Ruthenium-Na2CO3-catalyzed one-pot synthesis of ring-hydrogenated carbamates from aromatic amines and organic carbonates under H2

Article abstract of DOI:10.1016/j.apcata.2014.09.013

A facile and efficient one-pot procedure for the synthesis of ring hydrogenated carbamates from aromatic amine and alkylene carbonate under H₂ gas pressure has been developed using a heterogeneous catalyst system comprising ruthenium and alkali metal carbonates. The effects of temperature, H₂ pressure, catalyst (types of loaded metal and their supports), molar ratio of substrate/catalyst, and solvent were also investigated. Among the alkali metal carbonates, the sodium carbonate was found as best promoter for nucleophilic attack and ring-opening (NARO) reaction and thus increased the yield of ring hydrogenated carbamate up to 88% when using Ru/C as ring hydrogenation (RH) catalyst. This catalyst system could be reused at least five times without signi?cant loss of activity, which makes this process cost-effective and eco-friendly.

Full text of DOI:10.1016/j.apcata.2014.09.013

Applied Catalysis A: General 487 (2014) 82–90
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Ruthenium-Na2CO3-catalyzed one-pot synthesis of
ring-hydrogenated carbamates from aromatic amines and organic
carbonates under H2
Vivek Mishraa, Jin Ku Choa, Seung-Han Shina, Young-Woong Suhb,
Hoon Sik Kimc, Yong Jin Kima,∗
a Green Process Material Research Group, Korea Institute of Industrial Technology, Chungcheongnam-do 331-822, Republic of Korea
b Department of Chemical Engineering, Hanyang University, Seoul 133-791, Republic of Korea
c Department of Chemistry and Research Institute of Basic Sciences, Kyung Hee University, Seoul 130-701, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 May 2014
Received in revised form 6 August 2014
Accepted 9 September 2014
Available online 17 September 2014
A facile and efficient one-pot procedure for the synthesis of ring hydrogenated carbamates from aromatic
amine and alkylene carbonate under H2 gas pressure has been developed using a heterogeneous catalyst
system comprising ruthenium and alkali metal carbonates. The effects of temperature, H2 pressure, cat-
alyst (types of loaded metal and their supports), molar ratio of substrate/catalyst, and solvent were also
investigated. Among the alkali metal carbonates, the sodium carbonate was found as best promoter for
nucleophilic attack and ring-opening (NARO) reaction and thus increased the yield of ring hydrogenated
carbamate up to 88% when using Ru/C as ring hydrogenation (RH) catalyst. This catalyst system could be
reused at least five times without significant loss of activity, which makes this process cost-effective and
eco-friendly.
Keywords:
Aromatic amine
Alkylene carbonate
Carbamate
© 2014 Elsevier B.V. All rights reserved.
Ring hydrogenation
Ruthenium catalyst
Sodium carbonate
1. Introduction
reddish yellow or pale yellow, hence they can be hardly used in
areas where the absence of coloration is an important requirement
Carbamates represent an important class of compounds which
find wide applications in various areas as pharmaceuticals, agro-
chemicals such as pesticides, herbicides, insecticides, fungicides
etc. and as intermediates in organic synthesis, protection of amino
group in peptide chemistry [1–3]. Conventionally, the carbamates
have been formed by the Curtius rearrangement [4,5], phosgena-
tion [6], reductive carbonylation [7–9], and oxidative carbonylation
[10] (Scheme 1). However, all are suffering from the use of the
extremely toxic and highly flammable chemicals, e.g., isocyanates,
phosgenes, and carbon monoxide. A direct incorporation of CO2
with amines and alcohols towards carbamate formation might be
considered as benign option [11–14], but not worthy for aromatic
amines because it is too weak base to be incorporated with CO2,
especially in the presence of alcohols and furthermore, most of aro-
matic amine derivatives deeply absorb visible light and are colored
[15].
To overcome this drawback and to provide a better alterna-
tive technique, we developed a very convenient one-pot synthetic
methodology to produce ring-hydrogenated carbamates from aro-
matic amines using H2 and organic carbonates as reactants.
To the best of our knowledge, this type of reaction has not
been previously reported elsewhere in terms of the formation
of ring-hydrogenated carbamate as a key product from aromatic
amine.
Organic carbonates is classified as a non-toxic, non-flammable
polar aprotic solvent and one of the most important green materials
as electrolytes for secondary batteries [16]. During the course of our
study on the catalytic ring hydrogenation (RH) of aromatic amines
(1) [17–20] to produce alicyclic amines (3), the in-situ generation
of 3 was found to be very effective for the nucleophilic attack at
the trigonal carbon of the carbonyl group of the PC (4) followed by
ring opening (NARO) towards carbamate formation [21–23] pro-
viding a suitable phosgene-free and non-yellowing synthetic route
in a single reactor system. Herein, we report a facile synthesis of
∗
Corresponding author.
E-mail addresses: yjkim2005@gmail.com, yjkim@kitech.re.kr (Y.J. Kim).
http://dx.doi.org/10.1016/j.apcata.2014.09.013
0926-860X/© 2014 Elsevier B.V. All rights reserved.

V. Mishra et al. / Applied Catalysis A: General 487 (2014) 82–90
83
Scheme 1. Formation of carbamates using conventional and new methodology.
alicyclic carbamate such as HPCC from aromatic amine, e.g., aniline
2.2. Preparation of supports and catalysts
2.2.1. Carbon-supported Ru catalyst
using a catalyst system consisting of a catalyst for ring hydrogena-
tion (CatRH) and a catalyst for nucleophilic attack and ring opening
(CatNARO) and their catalytic activities in terms of variation of reac-
tion parameters therein (Scheme 2).
A colloidal solution of ruthenium nanoparticles stabilized by
polyvinyl alcohol was deposited on activated carbon, using the
procedure reported by Porta et al. [24]. Under vigorous stirring an
aqueous solution of RuCl3·xH2O (1.01 g, 5 mmol) was treated with
an aqueous solution of polyvinyl alcohol (PVA, 10 ml). To this, a
fresh solution of NaBH4 (38 ml, 0.1 M) was added at 50 ◦C for 2 h. The
RuNPs generated were immobilized simply by adding the active
carbon (2 g) into the metal dispersion. After 1 h, the resultant slurry
was dried for 3 h under vacuum. After being carbonized at 400 ◦C
in a constant N2 flow with 20 mL min−1 for 5 h, black solid could be
obtained.
2. Experimental
2.1. Materials and methods
Aniline, p-phenylene diamine, p-toluidine, p-anisidine, 4-
chloroaniline, cyclohexylamine, propylene carbonate, dimethyl
carbonate, ethylene carbonate, dicyclohexylamine, RuCl3·xH2O,
RhCl3·xH2O, palladium (II) chloride (PdCl2; 99.9%), chitosan,
tetraethylorthosilicate (TEOS), 1-butyl-3-methylimidazolium
tetrafluoroborate ([Bmim]BF4), active carbon, imidazole, NaBH4,
all the metal salts and solvents were purchased for Aldrich, South
Korea.
2.2.2. Carbon-supported Rh catalyst
Rhodium supported on carbon catalyst was prepared following
the same procedure as described above for ruthenium on carbon
using RhCl3·3H2O (1.02 g, 5 mmol).
Scheme 2. Process diagram for producing HPCC from aniline.

84
V. Mishra et al. / Applied Catalysis A: General 487 (2014) 82–90
˚
2.2.3. Carbon-supported Pd catalyst
to form a thin layer of platinum atoms on it with 92 A film thick-
nesses. The analyses were performed by employing 3 MA current
for 180 s. X-ray photoelectron spectroscopy (XPS) measurements
are carried out using a commercial Thermo Fisher K-Alpha XPS
system with a focused-beam monochromated K-Alpha source. We
use a 180◦ double focusing hemispherical analyzer with multi-
element, high-transmission spectrometer input lens-128-channel
detector for high-quality images. The scans are performed with
a step size of 0.9 eV and a dwell time of 50 ms/step. The specific
surface area (BET) of the catalysts was determined on a BELSORP-
max (MP) instrument. The catalyst was pre-treated at 250 ◦C under
vacuum for over 5 h to desorb contaminating molecules (mainly
water) from the catalyst surface. For the determination of BET
surface area, the value of ꢁ/ꢁ0 in the range 10−4 < ꢁ/ꢁ0 ≤ 0.997
was used, and nitrogen was used as the adsorbing gas. The spe-
cific surface area of the catalyst was calculated from adsorption
isotherms using the standard BET equation. The absolute errors
were ≤1%.
Palladium supported on carbon catalyst was prepared [25]
using the following steps: (i) 0.01 M aqueous solution of tetra-
chloropalladic acid (H2PdCl4) was prepared using PdCl2 solution in
equivalent amount of hot 0.04 M HCl diluted with distilled water;
and (ii) aqueous solution of H2PdCl4 was added dropwise on the
active carbon support with strong stirring. After 1 h, the resultant
slurry was dried for 3 h under vacuum. After being carbonized at
400 ◦C in a constant N2 flow with 20 mL min−1 for 5 h, black solid
could be obtained.
2.2.4. SiO2-supported Ru catalyst
In a typical procedure [26], RuCl3·xH2O (58.0 mg) was dissolved
in BMIm·BF4 (2.0 g) and ultrasonically treated for 0.5 h. Then, it was
mixed with TEOS (10 mL) and ethanol (3.5 mL) was added under
magnetic stirring at 60 ◦C, after the addition of hydrochloric acid
(5 mL, 5 M), a brown colloid formed in 0.5 h. The resultant colloid
was further aged at 60 ◦C for 12 h and then treated at 150 ◦C for 3 h
under vacuum. After being carbonized at 400 ◦C in a constant N2
flow with 20 mL min−1 for 5 h, ≈6 g black solid could be obtained.
2.4. Catalytic tests
2.2.5. ꢀ-Al2O3-supported Ru catalyst
All the RH and NARO reactions were carried out together in
a 100 mL autoclave reactor with a magnetic stirrer and an elec-
trical heater (Fig. 1). In a typical procedure, 15 mmol of aromatic
amine, 7.5 mmol of carbonate, 0.075 mmol of Ru-based catalyst,
0.375 mmol of metal salts as promotor, and 10 mL of isopropanol
(IPA) were put into the autoclave together with a magnetic bar.
0.5 mL of isooctane was put into the reactor as an internal standard
for a quantitative analysis. The reactor was purged with hydrogen
three times to remove any remaining air, followed by pressuriz-
ing the reactor with hydrogen gas up to 4 MPa. The reactor was
then heated to a specific temperature with addition of hydrogen
gas to 8.3 MPa. The pressure was maintained constantly using a
reservoir tank equipped with a high-pressure regulator and a pres-
sure transducer to monitor pressure drop during the reaction. After
completion of the reaction, the reactor was cooled to RT and the
reaction mixture was filtered off to remove catalyst for further
reaction. The resulting solution was analyzed on Agilent 6890N gas
chromatograph equipped with a flame ionization detector and on
an Agilent 6890N-5975 MSD-GC Mass spectrometer equipped with
HP-5 column (30 m × 0.32 m × 0.25 ␮m).
First, 0.20 g of RuCl3·xH2O was dissolved in 50 mL of ethylene
glycol and then 1.5 g of ␥-Al2O3 was added to form a suspension.
The mixture was stirred for 15 min at RT and the microwave-
solvothermal reaction was carried out under mild conditions at
170–180 ◦C, pressure 5 bar and the hold time of 10 min. After reac-
tion, the vessel was rapidly cooled down in an ice-water bath. A
grey solid was filtered off, washed with NaNO3 aqueous solution,
next with distilled water to remove the sodium and chloride ions,
dried under vacuum at RT and stored in a closed container until
used [27].
2.2.6. Chitosan-supported Ru catalyst
Chitosan-supported Ru nanoparticles catalysts were prepared
by impregnation method. Granules of chitosan-functionalized
polymer were crushed until the fine powders were formed. The
fine powders of chitosan were then impregnated into RuCl3·3H2O
solution prepared in ethanol. The mixture was stirred under N2
atmosphere for a period of 24 h. Finally, catalyst Ru/chitosan was
separated by filtration, washed with ethanol and dried to give dark
black. Energy dispersive X-ray spectroscopy confirmed that the
metal complex was present on the polymer in a metal to saccharide
unit ratio of 0.33 (based on the Ru/O ratio), with no loss of chlorine,
as observed by the Ru/Cl ratio of 0.47.
3. Results and discussion
To test the best RH catalyst, we loaded various metals (ruthe-
nium, rhodium, and palladium) on carbon, silica, alumina, and
chitosan. The preparation method of these catalysts was mentioned
in Section 2. In order to confirm the particle size of the loaded
metal over support and the amount of the catalyst loading, micro-
scopic analyses were carried out using TEM-EDX (Figs. 1 and 2) and
X-ray photoelectron spectroscopy (XPS), respectively, and it was
found that the particle size of the dispersed ruthenium was ranging
from 2.0 to 5.0 nm and 5 wt%, indicating that they were all properly
loaded according to the prepared method with equally distributed
on the these solid supports.
To choose proper catalyst for RH reaction, a series of reactions
were done using transition metal catalysts with various supports
and NaNO2 as a fixed promoter. The reason to choose NaNO2 as
promoter in this system is that it has already been proved as
a best promoter for RH reaction of aromatic amine to produce
ring-hydrogenated amine in our previous article [18]. For this pur-
pose, reactions were carried out by employing aniline as a model
aromatic amine as a substrate and PC as reactant (molar ratio
of aniline:PC:CatRH:CatNARO = 200:200:1:5) to investigate product
composition at 160 ◦C under 8.3 MPa of H2 in isopropanol (IPA)
2.3. Characterization of supports and catalysts
1H and 13C NMR spectra were recorded on a Bruker Avance
300 MHz NMR spectrophotometer in CDCl3 containing TMS as
the internal standard. Signals are quoted in parts per million
(ı ppm) relative to TMS. The FTIR spectra recorded by from pel-
lets in KBr (AR grade) using a Thermo Scientific Nicolet 6700
FT-IR Spectrometer. The resulting solution after catalytic RH and
NARO was analyzed using Agilent 6890N gas chromatograph
equipped with a flame ionization detector (FID) and on an Agi-
lent 6890N-5975 MSD-GC Mass spectrometer equipped with HP-5
column (30 m × 0.32 m × 0.25 ␮m). The product mixture was ana-
lyzed using Agilent 6890N gas chromatography (GC) equipped
with an FID and HP-5 capillary column. The transmission electron
microscopy with microprobe for spectrometry of dispersive X-ray
analysis (TEM + EDX) was used aiming at quantifying the main
elements found in the catalysts as well as to observing their mor-
phology. The analyses were performed with a JEOL device model
JEM-2100F. The initial stage consisted of metalizing the catalyst

V. Mishra et al. / Applied Catalysis A: General 487 (2014) 82–90
85
Fig. 1. TEM images of catalysts.
as a solvent for 2 h and the results are listed in Table 1. Among
the carbon-supported transition metal catalyst (entries 1–3), Ru/C
was best for the production of the ring-hydrogenated hydrox-
ypropyl carbamate (HPCC). We also prepared different supports
loaded with ruthenium metal such as silica, alumina, and chi-
tosan (entries 4–6), however, none of them showed better activity
toward the HPCC than Ru/C (13%; entry 3), which presents a sig-
nal for obtaining HPCC from aniline through the reaction of in-situ
generated cyclohexylamine (3, CHA) and PC. The catalytic activity
of the loaded metal on these supports was found in the follow-
ing order: Ru/C > Rh/C > Pd/C > Ru/silica > Ru/alumina > Ru/chitosan
and these results were also correlated with the Brunauer–
Emmett–Teller (BET) specific surface area analysis (Fig. 3). These
results imply that the yield of product (HPCC) might be enhanced
by tuning the reaction conditions or by replacing NaNO2 with one
that is more able to facilitate NARO reaction.
Fig. 2. TEM-EDX chromatogram images of catalysts.

86
V. Mishra et al. / Applied Catalysis A: General 487 (2014) 82–90
Table 1
Effect of catalyst on the product composition.a
Entry
Catalyst
Specific surface area (m2 g−1
)
Ani. conv. (%)
PC conv. (%)
HPCC yieldb (%)
DCHA yield (%)
Remain-CHA (%)
1
2
3
4
5
6
5 wt% Pd/C
5 wt% Rh/C
5 wt% Ru/C
5 wt% Ru/SiO2
5 wt% Ru/Al2O3
5 wt% Ru/chitosan
226
836
876
110
105
001
50
85
90
78
74
10
20
60
68
58
19
10
1
10
13
04
03
0
17
8
7
0
6
7
32
28
30
67
2
0
a
Reaction conditions: aniline (15 mmol), PC (15 mmol), catalyst (0.075 mmol), NaNO2 (0.375 mmol), IPA solvent (15 ml), T = 160 ◦C, P = 8.3 MPa, t = 2 h.
HPCC yield is calculated based on PC.
b
Table 2
Effect of aniline and PC ratio on the product composition.a
Entry
Ani:PC
Ani. conv. (%)
PC conv. (%)
HPCC yieldb (%)
DCHA yield (%)
Remain-CHA (%)
1
2
3
4
5
1:1
1:2
1:3
2:1
3:1
90
81
72
95
100
68
68
60
88
82
13
8
4
39
18
7
15
25
14
15
28
30
33
12
34
a
Reaction conditions: aniline (15 mmol), PC (5–45 mmol), CatRH (0.075 mmol), NaNO2 as CatNARO (0.375 mmol), IPA (15 ml), T = 160 ◦C, P = 8.3 MPa, t = 2 h.
HPCC yield is calculated based on PC.
b
Although the HPCC yield was not high enough at this moment
base during the reaction to facilitate the formation of HPCC. Exper-
imental results demonstrated that the 2 equimolar ratio of aniline
showed the most promoting effect for the synthesis of HPCC yield
(39%, Table 2, entry 4). In contrast, using 3 equiv. of aniline rather
decreased the yield of HPCC, indicating that there is certain opti-
mized ratio of aniline to PC for the best result. With using this molar
ratio, the following investigation was undertaken to improve the
productivity of HPCC.
(Table 1, entry 3), it shed some light for more generation of HPCC
because there is still room when considering the remaining amount
of in-situ generated 3 (28%). It is not clear that why the NARO reac-
tion to produce HPCC did not take place more rapidly; however, it is
probably because the existence of PC renders the reaction medium
less basic, which played a certain role in quenching of CatNARO activ-
ity. Therefore, to find out appropriate cause and to improve the yield
of HPCC, various equimolar ratios between aniline and PC were
tested and the results were summarized in Table 2. The results show
that the increase in the amount of PC from 1 to 3 equimolar, conver-
sion of aniline decreased and the production of HPCC also decreased
from 13 to 4% due to the increased acidity arising from PC while the
unutilized amount of 3 and yield of DCHA increased concomitantly
(Table 2, entries 1–3). For clarifying the role of increased basicity
by adding more aniline for obtaining higher yield of HPCC, a couple
of more experiments were conducted using 2 and 3 equimolar of
aniline compared to PC if the excess amount of amine may act as
In our previous article, we have reported that NaNO2 was found
as the best promoter for producing CHA (3) from nitrobenzene in
the presence of Ru/C as a main catalyst and IPA as solvent [18]
but the use of PC as a reactant retarded the NARO reaction, afford-
ing only 39% yield of HPCC (Table 2, entry 4). To overcome this
low productivity, various alkali metal and alkali earth metal salts
such as halides, bicarbonates, nitrites and nitrates, carbonates, sili-
cates, phosphates, and hydrogen phosphates were tested as a new
promoter (CatNARO, 5 equiv. to CatRH) in the Ru/C-catalyzed HPCC
formation reaction and the results are listed in Table 3. The absence
of metal salts (Table 3, entry 1) did not show any activity both for
RH of aniline and NARO reaction with PC. When adding a promoter,
the aniline and PC conversion retained approximately 73–100%.
KH2PO4, CaNO3·4H2O, MgNO3·6H2O, and Li2CO3 showed mod-
erately promoting effect, while others showed negligible effect.
Among all the used CatNARO for HPCC synthesis, Na2CO3 (entry 13)
was found to show most promoting effect to increase the yield of
HPCC up to 88% using Ru/C as CatRH in the presence of IPA. These
results clearly indicate that the HPCC yield was largely influenced
by the types of added promoter in this reaction, resulting in that
sodium carbonate was found to be the best CatNARO
.
In order to have a better understanding of the adding Na2CO3
(CatNARO) effect on the yield of HPCC with respect to ruthenium
catalyst (CatRH), various experiments were carried out and results
were highlighted in Fig. 4. The results show that the conversion of
aniline increased with increasing amount of Na2CO3 and the yield of
the HPCC increased with the simultaneous decrease in DCHA by the
addition of CatNARO from 1 to 5 equiv. to ruthenium, but thereafter
the yield of HPCC decreased with the concomitant increase in side
product. This result implies that the addition of CatNARO plays a
significant role in promoting the NARO reaction but has a certain
limit. The exact role of Na2CO3 is not clear at this moment but it
seems that an interaction between IPA and Na2CO3 plays an certain
Fig. 3. Specific surface area correlation with respect to catalytic reactivity for HPCC
formation.

V. Mishra et al. / Applied Catalysis A: General 487 (2014) 82–90
87
Table 3
Effect of CatNARO on the product composition.a
Entry
CatNARO
Ani. conv. (%)
PC conv. (%)
HPCC yieldb (%)
DCHA yield (%)
Remain-CHA (%)
1
2
3
4
5
7
8
9
10
11
12
13
14
15
16
17
18
None
KCl
NaI
LiCl
NaHCO3
KHCO3
CaNO3·4H2O
KNO3
0
86
75
89
84
88
98
90
90
90
99
100
73
48
84
99
97
50
81
85
84
89
85
90
78
90
94
87
95
91
72
0
1
4
0
4
0
6
4
23
9
13
26
26
12
15
18
16
9
12
28
11
16
60
14
16
20
20
10
13
4
43
24
48
60
48
57
50
63
88
19
9
MgNO3·6H2O
AlCl3
Li2CO3
Na2CO3
K2CO3
Cs2CO3
K2HPO4
KH2PO4
Na2SiO3·5H2O
3
6
18
22
100
87
99
17
64
51
25
16
20
a
Reaction conditions: aniline (15 mmol), PC (7.5 mmol), CatRH (0.075 mmol), CatNARO (0.375 mmol), IPA (15 ml), T = 160 ◦C, P = 8.3 MPa, t = 2 h.
HPCC yield is calculated based on PC.
b
role in promoting not only RH reaction by the in-situ formation of
maintained above 5.5 MPa (data not shown). Below 5.5 MPa, the
rate of the reaction becomes slower, but the effect on the rate is
much less pronounced than in the case of temperature.
active species like NaOCH(CH3)2 [17], but also NARO reaction by
rendering the reaction media more basic to facilitate nucleophilic
attack of amino group of CHA to carbonyl carbon of PC.
To find out the effect of temperature on the RH and NARO reac-
tion, a series of reactions were performed in the temperature range
of 80−200 ◦C and the results were demonstrated in Fig. 5. Aniline
disappeared completely at 160 ◦C and the HPCC yield was high-
est (88%), but thereafter a sharp decrease was observed with the
increase in the by-product formation, indicating the strong depend-
ency on the reaction temperature.
Inspired by these promising results and to broaden the scope of
the RH and NARO reaction, various aromatic amines and organic
carbonates were examined for the formation of ring-hydrogenated
carbamates using ruthenium-Na2CO3 catalyst system. To check
the performance of aromatic amine, we have chosen a variety
of aromatic amines like aniline, p-phenylene diamine (PPDA), p-
toluidine, p-anisidine, and 4-chloroaniline. The results in Table 4
show that PC and ethylene carbonate (EC) show near about simi-
lar reactivity with all the aromatic amines but their reaction with
dimethyl carbonate (DMC) was quite lower at 160 ◦C and a large
number of N-alkylated derivatives were observed with less forma-
tion of carbamate products (entries 3, 7, 10, 13, and 16). The reason
for this lower yield may be due to the fast methylation ability of
DMC than others under this operating conditions [28]. It is observed
that the selectivity of the carbonates was found in following orders:
PC > EC > DMC.
The results also suggest that above 160 ◦C, the reaction rates of
deamination and N-alkylation of isopropyl alcohol are facilitated
and might be higher than that of NARO and thus the formation of
by-products such as DCHA, IP-CHA, and 1,2-propanediol increased
with increasing temperature.
To study the influence of H2 pressure on the product composi-
tion, separate reactions were carried with a varying pressure range
of 1.4−14.0 MPa for 2 h at a constant reaction temperature of 160 ◦C.
The results show that H2 gas does not seem to have a significant
effect on the hydrogenation as long as the reaction pressure is
Fig. 4. Effect of molar ratio of CatNARO on the product composition: aAniline
(15 mmol), PC (7.5 mmol), CatRH (0.075 mmol), CatNARO (0.075–0.75 mmol), IPA
(15 ml), T = 160 ◦C, P = 8.3 MPa, t = 2 h; bHPCC yield is calculated based on PC.
Fig. 5. Effect of temperature on the product composition: aAniline (15 mmol), PC
(7.5 mmol), CatRH (0.075 mmol), CatNARO (0.375 mmol), IPA (15 ml), T = 80–200 ◦C,
P = 8.3 MPa, t = 2 h. bHPCC yield is calculated based on PC.

88
V. Mishra et al. / Applied Catalysis A: General 487 (2014) 82–90
Table 4
Scope of RH and NARO reaction for various aromatic amines and carbonates.a
Entry
Reactants
Amine conv. (%)
Carbonate conv. (%)
Carbamate yieldb (%)
Remaining ring-hydrogenated
amine (%)
1
100
95
88
16
2
3
100
95
100
88
85
15
18
20c
4
92
94
78d
15
5
6
85
77
75
79
52d,e
20
16
74d
7
8
68
88
74
23d
30
14
100
71d
9
89
89
90
70
70d
11d
16
26
10
11
100
95
70d
19
12
13
100
97
79
83
68d
21
25
18d

V. Mishra et al. / Applied Catalysis A: General 487 (2014) 82–90
89
Table 4 (Continued )
Entry
Reactants
Amine conv. (%)
Carbonate conv. (%)
Carbamate yieldb (%)
Remaining ring-hydrogenated
amine (%)
14
95
100
80d
12
15
16
94
90
81
95
76d
15
23
15d
a
Reaction conditions: amines (15 mmol), carbonates (7.5 mmol), CatRH (0.075 mmol), CatNARO (0.375 mmol), IPA (15 ml), T = 160 ◦C, P = 8.3 MPa, t = 2 h.
b
Carbamate yield is calculated based on carbonates.
So many by-products (e.g. 5–6 types of alkyl amines).
Data are based on GC-FID area (%).
c
d
e
1:1 ratio of amine and PC because of two amino groups available in moiety (mixture of carbamate formed).
To test the possibility of recycling the catalyst for the RH with
catalyst could be recycled five times without any loss of its original
reactivity, but at fifth recycle, only 75% HPCC was obtained.
NARO reaction from PC, experiments have been conducted with
the same catalyst system at 160 ◦C and 8.3 MPa for 2 h which were
responsible for 88% yield of HPCC from aniline (Fig. 6). After com-
pletion of the reaction, the product mixture was filtered to isolate
the insoluble Ru/C catalyst and dried for 12 h for further use of the
RH and NARO reactions.
The recycling experiments were repeated five times and all the
recovered catalysts were collected to make every run use equal
amount (0.19 mmol) of catalyst to exclude a factor arising from
catalyst loss after filtration. The recycling study revealed that the
4. Reaction mechanism
On the basis of overall results and discussion, a reasonable
mechanism for the production of ring-hydrogenated carbamate is
proposed in Scheme 3 and it distributes the overall mechanism into
two processes based on the RH and NARO reaction. The first step
goes through the catalytic RH reaction of the aniline (I) into CHA
(II). The catalytic RH reaction probably proceeds stepwise with the
Scheme 3. Plausible mechanism for the formation of HPCC through RH and NARO reaction.

90
V. Mishra et al. / Applied Catalysis A: General 487 (2014) 82–90
ring-hydrogenated carbamates with good yields. Because of these
points, this methodology will increase the importance and its scope
for industrial applicability since the carbamates find wide appli-
cations in various areas such as pharmaceuticals, agrochemicals,
intermediates in organic synthesis, protection of amino group in
peptide chemistry, and especially, important precursor for iso-
cyanates, a platform chemical for polymer chemistry.
Acknowledgment
This work was supported by “Fusion Research Program for Green
Technologies (NRF-2012M3C1A1054497)” funded by Ministry of
Education, Science, and Technology, Korea and by the Korea Insti-
tute of Industrial Technology (KITECH) grant funded by Internal
Research Program in KITECH.
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.apcata.2014.09.013.
Fig. 6. Catalytic reusability tests. Reaction conditions: aniline (15 mmol), PC
(7.5 mmol), CatRH (0.075 mmol), CatNARO (0.375 mmol), IPA (15 ml), T = 160 ◦C,
P = 8.3 MPa, t = 2 h. bHPCC yield is calculated based on PC.
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