Nitration of aromatic compounds catalyzed by divanadium-substituted molybdophosphoric acid, H5[PMo10V2O 40]

Article abstract of DOI:10.1007/s00706-007-0593-6

The nitration of aromatic compounds was carried out in the presence of divanadium-substituted molybdophosphoric acid, H₅PMo ₁₀V₂O₄₀, as catalyst and a mixture of nitric acid and acetic anhydride as nitrating agent. In the presence of this heteropolyacid the ortho- and para-nitro compounds were obtained in good to excellent yields under mild reaction conditions. Springer-Verlag 2007.

Full text of DOI:10.1007/s00706-007-0593-6

Monatshefte fu¨r Chemie 138, 449–452 (2007)
DOI 10.1007/s00706-007-0593-6
Printed in The Netherlands
Nitration of Aromatic Compounds Catalyzed by Divanadium-Substituted
Molybdophosphoric Acid, H5[PMo10V2O40]
Majid M. Heravi1;ꢀ, Khadijeh Bakhtiari1, Tina Benmorad1, Fatemeh F. Bamoharram2,
Hossein A. Oskooie1, and Maryam H. Tehrani1
1
Department of Chemistry, School of Sciences, Azzahra University, Vanak, Tehran, Iran
2
Department of Chemistry, School of Sciences, Islamic Azad University Mashhad-Branch, Mashhad, Iran
Received November 14, 2006; accepted (revised) November 23, 2006; published online March 16, 2007
# Springer-Verlag 2007
Summary. The nitration of aromatic compounds was
carried out in the presence of divanadium-substituted molyb-
dophosphoric acid, H5PMo10V2O40, as catalyst and a mixture
of nitric acid and acetic anhydride as nitrating agent. In the
dation of by-products are the disadvantages of this
reaction [2].
Zeolite-based solid acid catalysts such as ZSM-5
[3], X [4], Y [3–5], and ꢀ [3, 5, 6] have been used for
presence of this heteropolyacid the ortho- and para-nitro com-
nitration of various activated as well as deactivated
substrates [3, 4, 6–8].
pounds were obtained in good to excellent yields under mild
reaction conditions.
A variety of other solid acids such as silica gel [9],
clay supported metal nitrates [10–12], modified and
sulfated zirconia [13], and vapor phase nitration of
benzene by dilute nitric acid in the presence of het-
eropolyacid partially neutralized by Cs or Tl ions
[14] have also been applied for nitration of aromatic
compounds.
Heteropoly acids, HPAs, catalyze a wide variety of
reactions in homogeneous or heterogeneous (liquid–
solid, gas–solid, or liquid–liquid biphasic) systems,
offering strong options for more efficient and clean-
er processing compared to conventional mineral
acids [15–18]. Catalysts based on heteropolyacids
as Brønsted acids have many advantages over liquid
acid catalysts. They are non-corrosive and environ-
mentally benign, presenting fewer disposal problems.
Solid heteropolyacids have attracted much attention
in organic synthesis owing to easy work-up proce-
dures, easy filtration, and minimization of cost and
waste generation due to reuse and recycling of the
catalysts [19]. Being stronger acids, heteropolyacids
will have significantly higher catalytic activity than
conventional catalysts such as mineral acids, mixed-
Keywords. Catalyst; Heteropolyacid; Aromatic substitution;
Nitration; H5PMo10V2O40.
Introduction
The nitronium ion is usually the nitrating agent in
electrophilic aromatic nitration. The nitronium ion
is formed in situ from nitric acid, alkyl nitrate, acyl
nitrates (XONO2, X ¼ H, RC(O)), in which it is bound
to an oxygen atom [1].
On the other hand, nitration of aromatic substrates
is a widely studied reaction of great industrial sig-
nificance as many nitro-aromatics are extensively uti-
lized and act as chemical feedstock for a wide range
of useful material such as dyes, pharmaceuticals,
perfumes, and plastics. Aromatic nitration is quite
notorious for its unfriendly nature towards the en-
vironment. The use of large quantities of nitric and
sulfuric acids, corrosiveness, and potential danger of
explosion, low regioselectivity, and oxidative degra-
ꢀ
Corresponding author. E-mail: mmh1331@yahoo.com

450
M. M. Heravi et al.
occupy both anionic and cationic positions, is more
complex. In fact, under catalytic conditions a re-
building of the heteropolyanion generally occurs and
vanadyl salts are formed.
Scheme 1
However, initial attempts to carry out the reaction
in a solvent-free system failed. Thus, among the
tested solvents, acetic anhydride, Ac2O, was applied
as solvent of choice. Higher conversion with acetic
acid is attributed to the in situ formation of acetyl
nitrate as active nitrating agent in the presence of
nitric acid [5, 6]. Acetic anhydride reacts with nitric
acid to form acetyl nitrate intermediate species as
follows:
oxides, zeolites, etc. In particular, in organic media
the molar catalytic activity of heteropolyacid is often
100–1000 times higher than that of H2SO4 [17, 18].
This makes it possible to carry out the catalytic
process at a lower catalyst concentration and=or at
a lower temperature. As stable, relatively nontoxic
crystalline substances, heteropolyacids are also pref-
erable regarding safety and ease of handling.
The Keggin-type HPAs typically represented by
the formula of [XM12O40]nꢁ, when X is the heteroat-
om (most frequently Pþ5 or Siþ4), and M is the
addenda atom (usually Wþ6 or Moþ6), are the most
important for catalysis [15–18]. They have been wide-
ly used as acid and oxidation catalysts for organic
synthesis and found several industrial applications.
Among the Keggin HPAs, transition metal-substi-
tuted H3[PMo12O40] compounds have been reported
as effective catalysts in organic reactions [20–27].
Vanadium is the preferred element in heterogeneous
and homogeneous catalysts for various reactions. The
redox process of vanadium-substituted molybdophos-
phoric acid with Keggin structure is quite fast and
facile.
ðCH3COÞ2OþHNO3 !CH3COONO2 þCH3COOH
Ac2O as solvent has been claimed to efficiently
trap the water formed during the reaction. It acts
as a dehydrating agent and consumes the water pres-
ent in 65% HNO3 to form acetic acid thus increasing
the concentration of nitric acid and thereby enhanc-
ing the conversion of the substrate. AcONO2 is only
weakly dissociated in organic solvents and requires
the presence of acids to exhibit sufficient reactivity in
nitration [31]. Apparently, H5PMo10V2O40 can pro-
vide the required acidity for a facile dissociation of
AcONO2 to produce the nitronium ion for nitration.
Without catalyst, in the blank experiments, the re-
actions are sluggish and considerable amounts of
starting materials are recovered. The exact role of
the divanadium-substituted molybdophosphoric acid,
H5PMo10V2O40, in the nitration of phenol and its
mechanism is not yet very clear and more study is
needed to clarify this important point. The attempts
to isolate intermediates or to analyze them failed so
far in providing clear information. The catalytic per-
formances of vanadium(V)-substituted heteropoly-
molybdates are the overall effects of all isomers.
Positional isomers are always possible, and usually
coexist, when two or more vanadium atoms are incor-
porated into the Keggin structure. For example, there
are five positional isomers for the H5PMo10V2O40
[32] and the contribution of each isomer cannot be
obtained separately. However, a literature survey has
In continuation of our work on the catalytic prop-
erties of heteropolyacids [28] we developed a con-
venient, efficient, and eco-friendly procedure for the
nitration of aromatic compounds using a catalytic
amount of H5PMo10V2O40 (Scheme 1).
Results and Discussion
A variety of different aromatic compounds, contain-
ing activating and deactivating groups were subject-
ed to this reaction to investigate the generality of the
methodology.
The catalyst was synthesized according to Ref.
[29] and displays a Keggin structure [30]. At the first
stage, because of complexity of behavior for this cat-
alyst in a solvent, we studied nitration reactions in a
solvent-free system. Transition metal cations have an
important effect on the catalytic properties of these
compounds when they substitute molybdenum cat-
ions in the Keggin units or when they are present as
counter cations. The case of vanadium, which can
þ
shown that VO2 is formed in an isolated form or
within heteropolyacids, Eq. (1) [33–38].
HPA ꢁ n s VO2þ þ HPA ꢁ ðn ꢁ 1Þ
ð1Þ
We believe that in addition of Brønsted acidity
of H5PMo10V2O40 and an energy gap between the
highest occupied molecular orbital and the lowest

Nitration of Aromatic Compounds
451
Table 1. Heteropolyacid-catalyzed nitration of aromatic compounds
Entry
1
Substrate
Product
Time=h
Yield=%a
PhOMe
4-NO2PhOMe
2-NO2PhOMe
2-NO2PhOH
3
30
70
22
44
2
PhOH
3
4-NO2PhOH
3
4
4-BrPhOH
PhNHAc
4-Br-2,6-NO2-PhOH
2-NO2PhNHAc
4-NO2PhNHAc
2-NO2PhNMe2
2-NO2-Naphth
1,4-NO2-2-OH-Naphth
2-NO2PhBr
5
9
100
60.3
1.3
17
84
63
62
22
79
41
5
6
7
8
9
PhNMe2
Naphth
2-OH-Naphth
PhBr
PhI
0.7
3
1.5
1
7
0.25
9
2-NO2PhI
2,6-MePhNO2
3-NO2PhCOMe
10
11
3,5-MePh
PhCOMe
a
Yields analyzed by GC=MS
þ
unoccupied orbital, VO2 presents the key hetero-
polyacid structure responsible for our reaction.
Nitration of anisole in heterogeneous media was
carried out affording 70% o-nitroanisole and 30%
p-nitroanisole giving an o=p ratio of 2.3. A complete
conversion of anisole to the corresponding nitro
compounds is achieved under reflux condition. Upon
increasing the temperature from room temperature to
reflux o-nitroanisole was obtained with 70% selec-
tivity. The nitration of phenol occurred similarly to
that of anisole, yielding 2-nitro and 4-nitrophenol
with 44% selectivity of the p-isomer. Table 1 shows
examples of heterogeneous nitration of a variety of
aromatic compounds.
is a function of temperature, thus the yield increased
as the reaction temperature was raised. The results
are summarized in Table 1.
In conclusion, this study demonstrates that
H5PMo10V2O40 is an active and environmentally
friendly catalyst for the nitration of aromatic com-
pounds. This solid acid is superior in activity to the
conventional acid catalysts such as H2SO4 or zeo-
lites, which is in line with the stronger acidity of
HPA. The catalyst can be reused after a simple
work-up without any loss of catalytic activity.
Experimental
For the nitration of m-xylene, 1,3-dimethyl-2-nitro-
benzene was obtained in 79%. In this reaction no
nitration of the side-chain was observed (entry 10).
The nitration of alkanes with nitric acid by vanadium-
substituted polyoxometalates has been reported by
Schinachi et al. [39]. 2-Naphtol was nitrated under
the same condition to give only 1,4-dinitro-2-naphtol
in 63% yield. Interestingly, the nitration of acetamide
under the same reaction condition gave 2-nitroacetani-
lide and 4-nitroacetanilide in 60.3 and 1.3% yields,
respectively. It is noteworthy to mention that incom-
plete nitration of deactivated aromatic compounds
such as naphthalene, iodobenzene, and bromoben-
zene was observed under these reaction conditions
(Table 1).
Melting points were measured using the capillary tube method
with an electrothermal 9100 apparatus. IR spectra were re-
corded from KBr disks on the FT-IR Bruker Tensor 27. Yields
are based on GC=mass analysis using Agilent 6890 GC sys-
tem Hp-5 capillary 30mꢂ530 ꢁmꢂ1.5 ꢁm nominal. All prod-
ucts are known and their physical and spectral data were
compared with those of authentic samples. The heteropolyacid
was synthesized according to Ref. [29].
Nitration of Aromatic Compounds: Typical Procedure
To a magnetically stirring mixture of 1 cm3 acetic anhydride
and nitric acid (65%, 1 mmol) 108.7 mg anisole (1mmol) and
H5PMo10V2O40 (0.02 g, 0.01mmol) at room temperature, were
added. The mixture was then refluxed for appropriate time.
The progress of the reaction was monitored by TLC using
petroleum ether: ethyl acetate as eluent. After completion of
the reaction, the catalyst was filtered off. The mixture was then
washed with 10 cm3 satd. sodium hydrogen carbonate and
the product extracted with 2ꢂ5 cm3 dichloromethane. The
combined organic extracts were washed with 10 cm3 distilled
The effect of temperature was studied by carrying
out the reactions at different temperatures in the pres-
ence of this catalyst. It was observed that the yield

452
M. M. Heravi et al.: Nitration of Aromatic Compounds
water, dried (MgSO4), and the solvent was removed by evap-
oration to afford the nitrated product (Table 1).
[19] Schwegler MA, Vanbekkum H, Munck N (1991) Appl
Catal A 74: 191
[20] Mizuno N, Misono M (1997) Current Opinion in Solid
State & Materials Science 2: 84
[21] Moffat JB (1991) Appl Catal A 146: 65
Acknowledgements
`
[22] Albonetti S, Cavani F, Trifiro F, Koutyrev M (1995)
Catal Lett 30: 253
[23] Cavani F, Koutyrev M, Trifiro F (1996) Catal Today 28:
The authors are thankful to Azzahra University Council for the
partial financial support.
`
319
[24] Mizuno N, Tateishi M, Iwantoto M (1995) Appl Catal A
128: L165
[25] Mizuno N, Tateishi M, Iwamoto M (1994) J Chem Soc
Chem Commun 1411
References
[1] For a comprehensive listing of nitrating agents see: Olah
JA, Lin HC, Olah GA, Narang SC (1978) Proc Natl Acad
Sci USA 75: 1045
[2] Vione D, Maurino V, Minero C, Pelizzetti E (2004)
Chemospher 55: 941
[26] Mizuno N, Tateishi M, Iwamoto M (1996) J Catal
163: 87
´
`
[3] Choudary BM, Sateesh M, Kantam ML, Rao KK,
Ramprasad KV, Raghavan KV, Sarma JARP (2000)
Chem Commun 25
[4] Esakkidurai T, Pitchumani K (2000) J Mol Catal Chem
A 185: 305
[5] Smith K, Musson A, DeBoos GA (1998) J Org Chem
63: 8448
[6] Bernasconi S, Pringruber G, Kogelbauer A, Prins R
(2003) J Catal 219: 231
[7] Smith JM, Liu H, Resasco DE (1997) Stud Surf Sci Catal
111: 199
[8] Akolekar DB, Lemay G, Sayari A, Kaliaguine S (1995)
Res Chem Intermed 21: 7
[9] Riego JM, Sedin Z, Zaldivar JM, Marziano NC, Tortato C
(1996) Tetrahedron Lett 37: 513
[10] Laszlo P, Pennetreau P (1987) J Org Chem 52: 2407
[11] Cornelis A, Laszlo P, Pennetreau P (1983) J Org Chem
48: 4771
[27] Cavani F, Etienne E, Favaro M, Galli A, Trifiro F (1995)
Catal Lett 32: 215
[28] a) Heravi MM, Bakhtiari Kh, Bamoharram FF (2006)
Catal Commun 7: 373; b) Heravi MM, Bakhtiari Kh,
Bamoharram FF (2006) Catal Commun 7: 499; c) Heravi
MM, Behbahani FK, Bamoharram FF (2006) J Mol
Catal A 253: 16; d) Heravi MM, Derikvand F,
Bamoharram FF (2005) J Mol Catal A 242: 173; e)
Bamoharram FF, Heravi MM, Roshani M, Jahangir M
Gharib A (2006) Appl Catal A Chem 302: 42; f)
Bamoharram FF, Heravi MM, Roshani M, Jahangir
M, Gharib A (2006) J Mol Catal A Chem 252: 90; g)
Heravi MM, Motamedi R, Seifi N, Bamoharram FF
(2006) J Mol Catal A 249: 1
[29] Tsigdinos GA, Hallada CJ (1968) Inorg Chem 7: 437
[30] Bielanski A, Datka J, Gil B, Malecka-Lubanska A,
Micek-Ilnicka A (1999) Catal Lett 57: 61
[31] Olah GA, Malhotra R, Narang SC (1974) Nitration,
Methods and Mechanism, VCH, New York
[12] Gigantee B, Prazeres AO, Marcelo-Curto MJ, Cornelis
A, Laszlo P (1995) J Org Chem 60: 3445
[13] Kogelbauer A, Vassena D, Prins R, Armor JN (2000)
Catal Today 55: 151
[32] Pope MT, Scully TF (1975) Inorg Chem 14: 953
[33] Kozhevnikov IV, Matveev KI (1983) Appl Catal 5:
135
[14] Sato H, Nagai K, Yoshioka H, Nagaoka Y (1998) Appl
Catal A General 175: 209
[15] Izumi Y, Urabe K, Onaka M (1992) Zeolite, Clay and
heteropoly acid in organic Reactions, kodansha=VCH,
Tokyo
[16] Misono M (2001) Chem Commun 1141
[17] Kozhevnikov IV (1998) Chem Rev 98: 171
[18] Kozhevnikov IV (2002) Catalysts for fine chemicals. In:
Catalysis by Polyoxometalates, Wiely, Chichester, vol 2
[34] Kholdeeva OA, Golovin AV, Maksimovskaya RI,
Kozhevnikov IV (1992) J Mol Catal 75: 235
[35] Kozhevnikov IV (1995) Catal Rev-Sci Eng 37: 311
[36] Kozhevnikov IV (1997) J Mol Catal A 117: 151
[37] Mizuno N, Misono M (1994) J Mol Catal 86: 319
[38] Neumann R, de la Vega M (1993) J Mol Catal A 84:
93
[39] Schinachi S, Yahiro H, Yamaguchi K, Mizuno N (2004)
Chem-Eur J 241: 6489