One-pot tandem catalytic synthesis of α, β-unsaturated nitriles from alcohol with nitriles in aqueous phase

Article abstract of DOI:10.1016/j.catcom.2014.01.001

Pd₁-Au₁ bimetal catalysts supported on basic layered double hydroxide (LDH) have been prepared conveniently with surface impregnation methods and structurally characterized by XRD, TEM and XPS. The nanoparticles were highly dispersed on LDH with an average size of 2.08 ± 0.3 nm and showed a strong cooperative effect between Au and Pd for the step of the alcohol oxidation. Moreover, the present hydrotalcite-supported bimetal catalysts can catalyze efficiently one-pot α-arylation reactions of nitriles with various alcohols in aqueous phase through tandem reactions. The bimetal catalyst has been extended for a broad substrate scope and recycled for at least 4 times.

Full text of DOI:10.1016/j.catcom.2014.01.001

Catalysis Communications 47 (2014) 49–53
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Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
One-pot tandem catalytic synthesis of α, β-unsaturated nitriles from
alcohol with nitriles in aqueous phase
Chen Chen a,1, Hanmin Yang b, Jizhong Chen a,1, Ran Zhang a,1, Li Guo a,1, Huimei Gan a,1
,
Baoning Song a,1, Wenwen Zhu a,1, Li Hua a,1, Zhenshan Hou a,
⁎
a
Key Laboratory for Advanced Materials, Research Institute of Industrial Catalysis, East China University of Science and Technology, Shanghai 200237, China
b
Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission and Ministry of Education, Hubei Province, South-Central University for Nationalities,
1
Wuhan 430074, ChinaTel.: +86 21 64251686.
a r t i c l e i n f o
a b s t r a c t
Article history:
Pd1–Au1 bimetal catalysts supported on basic layered double hydroxide (LDH) have been prepared conveniently
Received 13 October 2013
Received in revised form 2 January 2014
Accepted 4 January 2014
with surface impregnation methods and structurally characterized by XRD, TEM and XPS. The nanoparticles were
highly dispersed on LDH with an average size of 2.08
0.3 nm and showed a strong cooperative effect between
Au and Pd for the step of the alcohol oxidation. Moreover, the present hydrotalcite-supported bimetal catalysts
can catalyze efficiently one-pot α-arylation reactions of nitriles with various alcohols in aqueous phase through
tandem reactions. The bimetal catalyst has been extended for a broad substrate scope and recycled for at least
4 times.
Available online 10 January 2014
Keywords:
Pd1–Au1 bimetal catalysts
Layered double hydroxide
Aqueous phase
© 2014 Elsevier B.V. All rights reserved.
Oxidation
Knoevenagel condensation
1. Introduction
catalysts were hardly reused. Thus recently, more efforts have been
devoted to the requirement of green chemistry and enhancing the
Oxidation of alcohols to the corresponding carbonyl products is
one of the most fundamental reactions in organic chemistry [1]. To
achieve environmental and economical acceptability, much effort
has been devoted to develop the recoverable catalyst with molecu-
lar oxygen as environmentally benign oxidizing agents. On the
other hand, the α, β-unsaturated nitriles are important building
blocks for synthesizing many important organic agents as interme-
diates in the synthesis of fine chemicals [2]. Usually, the main syn-
thetic method of α, β-unsaturated nitriles is stoichiometric
Knoevenagel condensation of nitriles with aldehydes in organic
solvents catalyzed by common bases like amines and their salts
[3]. Unfortunately, these catalysts suffer from significant limitation
of substrate scope and the sources of some aldehydes are unavail-
able. Besides, these traditional catalytic systems often have serious
drawbacks in that toxic organic solvent was normally used and the
recyclability of catalysts [4].
Layered Double Hydroxides (LDHs), also known as hydrotalcite-like
compounds have received much attention as advanced materials due to
their unique properties [5]. For example, the metal nanoparticles can be
well immobilized on LDH supports and employed for the alcohol oxida-
tion [6,7]. On the other hand, LDH was also an efficient solid base
catalyst for simple synthesis of α, β-unsaturated nitriles by Knoevenagel
condensation at a greater rate compared with known other solid base
catalysts [8].
It has been found that there existed a synergistic interaction
between the basic LDH and tunable metal site in efficient oxidation of
various alcohols [9]. Moreover, one-pot formation of α, β-unsaturated
nitriles from alcohol and nitriles can be achieved through sequential
reactions owning to the presence of both surface basic sites and metal
sites on LDH-derived catalysts. Although Ru/LDH catalysts have been
used for the synthesis of α, β-unsaturated nitriles [10,11], organic
solvents like toluene and DMF were always employed. In addition, the
effects of the oxidation and Knoevenagel condensation steps on the
rate of the sequential reaction have not been investigated. As part of
green chemistry efforts, water as a potential replacement for organic
solvents in various catalytic processes showed unique reactivity and
⁎
Corresponding author. Tel.: +86 21 64251686.
E-mail address: houzhenshan@ecust.edu.cn (Z. Hou).
Tel.: +86 21 64251686.
1
1566-7367/$ – see front matter © 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2014.01.001

50
Chen Chen et al. / Catalysis Communications 47 (2014) 49–53
Pd1–Au1/LDH (Fig. 2e and f) indicated the presence of metallic form at
the surface of LDH [14]. Also there were shifts of BE between monome-
tallic and bimetallic catalysts. For the Pd1–Au1/LDH catalyst, the BE of Pd
3d5/2 was 0.3 eV higher than that of the Pd1/LDH (334.9 eV), while Au
4f7/2 was 0.4 eV lower than that of the Au1/LDH (83.4 eV). This can be
confirmed further by the fact that if more high loading amount of Au
was employed, Au 4f7/2 signal indeed became sharper and Au 4f7/2 sig-
nal of bimetal Pd2–Au2/LDH (83.1 eV) was 0.5 eV lower than that of
the monometal Au2/LDH (83.6 eV) (Fig. 2S(b)), suggested that there
was electron transfer from Pd to Au atoms [15]. After four one-pot
tandem catalytic cycles, the oxidation state of Pd and Au remained
zero valent with the BE of 340.5 eV (Pd 3d3/2) and 83 eV (Au 4f7/2),
indicating that the bimetallic catalyst was stable under reaction
condition.
Because basicity would play a crucial role in sequential oxidation
and Knoevenagel condensation, CO2-TPD was carried out to exam-
ine the basicity of the catalysts. As seen from the CO2-desorption
curves in Fig. 3, some weak basic centers existed on the surfaces of
LDH-derived catalysts (around 100 °C), while there were only very
few basic sites on γ-Al2O3 supported catalyst. Moreover, a sharp
desorption band observed between 300 °C to 400 °C on LDH-
derived materials could result from the decomposition of the
interlayered carbonate [16]. This was further substantiated by the
pattern of typical TG/DTA (Fig. 3S).
Fig. 1. XRD patterns of LDH (a), Au1/LDH (b), Pd1/LDH (c), and Pd1–Au1/LDH before
reaction (d) and after reaction (e).
selectivity [12]. Furthermore, it could offer the easy approach for
separation of organic products from aqueous phase. Thus, the develop-
ment of the tandem reaction in water is highly desirable. On the basis of
our previous work [7], in this context the efficient bimetal Pd1–Au1/LDH
catalysts have been extended for transforming alcohol and nitriles into
the α, β-unsaturated nitriles through the tandem alcohol oxidation
and Knoevenagel condensation in water.
2.2. The tandem reactions over different catalysts
We employed a simple procedure for one-pot synthesis of α,
β-unsaturated nitriles by LDH-supported catalysts in aqueous
phase (Scheme 1). At first, the tandem reaction between benzyl
alcohol and ethyl cyanoacetate was chosen as model reaction.
From the 1H NMR spectra of products, the trans (E) isomer was
produced exclusively [17]. As displayed in Table 1, the tandem re-
action cannot happen without any catalyst or with only the LDH
support (Table 1, entries 1 and 2), because no metal sites were
available for the oxidation step. Nevertheless, the Pd1–Au1/LDH
catalyst exhibited higher activity than Pd1/LDH or Au1/LDH catalyst
(Table 1, entries 3, 4 and 5) under the same reaction conditions,
which indicated that there was some cooperation interaction
between Pd and Au on the bimetal catalyst [18]. Additionally,
activated carbon could not promote the one-pot reaction due to the
absence of basicity (Table 1, entry 7). Notably, the Pd1–Au1/γ-Al2O3
also exhibited good conversion but the selectivity to α, β-unsaturated
nitriles was lower than that of Pd1–Au1/LDH catalyst due to the
very few weak basic sites on the Pd1–Au1/γ-Al2O3 catalyst, which
did not promote the Knoevenagel condensation efficiently (Table 1,
entry 6). This can be proved from the fact that Pd1–Au1/γ-Al2O3
showed excellent conversion (98%) for the oxidation step, while
it exhibited only 74.3% conversion for the sequential Knoevenagel
condensation. The results revealed that both the base sites and
the metal sites played a crucial role in facilitating the tandem
reaction.
2. Results and discussion
2.1. Catalyst characterization
The LDH structure was firstly identified by X-ray diffraction (XRD).
The Mg-Al LDH exhibited some common features of layered materials.
The (003), (006), (009), (110) and (113) planes are corresponding to
the typical pattern of the LDH without any hydroxide-segregated
phases (Fig. 1a) [7] (JCPDS 22–0700). Moreover, the LDH structure
revealed a high degree of crystallinity and showed no changes after
the introduction of noble metal (Fig. 1b, c and d). Additionally, no
obvious Pd(0) or Au(0) characteristic diffraction peaks [13] over mono-
metallic and bimetallic catalysts was observed (Fig. 1b, c and d), which
was ascribe to the low contents of metals and the small size of the metal
particles. After reaction the Pd1–Au1/LDH catalyst showed similar
diffraction peaks, indicating that the layered structure of LDH remained
intact and the growth of nanoparticles was not obviously observed
(Fig. 1e).
TEM photographs of the size distribution of fresh and reused
Pd1–Au1/LDH catalysts were shown in Fig. 2. It can be seen that
metal particles were highly dispersed on the surface of LDH with
an average size of 2.38
0.3 nm (Fig. 2a, c), which accounted for
2.3. The step in the tandem reaction
the reason why metal particles on the LDH support showed invisible
diffraction peak. After four recycling, the nanoparticles were still well
As discussed above, the first oxidation step could be very critical
for the tandem reaction. As shown in Fig. 4a, it can be seen that
LDH did not afford any activity of alcohol oxidation, and Pd1/LDH
appeared more active than the Au1/LDH, giving about 90% conver-
sion after 1.5 h. Interestingly, Pd1–Au1/LDH catalyst afforded full
conversion under the same reaction conditions, which demonstrat-
ed the superiority of the bimetal catalyst in alcohols oxidation
[7,18]. Meanwhile, the reaction time profiles of Knoevenagel con-
densation between benzaldehyde and ethyl cyanoacetate revealed
that the condensation reaction proceeded very rapidly and was
completed at 80 °C within 30 min (Fig. 4b). However, these
dispersed with an average size of 3.12
0.3 nm (Fig. 2b, d), although
a slight growth was observed. Moreover, the Pd1/LDH and Au1/LDH cat-
alysts also exhibited the similar particle size of 2.25 nm (Fig. 1S(a),
1S(b)) and 2.78 nm (Fig. 1S(c), 1S(d)), respectively. In addition,
the γ-Al2O3-supported bimetallic catalyst displayed slightly larger
particle size of 4.38 nm (Fig. 1S(e), 1S(f)).
Additionally, the chemical state and the surface composition of the
catalysts were obtained by XPS analyses. Fig. 2 showed the Pd 3d and
Au 4f spectra for the monometallic and bimetallic catalysts. The binding
energy (BE) of Pd 3d5/2 (345.2 eV) and Au 4f7/2 (83.0 eV) for the bimetal

Chen Chen et al. / Catalysis Communications 47 (2014) 49–53
51
Fig. 2. TEM image of fresh Pd1–Au1/LDH (a, c) and used Pd1–Au1/LDH(b, d), and the XPS spectra of Pd 3d (e) and Au 4f (f). c and d were the corresponding enlargement of TEM image. A and
B in (e) and (f) corresponded to the fresh and used catalysts, respectively.
catalysts afforded a considerable difference in catalytic activity for
the tandem reaction (Table 1, entries 2–5), which was consistent with
the alcohol oxidation rate of LDH-derived catalysts (Fig. 4a). As a result,
the alcohol oxidation seemed to be a rate-determining step for the
whole reaction. It should be worth noting that the reaction rate of con-
densation step catalyzed by LDH-supported metal catalysts was slightly
faster than that by LDH. Similarly, it was found that the Pd1–Au1/γ-
Al2O3 catalyst exhibited higher conversion of benzalaldhyde (72.6%)
than that of γ-Al2O3 (59.1%) for the condensation step at 80 °C for 1 h.
The reason can be explained that apart from the basicity of the support,
the mental center may also play an important role in activating the
C\H bond of activated methylene compounds to promote the condensa-
tion step [19].
2.4. The generality and reusability of the catalyst
Sequentially, the substrates were extended to several benzyl alcohol
derivatives with ethyl cyanoacetate or malononitrile. As shown in
Table 2, most aromatic alcohols with nitriles were able to undergo the
corresponding tandem reaction, while alcohols with electron donating
group gave higher yield of α, β-unsaturated nitriles (Table 2, entries
1–3, 6–8). Apart from electronic effect, steric effect also influenced the
yield of products. The steric hindrance of the o-methyl group in aromat-
ic alcohol may hinder the condensation step, which resulted in worse
yields of products (Table 2, entries 4 and 9) [20]. Additionally, it can
be observed that malononitrile was more active than ethyl cyanoacetate
in the condensation step (Table 2, entries 4, 5, 9 and 10). This may

52
Chen Chen et al. / Catalysis Communications 47 (2014) 49–53
Table 1
Tandem reaction over various catalysts.a
Entry Catalysts
Con.(%) Sel.(%)
α,β-unsaturated Benzaldehyde Benzoic
nitriles
acid
1
2
3
4
5
6
7
None
LDH
Pd1/LDH
Au1/LDH
Pd1–Au1/LDH
Trace
Trace
90.2
46.3
≥99
Trace
Trace
89.4
92.3
96.6
74.3
48.9
Trace
Trace
9.8
7.7
3.4
Trace
Trace
0.8
Trace
Trace
0.8
Pd1–Au1/γ-Al2O3 98.5
Pd1–Au1/C
14.9
51.1
12.8
Trace
a
Reaction conditions; i) benzyl alcohol (1 mmol), H2O (3 mL), catalyst (0.1 g), benzyl
alcohol/metal = 67:1(molar ratio), 353 K, 1.5 h, O2 ballon (0.1 MPa); ii) ethyl cyanoacetate
(1.1 mmol), 353 K, 1 h, in Air.
Fig. 3. Temperature-programmed desorption of CO2 for indicated samples. (a) LDH;
(b) Au1/LDH; (c) Pd1/LDH; (d) Pd1–Au1/LDH; (e) Pd1–Au1/Al2O3.
the Doctoral Program of Higher Education of China (20100074110014),
and the Fundamental Research Funds for the Central Universities.
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.catcom.2014.01.001.
attribute to the stronger electron-withdrawing ability of the CN group,
so the methylene group of malononitrile is more activated than ethyl
cyanoacetate to react with aromatic aldehydes [20].
References
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catalytic activity and selectivity (Table 1S, entries 1–4). Nevertheless,
the yield of the product decreased to 76.7% in the fifth run (Table 1S,
entry 5). To identify the possible reason on the catalyst deactivation,
the loading amount of Pd and Au of the recycled catalyst was analyzed
by ICP-AES and found to be 0.78% and 0.67%, respectively, which was
lower than that of the fresh catalyst (0.98% and 0.95%, respectively). In
our previous work, it indicated that neglectable Pd and Au were leached
in the step of alcohol oxidation [7]. Therefore the strong coordination
ability of nitrile group to metals in the condensation reaction was
responsible for the loss of metal components.
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The tandem reaction of oxidation followed by Knoevenagel conden-
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Scheme 1. One-pot synthesis of α,β-unsaturated nitriles.

Chen Chen et al. / Catalysis Communications 47 (2014) 49–53
53
Fig. 4. Time variation of benzyl oxidation (a) and Knoevenagel condensation between benzyl aldehyde and ethyl cyanoacetate (b).
Table 2
Tandem reaction of different alcohols with active methylene compoundsa
.
Entry
R1
R2
R3
R4
Con (%)
Yield (%)b
1
2
3
H
H
H
CH3
H
H
H
H
CH3
H
H
H
H
H
Cl
H
H
H
H
Cl
H
COOEt
COOEt
COOEt
COOEt
COOEt
CN
CN
CN
CN
CN
≥99
≥99
≥99
90.4
94.8
≥99
≥99
≥99
90.1
90.5
97.6 (93.1)
94.3 (92.1)
90.1 (87.2)
63.0 (60.1)
67.7 (65.2)
98.0 (94.6)
97.9 (95.3)
93.1 (90.4)
85.2 (82.6)
72.4 (68.3)
CH3
OCH3
H
H
H
CH3
OCH3
H
4
5c
6
7
8
9
10c
H
a
Reaction conditions; i) aromatic alcohols (1 mmol), H2O (3 mL), Pd1–Au1/LDH catalyst
(0.1 g), alcohol/metal = 67:1 (molar ratio), 353 K, 1.5 h, O2 ballon (0.1 MPa); ii) nitriles
(1.1 mmol), 353 K, 1 h, in Air.
b
GC yield for the α, β-unsaturated nitriles; the values in the parentheses refer to the
isolated yield.
c
12 h for oxidation step.