A moderate and efficient method for oxidation of ethylbenzene with hydrogen peroxide catalyzed by 8-quinolinolato manganese(III) complexes

Article abstract of DOI:10.1016/j.molcata.2010.08.008

The oxidation of ethylbenzene with 30% aqueous hydrogen peroxide (H ₂O₂) in an acetone-water medium at 30 °C was investigated using hexadentate 8-quinolinolato manganese(III) complexes (Q ₃Mn^III) as catalysts. T

Full text of DOI:10.1016/j.molcata.2010.08.008

Journal of Molecular Catalysis A: Chemical 331 (2010) 106–111
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A moderate and efficient method for oxidation of ethylbenzene with hydrogen
peroxide catalyzed by 8-quinolinolato manganese(III) complexes
∗
Chunli Lu, Zaihui Fu , Yachun Liu, Fenglan Liu, Youyu Wu, Jinwei Qin, Xiangling He, Dulin Yin
Key Laboratory of Resource Fine-Processing and Advanced Materials of Hunan Province and Key Laboratory of Chemical Biology and Traditional Chinese Medicine Research (Ministry
of Education of China), College of Chemistry and Chemical Engineering, Hunan Normal University, Changsha 410081, China
a r t i c l e i n f o
a b s t r a c t
Article history:
The oxidation of ethylbenzene with 30% aqueous hydrogen peroxide (H O ) in an acetone–water
2
2
Received 16 December 2009
Received in revised form 20 July 2010
Accepted 7 August 2010
◦
III
medium at 30 C was investigated using hexadentate 8-quinolinolato manganese(III) complexes (Q3Mn
)
III
as catalysts. The results indicated that the Q3Mn complexes, with ammonium acetate and acetic
acid as additives, selectively catalyzed the side chain oxidation of ethylbenzene at secondary carbon
Available online 14 August 2010
III
atoms, affording acetophenone as a major product. Among the Q3Mn complexes examined, the 5,7-
III
dibrominated Q3Mn catalyst was the most active, and provided the ethylbenzene conversion of 26.1%
Keywords:
Ethylbenzene
Catalysis
and the oxidation yield of 65% under the optimum conditions. The influence of various parameters on
III
the reaction was checked in detail. Based on the UV–vis spectra, a free radical mechanism for the Q3Mn
catalytic system was also proposed.
Hydrogen peroxide
8
-Quinolinolato Mn(III) complexes
© 2010 Elsevier B.V. All rights reserved.
Selective oxidation
1
. Introduction
Acetophenone as an important intermediate is increasingly
oxidation systems reported to date have one or more disadvan-
tages, including the use of toxic reagents [19–21,26,27], relatively
high operation temperature [19–21], low ethylbenzene concen-
used for the synthesis of some perfumes, pharmaceuticals, resins,
alcohols, esters, aldehydes and tear gas, and as a solvent for cellu-
lose ethers. Therefore, there has been considerable interest in the
development of highly efficient processes for the production of ace-
tophenone from ethylbenzene. Among these processes reported to
date, the air oxidation process of ethylbenzene based on Co(II) and
Mn(II) catalysts in acetic acid media is known [1]. However, the
operation conditions in this process are often harsh, the reagent
mixture is corrosive (bromide is used as a promoter) and the
chemistry is rarely selective. N-Hydroxyphthalimide (NHPI) is usu-
ally used to improve the air oxidation of ethylbenzene [2–12],
tration [22,26], and unsatisfactory H O2 efficiency [19]. Still it is
2
highly desirable to develop an environmentally acceptable catalytic
partial oxidation of ethylbenzene that operates under moderate
conditions in the liquid phase with a high degree of selectivity.
In our previous works, we have found that hexadentate 8-
III
quinolinolato manganese(III) complexes (Q Mn presented in
3
Scheme 1) can efficiently catalyze the epoxidation of olefins [28,29],
the oxidation of alcohols [30] and the oxidation of thioanisole [31]
with H O2 in a green water–acetone or pure acetone medium.
2
III
Based on the recent successful applications of Q Mn catalysts in
3
the reactions mentioned above, we are interested in the potential of
III
but the use of toxic acetonitrile (CH CN) solvent and costly NHPI
Q Mn catalysts for ethylbenzene oxidation. Here, we report initial
3
3
III
hampers its industrial application. The oxidation process of ethyl-
benzene with t-butyl hydroperoxide (TBHP) as the oxidant has
been reported widely [13–17], but a higher TBHP wastage and the
use of poisonous reagents make this process lose the competitive
capacity. Aqueous hydrogen peroxide (H O ) would be the ulti-
results from using Q Mn complexes to catalyze ethylbenzene oxi-
3
dation with aqueous H O in a water–acetone medium containing
2
2
ammonium acetate (NH OAc) and acetic acid (HOAc).
4
2
2
2. Experimental
mate green oxidant since it produces water as the sole by-product,
and it is easy to be dealt with after reactions. The latest studies
have therefore focused on the catalytic oxidation of ethylbenzene
with H O as the terminal oxidant [18–27]. However, some of the
III
2
.1. Preparation and characterization of Q Mn complexes
3
2
2
8
-Hydroxyquinoline (8-HQ (a), 5-chloro-8-HQ (b), 5,7-dichloro-
8
-HQ (c) and 5,7-dibromo-8-HQ (d)) were purchased from Alfa
Aesar. The other commercially available chemicals, such as ethyl-
benzene, acetone, ammonium acetate, acetic acid, 30 wt% aqueous
H O and solvents, were laboratory-grade reagents from local sup-
2 2
∗ Corresponding author. Tel.: +86 731 88872576; fax: +86 731 88872531.
E-mail address: fzhhnu@tom.com (Z. Fu).
1
381-1169/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2010.08.008

C. Lu et al. / Journal of Molecular Catalysis A: Chemical 331 (2010) 106–111
107
during an appointed period (generally within half an hour). After
H O was consumed completely, as shown by an inspection with
2
2
potassium iodide–starch test paper, the catalyst was separated
from the reaction mixture by filtration. The filtrate was analyzed
on an Agilent 6890N gas chromatograph (GC) with an SE-54 quartz
capillary column (30 m × 0.32 mm × 0.25 ␮m) and flame ioniza-
tion detector (FID) using bromobenzene as an internal standard.
Scheme 1. The structures of Q3MnIII complexes.
◦
The colum temperature was 120 C. Both injector and detector
◦
temperatures were set at 250 C. The isolated acetophenone and
1
-phenylethanol were satisfactorily identified by comparing the
III
pliers. Q Mn complexes 1a–1d (Scheme 1) were prepared and
3
MS spectra with those of both the authentic samples. In addi-
tion, treating the filtrate for 1 h with triphenylphosphine hardly
changed the selectivity of products, which showed the absence of
alkyl hydroperoxide in the products [23].
characterized as following a reported procedure [28]. The liquid
UV–vis spectral measurement for the Q Mn -catalyzed ethyl-
benzene oxidation process was recorded from 200 to 700 nm
on a UV-3310 spectrophotometer (Hitachi) with a scanning rate
of 800 nm/min at room temperature and the measured process
III
3
◦
described as follows. At room temperature (20 C), 1 ␮mol of 1d
3. Results and discussion
was dissolved to 100 ml of acetone to obtain a slight yellow solu-
−5
3.1. Characterizations of Q3MnIII complexes
tion with 1d concentration of 1 × 10 M. After scanning the UV–vis
spectrum of 1d solution (4 ml), 1.5 ml of aqueous solution contain-
In our previous works, we showed that the Q3MnIII complexes
(1a–1d) had a hexadentate structure with the distorted octahedral
geometry via CHN and Mn elemental analyses, as well as a dif-
fuse reflectance UV–vis spectroscopy technique [28,29]. Moreover,
the B3LYP/6-311G+ (d) calculation indicated that the halogenated
ing 40 ␮mol NH OAC and 20 ␮mol HOAc were added to 10 ml of
4
1
d solution. After recording the spectral change of this solution,
2
0 ␮mol of ethylbenzene was further added to the solution and
then its spectral curve was measured. Finally, 30% H O2 (0.9 ␮l,
2
8
␮mol) was added to the solution and its spectral change with
III
time was recorded.
Q3Mn complexes had a stronger distortion effect than 1a [31].
2.2. Procedure of oxidation
3.2. Catalytic tests
III
The general procedure for ethylbenzene oxidation is
described as follows. At ambient temperature (30 C), to stirred
Table 1 summarizes the data for Q Mn -catalyzed ethylben-
3
◦
zene oxidation with H O in acetone–water media. In the absence
of catalyst, this reaction did not occur at 30 C (entry 1), but
it could proceed efficiently in the presence of Q Mn catalysts
2
2
◦
water–acetone (v/v, 1.5:5, 6.5 ml) a mixture of ethylbenzene
III
III
(
10 mmol), catalyst Q Mn (0.01 mmol), NH OAc (0.4 mmol),
3
4
3
and HOAc (0.2 mmol), 30% H O2 (3 mmol) was added dropwise
and NH OAc–HOAc additives (entries 2–5), and the oxidation
2
4
Table 1
The results obtained from Q3MnIII-catalyzed ethylbenzene oxidation with H2O2a
.
.
Time (h)
Entry
Catalyst
Additive (mmol)
TONb
Seletivityc (%)
Ketone
Oxidation yieldd (%)
Alcohol
1c
2
3
4
5
6
7
–
24
5
5
5
6
7
5
7
1.5
7
24
6
5
20
–
94
105
90
142
224
256
11.5
150
3.5i
52
–
82
79
73
74
78
80
61
100
51
80
80
80
80
–
18
21
27
26
22
20
27
–
31
35
30
47
56
51
6
75
–
17
20
27
23
NH4OAc (0.4) + HOAc
(0.2)
1a
1b
1c
1d
1d
1d
1d
1d
–
1d
1d
1d
1d
e
f
g
8
9
h
1
1
1
1
1
0i
1
2
3
4
–
25
20
20
20
20
No additive
Na2HPO4 (0.2)
NH4OAc (0.4)
HOAc (0.2)
60
80
70
a
◦
Reaction conditions: Ethylbenzene (EB), 10 mmol; catalyst, 0.01 mmol; 30% H2O2, 3 mmol and water/acetone (3/10, 6.5 ml) at 30 C. Conversion and selectivity were
determined by GC using an internal standard technique.
b
Number of moles of ethylbenzene consumed per mol of Mn ion.
Selectivity for acetophenone (ketone) and 1-phenylethanol (alcohol).
Mol% yield of oxidation products based on the amount of H2O2.
c
d
e
3
3
0% H2O2, 4 mmol.
0% H2O2, 5 mmol.
f
g
h
i
Catalyst, 0.02 mmol; 30% H2O2, 4 mmol; 2,4-di-tert-butylphenol, 0.02 mmol.
Using 1-phenylethanol (1 mmol), 30% H2O2 (0.4 mmol) and catalyst 1d (0.002 mmol).
Using 15% peracetic acid (4 mmol) as an oxidant, given ethylbenzene conversion.

1
08
C. Lu et al. / Journal of Molecular Catalysis A: Chemical 331 (2010) 106–111
Table 2
The effect of the concentration of ethylbenzene .
a
Entry
EB (mmol)
H2O2 (mmol)
Time (h)
EB conversion (mol%)
Oxidation yield (%)
Product selectivity (%)
Ketone
Alcohol
1
2
3
4
5
6
7
4.0
6.0
8.0
10.0
10.0
12.0
14.0
1.6
2.4
3.2
4.0
4.0
4.8
5.6
6
6
6
6
7
6
6
16.7
20.1
24.4
26.1
4.3
42
50
61
65
11
50
44
69
74
73
70
73
70
70
31
26
27
30
27
30
30
b
19.8
17.6
a
◦
Reaction conditions: Catalyst 1d, 0.02 mmol; acetone, 5 ml; water, 1.5 ml; HOAc, 0.2 mmol; NH4OAc, 0.4 mmol; temperature, 30 C.
b
1d system was treated with H2O2 for 30 min before ethylbenzene was added.
products obtained were acetophenone (selectivity, 73–82%) and
-phenylethanol (selectivity, 18–27%), arising from the side chain
oxidation of ethylbenzene at secondary carbon atoms. Among
In the following experiments, the influence of the concentration
1
of catalyst 1d on the reaction was checked at H O /ethylbenzene
2
2
molar ratio of 0.4. As illustrated in Fig. 1, the reaction rate and ethyl-
benzene conversion were dependent on the concentration of 1d,
when the concentration was ca. 0.1 mol%, the conversion smoothly
III
III
the Q Mn complexes examined, the 5,7-dibrominated Q Mn
3
3
(
1d) was most active for this reaction, affording a high turnover
number (TON, 142) and moderate oxidation yield (ca. 47%) at
H O /ethylbenzene molar ratio of 0.3 (entry 5), which was likely
increased with time and eventually got up to ca. 22.4% after H O2
2
was consumed (about 7 h). When the concentration increased to
ca. 0.2 mol%, the reaction was accelerated, eventually affording the
conversion of 26.1% and the oxidation yield of 65% after 6 h. How-
ever, an attempt to further increase the concentration (0.3 mol%)
was actually invalid in improving the conversion. By the way, the
selectivity of products was hardly influenced by the concentration
of catalyst and reaction time.
2
2
due to the stronger distortion effect of 1d than that of the other
III
Q Mn complexes, as supported by the DFT calculations [31].
3
Entries 5–7 illustrate the effect of the amount of H O2 on the
2
reaction. An increase in the amount from 3 to 4 mmol resulted
in increased TON from 142 to 224 and oxidation yield from 47 to
5
6%. However, an attempt to further increase the amount from 4
to 5 mmol resulted in a marginal decrease of the oxidation yield
from 56 to 51% (entries 5 vs 7). It is noteworthy that the selectiv-
ity of acetophenone slightly increased with the amount owing to
further oxidation of 1-phenylethanol. Entry 8 demonstrates that
the catalytic reaction was restrained markedly in the presence of
Finally, the effect of ethylbenzene amount on the reaction was
investigated using 1d catalyst (0.02 mmol) at H O /ethylbenzene
2
2
molar ratio of 0.4, and the results are listed in Table 2. Using the
amount from 4 to 10 mmol resulted in the continuous and con-
siderable increases of ethylbenzene conversion from 16.7 to 26.1%
and oxidation yield from 42 to 65%, respectively (see entries 1–4
in Table 2). Notably, while adding H O for 30 min and then ethyl-
2
,4-di-tert-butylphenol, indicating that it owns a feature of free
radical mechanism. Entry 9 illustrates that 1-phenylethanol was
oxidized easily to the corresponding acetophenone by H O in the
2
2
benzene, the catalysis efficiency was very low (see entry 5). This is
2
2
coexistence of 1d and NH OAc–HOAc. Entry 10 shows that 3.5%
likely because 1d reacts with H O in advance to form some inactive
4
2
2
of ethylbenzene was oxidized directly to acetophenone (51%), 1-
phenylethanol (25%) and benzaldehyde (24%) while using 0.4 equiv.
of peracetic acid.
The effect of additives on the reaction was further investigated
by using the most efficient 1d as a catalyst (entries 11–14). Entry 11
illustrates that the reaction proceeded very slowly in the absence of
additives and gave a relatively low TON (ca. 52) after 24 h. Among
intermediates for ethylbenzene oxidation in this situation and the
pre-existence of ethylbenzene may efficiently restrain the forma-
tion of these intermediates, as supported by the following UV–vis
spectral characterizations. This restraint effect should strengthen
with ethylbenzene concentration, which can lead to the afore-
mentioned concentration effect. However, an attempt to further
increase the concentration actually resulted in the decreased ethyl-
benzene conversion and oxidation yield (entries 6–7). It is likely
the additives examined, Na HPO4 (pH = 8.6 in the water–acetone
2
medium) obviously accelerated reaction but hardly improved TON
(
entry 12). NH OAc (pH = 8.1 here) significantly enhanced reaction
4
rate and slightly improved TON (entry 13), whereas the use of HOAc
pH = 5.2 here) in place of NH OAc resulted in a dramatic retarda-
(
4
tion of the reaction rate (entry 14). The best result was achieved
upon using NH OAc and HOAc mixtures as the additives (pH = 7.1
4
−
here), indicating that the pH value and OAc ions play key role in
the catalytic reaction. While using NH OAc or NH OAc–HOAc mix-
4
4
ture as the additive, two different roles are possible. First, the weak
III
basic NH OAc, as proposed for salen–Mn -catalyzed epoxidation
4
−
of alkenes with H O [32,33], can promote the formation of HO
2
2
2
from H O which facilitates the formation of a hydroperoxy com-
2
2
III
III
plex (Q Mn –OOH from Q Mn ). This was supported by the fact
3
3
that a weak basic Na HPO4 had an outstanding accelerated effect
2
on this reaction but a weak acidic HOAc did not. Another possi-
−
bility is that OAc ions likely participate in this catalytic oxidative
process via the formation of a peroxyacylmanganese(III) species
III
(
Q Mn –OOAc), as proposed by Montanari and co-workers for
3
III
porphyrin–Mn -catalyzed epoxidation of alkenes with H O in the
2
2
presence of a lipophilic nitrogen heterocycle ligand and a carboxylic
acid cocatalyst [34].
Fig. 1. The effect of the concentration of catalyst on the oxidation of ethylbenzene
(
(
reaction conditions: ethylbenzene (10 mmol); 30% H2O2 (4 mmol); water/acetone
1.5 ml/5 ml) at 30 C).
◦

C. Lu et al. / Journal of Molecular Catalysis A: Chemical 331 (2010) 106–111
109
−
5
Fig. 3. UV–vis spectra of (A) a solution of 1d in acetone–water (1.0 × 10 M, 4 ml);
(B ) adding 8 ␮mol peracetic acid to the A solution after 10 min; (B ) 30 min later;
Fig. 2. UV–vis spectra of (A) a solution of 1d in acetone (1.0 × 10− M, 4 ml); (B)
adding 40 ␮mol NH4OAC and 20 ␮mol HOAc aqueous solution; (C) 10 min later of
adding 20 ␮mol ethylbenzene to the solution B; (D) 20 min later of adding 30% H2O2
5
1
2
(C ) 10 min later of using NH ·H O to adjust the pH value of B solution to 7.5; (C2)
1
3
2
2
20 min later; (C ) 30 min later; (C ) 50 min later.
3
4
(
8 ␮mol) to the solution C; (E) 30 min later; (F) 1 h later; (G) 8 h later. Inset is the
amplified traces.
H O to the C solution further, the MLCT band immediately
2
2
shifted to ꢀmax ∼ 424 nm, and its intensity increased obviously (see
curve D). Notably, the reaction 1d with peracetic acid in acidic
acetone–water media resulted only in a marginal blue-shift and
that the solubility of ethylbenzene becomes worse at the higher
concentration, which can lead to an increase in the transfer mass
resistance.
significant decrease of the MLCT band, indicating that the forma-
III
tion of peroxyacyl manganese(III) species (Q Mn –OOAc) does not
3
3.3. Reaction mechanism
lead to the red-shift of MLCT band. When the pH value of this
reaction mixture was adjusted to 7.5 with NH ·H O, the red-shift
3
2
III
The Q Mn -catalyzed ethylbenzene oxidation process was fur-
immediately occurred (see Fig. 3), which was likely assigned to
3
IV
ther monitored by a UV–vis spectroscopy technique. Fig. 2 is a
stepwise overlay of UV–vis spectra for the 1d complex in an
acetone medium at room temperature. In this, curve A is the spec-
trum of 1d in acetone. The absorption band with ꢀmax ∼ 408 nm
can be assigned to the metal to ligand charge transfer (MLCT)
the ligand to metal charge transfer (LMCT) of the Mn
O species
generated via a homolytic cleavage of peroxyacyl manganese(III)
III
species (Q Mn –OOAc), as reported by Groves and co-workers
3
III
III
for the reaction of porphyrin–Mn and porphyrin–Fe with m-
chloro-peroxybenzoic acid in basic or neutral conditions [36,37].
IV
[
35]. When the NH OAc–HOAc aqueous solution was added to the
Subsequently, the Mn
O species gradually became obscure with
4
A solution, the MLCT band experienced a decrease in intensity
see curve B). After adding ethylbenzene to the B solution dur-
time, and eventually disappeared after 8 h (see curves E–G). At
the same time, the trace in 380–400 nm ran up in 30 min (see
(
ing 20 min, the MLCT absorbance decreased further (see curve C).
curve E), and then dropped slowly with time, finally disappeared
III
This hypochromic effect is likely originated from the transforma-
after 8 h (curves F–G), as observed by us for the Q Mn -catalyzed
3
III
tion of hexadentate Q Mn (1 in Scheme 2) to the corresponding
cyclohexanol oxidation with H O2 [30]. While the absorbance
3
2
pentadentate one (2) in the presence of NH OAc–HOAc, which
can lead to a decrease in its coordination capacity. On adding
in 500–700 nm, which was assigned to the LMCT band of the
Mn O generated through a heterolytic cleavage of O–O bond
4
V
Scheme 2. Possible catalytic pathways for Q3MnIII-catalyzed ethylbenzene.

1
10
C. Lu et al. / Journal of Molecular Catalysis A: Chemical 331 (2010) 106–111
III
From the above facts, the Q Mn -catalyzed oxidation of ethyl-
3
benzene with H O is envisioned to proceed via a following radical
2
2
pathway (see Scheme 2), as supported by the above experiment of
using 2,4-di-tert-butylphenol as a radical eliminating species (see
III
entry 8 in Table 1). First, Q Mn (1 in Scheme 2) easily cleaved the
3
III
+
−
longest Mn–O bond to form a pentadentate [Q Mn ] OAc with
3
a pendant hydroxyl group (2) in the presence of NH OAc–HOAc
4
III
or NH OAc. Then, 2 reacts with H O to form a Q Mn –OOAc
4
2
2
3
species (3). Finally, 3 rapidly undergoes a homolytic cleavage of
•
III
•
its O–O bond to a Q Mn –O (4a) and PhCHCH3 free radicals
3
in the participation of ethylbenzene, as described in some litera-
tures [36–39]. Notably, 4a, as reported by Groves and co-workers
for the homolytic O–O bond cleavage reaction of acylperoxo-
manganese(III) porphyrin [37], is quickly and reversibly converted
IV
to Q Mn
O (4b) through one electron transfer of metal to oxy-
3
gen, which just accords with the feature of the aforementioned
IV
Mn species in UV–vis spectra. A pathway is possible to result
Fig. 4. UV–vis spectra of (A) a solution of 1d in acetone (1.0 × 10−5 M, 4 ml); (B)
adding 40 ␮mol NH4OAC and 20 ␮mol HOAc aqueous solution; (H) adding 30% H2O2
in the generation of PhCH(OH)CH , First, 4a easily combines with
3
•
III
(
8 ␮mol) to the solution B; (I) 30 min later; (J) 30 min later after adding 20 ␮mol
PhCHCH3 to give Q Mn –O–CH(CH )Ph (5) before its transfor-
3
3
ethylbenzene to the solution I; (K) 30 min later; (L) 1 h later; (M) 8 h later. Inset is
the amplified traces.
mation to 4b, subsequently, the decomposition of 5 can result in
the formation of PhCH(OH)CH3 and the regeneration of catalyst
III
Q Mn . Two pathways are possible to result in the generation of
3
PhCOCH . First, another secondary H atom on 5 may be further
3
[
33,34], still existed in the whole process although its intensity
IV
abstracted by 4b to produce an Mn –OCCH Ph species 6 before
3
decreased slightly. These spectral changes likely imply that the
Mn
zene, but the Mn O species should not be mainly responsible
for the present oxidation process, which was further confirmed by
the following spectral experiments. Namely, (i) if the B solution
IV
its decomposition. Then, 6 is decomposed to give PhCOCH3 and
the regenerated catalyst 1. Another possibility is that 4b may oxi-
O species plays a key role in the oxidation of ethylben-
V
IV
dize the fresh formation of PhCH(OH)CH2 to give a Mn species
III
(
7), then, 7 is decomposed to generate a PhCOCH and Q Mn –OH
3
3
species (8), finally, the intramolecular dehydration of 8 can lead to
was treated with H O for 30 min before adding ethylbenzene, its
2
2
III
V
the regeneration of catalyst 1, as reported by us for the Q3Mn -
Mn O absorbance became more strong and the spectral change in
80–400 nm was obscure (see curves H–M in Fig. 4). And (ii) if the
catalyzed oxidation of alcohols with H O [30]. Notably, the above
2
2
3
reaction results, in which a high ketone/alcohol molar ratio was
obtained and this ratio was independent on the time, support that
the formation of PhCOCH3 is mainly originated from the first path-
B solution was only treated with H O2 for 8 h, its spectral change
could very clearly sketch the formation of Mn
its final transformation to the Mn O although the deactivation
of catalyst caused by its dimerization and oxidative degradation,
inevitably occurred under such situation (see Fig. 5). Both the spec-
2
IV
O species and
V
way. By the way, the disproportionation of 4b, as reported by some
V
literature [36,40,41], can lead to the generation of Q Mn O (9)
3
IV
and 8 although the formation of 9 via a heterolytic cleavage of
O–O bond of 3 cannot be excluded in the present conditions. It is
anticipated that this disproportionate reaction occurs more easily
in the absence of ethylbenzene, as observed in the UV–vis spectra.
The combination of 9 with 1 can lead to the formation of a deac-
tral experiments clearly indicate that the Mn
O species is easy to
V
be converted to the nonsignificant Mn O and deactivated species
in the absence of ethylbenzene, which can lead a very low catalysis
efficiency, as supported by the foregoing catalytic experiment (see
entry 5 in Table 2).
IV
IV
tivated ␮-oxomanganese(IV) dimer Q Mn –O–Mn Q3 (10) with
3
a characteristic absorption band at ꢀmax ∼ 364 nm, as reported by
III
Srinivasanetal. forthe salen–Mn -catalyzedepoxidation of olefins
[
42].
4. Conclusions
For the first time we have developed an efficient and moder-
ate method for ethylbenzene oxidation with H O catalyzed by
2
2
III
hexadentate Q Mn complexes in acetone–water media, and pro-
posed a free radical mechanism for the Q Mn -mediated catalytic
3
III
3
III
oxidation system. Having found these kinds of Q Mn complexes,
3
we are interested in exploiting the potential applications of the
other 8-quinolinolato metal complexes in organic synthesis.
Acknowledgements
Fig. 5. UV–vis spectra of (A) a solution of 1d in acetone (1.0 × 10−5 M, 4 ml); (B)
adding 40 ␮mol NH4OAC and 20 ␮mol HOAc aqueous solution; (H8) 8 h later after
adding 30% H2O2 (8 ␮mol) to the solution B; inset shows an initial visible absorption
spectral changes after adding 30% H2O2 (8 ␮mol) to the solution B, spectral scanning
is taken at average 3 min intervals (H1–H7).
We acknowledge the financial support for this work by
the National Natural Science Foundation of China (20873040,
2
0573035) and the Youth Foundation of Hunan Normal University
(53112-1658).

C. Lu et al. / Journal of Molecular Catalysis A: Chemical 331 (2010) 106–111
111
References
[22] M. Klopstra, R. Hage, R.M. Kellogg, B.L. Feringa, Tetrahedron Lett. 44 (2003)
581–4584.
4
[
[
23] G.B. Shul’pin, T. Sooknoi, L.S. Shul’pina, Petrol. Chem. 48 (2008) 36–39.
24] H.R. Lucas, L. Li, A.A.N. Sarjeant, M.A. Vance, E.I. Solomon, K.D. Karlin, J. Am.
Chem. Soc. 131 (2009) 3230–3245.
25] M. Szaleniec, M. Witko, J. Heider, J. Mol. Catal. A 286 (2008) 128–136.
26] V. Balland, D. Mathieu, N. Pons-Y-Moll, J.F. Bartoli, F. Banse, P. Battioni, J.J. Girerd,
D. Mansuy, J. Mol. Catal. A 215 (2004) 81–87.
[
[
[
1] H. Ma, J. Xu, C. Chen, Q.H. Zhang, J.B. Ning, H. Miao, L.P. Zhou, X.Q. Li, Catal. Lett.
13 (2007) 3–4.
2] S.S. Bhoware, S. Shylesh, K.R. Kamble, A.P. Singh, J. Mol. Catal. A 255 (2006)
23–130.
3] I.C. Chisem, K. Martin, M.T. Shieh, J. Chisem, J.H. Clark, R. Jachuck, D.J. Macquar-
rie, J. Rafelt, C. Ramshaw, K. Scott, Org. Process Res. Dev. 1 (1997) 365–369.
4] T. Hara, T. Iwahama, S. Sakaguchi, Y. Ishii, J. Org. Chem. 66 (2001) 6425–6431.
5] W.W.Y. Lam, S.M. Yiu, J.M.N. Lee, S.K.Y. Yau, H.K. Kwong, T.C. Lau, D. Liu, Z.Y.
Lin, J. Am. Chem. Soc. 128 (2006) 2851–2858.
1
[
[
1
[
[
[
[
[
[
27] K.O. Xavier, J. Chacko, K.K. Mohammed Yusuff, Appl. Catal. A 258 (2004)
[
[
251–259.
28] S. Zhong, Y.M. Tan, Z.H. Fu, Q.J. Xie, F. Xie, X.P. Zhou, Z.P. Ye, G.S. Peng, D.L. Yin,
J. Catal. 256 (2008) 154–158.
29] S. Zhong, Y.M. Tan, Z.H. Fu, Q.J. Xie, F. Xie, X.P. Zhou, Z.P. Ye, G.S. Peng, D.L. Yin,
Adv. Synth. Catal. 350 (2008) 802–806.
[
[
6] C. Walling, C. Zhao, G.M. El-Taliaw, J. Org. Chem. 48 (1983) 4910–4914.
7] T. Dohi, N. Takenaga, A. Goto, H. Fujioka, Y. Kita, J. Org. Chem. 73 (2008)
7
365–7368.
8] R. Alcántara, L. Canoira, P.G. Joao, J.M. Santos, I. Vázquez, Appl. Catal. A 203
2000) 259–268.
9] R. Alcántara, L. Canoira, P.G. Joao, J.P. Pérez-Mendo, Appl. Catal. A 218 (2001)
69–279.
10] Y. Ishii, T. Iwahama, S. Sakaguchi, K. Nakayama, Y. Nishiyama, J. Org. Chem. 61
1996) 4520–4526.
30] Z.P. Ye, Z.H. Fu, S. Zhong, F. Xie, X.P. Zhou, F.L. Liu, D.L. Yin, J. Catal. 261 (2009)
[
[
110–115.
(
31] X. Fang, Z.H. Fu, S. Zhong, Z.P. Ye, X.P. Zhou, F.L. Liu, C.Y. Rong, L.Q. Mao, D.L.
Yin, J. Mol. Catal. A 307 (2009) 93–97.
32] A.M.d’A. Rocha Gonsalves, R.A.W. Johnstone, M.M. Pereira, J. Shaw, J. Chem. Soc.
Perkin Trans. 1 (1991) 645–649.
33] P. Pietikäinen, Tetrahedron 54 (1998) 4319–4326.
34] P.L. Anelli, S. Banfi, F. Montanari, S. Quici, J. Chem. Soc. Chem. Commun. (1989)
2
[
(
[
[
[
[
11] I. Hermans, J. Peeters, P.A. Jacobs, J. Org. Chem. 72 (2007) 3057–3064.
12] S.D. George, S.C. Sherman, A.V. Iretskii, M.G. White, Catal. Lett. 65 (2000)
779–780.
1
81–183.
[
[
[
[
[
35] S.M. Crawford, Spectrochim. Acta 19 (1963) 225–270.
[
[
[
[
[
[
[
[
[
13] S. Vetrivel, A. Pandurangan, J. Mol. Catal. A 217 (2004) 165–174.
14] K. George, S. Sugunan, Catal. Commun. 9 (2008) 2149–2153.
15] T.H. Bennur, D. Srinivas, S. Sivasanker, J. Mol. Catal. A 207 (2004) 163–171.
16] M. Rogovin, R. Neumann, J. Mol. Catal. A 138 (1999) 315–318.
17] S. Boitsov, A. Riahi, J.C.R. Muzart, Surf. Chem. Catal. 3 (2000) 747–750.
18] M.R. Maurya, M. Kumar, U. Kumar, J. Catal. Mol. A 273 (2007) 133–143.
19] M.R. Maurya, A. Arya, P. Adao, J. Costa Pessoa, Appl. Catal. A 351 (2008) 239–252.
20] N.K. Mal, A.V. Ramaswamy, Appl. Catal. A 143 (1996) 75–85.
21] T. Radhika, S. Sugunan, Catal. Commun. 8 (2007) 150–156.
36] J.T. Groves, M.K. Stern, J. Am. Chem. Soc. 109 (1987) 3812–3814.
37] J.T. Groves, Y. Watanabe, Inorg. Chem. 25 (1986) 4808–4810.
38] J.T. Groves, Y. Watanabe, J. Am. Chem. Soc. 110 (1988) 8443–8452.
39] S. Ban, M. Cavazzini, F. Coppa, S.V. Barkanova, O.L. Kaliya, J. Chem. Soc. Perkin
Trans. 2 (1997) 1577–1583.
40] J.T. Groves, T. Takahashi, J. Am. Chem. Soc. 105 (1983) 2073–2074.
41] C.L. Hill, F.J. Hollander, J. Am. Chem. Soc. 104 (1982) 7318–7319.
42] K. Srinivasan, P. Michaud, J.K. Kochi, J. Am. Chem. Soc. 108 (1986) 2309–2320.
[
[
[