para-Selective nitration of halogenobenzenes using a nitrogen dioxide-oxygen-zeolite system

Article abstract of DOI:10.1039/b003731l

The nitration of halogenobenzenes using zeolite Hβ or zeolite HY as a solid inorganic catalyst and a combination of liquid nitrogen dioxide and gaseous oxygen as the nitrating reagent leads to high yields and significant para-selectivities in a relatively clean process for aromatic nitration.

Full text of DOI:10.1039/b003731l

para-Selective nitration of halogenobenzenes using a nitrogen
dioxide–oxygen–zeolite system
Keith Smith,* Saeed Almeer and Steven J. Black
Centre for Clean Chemistry, Department of Chemistry, University of Wales Swansea, Swansea, UK SA2 8PP.
E-mail: K.Smith@swansea.ac.uk
Received (in Cambridge, UK) 10th May 2000, Accepted 5th July 2000
Published on the Web 2nd August 2000
The nitration of halogenobenzenes using zeolite Hb or zeolite
HY as a solid inorganic catalyst and a combination of liquid
nitrogen dioxide and gaseous oxygen as the nitrating reagent
leads to high yields and significant para-selectivities in a
relatively clean process for aromatic nitration.
zeolites, in order to determine if they were able to catalyse the
process and impart para-selectivity.
(1)
Zeolites have been used before in the vapour phase nitration
of aromatic compounds using nitrogen dioxide. However, this
process did not involve oxygen, was complicated, required a
high flow rate for the carrier gas (N2, 880 ml min21) and
showed poor para-selectivity.14 We now report that certain
zeolites can indeed catalyse the process of nitration, as shown in
eqn. (1), whilst simultaneously providing enhanced para-
selectivity.
Initially, an attempt was made to reproduce approximately the
conditions of Suzuki for nitration of chlorobenzene. Liquid
N2O4 (approx. 10 ml) was condensed into a trap at 278 °C and
was then warmed to 0 °C. Fe(acac)3 (0.355 g) and chloro-
benzene (10 mmol) were then added, the system was flushed
with oxygen and the mixture was stirred at 0 °C for 48 h. The
product thus obtained contained nitrochlorobenzenes in propor-
tions (2-+3-+4-nitrochlorobenzene proportions of 32+ < 1+67)
that approximated to those reported by Suzuki, but also showed
significant quantities of a product based upon nitration of
acetylacetone.
We then carried out similar reactions in which various
zeolites were used as catalysts instead of Fe(acac)3 in an attempt
to determine which zeolite, if any, would be the most applicable
to para-selective aromatic nitration. Zeolite b and zeolite Y
have three dimensional channels and large pore sizes and were
selected on this basis. Mordenite, which has linear large pores,
and ZSM-5, which has a medium pore size, were chosen for
comparison. Additionally, variation of the cation type was
undertaken, with H+, Na+, K+ and NH4+ being used in the case
of zeolite b, and H+ and Na+ in the case of zeolite Y. Finally,
zeolite ZSM-5 was tested with two specific Si/Al ratios. Thus,
the effects of pore size, channel structure, acidity, cation size
and Si/Al ratio could all be assessed. A reaction in the presence
of chromatographic silica was also included for comparison.
The results are shown in Table 1.
As shown in Table 1, reaction occurred in the presence of all
of the zeolites, and all of the reactions gave higher yields than
in the absence of any catalyst. The large, three-dimensional-
pore zeolites gave higher yields, comparable with those
achieved with Fe(acac)3 as catalyst, but the medium pore
zeolites and the linear large pore zeolite gave lower yields, as
did the silica. All of the zeolites demonstrated higher para-
selectivity than that obtained with Fe(acac)3, except for NH4b.
This last result may reflect the fact that this was the only zeolite
not calcined (heated in air to a high temperature), since this
would have caused loss of ammonia and formation of Hb.
Mordenite and ZSM-5 gave lower para-selectivities as well
as lower yields, which probably reflects more restricted
diffusion through the pores and competition from reaction at the
external surface of the solid. The selectivity was also low for the
reaction in the presence of silica. The ZSM-5 sample with the
higher Si/Al ratio gave a higher para-selectivity than that with
the lower ratio, possibly because of the process of deal-
umination, which would have opened up the pore structure of
Electrophilic aromatic substitution reactions are of considerable
importance in the production of fine chemicals. However, the
traditional processes suffer a number of disadvantages, such as
low selectivity towards the desired product and the requirement
for large quantities of mineral or Lewis acids as activators. In
turn these acids are responsible for corrosion problems within
the plant and the generation of large volumes of spent reagents,
which, given the current environmentally conscious climate, are
increasingly unacceptable. Major efforts are therefore being
made towards developing processes that can reduce the volumes
of spent liquors produced. Inorganic solids can offer significant
benefits for these processes by providing both effective
catalysis and, in some cases, enhanced selectivity. Additionally
they are easily removed from reaction mixtures and in some
cases recycling is possible. For example, we have utilised
zeolites to enhance the para-selectivity in chlorination,1
bromination,2 acylation3 and methanesulfonylation4 reactions
of simple aromatic substrates.
Aromatic nitro compounds represent particularly versatile
chemical feedstocks for a wide range of industrial products,
such as pharmaceuticals, agrochemicals, dyestuffs and ex-
plosives. Traditionally, nitration has been performed by a
mixture of nitric and sulfuric acids (mixed acid method).5
However, the method is notoriously unselective for nitration of
substituted aromatic compounds and the disposal of the spent
acid reagents presents a serious environmental issue. In order to
address these problems several alternative methods for aromatic
nitration have been developed recently. For example, lanthanide
triflates have been used to catalyse nitration with nitric acid,
which avoids the use of large volumes of sulfuric acid in the
process.6 However, this provides no enhancement of selectivity.
Selectivity of the nitration process can be enhanced by solid
catalysts such as clays, but primarily zeolites, which can
improve selectivity using alkyl nitrates,7 acyl nitrates,8 or even
nitric acid itself.9,10 We have reported the use of zeolite Hb in
conjunction with a mixture of acetic anhydride and nitric acid,
which currently offers the best combination of yield and para-
selectivity for nitration of simple aromatic compounds.11 None
of these methods, however, are totally devoid of disadvan-
tages.
Another approach towards clean nitration involves the use of
dinitrogen tetroxide in combination with oxygen or ozone as an
oxidant.12 The method where ozone is employed most likely
involves dinitrogen pentoxide, as this is known to be a highly
active nitrating agent. The method utilising oxygen is less clear
cut and requires the use of tris(pentane-2,4-dionato)iron(III
)
(Fe(acac)3) as a catalyst in an organic solvent.13 In principle,
this could lead to a highly atom-efficient process [eqn. (1)], but
it is not regioselective. Therefore, we decided to study the use of
dinitrogen tetroxide as a nitrating agent in the presence of
DOI: 10.1039/b003731l
Chem. Commun., 2000, 1571–1572
This journal is © The Royal Society of Chemistry 2000
1571

Table 1 The effect of zeolite type on the nitration of chlorobenzenea
After 24 h toluene had been completely consumed and
produced a reasonable yield of mononitrotoluenes (85%). The
para-selectivity was fairly low, though greater than for mixed
acid nitrations. The reaction with benzene was slow, being only
ca. 50% complete after 48 h. However, all the halogeno-
benzenes gave good yields and reasonable para-selectivities.
This work therefore demonstrates that zeolites b and Y, with
H+, Na+ or K+ cations, can be efficient inorganic catalysts for
the nitration of halogenobenzenes with dinitrogen tetroxide and
oxygen and produce high para-selectivities and yields com-
pared to classical nitration methods.
Furthermore, this method represents a low energy and
potentially clean synthesis of halonitrobenzenes using an easily
recycled solvent and catalyst system. However, at this prelimi-
nary point the reactions involve a large excess of dinitrogen
tetroxide, long reaction times and the use of an undesirable
chlorinated solvent. Therefore, our future efforts in this area
will be concentrated on minimising these factors.
Proportionsb
Conversion Yield
Zeolite
Nonec
Si/Al
t/h
(%)b
(%)b
ortho meta para
—
—
25
24
24
25
30
28
50
50
50
50
50
50
50
50
50
72
72
6
40
100
100
97
2
28
90
96
92
70
91
91
28
42
32
39
29
14
15
21
30
16
16
27
28
20
0
< 1
< 1
0
0
1
2
1
0
2
61
70
85
85
79
69
82
83
73
70
79
c
SiO2
Hb
Nab
Kb
NH4b
HY
76
100
100
36
44
48
NaY
HMord.
HZSM-5
HZSM-5
10.5
50
150
< 1
a All reactions were carried out with zeolite (1.0 g), chlorobenzene (10.0
mmol), 1,2-dichloroethane (30 ml) and nitrogen dioxide (ca. 10 ml) at 0 °C.
b Calculated by quantitative GC. c For comparison.
The reaction of chlorobenzene illustrates the general proce-
dure for the nitration process. In an ice-water cooling bath was
placed a 100 ml round-bottom flask containing a mixture of
chlorobenzene (10 mmol), zeolite (1.0 g), and 1,2-dichloro-
ethane (30 ml). The flask was flushed with oxygen gas for 20
min at 0 °C. Liquid nitrogen dioxide (ca. 10 ml, ca. 280 mmol)
was added quickly all at once to the stirred mixture, and the
flask was connected to an oxygen gas balloon. After 50 h at
0 °C, the mixture was filtered through a medium porosity
sintered glass funnel, and the filtrate was diluted with water.
1,2-Dichloroethane was added and the organic phase was
separated and dried over magnesium sulfate. The isomer
distribution was determined by gas chromatography (PU 4400)
(octadecane was added as an internal standard).
the zeolite, causing it somewhat to resemble the larger pore
systems. However, the yield with the higher Si/Al ratio sample
was less, possibly because of the lower density of effective
catalytic sites. Interestingly, the nature of the cation present
appeared to have a negligible effect on the reactions, the H+,
Na+ and K+ forms of the zeolites giving very similar results for
each reaction where comparison was possible. Evidently, the
process does not rely upon strong acid catalysis and does not
depend significantly on cation size. Perhaps the role of the
active site is merely to bring together the reagents and substrates
within the confines of the pores by simple co-adsorption.
Alternatively, perhaps the active site facilitates cleavage of
dinitrogen tetroxide to give monomeric nitrogen dioxide, which
has been suggested as the active reagent in vapour phase
reactions.15
Notes and references
1 K. Smith, M. Butters, W. E. Paget, D. Goubet, E. Fromentin and B. Nay,
Green Chem., 1999, 2, 83.
2 K. Smith, P. He and A. Taylor, Green Chem., 1999, 1, 35.
3 K. Smith, Z. Zhenhua and P. K. G. Hodgson, J. Mol. Catal. A, 1998,
134, 121.
Zeolites Hb and Nab produced the greatest selectivity for
para-chloronitrobenzene (85%) and the highest yields (90 and
96%). Therefore, zeolite Hb was tested with a range of other
substrates. The results are shown in Table 2.
4 K. Smith, G. M. Ewart and K. R. Randles, J. Chem. Soc., Perkin Trans.
1, 1997, 1085.
Table 2 The nitration of toluene, benzene and halogenobenzenes with
nitrogen dioxide and zeolite Hb in 1,2-dichloroethanea
5 E. R. Ward, Chem. Br., 1979, 15, 297.
6 F. J. Waller, A. G. M. Barrett, D. C. Braddock and D. Ramprasad, Chem.
Commun., 1997, 613.
Proportionsb
7 T. J. Kwok and K. Jayasuriya, J. Org. Chem., 1994, 59, 4939.
8 A. Cornelis, A. Gerstmans and P. Laszlo, Chem. Lett., 1988, 1839.
9 K. Jayasuriya and R. Damavarapu, US Pat. Appl., 5946638, 1999.
10 B. M. Choudary, M. Sateesh, M. L. Kantam, K. K. Rao, K. V. R. Prasad,
K. V. Raghavan and J. A. R. P. Sarma, Chem. Commun., 2000, 25.
11 K. Smith, A. Musson and G. A. DeBoos, J. Org. Chem., 1998, 63,
8448.
12 H. Suzuki and T. Mori, J. Chem. Soc., Perkin Trans. 2, 1994, 479.
13 H. Suzuki, S. Yonezawa, N. Nonoyama and T. Mori, J. Chem.Soc.,
Perkin Trans. 1, 1996, 2385.
Conversion Yield
Substrate
t/h
(%)b
(%)b
ortho meta para
Toluene
Benzene
Fluorobenzene
Chlorobenzene
Bromobenzene
Iodobenzene
24
45
48
48
48
48
100
85
50
95
95
94
95
53
—
7
14
22
37
2
—
0
< 1
< 1
1
45
—
93
85
77
62
55
100
98
> 99
99
14 I. Schumacher, Eur. Pat. Appl., 0053031, 1981.
15 A. Germain, T. Akouz and F. Figueras, J. Catal., 1994, 147, 163; A.
Germain, T. Akouz and F. Figueras, Appl. Catal. A: Gen., 1996, 136,
37.
a All reactions were carried out with zeolite (1.0 g), substrate (10.0 mmol),
1,2-dichloroethane (30 ml) and nitrogen dioxide (ca. 10 ml) at 0 °C.
b Calculated by quantitative GC.
1572
Chem. Commun., 2000, 1571–1572