be attributed
to oxygen (O 1s), nitrogen (N 1s), palladium (Pd 3d) and carbon
(C 1s). The deconvolution of peaks (O 1s, N 1s and C 1s) was
carried out for Pd NPs-1. The C 1s spectrum (Fig. 4b) consists
of five signals, tentitatively attributed to C sp2 and C sp3, C
adjacents to carbonyls, ethers, carbonyls and carboxyls. These
functional groups provide a hydrophilic character to the catalyst,
which favours the efficiency in ‘‘green’’ hydroxylic solvents like
ethanol. The deconvolution of Pd 3d 3/2 and 5/2 signals shows
that PdO is predominant on the surface of Pd nuclei for Pd NPs-1
Table 1 Optimization of the reaction conditions
Pd NPs-1 or 2
Entrya (mequiv.)
Reaction Yield
time (h)
Solvent
(%)b
1
2
3
4
5
6
7
8
9
Pd NPs-1 (1 mequiv.) EtOH
Pd NPs-2 (1 mequiv.) EtOH
Pd NPs-2 (1 mequiv.) EtOH/H2O 1 : 1
Pd NPs-2 (1 mequiv.) iPrOH
Pd NPs-2 (1 mequiv.) Propane-1,2-diol
Pd NPs-1 (2 mequiv.) EtOH
Pd NPs-1 (2 mequiv.) EtOH
Pd NPs-1 (5 mequiv.) EtOH
Pd NPs-2 (5 mequiv.) EtOH
Pd NPs-2 (5 mequiv.) EtOH
6
6
6
6
6
6
1.25
1.25
1.25
2
64
62
n.r.
n.r.
o50
99
48
99
67
99
10
a
Reactions performed using 4-nitroacetophenone (2 mmol), the indi-
b
cated amount of Pd in EtOH (10 mL). Isolated yields after filtration of
Fig. 3 Nitrogen adsorption desorption isotherm and pore size distribution
of Pd NPs-1 and Pd NPs-2.
the Pd NPs-1 or Pd NPs-2, concentration and drying of the reaction
product.
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the catalyst o 0.6% of the initial amount of Pd was found in the
reaction mixture. It is noteworthy that Pd NPs-1 or Pd NPs-2
afforded chemospecifically the corresponding aromatic amine 1a
since the acetyl group remained unchanged. Finally, for compar-
ison purposes, the reaction was run in the optimized conditions
(Table 1, entry 8) with two widely used commercial catalysts: Pd/C
and Pd Encat NP30. It turned out that 1a was obtained in only
60% and 26% yields respectively.
The homogeneous and/or heterogeneous nature of the catalysis
was then determined. For this purpose, after 30 min of reaction
(conditions of Table 1, entry 8) the Pd NPs-1 were filtered off
(yield at that point: 48%) and the filtrate was placed under 1 atm of
H2 for another 45 min which brought the yield to only 52%. This
result indicated that soluble palladium entities seem to play no
significant role in this reaction. The possibility to recover the Pd
NPs-1 or Pd NPs-2 for reuse was then determined (Scheme 2). After
reaction the Pd NPs were recovered by filtration, dried and reused.
Both catalysts Pd NPs-1 and Pd NPs-2 could be reused at least
7 times (respectively in conditions of Table 1, entry 8 or 10) without
showing any loss of efficiency.
Scheme 2 Reuse of Pd NPs-1 and Pd NPs-2 (conditions of entry 8 for Pd
NPs-1 or 10 for Pd NPs-2).
Our preferred conditions are those of Table 1, entry 8 and
the scope of these hydrogenation conditions was determined
(Table 2). It turned out that almost quantitative isolated yields
of aromatic amines were obtained using nitroarenes bearing
either electro-attracting (entries 1–4) or electro-donating groups
(entries 7–10). Even the hydrogenation of 2-nitrobenzoic acid
(entry 3) or 2-nitroterephthalic acid (entry 4) proceeded in
excellent yields but required a longer reaction time (4 h).
Gratifyingly the industrially important hydrogenation of
4-nitrophenol was successfully performed in these mild conditions
(entry 10). Finally the reduction of 3-nitropyridine afforded the
corresponding 3-aminopyridine 1k in 99% yield.
The activity of Pd NPs-1 was then compared to that of some
representative heterogeneous catalysts reported in the litera-
ture for reduction of the industrially challenging 4-nitrophenol
under various conditions (Table 3). As shown, Pd NPs-1 is one
of the most active in terms of amount of supported palladium
necessary and turn over frequency (TOF). This excellent catalytic
activity could tentitatively be explained by the small size of the Pd
NPs and favourable interactions between electron-rich polyphenols
present in the phytochemical resin and the electron-poor nitro-
arenes. Moreover it is important to note that the major advantage
Table 2 Hydrogenation of various nitroarenes
Entry
R1
R2
Yieldc (%)
1a
2a
3b
4b
5a
6a
7a
8a
9a
10a
4-Ac
H
H
H
99 (1a)
99 (1b)
98 (1c)
92 (1d)
98 (1e)
98 (1f)
99 (1g)
98 (1h)
99 (1i)
99 (1j)
4-CO2Et
2-CO2H
2-CO2H
H
4-F
2-NH2
2-Me
5-CO2H
H
H
H
4-Me
H
H
4-NH2
4-OH
a
Reactions performed using a nitroarene (2 mmol), Pd NPs-1 in
EtOH (10 mL) at rt for 1.25 h. b Reactions performed using a nitroarene
c
(2 mmol), Pd NPs-1 in EtOH (10 mL) at rt for 4 h. Isolated yields after
filtration of the Pd NPs-1, concentration and drying of the reaction
product.
Table 3 TOF for the reduction of 4-nitrophenol to 4-aminophenol in the presence of some representative heterogeneous catalysts
Entry
Catalyst
Reducing agent, solvent
Catalyst (mequiv.)
TOF (hÀ1
174
6.25
200
200
100
200
)
1
2
3
4
5
6
7
8
Pd NPs-1 (this work)
H2
H2
H2
H2, EtOH
H2, EtOH
H2, EtOH
H2, EtOH
NaBH4, H2O
NaBH4, EtOH/H2O
NaBH4, H2O
NaBH4, H2O
NaBH4, H2O
H2N-NH2ÁH2O, MeOH
5
20
5
Rh NPs@polystyrene24
Pd@porous organic ligand46
Pd@porous organic polymer29
Pd@hollow mesoporous spheres31
Pd–Pt@carbon nanotube32
Co–Cu@N-doped porous carbon47
Pd@polypyrrole@Fe15
5
10
10
60
10
1.8
1
105
1
0.6
2.4
133
2128
1000
19
12 050
328
9
Pd@hypercrosslinked polymer48
Pd@PVP49
10
11
12
13
Cu NPs@C50
Au@PMelamine14
Pd@porous triazine polymer51
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of Pd NPs-1 resides in their ease of preparation under envir-
onmentally totally benign conditions. Indeed, a majority of the
catalysts shown in Table 3 are long and tedious to prepare44
and/or require large excess of reducing agents.46 In addition a
drop in the yields is observed during reuse of most of these
catalysts.29 Finally, non precious metals have also been used for
the reduction of nitroarenes. For example Fe NPs44 or N-doped
graphene supported Fe45 have been used but the reduction of
nitroarenes require either a large excess of Fe NPs (3 equiv.)44 or
45
a high pressure of H2 (3 MPa).17
4. Conclusions
Pd NPs surrounded by phytochemical resins obtained from a
decoction of Pulicaria odora L. roots have been prepared in one-
pot under mild and ‘‘green’’ conditions. In particular Pd NPs-1
showed an excellent activity for the chemospecific hydrogena-
tions of nitroarenes under hydrogen at atmospheric pressure
and rt in EtOH. Gratifyingly the Pd NPs-1 were recovered
quantitatively after reaction and used successfully seven times.
To the best of our knowledge we described one of the most easily
and fastly accessible reusable ‘‘green’’ biosourced Pd-catalyst for
hydrogenations of nitroarenes. It constitutes therefore an excellent
compromise between ease of preparation, activity and reusability.
Further investigations are in progress in our group to extend the
use of Pd NPs-1 for other reactions in fine chemistry.
17 J. Feng, S. Handa, F. Gallou and B. H. Lipshutz, Angew.
Chem., Int. Ed., 2016, 55, 8979.
Conflicts of interest
18 Z. Li, X. Li and Y.-W. Yang, Small, 2019, 15, 1805509.
19 X. Xu, J. Luo, L. Li, D. Zhang, Y. Wang and G. Li, Green
Chem., 2018, 20, 2038.
There are no conflicts to declare.
20 Q. Ashton Acton, Nitro Compounds Advances in Research and
Application, Scholarly Editions, 2013.
Acknowledgements
´
21 C. C. Torres, V. A. Jimenez, C. H. Campos, J. B. Alderetec,
´
We are grateful to the Fondation pour l’Ecole Nationale Superieure
R. Dinamarca, T. M. Bustamente and B. Pawelec, Mol. Catal.,
2018, 447, 21.
22 Y. Wang, A. V. Biradar and T. Asefa, ChemSusChem, 2012,
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de Chimie de Mulhouse for a doctoral grant and generous financial
support to Mohamed Enneiymy, to Prof. Rabiaa Fdil and Manal
Zefzoufi from the University Chouaib Doukkali (El Jadida, Morocco)
¨
for a generous gift of Pulicaria odora L. We also thank Dr Loıc Vidal
for TEM images, Dr Jean-Marc Le Meins for the XRD analyses,
Dr Cyril Vaulot for BET experiments, Philippe Fioux for XPS
analyses via IS2M technical platform and Dr Didier Le Nouen
¨
1
for H- and 13C-NMR spectra.
25 S. Jayakumar, A. Modak, M. Guo, H. Li, X. Hu and Q. Yang,
Chem. – Eur. J., 2017, 23, 7791.
26 Z.-C. Ding, C.-Y. Li, J.-J. Chen, J.-H. Zeng, H.-T. Tang, Y.-J.
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