A simple and efficient method for the oxidation of aryl substituted semicarbazide with NaNO2/NaHSO4-H2O/SiO 2 under mild conditions

Article abstract of DOI:10.1002/jccs.200200062

In this paper, eighteen aryl substituted semicarbazide underwent efficient oxidation to aryl azo compounds using NaNO₂/NaHSO₄· H₂O/SiO₂ under mild conditions with excellent yields.

Full text of DOI:10.1002/jccs.200200062

Journal of the Chinese Chemical Society, 2002, 49, 397-400
397
A Simple and Efficient Method for the Oxidation of Aryl Substituted
Semicarbazide with NaNO2/NaHSO4·H2O/SiO2 under Mild Conditions
Xiao-Chuan Lia (
), Yu-Lu Wanga* (
) and Jin-Ye Wangb* (
)
aCollege of Chemical and Environmental Science, Henan Normal University, Xinxiang, 453002, P. R. China
and The Key Laboratory of Environmental Science and Technology of Higher Education of Henan Province,
P. R. China
bShanghai Institute of Organic Chemistry, Chinese Academy of Science, Shanghai, 200032, P. R. China
In this paper, eighteen aryl substituted semicarbazide underwent efficient oxidation to aryl azo com-
pounds using NaNO2/NaHSO4·H2O/SiO2 under mild conditions with excellent yields.
INTRODUCTION
Azo compounds have caused great interest in organic
tive oxidizing agent for its dehydrogenation.14 We rational-
ized that NaNO2/NaHSO4·H2O might be suitable for the oxi-
dation of aryl substituted semicarbazide. After our experi-
ments, it was demonstrated that this is an effective reagent.
All reactions were performed smoothly at room temperature
(Scheme I) and completed within 30 min with excellent
yields.
synthesis. They are widely used as dyes and analytical re-
agents.1 Optical-switching and image storage can be made by
azobenzene liquid crystal film.2,3 Recently, many noteworthy
studies have shown that some azo compounds possess excel-
lent optical memory and photoelectric properties.4,5
Substituted semicarbazide or carbazide can make many
reactions,6,7 such as oxidation, reduction, substitution, cy-
clization, condensation and addition. The oxidation of aryl
substituted semicarbazide into aryl azo compounds is an im-
portant transformation in organic synthesis. We have been
paying particular and continuous attention to this field. In our
laboratory, FeCl3·6H2O,8 DMF-NOx,9 KClO3/H2SO4/FeSO4,10
Galvinoxy11 and NBS/pyridine12 have been used as effective
oxidants and gotten relatively better results. But most of the
methods are deficient because of tedious operation,11,12 ex-
pensive catalysts,11 the use of a large amount of solvent,11,12
or strong acid or basic media.8,10 These limit their application
in organic synthesis. Therefore, there is much room for im-
provement of the existing methods.
Scheme I
Table 1. Oxidation of 1a (1 mmol) in the Presence of SiO2 (0.3
g, 60-100 mesh) with Different Molar Ratios of
a
NaNO2 :NaHSO4·H2Oa
Entry NaNO2:NaHSO4·H2O
Reaction time
Yield ( )
RESULTS AND DISCUSSION
1
2
3
4
5
6
7
8
1:1
1.5:1.5
2:2
2.5:2.5
3:3
3:3
3:3
3:0
30 min
30 min
30 min
30 min
30 min
3 h
40
55
65
80
98
In continuation of our studies on the synthesis of azo
compounds, we decided to develop a new reagent or reagent
system to overcome the above limitations. The combination
of NaNO2 and NaHSO4·H2O in the presence of SiO2 has been
used as an effective oxidizing agent for the dehydrogenation
of 4-substituted-1,2,4-triazole-3,5-diones successfully.13 The
95
30 min
24 h
40b
a little
a crushed to a fine powder b without SiO2
[NO+·crown·H(NO3)2 ] complex is also reported as an effec-
-

398 J. Chin. Chem. Soc., Vol. 49, No. 3, 2002
Li et al.
In the oxidation study, we selected 1a as a model, a rela-
tively unreactive substrate. The optimum molar ratio was
searched by reaction using 1a (1 mmol) and SiO2 (0.3 g,
60-100 mesh) with various molar ratios of NaNO2:NaHSO4·
H2O. The results are summarized in Table 1. If NaNO2 was
used for the oxidation alone, the reaction did not occur after
stirring 24 h. The oxidation of 1a was efficiently achieved
with this oxidation system. The presence of SiO2 is crucial.
Although the reaction occurs without SiO2, the reaction pe-
riod would be much longer. Therefore, we thought that the
presence of SiO2 will act as a media and will provide a hetero-
geneous effective surface area for the generation of HNO2.
No additional products were identified from this reaction.
The possible mechanism is shown in Scheme II.
NaNO2 (0.207 g, 3 mmol) and NaHSO4·H2O (0.324 g, 3
mmol) and SiO2 (0.3 g, 60-100 msh) in acetone (15 mL) was
vigorously stirred at room temperature. After completion of
the reaction (TLC), the reaction mixture was filtered. Then
cool water (30 mL) was poured into the filtrate slowly. After
30 min, the resulting precipitate was collected, washed with
water, recrystallized from EtOH-H2O (3:1) mixture and dried
under vacuum.
2a: red tabular; Yield 98%; mp 109-111 C; IR (KBr)
1
max: 3232, 3060, 1680, 1600, 1500, 1420 (cm-1); H NMR
(CDCl3) (ppm): 7.03-7.80 (m, 10H, Ar-H), 8.90 (s, 1H,
NH); MS (m/z): 225 (M+), 120 (B), 105, 92, 91, 77; Anal.
Calcd. for C13H11N3O: C, 69.31; H, 4.93; N, 18.66. Found: C,
69.07; H, 5.11; N, 18.89.
2b: orange tabular; Yield 94%; mp 103-104 C; IR
(KBr) max: 3240, 3060, 2995, 1682, 1580, 1480, 1402 (cm-1);
1H NMR (CDCl3) (ppm): 2.27 (s, 3H, CH3), 7.06-7.98 (m,
9H, Ar-H), 8.90 (s, 1H, NH); Anal. Calcd. for C14H13N3O: C,
70.29; H, 5.44; N, 17.57. Found: C, 70.14; H, 5.38; N, 17.85.
2c: orange tabular; Yield 95%; mp 70-72 C; IR (KBr)
max: 3260, 3030, 2970, 2850, 1685, 1598, 1470, 1425 (cm-1);
1H NMR (CDCl3) (ppm): 2.26 (s, 3H, CH3), 6.80-8.02 (m,
9H, Ar-H), 8.25 (s, 1H, NH); Anal. Calcd. for C14H13N3O: C,
70.29; H, 5.44; N, 17.57. Found: C, 70.11; H, 5.62; N, 17.81.
2d: orange tabular; Yield 94%; mp 103-105 C; IR
(KBr) max: 3320, 3050, 2990, 2850, 1685, 1600, 1580, 1442
(cm-1); 1H NMR (CDCl3) (ppm): 2.27 (s, 3H, CH3), 7.10-
8.05 (m, 9H, Ar-H), 8.26 (s, 1H, NH); Anal. Calcd. for
C14H13N3O: C, 70.29; H, 5.44; N, 17.57. Found: C, 70.15; H,
5.31; N, 17.84.
Scheme II
Overall, we recommend this simple, clean and econom-
ical procedure for the oxidation of aryl substituted semicar-
bazide with excellent yields under mild conditions. In all
cases, clean transformation could be detected by TLC. We be-
lieve that the present methodology is an important addition to
existing methodology.
2e: orange needle; Yield 96%; mp 125-126 C; IR
(KBr) max: 3320, 3050, 2995, 2880, 1675, 1580, 1490, 1433
(cm-1); 1H NMR (CDCl3) (ppm): 1.27 (t, 3H, CH3), 3.90 (q,
2H, CH2), 6.81-8.00 (m, 9H, Ar-H), 8.25 (s, 1H, NH); Anal.
Calcd. for C15H11N3O: C, 66.91; H, 5.58; N, 15.61. Found: C,
67.01; H, 5.30; N, 15.42.
EXPERIMENTAL SECTION
Melting points were determined on a Kolfler micro
melting points apparatus and measured in C without correc-
tion. Elemental analyses were performed on a Perkin-Elmer
240C analytical instrument. Infrared spectra were recorded
on a SP3-300 spectra photometer using KBr pellets. 1H NMR
spectra were measured in CDCl3 using TMS as internal stan-
dard with a JEOL-90Q NMR spectrometer. Mass spectra
were recorded on a KRATOS-AEI-MS50 (U.K.).
2f: brown tabular; Yield 92%; mp 122-124 C; IR
(KBr) max: 3220, 3020, 2965, 2900, 1695, 1580, 1495, 1430
(cm-1); 1H NMR (CDCl3) (ppm): 2.20 (s, 6H, 2CH3), 7.02-
8.02 (m, 8H, Ar-H), 8.21 (s, 1H, NH); Anal. Calcd. for
C15H15N3O: C, 71.15; H, 5.93; N, 16.60. Found: C, 70.94; H,
5.65; N, 16.79.
2g: yellow tabular; Yield 91%; mp 120-122 C; IR
(KBr) max: 3225, 3040, 2960, 2850, 1680, 1580, 1490, 1450
(cm-1); 1H NMR (CDCl3) (ppm): 2.25 (s, 6H, 2CH3), 7.80-
8.02 (m, 8H, Ar-H), 8.20 (s, 1H, NH); Anal. Calcd. for
C15H15N3O: C, 71.15; H, 5.93; N, 16.60. Found: C, 71.10; H,
5.75; N, 16.80.
General Procedure for the Preparation of Aryl Azo
Compounds
A mixture of aryl substituted semicarbazide (1 mmol),

Oxidation of Aryl Substituted Semicarbazide with NaNO2/NaHSO4·H2O/SiO2 J. Chin. Chem. Soc., Vol. 49, No. 3, 2002 399
2h: orange tabular; Yield 97%; mp 118-120 C; IR
(KBr) max: 3300, 3010, 2950, 2840, 1685, 1580, 1485, 1435
(cm-1); 1H NMR (CDCl3) (ppm): 2.24 (s, 6H, 2CH3), 7.42-
8.02 (m, 8H, Ar-H), 8.77 (s, 1H, NH); Anal. Calcd. for
C15H15N3O: C, 71.15; H, 5.93; N, 16.60. Found: C, 71.05; H,
5.73; N, 16.50.
(CDCl3) (ppm): 7.08-8.57 (m, 9H, Ar-H), 9.05 (s, 1H, NH);
Anal. Calcd. for C13H10N3OBr: C, 51.49; H, 3.33; N, 13.86.
Found: C, 51.60; H, 3.41; N, 13.71.
2q: red tabular; Yield 96%; mp 138-140 C; IR (KBr)
1
max: 3325, 3040, 1680, 1580, 1490, 1450 (cm-1); H NMR
(CDCl3) (ppm): 7.08-8.57 (m, 9H, Ar-H), 9.05 (s, 1H, NH);
MS (m/z): 305 (M+2), 303 (M+), 200, 198, 172, 170 (B), 105,
90, 77; Anal. Calcd. for C13H10N3OBr: C, 51.49; H, 3.33; N,
13.86. Found: C, 51.63; H, 3.44; N, 13.87.
2i: orange tabular; Yield 96%; mp 126-128 C; IR
(KBr) max: 3250, 3060, 2965, 2900, 1690, 1590, 1445, 920
(cm-1); 1H NMR (CDCl3) (ppm): 2.20 (s, 6H, 2CH3), 7.05-
8.02 (m, 8H, Ar-H), 8.22 (s, 1H, NH); Anal. Calcd. for
C15H15N3O: C, 71.15; H, 5.93; N, 16.60. Found: C, 71.01; H,
5.76; N, 16.88.
2r: orange tabular; Yield 97%; mp 133-135 C; IR
1
(KBr) max: 3300, 3020, 1680, 1580, 1485, 1440 (cm-1); H
NMR (CDCl3) (ppm): 7.26-8.00 (m, 9H, Ar-H), 8.57 (s, 1H,
NH); MS (m/z): 351 (M+), 246, 218 (B), 105, 90, 77; Anal.
Calcd. for C13H10N3OBr: C, 51.49; H, 3.33; N, 13.86. Found:
C, 51.63; H, 3.44; N, 13.87.
2j: orange needle; Yield 96%; mp 134-136 C; IR
(KBr) max: 3260, 3040, 1685, 1590, 1478, 1440, 923 (cm-1);
1H NMR (CDCl3) (ppm): 7.04-8.24 (m, 12H, Ar-H), 8.83 (s,
1H, NH); Anal. Calcd. for C17H13N3O: C, 74.18; H, 4.73; N,
15.27. Found: C, 74.42; H, 4.53; N, 15.50.
Received November 7, 2001.
2k: yellow needle; Yield 95%; mp 106-108 C; IR
1
(KBr) max: 3340, 3020, 1710, 1600, 1500, 1420 (cm-1); H
Key Words
NMR (CDCl3) (ppm): 7.09-8.03 (m, 9H, Ar-H), 8.45 (s, 1H,
NH); MS (m/z): 243 (M+), 138, 110 (B), 105, 90, 77; Anal.
Calcd. for C13H10N3OF: C, 64.19; H, 4.14; N, 17.28. Found:
C, 64.28; H, 4.18; N, 17.20.
Aryl substituted semicarbazide;
NaNO2/NaHSO4·H2O/SiO2; Mild conditions.
2l: orange tabular; Yield 92%; mp 82-84 C; IR (KBr)
1
max: 3340, 3020, 1710, 1600, 1500, 1420 (cm-1); H NMR
REFERENCES
(CDCl3) (ppm): 7.09-8.03 (m, 9H, Ar-H), 8.45 (s, 1H, NH);
Anal. Calcd. for C13H10N3OCl: C, 60.13; H, 3.88; N, 16.18.
Found: C, 60.21; H, 3.90; N, 16.15.
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2m: red tabular; Yield 98%; mp 84-86 C; IR (KBr)
1
max: 3260, 3030, 1680, 1600, 1480, 1430 (cm-1); H NMR
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2n: red tabular; Yield 95%; mp 139-141 C; IR (KBr)
1
max: 3320, 3050, 1680, 1600, 1585, 1440 (cm-1); H NMR
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2o: red tabular; Yield 93%; mp 70-72 C; IR (KBr)
:
max
3280, 3040, 1680, 1580, 1500, 1435 (cm-1); 1H NMR (CDCl3)
(ppm): 7.10-8.60 (m, 9H, Ar-H), 9.04 (s, 1H, NH); Anal.
Calcd. for C13H10N3OBr: C, 51.49; H, 3.33; N, 13.86. Found:
C, 51.79; H, 3.36; N, 13.94.
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2p: orange needle; Yield 98%; mp 94-96 C; IR (KBr)
1
max: 3320, 3030, 1700, 1580, 1500, 1430 (cm-1); H NMR
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