Cellulose-supported Ni(NO3)2.6H2O/2,4,6- trichloro-1,3,5-triazine (TCT) as a mild, selective, and biodegradable system for nitration of phenols

Article abstract of DOI:10.1080/00397911.2010.516054

Nitration of certain phenols and naphthols in the presence of biodegradable cellulose-supported Ni(NO₃)₂.6H₂O/2,4,6- trichloro-1,3,5-triazine was carried out in acetonitrile at room temperature. Ortho nitrated phenols were obtained regioselectively within a short reaction time with good yields. The reaction condition was mild, and the employed cellulose could be recovered several times for further use. Copyright

Full text of DOI:10.1080/00397911.2010.516054

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Cellulose-Supported
Ni(NO ) · 6H O/2,4,6-Trichloro-1,3,5-
3
2
2
triazine (TCT) as a Mild, Selective, and
Biodegradable System for Nitration of
Phenols
a
a
b
Firouzeh Nemati , Hossein Kiani & Yaser Saeidi Hayeniaz
a
Department of Chemistry, Faculty of Science, Semnan University,
Semnan, Iran
b
Faculty of Chemistry, Tarbiat Moallem University, Tehran, Iran
Published online: 11 Jul 2011.
To cite this article: Firouzeh Nemati , Hossein Kiani & Yaser Saeidi Hayeniaz (2011): Cellulose-
Supported Ni(NO ) · 6H O/2,4,6-Trichloro-1,3,5-triazine (TCT) as a Mild, Selective, and
3
2
2
Biodegradable System for Nitration of Phenols, Synthetic Communications: An International Journal
for Rapid Communication of Synthetic Organic Chemistry, 41:20, 2985-2992
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1
Synthetic Communications , 41: 2985–2992, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.516054
CELLULOSE-SUPPORTED Ni(NO ) ꢀ 6H O/
3
2
2
2,4,6-TRICHLORO-1,3,5-TRIAZINE (TCT) AS A MILD,
SELECTIVE, AND BIODEGRADABLE SYSTEM FOR
NITRATION OF PHENOLS
1
1
Firouzeh Nemati, Hossein Kiani, and Yaser Saeidi Hayeniaz
2
1
Department of Chemistry, Faculty of Science, Semnan University,
Semnan, Iran
Faculty of Chemistry, Tarbiat Moallem University, Tehran, Iran
2
GRAPHICAL ABSTRACT
Abstract Nitration of certain phenols and naphthols in the presence of biodegradable
cellulose-supported Ni(NO O/2,4,6-trichloro-1,3,5-triazine was carried out in
3
)
2
ꢀ 6H
2
acetonitrile at room temperature. Ortho nitrated phenols were obtained regioselectively
within a short reaction time with good yields. The reaction condition was mild, and the
employed cellulose could be recovered several times for further use.
Keywords Biodegradable; cellulose; nitration; phenols; 2,4,6-trichloro-1,3,5-triazine
INTRODUCTION
Nitration of aromatic compounds is an industrially important reaction because
nitro-aromatic compounds are considered to be key building blocks for a broad
[1]
range of drugs and pharmaceuticals. Among these compounds, o-nitro phenols
and naphthols are widely used for the synthesis of commercially valuable
[
2]
compounds such as dyes, pharmaceuticals, plastics, and explosives.
In the classic procedure for the nitration of phenols, use of nitric and sulfuric
acid mixtures would result in the formation of ortho and para products with a ratio
[3]
of about 2:1. Because of these disadvantages, it is desirable to develop a new
method showing more regioselectivity and using less toxic reagents.
Many new versions of this classic procedure are reported in literature, mostly
using new nitration agents or acid catalysts such as impregnated alumina and silica
Received April 14, 2010.
Address correspondence to Firouzeh Nemati, Department of Chemistry, Faculty of Science,
Semnan University, Semnan, Iran. E-mail: fnemati_1350@yahoo.com
2
985

2986
F. NEMATI, H. KIANI, AND Y. S. HAYENIAZ
[
with N O , claycop, montmorillonite impregnated with bismuth nitrate,
4]
[5]
[6]
2
4
[
7]
[8]
[9]
[10]
clayfen,
[
zeofen,
modified silica,
[12]
metal nitrates,
ionic liquids,
nitronium tetrafluoro
[14]
zeolite-based solid acid catalysts,
11]
[13]
borate,
peroxy nitrile,
zirconyl nitrate,
[15]
[16]
Yb(OTf) and Hf(OTf) in conjunction with HNO ,
4
nitrogen
3
3
[
17]
[18]
[19]
oxides,
supported system,
heteropoly acids,
MCM-41,
polyethylene glycol (PEG)–N O ,
Zn(NO ) ꢀ 2 N O and its charcoal-
3
2
2
4
[20]
[21]
tert-butyl nitrite in
2
4
[22]
[23]
solution and on solid support, aluminum nitrate and silica sulfuric acid, metal
[
24]
salts impregnated with Yb-Mo-montmorillonite KSF,
oxide supported on sulfated SnO2.
and nano-sized tungsten
[25]
The new trends in science and technology toward using natural materials and
reusable systems, in addition to the environmental hazards of the current methods,
make green and ecofriendly methods for regioselective nitration of phenols desirable.
Some of the newly investigated alternatives that could fit these standards are natural
biopolymers, especially cellulose, which could be used as a support for sulfuric
[
26,27]
acid.
RESULTS AND DISCUSSION
[
28–31]
In continuation of our earlier studies of organic transformations,
here we
report our results on the regioselective nitration of some phenols using
cellulose-supported Ni(NO ) ꢀ 6H O, with excellent yields in the presence of 3 mol%
3
2
2
of 2,4,6-trichloro-1,3,5-triazine (TCT) at room temperature in acetonitrile TCT
(cyanuric chloride) (Scheme 1) was employed as a cheap and commercially available
[
32]
reagent. It performed as the required acid catalyst source in the nitration process
instead of Brønsted or Lewis acids. Actually, TCT reacts with incipient moisture and
[
33]
releases 3 mol of HCl and cyanuric acid, which is the by-product of this reaction
Scheme 1).
(
Using cellulose-supported Ni(NO ) ꢀ 6H O for the nitration of phenols is a
3
2
2
brand new idea that has several advantages. One of the most important advantages
is the noncorrosiveness of TCT, which is a crucial factor for industrial applications.
The by-product, cyanuric acid, can be easily removed by washing the reaction
mixture with water.
Nitration of phenol was examined in the presence of TCT and various metal
nitrates and conditions. Initially, the reaction of phenol with some metal nitrates
was selected as a model. We used acetonitrile solution of phenol (1 mmol) and metal
þ
Scheme 1. Reaction of TCT with water, producing NO .
2

SELECTIVE SYSTEM FOR NITRATION OF PHENOLS
2987
Table 1. Nitration of phenol using different metal nitrates in the presence of 2 or 3 mol% TCT in aceto-
nitrile at room temperature
Entry
Metal nitrates
TCT (mmol)
Time (h)
o-Nitro phenol (%)
1
2
3
4
5
6
7
8
9
NaNO
NaNO
2
0.03
0.03
0.03
0.02
0.03
0.03
0.02
0.03
0.02
0.03
0.03
0.03
0.03
18
16
1
60
55
40
55
55
50
60
75
55
75
60
80
60
3
Cr(NO
Fe(NO
Fe(NO
3
3
3
)
)
)
3
3
3
ꢀ 9H
ꢀ 9H
ꢀ 9H
2
2
2
O
O
O
0.5
0.5
10
4
Co(NO
3
)
2
ꢀ 6H
2
O
O
O
Ni(NO
Ni(NO
3
)
)
2
2
ꢀ 6H
ꢀ 6H
2
3
2
2
Mn(NO
Mn(NO
3
)
)
2
ꢀ 4H
ꢀ 4H
2
O
O
5
1
1
1
1
0
1
2
3
3
2
2
3
Bi(NO
Zn(NO
Cu(NO
3
)
3
ꢀ 5H
2
O
9
3
)
2
ꢀ 6H
2
O
1.5
7
3
)
2
ꢀ 3H
2
O
nitrates (1 mmol) in the presence of different amounts of TCT, which was stirred at
room temperature for 0.5–18 h. The results are summarized in Table 1.
Some good results were observed in the presence of Ni(NO ) ꢀ 6H O,
3
2
2
Mn(NO ) ꢀ 4H O, and Zn(NO ) ꢀ 6H O (Table 1, entries 8, 10, and 12), but gener-
3
2
2
3 2
34]
2
[
ally the reaction time was long.
Surprisingly, a remarkable regioselectively and
short reaction time was observed when those metal nitrates were supported on cellu-
lose in 3% mol of TCT and treated with phenol in acetonitrile. Within the results, the
ortho-isomer was an exclusive product (Table 2, entries 2, 4, and 6). Apparently,
cellulose-supported Ni(NO ) ꢀ 6H O shows the most ortho-selectivity with the short-
3
2
2
est reaction time (Table 2, entry 6). An increase in the amount of TCT or
cellulose-supported reagent has no obvious effect on the results of the reaction.
According to the obtained data, use of 0.5 g cellulose-supported Ni(NO ) ꢀ
3
2
6
H O in presence of 3% mol TCT in acetonitrile is the best circumstance for the
2
nitration of phenol.
Table 2. Nitration of phenol using cellulose-supported metal nitrates in the presence of TCT in aceto-
nitrile at room temperature
Reagent
(g)
TCT
(mmol)
Time
(min)
o-Nitro
phenol (%)
Entry
Reagent
1
2
3
4
5
6
7
8
9
Cellulose–Zn(NO
Cellulose–Zn(NO
3
)
)
2
2
ꢀ 6H
2
2
O
O
0.5
0.5
0.02
0.03
0.02
0.03
0.02
0.03
0.04
0.03
0.03
0.03
90
60
90
60
60
45
45
45
45
90
60
80
55
75
75
80
80
80
70
75
3
ꢀ 6H
Cellulose–Mn(NO
Cellulose–Mn(NO
3
)
)
2
ꢀ 4H
ꢀ 4H
2
O
0.5
0.5
3
2
2
O
Cellulose–Ni(NO
Cellulose–Ni(NO
Cellulose–Ni(NO
Cellulose–Ni(NO
Cellulose–Ni(NO
3
3
3
3
3
)
)
)
)
)
2
2
2
2
2
ꢀ 6H
2
2
2
2
2
O
O
O
O
O
0.5
0.5
ꢀ 6H
ꢀ 6H
ꢀ 6H
ꢀ 6H
0.5
0.6
0.7
0.5 g cellulose and 1 mmol
1
0
Physical mixture of cellulose
and Ni(NO
3
)
2
ꢀ 6H
2
O
Ni(NO
3
)
2
2
ꢀ 6H O

2988
F. NEMATI, H. KIANI, AND Y. S. HAYENIAZ
Table 3. Nitration of phenols using 0.5 g cellulose-supported Ni(NO
.03 mmol TCT in acetonitrile at room temperature
3
)
2
ꢀ 6H
2
O in the presence of
0
a
Entry
Substrate
Products
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
9
Phenol
o-Nitro phenol
45
45
50
30
30
50
60
40
30
80
80
90
65
60
80
85
90
90
Naphthalen-1-ol
Naphthalen-2-ol
m-Cresol
2-Nitronaphthalen-1-ol
1-Nitronaphthalen-2-ol
5-Methyl-2-nitrophenol
4-Nitrobenzene-1,3-diol
2-Hydroxy-3-nitrobenzaldehyde
2-Chloro-6-nitrophenol
4-Chloro-2-nitrophenol
4-Methyl-2-nitrophenol
Resorcinol
2-Hydroxybenzaldehyde
2-Chlorophenol
4-Chlorophenol
p-Cresol
a
Yields are based on isolated products.
The extent of generality of this reaction is shown with several examples in
Table 3. All the selected phenols yielded exclusively the o-nitro product in good to
excellent yields.
Thus, cellulose provides an ideal system for milder, safer, and more regioselec-
tive nitration of phenols. It is also reusable and ecofriendly.
Scheme 2. Plausible mechanism.
Table 4. Comparison of results using cellulose-supported Ni(NO
other workers for the nitration of phenol
3
)
2
ꢀ 6H
2
O=TCT with results obtained by
a
Time (min) Yield (%) Ref.
Entry
Nitrating agent and acid catalyst
Conditions
1
2
3
4
5
6
7
8
MCM-41=HNO 30%
3
DCE=rT
ꢁ
120
60
90
80
40
41
36
30
93
80
19
25
12
40
37
36
35
—
b
WSSnO
ZrO(NO
Metal-modified KSF=HNO
Mg(HSO =NaNO
NaNO =SSA=wet SiO
Acetyl nitrate=SiO
Cellulose-supported Ni(NO
2
=HNO
3
60 C
Acetone=rT
3
)
2
ꢀ xH
2
O
30
ꢁ
3
THF=30 C
720
30
4
)
2
3
=wet SiO
2
CH
CH
2
Cl
Cl
2
=rT
2
2
2
2
=rT
ꢁ
90
2
CHCl
CH
3
=ꢂ20 C
120
45
3
)
2
ꢀ 6H
2
O=TCT
3
CN=rT
a
o-Nitro phenol.
b
2
Nano-sized tungsten oxide supported on sulfated SnO .

SELECTIVE SYSTEM FOR NITRATION OF PHENOLS
2989
The suggested mechanism is depicted in Scheme 2. We propose that cellulose
acts as a template by forming hydrogen bonds between their OH groups, phenol,
and nitrate anions. This complex would transform into the intermediate and then
[
35]
undergoes a rearrangement to o-nitro phenol.
In Table 4, the efficiency of our method for the nitration of phenols is compared
with some other published works in literature. Each of these methods has its own
advantages, but they all suffer from some disadvantages, including difficulty in prep-
aration of reagent or catalyst (entry 2), poor regioselectivity (entries 3, 4, 5, and 6),
use of corrosive reagent (entries 1, 2, and 4), long reaction time (entry 4), and harsh
reaction condition (entry 7).
EXPERIMENTAL
Chemicals were purchased from the Fluka, Merck, and Aldrich chemical com-
panies. Melting points were determined on an Electrothermal 9100, without further
corrections. The nitration products are characterized through comparison of their
1
spectral data [infrared (IR), H NMR], thin-layer chromatography (TLC), and melt-
ing points with the corresponding authentic samples reported in literature.
General Procedure for Preparation of Cellulose-Supported
Metal Nitrates
The reagents were prepared by impregnation: Metal nitrates (2.5 g) were dis-
solved in the mixture of H O and acetone (20.0 ml, 50:50). After addition of cellulose
2
(
(
5.0 g), the solution was stirred for 1 h using a magnetic stirrer at room temperature
ꢁ
20 C). The excess solvent was removed by a vacuum rotary under mild vacuum
pressure, and finally the remaining solid was dried in a vacuum oven at room
temperature for 6 h.
Recycling of Cellulose
Cellulose was separated from the reaction mixture by paper filtration. Then it
was washed thoroughly with H O and acetone and dried in a vacuum oven for 8 h to
2
give recycled cellulose. It can be reused in the preparation of reagent up to three
times.
Typical Procedure for Mononitration of Phenols
Phenol (0.094 g, 1 mmol), cellulose-supported metal nitrates (0.5 g), and TCT
0.006 g, 0.03 mmol) were stirred in 5 mL of acetonitrile at room temperature. After
(
the completion of the reaction, the reaction mixture was filtered (the progress of the
reaction was monitored by TLC). The residue was washed with acetonitrile (2–5 mL)
and dried over anhydrous sodium sulfate, and finally the solvent was removed under
ꢁ
vacuum (35–40 C). The crude product was treated with n-pentane (4-nitrophenol is
insoluble in n-pentane), and then the n-pentane was evaporated by water bath (35–
[36]
ꢁ ꢁ ꢁ
4
0 C) to give 2-nitrophenol. The yield was 0.11 g (80%), mp 43 C (lit. mp 44 C).

2990
F. NEMATI, H. KIANI, AND Y. S. HAYENIAZ
The other nitro phenols were purified by silica-gel dry flash chromatography using
petroleum ether–ethyl acetate (98:2) as eluent.
1
Spectral (IR, H NMR) and Analytical Data
ꢁ
[10]
5
-Methyl-2-nitrophenol (Entry 4, Table 3). Mp 53–54 C (lit.
mp
(cm ): 3249, 1632, 1332, 766; H NMR (300 MHz;
ꢁ
3–56 C); IR (KBr) t
max
ꢂ1
1
5
CDCl ; Me Si): d 10.75 (s, 1H), 7.79 (d, J ¼ 8.4 Hz, 1H), 6.91 (s, 1H), 6.76 (d,d,
3
4
J ¼ 8.4, J ¼ 0.9 Hz, 1H), 2.29 (s, 3H).
-Methyl-2-nitrophenol (Entry 9, Table 3). Mp 32–33 C (lit. mp 31 C);
ꢁ
[37]
ꢁ
4
ꢂ1
1
IR (KBr) tmax (cm ): 3254, 1634, 1539, 1323; H NMR (300 MHz; DMSO; Me Si):
4
d 10.63 (s, 1H), 7.67 (s, 1H), 7.35–7.32 (m, 1H), 7.01 (d, J ¼ 8.46Hz, 1H), 2.24 (s, 3H).
ꢁ
[38]
2
-Hydroxy-3-nitrobenzaldehyde (Entry 6, Table 3). Mp 107–108 C (lit.
1
ꢁ
mp 105–109 C); H NMR (300 MHz; CDCl ; Me Si): d 11.84 (s, br, 1H), 10.27 (s,
3
4
1
H), 8.34 (d, d, J ¼ 9.1, J ¼ 2.9 Hz, 1H), 8.25 (d, d, J ¼ 8.1, J ¼ 1.7 Hz, 1H), 8.04
(d,d, J ¼ 7.6, J ¼ 1.7 Hz, 1H).
ꢁ
[39]
1
-Nitronaphthalen-2-ol (Entry 3, Table 3). Mp: 100–102 C (lit.
1
mp
ꢁ
1
1
04 C); H NMR (300 MHz; CDCl ; Me Si): d 11.39 (s, 1H), 8.02 (d, J ¼ 9 Hz,
3
4
H), 7.94 (d, J ¼ 8.1 Hz, 1H), 7.64–7.54 (m, 3H), 7.32 (d, J ¼ 9 Hz, 1H).
CONCLUSION
In summary, the ortho nitration of phenols in the presence of
cellulose-supported Ni(NO ) ꢀ 6H O and a catalytic amount of TCT has been
3
2
2
achieved with high regioselectivity and excellent yields. This procedure has several
advantages in comparison to the other reported methods including use of inexpen-
sive acid catalyst and biodegradable and reusable reagents along with easily access-
ible nitration agent. The temperature-control-free nature of this process made it a
green methodology with wide synthetic and commercial utility. It is also worth men-
tioning that the by-product of the preparation of TCT is cyanuric acid, which can be
easily removed by washing.
ACKNOWLEDGMENT
We thank the Department of Chemistry and Office of Gifted Students at
Semnan University for financial support.
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