Acceleration of Suzuki coupling reactions by abundant and non-toxic salt particles

Article abstract of DOI:10.1039/c3gc42088d

Enhancement of reaction efficiency using non-toxic, abundant, and cheap additives is an interesting topic in green chemistry. In this paper, we report the first work to study the effect of salt particles on organic reactions in different solvents, in which the salts were not soluble, and it was discovered that NaCl, KCl, Na₂SO₄ and K₂SO₄ particles could considerably accelerate Suzuki coupling reactions catalyzed by the Pd nanocatalysts. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) studies indicated that there exist strong interactions between the salts and the catalyst (Pd) and between the salts and the reactants, which are important reasons for the synergistic effect of the catalyst and the salts. The application of salt particles suspended in organic reaction systems may become a useful strategy to develop new and green reaction routes.

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Table of Contents
Acceleration of Suzuki coupling reaction by abundant and non-toxic salt
particles
Binbin Zhang, Jinliang Song, Huizhen Liu, Jinghua Shi, Jun Ma, Honglei Fan, Weitao Wang, Peng
Zhang and Buxing Han*
Simple salt particles and Pd catalyst in organic solvents have excellent synergistic effect for promoting Suzuki
coupling reactions.

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DOI: 10.1039/C3GC42088D
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ARTICLE TYPE
Acceleration of Suzuki coupling reaction by abundant and non-toxic salt particles
Binbin Zhang, Jinliang Song, Huizhen Liu, Jinghua Shi, Jun Ma, Honglei Fan, Weitao Wang, Peng
Zhang and Buxing Han*
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
Enhancement of reaction efficiency using non-toxic, abundant, and cheap additives is an interesting topic
in green chemistry. In this work, we conducted the first work to study the effect of salt particles on
organic reactions in different solvents, in which the salts are not soluble, and it was discovered that NaCl,
KCl, Na2SO4 and K2SO4 particles could accelerate Suzuki coupling reactions catalyzed by Pd
10 nanocatalysts considerably. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared
spectroscopy (FT-IR) studies indicated that there exist strong interactions between the salts and the
catalyst (Pd) and between the salts and the reactants, which are important reasons for the synergistic
effect of the catalyst and the salts. Application of salt particles suspended in organic reaction systems may
become a useful strategy to develop new and green reaction routes.
It is well accepted that in a salt solution each anion or cation
15 1. Introduction
45 is surrounded by a number of solvent molecules to form solvent
shell, while inorganic salt particles belong to typical ionic crystals.
Many simple inorganic salts, such as sodium chloride, sodium
sulfate, potassium chloride, potassium sulfate are cheap, abundant,
non-toxic and chemically inert to organic reactions. The salts are
widely used in different fields. As additives, salts dissolved in
20 solutions can accelerate some organic reactions.1-7 For example,
Diels–Alder cycloadditions in lithium perchlorate–diethyl ether
were accelerated significantly when compared with the salt-free
organic solvent-based reactions.8 Alkali and alkaline earth metal
salts dissolved in methanol and acetonitrile had notable effect on
25 the rates of the α-tocopherol regeneration reaction of ubiquinol-
10.9 The Baylis-Hillman reaction was shown to be accelerated in
salt solutions of water and the “water-like” structured solvents,
such as formamide and N-methylformamide.10 Salts in solution
were found to have considerable impact on endo/exo ratios of
30 Diels–Alder reaction products in both aqueous and nonaqueous
salt solutions.11-13 Dissolved salts were also reported to influence
In the ionic crystals, as surface ions do not have its outer layer of
ions, the crystal surface is partially charged,23,
24
as shown
schematically by Figure S1 in Supplementary Information. The
50 partially charged ions or dipoles may affect some organic
reactions significantly. But the effect of solid salt particles on
organic reactions should be different from that in salt solutions.
To date, study of the effect of inorganic salts on organic reactions
is limited to their solutions. Whether the salt particles in organic
55 solvents affect organic reactions is unknown.
In this work, we studied the effect of suspended salt particles
in organic solvents on organic reactions for the first time. It was
found that NaCl, KCl, Na2SO4 and K2SO4 particles could
considerably accelerate Suzuki coupling reaction catalyzed by Pd
60 nanoparticles, which is a very powerful route for the formation of
C-C bond.25-27 Further study indicated that the partially charged
salt surface interacts strongly with the catalyst and the reactants,
which are the important reasons for the synergistic effect of the
catalyst and the salts.
monomolecular heterolysis reactions,14 nucleophilic substitution
16
reactions,15,
proton-transfer reactions in the 3,5-
dinitrohydroxybenzoic acid/ammonia system,17 Wittig reaction
35 on water,18 solvolysis reaction,19 the reaction of Glc with amino
acids and peptides,20 etc. Generally, the effect of salt in solution
on organic reactions are attributed to the influence of ions on
hydrophobic packing, solvent pressure, hydrogen bonding,
65
Experimental
Materials: Bromobenzene, phenylboronic acid, 4-
bromonitrobenzene, 4-bromotoluene, di-n-butyl ether, potassium
hydroxide were all analytical grade and were purchased from
70 Alfa Aesar China Co., Ltd. Sodium chloride, sodium sulfate,
potassium chloride, potassium sulfate, benzene, and toluene were
analytical grade and were provided by Beijing Chemical Reagent
Company. The catalyst Pd/C was purchased from Baoji Rock
Pharmachem Co., Ltd., China (5 wt% Pd, Product No. D5L3),
hydrophobic hydration, and salting-out and salting-in effects,
11, 21
Recently, NaCl aqueous solution are reported to
40 etc.3,
improve depolymerization of cellulose catalyzed by organic acid
because the salt in the solution enhances the disruption of the
hydrogen-bond matrix among cellulose fibers.22
This journal is © The Royal Society of Chemistry [year]
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DOI: 10.1039/C3GC42088D
which had a BET surface area of 1202 m2•g-1 and a pore volume
Scheme 1. Suzuki coupling reaction of bromobenzene and phenylboronic acid.
of 0.82 cm3•g-1，and the detailed characterization of the catalyst
was provided previously.28 For all the salts, the particles between
40 and 50 meshes were used in the reactions.
55
We studied the effect of the salts on Suzuki coupling reaction
in di-n-butyl ether, and the reactions of other substrates in toluene,
and the results are presented in Table 1. To show the effect of the
salts clearly, the experiments were conducted in a shorter time
with low conversion. The data in the table illustrates that the salt
5
Suzuki coupling reactions: As an example, Suzuki coupling
reaction of bromobenzene and phenylboronic acid is described
because other reactions were similar. In a typical experiment,
bromobenzene (2 mmol), phenylboronic acid (2.5 mmol), KOH
(8 mmol), Pd/C (0.7 mol % relative to bromobenzene), inorganic
60 particles could also accelerate the reactions of the substrates
considerably in different solvents although the extents of the
effect in different solvents are different.
10 salt, and solvent (6 mL) were charged into a flask of 50 mL
equipped with a magnetic stirrer and a reflux condenser. The
reaction mixture was stirred at 100 oC for 1 h. After the reaction,
the reaction mixture was cooled to room temperature. Then
inorganic salt and the catalyst were removed by centrifugation.
15 The quantitative analysis of the reaction mixture was conducted
using a gas chromatography (GC, Agilent 6820) equipped with a
flame ionization detector (FID) and a PEG-20M capillary column
(0.25 mm in diameter, 30 m in length) using benzene as the
internal standard. Identification of the products and reactant was
20 done using GC-MS (SHIMADZU-QP2010) as well as by
comparing the retention times of the standards in GC traces
100
NaCl
Na SO
2
4
90
80
70
60
50
40
KCl
K SO
2
4
X-ray photoelectron spectroscopy (XPS): To prepare the
Pd/KCl sample, PdCl2 (0.2 g) and NaCl (4 g) were mixed and
o
grinded. The mixed powder was then calcined at 800 C in a
No Salt(43.5%)
25 quartz tube under Argon protection. The prepared PdCl2/KCl
solid was then grinded to power, followed by reduction in the
o
flow of hydrogen at 150 C. To prepare the corresponding Pd
0
1
2
3
Salt (g)
4
5
6
Figure 1. Effect of salts on Suzuki coupling reaction of bromobenzene and
65 phenylboronic acid. Reaction conditions: 2.0 mmol bromobenzene, 2.5 mmol
phenylboronic acid, 6 mL solvent, 8.0 mmol KOH, Pd/C (5 wt%, 0.7 mol% Pd
relative to bromobenzene), 100 oC, 1 h. Yields were determined by GC analysis with
benzene as an internal standard.
particle, the Pd/KCl was washed to remove KCl. The X-ray
photoelectron spectroscopy data were obtained with a Thermo
30 ESCALAB250 Xi electron spectrometer from VG Scientific
using 300W AlKα radiation. The base pressure was about
1.68×10-9 mbar. The binding energies were referenced to the C1s
line at 284.8 eV from adventitious carbon.
Table 1. Acceleration of Suzuki coupling reaction by inorganic salts a
FT-IR study of reactant/salt interaction:
1 µL of
Entry
1
Substrate
Solvent
Salt/g
0
Yieldb/%
10.9
35 bromobenzene was dropped on a sodium chloride plate of 13 mm
in diameter and 0.5 mm in thickness, which was prepared at 10
MPa. The FT-IR spectrum of the as prepared sample was
recorded on a BRUKER TENSOR27 instrument with the sodium
chloride plate as background.
Bromobenzene
Di-n-butyl ether
2
3
4
5
6
7
8
9
Bromobenzene
Bromobenzene
Di-n-butyl ether
Di-n-butyl ether
Di-n-butyl ether
Di-n-butyl ether
Toluene
Na2SO4/6
NaCl/6
KCl/6
K2SO4/6
0
21.7
24.7
14.8
21.4
78.4
99.1
31.6
58.6
40 2. Results and Discussion
We carried out the Suzuki coupling reaction of bromobenzene
and phenylboronic acid (Scheme 1) in toluene with and without
NaCl, KCl, Na2SO4 and K2SO4 particles. The characterization of
the commercial Pd/C catalyst used was provided in detail in our
45 previous paper.28 Toluene was used as the solvent in order to
avoid dissolution of the salts, and the results are shown in Figure
1. No by-product was detected in the reaction. For all the salts,
the yield of the product increased steadily with the amounts of the
salts, and their effects follow the order of Na2SO4>KCl>NaCl≈
50 K2SO4. Our experiments showed that without the catalyst (Pd/C),
the inorganic salts themselves could not catalyze the reaction,
indicating the synergistic effect of the catalyst and the salts.
Bromobenzene
Bromobenzene
4-Bromonitrobenzene
4-Bromonitrobenzene
4-Bromotoluene
4-Bromotoluene
Toluene
NaCl/6
0
Toluene
Toluene
NaCl/6
a
70 Reaction conditions: 2.0 mmol halobenzene, 2.5 mmol phenylboronic acid, 6 mL
solvent, 8.0 mmol KOH, Pd/C (5 wt%, 0.7 mol% Pd relative to halobenzene), 100
2
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DOI: 10.1039/C3GC42088D
b
oC, 1 h. Yields were determined by GC analysis with benzene as an internal
Figure 3. The Pd 3d 5/2 peaks in XPS spectra of the Pd/KCl (Pd: KCl mass ratio=1:
33) and the corresponding Pd prepared by removing KCl from Pd/KCl.
standard.
We also studied the interaction between bromobenzene and the
salts using FT-IR methods. Figure 4 shows the FT-IR spectra of
35 the bromobenzene with and without NaCl. The typical
unsaturated C-H stretching vibration bands are in the range of
3000-3100 cm-1.35 However, the bands shifted to the range of
2850-3000 cm-1 after adsorbed on NaCl surface, indicating
considerable interaction between bromobenzene and the salt. This
40 may result from the electron-donating effect of the partial
negative charges on the salt surface to the bromobenzene
molecules adsorbed (Figure 2).
The reaction mechanism of Suzuki coupling reaction has been
26
studied extensively, which can be expressed by Figure 2.25,
5
Suzuki reaction consists mainly of three steps, which are
oxidative addition, transmetalation and reductive elimination.
Generally, the oxidative addition step is believed to be the rate-
determining step.25,
29
For Pd-catalyzed Suzuki reaction, many
ligands containing phosphorus and nitrogen atoms have been
10 used to increase the electron density of Pd, which can accelerate
the oxidative addition step, and improves the reaction rate.30-32 In
order to study the reasons for the salts to enhance the reactions,
we investigated the interactions of the species in the reaction
system, which are discussed in the following.
Bromobenzene
Bromobenzene+NaCl
2959
3004
2852
2923
3079
3067
3200 3100 3000 2900 2800
-1
15
Figure 2. Suzuki coupling reaction of bromobenzene and phenylboronic acid.
cm
We investigated the interaction between the catalyst Pd and the
salts using XPS method. The XPS spectra (Figure 3) showed that
Pd 3d 5/2 peaks of the Pd/KCl, and corresponding Pd particle
20 were 335.18 eV and 335.72 eV, respectively. This indicates that
the salt particles could reduce binding energy of Pd through
electron-donating effect of the negative charges at the salt surface.
In the reaction, the anions at the surface of the solid salt particles
acted as electron donors for Pd, which increased the electron
25 density of Pd. This effect could promote the oxidative step to
form intermediate Ph-PdII-Br (a) (Figure 2). Therefore, the
reaction is accelerated because this is the rate determining step. In
other words, the electron-donation effect could enhance the
activity of the catalyst through increasing electron density of Pd.
Figure 4. FT-IR spectra of the neat and adsorbed bromobenzene. The spectrum of
45 the neat bromobenzene was measured with liquid bromobenzene in a ZnS cuvette;
The spectrum of the adsorbed bromobenzene was measured with a very small
amount of bromobenzene absorbed in a pellet of NaCl, and the background was
measured with the same empty pellet of NaCl.
Conclusions
50 In summary, the NaCl, KCl, Na2SO4 and K2SO4 particles and Pd
catalyst in organic solvents have excellent synergistic effect for
promoting Suzuki coupling reactions. The interactions of the
partially charged salt surface with the catalyst and reactants are
the main reasons for the effects. This green method to enhance
55 the reaction efficiency has potential applications. We believe that
utilization of non-toxic, cheap, and abundant salt particles as
additives can also be used to enhance the rate and/or selectivity of
some other reactions, which provides a simple methodology to
develop new and greener reaction routes.
335.18
Pd/KCl
Background
60 Acknowledgement
The authors thank the National Natural Science Foundation of
China (21003133, 20932002, 21173234, 21021003), and the
Chinese Academy of Sciences (KJCX2.YW.H30).
344
342
340
338
336
334
Pd prepared by removing KCl from Pd/KCl
Background
Notes and references
335.72
336
65 Beijing National Laboratory for Molecular Sciences
CAS Key Laboratory of Colloid and Interface and Thermodynamics, Institute of
344
342
340
338
334
30
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Chemistry Chinese Academy of Sciences, Beijing, China. Fax: 86-10-62559373
E-mail: Hanbx@iccas.ac.cn
;
† Electronic Supplementary Information (ESI) available: [Structure of
NaCl crystal surface]. See DOI: 10.1039/b000000x/
5
10
15
20
1
2
3
4
T. V. Pham, K. C. Westaway, Can. J. Chem. 1996, 74, 2528.
J. F. Blake, W. L. Jorgensen, J. Am. Chem. Soc. 1991, 113, 7430.
A. Kumar, Chem. Rev. 2001, 101, 1.
S. Alunni, A. Pero and G. Reichenbach, J. Chem. Soc., Perkin Trans.
2 1998, 1747.
5
P. Jones, R. Harrison and L. Wynne-Jones, J. Chem. Soc. Perkin
Trans. 2 1979, 1679.
6
7
M. J. Pregel, E. Buncel, J. Am. Chem. Soc. 1993, 115, 10.
L. Huang, H. Jiang, C. Qi and X. Liu, J. Am. Chem. Soc. 2010, 132,
17652.
8
9
P. A. Grieco, J. J. Nunes and M. D. Gaul, J. Am. Chem. Soc. 1990,
112, 4595.
K. Mukai, M. Oi, A. Ouchi and S. Nagaoka, J. Phys. Chem. B 2012,
116, 2615.
10 A. Kumar, S. S. Pawar, Tetrahedron 2003, 59, 5019.
11 D. Sarma, A. Kumar, Org. Lett. 2006, 8, 2199.
12 A. Kumar, U. D. Phalgune and S. S. Pawar, J. Phys. Org. Chem.
2001, 14, 577.
25 13 V. D. Kiselev, A. V. Bolotov, H. A. Kashaeva, L. N. Potapova, I. I.
Shakirova and A. I. Konovalov, Fluid Phase Equilibr. 2011, 312, 1.
14 G. F. Dvorko, E. A. Ponomareva and N. E. Ponomarev, Russ. J. Gen.
Chem. 2006, 76, 1368.
15 K. C. Westaway, Y. Gao and Y. R. Fang, Org. Chem. 2003, 68, 3084.
30 16 M. J. Pregel, E. Buncel, J. Chem. Soc., Perkin Trans. 2 1991, 307.
17 A. Sánchez, A. García-Santana and M. Galán, J. Phys. Chem. A 1998,
102, 7931.
18 S. Tiwari, A. Kumar, Chem. Commun. 2008, 4445.
19 L. C. Manege, T. Ueda and M. Hojo, Bull. Chem. Soc. Jpn. 1998, 71,
35
589.
20 K. Yamaguchi, Y. Noumi, K. Nakajima, C. Nagatsuka, H. Aizawa,
R. Nakawaki, E. Mizude, Y. Otsuka, T. Homma and N. V. Chuyen,
Biosci. Biotechnol. Biochem. 2009, 73, 2379.
21 R. Breslow, Acc. Chem. Res. 1991, 24, 159.
40 22 T. vom Stein, P. Grande, F. Sibilla, U. Commandeur, R. Fischer, W.
Leitner and P. D. de María, Green Chem. 2010, 12, 1844.
23 H. Lyklema, Solid-liquid lnterfaces. In Fundamentals of Interface
and Colloid Sciences, 1st ed.(Ed: J. Lyklema), Academic Press:
London, England, 1995.
45 24 K. Sangwal, Additives and Crystallization Process: From
Fundamentals to Applications, 1st ed.; John Wiley & Sons:
Chichester, England, 2007.
25 N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457.
26 C. Amatore, A. Jutand and G. Le Duc, Chem. Eur. J. 2011, 17, 2492.
50 27 A. Balanta, C. Godard and C. Claver, Chem. Soc. Rev. 2011, 40,
4973.
28 H. Z. Liu, T. Jiang, B. X. Han, S. G. Liang and Y. Zhou, Science
2009, 326, 1250.
29 V. Favina, V. Krishnamurihy and W. J. Scott, The Stille Reaction in
55
Organic Reactions, John Wiley & Sons: New York, Vol. 50, 1997.
30 K. Matos, J. A. Soderquist, J. Org. Chem. 1998, 63, 461.
31 T. E. Barder, S. D. Walker, J. R. Martinelli and S. L. Buchwald, J.
Am. Chem. Soc. 2005,127, 4685.
32 T. Fujihara, S. Yoshida, H. Ohta and Y. Tsuji, Angew. Chem. Int. Ed.
2008, 47, 8310.
60
33 M. A. Aramendía, V. Boráu, I. M. Garcıa, C. Jiménez, J. M. Marinas
and F. J. Urbano, Appl. Catal., B 1999, 20, 101.
34 P. Y. Bruice, Organic chemistry, 4th ed.; Prentice-Hall: Upper Saddle
River, NJ, 2004.
65 35 L. G. Wade, Organic Chemistry, 5th ed.; Prentice-Hall: Upper Saddle
River, NJ, 2003.
4
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