Silica-acetate complex of N2O4: A heterogeneous reagent for the selective nitration of phenols and nitrosation of thiols

Article abstract of DOI:10.1081/SCC-120016310

Complexation of gaseous N₂O₄ with acylated silica gel affords an addition compound, which is an efficient heterogeneous reagent for the selective mono- and dinitration of phenol, substituted phenols and nitrosation of thiols.

Full text of DOI:10.1081/SCC-120016310

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Silica-Acetate Complex of N2O4: A Heterogeneous
Reagent for the Selective Nitration of Phenols and
Nitrosation of Thiols
N. Iranpoor a , H. Firouzabadi a & R. Heydari a
a Chemistry Department , College of Sciences , Shiraz University , Shiraz, Iran
Published online: 17 Aug 2006.
To cite this article: N. Iranpoor , H. Firouzabadi & R. Heydari (2003) Silica-Acetate Complex of N2O4: A Heterogeneous
Reagent for the Selective Nitration of Phenols and Nitrosation of Thiols, Synthetic Communications: An International Journal
for Rapid Communication of Synthetic Organic Chemistry, 33:5, 703-710, DOI: 10.1081/SCC-120016310
To link to this article: http://dx.doi.org/10.1081/SCC-120016310
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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 5, pp. 703–710, 2003
Silica-Acetate Complex of N2O4:
A Heterogeneous Reagent for the Selective
Nitration of Phenols and Nitrosation of Thiols
*
N. Iranpoor, H. Firouzabadi, and R. Heydari
*
Chemistry Department, College of Sciences,
Shiraz University, Shiraz, Iran
ABSTRACT
Complexation of gaseous N2O4 with acylated silica gel affords an
addition compound, which is an efficient heterogeneous reagent for
the selective mono- and dinitration of phenol, substituted phenols
and nitrosation of thiols.
*Correspondence: N. Iranpoor and H. Firouzabadi, Chemistry Department,
College of Sciences, Shiraz University, Shiraz 71454, Iran; E-mail: iranpoor@
chem.susc.ac.ir or firouzabadi@chem.susc.ac.ir.
703
DOI: 10.1081/SCC-120016310
Copyright & 2003 by Marcel Dekker, Inc.
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704
Iranpoor, Firouzabadi, and Heydari
There are many important synthetic transformation such as
nitration, nitrosation, oxidation, and oxidative cleavage reactions
which are performed with gaseous dinitrogen tetroxide.[1–13] The reac-
tions with this reagent usually suffer from high reactivity of the reagent
and needs to be carefully controlled by lowering the reaction tempera-
ture[14–16] to avoid side reactions. Molecular addition compounds of
N2O4 gas with some oxygen containing organic compounds such as
1,4-dioxane or 18-crown-6 have been also prepared and their structures
have been elucidated.[17,18] Recently, we reported on the application of
18-crown-6 complex of N2O4 for nitration of phenols and also nitrosa-
tion of thiols.[19,20] In comparison with the gaseous N2O4, the use of
18-crown-6/N2O4 complex has some reported advantages over N2O4,
but the remained problems with this complex is that 18-crown-6 is
relatively an expensive precursor and its N2O4 complex is very soluble in
organic solvents. Due to the solubility of this complex in organic solvents,
in the work-up procedure, chromatography is required. Especially, in the
case of in situ synthesis of unstable thionitrites from thiols, the presence
of soluble 18-crown-6/N2O4 in the reaction mixture does not let to have a
pure solution of thionitrites for further synthetic applications.
Recently we introduced silica-acetate/N2O4 complex and used itfor
selective oxidation of sulfides.[21] Now, we report on the application of
this cheap and easily prepared solid complex as a heterogeneous reagent
for selective mono- and dinitration of phenol, substituted phenols and
nitrosation of thiols.
We first optimized the reaction conditions for the nitration of phenol.
We observed that in the presence of this reagent in CH2Cl2, the reaction
goes to completion immediately with the formation of ortho- and para-
nitrophenol in 33% and 53% respectively. When this reaction was
refluxedinethylacetateinthepresenceof2molarequivalentsofthereagent,
the reaction furnished 2,4-dinitrophenol in 78% together with the forma-
tion of 2,4,6-triphenol in 8% yields. The formation of some quinone in
the nitration reaction of phenol with N2O4 or its organic and inorganic
complexes is inevitable and here is also some of it formed[19,23] (Sch. 1).
We then used this reagent for the nitration of different substituted
phenols. The mono- and dinitration reaction of phenols having different
halogens, methyl and acetyl as substitutes were performed selectively
under different reaction conditions. The mono-nitration reactions per-
formed in CH2Cl2 at room temperature, while; dinitration reactions pro-
ceeded in refluxing ethyl acetate. The results are shown in Tables 1 and 2.
Although the use of heterogeneous reagents such as ‘claycop’ and
‘clayfen’ (clay impregnated with copper nitrate and ferric nitrate, respec-
tively) have been used for nitrosation of thiols,[22] but, the produced

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Silica-Acetate Complex of N2O4
705
(33 %)
(53 %)
(7 %)
2-Nitrophenol
4-Nitrophenol
Benzoquinone
Silica acetate/N O
2 4
CH Cl , r.t., immed.
2
2
Phenol
(74 %)
2,4-Dinitrophenol
Silica acetate/N O
2 4
EtOAc, reflux, 10 min.
(8 %)
2,4,6-Trinitrophenol
Benzoquinone
(10 %)
Scheme 1.
Table 1. Mononitration of substituted phenols with one molar equivalents of
silica-acetate/N2O4 in CH2Cl2 atr..t
Entry
Substrate
Time (min)
Product (isolated %)
1
2
3
4
5
6
7
4-Fluoro-
4-Chloro-
5
5
4-Fluoro-2-nitro- (91)
4-Chloro-2-nitro- (95)
4-Bromo-2-nitro- (90)
4-Methyl-2-nitro- (86)
4-Acetyl-2-nitro- (88)
2,6-Dichloro-4-nitro- (96)
2,6-Dimethyl-4-nitro- (83)
4-Bromo-
4-Methyl-
4-Acetyl-
10
5
10
5
2,6-Dichloro-
2,6-Dimethyl-
5
Table 2. Dinitration of substituted phenols with two molar equivalents of
silica-acetate/N2O4 in reflux conditions.
Entry
Substrate
Solvent
Time (min)
Product (isolated %)
1
2
3
4
5
4-Fluoro-
4-Chloro-
4-Bromo-
4-Methyl-
4-Acetyl-
EtOAc
EtOAc
EtOAc
EtOAc
BuOAc
30
45
45
20
30
4-Fluoro-2,6-dinitro- (94)
4-Chloro-2,6-dinitro- (96)
4-Bromo-2,6-dinitro- (83)
4-Methyl-2,6-dinitro- (95)
4-Acetyl-2,6-dinitro- (74)
thionitrite is immediately oxidized into the corresponding disulfides by
the copper and iron ions present in the reagents. Similarly, the use of
[23]
[23]
Cu(NO3)2ÁN2O4
and Fe(NO3)3Á1.5N2O4
for nitrosation of thiols
suffer from the over-oxidation of the obtained thionitrite into their
corresponding disulfides.
In order to overcome the problems encounter in the conversion
of thiols into thionitrites under homogeneous conditions and having

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706
Iranpoor, Firouzabadi, and Heydari
the possibility of performing the reaction under heterogeneous
conditions, we used successfully silica-acetate/N2O4 complex for this
purpose (Sch. 2).
This reagents converted structurally different thiols into their
corresponding thionitrites without the formation of any disulfide
or over-oxidized products in solvents such as diethyl ether, dichloro-
methane, ethyl acetate or t-butanol at room temperature. The use of
t-butanol as the solvent of the reaction has the advantageous that
after filtration of the insoluble reagent, the obtained pure solution of
thionitrite can be solidified by keeping it in a fridge and stored without
any change for days. The obtained thionitrites were characterized on the
basis of their UV spectral data and comparison with the literature[15,16]
(Table 3).
In conclusion, the use of silica-acetate/N2O4 complex provides the
possibility of performing the selective mono- and dinitration of phenols
and also nitrosation of thiols under heterogeneous conditions. The ease
of preparation, handling and cheapness of the reagent, heterogeneous
Silica-acetate/N O
2 4
RSH
RSNO
t-butanol , r.t.
Scheme 2.
Table 3. Reaction of thiols (R–SH) with silica-acetate/N2O4 in t-butanol at
room temperature.a
Entry
R
Productb
ꢀmax (nm)/absorbance
1
7
8
2
3
n-Bu
n-Pr
CH3(CH2)2CH2SNO
CH3CH2CH2SNO
PhCH2SNO
338.3/2.16, 552/0.27
341.9/1.71, 598.2/0.15
342/1.94, 551.8/0.11
368.9/0.95, 572/0.22
339/0.87, 553.4/0.19
PhCH2
Ph
Cyclohexyl
PhSNO
SNO
4
5
6
n-Octyl
Et
CH3(CH2)6CH2SNO
3CH2SNO
339.6/2.11, 551/0.16
337.5/1.76, 551.8/0.13
340/1.65, 550.2/0.18
CH
–CH2CH2CH2–
ONS
SNO
aThe reaction occurs immediately.
bThe products are identified by comparison of their UV spectral data with the
literature.[15,16]

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Silica-Acetate Complex of N2O4
707
nature of the reactions and ease of the work-up, and the possibility of
obtaining pure solution of thionitrites can be considered as advantageous
of this reagent.
EXPERIMENTAL
Thin layer chromatography on commercial plates of silica gel 60 F254
was used to monitor the progress of the reactions. Column chromato-
graphy was carried out using silica gel 60. All the products of nitration
reactions are known compounds and were characterized by comparison
of their physical and spectral data with authentic samples. Thionitrites
were identified in the solution and characterized by comparison of their
UV spectral data with literature. UV spectra were recorded on Pye
Unicam 8725 spectrometer. IR spectra were recorded on a Perkin
Elmer 781 spectrometer. NMR spectra were recorded on a Bruker
DPX 250.
Mononitration of Phenol with
Silica-Acetate/N2O4 Complex
A mixture of phenol (0.094 g, 1 mmol) and silica-acetate/N2O4 com-
plex (1.2 g) in CH2Cl2 (4 mL) was stirred vigorously at room temperature.
The reaction completed immediately. Acetone (5 mL) was added and the
mixture was filtered. The resulted mixture was presorbed on silica gel
(5 g) and was applied on a silica gel column and eluted with peroleum
ether/acetone (9:1). 4-Nitrophenol 0.069 g, 53%, m.p. 112ꢀC, [Lit.[24]
m.p. 112–114ꢀC], 2-nitrophenol 0.043 g, 33%, m.p. 45ꢀC, [Lit.[24] m.p.
45–46ꢀC] and benzoquinone 0.008 g, 7%, m.p. 113ꢀC, [Lit.[24] m.p.
112.5–113.5ꢀC] were obtained respectively.
Dinitration of Phenol with
Silica-Acetate/N2O4 Complex
A mixture of phenol (0.094 g, 1 mmol) and silica acetate/N2O4
complex (2.5 g) in EtOAc (5 mL) was stirred for 10 min. under reflux
conditions. Acetone (5 mL) was added and the mixture was filtered. The
resulted mixture was presorbed on silica gel (5 g) and was applied on silica
gel column and eluted with chloroform as an eluent. 2,4-Dinitrophenol
0.136 g, 74%, m.p. 111ꢀC, [Lit.[24] m.p. 111–113ꢀC, 2,4,6-trinitrophenol

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708
Iranpoor, Firouzabadi, and Heydari
0.018 g, 8%, m.p. 120–122ꢀC, [Lit.[24] m.p. 121–122ꢀC] and benzoquinone
0.01 g (10%) were obtained respectively.
Mononitration of 4-Chlorophenol with
Silica-Acetate/N2O4 Complex as a Typical Procedure
A mixture of 4-chlorophenol (0.129 g, 1 mmol) and silica-acetate/
N2O4 complex (1.2 g) in CH2Cl2 (4 mL) was stirred vigorously at room
temperature for 5 min. Acetone (5 mL) was added and the mixture was
filtered. The resulted mixture was presorbed on silica gel (5 g) and was
applied on silica gel column and eluted with peroleum ether/acetone
(9:1). 4-Chloro-2-nitrophenol 0.164 g, 95%, m.p. 90ꢀC, [Lit.[25] m.p. 91ꢀC]
was obtained as yellow needle crystals.
Dinitration of 4-Chlorophenol with Silica-Acetate/N2O4
Complex as a Typical Procedure
To a solution of 4-chlorophenol (0.129 g, 1 mmol) in EtOAc (5 mL),
silica-acetate/N2O4 complex (2.5 g) was added. The mixture was refluxed
for 45 min. Aceton (5 mL) was added and the mixture was filtered. The
resulted mixture was presorbed on silica gel (5 g) and was applied on silica
gel column and eluted with peroleum ether/acetone (8:2). 4-Chloro-2,6-
dinitrphenol was obtained, 0.20 g, 96%, m.p. 80ꢀC, [Lit.[26] m.p. 81ꢀC].
Nitrosation of Thiophenol with Silica-Acetate/N2O4
Complex as a Typical Procedure
To a solution of thiophenol (0.11 g, 1 mmol) in t-butanol (5 mL),
silica-acetate/N2O4 complex (1.2 g) was added. The resulting mixture
was stirred at room temperature. The reaction was completed immedi-
ately and a bright red solution was obtained. This mixture can be froze
and keptfor several days withoutany change.
ACKNOWLEDGMENT
We are grateful to the Ministry of Science, Research, and
Technology of Iran and Shiraz University Research Council for
supporting this work with grant number 80-SC-3.RM.

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Silica-Acetate Complex of N2O4
REFERENCES
709
1. Squadrito, G.L.; Church, D.F.; Pryor, W.A. J. Am. Chem. Soc.
1987, 109, 6535.
2. (a) Squadrito, G.L.; Fronczek, F.R.; Watkins, S.F.; Church, D.F.;
Pryor, W.A. J. Org. Chem. 1990, 55, 4322; (b) Radner, F. J. Org.
Chem. 1988, 53, 702.
3. Challis, B.C.; Kyrtopoulos, S.A. J. C. S. Perkin I 1979, 299.
4. Aziz, A.; Hoharum, M.; Khalil, M.I. J. Chem. Soc. Faraday Trans. I
1981, 77, 1737.
5. Boyer, J.H.; Pillai, T.P. J. Chem. Soc. Perkin Trans. I 1985, 1661.
6. Street, G.B.; Gill, W.D.; Geiss, R.H.; Greene, R.L.; Mayerle, J.J.
J. C. S. Chem. Comm. 1977, 407.
7. Oae, S.; Shinhama, K.; Kim, Y.H. Tetrahedron Lett. 1979, 35,
3307.
8. Wilkes, J.B.; Wall, R.G. J. Org. Chem. 1980, 45, 247.
9. Giamalva, D.H.; Kenion, G.B.; Church, D.F.; Pryor, W.A. J. Am.
Chem. Soc. 1987, 109, 7059.
10. Kim, K.; Kim, Y.H. Bull. Korean Chem. Soc. 1993, 14, 649.
11. Kim, K.; Kim, Y.H. Bull. Korean Chem. Soc. 1994, 15, 100.
12. Mukherjee, A.K.; le Noble, W.J. J. Org. Chem. 1993, 58, 7955.
13. Mehta, G.; Uma, R. Tetrahedron Lett. 1996, 37, 1897.
14. Oae, S.; Kim, Y.H.; Fukushima, D.; Shinhama, K. J. Chem. Soc.,
Perkin Trans. 1 1978, 913.
15. (a) Oae, S.; Kim, Y.H.; Fukushima, D. J. Chem. Soc. Chem.
Commun. 1977, 407; (b) Oae, S.; Shinhama, K.; Fujimori, K.;
Kim, Y.H. Bull. Chem. Soc. Jpn. 1980, 53, 775; (c) Oae, S.;
Shinhama, K. Org. Prep. Proced. Int. 1983, 15, 165.
16. (a) Kim, Y.H.; Shinhama, K.; Fukushima, D.; Oae, S. Tetrahedron
Lett. 1978, 1211; (b) Capozzi, G.; Modena, G. Chemistry of the
Thiol Group; Patai, S., Ed.; Wiely: New York, 1974; Chapter 17,
p. 785.
17. Gibbins, B.J.; Eichhorn, G.L.; Sisler, H.H. J. Am. Chem. Soc. 1954,
76, 4668.
18. Richard, S.; Audet, P.; Savoie, R. J. Molecular Structure 1988,
178, 135.
19. Iranpoor, N.; Firouzabadi, H.; Heydari, R. Synth. Commun. 1999,
29, 3295–3298.
20. Iranpoor, N.; Firouzabadi, H.; Heydari, R. J. Chem. Res. (S) 1999,
668–669.
21. Firouzabadi, H.; Iranpoor, N.; Heydari, R. Synth. Commun. 2001,
31, 2037.

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710
Iranpoor, Firouzabadi, and Heydari
22. (a) Cornelis, A.; Depaye, N.; Gerstmans, A.; Laszlo, P. Tetrahedron
Lett. 1983, 24, 3103; (b) Cornelis, A.; Laszlo, P. Synthesis 1985, 909;
(c) Cornelis, A.; Laszlo, P. Synlett 1994, 155.
23. Iranpoor, N.; Firouzabadi, H.; Zolfigol, M.A. Synth. Commun.
1998, 28, 367.
24. Fluka Chemica-Biochemica, 1993/94.
25. Olah, G.A.; Wong, Q.; Li, X.Y.; Bucsi, I. Synthesis 1992,
1085–1086.
26. Bruice, T.C.; Gregor, M.G.; Walters, S.L. J. Am. Chem. Soc. 1986,
90, 1612.
Received in the Netherlands February 18, 2002