One-pot synthesis of secondary amines from alcohols and nitroarenes on TiO2 loaded with Pd nanoparticles under UV irradiation

Article abstract of DOI:10.1039/c4nj01851f

Photoirradiation (λ > 300 nm) of TiO₂ loaded with Pd nanoparticles (2 wt%, ca. 5 nm diameter) in water containing benzyl alcohol and nitrobenzene at room temperature successfully produces the corresponding secondary amine (N-benzylaniline) with 96% yield. This is achieved via three consecutive catalytic reactions: (i) photocatalytic oxidation of alcohol (aldehyde formation) and reduction of nitrobenzene (aniline formation); (ii) catalytic condensation of the formed aldehyde with aniline on the TiO₂ surface (imine formation); and, (iii) photocatalytic hydrogenation of the formed imine (secondary amine formation). This catalytic system successfully produces several kinds of secondary amines, even those containing reducible substituents such as -CN, -COOH, or -CHO with >76% yields.

Full text of DOI:10.1039/c4nj01851f

View Article Online
View Journal
NJC
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: S. Kaliyamoorthy,
H. Sakamoto, Y. Shiraishi and T. Hirai, New J. Chem., 2014, DOI: 10.1039/C4NJ01851F.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/njc

Page 1 of 8
New Journal of Chemistry
View Article Online
DOI: 10.1039/C4NJ01851F
Journal Name
RSCPublishing
ARTICLE
One-pot synthesis of secondary amines from
alcohols and nitroarenes on TiO2 loaded with Pd
nanoparticles under UV irradiation†
Cite this: DOI: 10.1039/x0xx00000x
Kaliyamoorthy Selvam,a Hirokatsu Sakamoto,a Yasuhiro Shiraishi*a,b and
Takayuki Hiraia
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
Photoirradiation (
containing benzyl alcohol and nitrobenzene at room temperature successfully produces the
corresponding secondary amine ( -benzylaniline) with 96% yield. This is achieved via three consecutive
λ >300 nm) of TiO2 loaded with Pd nanoparticles (2 wt%, ca. 5 nm diameter) in water
www.rsc.org/
N
catalytic reactions: (i) photocatalytic oxidation of alcohol (aldehyde formation) and reduction of
nitrobenzene (aniline formation); (ii) catalytic condensation of the formed aldehyde with aniline on the
TiO2 surface (imine formation); and, (iii) photocatalytic hydrogenation of the formed imine (secondary
amine formation). This catalytic system successfully produces several kinds of secondary amines, even
those containing reducible substituents such as –CN, –COOH, or –CHO with >76% yields.
Another problem for these catalytic systems is the use of
unstable "anilines" as substrates; they are oxidized very easily by
Introduction
Secondary amines are one of the most important classes of
chemicals that are versatile intermediates for the synthesis of
pharmaceuticals and agricultural chemicals.1 These compounds
are usually synthesized by Nꢀalkylation of primary amines with
alkyl halides. This method, however, requires stoichiometric or
excess amount of inorganic bases with a concomitant formation
of large amounts of inorganic salts as wastes.2,3
autooxidation.21 Alternative methods with stable substrates
such as nitroarenes are necessary. Several homogeneous Ru
catalysts promote oneꢀpot synthesis of secondary amines from
alcohols and stable nitroarenes.22–25 Heterogeneous catalysts
such as Ag particles supported on Al2O3,26 Au particles supported
27
Fe2O3, TiO2,28 or AgꢀMo nanorods29 have also been proposed.
They, however, still require relatively high reaction temperatures
(>363 K). Improved methods capable of producing secondary
amines at room temperature are therefore desired for green
organic synthesis.
The purpose of this work is to design a heterogeneous
catalytic system that promotes one-pot synthesis of secondary
amines from alcohols and nitroarenes at room temperature. We
used a semiconductor TiO2 loaded with Pd particles (Pd/TiO2)
An alternative environmentallyꢀfriendly way for secondary
amine synthesis is the Nꢀalkylation of primary amines with
alcohols as alkylating agents in the presence of transition metal
catalysts, via the borrowing hydrogen (H) mechanism.4–8 These
systems promote three consecutive catalytic steps in one pot: (i)
dehydrogenation of alcohol produces aldehyde and H atoms on
the metal (H−metal species); (ii) catalytic condensation of the
formed aldehyde with primary amine produces imine; and (iii)
hydrogenation of the imine by the H–metal species produces
secondary amine. Many homogeneous catalysts such as Pt, Ru,
Ir complexes have been proposed so far,9–12 but there are
difficulties in the recovery and reuse of expensive catalysts.
Heterogeneous systems have also been proposed with several
catalysts such as PdOx particles supported on Fe2O3,13 Pd
particles supported on boehmite,14 Ag clusters supported on
Al2O3,15 Ru(OH)x or Cu(OH)x supported on Al2O3,16,17 Au
particles supported on TiO2,18 Pd particles supported on MgO,19
and sulfated tungstate.20 All of these systems selectively produce
secondary amines, but need relatively high reaction temperatures
(>363 K).
as a catalyst under UV irradiation (λ >300 nm). Our hypothesis
is briefly summarized in Scheme 1 and as follows. Photoexcited
TiO2 oxidizes alcohol, producing aldehyde and protons (H+).30
Photoexcited electrons reduce H+ on the Pd particles and
produce H atoms (H–Pd species).31 These H–Pd species may
reduce nitroarene and produce aniline. Catalytic condensation
of the formed aniline and aldehyde by the Lewis acid sites on
the surface of TiO2 may produce imine.32 The imine is then
hydrogenated by the H−Pd species and is converted to the
product secondary amine. These photocatalytic and catalytic
sequences may therefore facilitate oneꢀpot synthesis of
secondary amine from alcohols and nitroarenes at room
temperature.
This journal is © The Royal Society of Chemistry 2013
J. Name., 2013, 00, 1-3 | 1

New Journal of Chemistry
Page 2 of 8
View Article Online
ARTICLE
DOI: 10.103J9o/Cu4rNnJa0l1N85a1mF e
loadings enhance the formation of
1
. Among them, Pd2/TiO2
(entry 2) exhibits the highest activity:
1
is produced with almost
quantitatively (96%). Further Pd loading (Pd4/TiO2), however,
decreases the activity (entry 5). As shown by entries 6 and 7,
the catalysts loaded with other metal particles such as Pt and
Ag show much lower
1 yields (<10%). In particular, TiO2
loaded with Au particles (Au2/TiO2; entry 8), which has been
proposed for secondary amine synthesis from nitroarenes and
ethanol, exhibit very low
1
yield (3%).36 These data clearly
suggest that Pd/TiO2 catalyst is effective for oneꢀpot synthesis
of secondary amine from alcohol and nitroarene.
Scheme 1 Proposed pathway for secondary amine formation from alcohols and
nitroarenes on the photoactivated Pd/TiO2 catalyst.
Here we report that the above hypothesis is realized by the
Pd/TiO2 catalyst under UV irradiation, and several kinds of
secondary amines are successfully obtained with high yields
(>76%). We found that the reaction efficiency strongly depends
on the amount of Pd loaded. The catalyst loaded with 2 wt %
Pd, which contains about 5 nm Pd particles, exhibits very high
activity for oneꢀpot synthesis of secondary amines.
Results and Discussion
Preparation and characterization of catalysts
The Pd /TiO2 catalysts with different Pd loadings [x (wt%) = Pd
x
/ TiO2 × 100] were prepared by impregnation of Pd(NO3)2 onto
P25 TiO2 (anatase/rutile ratio = ~80/20; average particle size,
24 nm; BET surface area, 59 m2 g–1) followed by reduction
with H2.33,34 Fig. 1 shows typical transmission microscopy
(TEM) images of the respective Pdx/TiO2 catalysts. All of them
contain spherical Pd particles, and their sizes increase with the
Pd loadings: the average diameters for
x = 0.5, 1, 2, and 4
catalysts were 2.6, 4.1, 5.0, and 6.5 nm, respectively. As shown
in Fig. 2, highꢀresolution TEM images of the catalysts revealed
that these Pd particles can be indexed as fcc structures as same
as bulk metallic Pd (JCPDS 46ꢀ1043). Fig. S1 (ESI†) shows the
diffuseꢀreflectance UVꢀvis spectra of catalysts. The higher Pd
loading catalysts exhibit increased absorbance at
due to the light scattering by the Pd particles.33,35
λ >300 nm
Photocatalytic activity
Photocatalytic reactions of benzyl alcohol and nitrobenzene
were performed with respective catalysts. An water (4.5 mL)
containing benzyl alcohol (0.5 mL), nitrobenzene (25 µmol),
and catalyst (10 mg) was photoirradiated by a Xe lamp at
λ
>300 nm under N2 atmosphere (1 atm) at room temperature for
4 h. Table 1 summarizes the conversion of nitrobenzene and the
yield of
TiO2 (entry 1) produces only a small amount of imine (
scarcely produces secondary amine (
N
ꢀbenzylaniline (
1
) and
N
ꢀbenzylidenaniline (
2
). Bare
2
) and
Fig. 1 (left) Typical TEM images and (right) size distribution of Pd particles on (a)
1
). In contrast, Pdx/TiO2 Pd0.5/TiO2, (b) Pd1/TiO2, (c) Pd2/TiO2, and (d) Pd4/TiO2 catalysts.
(entries 2–5) produce very large amount of
1. Increased Pd
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

Page 3 of 8
Journal Name
New Journal of Chemistry
View Article Online
ARTICLE
DOI: 10.1039/C4NJ01851F
Catalytic condensation of the formed aldehyde with aniline by
the Lewis acid site on the TiO2 surface produces imine.32
→
←
R1–CHO + R2–NH2
R1–CH=N–R2 + H2O
(5)
The formed imine is then hydrogenated by the H
and transformed to the product secondary amine.37
−
Pd species
R1–CH=N–R2 + 2H–Pd → R1–CH2–NH–R2 + 2Pd
(6)
Fig. 3c shows the timeꢀdependent change in the amounts of
substrate and products during photoreaction of benzyl alcohol
and nitrobenzene on the Pd2/TiO2 catalyst. At the initial stage,
photoirradiation decreases the amount of nitrobenzene (black),
Fig. 2 High-resolution TEM images of Pd2/TiO2 catalyst. (a) The incident beam
direction is [0, 1, 1], and (b) this particle is a twinned one and the incident beam
directions are [0, 1, 1] and [0, 1, 1], respectively.
̶
̶
̶
along with a formation of benzaldehyde (white) and aniline (3,
Reaction mechanism
Secondary amine ( ) is produced by tandem photocatalytic and
catalytic reactions on Pd/TiO2 (Scheme 1). The reaction is
initiated by photoexcitation of TiO2, producing the electron (e–)
and positive hole (h+) pairs.
blue). This suggests that, as shown by eqs. 1–4, photoexcitation
of Pd/TiO2 indeed promotes oxidation of alcohol (aldehyde
formation) and reduction of nitrobenzene (aniline formation).
The amount of aniline decreases with time, along with a
1
formation of imine (2, green), suggesting that condensation of
the formed aldehyde and aniline produces imine (eq. 5). The
amount of imine then decreases, associated with a formation of
TiO2 + h
ν
→ e– + h+
(1)
product secondary amine (1, red). This suggests that, as shown
by eq. 6, hydrogenation of imine produces the secondary amine.
Photoirradiation for 4 h leads to almost complete conversion of
The h+ oxidize alcohol and produces aldehyde and H+.
R1–CH2OH + 2h+ → R1–CHO + 2H+
(2)
nitrobenzene to 1. These substrate and product profiles suggest
that the above reaction sequence (Scheme 1, eqs. 1–6) proceeds
efficiently on the Pd2/TiO2 catalyst. In addition, prolonged
The formed H+ are reduced on the surface of Pd particles by the
e– transferred from the TiO2 conduction band, and converted to
the surface H atoms (H–Pd species).33
photoirradiation for >4 h scarcely changes the amount of
1,
H+ + e− + Pd → H–Pd
(3)
suggesting that further reaction of does not occur.
1
Furthermore, as shown in Table 1 (entry 4), the Pd2/TiO2
catalyst, when reused for further photoreactions, shows almost
the same activity as the fresh catalyst. This indicates that the
catalyst is reusable without the loss of activity.
Nitrobenzene is reduced by the H–Pd species and transformed
to the corresponding aniline.
R2–NO2 + 6H–Pd → R2–NH2 + 2H2O + 6Pd
(4)
Table 1. Catalyst properties and results for oneꢀpot synthesis of secondary amine from nitrobenzene and benzyl alcohol under UV irradiation.
NO2
NH2
OH
hv (>300 nm), 4 h
+
+
+
N
N
catalyst (10 mg)
H
water (4.5 mL), N2, 298 K
1
2
3
25 ꢀmol
0.5 mL
Yields / %b
Amount of product formed (µmol)
Size of metal
Nitrobenzene
conv. / %
Entry
Catalyst
particles / nma
1
2
28
30
25
3
Benzaldehyde
Toluene
<0.1
1.0
3
12.8
2.0
1.8
<0.1
0
1
2
3
4
TiO2
86
>99
>99
>99
>99
>99
>99
>99
>99
60
0
35.2
61.8
65.6
70.5
68
Pd0.5/TiO2
Pd1/TiO2
Pd2/TiO2
1st reuse
2nd reuse
3rd reuse
4th reuse
Pd4/TiO2
Pt2/TiO2
Ag2/TiO2
Au2/TiO2
2.6 ± 0.5
4.1 ± 0.9
5.0 ± 0.9
56
64
96
96
95
94
92
71
2
1.1
2.6
3
2.8
4
67.1
65.3
63.8
68.0
27.0
28.8
33.0
3.0
0
5
2.8
0
7
3.1
0
5
6
7
8
6.5 ± 1.3
3.1 ± 0.8c
4.6 ± 1.2c
3.7 ± 0.5c
11
13
8
6.3
4.1
6.9
9.0
9.3
<0.1
<0.1
<0.1
88
8
95
3
14
a Average diameter of metal particles determined by TEM observations. b = [product formed (ꢀmol)] / [initial amount of nitrobenzene (25 ꢀmol)] × 100. c TEM
images of the catalysts and size distribution of metal particles are summarized in Fig. S2 (ESI†)
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 3

New Journal of Chemistry
Page 4 of 8
View Article Online
ARTICLE
DOI: 10.103J9o/Cu4rNnJa0l1N85a1mF e
a Pd0.5/TiO2
b Pd1/TiO2
100
100
20
20
10
0
10
1
2
0
0
0
0
2
4
6
8
3
0
2
4
6
8
t / h
t / h
c Pd2/TiO2
d Pd4/TiO2
e Pd2/TiO2 (without water)
100
100
100
20
20
20
10
10
0
10
0
0
0
0
0
0
0
2
4
6
8
2
4
6
8
0
2
4
6
8
t / h
t / h
t / h
Fig. 3 Time-dependent change in the amounts of substrate and products during photoreaction of benzyl alcohol and nitrobenzene with (a) Pd0.5/TiO2, (b) Pd1/TiO2, (c)
Pd2/TiO2, (d) Pd 4/TiO2 catalysts, respectively. The reaction conditions are identical to those in Table 1. (e) The data obtained on Pd2/TiO2 catalyst in benzyl alcohol (5
mL) without water.
This is further confirmed by the photoreaction of imine (
starting material in benzyl alcohol with respective catalysts. As
shown in Fig. 4, the secondary amine ( , black) is produced very
efficiently on the Pd2/TiO2 catalyst, but other catalysts exhibit
lower amine yields. The results clearly indicate that the Pd2/TiO2
2) as a
Effect of Pd loadings
As shown in Table 1, the Pd2/TiO2 catalyst shows the highest
activity for secondary amine formation, and the catalysts with
lower or higher Pd loadings show decreased activity. Effect of
the Pd amount on the respective reaction steps in Scheme 1 was
therefore studied. Fig. 3 shows the timeꢀcourse profiles for the
amounts of substrate and products during the photoreaction of
benzyl alcohol and nitrobenzene on the catalysts with different
Pd loadings. All of the catalysts lead to complete disappearance
of nitrobenzene by 4 h reaction. This indicates that, on all of the
catalysts, photocatalytic reduction of nitrobenzene (aniline
formation) occurs efficiently. Fig. S3 (ESI†) shows the time
profiles for the amounts of substrate and products during the
photoreaction with aniline as a starting material in a benzyl
alcohol solution on Pd2/TiO2. The formation rate of secondary
amine is similar to that obtained with nitrobenzene as a starting
material (Fig. 3c). These data clearly suggest that the reactions
(eqs. 2–4) are not the rateꢀdetermining steps for secondary
amine formation. Condensation of the formed aniline and
aldehyde (eq. 5) is also not the rateꢀdetermining step. This is
confirmed by stirring aniline and benzaldehyde in the dark
1
catalyst promotes efficient hydrogenation of imine (
2) to amine
(1) and, hence, facilitates consecutive catalytic sequences shown
in Scheme 1.
condition. As shown in Fig. S4 (ESI†), the yield of imine (
2) is
scarcely affected by the amount of Pd loaded. This is because
Fig. 4 The yields of secondary amine (1) formed by photoirradiation of a benzyl
the reaction is catalyzed by the Lewis acid site on the TiO
surface.32
2
alcohol solution containing imine (2) and respective Pdx/TiO2 catalysts.
The rateꢀdetermining step in the reaction sequence is the
hydrogenation of imine by the H Pd species (eq. 6). As shown in
Fig. 3c, on the Pd2/TiO2 catalyst, the imine ( , green) is rapidly
The lower activity for imine hydrogenation on lower Pd
loadings catalysts (Pd0.5/TiO2 and Pd1/TiO2) is due to the smaller
number of surface Pd atoms, as observed in related systems.38
−
2
consumed by 4 h photoreaction, but lower or higher Pd loading
catalysts (Fig. 3a, b, d) are ineffective for imine hydrogenation.
This may produce a smaller number of H−Pd species and result
in inefficient hydrogenation activity. In contrast, Pd4/TiO2 may
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

Page 5 of 8
Journal Name
New Journal of Chemistry
View ArticAle ROnTliInCeLE
DOI: 10.1039/C4NJ01851F
have a larger number of surface Pd atoms, but shows lower vertex, edge, square, and triangle sites, each of which shows
hydrogenation activity. This dilemma is probably caused by different activity for the reactions. The number of these atoms
hydrogenation of "alcohols". As shown in Fig. 4, photoreaction changes substantially with the particle size. As shown in Table 1,
of imine (2) in benzyl alcohol with respective catalysts also Pd4/TiO2 possesses larger Pd particles than other catalysts. These
produces toluene (gray). This indicates that H–Pd species Pd particles probably contain a larger number of specific surface
promote hydrogenolysis of benzyl alcohol as well as imine Pd atoms that promote preferential reaction of alcohols, resulting
hydrogenation. The amount of toluene formed increases with the in inefficient imine hydrogenation. As a result of this, Pd2/TiO2
Pd loadings. The Pd4/TiO2 catalyst produces much larger amount with appropriate size of Pd particles (ca. 5 nm) exhibits the
of toluene than Pd2/TiO2, although the amount of secondary highest activity for imine hydrogenation.
amine (
1) formed is much smaller. The enhanced formation of
It must be noted that the use of water as solvent affects
toluene on higher Pd loading catalyst is also confirmed by the strongly on the catalytic activity. Fig. 3e shows the time profiles
photoreaction of benzyl alcohol and nitrobenzene (Table 1). of the substrate and products during reaction of nitrobenzene in
These data suggest that, on Pd4/TiO2, alcohols react preferentially benzyl alcohol without water in the presence of Pd2/TiO2 catalyst.
with the H
−
Pd species: this may suppress imine hydrogenation.
The rate of secondary amine formation is much slower than that
The preferential reaction of alcohols on Pd4/TiO2 is probably obtained with water (Fig. 3c). The water addition probably
due to the size of Pd particles. It is well known that39−42 metal suppresses the adsorption of alcohols onto the Pd surface. This
particles contain different types of surface atoms located at the may accelerate the reduction reactions.
Table 2. Oneꢀpot synthesis of various kinds of secondary amines on the photoactivated Pd2/TiO2 catalysta
Run
1
Alcohol
Nitroarene
t / h
Nitroarene conv. / %
>99
Product
GC yield / % b
99
2
2
3
5
5
>99
>99
99
99
4
4
>99
>99
96
5c
72
85 (85d)
6
5
>99
98
7
5
8
>99
>99
>99
95
91
85
92
76
8e
9
6
COOH
10e
11e
12
13e
12
12
6
N
H
95
87
>99
>99
57f
95g
6
b
a Reaction conditions: water (4.5 mL), alcohol (0.5 mL), nitroarene (25 ꢁmol), Pd2/TiO2 catalyst (10 mg), temperature (298 K), N2 (1 atm), λ > 300 nm.
=
[product formed (ꢀmol)] / [initial amount of nitrobenzene (25 ꢀmol)] × 100. c Reaction conditions: nitrobenzene (0.5 mmol), water (5 mL), benzyl alcohol (5
d
mL), Pd2/TiO2 catalyst (100 mg), temperature (298 K), N2 (1 atm), λ > 300 nm. Isolated yield obtained after a silica gel column chromatography with a
mixture of nꢀhexane, diethyl ether, and triethylamine (98/1/1 v/v/v). e Catalyst (15 mg). f The yield of –Cl substituted product was 42%. g The vinylꢀsubstituted
product was not detected by GC analysis.
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 5

New Journal of Chemistry
Page 6 of 8
View Article Online
ARTICLE
Journal Name
DOI: 10.1039/C4NJ01851F
All of the reagents used were supplied from Wako, Tokyo
Kasei, and SigmaꢀAldrich, and used without further
Synthesis of various secondary amines
The Pd2/TiO2 catalyst is applicable for the synthesis of various purification. Water was purified by the Milli Q system. JRCꢀ
types of secondary amines. The results are summarized in Table TIOꢀ4 TiO2 (equivalent to Deggusa P25 TiO2) were kindly
2. Reaction of aliphatic alcohols and nitrobenzene (entries 1–3) supplied from the Catalyst Society of Japan.
produces the secondary amines with almost quantitative yields
Pdx/TiO2 catalysts [x (wt%) = Pd/TiO2 ×100; x = 0.5, 1, 2,
(99%), as is the case for the benzyl alcohol/nitrobenzene system 4] were prepared as follows:43 TiO2 (1.0 g) and Pd(NO3)2 (10.9,
(entry 4). A large scale reaction is also successfully carried out. 21.9, 44.2, or 90.2 mg) were added to water (40 mL), and the
As shown by entry 5, 0.5 mmol of nitrobenzene is transformed solvents were evaporated with vigorous stirring at 353 K for 12
to the secondary amine with 85% isolated yield although the h. The obtained powders were calcined at 673 K under air flow
reaction requires relatively long photoirradiation time (72 h). (0.5 L min–1) and then reduced at 673 K under H2 flow (0.2 L
Reactions of nitrobenzene with –CH3, –OCH3, and –OH groups min–1). The heating rate and the holding time at 673 K for these
(entries 6–8) also gave the products with very high yields treatments were 2 K min–1 and 2 h, respectively. Ag2/TiO2 and
(≥85%). Nitrobenzenes with reducible substituents such as –CN, Pt2/TiO2 were prepared in a similar manner to Pdx/TiO2 with
–COOH, and –CHO (entries 9–11) are converted to the AgNO3 (16 mg) or H2PtCl6•6H2O (54 mg) as metal precursors.
secondary amines with high yields (≥76%) while retaining the
substituents as they are. There are, however, some unsuccessful method as follows:44 HAuCl4•4H2O (45.8 mg) was added to
examples; reaction of ꢀchloronitrobenzene (entry 12) mainly water (50 mL). The pH of the solution was adjusted to 7 by an
gave the dechlorinated product because H–Pd species also addition of 1 M NaOH. TiO2 (1.0 g) was added to the solution
promote dehalogenation.33 In addition, reaction of
ꢀnitrostyrene and stirred vigorously at 353 K for 3 h. The particles were
Au2/TiO2 was prepared by a depositionꢀprecipitation
p
p
(entry 13) produced ethylꢀsubstituted product via the recovered by centrifugation and washed with water. They were
hydrogenation of vinyl group by the H–Pd species.40,41 These calcined at 673 K under an air flow (0.5 L min–1).
results suggest that Pd2/TiO2 facilitates oneꢀpot synthesis of
Photoreaction
several kinds of secondary amines, although some cases are
unsuccessful due to the subsequent hydrogenation of functional Each of the respective catalysts (10 mg) was added to an
groups.
alcohol/water mixture (0.5/4.5 mL/mL) containing a nitroarene
within a Pyrex glass tube (20 cm3;
16.5 mm). The tube was
sealed using a rubber septum cap, and N2 gas bubbled through
ϕ
Conclusion
We found that Pd2/TiO2 catalyst facilitates oneꢀpot synthesis of the solution. The tube was photoirradiated with magnetic
secondary amines from alcohols and nitroarenes under UV light, stirring by a Xe lamp (2 kW; Ushio Inc.). The temperature of
via tandem photocatalytic and catalytic reactions consisting of the solution during photoirradiation was about 298 K, and the
(i) photocatalytic oxidation of alcohol (aldehydes formation) light intensity was 18.2 W m–2 (at 300–400 nm). The gas phase
and reduction of nitroarenes (anilines formation); (ii) catalytic product was analyzed by GCꢀTCD (Shimadzu; GCꢀ8A). The
condensation of the formed aldehydes and anilines; and, (iii) resulting solution was extracted with diethyl ether (2
× 2 mL),
photocatalytic hydrogenation of the formed imines (secondary and the obtained solution was analyzed by GCꢀFID (Shimadzu;
amines formations). Several secondary amines are successfully GCꢀ1700). The amounts of substrate and products were
produced with high yields. The present system employs Xe determined with authentic samples.
lamp as a light source with large electricity consumption. Use
Analysis
of LED light or sunlight is required for practical synthesis
although the intensity of UV light contained in these light The total amounts of metals on the respective catalysts were
sources is weaker than that in Xe lamp. Activity improvement determined by an Xꢀray fluorescence spectrometer (Seiko
of the catalyst is therefore necessary for practical applications. Instruments, Inc.; SEA 2110). Diffuse reflectance UVꢀvis
Nevertheless, the present system have several advantages: (i) spectra were measured on an UVꢀvis spectrophotometer (Jasco
easily recoverable and recyclable heterogeneous catalyst; (ii) Corp.; Vꢀ550 with Integrated Sphere Apparatus ISVꢀ 469) with
mild reaction conditions (room temperature and atmospheric BaSO4 as a reference. TEM observations were carried out using
pressure); and, (iii) cheap and stable substrates (alcohol and an FEI Tecnai G2 20ST analytical electron microscope
nitroarenes). The present system based on the tandem operated at 200 kV.45
photocatalytic and catalytic actions, therefore, have a potential
to be a powerful method for oneꢀpot green synthesis of
secondary amines.
Acknowledgment
This work was partly supported by a GrantꢀinꢀAid for Scientific
Research (No. 26289296) from the Ministry of Education,
Culture, Sports, Science and Technology, Japan (MEXT).
Experimental
Materials
Notes and references
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

Page 7 of 8
Journal Name
New Journal of Chemistry
View ArticAle ROnTliInCeLE
DOI: 10.1039/C4NJ01851F
a
Research Center for Solar Energy Chemistry, and Division of Chemical
27 Q. Peng, Y. Zhang, F. Shi and Y. Q. Deng, Chem. Commun., 2011,
47, 6476–6478.
Engineering, Graduate School of Engineering Science, Osaka University,
Toyonaka 560-8531, Japan.
b PREST, JST, Saitama 332-0012, Japan.
28 C. H. Tang, L. He, Y. M. Liu, Y. Cao, H. Y. He and K. N. Fan,
Chem. Eur. J., 2011, 17, 7172–7177.
E-mail: shiraish@cheng.es.osaka-u.ac.jp; Fax: +81 6-6850-6273; Tel: +81
6-6850-6271.
29 X. Cui, C. Zhang, F. Shi and Y. Deng, Chem. Commun., 2012, 48
,
†
Electronic
Supplementary
Information
(ESI)
available:
9391–9393.
supplementary data (Figs. S1–S4). See DOI: 10.1039/c000000x/
30 Y. Shiraishi, K. Fujiwara, Y. Sugano, S. Ichikawa and T. Hirai, ACS
Catal., 2013, , 312–320.
31 Y. Sugano, K. Fujiwara, Y. Shiraishi, S. Ichikawa and T. Hirai,
Catal. Sci. Technol., 2013, , 1718–1724.
3
1
2
3
4
5
6
7
R. N. Salvatore, C. H. Yoon and K. W. Jung, Tetrahedron, 2001, 57,
7785–7811.
3
S. L. Buchwald, C. Mauger, G. Mignani and U. Scholz, Adv. Synth.
Catal., 2006, 348, 23–39.
32 W. B. Jennings and C. J. Lovely, Tetrahedron, 1991, 47, 5561–5568.
33 Y. Shiraishi, Y. Takeda, Y. Sugano, S. Ichikawa, S. Tanaka and T.
Hirai, Chem. Commun., 2011, 47, 7863–7865.
O. Navarro, N. Marion, J. Mei and S. P. Nolan, Chem. Eur. J., 2006,
12, 5142–5148.
34 Y. Shiraishi, D. Tsukamoto, Y. Sugano, A. Shiro, S. Ichikawa, S.
G. Guillena, D. J. Ramon and M. Yus, Angew. Chem., Int. Ed. 2007,
46, 2358–2364.
Tanaka, T. Hirai, ACS Catal., 2012, 2, 1984–1992.
35 Y. Shiraishi, Y. Sugano, S. Tanaka, T. Hirai, Angew. Chem., Int. Ed.,
2010, 49, 1656–1660.
M. H. S. A. Hamid, P. A. Slatford and J. M. J. Williams, Adv. Synth.
Catal. 2007, 349, 1555–1575.
36 D. Stıbal, J. Sa and J. A. van Bokhoven, Catal. Sci. Technol., 2013, 3,
G. Guillena, D. J. Ramon and M. Yus, Chem. Rev., 2010, 110, 1611–
1641.
94–98.
37 J. Krupka and J. Patera, Appl. Catal. A, 2007, 330, 96–107.
T. D. Nixon, M. K. Whittlesey and J. M. J. Williams, Dalton Trans.,
38 B. Coq, J. M. Cognion, F. Figueras and D. Tournigant, J. Catal.,
1993, 141, 21–33.
2009, 5, 753–762.
8
9
K. Shimizu, Catal. Sci. Technol., DOI: 10.1039/c4cy01170h.
Y.Tsuji, R. Takeuchi, H. Ogawa and Y. Watanabe, Chem. Lett.,1986,
15, 293–294.
39 N. Semagina, A. Renken, D. Laub and L. KiwiꢀMinsker, J. Catal.,
2007, 246, 308–314.
40 J. L. Bars, U. Specht, J. S. Bradlay and D. G. Blackmond, Langmuir
,
10 Y. Watanabe, Y. Tsuji and Y. Ohsugi, Tetrahedron Lett., 1981, 22
,
1999, 15, 7621–7625.
2667–2670.
41 B. Coq and U. F. Figueras, J. Mol. Catal. A, 2001, 173, 117–134.
11 K. Fujita, Y. Enoki and R.Yamaguchi, Tetrahedron, 2008, 64, 1943–
1954.
42 A. Molnár, A. Sárkány and M. Varga, J. Mol. Catal. A, 2001, 173
,
185–221.
12 S. Michlik and R. Kempe, Chem. Eur. J., 2010, 16, 13193–13198.
13 Y. Zhang, X. Qi, X. Cui, F. Shi and Y. Deng, Tetrahedron Lett.,
2011, 52, 1334–1338.
43 Y. Sugano, Y. Shiraishi, D. Tsukamoto, S. Ichikawa, S. Tanaka and T.
Hirai, Angew. Chem., Int. Ed., 2013, 52, 5295–5299.
44 D. Tsukamoto, Y. Shiraishi, Y. Sugano, S. Ichikawa, S. Tanaka and
T. Hirai, J. Am. Chem. Soc., 2012, 134, 6309–6315.
14 M. S. Kwon, S. Kim, S. Park, W. Bosco, R. K. Chidrala and J. Park,
J. Org. Chem., 2009, 74, 2877–2879.
45 Y. Shiraishi, K. Tanaka, E. Shirakawa, Y. Sugano, S. Ichikawa, S.
Tanaka and T. Hirai, Angew. Chem., Int. Ed., 2013, 52, 8304–8308.
15 K. Shimizu, M. Nishimura and A. Satsuma, ChemCatChem, 2009,
497–503.
1,
16 K. Yamaguchi and N. Mizuno, Synlett, 2010, 16, 2365–2382.
17 J. He, K. Yamaguchi and N. Mizuno, Chem. Lett., 2010, 39, 1182–
1183.
18 L. He, X.B. Lou, J. Ni, Y.ꢀM. Liu, Y. Cao, H.ꢀY. He and K. N. Fan,
Chem. Eur. J. 2010, 16, 13965–13969.
19 A. Corma, T. Ro denas and M. J. Sabater., Chem. Eur. J. 2010, 16
,
254–260.
20 S. P. Pathare and K. G. Akamanchi, Appl. Catal. A, 2013, 452, 29–
33.
21 A. G. Siraki, Adv. Molecular Toxicol., 2013, 7l, 39–82.
22 Y. Liu, W. Chen, C. Feng and G. Deng, Chem. Asian J., 2011, 6,
1142–1146.
23 Z. Alessandro, J. A. Mata and E. Peris, Chem. Eur. J., 2010, 16
,
10502–10506.
24 X. J. Cui, Y. Zhang, F. Shi and Y. Q. Deng, Chem. Eur. J., 2011, 17
,
2587–2591.
25 C. C. Lee and S. T. Liu, Chem. Commun., 2011, 47, 6981–6983.
26 K. Shimizu, K. Shimura, M. Nishimura and A. Satsuma,
ChemCatChem, 2011, , 1755–1758.
3
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 7

New Journal of Chemistry
Page 8 of 8
View Article Online
DOI: 10.1039/C4NJ01851F
Manuscript title: One-pot synthesis of secondary amines from alcohols and nitroarenes on
TiO2 loaded with Pd nanoparticles under UV irradiation
Authors: Kaliyamoorthy Selvam, Hirokatsu Sakamoto, Yasuhiro Shiraishi,* and Takayuki
Hirai
Graphical Abstract
TiO2 loaded with Pd nanoparticles, when irradiated by UV light in alcohols with nitroarenes,
successfully produces the corresponding secondary amines with almost quantitative yield, via
tandem photocatalytic and catalytic actions.