Biomimetic Nitration of Phenols Using Metalloporphyrins/H2O2/NO2 -

Article abstract of DOI:10.1007/s10562-015-1610-8

An efficient metalloporphyrins/H₂O₂/NO₂ ^- nitration of phenols has been developed. The total yield of nitrophenol could reach up to 55.1 %, which is about 4 and sixfold higher than that of horse radish peroxidase catalysis and peroxynitrite nitration, respectively. Furthermore, the nitration system attained an enhanced regioselectivity of 1.0 o/p ratio, and exhibited a good substrate scope of monophenols. This protocol is environmentally friendly compared with HNO₃/H₂SO₄ nitration, and stable, inexpensive and organic solvent tolerant compared with enzyme catalytic nitration and peroxynitrite nitration reaction. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-015-1610-8

Catal Lett (2015) 145:1991–1999
DOI 10.1007/s10562-015-1610-8
Biomimetic Nitration of Phenols Using Metalloporphyrins/H O /
2
2
2
NO2
1
1
1
1
1
Weizhi Sun
•
Yaojie Liu
•
Haibo Zhang
•
Mo Xian
•
Huizhou Liu
Received: 3 July 2015 / Accepted: 13 August 2015 / Published online: 25 August 2015
Ó Springer Science+Business Media New York 2015
-
Abstract An efficient metalloporphyrins/H O /NO
2
1 Introduction
2
2
nitration of phenols has been developed. The total yield of
nitrophenol could reach up to 55.1 %, which is about 4 and
sixfold higher than that of horse radish peroxidase catalysis
and peroxynitrite nitration, respectively. Furthermore, the
nitration system attained an enhanced regioselectivity of
Nitrophenols represents an important class of compounds
and useful building blocks, in particular of various phar-
maceuticals, energetic materials, dyes, chemical fibers and
rubber products [1, 2]. The traditional nitration method is
performed using nitric acid and sulfuric acid, which results
in serious pollution, corrosion resstance, by-products
formation.
1
.0 o/p ratio, and exhibited a good substrate scope of
monophenols. This protocol is environmentally friendly
compared with HNO /H SO nitration, and stable, inex-
3
2
4
pensive and organic solvent tolerant compared with
enzyme catalytic nitration and peroxynitrite nitration
reaction.
In recent years, enzymatic methods have become
increasingly important in nitration of phenolic compounds,
which are well known for their high efficiency and selec-
tivity under mild reaction conditions, especially for per-
oxidases. Peroxidases have been used in a broad range of
reactions including oxidation, nitration halogenation,
hydroxylation, demethylation, sulfoxidation, epoxidation
and polymerization [3–5]. In vivo, peroxidases can lead to
nitration of tyrosine and tryptophan [6–8]. Inspired by
natural metabolism, some kinds of peroxidases have been
Graphical Abstract
-
researched for the nitration of phenols in the H O /NO
2
2
2
system in vitro, such as horse radish peroxidase [9, 10],
soybean peroxidase [11], myeloperoxidase [12],
microperoxidase [13, 14] and hemin–peptide mimic
Keywords Phenol Á Nitration Á Mentalloporphyrin Á
Mimic enzyme
III
enzyme (Fe –mimochrome VI). However, the yields are
usually low. For example, the highest yield of nitrophenol
catalyzed by horseradish peroxidase was only 25 % [10].
Furthermore, the thermo sensitivity, poor stability, and
scarce resources of enzyme limit the application.
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-015-1610-8) contains supplementary
material, which is available to authorized users.
&
&
Mo Xian
xianmo@qibebt.ac.cn
It is generally known that iron porphyrin is the active
center of peroxidase (Scheme 1). Actually, several resear-
ches showed that metalloporphyrins could catalyze nitra-
Huizhou Liu
liuhuizhou@qibebt.ac.cn
-
tion of phenols in the presence of peroxynitrite (ONOO ),
1
which could be prepared by H O and NaNO [16–18].
2
2
2
CAS Key Laboratory of Biobased Materials, Qingdao
Institute of Bioenergy and Bioprocess Technology, Chinese
Academy of Sciences, Qingdao 266101, China
Thus, metalloporphyrins may have the potential to catalyze
-
nitration reaction in the H O /NO system. Compared to
2
2
2
123

1
992
W. Sun et al.
All of the products are known compounds, the identifica-
tion of whom was determined by NMR, HRMS, HPLC and
TLC. TLC was performed on a silica gel plate purchased
from Merck Ltd. (Darmstadt, Germany). NMR data were
obtained on a Bruker Avance III 600 MHz NMR Spec-
trometer. HRMS data were obtained on a Bruker Q-TOF
maXis Spectrometer. HPLC analysis was performed on a
Agilent 1100A chromatograph with a ODS C18 column
(4.6 9 250 mm, KR100-5C ) and methanol/water (35:65)
18
mixture as eluent (pH 3). The flow rate was 1 mL/min with
a column temperature of 25 °C. Samples were monitored at
254 nm. The quantitative analytical method was external
Scheme 1 Mechanism for the nitration of protein with peroxidase
15]
standard calibration curve method, using commercial
standard samples as external standard.
[
enzymes, these ‘‘mimic enzymes’’ are thermal-insensitive,
stable and inexpensive. So in this study, we try to develop
2.1 Catalyst Preparation
-
an efficient and economical metalloporphyrins/H O /NO
2
2
2
system for nitration of phenols.
2.1.1 General Procedure of the Synthesis of Porphyrins
Here, we have synthesized four series of metallopor-
phyrins as ‘‘mimic enzymes’’: metal-tetraphenylporphyrin
Porphyrins were prepared using the typical Adler reaction.
Pyrrole (30 mmol) was slowly added to a mixture of sub-
stituted benzaldehyde (30 mmol) and propionic acid
(
MTPP), metal-tetra (p-nitrophenyl) porphyrin (MTNPP),
metal-tetra (p-carboxyphenyl) porphyrin (MTCPP) and
metal-tetra (p-sulfophenyl) porphyrin (MTSPP), to cat-
(105 mL) through a dropping funnel. The mixture was
-
alyze nitration of phenols in H O /NO system (Fig. 1).
2
2
2
heated to 120–140 °C for 1–3 h. After cooling, the reaction
mixture was filtered, washed and dried under vacuum to
obtain the crystal of porphyrins.
Then a study of the catalytic ability under various reaction
conditions has been done. The nitration effects of hemin,
horse radish peroxidase and laccase have also been inves-
tigated as controls.
2.1.2 General Procedure of the Synthesis
of Metalloporphyrins
2
Experimental Section
Metalloporphyrins were prepared by refluxing porphyrins
0.33 mmol) with FeCl , CoCl , MnCl , CuCl , or
(
3
2
2
2
All of the products and metalloporphyrins synthesized in
this research were known compounds and the data accor-
ded with those given in the references. All metallopor-
phyrins were synthesized in our laboratory by Alder
reaction according to the literature [19–22]. Other reac-
tants, solvents and standard samples were purchased from
commercial sources, and used without further purification.
0
Zn(OAc) (1.82 mmol) in N,N -dimethylformamide (DMF,
2
7
0 mL) for 12 h. DMF was removed by distillation and the
metalloporphyrins were precipitated by adding water. The
precipitate was dissolved in 0.1 M NaOH solution and
recrystallized by adding 1 M HCl solution. Finally, met-
alloporphyrins were filtered and dried under vacuum.
2.2 General Procedure of Nitration of Phenols
To a solution contained phosphate sodium buffer (50 mL,
.1 M, pH 7.0), phenols (1 mmol) and NaNO2
50–60 mmol), H O (30 % aqueous solution, 3 mmol)
0
(
2
2
was added dropwise in 80 min. The reaction was initiated
by adding metalloporphyrin (50–60 mg) at room temper-
ature. After stirring for 80 min, the reaction products were
extracted several times with chloroform or ethyl acetate,
and the organic phase was combined, dried with sodium
sulfate. The organic solvent was removed under vacuum.
The residue was dissolved in methanol and quantitatively
analyzed by HPLC.
Fig. 1 Metalloporphyrins used in nitration of phenols
1
23

-
2
Biomimetic Nitration of Phenols Using Metalloporphyrins/H
2 2
O /NO
1993
3
Results and Discussion
3.2 Nitration of Phenol in FeTCPP (FeTSPP)/H
2
NO2 System
2
O
/
2
3
.1 Nitration of Phenol in Metalloporphyrins/H O /
2
2
2
NO2 System
Then great efforts to optimize reaction conditions for
FeTCPP or FeTSPP catalyzed nitration of phenol were
conducted to increase the yields. The effect of metallo-
We began the study by screening and evaluating catalysts
-
for phenol nitration. Nitration of phenol in H O /NO
2
porphyrin content, NaNO content, H O content, pH,
2 2 2
2
2
system was carried out using serious of porphyrins com-
bined with different metals. Products and residual sub-
strates were quantitatively analyzed by external standard
calibration curve method. Reaction of phenol in the pres-
temperature, reaction time and solvent were investigated,
respectively (Figs. 3, 4).
As shown in Fig. 3, experiments were set up under
various conditions. It was observed that there was rapidly
increase of the nitrophenol yield up to 0.05 g FeTCPP
(5.9 mol% of phenol). Thereafter, no notable increase of
the yield was noticed. This result suggested that the opti-
mum content of FeTCPP was 5.9 mol% of reaction sub-
-
ence of FeTSPP, H O and NO resulted in the formation
2
2
2
of 4-nitrophenol and 2-nitrophenol (Fig. 2). The products
were analyzed by HPLC and comfirmed by comparing with
the commercial samples.
The effect of different metalloporphyrins on nitration
was investigated under the conditions: phenol (1 mmol),
NaNO2 (20 mmol), H O (30 % aqueous solution,
strate (Fig. 3a). Similarly, the optimum content of NaNO
was 50 mmol and H was 3 mmol (Fig. 3b, c). The
2
O
2 2
highest yields of 4- and 2-nitrophenol were 21.2 and
22.5 %, respectively.
2
2
2
mmol), phosphate sodium buffer (PBS, 50 mL, 0.1 M,
pH 7.0), 80 min at 25 °C. The results are given in
Table 1.
Therefore, all the nitration experiments were performed
under the conditions of 5.9 mol% FeTCPP, 50 mmol
As expected, the blank experiment generated only a
trace of nitration products (Table 1, entry 1), and metal-
loporphyrins could increase the conversion of phenol
NaNO and 3 mmol H O . The effect of pH on the activity
2 2 2
was then examined (Fig. 3d). The pH profile of the yield
for nitrophenol formation wascharacterized by a bell-
shaped curve. The maximum activity was at pH 7, which
was similar to the optimum pH of common peroxidases.
Next, the effect of reaction time and temperature were
investigated (Fig. 3e). The yield of 4- and 2-nitrophenol in
40 min increased rapidly and then increased slowly.
80 min was found to be the optimum reaction time.
Reaction temperature had relatively little effect on the
yield of nitrophenol (Fig. 3f). The yield increased by
raising temperature from 0 to 25 °C and then it decreased.
In addition, the product distribution changed to some extent
with temperature increasing. The o/p ratio decreased to
below 1.0 when the temperature reached 45 °C or higher.
(
Table 1, entries 2–23). Among the catalyst screening,
iron porphyrins (FeTPP, FeTNPP, FeTCPP, FeTSPP)
performed the best catalytic activity (Table 1, entries 4, 9,
1
4, 19). FeTCPP and FeTSPP showed better yields than
FeTPP and FeTNPP which could be attributed to the
water solubility. The best yield was 14.6 % and o/p ratio
was0.62. As a control, corresponding chlorinated metal
salts were also investigated (Table 1, entries 24–28). No
significant change in phenol conversion was observed.
This result proved the nitration activity of
metalloporphyrins.
Fig. 2 HPLC data of products
2 2
of nitration in FeTSPP/H O /
-
2
NO
system
123

1
994
W. Sun et al.
Table 1 Effects of metalloporphyrins on nitration of phenol
performed. The yields were almost equal those in water
and PBS system proving the potential of this mimic
enzyme nitration reaction in organic solvents.
To sum up, the optimum reaction parameters are:
n(phenol) : n(FeTCPP) : n(NaNO ) : n(H O ) = 1 : 0.059 :
2
2 2
5
0 : 3, pH 7.0, 80 min and 25 °C. Under this condition, the
total yield of 4- and 2-nitrophenol is 43.7 %. And com-
a
b
c
Entry
Catalyst
Yield (%)
o/p Ratio
pared with the 1.67 o/p ratio of the nitration of phenol in
-
HNO /H SO , the nitration in FeTCPP/H O /NO system
3
2
4
2
2
2
4
-Nitrophenol
2-Nitrophenol
shows enhanced regioselectivity, the o/p ratio of which is
about 1.06.
1
2
3
4
5
6
7
8
9
Blank
TCPP
TSPP
Trace
\0.5
\0.5
5.1
Trace
\0.5
\0.5
8.0
–
–
As shown in Fig. 4, similar results were observed in the
-
experiments in FeTSPP/H O /NO system. The optimum
–
2
2
2
FeTCPP
CoTCPP
MnTCPP
CuTCPP
ZnTCPP
FeTSPP
CoTSPP
MnTSPP
CuTSPP
ZnTSPP
FeTPP
1.57
parameters are: n(phenol) : n(FeTCPP) : n(NaNO ) :
2
\0.5
\0.5
\0.5
\0.5
9.0
\0.5
\0.5
\0.5
\0.5
5.6
–
n(H O ) = 1:0.056:60:3, pH 7.0, 80 min and 25 °C. The
2
2
–
total yield of 4- and 2-nitophenol is 55.1 % under the
optimum conditions. The 0.97 o/p ratio is even lower than
that of FeTCPP catalyzed nitration, which shows better
regioselectivity.
–
–
0.62
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
\0.5
\0.5
\0.5
\0.5
2.3
\0.5
\0.5
\0.5
\0.5
2.4
–
–
3.3 Nitration of Phenol in Different Systems
–
–
In order to evaluate the catalytic effect of metallopor-
-
1.04
phyrins/H O /NO
2
2
2
system, we compared this protocol
CoTPP
\0.5
1.3
\0.5
1.1
–
with the nitration reaction of phenol catalyzed by different
enzymes and performed by peroxynitrite reaction
MnTPP
CuTPP
0.85
(Table 2).
\0.5
\0.5
2.7
\0.5
\0.5
2.0
–
As the active center of various enzymes, hemin is
ZnTPP
–
commonly used as a mimic enzyme of peroxidases. The
result showed that hemin could also promote the nitration
of phenol under the optimum conditions, albeit with lower
yields (Table 2, entry 4).
FeTNPP
CoTNPP
MnTNPP
CuTNPP
ZnTNPP
0.74
\0.5
1.8
\0.5
2.1
–
1.17
–
\0.5
\0.5
Trace
Trace
Trace
Trace
Trace
\0.5
\0.5
Trace
Trace
Trace
Trace
Trace
In the presence of 1 mg horse radish peroxidase, the
–
total yield of nitrophenol was only 14.8 %, about fourfold
-
FeCl
CoCl
MnCl
CuCl
ZnCl
3
–
lower than that in TSPP/H O /NO
2
system (Table 2,
2
2
2
–
entry 5). So we increased the content of horse radish per-
oxidase to 10 mg. The conversion was raised to 65 %, but
the products were very complicated and almost no nitro-
phenol was detected (Table 2, entry 6). As described in the
literatures, peroxidases can catalyze further reactions, such
as oxidative decomposition. So too much peroxidase not
only promoted various side reactions of phenol, but also
resulted in the following reactions of nitrophenols. That’s
why peroxidase is less application in nitration reaction so
far.
2
–
2
–
2
–
Reaction conditions: phenol (1 mmol), NaNO
(
2 2 2
(20 mmol), H O
30 % aqueous solution, 2 mmol), phosphate sodium buffer (50 mL,
0
a
.1 M, pH 7.0), 80 min at 25 °C
Catalyst content: 0.03 g
HPLC yields
b
c
Calculated from original HPLC data
Another common metalloenzyme, laccase, was also
used as a comparison. Laccase is copper-containing oxi-
dase enzyme and requires oxygen as a second substrate for
the enzymatic reaction. So oxygen was used instead of
H O , and moreover, the pH was adjusted to 5, the opti-
The effect of solvent was also investigated (Fig. 3g).
The yield of nitrophenol in pure aquatic system was only
3.5 %, obviously lower than that in PBS system. The
2
result indicated the importance of pH stability. No reaction
was observed in MeOH system. That could be attributed to
2
2
mum pH of laccase. However, no reaction was observed
(Table 2, entries 7 and 8), which indicated the important
roles of iron ion and porphyrins.
the indissolubility of NaNO . So experiments in water/
2
MeOH and water/PBS mixed solution system were
1
23

-
2
Biomimetic Nitration of Phenols Using Metalloporphyrins/H
2 2
O /NO
1995
Fig. 3 Effects of various
a 14
b 25
reaction conditions on nitration
of phenol catalyzed by FeTCPP.
a Effects of FeTCPP content.
Conditions: phenol (1 mmol),
12
2
1
1
0
5
0
5
0
1
0
8
6
4
2
0
NaNO
(
2
(20 mmol), H
2 mmol), pH 7.0, 80 min,
2 2
O
2
5 °C. b Effects of NaNO
2
content. Conditions: phenol
1 mmol), FeTCPP (50 mg,
4
-nitrophenol
2-nitrophenol
4-Nitrophenol
2-Nitrophenol
(
5
7
9 lmol), H
.0, 80 min, 25 °C. c Effects of
content. Conditions:
phenol (1 mmol), FeTCPP
2 2
O (2 mmol), pH
0
0
0
0.02 0.04 0.06 0.08
FeTCPP content/mol%
0.1
0.12
0
20
40
60
80
100
2 2
H O
n(NaNO )/n(phenol)
2
(
(
50 mg, 59 lmol), NaNO
50 mmol), pH 7.0, 80 min,
2
c 25
d 30
25 °C. d Effects of pH.
Conditions: phenol (1 mmol),
FeTCPP (50 mg, 59 lmol),
2
5
2
1
0
5
20
15
NaNO
(
2 2 2
(50 mmol), H O
3 mmol), 80 min, 25 °C.
e Effect of reaction time.
Conditions: phenol (1 mmol),
FeTCPP (50 mg, 59 lmol),
10
5
1
0
5
0
4
2
-Nitrophenol
-Nitrophenol
4-Nitrophenol
2-Nitrophenol
NaNO
3 mmol), pH 7.0, 25 °C.
f Effects of temperature.
2 2 2
(50 mmol), H O
(
0
1
2
3
4
5
6
7
5.5
6
6.5
7
7.5
8
8.5
Conditions: phenol (1 mmol),
FeTCPP (50 mg, 59 lmol),
n(H O )/n(phenol)
pH
2
2
e 30
f 30
NaNO
2 2 2
(50 mmol), H O
(3 mmol), pH 7.0, 80 min.
g Effect of solvent. Conditions:
2
2
5
0
25
20
15
10
5
phenol (1 mmol), FeTCPP
(
(
7
50 mg, 59 lmol), NaNO
50 mmol), H (3 mmol), pH
.0, 80 min, 25 °C, vwater:vMeOH
2
2
O
2
15
10
5
=
1:1, vPBS:vMeOH = 1:1
4
2
-Nitrophenol
-Nitrophenol
4-Nitrophenol
2-Nitrophenol
0
0
25
50
75
100 125 150 175
0
10
20
30
40
50
60
70
Temperature/°C
Time/min
g 50
4
4
3
3
2
2
1
1
5
0
5
0
5
0
5
0
5
0
2
-Nitrophenol
4-Nitrophenol
water PBS MeOH water + PBS +
MeOH MeOH
Solvent
Peroxynitrite reaction was another common method in
reaction with or without catalyst. As the result showed,
-
ONOO without catalyst could produce a small amount of
the research of protein and other aromatic compounds’
-
nitration. We synthesized the ONOO solution according to
nitrophenols (Table 2, entry 9). Catalyst FeTSPP and horse
radish peroxidase could obviously improve the conversion
the literatures [23, 24], to perform the peroxynitrite
123

1
996
W. Sun et al.
Fig. 4 Effects of various
a
c
e
b 30
1
1
6
4
reaction conditions on nitration
of phenol catalyzed by FeTSPP.
a Effect of FeTSPP content.
Conditions: phenol (1 mmol),
25
12
20
15
1
0
8
6
4
2
0
NaNO
(
2
(20 mmol), H
2 mmol), pH 7.0, 80 min,
2 2
O
2
5 °C. b Effect of NaNO
2
1
0
5
0
content. Conditions: phenol
1 mmol), FeTSPP (50 mg,
4-Nitrophenol
2-Nitrophenol
4-Nitrophenol
2-Nitrophenol
(
5
7
6 lmol), H
.0, 80 min, 25 °C. c Effect of
content. Conditions:
phenol (1 mmol), FeTSPP
2 2
O (2 mmol), pH
0
0.02
0.04
0.06
0.08
0.1
0.12
0
20
40
60
80
100
2 2
H O
FeTSPP content/mol%
n(NaNO
2
)/n(phenol)
(
(
60 mg, 56 lmol), NaNO
60 mmol), pH 7.0, 80 min,
2
3
2
2
0
5
0
d 35
4
2
-Nitrophenol
-Nitrophenol
2
5 °C. d Effect of pH.
Conditions: phenol (1 mmol),
3
2
2
1
1
0
5
0
5
0
5
0
FeTSPP (60 mg, 56 lmol),
NaNO
(
2 2 2
(60 mmol), H O
3 mmol), 80 min, 25 °C.
15
e Effect of reaction time.
Conditions: phenol (1 mmol),
FeTSPP (60 mg, 56 lmol),
1
0
5
0
4
-Nitrophenol
-Nitrophenol
2
NaNO
3 mmol), pH 7.0, 25 °C.
f Effect of temperature.
2 2 2
(60 mmol), H O
(
0
1
2
3
4
5
6
7
5.5
6
6.5
7
7.5
8
8.5
Conditions: phenol (1 mmol),
FeTSPP (60 mg, 56 lmol),
n(H O )/n(phenol)
pH
2
2
f 35
30
25
20
15
10
5
35
30
25
20
15
10
5
0
NaNO
2 2 2
(60 mmol), H O
(3 mmol), pH 7.0, 80 min.
g Effect of solvent. Conditions:
phenol (1 mmol), FeTSPP
(
(
=
60 mg, 56 lmol), NaNO
60 mmol), H (3 mmol), pH
7.0, 80 min, 25 °C,
2
2 2
O
v
water:vMeOH = 1:1, vPBS:vMeOH
4
-Nitrophenol
4-Nitrophenol
2-Nitrophenol
=
1:1
2-Nitrophenol
0
0
25
50
75
100 125 150 175
0
10
20
30
40
50
60
70
Time/min
Temperature/°C
g 60
5
4
3
2
1
0
0
0
0
0
0
2
4
-Notrophenol
-Notrophenol
water PBS MeOH water + PBS +
MeOH MeOH
Solvent
of phenol and the yield of nitro-product. But the highest
yield was only 9.9 %, about sixfold lower than that in
3.4 Nitration of Different Phenolic Compounds
2
in FeTSPP/H
O
2
/NO
System
2
2
-
TSPP/H O /NO system. This may be attributed to the
2
2
2
-
instability of ONOO ion, and because of this, peroxynitrite
reaction is unpractical in the synthesis of nitrophenols.
At last, the general scope and versatility of this mimic
enzyme nitration system were investigated. The catalytic
1
23

-
2
Biomimetic Nitration of Phenols Using Metalloporphyrins/H
2 2
O /NO
1997
Table 2 Effects of different system on nitration of phenol
a
b
c
b
Entry
Catalyst (content)
Nitration system
Conversion (%)
Yield (%)
o/p Ratio
4
-Nitrophenol
2-Nitrophenol
-
1
2
3
4
5
6
7
8
9
Blank
H
H
H
H
H
H
O
O
2
2
2
2
2
2
2
2
O
O
O
O
O
O
2
2
2
2
2
2
/NO
/NO
/NO
/NO
/NO
2
2
2
2
2
2
\0.1
45
Trace
21.2
28.0
15.5
6.7
Trace
22.5
27.1
15.9
8.1
–
-
-
-
-
-
FeTCPP (50 mg, 5.9 mol%)
1.06
0.97
1.03
1.21
–
d
FeTSPP (60 mg, 5.6 mol%)
Hemin (50 mg, 7.7 mol%)
Horse radish peroxidase (1 mg)
57
34
e
41
e
Horse radish peroxidase (10 mg)
f
Laccase (1 mg)
/NO
65
\0.1
\0.1
\0.1
0.8
\0.1
\0.1
\0.1
1.1
-
2
/NO
/NO
\0.1
\0.1
\2
7
–
f
-
2
Laccase (10 mg)
–
-
g
g
Blank
ONOO
ONOO
ONOO
1.38
1.17
1.48
-
1
1
a
0
FeTSPP (60 mg, 5.6 mol%)
2.4
2.8
e
-g
1
Horse radish peroxidase (1 mg)
19
4.0
5.9
Reaction conditions: phenol (1 mmol), NaNO
Calculated from original HPLC data
HPLC yields
2
(50 mmol), H
2
O
2
(3 mmol), PBS (50 mL, 0.1 M, pH 7.0), 80 min at 25 °C
b
c
d
e
2
Reaction conditions: NaNO (60 mmol)
Enzyme activity: [200 IU/mg
f
Enzyme activity: [50 IU/mg. Reaction pH: 5
g
Reaction conditions: phenol (1 mmol), NaONOO (9.6 mmol), PBS (20 mL, 0.1 M, pH 7.0), 30 min at 25 °C
performance of iron porphyrins FeTSPP to the nitration
reaction of hydroquinol, resorcinol, phloroglucinol and p-
cresol were tested under the optimum reaction conditions
methylphenol were obtained, and no oxidative product was
detected.
(
Table 3).
-
As seen from Table 3, metalloporphyrins/H O /NO
2
4 Conclusions
2
2
system was an efficient nitration system for monophenols.
But this protocol showed lower nitration efficiency and
higher oxidation efficiency for polyphenols.
-
In summary, an efficient metalloporphyrins/H O /NO
2
2
2
nitration system under mild conditions has been developed.
Under the optimum conditions, catalyzed by FeTSPP, the
total yield of 4- and 2-nitrophenol can reach 55.1 %, and an
enhanced regioselectivity of 1.0 o/p ratio was attained. This
The results showed that the yields of nitration of
-
diphenols in TSPP/H O /NO system were only 20 % or
2
2
2
so (Table 3, entries 2 and 3). Furthermore, the nitration of
phloroglucinol obtained 68 % conversion but only 1.3 %
yield of nitro product (Table 3, entry 4). Actually,
phloroglucinol almost completely decomposed after 24 h
in this system. It is noted that phloroglucinol was very
easily oxidized and degraded, so this result proved that
metalloporphyrins couldcatalyze both nitration and oxida-
-
iron porphyrins/H O /NO system can effectively pro-
2
2
2
mote nitration of phenols in the presence of organic co-
solvent, such as MeOH. Meanwhile, the yield of this pro-
tocol is about fourfold higher than that of horse radish
peroxidase catalysis, and sixfold higher than that of per-
oxynitrite nitration. Furthermore, this nitration system
exhibits a good substrate scope of monophenols. In addi-
tion, this protocol is environmentally friendly avoiding the
usage of HNO /H SO , and thermal-insensitive, stable,
-
tion in H O /NO system. By contrast, the nitration of
2
2
2
more stable phenolic compound p-cresol showed a higher
9 % conversion and 66.8 % yield of 2-nitro-4-
6
3
2
4
methylphenol (Table 3, entry 5). In addition, a small
amount of 4-nitrophenol and dinitro-product 2,6-dinitro-4-
inexpensive and organic solvent tolerant compared with
enzyme catalytic nitration reaction and peroxynitrite
123

1
998
W. Sun et al.
-
2
Table 3 Nitration of different phenolic compounds in FeTSPP/H
2 2
O /NO
system
Phenolic
compound
Conversion
c
Entry
1
Nitration product and yield (%)
b
(%)
57
2
2
8.0
0.3
27.1
2
3
47
42
11.8
9.9
4
5
68
69
1
.3
6
6.8
0.56
0.88
a
b
c
Reaction conditions: phenolic compounds (1 mmol), NaNO
Calculated from original HPLC data
HPLC yields
2
(50 mmol), H
O
2 2
(3 mmol), PBS (50 mL, 0.1 M, pH 7.0), 80 min at 25 °C
reaction. Further explorations of ‘‘mimic enzymes’’ met-
alloporphyrins are currently undergoing in our laboratory.
2. Olah GA, Malhotra R, Narang SC (1989) Nitration: Methods and
Mechanism. VCH, New York
3
4
5
6
7
. Colonna S, Gaggero N, Richelmi C, Pasta P (1999) Trends
Biotechnol 17:163
. Santos AS, Pereira N Jr, da Silva IM, Sarquis MIM, Antunes
OAC (2004) Process Biochem 39:2269
. Li J, Tian J, Fei X, Wang X, Xu L, Wang Y (2013) J Mol Catal B
Enzym 98:87
. Ohshima H, Friesen M, Brouet I, Bartsch H (1990) Food Chem
Toxicol 28:647
Acknowledgments This work was supported by Key Program of
the Chinese Academy of Sciences (KGZD-EW-606-1-3) and Taishan
Scholars Climbing Program of Shandong (No. tspd20150210).
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