Manganese(II) naphthenate as effective catalyst for the clean oxidation of 2-methylnaphthalene by hydrogen peroxide

Article abstract of DOI:10.1007/s11164-012-0507-z

Oxidation of 2-methylnaphthalene (2-MN) with aqueous hydrogen peroxide was conducted in acetic acid. The epoxidation pathway was investigated by increasing the CH₃CO₃H content and adding manganese(II) naphthenate (MnPc) as catalyst. 2-Methyl-1,4-naphthoquinone was obtained in 75.6% conversion and with 80.0% selectivity under the latter conditions. A probable mechanism in which MnPc catalyzes the oxidation of 2-MN by hydrogen peroxide in acetic acid is proposed. Springer Science+Business Media B.V. 2012.

Full text of DOI:10.1007/s11164-012-0507-z

Res Chem Intermed (2012) 38:1839–1846
DOI 10.1007/s11164-012-0507-z
Manganese(II) naphthenate as effective catalyst
for the clean oxidation of 2-methylnaphthalene
by hydrogen peroxide
•
Tingfeng Yan Mei Hong Lei Niu
•
•
•
Feng Jiang Guomin Xiao
Received: 19 September 2011 / Accepted: 9 February 2012 / Published online: 24 February 2012
Ó Springer Science+Business Media B.V. 2012
Abstract Oxidation of 2-methylnaphthalene (2-MN) with aqueous hydrogen per-
oxide was conducted in acetic acid. The epoxidation pathway was investigated by
increasing the CH3CO3H content and adding manganese(II) naphthenate (MnPc) as
catalyst. 2-Methyl-1,4-naphthoquinone was obtained in 75.6% conversion and with
80.0% selectivity under the latter conditions. A probable mechanism in which MnPc
catalyzes the oxidation of 2-MN by hydrogen peroxide in acetic acid is proposed.
Keywords 2-Methylnaphthalene ꢀ 2-Methyl-1,4-naphthoquinone ꢀ
Hydrogen peroxide ꢀ Manganese(II) naphthenate ꢀ Oxidation ꢀ Vitamin K3
Introduction
Vitamins are fine chemicals produced in amounts ranging between 1,000 and 10,000
tons per annum [1]. It is well known that quinones have pronounced bio-activity and
are important in medicinal applications. Since 2-MNQ (vitamin K3), used therapeu-
tically under the name menadione, was found to have more antibleeding activity than
the natural vitamins K1 or K2 [2], many methods have been described for controlled
oxidation of 2-MN (Scheme 1) using a variety of oxidizing agents in the presence of
catalyst [3–9]. Traditionally, menadione is produced on an industrial scale by
stoichiometric oxidation of 2-MN by CrO3 in sulfuric acid. Yield and selectivity are
moderate (typically approx. 50%) [10]. The drawbacks of this method are obvious:
production of inorganic salts as by-product (18 kg salt per kg product) and necessary
treatment of chromium-containing waste water [11, 12]. Adam and co-workers [13]
described the use of acetic acid, hydrogen peroxide, and methyl trioxorhenium
T. Yan ꢀ M. Hong ꢀ L. Niu ꢀ F. Jiang ꢀ G. Xiao (&)
School of Chemistry and Chemical Engineering, Southeast University, Jiangning, Nanjing 211189,
China
e-mail: xiaogm@seu.edu.cn
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T. Yan et al.
(conversion of 2-MN was 81%, affording 47% 2-MNQ; Pd(II)-polystyrene sulfonic
acid resin [14] was used as catalyst). The rhenium catalyzed oxidation of 2-MN, using
85% H2O2 solution gave conversion of 93% at 40 °C after 4 h. However, this reaction
is rather hazardous, because concentrated hydrogen peroxide is potentially explosive
[15]. In another method, metalloporphyrin-catalyzed oxidation of 2-MN by potassium
monopersulfate was reported [16], with selectivity up to 53% for 2-MNQ.
Phthalocyanine-like compounds (PCS) are similar to metalloporphyrins in many
chemical properties, so their use as catalysts could enable effective oxidation of
organics with similar steric configuration and electron configuration as for use of the
metalloporphyrins [17, 18], especially mild oxidation of organics at room temperature
by hydrogen peroxide or other organic peroxides [19]. In this work we studied the
oxidation of 2-MN in detail using two kinds of oxidant (30% H2O2 and a mixture of
H2O2 and CH3CO3H) in the presence of acetic acid. Manganese(II) naphthenate
(MnPc), as catalyst, was also added to investigate the epoxidation pathway. A possible
mechanism of the catalysis by MnPc is proposed in this paper. The highest yield was
60.5%, with conversion and selectivity of 75.6 and 80.0%, respectively.
Experimental
Materials and methods
Reagents A and B, which were mixed together in the ratio 1:1 (v/v) then left at room
temperature for several days to form a mixture of the oxidants CH3CO3H and H2O2,
were bought from Aladdin corporation. KMnO4 solution (0.01 M) and Na2S2O3
solution (0.01 M) were used to detect the amounts of H2O2 and CH3CO3H
separately; the results are listed in Table 1.
2-MN and 30% H2O2 were purchased from National Reagents Corporation.
MnPc was purchased from TCL Corporation.
Preparation of 2-methyl-1,4-naphthoquinone
2-MN (2.5 g, 17.6 mmol) and MnPc (0.65 g, 0.92 mmol) were dissolved in 35 ml
glacial acetic acid in a 100-ml four-necked flask equipped with a stirring bar, a
reflux condenser, a thermometer, and a 50-ml dropping funnel. The mixture was
heated to 60 °C, at which temperature the oxidant 30% H2O2 or mixture of oxidants
was added to the raw material solution over a period of 1.5 h. The mixture was kept
Scheme 1 Oxidation of 2-MN
to 2-MNQ
O
oxidation
O
2-MN
2-MNQ
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Manganese(II) naphthenate as effective catalyst
1841
12
Table 1 Amounts of CH3CO3H and H2O2
Time/day
3
5
6
7
Amounts/w%
CH3CO3H
H2O2
13.5
15.4
16.8.
13.1
22.5
9.9
23.7
8.4
26.2
6.3
At room temperature (approx. 20 °C); reagent A:reagent B = 1:1 (v/v)
warm for 1.5 h. At the beginning of the reaction the solution was light green but the
color gradually deepened as time passed. There was a color-change from green to
orange after a specific time. Finally the solution turned bright orange. It should be
noted that at different temperatures the reaction mixture has different colors for
different periods. At low temperatures (40 and 60 °C) the green color should stay
for a long time, even for several minutes after the oxidant was added; the reaction
mixture then turns orange. At higher temperatures (100 and 80 °C), the color
changed quickly from green to black, and ended as orange.
Analysis
The crude product solution was analyzed by HPLC under the following operating
conditions:
ODS C18, 250 mm 9 4.6 mm (inner diameter) particle size 5 lm
Mobile phase: CH3OH–H2O–CH3CN 1:1:1 (v/v/v)
Flow rate: 1.0 mL/min
Detection wavelength: 254 nm
Sample volume: 20 ll
Figure 1 shows the result from HPLC analysis of the solution of the crude
product. The compounds at retention times 4.080 and 9.168 min are 2-MNQ and
2-MN, respectively
Results and discussion
In the presence of acetic acid, 2-MN is oxidized by hydrogen peroxide to, mainly,
2-MNQ. Anne Bohle [20] supplied us with an epoxidation pathway (Scheme 2).
Because CH3CO3H was the effective oxidant in the reaction, two types of oxidant
were investigated in detail for oxidation of the raw material, 30% H2O2 and
mixtures of H2O2 and CH3CO3H containing the amounts of H2O2 and CH3CO3H
listed in Table 1. The table shows that after 7 days the amount of CH3CO3H had
increased slowly to approximately 24%, so the oxidant mixture we used later in the
work was always the solution which had been left for 7 days.
Effect of two types of oxidant without any catalyst in the reaction
The effect of two types of oxidant on the selectivity, conversion, and yield of
oxidation reaction were studied in detail (Table 2).
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T. Yan et al.
Fig. 1 HPLC of the solution of the crude product
Scheme 2 Epoxidation pathway from 2-MN to 2-MNQ
Table 2 Oxidation of
2-methylnaphthalene by two
types of oxidant
Oxidant
Temperature
(°C)
Conversion
(%)
Selectivity
(%)
Yield
(%)
1. 30% H2O2
40
50
44.5
50.7
74.3
86.2
90.0
51.3
51.7
53.4
45.2
52.8
22.7
28.2
38.1
31.9
19.0
71.3
63.3
61.8
43.8
34.3
10.1
14.3
28.3
27.5
17.1
36.6
32.7
33.0
19.8
18.1
60
80
100
40
2. mixture
50
60
2-MN = 2.5 g, acetic
acid = 35 ml, reaction = 3 h,
30% H2O2 = 15 ml or mixed
solution = 15 ml
80
100
There was an equilibrium in our reaction system using hydrogen peroxide as sole
oxidant in acetic acid, as follows [21]:
CH3COOH þ H2O2 ꢀ CH3COOOH þ H2O
Because CH3CO3H was the effective oxidant in the reaction [20], the mixture
which contained CH3CO3H prepared in advanced is always more selective than
123

Manganese(II) naphthenate as effective catalyst
1843
30% H2O2. However, conversion by the mixture decreased obviously compared
with 30% H2O2, mainly because CH3CO3H is less stable than H2O2.
With increasing temperature, the oxidizing strength of 30% H2O2 increased,
leading to distinctly improved conversion. For the mixed oxidant, however,
decomposition of CH3CO3H countered the effect of increasing the temperature.
So there was an evident minimum in the conversion tendency of 2-MN at 80 °C.
The combined effect of this behavior was that the respective highest yields of
2-MNQ as a result of oxidation by 30% H2O2 and by the mixture were 28.3% at
60 °C and 36.6% at 40 °C.
MnPc as catalyst in the presence of CH3CO2H
Decomposition of CH3CO3H sharply reduces the amount in the reaction liquid,
which leads to lack of enough oxidant for our target reaction. To solve this problem,
MnPc was added as catalyst because of its sensitivity to superoxides; a specific
metal oxy-compound formed was assumed to be an effective oxidant. We hoped
to improve the experimental results by fixing oxygen in the form of a manganic
oxy-compound. All related experimental results are listed in Table 3.
Effect of MnPc as catalyst
There was a distinct point at 60 °C in the conversion of 2-MN when MnPc as
catalyst of the oxidation reaction, compared with nothing added, resulted in greater
conversion than the latter. It was supposed that temperature has a substantial effect
on oxidation. The results at low temperature show the positive effect of the
formation of the manganic oxy-compound, which is effective as an oxidant in our
Table 3 MnPc as catalyst in
the oxidation of 2-MN
System
Temperature Conversion Selectivity Yield
(%)
(°C)
(%)
(%)
1. 30%H2O2
MnPc ?
CH3CO2H
?
40
50
62.2
65.3
75.6
57.7
34.2
27.4
29.7
35.0
52.6
64.8
40.0
41.1
43.5
49.9
53.6
11.4
25.1
80
7.1
16.4
60.5
23.6
9.7
60
80
40.9
28.4
46
100
40
2. Mixture ?
MnPc ?
H3CO2H
12.6
12.9
14.5
18.6
11.5
6.5
50
43.4
41.3
35.4
17.7
16.3
18.8
21
60
80
100
40
3. Mixture ?
MnPc ? DMF
2-MN = 2.5 g, acetic
acid = 35 ml or DMF = 35 ml,
reaction = 3 h, MnPc
solution = 0.6 ml, 30%
H2O2 = 15 ml or
50
7.8
60
9.1
80
19.8
17.2
9.9
100
9.2
mixture = 15 ml
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T. Yan et al.
reaction, however it seems that this manganic oxy-compound tended to be more
abundant at 60 °C than 40 °C. In contrast, higher temperatures than 60 °C led to
faster decomposition of the manganic oxy-compound with lower conversion of
2-MN.
In a similar tendency to the influence of MnPc as catalyst on the conversion, there
was also a distinct point at 60 °C for selectivity. Expect for 40 °C, all other
selectivities for 2-MNQ with MnPc as catalyst were better than with nothing added;
this was especially true for 60 °C.
The combined effect of this behavior was that the highest yield of 2-MNQ by
oxidation with 30% H2O2 and MnPc as catalyst was 60.5% with conversion 75.6%
and selectivity 80%.
Effect of oxidant type in the reaction with MnPc as catalyst
When the mixture referred to above was used in place of 30% H2O2 to oxidize
2-MN to 2-MNQ with MnPc as catalyst, the results showed a mainly negative effect
on our target product. There was a sharp decrease both in the conversion of 2-MN
and selectivity for 2-MNQ at 60 °C, which implied the supposed manganic
oxy-compound cannot be formed by MnPc reacting with CH3CO3H generated in
advance. Use of CH3CO3H resulted in better selectivity for 2-MNQ than 30% H2O2;
however, this gradually decreased with increasing temperature because of the
increasing decomposition of CH3CO3H. It can also be inferred that CH3CO2H could
not be combined with MnPc directly to take part in the reaction. However molecular
H2O2 seems to be effective when it combines with MnPc before participating in the
oxidation.
Effect of solvent type on selectivity and conversion with MnPc as catalyst
N,N-Dimethylformamide (DMF) is a classic nonprotonic solvent different from
CH3CO2H, which is a strong proton-donating solvent in reactions to form a new
compound with much more stability via a reactive intermediate. To confirm that
CH3CO2H participated in the oxidation, we replaced it with DMF as solvent. As a
result, selectivity for 2-MNQ with DMF as solvent was very low—approximately
20%, which was much different from when CH3CO2H was used as solvent. There
was a similar contrast in the conversion of 2-MN under these two conditions. The
different proton-donor capacity of DMF and CH3CO2H to form reactive interme-
diates explains this discrepancy.
From all the analysis above, a probable reaction process with MnPc as catalyst in
the presence of acetic acid in the oxidation of 2-MN by 30% H2O2 was proposed
(Process 1). The molecule of H2O2 seems to be effective, and this combines with
MnPc, in contrast with CH3CO3H. A five-membered ring could then be formed
from the solvent-CH3CO2H close to the H2O2. Subsequent loss of H2O improves the
electrophilicity of the oxygen–oxygen bond. With regard to steric configuration in
the oxidation of 2-MN, simultaneous cyclo-oxidation has also been proposed by
Svetlana V. Barkanova and others [22]. Further experiments on this reaction should
be carried out in the near future.
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Manganese(II) naphthenate as effective catalyst
1845
Process 1 Probable progress of reaction with MnPc as catalyst in the H2O2–HAc system
Conclusion
It was speculated that use of CH3CO3H improve production of our target compound
because of its higher selectivity than 30% H2O2. Its activity is mild, however,
because of decomposition of the peroxide or superoxide which is the effective
oxidant. Prolonging its lifetime is of crucial importance to obtaining good selec-
tivity and conversion in the oxidation. Manganese(II) naphthenate seems promising
in forming an available peroxide, improving the stability of H2O2, and then achiev-
ing selective oxidation of 2-MN. For 2.5 g 2-MN and 35 ml CH3CO3H, selectivity
and conversion for MnPc were 80.0 and 75.6% and the yield was 60.5%.
Acknowledgments We are grateful to the Department of Chemistry and Chemical Engineering of
Southeast University.
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