Efficient tandem aqueous room temperature oxidative amidations catalysed by supported Pd nanoparticles on graphene oxide

Article abstract of DOI:10.1039/c5cy01596k

Pd nanoparticles deposited onto graphene oxide nanosheets (SE-GO/Pd_NPs) were found to successfully promote two oxidative processes for the synthesis of amides, providing alternative possibilities to these important compounds. SE-GO/Pd_NPs exhibited excellent activities with an optimum efficiency in tandem one-pot conversion of alcohols to amides in the presence of various amines.

Full text of DOI:10.1039/c5cy01596k

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Efficient tandem aqueous room temperature oxidative amidations catalysed by supported
Pd nanoparticles on graphene oxide
Sadegh Rostamnia,a,* Esmail Doustkhah,a,b Habib GolchinꢀHosseini,a Behzad Zeynizadeh,b,*
Hongchuan Xin, c,* Rafael Luque d
a
Organic and Nano Group (ONG), Department of Chemistry, Faculty of Science, University of
Maragheh, PO Box 55181ꢀ83111, Maragheh, Iran. Email: rostamnia@maragheh.ac.ir;
srostamnia@gmail.com
b
Department of Chemistry, Faculty of Science, Urmia University, Urmia 57159ꢀ165, Iran.
Email: bzeynizadeh@gmail.com
cKey Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology,
Chinese Academy of Sciences, Qingdao 266101, China. Email: xinhc@qibebt.ac.cn
d
Departamento de Quimica Organica, Universidad de Cordoba, Edificio Marie Curie, Ctra
Nnal IV, Km 396, Eꢀ14014, Cordoba, Spain. Eꢀmail: q62alsor@uco.es; Fax: +34 957212066;
Tel:+34 957211050
Abstract: Pd nanoparticles deposited onto graphene oxide nanosheets (SEꢀGO/PdNPs) were
found to successfully promote two oxidative processes for the synthesis of amides, providing
alternative possibilities to these important compounds. SEꢀGO/PdNPs exhibited excelling
activities with an optimum efficiency in tandem oneꢀpot conversion of alcohol to amides in the
presence of various amines.
Keywords: Oxidative amidations; tandem oxidation; SEꢀGO/PdNPs; graphene oxide (GO);
surfactant exfoliated GO.
1

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Introduction
Heterogeneous catalysts possess inherent advantages as compared to homogeneous
catalysts including recyclability, easy workꢀup and consequently cleaner and often also greener
reaction workup [1]. Importantly, the use of recyclable heterogeneous catalytic systems may be
easier implemented in industrial scale, especially in continuous flow processes [2]. The stability
and activity of certain heterogeneous catalysts can be however compromised by reaction
conditions (i.e. temperature, pressure, acidic media) for which these critical parameters needs to
be carefully designed/controlled in a catalytic process [3]. Nanotechnology and nanocatalysis
opened up a new concept in heterogeneous catalysis in which the design of
nanomaterials/nanocatalysts based on nanoparticles is able to provide highly active and stable
catalysts for a number of chemistries due to the excelling properties of some of the catalyst
active sites in the nanoscale (i.e. enhanced selectivity and activities) [4].
Amide functionalities are ubiquitously present in a large number of organic compounds,
polymers, natural and pharmaceutical compounds. Synthesis of amides using conventional
protocols (i.e. reactions of acyl halides or anhydrides with and amines) could be inconvenient
especially in larger scales or in a total synthetic approach. While alternative methods have been
considered in recent years [5], oxidative amidations have provided considerable advances in the
field in recent years. Advantages of these protocols include a simple and costꢀcompetitive
method based on cheap and available starting materials [6]. A range of homogeneous catalysts
for efficient syntheses of amides have been recently developed [7ꢀ10]. However, these catalysts
are generally not heterogeneous and recyclable. A recent copper grafted SBAꢀ15 was reported as
an efficient catalyst for synthesis of primary amides via a Beckmannꢀtype rearrangement of
oximes [11]. Due to the fact that basic media is not suitable for SBAꢀ15ꢀtype materials, we
2

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aimed to turn our attention to the synthesis of secondary and tertiary amides via a tandem green
oxidativeꢀamidation using Pd nanoparticles supported on graphene oxide as a robust and stable
carbonꢀbased nanosheet support (surfactant exfoliated Pdꢀsupported graphene oxide,
SEꢀGO/PdNPs).
Tandem methods for oxidative amidation reactions directly from alcohols can be
appealing pathways to decrease the consumption of organic compounds, synthetic costs as well
as avoiding tedious and complex synthetic methods. In this regard, Milstone and coꢀworkers
found that the reaction of primary amine and alcohols generates amide and molecular hydrogen
with the use of ruthenium based complexes [12]. Also, Kobayashi and coꢀworkers reported Au
nanoparticles and Auꢀsupported systems as heterogeneous catalysts for the tandem synthesis of
various types of aliphatic, aromatic and cyclic (lactame) amides directly from alcohols under
aerobic conditions [13ꢀ15]. The same group also found that the gold nanoparticle size possessed
different catalytic effects while most interestingly appropriate particle sizes could directly
convert alcohols to amides in the presence of amines under aerobic conditions [16].
The design new or develop Pd decorated heterogeneous nanocatalysts has been one of the
major interests from our groups [17ꢀ21]. Pd based nanocatalysts are generally used in coupling
chemistries [22ꢀ24]. However, there are few reports on oxidative amidations catalyzed by
palladiumꢀbased catalysts which generally suffer from nanoparticle aggregation and catalyst
deactivation in each run [25ꢀ27]. Recently palladium supported graphene oxide (Pd/GO)
synthesized by reduction of Pd ions on the surface of GO was reported to be an efficient,
recyclable and convenient catalytic system for a range of heterogeneously catalysed reactions
[28ꢀ31]. This is due to suitable interaction of Pd species with carbon based structures [32, 33].
However, GO and Pd/GO nanosheets tend to selfꢀassembly in relatively higher concentrations
3

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and temperatures especially in aqueous media. Recently, we have established the study of GO
and Pd/GO exfoliation by surfactant and catalytic activity in the presence of surfactants. The
addition of a surfactant during Pd/GO catalysed reaction can provide remarkable improvements
and activation of catalytic sites by exfoliation of the GO sheets [34].
In this work, we aim to report the excelling catalytic activity of Pd/GO in the presence of
different surfactants for various types of oxidative amidation reactions, namely two approaches.
Secondary and tertiary amides were produced from oxidative reactions of aldehydes and various
amines (Figure 1, Method A) as compared to a tandem method from in situ production of
aromatic aldehydes from benzylic alcohols followed by reaction with amines (Figure 1, Method
B). Method B is a promising strategy to directly convert alcohols to amides in a oneꢀpot
approach [27, 35, 36]. In spite of previous reports employing homogeneous palladium catalysts
and/or Pdꢀcontaining homogeneous metal mixtures, this is the first report of Pd supported NPs in
oxidative amidation reactions.
Figure 1. Schematic illustration of our work.
4

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Results and discussion
SEM and TEM images of the synthesized GO/PdNPs showed that Pd nanoparticles are uniformly
dispersed on the surface of GO nanosheets. The estimated average particle size of deposited
PdNPs by SEM and TEM is around 21ꢀ22.5 nm (Fig. 2 and Fig. 3). The particle size histogram of
GO/PdNPs shows that particle size ranged from 18 nm to 34 nm (Fig. 2b and Fig. 3b).
Figure 1. SEM images of (a) PdNPsꢀGO and (b) particle size histogram.
FTꢀIR spectra of GO shows two distinct peaks at 598 and 1637 cmꢀ1, and a broad band ranging in
3300ꢀ3600 cmꢀ1 (related to ꢀOH of surface). After reduction of Pd2+ ions on the surface of rGO,
relative functional groups for both GO and rGO can be seen. However, the XRD analysis proves
that the final structure of graphene is GO (supporting information).
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Figure 2. TEM images of (a) PdNPsꢀGO and (b) particle size histogram.
Fig. 4 shows the XRD patterns of rGO, 7th reused PdNPsꢀGO and EDX of PdNPsꢀGO (see also Fig.
1). In Fig 4a a wide peak at 2θ = 24o could be assigned to rGO sheets [37] and for PdNPsꢀGO, a
peak around 2θ = 11 ° assigned to GO sheets in Fig 4a, which in that the wellꢀdefined peaks
around 39°, 44° can be assigned to (111) and (200) crystal planes of Pdꢀnanoparticle. EDX
analysis was performed to confirm the composition of the asꢀprepared products (Fig. 4b). The
EDX analysis, the elemental analysis, confirms the existence of elements Pd, C and O in PdNPs
ꢀ
GO.
Figure 3. XRD patterns of (a) rGO, PdNPsꢀGO and 7th reused of PdNPsꢀGO. SEMꢀEDX of
PdNPsꢀGO.
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Catalysts were then explored in the oxidative amidation reactions in the presence of H2O2
(30%). All reactions were optimized using benzaldehyde and aniline as model reaction (Table 1).
In method A, we attempted to engage our catalytic system to synthesize benzanilide. Various
conditions were taken to account to find out optimized conditions. Several parameters including
surfactant, base, solvent and reaction time and temperature were examined in this optimization.
For this catalyst, we chose four types of surfactants to exfoliate PdNPsꢀGO sheets during the
catalysis, which includes cetyltrimethylamonium bromide (CTAB), sodium dodecylsulfate
(SDS), and a triblock copolymer of P123 and F127. The only difference between P123 and F127
is in the number of monomers, ethylene oxideꢀpropylene oxideꢀethylene oxide (EOꢀPOꢀEO). The
number of each monomers are higher than P123. In our prediction, F127 due to longer chain,
better exfoliation could be seen for both exfoliation and reaction catalysis. However in spite of a
better exfoliation from F127, a lower catalytic activity was observed towards production of
amide. It seems that, wellꢀexfoliation of GO/Pd is not the mere reason for higher catalytic
activity in the presence of P123. These three surfactants were compared in the oxidative
amidation of benzaldehyde and aniline under the similar conditions. Based on this study, P123
was a suitable agent for exfoliation of GO/PdNPs (Fig. 5).
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Figure 4. Effect of surfactant type and amount on the catalytic activity of GO/PdNPs in oxidative
amidation: benzaldehyde (1 mmol), aniline (1.5 mmol), H2O2 (4 mmol) in 3 mL of Pd/GO suspension
(1 mol% of Pd, 2 g/100 mL of solution) at room temperature during 15 h.
After selection of a suitable P123, we extended our catalytic (SEP123ꢀGO/PdNPs) system to two
types of oxidative amidation reactions. Scheme 1 indicate a general route to manufacture and use
of catalyst in the amidation syntheses. In recent method, as shown in Table 1, we attempted to
extend the catalytic capability of SEP123ꢀGO/PdNPs for the synthesis of benzanilide from
benzaldehyde and aniline in the presence of oxidant. Several bases including sodium carbonate,
potassium carbonate, potassium phosphate and triethylamine were also selected to investigate the
base effect on the reaction. Accordingly, a better result was matched with potassium carbonate.
Among various oxidants such as H2O2, SeO2, MnO2, etc., the H2O2 was selected thanks to its
availability, lower price and lower side products of H2O2 (Table 1).
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Table 1. Investigation of SEꢀGO/PdNPs in the presence of various types of oxidants and
surfactants. a
Entry
Surfactant
Cat.
suspension b
3 mL
Time oxidant
(h)
T
(oC)
25
25
25
25
25
25
25
25
25
Yield
(%)
75
62
76
74
81
40
30
1
2
3
4
5
6
7
8
9
CTAB
CTAB
SDS
15
15
15
15
15
15
15
15
18
H2O2
SeO2
3 mL
3 mL
6 mL
3 mL
6 mL
9 mL
1 mL
3 mL
MnO2
H2O2
H2O2
DDQ
NaClO
H2O2
H2O2
SDS
F127
F127
P123
P123
P123
80
90
a Reaction conditions: benzaldehyde (1 mmol), aniline (1.5 mmol), oxidant (4 mmol) and
GO/PdNPs (variant mol% of Pd) in 3 mL H2O at room temperature in specific time. b mL of asꢀ
prepared SEꢀGO/PdNPs suspension and 0.03 g surfactant at room temperature.
Solvent studies for oxidative amidation from benzaldehyde and aniline were also conducted
(Fig. 6). The use of water as solvent provided improved product yields which can be attributed to
a good exfoliation of Pd/GO in the water/P123 system. Another reason can be related to
polymeric nature of P123 which acts as a spectator species during the reaction which cause to
produce an excellent media for reactants. Therefore, this examination led to disclose water as a
good solvent for P123 to exfoliate the Pd/GO/P123 and interconnect aqueous and organic phases.
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Figure 5. Study of solvent effect; reaction conditions: benzaldehyde (1 mmol), aniline (1.5
mmol), H2O2 (4 mmol) and 3 mL of asꢀprepared SEP123 GO/PdNPs suspension (1 mol% of Pd) in 5 mL
ꢀ
solvent at room temperature during 15 h.
In this investigation, the reaction at room temperature during 18ꢀ20 h proceeded with convenient
results. These conditions were chosen as an optimized pathway to synthesize other derivatives of
amides (Table 2).
Table 2. Scope of amines.a
yrtnEa
1
enimA
imAde
Conversion (%)
97
T (h)
18
deiYb (%)
90
24
74
95
2
10

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18
92
97
3
4
24
18
84
82
95
97
5
6
24
76
86
a
Reaction conditions: reactions were performed by benzaldehyde (2 mmol), amine (3 mmol), H2O2 (4
mmol), 3 mL of asꢀprepared SEP123
conditions; b isolated yields.
ꢀGO/PdNPs (1 mol% of Pd) suspension at room temperature in aqueous
After testing this catalytic system under the optimized conditions in the oxidative amidation of
benzaldehyde with various types of aromatic amines, other kinds of aldehyde including aromatic
and aliphatic ones were reacted with different types of amines even with secondary aliphatic
amine (Table 3). All products were obtained in good yields with high selectivity. This study
revealed that electron donating substituents on the aromatic ring of amine lead to higher yields of
amide. On the other side, aliphatic aldehyde showed relatively lower activity towards oxidative
amidation.
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Table 3. Synthesis of amides with various types of aldehydes through oxidative amidation. a
T (h)
20
deiYb (%)
62
yrtnE
R
enimA
Conversion
84
1
CH3
85
18
66
2
3
4
CH3
Phꢀ
18
18
84
76
93
95
pꢀPhꢀNO2
5
6
pꢀPhꢀNO2
Phꢀ
90
87
18
20
81
77
a Reactions were performed by benzaldehyde (1 mmol), amine (1.5 mmol), H2O2 (4 mmol), 3 mL
of asꢀprepared SEP123
GO/PdNPs suspension (1 mol% of Pd) at room temperature; b isolated yields.
ꢀ
The reactivity of less active amines (e.g. diphenylamine) with aliphatic and aromatic aldehydes
(i.e. acetaldehyde and benzaldehyde, respectively) under identical reaction conditions was
studied. Aromatic aldehydes were observed for be more active as compared to aliphatic
aldehydes (Scheme 1).
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Scheme 1. Reactivity comparison of aromatic and aliphatic aldehyde in the amidation with
diphenylamine.
In the optimization of reaction conditions for tandem synthesis of amides from benzyl
alcohol, we also substituted some other solvents both for studying exfoliation effect and solvent
effect on reaction of reactants under the similar conditions. Likewise, it was found that
water/P123 was a good pair for the reaction progress at room temperature. Once, we found that
SEP123
ꢀGO/PdNPs is good catalytic system, and following to our previous experience on the oxidative
activity of SEP123
ꢀ
GO/PdNPs in the oxidation of alcohols [3 ], we promoted this system to a tandem
3
synthesis of amides starting from alcohols in oneꢀpot conditions (Table 4). This investigation led to
formation of amide from a consecutive oxidation of alcohol to aldehyde and then oxidation to amide
formation via amine in oneꢀpot conditions. In the first oxidation step, aromatic aldehydes, specifically
those have electron withdrawing groups, were more active to be oxidized.
Recyclability studies of SEP123ꢀGO/PdNPs were subsequently investigated. Reuse studies
demonstrated an extraordinary recyclability of the catalyst up to 9 reaction runs (Figure 7) with
an almost unchanged catalytic activity (<20% activity loss) as compared to the fresh catalyst.
Based on atomic absorption spectroscopy (AAS) results, there was no evidence to confirm that
significant Pd leaching happened after 9 runs for each method. However, continued reaction runs
demonstrated that the catalyst exhibited a continuous loss of catalytic activity after 9 reuses.
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Table 4. Tandem oxidative amidation of benzylic alcohols. a
T1 (h)
2
T (h)
18
Yield b (%)
82
yrtnE
1
R
enimA
Conversion (%)
Phꢀ
90
87
2
2
18
18
70
84
2
Phꢀ
3
4
5
Phꢀ
CH3
Phꢀ
92
2
2
20
18
64
73
80
77
2
18
74
6
Phꢀ
87
7
8
Phꢀ
Phꢀ
2
2
18
18
18
77
62
71
92
94
9
pꢀPhꢀNO2
pꢀPhꢀNO2
Phꢀ
1.5
91
94
77
10
11
1.5
2
18
20
74
69
a
Reaction conditions: benzaldehyde (1 mmol), amine (1.5 mmol), 5 mL of asꢀprepared SEP123
GO/PdNPs suspension (1.7 mol% of Pd); b isolated yields.
ꢀ
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Figure 6. Recyclability of both methods under their optimized conditions.
Due to the fact that there are few reports for these reactions with palladium and we have not
investigated the exact mechanism of amidations, we can also speculate two types of possible
mechanism for these processes. On the other hand, there are some similar reports that can
reinforce our proposed mechanisms [25, 34, 38]. Scheme 2 indicates the possible pathways to
amide production. The presence of imine formation as an intermediate during the reaction (and
the fact that the reaction also seems to work with imines as substrates) seems to point out the
pathway A as main reaction mechanism. However, Path B and the reaction taking place from
carboxylic acids (not mentioned in Scheme 2) cannot be ruled out in the formation of the final
products.
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O
[O]
Ar
Path A
N
[O]
[O]
Ar
N
R
H
H
R
OH
O
R-NH2
+
+
Ar
H
Ar
H
OH
Path B
R
O
Ar
N
H
R
Ar
N
method A
H
method B
Scheme 2. Proposed mechanisms for oxidative amidations [41].
Our proposed approach was finally compared with other previously reported strategies of
oxidative amidations either from alcohol or benzaldehyde, in which the catalysts are Pdꢀbased,
Cuꢀ and Ruꢀbase or even metalꢀfree (Table 5). The main advantages of our method rather to
others are the recyclability of the catalyst, the use of no ligand, green chemical procedure, and
low mol percent of Pd in each reaction which have made the presence method superior to others
[39ꢀ44].
Table 5. Comparison of the presence method in oxidative amidation with previously published
methods.
Metal
PdCl2 (2.5 mol%)
Au/Pd/resin
Ligand
Xantphos (2.5 eq)
Oxidant
H2O2ꢀUrea
O2
Conditions
20 h/ MeOH/CH3CN/50 oC
NaOH/ 25ꢀ40 oC/
%Yield [Ref]
> 86[25]
ꢀ
49ꢀ99[27]
61ꢀ88[40]
CuI (2ꢀ20 mol%)
2ꢀpyrimidonate (4
Open air
Toluene/reflux/20 h
mol%)
CuSO4.5H2O (5
mol%)
CuI/AgIO3
[Ru(pꢀcymene)Cl2]2
(2.5 mol%),
[Ru(benzene)Cl2]2 (2.5
mol%)
ꢀ
TBHP
CaCO3/MeCN/rtꢀ60 oC/6ꢀ24
h
> 96[41]
TꢀHYDRO®
NHC carbene
precursor (5 mol%)
tꢀBuOOH
CaCO3/MeCN/40 oC/6h
NaH (15 mol%), and
pyridine (5 mol%) in
toluene at reflux for 36 h
39ꢀ91[42]
19ꢀ99[43]
ꢀ
ꢀ
RuH2(PPh3)4 (5 mol%)
Imidazolium ionic
NaH/toluene/reflux/24 h
THF/water/12 h/40 oC
r.t./ 18h/H2O
29ꢀ96[44]
liquid/MeCN
ꢀ
Supported AuNPs (1.5
mol%)
SEP123ꢀGO/PdNPs
suspension (1 mol%)
O2
10ꢀ97%[13]
H2O2
62ꢀ90 [This
work]
-
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Conclusion
A highly active, stable and reusable SEP123ꢀGO/PdNPs was synthesized using a straightforward
methodology and tested as efficient catalytic system in oxidative amidation reactions, providing
excellent yields to products for a wide range of substrates and two different methodologies
including a oneꢀpot alcohols conversion to amides. The catalytic system in this work was able to
oxidize aliphatic and aromatic alcohols for in situ production of aldehydes and then a further oxidative
amidation with various amines including electron withdrawing and releasing functions, and even with
secondary aliphatic amine. The proposed methodology has the potential to pave the way to the utilisation
of highly active and reusable supported Pd catalysts for more challenging oxidative/dehydrogenation
reactions that will be reported in due course.
Experimental
Catalyst synthesis and characterization
A novel strategy was devised to synthesize PdNPs supported on the surface of GO (Figure 8).
Firstly, graphite oxide powder was obtained via chemical oxidation of graphite according to the
method by Hummer et al. method and based on our previous experiences [45]. Briefly, graphite
was oxidized by treating with KMnO4 and NaNO3 in concentrated H2SO4 to form graphite oxide.
2 g of the obtained graphite oxide was then exfoliated to graphene oxide (GO) in 400 mL of
water under sonication for 2 h. The extent of exfoliation after sonication was measured by
conductivity (5900 S.cmꢀ1). NaBH4 (0.1 g in 4 mL methanol) was subsequently added to the
dispersion of GO under sonication and the mixture was further stirred for 15 min. The reductive
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behaviour of reduced GO (rGO) in the presence of Pd ions was then investigated. A solution of
PdCl2 (0.004 g in 10 mL water, 5 mL methanol and 3 drops of HCl) was added to dispersed rGO
(0.2 g in 10 mL water) under ultrasonic irradiation. The solution was centrifuged and washed
with methanol several times before analysis. The obtained TEM images indicate that Pd ions
were reduced to PdNPs by rGO while rGO itself was partially converted to GO (see supporting
information). The obtained Pd supported GO (PdNPꢀGO) was subsequently exfoliated using
Pluronics P123, a nonꢀionic surfactant, to generate the final SEP123ꢀGO/PdNPs. (Fig. 8) to be used
as catalyst [2 g PdNPꢀGO in 100 mL of related solution in the presence of P123 (0.6 g)], with a
palladium content of 1.86 wt% as measured by ICPꢀAES.
Figure 8. Preparation and application of SEP123ꢀGO/PdNPs
.
All reagents were purchased from Fluka, Sigmaꢀaldrich and Merck and used without further
purification. The physicochemical properties of PdNPs/GO nanomaterials were characterized
using FTIR spectroscopy (Shimadzu IRꢀ460 spectrometer), Xꢀray diffraction (XRD) (Philipsꢀ
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PW1800 diffractometer), scanning electron microscopy (SEM) (ZeissꢀDSM 960A microscope),
transmission electron microscopy (TEM) (Zeiss EM 900 electron microscope), and Xꢀray
analysis (EDX). A multiwave ultrasonic generator (Sonicator_3000; Misonix Inc., Farmingdale,
NY, USA), equipped with a converter/transducer and titanium oscillator (horn), 12.5 mm in
diameter, was operated as continuous irradiation with a maximum power output of 600 W.
Frequencies below 50 kHz are usually suitable for the heterogeneous systems due to the more
intense mechanical effects. Hence, we selected 19.6 kHz as optimum for sonication.
Oxidative amidation catalytic experiments
General procedure for the synthesis of secondary amides from aldehydes
In a typical reaction, benzaldehyde (1.0 mmol), aniline (1.5 mmol), H2O2 (4 mmol, 30%) and a
dispersion of asꢀprepared SEP123ꢀGO/PdNPs (5 mL) were added to a 25 mL round bottomed flask.
The reaction was allowed to stir at room temperature for 18 h. Upon reaction completion, the
catalyst was separated by centrifugation and the organic residue was extracted with ethyl acetate
and evaporated under reduced pressure. The final product was purified by column
chromatography.
General procedure for the one-pot synthesis of secondary amides
In a typical experiment, benzyl alcohol (1.1 mmol), 2 mmol of aqueous H2O2 (30%) and 5 mL of
asꢀprepared SEP123ꢀGO/PdNPs in water were added to a 25 mL round bottomed flask and allowed
to react at room temperature for 2 h, followed by the addition of 1.5 mmol of aniline and 4 extra
mmol of H2O2. The reaction was monitored during 18 h at room temperature. Upon reaction
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completion, the catalyst was separated by centrifugation and the organic residue was extracted
with ethyl acetate and evaporated under reduced pressure.
All synthesized amides in both methods are known and they were identified and characterized by
FTIR, 1H and 13C NMR spectroscopy. Some key spectral data have been included below:
Spectral data
o
1
N-Phenylbenzamide. White solid, Mp: 162ꢀ163 C. H NMR (CDCl3, 400 MHz) δ: 7.98 (s, 1
H), 7.80ꢀ7.06 (m, 10 H). 13C NMR (CDCl3, 100 MHz) δ: 165.71, 137.96, 135.09, 131.80,
129.09, 128.78, 127.00, 124.57, 120.21.
1
N,N-Diphenylbenzamide. H NMR (CDCl3, 400 MHz) δ: 7.494ꢀ7.172 (m, 15 H). 13C NMR
(CDCl3, 100 MHz) δ: 170.572, 143.985, 136.227, 130.090, 129.148, 129.059, 127.820, 127.497,
126.291.
N-(3-Chlorophenyl)-4-nitrobenzamide .1H NMR (CDCl3, 400 MHz) δ: 8.30ꢀ7.19 (m, 9 H). 13C
NMR (CDCl3, 100 MHz) δ: 161.08, 142.96, 136.803, 129.309, 128.259, 125.369, 124.100,
120.362, 116.894, 116.804, 116.520.
1
4-Nitro-N-phenylbenzamide. White solid, Mp: 214ꢀ216 °C. H NMR (CDCl3, 400 MHz) δ:
8.30ꢀ7.109 (m, 10 H). 13C NMR (CDCl3, 100 MHz) δ: 163.66, 154.68, 140.04, 138.31, 130.24,
128.27, 125.42, 124.12, 120.54.
1
N-(3-Chlorophenyl)benzamide. H NMR (CDCl3, 400 MHz) δ: 8.138 (s, 1 H), 7.75ꢀ7.13 (m, 9
H). 13C NMR (CDCl3, 100 MHz) δ: 166.11, 139.11, 134.66, 134.48, 132.07, 130.01, 128.78,
127.11, 124.61, 120.51, 118.40.
Phenyl(pyrrolidin-1-yl)methanone. Colorless liquid. 1H NMR (CDCl3, 400 MHz) δ: 7.44ꢀ7.301
(m, 5 H), 3.57 (t, J = 6.6 Hz, 2 H), 3.33 (t, J = 6.2 Hz, 2 H), 1.87 (t, J = 6.5 Hz, 2 H), 1.79 (t, J =
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13
6.2 Hz, 2 H). C NMR (CDCl3, 100 MHz) δ: 168.71, 136.30, 128.72, 127.21, 126.07, 45.13,
25.37.
1
Ethyl-2-(benzamido)benzoate. H NMR (CDCl3, 400 MHz) δ: 12.10 (s,1 H), 8.97ꢀ7.14 (m, 9
H), 4.45 (q, J = 1.8 Hz, 2 H), 1.45 (t, J = 1.8 Hz, 3 H) 13C NMR (CDCl3, 100 MHz) δ: 168.62,
165.70, 141.93, 135.02, 134.64, 131.84, 130.90, 128.76, 127.39, 122.51, 120.50, 115.54, 61.47,
14.18.
N-(4-Bromophenyl)acetamide. 1H NMR (CDCl3, 400 MHz) δ: 8.00 (s, 1 H), 7.461ꢀ7.281 (m, 4
13
H), 2.185 (s, 3 H). C NMR (CDCl3, 100 MHz) δ: 168.97, 138.34, 131.97, 121.35, 114.95,
24.47.
N-(4-Bromophenyl)benzamide. White solid, Mp: 198ꢀ200 °C. 1H NMR (CDCl3, 400 MHz) δ:
7.97 (s, 1H), 7.189ꢀ7.797 (m, 9H). 13C NMR (CDCl3, 100 MHz) δ: 168.14, 137.01, 134.86,
132.08, 128.88, 126.99, 121.69, 114.51.
N-(4-Hydroxyphenyl)benzamide. 1H NMR (CDCl3, 400 MHz) δ: 8.06 (s, 1 H), 8.04ꢀ7.18 (m, 9
H), 5.08 (s, 1 H) 13C NMR (CDCl3, 100 MHz) δ: 171.59, 158.62, 133.77, 130.21, 129.26,
129.04, 128.86, 128.59, 128.493.
N-(Pyridin-2-yl)benzamide. White solid, Mp: 80ꢀ82 °C. 1H NMR (CDCl3, 400 MHz) δ: 9.23
13
(br, 1 H), 8.47ꢀ7.09 (m, 9 H). C NMR (CDCl3, 100 MHz) δ: 173.04, 151.75, 149.30, 147.36,
138.79, 132.47, 129.31, 127.44, 119.87, 114.60. FTꢀIR (KBr, cmꢀ1) 1458, 1528, 1579, 1598,
3173.
N-Benzylbenzamide. White solid, Mp: 102ꢀ103 °C. 1H NMR (CDCl3, 400 MHz) δ: 8.11 (s, 1
H), 7.82ꢀ7.28 (m, 10 H), 4.64 (d, J = 5.63 Hz, 2 H). 13C NMR (CDCl3, 100 MHz) δ: 167.485,
138.28, 134.39, 131.533, 128.758, 128.572, 127.883, 127.565, 127.039, 44.097.
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N-Phenylacetamide. White solid, Mp: 113ꢀ115 °C. 1H NMR (CDCl3, 400 MHz) δ: 7.592ꢀ7.11
(m, 5 H), 2.18 (s, 3 H). 13C NMR (CDCl3, 100 MHz) δ: 168.43, 137.97, 128.95, 124.29, 119.97,
24.49.
o
1
N,N-Diphenylacetamide .White solid, Mp: 102ꢀ103 C. H NMR (CDCl3, 400 MHz) δ: 6.93ꢀ
13
7.31 (m, 10 H), 2.08 (s, 3 H). C NMR (CDCl3, 100 MHz) δ: 169.93, 143.13, 129.34, 121.00,
117.82, 23.83.
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Efficient tandem aqueous room temperature oxidative amidations catalysed by supported
palladium nanoparticles on graphene oxide
Sadegh Rostamnia, Esmail Doustkhah, Habib GolchinꢀHosseini, Behzad Zeynizadeh, Hongchuan Xin,
Rafael Luque
O
O
OH
Cat.[ox]
H
H2O2
Cat.[ox]
H2O2
R
R-NH2
+
R-NH2
Cat.[ox]
+
Ar
H
N
Ar
Ar
H
= SEP123ꢀGO/PdNPs
Single-pot
25