Melamine-(H2SO4)3/Melamine-(HNO3)3 Instead of H2SO4/HNO3: Benign System for Oxidation/Nitration Reactions from in situ NO2 +

Full text of DOI:10.1080/00304948.2019.1677994

Organic Preparations and Procedures International
The New Journal for Organic Synthesis
ISSN: 0030-4948 (Print) 1945-5453 (Online) Journal homepage: https://www.tandfonline.com/loi/uopp20
Melamine-(H2SO4)3/Melamine-(HNO3)3 Instead
of H2SO4/HNO3: Benign System for Oxidation/
+
Nitration Reactions from in situ NO2
Gholamabbas Chehardoli & Seyedeh Bahareh Azimi
To cite this article: Gholamabbas Chehardoli & Seyedeh Bahareh Azimi (2019): Melamine-
(H2SO4)3/Melamine-(HNO3)3 Instead of H2SO4/HNO3: Benign System for Oxidation/Nitration
+
Reactions from inꢀsitu NO2 , Organic Preparations and Procedures International, DOI:
10.1080/00304948.2019.1677994
To link to this article: https://doi.org/10.1080/00304948.2019.1677994
Published online: 06 Nov 2019.
Submit your article to this journal
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
https://www.tandfonline.com/action/journalInformation?journalCode=uopp20

Organic Preparations and Procedures International, 0:1–6, 2019
# 2019 Taylor & Francis Group, LLC
ISSN: 0030-4948 print / 1945-5453 online
DOI: 10.1080/00304948.2019.1677994
OPPI BRIEF
Melamine-(H2SO4)3/Melamine-(HNO3)3 Instead
of H2SO4/HNO3: Benign System for Oxidþation/
Nitration Reactions from in situ NO2
Gholamabbas Chehardoli1
and Seyedeh Bahareh Azimi2
1Medicinal Plants and Natural Products Research Center, Hamadan University
of Medical Sciences, Hamadan, Iran
2Research Center of Environment and Sustainable Development, Tehran, Iran
In spite of the tremendous importance of sulfuric and nitric acids,1,2 their uses are increas-
ingly limited, due to concerns about worker safety.3 There is a fundamental need to find
safer alternatives to these acids. One of these alternatives is the use of solid acids.4
Over the last two decades, applications of solid acids have become popular. Their
many benefits include easy handling, enhanced worker safety, fewer reactor corrosion
problems and the minimization of waste and by-products. The solid acids have proved
to be helpful in chemistry due to the useful activation of starting materials, reduction in
reaction times, substrate selectivity, and easy work-up.5
In previous studies on the application of solid acids,6–8 we had found that mela-
mine easily reacts with neat sulfuric acid and concentrated nitric acid to produce mela-
mine-(H2SO4)3 (I) and melamine-(HNO3)3 (II), respectively, in fast and clean reactions
(Scheme 1).9
The present paper shows that a mixture of these solid acids can be used as an oxi-
dizing system for the oxidation of urazoles and alcohols and can also be used for the
nitration of active aromatic rings under solvent-free conditions.
Initially, oxidation of 4-phenylurazole was run with melamine-(HNO3)3 in the
absence of melamine-(H2SO4)3. It was found that the reaction did not occur using a
ten-fold excess of melamine-(HNO3)3 even after a long reaction time. However, after
the simple addition of the melamine-(H2SO4)3, the reaction was complete within
5 minutes. This result prompted us to carry out the oxidation of a range of urazoles in
the presence of melamine-(H2SO4)3 [(I), 0.5 mmol] and melamine-(HNO3)3 [(II),
0.5 mmol] at room temperature in the absence of organic solvents. These conditions
were also successfully applied to the nitration of active aromatic rings. Since our mela-
mine-(H2SO4)3/melamine-(HNO3)3 system could not oxidize alcohols alone (Table 1,
Received June 19, 2018; in final form July 8, 2019.
Address correspondence to Gholamabbas Chehardoli, Medicinal Plants and Natural Products
Research Center, Hamadan University of Medical Sciences, Hamadan, Iran. E-mail:
cheh1002@gmail.com
Color versions of one or more of the figures in the article can be found online at www.tandfon-
line.com/uopp.
1

2
Chehardoli and Azimi
Scheme 1. Simple synthesis of melamine-(H2SO4)3 (I) and melamine-(HNO3)3 (II).
Scheme 2. Suggested mechanism for the oxidation of alcohols by melamine-(H2SO4)3/melamine-
(HNO3)3 system in the presence of KBr as the catalyst.
entry 19), we used KBr as a catalyst in the presence of several drops of water. All our
reactions were complete within 5-10 minutes. All products were obtained with good
yields (Table 1).
These oxidation/nitration reactions, using the melamine-(H2SO4)3/melamine-
(HNO3)3 system, have the following advantages: a) in comparison with concentrated
sulfuric acid and fuming nitric acid, melamine-(H2SO4)3 and melamine-(HNO3)3 are
benign and easy to handle; b) the formation of these solid acid reagents is facile; c) the
procedure is efficient; d) yields are good to excellent; e) work-up is convenient since
these acids are insoluble in CH2Cl2 and many other solvents; and g) the procedure is
solvent-free and matches with some of the goals of green chemistry.10
As we reported in our previous papers,11 there is a reasonable mechanism for the
oxidation of alcohols by the melamine-(H2SO4)3/melamine-(HNO3)3 system in the pres-
ence of KBr as caþtalyst and a few drops of H2O. This mechanism proceeds via in situ
generation of NO2 and then Brþ (Scheme 2).
In summary, melamine-(H2SO4)3 and melamine-(HNO3)3 are two benign and easy-
handling organic solid acids. A mixture of them acts as an efficient system for the oxi-
dation of urazoles and alcohols as well as for the nitration of active aromatic rings
under heterogeneous and mild conditions. Our results should be set within the context
of our previous reports.6,12–14 Compared to the use of the parent mineral acids, this
method gives convenience, enhanced worker safety, and the minimization of waste.
Experimental Section
We purchased chemicals from Merck and Sigma-Aldrich chemical companies and used
them as received. The products were characterized by comparison of their spectral (1H-
NMR, 13C-NMR or IR) and physical data with reported values, and representative pro-
cedures are given below. We prepared the melamine-(H2SO4)3 and melamine-(HNO3)3
according to our previous report.9

Benign System for Oxidation/Nitration Reactions
3
Table 1
Fast Oxidation of Urazoles, Alcohols, and Nitration of Activated Aromatic Rings by
Melamine-(H2SO4)3/Melamine-(HNO3)3 System in the Absence of Organic Solvents
Entry
1
Substratea,b
Product
Isolated Yield (%)
87
85
81
90
2
3
4
5
92
6
7
77
87
8
80
(Continued)

4
Chehardoli and Azimi
Table 1
(Continued)
Entry
9
Substratea,b
Product
Isolated Yield (%)
77
10
11
83
78
12
13
14
15
82
77
85
79
16
17
–
–
–
–
18
Benzyl alcohol
Benzaldehyde
84
(Continued)

Benign System for Oxidation/Nitration Reactions
5
Table 1
(Continued)
Entry
Substratea,b
Product
Isolated Yield (%)
c
19
20
21
22
23
Benzyl alcohol
–
–
4-Cl-Benzyl alcohol
4-Br-Benzyl alcohol
4-F-Benzyl alcohol
Benzhydrol
4-Cl-Benzaldehyde
4-Br-Benzaldehyde
4-F-Benzaldehyde
Benzophenone
85
89
91
83
aMelamine-(H2SO4)3/melamine-(HNO3)3/substrate: (0.5:0.5:1 mmol).
bFor the oxidation of alcohols, a catalytic amount of KBr and 3 drops of water are needed.
cWithout KBr.
Oxidation of 4-Phenylurazole
4-Phenylurazole (3a, 0.177 g, 1 mmol) was added to the mixture of melamine-(H2SO4)3
(0.21 g, 0.5 mmol), and melamine-(HNO3)3 (0.16 g, 0.5 mmol) and the mixture was
ground with a mortar and pestle for 5-10 minutes. Then, the product (4-phenyl-1,2,4-tri-
azole-3,5-dione) was extracted with dichloromethane (2 ꢀ 10 mL). Simple distillation of
1
the CH2Cl2 gave the pure product. H-NMR (FT-90 MHz-CDCl3) d 7.48 (s, 5H, Ar);
13C-NMR (FT-22.5 MHz-CDCl3) d 124.2, 129.01, 129.9, 157.971.15
Nitration of 4-Hydroxybenzonitrile
4-Hydroxybenzonitrile (13a, 0.119 g, 1 mmol) was added to the mixture of melamine-
(H2SO4)3 (0.21 g, 0.5 mmol), and melamine-(HNO3)3 (0.16 g, 0.5 mmol) and the mix-
ture was ground with a mortar and pestle for 5-10 minutes. Then, the product (4-
hydroxy-3-nitrobenzonitrile) was extracted with CH2Cl2 (2 ꢀ 10 mL). Simple distillation
of the solvent gave the pure product. IR (KBr) cmꢁ1 3253, 2239, 1525, 1363, 1620,
1487; 1H-NMR (FT-90 MHz-CDCl3) d 10.83 (b, 1H), 8.43 (d, 1H), 7.77 (m, 1H),
7.322(d, 1H).16
Oxidation of Benzhydrol
Benzhydrol (23a, 0.184 g, 1 mmol), was added to the mixture of melamine-(H2SO4)3
(0.21 g, 0.5 mmol), melamine-(HNO3)3 (0.16 g, 0.5 mmol), KBr (0.023 g, 0.2 mmol) and
3 drops of water. The mixture was ground with a mortar and pestle for 5-10 minutes.
Then the product (benzophenone) was extracted with CH2Cl2 (2 ꢀ 10 mL). The solution
was dried by anhydrous sodium sulfate (3 g) and filtered off after 5 minutes. Simple dis-
tillation of the solvent gave the pure product. IR (KBr) (cmꢁ1) 3055, 1656, 1593, 1572,
1316, 971; 1H-NMR (FT-90 MHz-CDCl3) d 7.43-7.71(m, 10H, Ar).17
Acknowledgments
The authors thankfully acknowledge partial support for this research by the Deputy of
Research, Hamadan University of Medical Sciences (Grant No. 940208495).

6
Chehardoli and Azimi
ORCID
Gholamabbas Chehardoli
http://orcid.org/0000-0002-8760-3837
References
1. R. A. Cox, Acc. Chem. Res., 20, 27 (1987).
2. M. Thiemann, E. Scheibler, and K. W. Wiegand, Ullmann's Encyclopedia of Industrial
Chemistry, Weinheim, Wiley-VCH Verlag GmbH & Co., 2012, p. 170 .
3. A. Flammiger and H. Maibach, Cutan. Ocul. Toxicol., 25, 55 (2006).
4. S. Singhal, S. Agarwal, S. Arora, N. Singhal, and A. Kumar, Catal. Sci. Technol., 7, 5810
(2017).
5. P. Gupta and S. Paul, Catal. Today, 236, 153 (2014).
6. G. Chehardoli, M. A. Zolfigol, S. B. Azimi, and E. Alizadeh, Chin. Chem. Lett., 22, 827
(2011).
7. A. Hasaninejad, M. A. Zolfigol, G. Chehardoli, and M. Mokhlesi, J. Serb. Chem. Soc., 75,
307 (2010).
8. M. A. Zolfigol, M. Bagherzadeh, S. Mallakpour, G. Chehardoli, E. Kolvari, A. G.
Choghamarani, et al., Catal. Commun., 8, 256 (2007).
9. G. Chehardoli and M. A. Zolfigol, J. Sulfur Chem., 36, 606 (2015).
10. G. Imanzadeh and R. Hadi, Iran. Chem. Commun., 6, 70 (2018).
11. M. A. Zolfigol, F. Shirini, G. Chehardoli, and E. Kolvari, J. Molecul. Catal. A: Chem., 265,
272 (2007).
12. G. Chehardoli, M. A. Zolfigol, E. Ghaemi, E. Madrakian, K. Niknam, and S. Mallakpour, J.
Heterocycl. Chem., 49, 596 (2012).
13. M. Rasouli, M. A. Zolfigol, M. H. Moslemin, and G. Chehardoli, Green Chem. Lett. Rev.,
10, 117 (2017).
14. M. A. Zolfigol, M. Bagherzadeh, G. Chehardoli, S. E. Mallakpour, and M. Mamaghani, J.
Chem. Res. (S), 390 (2001).
15. S. E. Mallakpour, J. Chem. Educ., 69, 238 (1992).
16. A. Cornlis, P. Laszlo, and P. Pennetreau, Bull. Soc. Chim. Belg., 93, 961 (1984).
17. A. Khazaei, F. Abbasi, M. Kianiborazjani, and S. Saednia, J. Braz. Chem. Soc., 25, 361
(2014).