Nitration of arenes by 1-sulfopyridinium nitrate as an ionic liquid and reagent by in situ generation of NO2

Article abstract of DOI:10.1039/c6ra15922b

1-Sulfopyridinium nitrate was synthesized as a potent nitrating agent for the nitration of arenes without the need for any co-catalysts. A variety of nitro compounds were synthesized and fully characterized by IR, ¹H NMR, ¹³C NMR, thermal gravimetric analysis (TGA), differential thermal gravimetry (DTG), CHN analysis and mass spectroscopy. Mechanistically, in situ generated nitrogen dioxide as a radical from the reagent is proposed for the presented nitration protocol.

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Nitration of arenes by 1-sulfopyridinium nitrate as an ionic liquid and
reagent by in situ generation of NO2
Ahmad Reza Moosavi-Zare,*a Mohammad Ali Zolfigol,b Mahmoud Zarei,b Ehsan Noroozizadehb and M.
Hassan Beyzavic
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
1ꢀsulfopyridinium nitrate was synthesized as a potent nitrating agent for the nitration of arenes without the need for any coꢀcatalysts. A
1
variety of nitro compounds were synthesized and fully characterized by IR, H NMR, 13C NMR, thermal gravimetric analysis (TGA),
differential thermal gravimetry (DTG), CHN analysis and mass spectroscopy. Mechanistically, in situ generated nitrogen dioxide as a
10 radical from the reagent is proposed for the presented nitration protocol.
Nitro compounds are one of the principal group of compounds 50 1ꢀsulfopyridinium nitrate and found it is a highly efficient and
that have been widely used in organic chemistry and industry [1ꢀ
5]. Nitro compounds hold many applications such as in highꢀ
15 energy materials, dyes, pharmaceuticals, perfumes, medicine and
plastics and also play a significant role in the development of
concept of mechanisms [6]. Therefore, high attention has been
centered on the development of efficient and practical approaches
for the synthesis of nitro compounds. The conventional nitration
20 protocols are performed by the use of an excess of nitric acid or a
mixture of nitric acid and sulfuric acid or dinitrogen pentoxide.
green reagent without the need of a coꢀcatalyst for the nitration of
arenes and alkenes (Figure 1, Schemes 1 & 2).
55
As an alternative, yet efficient procedures, mixtures of nitric acid 60 Figure 1. The structure and color of [Pyridine–SO3H]NO3.
with aluminum chloride, polyphosphoric acid, perchloric acid,
methanesulfonic acid, hydrogen fluoride and superacids such as
25 boron trifluoride, triflic acid, fluorosulfonic acid and many others
have been reported [7]. However, many of the reported
approaches are associated with some drawbacks including: low
yields, long reaction times, over nitration, the use of a large
catalyst loading, low regioselectivity, oxidation of reagents and
30 safety problems [8]. Therefore, designing an efficient nitration
protocol is still of practical importance.
65
Scheme 1. Preparation of 1ꢀsulfopyridinium nitrate {[Pyridine–
SO3H]NO3}.
Recently, we reported sulfonic acid functionalized imidazolium
salts (SAFIS) as a new class of acidic ionic liquids in which S–N
bond has been formed leading to imidazole derivatives, as
35 fiveꢀmembered heterocyclic compounds. We found these
materials have interesting applications as green and ecoꢀfriendly
70
Scheme 2. Nitration of aromatic compounds using [Pyridine–
SO3H]NO3.
solvents, catalysts and reagents in organic transformations [8ꢀ23]. 75 1ꢀsulfopyridinium chloride was synthesized by the reaction of
In continuation of our previous works, we also recently reported a
new category of ionic liquids, namely sulfonic acid
40 functionalized pyridinium salts (in which a S–N bond are formed
in the pyridine ring leading to six membered heterocycles and
pyridine with ClSO3H according to literature [24,25]. Then, by
the reaction of [Pyridine–SO3H]Cl with HNO3, [Pyridine–
SO3H]NO3 was prepared and characteized by IR, 1H and 13C
NMR, mass spectroscopy as well as CHN analysis.
used them as organocatalysts for the synthesis of 80 The IR spectrum of the reagent shows two strong peaks at about
bis(pyrazolil)methans [24], xanthene derivatives [25],
bis(coumarin)methans [26] and hexahydroquinolines [27].
1308 cmꢀ1 and 1543 cmꢀ1 which are typical of ʋO–N=O symmetric
stretching vibration and ʋO–N=O asymmetric stretching vibration,
respectively (Figure 2). Moreover, two peaks observed at 1183
cmꢀ1 and 1334 cmꢀ1 are related to vibrational modes of N–SO2
45 Having above facts and according to our previous work in the
field of nitration [8], we were interested in the development of
green chemistry protocols using new approaches such as the use 85 and O–SO2 bonds and a broad peak at 3100–3600 cmꢀ1 could be
of ionic liquids to reduce/eliminate coꢀcatalysts and/or solvents.
We prepared the ionic liquid
This journal is © The Royal Society of Chemistry [year]
signatures of O–H stretching of SO3H group.
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The thermogram (TG) of the reagent was studied and showed two
main weight losses. The first loss of weight of the reagent was
50 observed during the range of 60 ºC to 160 ºC, which could be
related to loss of NO2. The second weight loss occurred between
240 ºC and 320 ºC and the loss after 320 ºC is related to
molecular decomposition (Figure 4).
55
60
Figure 2. IR spectrum of 1ꢀsulfopyridinium chloride {[Pyridine–
SO3H]NO3}.
The 1H NMR spectrum of [Pyridine–SO3H]NO3 shows the acidic
hydrogen (SO3H) peak at 11.37 ppm (Figure 2). To confirm that
this peak is indeed related to the hydrogen of SO3H in the
5
1
65
compound, we also compared the H NMR spectra of ClSO3H,
[PySO3H]Cl and pyridinium chloride with HNO3 in DMSOꢀd6. In
these spectra, the peaks of the acidic hydrogens of [Pyridine–
Figure 4. TG/DTG of the 1ꢀsulfopyridinium nitrate.
10 SO3H]NO3, ClSO3H, [Pyridine–SO3H]Cl, pyridinium chloride
and HNO3 were observed at 11.37, 13.45, 13.96, 8.46, and 13.01
ppm, respectively (Figure 3) [8,24]. The mass spectrum of the
compound gave the consistent molecular ion peak at 222 m/z.
In another experiment, the gas (nitrogen dioxide) that was
released from [Pyridine–SO3H]NO3 upon heating at about 60°C
70 was collected in a test tube, transferred to a roundꢀbottomed flask
in the presence of copper powder and ethyl acetate. NO2 in
equilibrium with dinitrogen tetroxide (N2O4)[28] reacts with
copper metal to give Cu(NO3)2. In this reaction, appearance of the
blue color due to copper nitrate formation in anhydrous media is
75 a convincing evidence of the release of nitrogen dioxide (Figure
5) [8, 29]. Additionally, the excess copper powder residue turned
black over time, suggesting that O2 is produced from [Pyridine–
SO3H]NO3 as well. Oxygen reacts with copper metal to form the
black copper oxide as an insoluble residue (Scheme 3).
15
20
25
30
35
40
80
85
90
95
100
45
Figure 3. The 1HNMR and 13CNMR spectra of the 1ꢀ
sulfopyridinium nitrate.
Scheme 3. The identification of nitrogen dioxide and oxygen
using copper powder.
2
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35
Scheme 4. Regioselective nitration of styrene.
5
In a proposed mechanism which is supported by literature [8],
40 NO2 gas released from [Pyridine–SO3H]NO3 reacts with aromatic
compound to give the aromatic radical and nitrous acid (HNO2).
Second NO2 radical and the aromatic radical react to yield nitro
naphthalene (Scheme 5).
10
Figure 5. Preparation of copper nitrate (with blue color, right
picture) from copper powder (left picture) as an evidence for the
release of nitrogen dioxide.
45
A wide range of compounds including benzene, toluene, oꢀ
15 xylene, naphthalene, anthracene, phenols, anisol, 2ꢀnaphthol,
anilines, styrene and bromobenzene were also nitrated with
[Pyridine–SO3H]Cl (Table 1). By the reaction of [Pyridine–
SO3H]NO3 with benzenethiol and naphthaleneꢀ2ꢀthiol the main
products were 1,2ꢀdiphenyldisulfane and 1ꢀ(naphthalenꢀ2ꢀyl)ꢀ2ꢀ
20 (naphthalenꢀ6ꢀyl) disulfane respectively. (Table 1, Entries 11 and
50
Scheme 5. The proposed mechanism for the nitration of aromatic
14) In this reaction conditions thiols were converted to the 55 compounds using [Pyridine–SO3H]NO3.
corresponding ArꢀS• radical in the presence of NO2. Two of these
radicals dimerize to give diaryldisulfane and nitrous acid as a
byproduct. Nitration of styrene as olefin compound was also
To investigate the regeneration of [Pyridine–SO3H]NO3, the
reaction of 2ꢀnaphtol with reagent was carried out several times,
and the resulting ionic liquid phases (unreacted [Pyridine–
25 studied
and
only the
E
isomer
was
obtained.
1ꢀ((E)ꢀ2ꢀnitrovinyl)benzene was prepared in 62% yield after three 60 SO3H]NO3, the zwitterionic salt, and pyridinium salt) were
minutes in presented reaction conditions. In our presented
method, the regioselective nitration of styrene by
1ꢀsulfopyridinium nitrate is more efficient in compared with
30 previous literature reports (Scheme 4) [30].
combined. Water was added to the reaction mixture, and the
reaction mixture was stirred for 5 min and then filtered.
[Pyridine–SO3H]NO3 and zwitterionic salt is soluble in water and
separated from the remained starting material and the product.
Table 1. Nitration of Aromatic and aliphatic Compounds by 65 [Pyridine–SO3H]NO3 and the zwitterionic salt were hydrolyzed in
Using {[Pyridine–SO3H]NO3.
aqueous media. A solution of NaOH (10%) was then added to the
reaction media, and the mixture was stirred for 5 min to give
pyridine. The solution was extracted with ethyl acetate, washed
with water, and dried. By the evaporation of the solvent, pyridine
70 was separated (96% recovery). The recovered pyridine was
reacted with chlorosulfonic acid to afford [Pyridine–SO3H]NO3.
Then, [Pyridine–SO3H]NO3 reacted with nitric acid (100 %) to
prepare [Pyridine–SO3H]NO3. The activity of the reproduced
[Pyridine–SO3H]NO3 as nitration agent was almost identical to
75 the original version (Scheme 6).
Product
Time (min)
Yielda (%) m.p / b.p (˚C)
[ref]
Nitrobenzene (1)
2
2
84
83
53
35
92
209ꢀ211 [31a]
52ꢀ54 [31a]
44ꢀ47 [32]
114ꢀ116 [31a]
101ꢀ103 [32]
4ꢀnitrotoluene (2)
2ꢀnitrophenol (3a)
4ꢀnitrophenol (3b)
1ꢀnitronaphtalene−2ꢀol (4)
1
immediately
4ꢀ chloroꢀ2ꢀnitrophenol (5)
4ꢀbromoꢀ2ꢀnitrophenol (6)
1ꢀnitronaphthalene (7)
2
78
85
82
83
81
83ꢀ85 [31b]
82ꢀ84 [31b]
58ꢀ61 [8]
137ꢀ140 [33]
83ꢀ86
immediately
immediately
9ꢀnitroanthracene (8)
2
1
2ꢀnitro4ꢀbenzyl phenol (9)
80
2ꢀnitroaniline (10a)
4ꢀnitroaniline (10b)
45
40
71ꢀ73 [34]
148ꢀ151 [35]
immediately
1,2ꢀdiphenyldisulfide (11)
2
2
83
80
62ꢀ65 [31a]
1ꢀbromo 4ꢀnitrobenzene (12)
122ꢀ124
85
1ꢀ(naphthalenꢀ2ꢀyl)ꢀ2ꢀ
2
1
3
75
90
62
138ꢀ141
52ꢀ54 [31a]
55ꢀ58 [30]
(naphthalenꢀ6ꢀyl)disulfane (13)
4ꢀnitro anisol (14)
1ꢀ((E)ꢀ2ꢀnitrovinyl)benzene
(15)
90
aYield of purified product.
Scheme 6. Regeneration of [Pyridine–SO3H]NO3.
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To compare the efficiency of the solution versus solventꢀfree
Table 4. Comparison of the results on the nitration of toluene
conditions, a mixture of 2ꢀnaphtol (1 mmol) and [Pyridine– 40 using [Pyridine–SO3H]NO3 with those obtained by the recently
SO3H]NO3 (1 mmol) in some various solvents was investigated at
room temprature. In the persence of several various solvents such
as CH2Cl2, CHCl3, EtOAc, EtOH and H2O, the product was
obtained in low yields (Table 2).
reported methods.
Reaction Condition
Time (min)
120
Yielda (%)
Ref.
37
5
PVPꢀHNO3 and PVPꢀH2SO4
CH2Cl2, r.t.
Bi(NO3)3.5H2O (1.5 equv)
bmim (PF6), 85 °C
Bi(NO3)3.5H2O (1.5 equv)
1,2ꢀDCE, 85 °C
55
39
50
90
38
Table 2. Effect of various solvents on the reaction of 2ꢀnaphtol (1
mmol) with {[Pyridine–SO3H]NO3 (1 mmol) at room temprature.
1380
38
Yielda
65
[Msim] NO3, CH2Cl2, r.t.
2
6
70
41
8
Solvent
EtOAC
Time (min)
60
VO(NO3)3, CH2Cl2, r.t.
Toluene (1 mmol),
NaNO2 (1 mmol),
39
CHCl3
CH2Cl2
EtOH
H2O
60
10
60
60
60
92
25
15
240
2
48
83
40
ꢀb
CF3CO2H (34 mmol), r. t.
[Py–SO3H]NO3, solventꢀfree, r. t.
aIsolated yield. bOur work.
Conclusions
10 aYield of purified product.
Herein, we designed and synthesized the ionic liquid
45 1ꢀsulfopyridinium nitrate [Pyridine–SO3H]NO3 as a new, a highly
efficient and organic reagent without the need of a coꢀcatalyst and
solvent for the nitration of various aromatic compounds at room
temperature.
To confirm the existence of NO2 radical in the reaction media, we
studied the effective application of NO2 with iodine or butylated
hydroxytoluene (BHT) as a radical scavenger on a model reaction
15 with naphthalene (Scheme 7) [36]. In the presence of iodine; the
yield of 1ꢀnitro naphthalene was very low even after 24 hours.
Nitration of naphthalene was also tested using butylated
hydroxytoluene (BHT) as a radical scavenger. In this reaction
condition, nitration process was carried out slowly and the yield
20 of 1ꢀnitronaphthalene was decreased even after long reaction time
due to major suppression of the active species in this reaction
condition (Table 3).
Acknowledgements
50 We thank BuꢀAli Sina University and Iran National Science
Foundation (INSF) (The Grant of Allameh Tabataba'i's Award,
Grant Number BN093) and Sayyed Jamaleddin Asadabadi
University for providing support to this work.
25
55 Experimental
2. Experimental
2.1. General
Scheme 7. Trapping NO2 Radical with Iodine and Butylated
Hydroxytoluene (BHT).
All chemicals were purchased from Merck or Fluka Chemical
Companies. The known products were identified by comparison
60 of their melting points and spectral data with those reported in the
literature. Progress of the reactions was monitored by TLC using
silica gel SIL G/UV 254 plates.
30 Table 3. Effect of Iodine and butylated hydroxytoluene as radical
scavengers on the nitration of naphthalene (1mmol) in the
presence of {[Pyridine–SO3H]NO3 (1mmol)
Yielda (%)
92
1
The H NMR (400 or 300 MHz) and 13C NMR (100 or 75 MHz)
Entry
1
Radical scavenger (mmol)
ꢀ
Time (min)
immediately
were recorded on a Bruker Avance DPX FTꢀNMR spectrometer
65 (δ in ppm). Melting points were recorded on a Büchi Bꢀ545
apparatus in open capillary tubes. Thermogravimetric (TG) and
differential thermal gravimetric (DTG) were analyzed by a Perkin
Elmer (Model: Pyris 1). TG/DTG analysis (0 to 600 °C,
temperature increase rate of 10 °C. minꢀ1, nitrogen atmosphere).
70 2.2. General Procedure for the Preparation of the Ionic Liquid
[Pyridine–SO3H]NO3.
A solution of pyridine (0.395 g, 5 mmol) in CH2Cl2 (40 mL) was
added dropwise to a stirring solution of chlorosulfonic acid (0.58
g, 5 mmol) in dry CH2Cl2 (40 mL) over a period of 10 min at 0
75 ◦C. After the addition was completed, the reaction mixture was
stirred for 20 min, stood and for 5 min, and the CH2Cl2 was
decanted. Afterwards the liquid residue was triturated with
CH2Cl2 (3× 10 mL), and dried under powerful vacuum at 90 ◦C to
give [Pyridine–SO3H]Cl as a viscous colorless oil in 95% yield
2
3
4
5
6
7
I2 (0.3)
1440
1440
1440
1440
1440
1440
35
20
10
45
35
20
I2 (0.7)
I2 (1)
BHT (0.3)
BHT (0.7)
BHT (1)
aYield of purified product.
35 To compare the efficiency of [Pyridine–SO3H]NO3 with the
reported nitrating methods nitration of toluene was chosed. As
Table 4 indicates that, [Pyridine–SO3H]NO3 has remarkably
improved result compared with other methods shown in Table 4.
4
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(0.929 g) [24, 25]. Then, nitric acid 100% (0.315 g, 5 mmol) was
65
70
dropwise added to [PySO3H]Cl (0.993 g, 5 mmol) over a period
of 5 min at room temperature under a continuous flow of nitrogen
to remove the HCl gas that is produced. The resulting mixture
was stirred for 10 min under these conditions to give [Pyridine–
SO3H]NO3 as a viscous yellow red oil in 97% yield.
5
1ꢀsulfopyridinium nitrate. Yellow Red oil; IR (Nujol) cm−1; 1183,
1308, 1543, 3100ꢀ3600; 1H NMR (300 MHz, DMSOꢀd6) δ (ppm)
8.11ꢀ8.14 (t, J = 9 Hz, 2H), 8.64ꢀ8.69 (m,1H), 8.95ꢀ8.97 (d, J = 6
10 Hz, 2H), 11.37 (s, 1H); 13C NMR (75 MHz, DMSOꢀd6) δ (ppm)
127.85, 142.17, 147.23. Anal. Calcd (%) for C5H6N2O6: C, 25.03;
H, 3.36; N, 11.66; S, 13.35. Found: C, 24.22; H, 3.115; N, 11.95 ;
S, 13.51.
75
2.3. General Procedure for the Nitration of Compounds.
15 To a roundꢀbottomed flask (10 mL) was added [Pyridine–
SO3H]NO3 (0.222 g, 1 mmol). The aromatic compound (1 mmol)
was then added, and the mixture was stirred at room temperature.
After the reaction was completed (monitored with TLC),
dichloromethane (5 mL) was added to the reaction mixture, and
20 the mixture was stirred for 2 min and separated. The organic
solvent was evaporated, and the product was easily purified by
short column chromatography. Note: For the nitration of aniline,
after the reaction was completed, the reaction mixture was
basified to pH 8 by the slow addition of 10% NaOH solution. The
25 organic layer was separated, and the aqueous layer was extracted
with dichloromethane. The combined organic solution was
washed with brine, dried over MgSO4, filtered, and concentrated
to give a crude product, which was purified with short column
chromatography.
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30 Notes and references
aDepartment of Chemistry, Sayyed Jamaleddin Asadabadi University,
Asadabad 6541835583, Iran
bFaculty of Chemistry, Bu-Ali Sina University, Hamedan 6517838683,
Iran
35 cDepartment of Chemistry and Chemical Biology, Harvard University, 12
Oxford St., Cambridge MA 02138, USA
† Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/b000000x/
40 ‡ Footnotes should appear here. These might include comments relevant
to but not central to the matter under discussion, limited experimental and
spectral data, and crystallographic data.
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DOI: 10.1039/C6RA15922B
Graphical Abstract
Nitration of arenes by 1-sulfopyridinium nitrate as an ionic liquid
and reagent by in situ generation of NO2
Ahmad Reza Moosavi-Zare,* Mohammad Ali Zolfigol, Mahmoud Zarei, Ehsan Noroozizadeh,
and M. Hassan Beyzavi
NO2
[Pyridine–SO3H]NO3
Solvent-Free, r.t.
1-sulfopyridinium nitrate was synthesized as a potent nitrating agent for the nitration of arenes without
the need for any co-catalysts.