Metal hydrogen sulfates M(HSO4)n: As efficient catalysts for the synthesis of quinoxalines in EtOH at room temperature

Article abstract of DOI:10.1002/jccs.200800206

A convenient method for the synthesis of quinoxalines catalysed by metal hydrogen sulfates by the reaction of 1,2-diamino compounds and 1,2-dicarbonyl compounds in ethanol as solvent at room temperature is reported.

Full text of DOI:10.1002/jccs.200800206

Journal of the Chinese Chemical Society, 2008, 55, 1373-1378
1373
Note
Metal Hydrogen Sulfates M(HSO4)n: As Efficient Catalysts for the
Synthesis of Quinoxalines in EtOH at Room Temperature
Khodabakhsh Niknam,a,* Mohammad Ali Zolfigol,b Ziba Tavakolic and Zahra Heydaric
aDepartment of Chemistry, Faculty of Sciences, Persian Gulf University, Bushehr 75169, Iran
bFaculty of Chemistry, Bu-Ali Sina University, Zip code 6517838683, Hamedan, Iran
cIslamic Azad University, Gachsaran Branch, Gachsaran, Iran
Aconvenient method for the synthesis of quinoxalines catalysed by metal hydrogen sulfates by the re-
action of 1,2-diamino compounds and 1,2-dicarbonyl compounds in ethanol as solvent at room tempera-
ture is reported.
Keywords: Quinoxalines; Diamino compounds; Dicarbonyl compounds; Metal hydrogen sul-
fates.
INTRODUCTION
there are several reports about using these solid acids in or-
ganic transformation.
In recent years, the search for environmentally be-
nign chemical processes or methodologies has received
much attention from chemists, because they are essential
for the conservation of the global ecosystem. The develop-
ment of heterogeneous catalysts for fine chemical synthesis
has become a major area of research, as the potential ad-
vantages of these materials (simplified recovery and reus-
ability; the potential for incorporation in continuous reac-
tors and micro reactors) over homogeneous systems can
lead to novel environmentally benign chemical proce-
dures for academia and industry.1 From this viewpoint,
catalytic reaction is a valuable process because the use of
stoichiometric reagents that are often toxic poses inherent
limitations from both economical and environmental view-
points regarding product purification and waste manage-
ment.2
The preparation of quinoxaline and its derivatives
plays an important role in organic synthesis.9 Quinoxaline
and its derivatives are an important class of benzohetero-
cycles displaying a broad spectrum of biological activities
which have made them privileged structures in pharmaco-
logically active compounds.10-12 They have also found ap-
plications as building blocks in the synthesis of organic
semiconductors,13 rigid subunits in macro cyclic receptors
or molecular recognition,14 and chemically controllable
switches.15 In general, these compounds could be achieved
via the condensation of aryl 1,2-diamines with 1,2-dicar-
bonyl compounds in organic solvents for 2-12 h under
refluxing conditions with 34-85% yields.16 However, most
of the traditional processes suffer from a variety of disad-
vantages, such as pollution, high cost, poor chemical yields,
requirements for long reaction time, and tedious work-up
procedures, which limit their use under the aspect of envi-
ronmentally benign processes.
Application of solid acids in organic transformation
have an important role, because solid acids have many ad-
vantages such as simplicity in handling, decreased reactor
and plant corrosion problems, and more environmentally
safe disposal. On the other hand, any reduction in the amount
of liquid acid needed and/or any simplification in handling
procedures is required for risk reduction, economic advan-
tage and environmental protection.3-8 Among solid acids,
silica sulfuric acid3 and Al(HSO4)36,7 are two nice alterna-
tives for very dangerous concentrated sulfuric acid and
Progress has been reported in the literature for the
synthesis of quinoxaline derivatives compounds, such as
the Bi-catalyzed oxidative coupling reaction,17 via a tan-
dem oxidation process using Pd(OAc)2 or RuCl2-(PPh3)3-
TEMPO,18 and MnO2,19 heteroannulation of nitroketene
N,S-arylaminoacetals with POCl3,20 a solid-phase synthe-
sis on Synphase TM Lanterns,21 cyclization of a-arylimino
* Corresponding author. E-mail: niknam@pgu.ac.ir; khniknam@gmail.com

1374 J. Chin. Chem. Soc., Vol. 55, No. 6, 2008
Niknam et al.
oximes compounds under refluxing conditions in acetic
anhydride,22 the condensation of a-phenylene diamines
and 1,2-dicarbonyl compounds in MeOH/AcOH under mi-
crowave irradiation,23 and the molecular iodine-catalyzed
cyclocondensation reaction in DMSO and CH3CN,24
CuSO4.5H2O in water and Zn[(L)proline] in HOAc,25
task-specific ionic liquid,26 montmorillonite K-10,27 oxalic
acid,28 and very recently Mozumdar and coworkers re-
ported the synthesis of quinoxaline derivatives catalyzed
by Ni-nanoparticles.29 The search for new readily available
and green catalysts is still being actively pursued.
Table 1. The influence of the solvent on the condensation
reaction of o-phenylenediamine (1 mmol) and benzil (1
mmol) catalyzed by Al(HSO4)3 (0.05 mmol)
Entry
Solvent
Time (min)
Yield (%)a
1
2
3
4
5
6
H2O
C2H5OH
CH3OH
CHCl3
CH2Cl2
C6H6
1200
20
40
97
95
63
59
50
20
60
60
60
a Isolated yield.
Table 2. Influence of the amounts of M(HSO4)n on the
condensation reaction of o-phenylenediamine (1 mmol)
and benzil (1 mmol)
RESULTS AND DISCUSSION
In continuation of our studies on the applications of
metal hydrogen sulfates in organic transformations,6,7 we
were interested to find a simple and efficient method for the
synthesis of quinoxaline derivatives under mild conditions
(Scheme I). To optimize the reaction conditions, for the be-
ginning of this work, the condensation reaction between
benzil and o-phenylenediamine was employed as the model
reaction to screen the suitable solvent (Table 1). As shown
in Table 1, condensation reaction in ethanol and methanol
gave the best results in the case of time and yield, and we
chose ethanol for environmental reasons. Although water
is a desirable solvent for chemical reactions for reason of
cost, safety and environmental concerns, we found that us-
ing water in this reaction gave moderate yields of products
at room temperature after long reaction times.
Catalyst
(mmol)
Time
(min)
Yield
(%)a
Entry
Catalyst
1
2
3
4
5
6
7
8
None
None
0.01
0.03
0.05
0.05
0.05
0.05
0.05
24 h
12 h
120
20
0
Al(HSO4)3
Al(HSO4)3
Al(HSO4)3
NaHSO4.H2O
KHSO4
31
79
97
95
88
79
86
15
15
Mg(HSO4)2
Ca(HSO4)2
5
5
a Isolated yield.
lutely necessary for this condensation reaction. When the
amount of metal hydrogen sulfate was increased, a ramp in
the yields of quinoxaline derivatives was clearly observed.
The optimal amount of metal hydrogen sulfates was 0.05
mmol per 1 mmol of 1,2-diketone and also 1 mmol of o-
phenylenediamine in ethanol (2 mL).
The effect of the amounts of metal hydrogen sulfates
on the yield of the condensation reaction in EtOH was then
explored using the same model reaction (Table 2).
It showed that no product can be detected when a
mixture of 10 mmol benzil and 10 mmol o-phenylenedi-
amine was stirred for 24 h in the absence of metal hydrogen
sulfates (entry 1), which indicated that the catalyst is abso-
The scope and generality of the present method was
then further demonstrated by the condensation of various
benzil with o-phenylenediamine derivatives using 0.05
Scheme I Synthesis of quinoxaline derivatives catalyzed by metal hydrogen sulfates

Quinoxaline Synthesis by Using M(HSO4)n
J. Chin. Chem. Soc., Vol. 55, No. 6, 2008 1375

1376 J. Chin. Chem. Soc., Vol. 55, No. 6, 2008
Niknam et al.
mmol metal hydrogen sulfates in ethanol at room tempera-
ture, and the results are presented in Table 3. The reaction
proceeds very cleanly at room temperature and was free of
side products. After completion of the reaction (monitored
by TLC), a precipitate was obtained that a simple filtration
affords the products in excellent yields.
those reported in the literature.17-25
General procedure
To a stirred solution of 1,2-phenylenediamine (1
mmol), and dicarbonyl compound (1 mmol) in EtOH (2
mL) was added M(HSO4)n [M = Al, Mg, Ca, K, Na] (0.05
mmol) and stirred at room temperature for the times speci-
fied in Table 3. The reaction was followed by TLC. After
completion of the reaction, the product that was precipi-
tated was separated by simple filtration. For further purifi-
cation the products were recrystallized from hot ethanol.
Spectral data
It can easily be seen that the condensation reaction
proceeded smoothly in ethanol and gave reasonable good
to excellent yields ranging from 70% to 97% and no unde-
sirable side reactions were observed. In the case of 1,2-di-
ketones, either electron-withdrawing or electron-donating
substituents (R1) on the aromatic ring gave almost the same
yields. But for substituents on o-phenylenediamine (R2),
the order of the reactivity for condensation reaction was
found to be: H > CH3 > NO2.
3a: mp 126-127 °C, (Lit.25b 128-129 °C); H NMR
1
(500 MHz, CDCl3): d (ppm) 7.40 (m, 6H), 7.58 (m, 4H),
7.83 (m, 2H), 8.23 (d, 2H, J = 8.0 Hz). 13C NMR (125 MHz,
CDCl3): d (ppm) 128.70, 129.23, 129.65, 130.28, 130.37,
139.54, 141.68, 153.91.
1
CONCLUSION
3b: mp 116-117 °C, (Lit.25b 117-118 °C); H NMR
In conclusion, the cheapness and availability of the
reagents, easy and clean work-up, and high yields make
this method practical for quinoxaline synthesis. We believe
that the present methodology could be an important addi-
tion to the existing methodologies.
(500 MHz, CDCl3): d (ppm) 2.64 (s, 3H), 7.35 (m, 6H),
7.54 (m, 4H), 7.63 (d, 1H, J = 8.5 Hz), 8.03 (s, 1H), 8.14 (d,
1H, J = 8.5 Hz). 13C NMR (125 MHz, CDCl3): d (ppm)
22.01, 127.69, 128.31, 128.52, 128.88, 128.98, 129.89,
129.94, 132.68, 138.55, 138.68, 139.48, 140.81, 141.02,
152.47, 153.07.
1
EXPERIMENTAL SECTION
3c: mp 192-193 °C, (Lit.25b 193-194 °C); H NMR
General
(400 MHz, CDCl3): d (ppm) 7.42 (m, 6H), 7.58 (m, 4H),
8.32 (d, 1H, J = 8.0 Hz), 8.57 (m, 1H), 9.10 (s, 1H). 13C
NMR (100 MHz, CDCl3): d (ppm) 124.41, 126.74, 129.54,
129.61, 130.80, 130.93, 130.99, 131.07, 131.90, 139.17,
Chemicals were purchased from Fluka, Merck and
Aldrich chemical companies. The products were character-
ized by comparison of their spectral and physical data with

Quinoxaline Synthesis by Using M(HSO4)n
J. Chin. Chem. Soc., Vol. 55, No. 6, 2008 1377
139.23, 141.07, 144.70, 148.96, 156.80, 157.43.
1
155.19.
1
3d: mp 167-169 °C, (Lit.30 167 °C); H NMR (500
3k: mp > 300 °C, H NMR (500 MHz, CDCl3): d
(ppm) 2.60 (s, 3H), 7.55 (d, 1H, J = 8.25 Hz), 7.79 (t, 2H, J
= 7.5 Hz), 7.95 (s, 1H), 8.03-8.07 (m, 3H), 8.35 (t, 2H, J =
6.3 Hz). 13C NMR (125 MHz, CDCl3): d (ppm) 22.19,
121.97, 122.12, 129.01, 129.03, 129.21, 129.53, 129.60,
129.75, 130.39, 131.72, 132.44, 136.68, 140.06, 140.10,
141.73, 153.76, 154.48. Anal. Calc. for C19H12N2: C, 85.05;
H, 4.51; N, 10.44; found: C, 84.92; H, 4.43; N, 10.30; IR
(KBr): 3052, 2910, 1575, 1375, 1332, 1294, 1097, 822,
778 (cm-1).
3l: mp > 300 °C, (Lit.32 > 300 °C); 1H NMR (500
MHz, DMSO-d6): d (ppm) 8.00 (t, 2H, J = 8.0 Hz),
8.37-8.42 (m, 3H), 8.50-8.55 (m, 3H), 8.97 (d, 1H, J = 2.3
Hz).
MHz, CDCl3): d (ppm) 1.46-1.50 (m, 2H), 1.67-1.70 (m,
2H), 1.93-1.96 (m, 2H), 2.54-2.57 (m, 2H), 2.88-2.90 (m,
2H), 7.25-7.29 (m, 4H), 7.31-7.34 (m, 2H), 7.42-7.44 (m,
4H). 13C NMR (125 MHz, CDCl3): d (ppm) 25.87, 33.956,
59.95, 128.45, 128.55, 129.88, 138.23, 160.10.
3e: mp 195-196 °C, (Lit.25b 195-196 °C); H NMR
1
(500 MHz, CDCl3): d (ppm) 7.39 (dt, 4H, J1 = 8.5 Hz, J2 =
2.0 Hz), 7.51 (dt, 4H, J1 = 8.5 Hz, J2 = 2.0 Hz), 7.83 (dd,
2H, J1= 6.3 Hz, J2= 3.4 Hz), 8.20 (dd, 2H, J1 = 6.3 Hz, J2 =
3.4 Hz). 13C NMR (125 MHz, CDCl3): d (ppm) 129.15,
129.63, 130.79, 131.61, 135.78, 137.69, 141.67, 152.34.
3f: mp 178-180 °C, (Lit.25b 180 °C); 1H NMR (500
MHz, CDCl3): d (ppm) 2.66 (s, 3H), 7.38 (d, 4H, J = 8.0
Hz), 7.50 (dd, 4H, J1 = 8.4 Hz, J2 = 1.0 Hz), 7.67 (dd, 1H, J1
= 8.5 Hz, J2 = 1.8 Hz), 7.97 (s, 1H), 8.08 (d, 1H, J = 8.5 Hz).
13C NMR (125 MHz, CDCl3): d (ppm) 22.36, 128.42,
129.09, 129.11, 131.58, 131.60, 133.16, 135.56, 135.64,
137.85, 140.17, 141.43, 141.75, 151.43, 152.20.
3m: mp 304-306 °C, (Lit.28 304-306 °C); H NMR
1
(400 MHz, CDCl3): d (ppm) 2.51 (s, 6H), 7.78 (m, 2H),
7.89 (s, 2H), 8.03 (m, 2H), 8.34 (m, 2H). 13C NMR (100
MHz, CDCl3): d (ppm) 20.3, 121.5, 127.8, 128.0, 128.6,
128.9, 129.1, 139.5, 140.0, 148.5, 153.3.
1
3g: mp 175-176 °C, (Lit.25b 176 °C); 1H NMR (500
MHz, CDCl3): d (ppm) 7.43 (d, 4H, J = 7.6 Hz), 7.54-7.57
(m, 4H), 8.32 (d, 1H, J = 9.1 Hz), 8.58 (dd, 1H, J1 = 9.1 Hz,
J2 = 2.5 Hz), 9.08 (d, 1H, J = 2.5 Hz). 13C NMR (125 MHz,
CDCl3): d (ppm) 124.08, 125.99, 129.37, 131.20, 131.58,
131.66, 136.60, 136.67, 136.72, 136.87, 140.40, 143.91,
148.53, 154.57, 155.18.
3n: mp 192-194 °C, (Lit.33 195-197 °C); H NMR
(500 MHz, CDCl3): d (ppm) 7.41 (dt, 4H, J1 = 8.5 Hz, J2 =
2.0 Hz), 7.51 (dt, 4H, J1 = 8.5 Hz, J2 = 2.0 Hz), 7.79 (dd,
2H, J1 = 6.5 Hz, J2 = 3.5 Hz), 8.15 (dd, 2H, J1 = 6.5 Hz, J2 =
3.5 Hz). 13C NMR (125 MHz, CDCl3): d (ppm) 124.13,
129.64, 130.84, 131.86, 132.12, 138.12, 141.68, 152.34.
3h: mp 223-225 °C, (Lit.31 224.8-225.7 °C); 1H NMR
(400 MHz, CDCl3): d (ppm) 7.51-7.66 (m, 6H), 8.10-8.13
(m, 2H), 8.33 (d, 2H, J = 8.0 Hz), 9.18 (d, 2H, J = 8.1 Hz).
13C NMR (100 MHz, CDCl3): d (ppm) 124.01, 127.35,
129.01, 130.51, 130.81, 131.41, 133.23, 143.23, 143.51.
Received July 15, 2008.
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