CuI-nanoparticles-catalyzed selective synthesis of phenols, anilines, and thiophenols from aryl halides in aqueous solution

Article abstract of DOI:10.1021/jo102506x

CuI-nanoparticles-catalyzed selective synthesis of phenols, anilines, and thiophenols from aryl halides was developed in the absence of both ligands and organic solvents. Anilines were formed selectively with ammonia competing with hydroxylation and thiophenols were generated selectively with sulfur powder after subsequent reduction competing with hydroxylation and amination.

Full text of DOI:10.1021/jo102506x

NOTE
pubs.acs.org/joc
CuI-Nanoparticles-Catalyzed Selective Synthesis of Phenols, Anilines,
and Thiophenols from Aryl Halides in Aqueous Solution
Hua-Jian Xu,*,†,‡ Yu-Feng Liang,† Zhen-Ya Cai,† Hong-Xia Qi,† Chun-Yan Yang,† and Yi-Si Feng*,†,‡
†School of Chemical Engineering, Hefei University of Technology, Hefei 230009, People's Republic of China
‡Anhui Key Laboratory of Controllable Chemistry Reaction & Material Chemical Engineering, Hefei 230009, People's Republic of China
S Supporting Information
b
ABSTRACT: CuI-nanoparticles-catalyzed selective synthesis of phe-
nols, anilines, and thiophenols from aryl halides was developed in the
absence of both ligands and organic solvents. Anilines were formed
selectively with ammonia competing with hydroxylation and thiophe-
nols were generated selectively with sulfur powder after subsequent
reduction competing with hydroxylation and amination.
henols, anilines, and thiophenols are important building
blocks for constructing natural products, pharmaceutical
characteristics of heterogeneous catalysis (recovery and re-
cyclability) and those of homogeneous catalysis (relatively low
catalyst loadings and good selectivity) were combined in nano-
particles catalyst. In addition, because of their large surface area,
metal nanoparticles usually showed high reactivity under mild
conditions.12 Thus, transition metal nanoparticles have been
used widely as catalysts for organic synthesis.13 Herein, we
disclosed a very simple, efficient, ligand-free CuI-nanoparticles-
catalyzed selective synthesis of phenols with water as the solvent
under very mild conditions.14 To our surprise, the coupling
P
and medicinal compounds, as well as in polymers and materials.1-3
The development of a mild and highly efficient method for
synthesis of them over classical protocols has gained considerable
attention in synthetic chemistry. Recently, several efficient
palladium/phosphine-catalyzed processes have been developed
for selective formation of phenols,4 anilines,5 and thiophenols.6
However, the replacement of palladium with less expensive
copper(I) salt as catalyst would be allowed for economic benefits
and low toxicity issues. The development of a cheaper system
enabling the hydroxylation,7 amination,8 and thiolation9 of aryl
halides has become an important goal. More recently, a highly
efficient copper-catalyzed procedure for the direct hydroxylation
of aryl halides in the presence of ligands was disclosed by You7b
and Taillefer7c independently and research showed that a well-
defined ratio of water/organic solvent was the key factor, whereas
water alone was inefficient. It is well-known that water is the most
economical and environmentally friendly solvent in the world.10
Organic solvents contributed the largest amount of “auxiliary
waste” in most chemical productions.11 Very recently, efficient
copper-mediated and ligand-assisted catalytic systems for direct
conversion of aryl halides into phenols7f,g or anilines8a,b in water
have been developed. Ma developed a protocol for thiophenols
involving CuI-catalyzed coupling of aryl iodides with sulfur and
subsequent reduction.9 Unfortunately, all the above catalytic
reactions are inefficient in neat aqueous medium in the absence
of ligands.
reaction gave selectively anilines when NH3 H2O was added
3
into the system. And thiophenols would be obtained selectively
after reduction appending sulfur powder. To the best of our
knowledge, there are no reports on this interesting chemoselec-
tive arylation.
The study was initiated by an investigation of hydroxylation of
iodobenzene with CuI nanoparticles in water without any
ligands. As shown in Table 1, tetra-n-butylammonium hydroxide
was used as the base at 60 °C with CuI nanoparticles as the
catalyst (1.5 mol %) in water (Table 1, entry 1), and the reaction
gave selectively phenol in 97% yield, the corresponding sym-
metric ether appearing in only 0.3% yield. When the base was
altered to KOH, CsOH, Me4NOH, and Et4NOH, low yields
were obtained (Table 1, entries 2-5). The copper(I) salts such
as CuBr, CuCl, Cu2O, and CuI were found to be inferior to CuI
nanoparticles (Table 1, entries 6-9). Control experiments
confirmed that no conversion occurred without catalyst (Table 1,
Metal nanoparticles have drawn much attention due to the
advantages offered by these “semi-heterogeneous catalysts”. The
Received: December 18, 2010
Published: February 28, 2011
r
2011 American Chemical Society
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|

The Journal of Organic Chemistry
NOTE
Table 1. Optimization of Hydroxylation of Aryl Halides
Catalyzed by CuI Nanoparticles in Watera
Table 2. Hydroxylation of Aryl Iodides Catalyzed by CuI
Nanoparticles in Watera
entry
X
[Cu] (mol %)
base
T/°C
yield/%b
1
2
I
CuI(np(1.5))
CuI(np(1.5))
CuI(np(1.5))
CuI(np(1.5))
CuI(np(1.5))
CuBr(10)
nBu4NOH
KOH
60
60
60
60
60
60
60
60
60
60
50
60
80
60
60
80
80
80
90
80
80
97
57
63
79
87
19
16
15
33
trace
80
71
83
75
trace
11
42
45
27
78
12
I
3
I
CsOH
4
I
Me4NOH
Et4NOH
5
I
6
I
nBu4NOH
nBu4NOH
nBu4NOH
nBu4NOH
nBu4NOH
nBu4NOH
nBu4NOH
nBu4NOH
nBu4NOH
nBu4NOH
nBu4NOH
nBu4NOH
nBu4NOH
nBu4NOH
nBu4NOH
nBu4NOH
7
I
CuCl(10)
8
I
Cu2O(10)
9
I
CuI(10)
a CuI nanoparticles (1.5 mol %), Ar-I (1.0 mmol), 40% nBu4NOH aq
(2.0 mL/3.0 equiv) at 60 °C under N2 for 24 h; isolated yield. b At 80 °C
for 36 h.
10
11
12
13
14c
15d
16d
17d
18d,e
19d
20d
21d,e
I
I
CuI(np(1.5))
CuI(np(1.0))
CuI(np(1.0))
CuI(np(1.5))
CuI(np(10))
CuI(np(10))
CuI(np(50))
CuI(np(50))
CuI(np(50))
CuI(np(110))
CuI(np(110))
I
I
Table 3. Hydroxylation of Aryl Bromides Catalyzed by CuI
Nanoparticles in Watera
I
Br
Br
Br
Br
Br
Br
Cl
a Reaction conditions: halogenated benzene (1.0 mmol), base (3.0
equiv), H2O (2.0 mL) under N2 for 24 h. b Determined by GC.
c Reaction time is 15 h. d Reaction time is 48 h. e With 5.0 equiv of
nBu4NOH. np = nanoparticles.
entry 10). Low yields were obtained when the reaction time,
temperature, or amount of CuI nanoparticles were reduced
(Table 1, entries 11-14). The optimal conditions of 1.5 mol %
of CuI nanoparticles, 3.0 equiv of nBu4NOH in water at 60 °C were
used for further investigations.
With this efficient system in hand we next extended the scope
of the substrate to various aryl iodide derivatives (Table 2). We
found that the reaction was applicable to a broad range of
derivatives and was not affected strongly by electron-donating
or electron-withdrawing groups. But, the reactions seemed to be
sensitive to the steric hindrance on the substrate. For example,
1-chloro-2-iodobenzene was hydroxylated under optimized con-
ditions, only 47% isolated yield was obtained. Fortunately, the
reaction was accelerated significantly at elevated temperature and
longer reaction time. Almost quantitative conversions were
obtained from 4-iodobenzoic acid and 2-iodobenzoic acid to
the corresponding products.
Although aryl bromides are less reactive than aryl iodides, the
greater interest for industrial applications fixed our attention. In
spite of the slightly higher temperature that was needed, a series
of phenols were generated from activated aryl bromides
(Table 3). We only obtained a few phenols whose yields are
very close to the catalyst loading (Table 1, entries 16-20) with
bromobenzene as substrate. The yield decreased with reaction
a CuI nanoparticles (1.5 mol %), Ar-Br (1.0 mmol), 40% nBu4NOH aq
(2.0 mL/3.0 equiv) at 80 °C under N2 for 48 h; isolated yield. b With 110
mol % of CuI nanoparticles, nBu4NOH 40% aq (3.3 mL/5.0 equiv).
temperature elevating, probably because nBu4NOH decom-
posed at higher temperature (Table 1, entry 19). However, we
were able to obtain phenol in good yield (78%) when the amount
of catalyst was increased to 110 mol % (Table 1, entry 20). This
method was extended successfully to aryl bromides with elec-
tron-donating substituents such as p- or o-methyl and p-, or o-
methoxy. 1- and 2-bromonaphthalenes were also converted selec-
tively into the corresponding naphthols under these conditions.
Inspired by metal-catalyzed chemoselective N- or O-
arylations,15 we wondered whether N-arylation would take place
when aqueous NH3 solution was added into the system with
existing N, O nucleophilic competition. To our delight, the N-
arylation readily occurred even at room temperature, and the
product of O-arylation was detected in small quantity (<3%).
Next, the scope of aryl iodides was investigated for the N-
arylation reaction with aqueous ammonia at room temperature in
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NOTE
Table 4. CuI-Nanoparticles-Catalyzed Amination of Aryl
Table 6. CuI-Nanoparticles-Catalyzed Synthesis of
Thiophenols from Aryl Halides in Watera
Iodides with NH3 H2O at Room Temperature in Watera
3
a CuI nanoparticles (1.5 mol %), Ar-X (1.0 mmol), 40% nBu4NOH aq
(1.3 mL/2.0 equiv), sulfur power (3.0 equiv) at 40 °C under N2 for 24 h;
a CuI nanoparticles (1.5 mol %), Ar-I (1.0 mmol), 40% nBu4NOH aq
(1.3 mL/2.0 equiv), commercial 28% aqueous NH3 (5.0 equiv) at room
temperature (25 °C) under N2 for 24 h; isolated yield. b Reaction time
is 48 h. c At 45 °C. d 4,40-Diiodobiphenyl as substrate, commercial 28%
aqueous NH3 (10.0 equiv).
c
isolated yield. b At room temperature (25 °C). With 3.0 mol % CuI
nanoparticles at 80 °C for 48 h.
Scheme 1. Experiment of Intermolecular Competition
Table 5. CuI-Nanoparticles-Catalyzed Amination of Aryl
Bromidesa
Scheme 2. One-Pot Synthesis of 4-Aminophenol from
1-Bromo-4-iodobenzene
a CuI nanoparticles (3.0 mol %), Ar-Br (1.0 mmol), 40% nBu4NOH aq
(1.3 mL/2.0 equiv), commercial 28% aqueous NH3 (10.0 equiv) at
80 °C under N2 for 48 h; isolated yield.
We were pleased to observe that the coupling reaction
produces selectively thiophenols after subsequent reduction
when sulfur powder was added instead of aqueous ammonia
(Table 6).17 Aryl thiols were obtained with both inactivated and
activated aryl iodide derivatives. No matter if the aryl iodides
were electron-rich, electron-poor, or sterically hindered, all of
them afforded good to excellent yields. Moreover, aryl thiols of
high yield were obtained with aryl bromides bearing electron-
withdrawing groups. Low conversions occurred for inactivated
aryl bromides.
Since chemoselective N-arylation and S-arylation were accom-
plished as opposed to O-arylation, a competitive experiment was
performed to check out which arylation reaction would occur
when the three substrates existed at the same time (Scheme 1).
Under the standard conditions (see SI), iodobenzene was
water (Table 4). In general, all the aryl iodides gave the correspond-
ing anilines with good to excellent yields. Ortho substituents had no
obvious effect on yields of products to some extent, and a variety of
functional groups could be tolerated in the reaction.
Although little p-nitroaniline was detected when p-nitrobro-
mobenzene was reacted with aqueous ammonia at room tem-
perature, 73% yield was obtained when the reaction was carried
out at 80 °C for 48 h. Futhermore, p-nitroaniline was obtained
with 87% yield when 3.0 mol % of CuI nanoparticles and 10.0
equiv of NH3 were applied. As shown in Table 5, all the examined
aryl and heteroaryl bromides coupled with aqueous ammonia to
afford the corresponding anilines with good to excellent yields.
On the other hand, aryl bromides bearing electron-donating
substituents were less effective. In addition, the reactivity of aryl
chlorides decreased dramatically in the present system.16
reacted in the presence of both NH3 H2O and S, thiophenol
3
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The Journal of Organic Chemistry
NOTE
Table 7. Recyclability of CuI Nanoparticles
unchanged before and after the reaction (Figure 1a-c). Likewise,
the powder X-ray diffraction analysis exhibited identical peaks for
both the fresh and recovered CuI nanoparticles (Figure 1d,e).
In conclusion, we have demonstrated that selective O-
arylation,20 N-arylation, and S-arylation could be achieved in
water without assisted ligand at relatively mild conditions (no
higher than 80 °C).4a A variety of aryl iodides and bromides
could be coupled with available nBu4NOH, NH3 H2O, and S in
3
run
catalyst recovery (%)
product yield (%)c
this simple and efficient protocol to give the corresponding
products in high yields. The competition experiment showed
that S had the best reactivity. Furthermore, the catalyst could be
reused for three cycles with slight loss of its activity.
1a
2b
3b
95
89
82
95
87
80
a CuI nanoparticles (1.5 mol %), iodobenzene (1.0 mmol), 40%
nBu4NOH aq (1.3 mL/2.0 equiv), commercial 28% aqueous NH3
(5.0 equiv) at 25 °C under N2 for 24 h. b The recovered catalyst was
used under identical reaction conditions to those for the first run.
c Determined by GC.
’ EXPERIMENTAL SECTION
General Procedure for Hydroxylation of Aryl Iodides. An
oven-dried Schlenk tube equipped with a magnetic stirring bar was
charged with CuI nanoparticles (1.5 mol %, 2.9 mg), the aryl iodides if a
solid (1 mmol). The tube was evacuated and backfilled with nitrogen.
Under a counter flow of nitrogen, aryl iodides if a liquid (1 mmol,
1 equiv) and degassed 40% tetra-n-butylammonium hydroxides water
solution (2.0 mL) were added. The tube was sealed and the mixture was
allowed to stir at 60 °C for 24 h. The reaction mixture was then allowed
to cool to ambient temperature, then 10 mL of ethyl acetate and 1 mL of
HCl (37%) were added. For the general workup and detailed experi-
ments, please see the Supporting Information.
’ ASSOCIATED CONTENT
S
Supporting Information. Preparation of the catalyst,
b
general synthetic procedures, and characterization of products.
This material is available free of charge via the Internet at http://
pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: hjxu@hfut.edu.cn and ysfeng@hfut.edu.cn.
’ ACKNOWLEDGMENT
We gratefully acknowledge financial support from the Na-
tional Natural Science Foundation of China (Nos. 20802015,
21072040, 21071040). We thank Yong-Qiang Zhao in this
research group for reproducing some results in Tables 2-6.
Figure 1. (a) TEM image of fresh CuI nanoparticles; (b) TEM image of
CuI nanoparticles after the third catalytic cycle; (c) TEM image of fresh
CuI nanoparticles at 50 nm; (d) XRD pattern of fresh CuI nanoparticles;
(e) XRD pattern of CuI nanoparticles after the third catalytic cycle.
was formed selectively after reductive step, proving the order of
S > N > O.
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