Metal complexes catalyzed oxidative coupling of 2,6-dimethylphenol in micellar media

Article abstract of DOI:10.1016/j.molcata.2010.06.003

The oxidative coupling reaction of 2,6-dimethylphenol (DMP) with H ₂O₂ catalyzed by two copper(II) complexes (2,2′-dipyridylamine copper(II), L¹Cu and N,N′-bis (2-pyridinecarbonyl) ethylenediamine copper(II), L²Cu) in cationic surfactant cetyl trimethylammonium bromide (CTAB), gemini surfactants ethanediyl-1,2-bis(dodecyldimethylammonium bromide) (12-2-12), dimethylene-1,2-bis(cetyltrimethylammonium bromide) (16-2-16), anionic surfactant sodium dodecyl benzene sulfornate (SDBS) and nonionic surfactant Triton X-100 (TX-100) micellar media were comparatively investigated at 25 °C. The kinetics of formation of 3,3′,5,5′-tetramethyl-4, 4′-diphenoquinone (DPQ) was studied. The kinetic parameters k₂ and K_m were obtained at pH 7.01. L¹Cu displayed better catalytic activity than L²Cu in mentioned above systems. For L ¹Cu catalyzed systems, the cationic surfactant CTAB, 12-2-12 and 16-2-16 micellar media accelerated the oxidation of DMP. And the TX-100 and SDBS micelles showed little effect on reaction rate compared with the buffer solution. For the L²Cu catalyzed systems, these surfactants all inhibited the oxidation of DMP, and especially, the oxidation of DMP was not found in SDBS micellar solution in the catalyzed system at pH 7.01 and 25 °C. Micelles showed great influence on the yield of product and the selectivity of PPO. Under this work's conditions, DPQ was easily generated in aqueous solution, while PPO was remarkably promoted in micellar media, especially in SDBS micellar solution. As a green technology process, one outstanding advantage of this catalyzed system was that the products of polymer can be easily separated from the solution and the catalysts still remain in the micellar solution.

Full text of DOI:10.1016/j.molcata.2010.06.003

Journal of Molecular Catalysis A: Chemical 328 (2010) 88–92
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Metal complexes catalyzed oxidative coupling of 2,6-dimethylphenol
in micellar media
Xiao-Hong Lia, Xiang-Guang Menga,∗, Qin-Hui Panga, Shan-Dong Liub,
Jian-Mei Lia, Juan Dua, Chang-Wei Hua
a Key Laboratory of Green Chemistry and Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu 610064, PR China
b College of Physics Science, Qingdao University, Qingdao 266071, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
The oxidative coupling reaction of 2,6-dimethylphenol (DMP) with H2O2 catalyzed by two
copper(II) complexes (2,2ꢀ-dipyridylamine copper(II), L1Cu and N,Nꢀ-bis (2-pyridinecarbonyl) ethylene-
diamine copper(II), L2Cu) in cationic surfactant cetyl trimethylammonium bromide (CTAB), gemini
surfactants ethanediyl-1,2-bis(dodecyldimethylammonium bromide) (12-2-12), dimethylene-1,2-
bis(cetyltrimethylammonium bromide) (16-2-16), anionic surfactant sodium dodecyl benzene sulfornate
(SDBS) and nonionic surfactant Triton X-100 (TX-100) micellar media were comparatively investigated
at 25 ◦C. The kinetics of formation of 3,3ꢀ,5,5ꢀ-tetramethyl-4,4ꢀ-diphenoquinone (DPQ) was studied. The
kinetic parameters k2 and Km were obtained at pH 7.01. L1Cu displayed better catalytic activity than
L2Cu in mentioned above systems. For L1Cu catalyzed systems, the cationic surfactant CTAB, 12-2-12 and
16-2-16 micellar media accelerated the oxidation of DMP. And the TX-100 and SDBS micelles showed
little effect on reaction rate compared with the buffer solution. For the L2Cu catalyzed systems, these
surfactants all inhibited the oxidation of DMP, and especially, the oxidation of DMP was not found in
SDBS micellar solution in the catalyzed system at pH 7.01 and 25 ◦C. Micelles showed great influence on
the yield of product and the selectivity of PPO. Under this work’s conditions, DPQ was easily generated
in aqueous solution, while PPO was remarkably promoted in micellar media, especially in SDBS micellar
solution. As a green technology process, one outstanding advantage of this catalyzed system was that
the products of polymer can be easily separated from the solution and the catalysts still remain in the
micellar solution.
Received 18 March 2010
Received in revised form 24 May 2010
Accepted 1 June 2010
Available online 8 June 2010
Keywords:
Oxidative coupling
2,6-Dimethylphenol
Micelle
Metallomicelle-catalyzed
PPO
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
decades, however, no mechanism could be formulated yet that was
able to solve all experimental findings. Up to now, several mecha-
Poly(2,6-dimethyl-1,4-phenylene ether) (PPO) was widely used
as a high-performance engineering plastic due to its good mechan-
ical character, high glass transition temperature and the properties
of chemical stability and self-extinguish [1–6]. PPO was generally
prepared by the oxidative coupling of 2,6-dimethylphenol. In this
reaction, PPO was formed by C–O coupling of phenolic moieties.
The other product diphenoquinone (DPQ) generated from C–C cou-
pling of two monomeric phenols, which was also recognized as an
important material for electron transport [7].
Many copper(II) complexes were found as efficient catalysts in
the catalysis process of oxidative coupling of DMP in organic sol-
vents and water [8–12]. The use of water as the solvent for the
oxidative polymerization was a green chemical process [12,13].
This reaction has been investigated extensively during the last
nistic proposals have been made accordingly which were thought
to involve coupling of free phenoxy radicals, coupling of phenoxy
radicals coordinated to catalyst, coupling of phenoxonium cation
with phenol [14–17]. However the mechanism was yet not entirely
clear.
Surfactant possesses hydrophilic and hydrophobic groups in
their molecule. Surfactant and its micelle can alter reaction
rate, mechanism and region- and stereochemistry [18–20]. Fur-
thermore, the reactive intermediate could be inferred by the
electrostatic effects of micelles [20]. In previous studies, we found
that micelle and metallomicelle could efficiently increase the rate
of hydrolysis and oxidation reactions [21–25]. In this work, we fur-
therly found that the distribution of products of the oxidation of
DMP with H2O2 catalyzed by copper(II) complexes was also greatly
changed by micelles. We were particularly interested in the prop-
erty of the catalysis system in which the products of polymer could
be easily separated from metallomicelle-catalyzed system under
mild conditions.
∗
Corresponding author. Tel.: +86 28 85462979; fax: +86 28 85412907.
E-mail address: mengxgchem@163.com (X.-G. Meng).
1381-1169/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2010.06.003

X.-H. Li et al. / Journal of Molecular Catalysis A: Chemical 328 (2010) 88–92
89
2. Experimental
2.1. Materials
CuCl2·2H2O, chloroform, absolute ethanol, 30% hydrogen perox-
ide, 2,2ꢀ-dipyridylamine, bromohexadecane, N,N,Nꢀ,Nꢀ-tetramethyl
ethylenediamine, sodium hydroxide, 1-dodecane bromide, 2,6-
dimethylphenol (DMP), sodium dodecyl benzene sulfornate
(SDBS), cetyl trimethylammonium bromide (CTAB), Triton X-100
(TX-100) were all analytical grade and were purchased from com-
mercial sources. The 2,6-dimethylphenol (DMP) was purified by
recrystallization. All other chemicals and solvents used were also
analytical grade.
Fig. 1. Structure of two copper(II) complexes L1Cu and L2Cu.
by ICP-AES. The two copper(II) complexes were outlined in
Fig. 1.
2.2. Synthesis of gemini surfactants and preparation of copper(II)
complexes
2.3. Instruments and methods
2.2.1. Synthesis of gemini surfactant 16-2-16
The 16-2-16 was synthesized according to the literature [26].
The reaction was performed in absolute ethanol under reflux for
24 h in the presence of 1:3 proportion of N,N,Nꢀ,Nꢀ-tetramethyl
ethylenediamine and bromohexadecane. The solvent was removed
by evaporation and the solid was recrystallized by ethyl acetate
and ethanol to yield pure product. Anal. calcd. for C38H82N2Br2:
C, 62.81; H, 11.29; N, 3.86%; found: C, 61.96; H, 11.02; N, 3.58%.
1H NMR (300 MHz, CDCl3), ı 0.9 (t, 6H, CH2CH3), 1.26 (m, 56H,
CH2), 1.83 (t, 4H, N-CH2), 3.44–3.52 (s, 12H, N-CH3), 3.73 (t, 4H,
NCH2CH2N).
Mass spectrometry was implemented with a Finnigan MAT
45001 mass spectrometer. Ultraviolet–visible absorbance mea-
surements were performed with a TU-1901 UV-vis spectropho-
tometer (Beijing Purkinje General Instrument Co., Ltd.) equipped
with a thermostatic cell holder. Elemental analysis was imple-
mented with a Carlo Erba 1106 instrument. The residual amount
of DMP was implemented with FULI 9790 gas chromatograph.
0.01 M Tri (hydroxylmethy) aminomethane (Tris) buffer solu-
tion was employed for all reactions. The concentration of H2O2 was
determined by titrating a standardized ceric sulfate solution.
The typical reaction solution contained 5.0 × 10−5 M catalyst,
0.01 M hydrogen peroxide and desired concentration DMP. The
reaction was carried out at 25 0.2 ◦C. The initial DPQ reaction rate
R0 was measured by monitoring the Formation of DPQ at 421 nm
vs. time: R0 = ꢀA/(εlꢀt). The unreacted amount of DMP was imple-
mented with gas chromatograph.
2.2.2. Synthesis of gemini surfactant 12-2-12
The 12-2-12 was also synthesized according to the literature
[26]. By using the similar method as the synthesis of 16-2-16 in
which 1-dodecane bromide was substituted for bromohexadecane.
The crude products were recrystallized by acetone and ethanol.
Anal. calcd. for C30H66N2Br2: C, 58.23; H, 10.75; N, 4.56%; found:
C, 57.27; H, 10.23; N, 4.16%. 1H NMR (300 MHz, CDCl3), ı 0.89 (t,
6H, CH2CH3), 1.17 (m, 40H, CH2), 1.81 (t, 4H, N-CH2), 3.54 (s, 12H,
N-CH3), 3.68 (t, 4H, NCH2CH2N).
In the enlarged experiment, the 5.0 × 10−3 M catalysts, 2.0 M
hydrogen peroxide, and 1.0 × 10−1 M DMP were mixed and the
solution was kept at 25 0.2 ◦C for 48 h. The insoluble solid product
was filtered off from solution, dried and weighed.
2.2.3. Preparation of L1Cu
3. Results and discussion
The L1Cu was prepared according to the literature [27].
2,2ꢀ-Dipyridylamine (1.71 g, 9.8 mmol) was added to hot
trichloromethane (60 ml), and then to a hot CuCl2·2H2O (1.7 g,
10 mmol) in DMF (20 ml) solution under gentle stirring. Then,
green precipitate was formed immediately. After some minutes
it was filtered off, washed with trichloromethane and dried in
vacuo. Anal. calcd. for C10H9N3CuCl2: C, 39.30; H, 2.95; N, 13.75;
Cl, 23.22%; found: C, 39.38; H, 2.90; N, 13.45; Cl, 23.22%. The Cu
loading was determined to be 3.17 mmol/g by ICP-AES.
3.1. Effects of micelles on the rate of formation of DPQ
The oxidative coupling of DMP catalyzed by two copper(II) com-
plexes were carried out in cationic CTAB, gemini 12-2-12 and
16-2-16, anion SDBS and nonionic TX-100 micelles, respectively.
The initial reaction rates of formation of DPQ in aqueous solu-
tion and micellar media at pH 7.01 and 25 ◦C were calculated and
shown in Table 1. From Table 1, it can be seen that L1Cu displayed
2.2.4. Preparation of L2Cu
Table 1
N,Nꢀ-bis (2-pyridinecarbonyl) ethylenediamine was prepared
according to the literature [28]. Picolinate (2.46 g, 0.02 mol) in
pyridine solution (8 ml) was added to ethylenediamine (0.01 mol,
0.68 ml) in pyridine (4 ml) under gentle stirring. Then triphenyl
phosphate (5.21 ml, 0.0198 mol) was added slowly into the reac-
tion mixture under reflux for 4 h in a water bath. Crystals formed
overnight at room temperature and recrystallized by chloroform
to yield the pure N,Nꢀ-bis (2-pyridinecarbonyl) ethylenediamine
1. 1 (0.2 g) dissolved in hot ethanol was dropwise added into the
CuCl2·2H2O (2.052 g, 0.012 mol) ethanol solution and the mixture
was stirred for 2 h. Products were isolated by filtration, washed
with cold ethanol and water. Anal. calcd. for C14H13N4O2CuCl: C,
45.66; H, 3.53; N, 15.22; Cl, 9.51%; found: C, 45.71; H, 3.45; N,
15.12; Cl, 9.57%. The Cu loading was determined to be 3.17 mmol/g
The initial reaction rates R0 of formation of DPQ in micellar media at pH 7.01 and
25 ◦C.
Systems
×109R0 M s−1
L1Cu
L2Cu
Buffer
CTAB
12-2-12
16-2-16
Tx-100
SDBS
14.00
26.10
26.00
32.61
14.92
14.80
1.18
0.69
1.05
1.08
0.52
a
–
Note: [LCu] = 5.0 × 10−5 M, [H2O2]0 = 0.01 M, [DMP]0 = 1.0 × 10−3 M, [CTAB] = 0.01 M,
[TX-100] = 3.3 × 10−3 M,
[SDBS] = 0.012 M,
[12-2-12] = 0.01 M,
[16-2-
16] = 1.0 × 10−3 M.
a
Too small to be determined.

90
X.-H. Li et al. / Journal of Molecular Catalysis A: Chemical 328 (2010) 88–92
Scheme 1.
better catalytic activity than L2Cu. For L1Cu catalyzed systems,
these cationic micelles accelerated the reaction, while the non-
ionic micelle TX-100 and anionic micelle showed a little effect on
the reaction rate. For L2Cu, the initial formation rate of DPQ R0
decreased in all of the micelles solution compared with the buffer
solution, especially for SDBS, its reaction rate was too slow to be
evaluated.
Fig. 2. Plot of 1/R0 vs. 1/[DMP]0 catalyzed by L1Cu, at pH 7.01 and 25 ◦C.
[L1Cu] = 5 × 10−5 M, [H2O2]0 = 0.01 M, [CTAB] = 0.01 M, [TX-100] = 3.3 × 10−3 M,
[SDBS] = 0.012 M, [12-2-12] = 0.01 M, [16-2-16] = 1.0 × 10−3 M.
3.2. Kinetic analysis
It was found that the oxidative coupling reaction of DMP with
H2O2 did not occur in the absence of catalysts, which showed that
the copper(II) complexes displayed special catalytic characteristic
for the oxidative coupling of DMP by H2O2 in aqueous solution and
micellar media. As reported in previous studies [29,30], the cop-
per(II) complexes with H2O2 may form an active oxygen species
(M*). In this work, we also thought the active oxygen species (M*)
as oxidant reacted with substrate DMP to produce DPQ. Accord-
ing to the experimental data, it can be found that the plots of
R0 vs. [DMP]0 were all saturated curves, which had the character
of Michaelis–Menten mechanism model. Thus the kinetic model,
which was similar to Michaelis–Menten form, was proposed as
Scheme 1.
In the first step, the active oxidant (M*) could combine with
substrate DMP (S) reversibly to form the intermediates (M*S) with
rate constants k1 and k
Then the intermolecular reaction of M*S
−1.
occurred, which was the rate-determining step with a rate constant
k2. The process that catalyst M was oxidized to M* again by H2O2
rapidly, and the rate constant kreox was far larger than k2. In this
work, the concentration of H2O2 was far excessive over copper(II)
complex. So, almost all of M was oxidized to active state M*. Thus
based on Scheme 1, Eq. (1) could be obtained:
Fig. 3. Plot of 1/R0 vs. 1/[DMP]0 catalyzed by L2Cu, at pH 7.01 and 25 ◦C.
[L2Cu] = 5 × 10−5 M, [H2O2]0 = 0.01 M, [CTAB] = 0.01 M, [TX-100] = 3.3 × 10−3 M,
[SDBS] = 0.012 M, [12-2-12] = 0.01 M, [16-2-16] = 1.0 × 10−3 M.
owing to the electrostatic effect, the cationic micelle could promote
the reaction rate by attracting and steadying the electronegative
intermediate. On the other hand, micelle could concentrate reac-
tion substrate due to the hydrophobic effect and hence accelerate
reaction rate. Thus neutral TX-100 showed somewhat increase in
the reaction rate. And electronegative SDBS micelle showed some-
what decrease in rate owing to the electrostatic effect and the
concentrated effect.
1
R0
1
Km
=
+
(1)
k2[M]T
k2[M]T [S]0
where [M]T was the total concentration of catalyst. [S]0 was the
initial concentration of DMP. Km was the Michaelis constant.
k
−1 + k2
Km
=
(2)
k1
According to Eq. (1), the plot of 1/R0 vs. 1/[S]0 should be lin-
ear relationship. The experimental results indicated that 1/R0 vs.
1/[DMP]0 for the two copper(II) complexes catalyzed reactions dis-
played really good linear relationship (all the correlation coefficient
R > 0.99) in the buffer solution and micellar media as shown in
Figs. 2 and 3. The kinetic parameters k2 and Km could be obtained
from the slope and intercept of the plot of 1/R0 vs. 1/[DMP]0, which
were listed in Table 2.
In this oxidative coupling reaction, the DPQ generated from C–C
coupling of two monomeric phenols. From Table 2 it can be found
that for L1Cu catalyzed systems, these cationic micelles (CTAB, 12-
2-12, 16-2-16) all increased the formation rate of DPQ, while the
nonionic micelle TX-100 and anionic micelle SDBS showed a little
effect. This fact indicated that a reactive intermediate with nega-
tive charge may be formed in the process of generation of DPQ. So
Table 2
Effects of micelles on the kinetic parameters k2 and Km at pH 7.01 and 25 ◦C.
Systems
L1Cu
L2Cu
×104k2 s−1
×105Km
M
×105k2 s−1
×104Km
M
Buffer
CTAB
12-2-12
16-2-16
Tx-100
SDBS
2.86
5.57
5.59
6.69
3.05
2.67
4.33
9.78
9.42
4.39
2.49
7.06
3.01
1.88
1.00
2.62
1.24
2.56
4.42
1.88
2.57
1.61
a
a
–
–
Note:
[LCu] = 5.0 × 10−5 M,
[H2O2]0 = 0.01 M,
[CTAB] = 0.01 M,
[TX-
100] = 3.3 × 10−3 M, [SDBS] = 0.012 M, [12-2-12] = 0.01 M, [16-2-16] = 1.0 × 10−3 M.
a
Too small to be determined.

X.-H. Li et al. / Journal of Molecular Catalysis A: Chemical 328 (2010) 88–92
91
Table 3
Table 5
The yields and ratios of products of reaction catalyzed by L1Cu complex in aqueous
solution and micellar media after 48 h at pH 7.01 and 25 ◦C.
The yield and ratio of products of reaction catalyzed by LCu complexes at pH 7.01
and 25 ◦C.
Systems
Residua of
DMP (%)
Yield of
DPQ (%)
Yield of
PPO (%)
WPPO/WDPQ
Systems
L1Cu
L2Cu
Yield (%)a
WPPO/WDPQ
Yield (%)a
WPPO/WDPQ
Buffer
TX-100
SDBS
CTAB
16-2-16
12-2-12
0
0
0
0
56.14
15.61
10.88
15.50
26.62
11.82
43.86
84.39
89.12
84.50
58.38
57.17
0.78
5.41
8.19
5.45
2.21
4.84
Buffer
TX-100
SDBS
CTAB
16-2-16
12-2-12
72.30
73.22
82.60
71.91
62.91
48.70
1.62
4.91
7.27
5.20
2.98
2.04
45.4
43.2
38.8
36.8
40.2
22.3
1.57
4.40
7.81
4.78
3.08
4.86
15.00
31.10
Note:
[L1Cu] = 5.0 × 10−5 M,
[H2O2]0 = 0.02 M,
[DMP]0 = 1.0 × 10−3 M,
Note: [LCu] = 5.0 × 10−3 M, [H2O2]0 = 2.0 M, [DMP]0 = 1.0 × 10−1 M, [CTAB] = 0.01 M,
[CTAB] = 0.01 M, [TX-100] = 3.3 × 10−3 M, [SDBS] = 0.012 M, [12-2-12] = 0.01 M,
[16-2-16] = 1.0 × 10−3 M.
[TX-100] = 3.3 × 10−3 M,
[SDBS] = 0.012 M,
[12-2-12] = 0.01 M,
[16-2-
16] = 1.0 × 10−3 M.
a
The yield of insoluble product.
Table 4
The yields and ratios of products of reaction catalyzed by L2Cu complex in aqueous
solution and micellar media after 48 h at pH 7.01 and 25 ◦C.
dation of DMP, although the initial rate of formation of DPQ was
accelerated (shown in Table 2). Since gemini has two hydrophobic
long chain, its micelle has looser bulk than singe chain surfactant. So
it was possible that the products dissolved in gemini micelle were
not easy to break away from the micelle and prevent the reagent
DMP into the micelle, and therefore result in the decrease of the
reaction rate with the reaction goes on. The anionic micelles with
electronegative region can significantly improve the yield of PPO.
The ratio of the PPO to DPQ increased from 0.79 in aqueous solu-
tion to 8.19 in SDBS micellar media. This observation supported
the mechanism that phenoxonium cation intermedium may form
and favor the C–O coupling of oligomeric phenols [14,17]. From
Table 4 we found that for L2Cu catalyzed system the micelles all
inhibited the oxidation of DMP, a large amount of DMP remained
in the reaction solution after 48 h and SDBS micelle still showed the
best selectivity of PPO. The construct of L2Cu complex was differ-
ent from L1Cu. The four coordinative Cu2+ in L2Cu complex were
difficult to associate simultaneously with both H2O2 and DMP due
to the effects of electron and steric hindrance.
In order to check the feasibility in industry application, reactions
of 100-fold enlarged concentrations were carried out under simi-
lar experimental conditions. An interesting observation was found
that the insoluble solid products formed and precipitated from the
solution. The analysis results were listed in Table 5. From Table 5, it
could be seen that there were relatively good product yields after
48 h reaction. Micellar medium significantly increased the ratio of
PPO to DPQ. Especially in the SDBS system, PPO had the highest
yield. It was worth to note that a little number of –CH3 group in
benzene was furtherly oxidized into aldehyde or acid. Although
some aspects need make further investigation, several advantages
for the preparation of polymer in metallomicelle catalyzed system
were obvious: water as green solvent, mild reaction conditions and
products could be easily separate from the solution while catalysts
remain in micellar media.
Systems
Residua of
DMP (%)
Yield of
DPQ (%)
Yield of
PPO (%)
WPPO/WDPQ
Buffer
TX-100
SDBS
CTAB
16-2-16
12-2-12
10.20
15.52
33.91
35.50
42.53
59.80
52.00
14.64
6.12
13.19
21.64
8.89
37.80
69.84
59.97
51.31
35.83
31.28
0.73
4.76
9.78
3.89
1.65
3.52
Note:
[L2Cu] = 5.0 × 10−5 M,
[H2O2]0 = 0.02 M,
[DMP]0 = 1.0 × 10−3 M,
[CTAB] = 0.01 M, [TX-100] = 3.3 × 10−3 M, [SDBS] = 0.012 M, [12-2-12] = 0.01 M,
[16-2-16] = 1.0 × 10−3 M.
For L2Cu-catalyzed systems, L2Cu showed remarkable dif-
ference from L1Cu in reaction activity and in sensitivity to
microenvironment. It was possible that the four-coordinated cop-
per(II) complex of L2Cu more difficult to associate with DMP owing
to the steric hindrance and consequently resulted in the greater
Michaelis constant Km than L1Cu (Table 2) and thus lead to the
lower catalytic activity.
Compared with L1Cu, L2Cu has better hydrophobic property and
more poor solubility in water. Therefore, in micellar solution L2Cu
may be solubilized in deeper inner of micelle (fence region), while
L1Cu could be solubilized on the surface of micelle (stern layer).
Hence in micellar solution for L1Cu and L2Cu catalyzed reaction,
the catalysis reaction may take place in different region of micelle.
In addition, most of substrate DMP molecule could be solubilized
in stern layer of micelle (surface region) due to its good solubility
in water and only a few could enter the inner of micelle, therefore
for the L2Cu catalyzed system, the presence of micelle decreased
the reaction rate.
4. The selectivity of PPO
In this oxidative coupling reaction, PPO was also formed by C–O
coupling of phenolic moieties besides the DPQ generated from C–C
coupling of two monomeric phenols. In order to analyze the amount
of PPO generated in this reaction, the reactions were performed in
different media at pH 7.01 and 25 ◦C for 48 h. Then the content
of DMP in reaction solution was determined by gas chromato-
graph analysis. The reaction product was dissolve in acetone and
the amount of DPQ was obtained by monitoring the absorbance at
421 nm by UV–vis analysis. Thus, the amount of PPO was evaluated
by subtracting the weight of DPQ and of residual unreacted DMP
from that of initial DMP. The results were listed in Tables 3 and 4.
From Tables 3 and 4 it could be found that the micellar media caused
great influence on the property of reaction. The micelle changed the
reaction rate of formation of DPQ and that of PPO, which led to the
variety of ratio of PPO to DPQ. From Table 3 it could be seen that
the gemini surfactants has a significant inhibitory effect on the oxi-
5. Conclusions
This study indicated that the oxidative coupling of DMP by H2O2
could take place in the buffer and micellar solution by using cop-
per(II) complexes as catalysts at pH 7.01 and 25 ◦C. The micelles
showed different influence on the oxidative coupling reaction. For
L1Cu catalyzed systems, the CTAB, 12-2-12 and 16-2-16 micellar
media accelerated the oxidation of DMP. And the TX-100 and SDBS
micelles showed little effect on reaction rate compared with the
buffer solution. For the L2Cu catalyzed systems, these surfactants
all inhibited the oxidation of DMP. The micelles also showed great
influence on the yield of product and the selectivity of PPO. DPQ was
easily generated in aqueous solution, while PPO was remarkably
promoted in micellar media, especially in SDBS micellar solution.
Gemini surfactants 12-2-12 and 16-2-16 did not display especial

92
X.-H. Li et al. / Journal of Molecular Catalysis A: Chemical 328 (2010) 88–92
property in catalysis. This study also supported the mechanism
that phenoxonium cation intermedium may form and favor the
C–O coupling of oligomeric phenols. This study showed that the
metallomicelle exhibited excellent catalytic characteristic for the
oxidative coupling of DMP and it may be a potential catalysis system
for the preparation of other organic materials.
[10] Y.M. Chung, W.S. Ahn, P.K. Lim, J. Mol. Catal. A: Chem. 148 (1999) 117.
[11] H. Higashimura, K. Fujisawa, Y. Moro-oka, M. Kubota, A. Shiga, A. Terahara,
H. Uyama, S. Kobayashi, J. Am. Chem. Soc. 120 (1998) 8529.
[12] K. Saito, N. Kuwashiro, H. Nishide, Polymer 47 (2006) 6581.
[13] C.J. Li, L. Chen, Chem. Soc. Rev. 35 (2006) 68.
[14] P. Gamez, S. Gupta, J. Reedijk, C. R. Chim. 10 (2007) 295.
[15] K. Saito, T. Masuyama, K. Oyaizu, H. Nishide, J. Chem. Eur. 9 (2003) 4240.
[16] J.L. Roubaty, M. Bréant, M. Lavergne, A. Revillon, Macromol. Chem. 179 (1978)
1151.
[17] P.J. Baesjou, W.L. Driessen, G. Challa, J. Reedijk, J. Am. Chem. Soc. 119 (1997)
12590.
Acknowledgments
[18] Y.J. Li, P.X. Li, C.C. Dong, X.Y. Wang, Y.L. Wang, H.K. Yan, R.K. Thomas, Langmuir
22 (2006) 42.
[19] S. Tascioglu, Tetrahedron 52 (1996) 11113.
[20] T. Dwars, E. Paetzold, G. Oehme, Angew. Chem. Int. Ed. 44 (2005) 7174.
[21] J. Zhang, X.G. Meng, X.C. Zeng, X.Q. Yu, Coord. Chem. Rev. 253 (2009)
2166.
[22] D. Kou, X.G. Meng, Y. Liu, J. Du, X.M. Kou, X.C. Zeng, Colloid Surf. A 324 (2008)
189.
This work has been supported by the National Natural Sci-
ence Foundation of China (No. 20803050) and the National Basic
Research Program of China (No. 2007CB210203) and the Research
Fund for the Doctoral Program of Higher Education of China (No.
20090181110074).
[23] F.B. Jiang, L.Y. Huang, X.G. Meng, J. Du, X.Q. Yu, Y.F. Zhao, X.C. Zeng, J. Colloid
Interface Sci. 303 (2006) 232.
References
[24] X.G. Meng, Y. Guo, C.W. Hu, X.C. Zeng, J. Inorg. Biochem. 98 (2004) 2107.
[25] S.Q. Cheng, X.C. Zeng, X.G. Meng, X.Q. Yu, J. Colloid Interface Sci. 224 (2000)
333.
[26] R. Zana, M. Benrraou, R. Rueff, Langmuir 7 (1991) 1072.
[27] A. Camus, A. Facchinetti, N. Marsich, A.M.M. Lanfredi, F. Ugozzoli, Inorg. Chim.
Acta 290 (1999) 180.
[1] J. Gao, S.H. Zhong, R.A. Zingaro, J. Mol. Catal. A: Chem. 207 (2004) 15.
[2] B. Xiao, H.W. Hou, Y.T. Fan, J. Organomet. Chem. 692 (2007) 2014.
[3] D. Sakar, O. Cankurtaran, F. Karaman, Plast. Rubber Compos. 37 (2008) 276.
[4] F. Sadeghi, A.Y. Tremblay, B. Kruczek, J. Appl. Polym. Sci. 109 (2008) 1454.
[5] T.W. Xu, D. Wu, L. Wu, Prog. Polym. Sci. 33 (2008) 894.
[28] C.F. Fortney, R.E. Shepherd, Inorg. Chem. Commun. 7 (2004) 1065.
[29] J.M. Li, X.G. Meng, C.W. Hu, J. Du, X.C. Zeng, J. Mol. Catal. A: Chem. 299 (2009)
102.
[30] A. Kunishita, J.D. Scanlon, H. Ishimaru, K. Honda, T. Ogura, M. Suzuki, C.J. Cramer,
S. Itoh, Inorg. Chem. 47 (2008) 8222.
[6] T.J. Lee, Y.D. Fang, W.G. Yuan, K.M. Wei, M. Liang, Polymer 48 (2007) 734.
[7] P.M. Borsenberger, W.T. Gruenbaum, M.B. Oregan, L.J. Rossi, J. Polym. Sci. Polym.
Phys. 33 (1995) 2143.
[8] E.P. Zhang, H.W. Hou, H.Y. Han, Y.T. Fan, J. Organomet. Chem. 693 (2008) 1927.
[9] S.J.A. Guieu, A.M.M. Lanfredi, C. Massera, L.D. Pachón, P. Gamez, J. Reedijk, Catal.
Today 96 (2004) 259.