Ultrasonically Assisted Rate Enhancements in Trichloroisocyanuric Acid/DMF/NaNO2 Triggered Nitration of Aromatic Compounds and Decarboxylative Nitration of α,β-Unsaturated Acids

Article abstract of DOI:10.1080/00397911.2015.1075044

An efficient and safe method for nitration of aromatic compounds and decarboxylative nitration of α,β-unsaturated acids was developed using trichloroisocyanuric acid (TCICA)/dimethylformamide (DMF) in the presence of NaNO₂. The reaction times of conventional protocol reduced from 8-10 h to 1.0-1.5 h (60-90 min) under sonication, even though the yields are comparable under both the conditions.

Full text of DOI:10.1080/00397911.2015.1075044

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: http://www.tandfonline.com/loi/lsyc20
Ultrasonically Assisted Rate Enhancements
in Trichloroisocyanuric Acid/DMF/NaNO2
Triggered Nitration of Aromatic Compounds and
Decarboxylative Nitration of α,β-Unsaturated Acids
Mukka Satish Kumar, Kamatala Chinna Rajanna, Marri Venkateswarlu,
Purugula Venkanna & Pondichery Kuppuswamy Saiprakash
To cite this article: Mukka Satish Kumar, Kamatala Chinna Rajanna, Marri Venkateswarlu,
Purugula Venkanna & Pondichery Kuppuswamy Saiprakash (2015): Ultrasonically Assisted
Rate Enhancements in Trichloroisocyanuric Acid/DMF/NaNO2 Triggered Nitration of
Aromatic Compounds and Decarboxylative Nitration of α,β-Unsaturated Acids, Synthetic
Communications, DOI: 10.1080/00397911.2015.1075044
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Date: 09 September 2015, At: 06:22

Synthetic Communications1, 0: 1–8, 2015
Copyright © Taylor & Francis Group, LLC
ISSN: 0039-7911 print/1532-2432 online
DOI: 10.1080/00397911.2015.1075044
ULTRASONICALLY ASSISTED RATE ENHANCEMENTS
IN TRICHLOROISOCYANURIC ACID/DMF/NaNO2
TRIGGERED NITRATION OF AROMATIC COMPOUNDS
AND DECARBOXYLATIVE NITRATION OF
a,b-UNSATURATED ACIDS
Mukka Satish Kumar, Kamatala Chinna Rajanna, Marri
Venkateswarlu, Purugula Venkanna, and Pondichery
Kuppuswamy Saiprakash
Department of Chemistry, Osmania University, Hyderabad, India
GRAPHICAL ABSTRACT
Abstract An efficient and safe method for nitration of aromatic compounds and
decarboxylative nitration of a,b-unsaturated acids was developed using trichloroisocyanuric
acid (TCICA)=dimethylformamide (DMF) in the presence of NaNO2. The reaction times
of conventional protocol reduced from 8–10 h to 1.0–1.5 h (60–90 min) under sonication,
even though the yields are comparable under both the conditions.
Keywords Aromatic compounds; decarboxylative nitration of a,b-unsaturated acids;
NaNO2; nitration; rate enhancements; sonication; trichloroisocyanuric acid=DMF
INTRODUCTION
Nitro aromatic compounds, nitro styrene, and nitro olefin derivatives are
important key intermediates widely used as building blocks in the synthesis of many
Received April 4, 2015.
Address correspondence to K. C. Rajanna, Department of Chemistry, Osmania University,
Hyderabad 500 007, India. E-mail: kcrajannaou@yahoo.com
1

2
M. S. KUMAR ET AL.
diverse products of pharmaceutical importance, polymers, dyes, pesticides, and
explosives. Nitration of aromatic compounds is attained by means of the electrophi-
lic substitution reaction has attracted great interest for more than five decades.[1]
Nitration using mixed acid is a universal nitration technique that proceeds rapidly
and giving excellent yields of nitro products.[2] In this procedure nitronium ion is
generated by ionization of HNO3 in the presence of concentrated mineral acids such
as H2SO4. A major drawback in this procedure is excessive acid waste stream, which
creates pollution and is hazardous to the environment. Several nitration protocols
have been reported in literature that modify the classical nitration procedure.
Reagents[3] such as guanidine nitrate, nitrate ester, and ethylene glycol dinitrate
are noteworthy among these, which reduced reaction times and enhanced product
yields significantly. Efficient and facile nitration of phenols has achieved ultrasoni-
cally[4] using HNO3=ZnCl2, which significantly afforded the nitro compounds with
high region- and chemoselectivity. Aromatic nitration has also been reported using
urea nitrate, nitro urea,[5] and thiourea nitrate[6] in concentrated sulfuric acid; corre-
sponding mono nitro derivatives were obtained with abnormal yields under mild
conditions. Recently, it was found that nitration of aromatic compounds could be
carried out in the presence of perfluorinated rare-earth metal salts[7] with various
fluorous solvents using 60% HNO3. A novel method for nitration of aromatic
compounds has been found using Mg (NO3)2 · 6H2O in water medium catalyzed
by alumina sulfuric acid.[8] Synthesis of nitro derivatives of 4-hydroxybenzaldehyde
and picric acid was achieved from 4-hydroxyphenylglycine using HNO3 in water.[9]
Researchers[10] recently reported the nitro decarboxylation of a,b-unsaturated car-
boxylic acids using nitric acid, catalyzed by AIBN. Nitration and nitro decarboxyla-
tion could be achieved conveniently by using tertiary butyl nitrite[11–14] and several
other reagents[15–21] under acid-free conditions. For the past few years, our research
group has also been involved in the development of nitration methods under
conventional and nonconventional conditions[22–27] for the synthesis of nitro
aromatic compounds, nitro olefins, and b-nitrostyrenes using a variety of reagents
and=or catalysts.
Trichloroisocyanuric acid (TCICA) is an inexpensive, less toxic, less corrosive,
and more effective bleaching agent as well as laboratory reagent used in organic syn-
thesis.[28] A recent review[29] provided an excellent bibliography on TCICA as a safe
and efficient reagent for an array of oxidation and chlorination reactions.[30–33]
Recently we have reported that TCICA=DMF is an efficient reagent for chlorodehy-
dration of alcohols.[34] Encouraged by these results, we have undertaken nitration of
aromatic compounds and decarboxylative nitration of a,b-unsaturated carboxylic
acids using TCICA=DMF reagent in the presence of NaNO2 under mineral acid-free
conditions. Control experiments indicated that the reactions under conventional con-
ditions are too sluggish even at elevated temperatures. Ever since the concept of
chemical ultrasonics was introduced in 1927, a number of chemical reactions have
been observed to occur under sonicated conditions.[35] Ultrasonically assisted syn-
thesis has now become the method of choice for many chemists and biochemists
for a multitude of reactions for one reason: Reactions that took hours, or even days,
to complete can now be performed in minutes with better yields and cleaner chemis-
tries. In the recent past, a wide number of synthetically useful organic reactions have
been conducted under ultrasonic sonication.[36–38] In a recent review,[37] Bremner

TCICA/DMF/NaNO2 NITRATION
3
Scheme 1. TCICA=DMF=NaNO2-triggered nitration reactions.
excellently elaborated some of the more modern uses of ultrasound in organic
synthesis in different sections such as oxidations, carbon–nitrogen bond formation,
carbon–carbon bond formation, cycloadditions, and bond cleavage reactions in
biological systems and sonochemical switching. Encouraged by these findings, we
have studied the reactions under ultrasonication and have been successful in
enhancing the reaction rates (Scheme 1).
RESULTS AND DISCUSSION
Nitration of aromatic compounds and decarboxylative nitration of a,b-
unsaturated carboxylic acids went smoothly (Scheme 1) with TCICA=DMF=NaNO2
reagent system under mineral-acid-free conditions. Representative data are presented
in Tables 1 and 2.
Mechanism of the reaction could be explained through the formation of
[TCICA-DMF] adduct comprising the chloro methyleniminum moiety in the pre-
equilibrium step as shown in Scheme 2. Infrared spectroscopic (IR) studies of
DMF, TCICA, and prepared adduct were taken up separately to confirm the forma-
tion of TCICA=DMF adduct. IR spectrum of DMF (liquid film) depicted a broad
band at 1675 cmꢀ1 corresponding to C=O stretching frequency, which is lower than
an unsubstituted C=O bond. The observed reduction in the bond order of the car-
bonyl C=O bond followed by an increase in the carbon–nitrogen bond order could
be explained probably because of the two possible resonance structures of amide.
Another broad band appeared in the in the range of 3336–3485 cmꢀ1 may be attrib-
uted to probably due to O-H arising from trace amounts of alcohol impurities
present in the commercial sample. The infrared spectrum of TCICA indicated a
broad band at 1737 cmꢀ1, attributed to C=O stretching frequency. However, in
any case the infrared spectrum recorded for the mixture of TCICA=DMF showed
that 1671 (H, broad) and 1747.15 (M to H) bands underwent significant shifts, indi-
cating the interaction of TCICA with DMF leading to the formation of [TCICA-
DMF] adduct, in the lines of Vilsmeier–Haack adduct formation in Vilsmeier–Haack
reactions.[39] [TCICA-DMF] adduct, being a chloro iminium species, probably reacts
with NaNO2 to generate (in situ) nitro iminium ion (nitro methyleniminum ion),

4
M. S. KUMAR ET AL.
Table 1. Nitration of aromatic compounds using TCICA=DMF and NaNO2 (isolated yields)
Conventional
RT (h) Yield (%)
Sonication
No.
Substrate
Phenol
Toluene
Benzoic acid
Aniline
Benzaldehyde
Nitro benzene
Benzamide
Acetanilide
Chloro benzene
Furan
Product
RT (min)
Yield (%)
1
2
3
4
5
6
7
8
p-NO2 phenol
p-NO2 toluene
m-NO2 benzoic acid
p-NO2 aniline
m-NO2 benzaldehyde
m- di NO2 benzene
m-NO2 benzamide
p-NO2 acetanilide
p-NO2 chloro benzene
2-NO2 furan
7.5
8.0
9.5
8.0
10.0
9.0
9.0
8.5
8.0
8.5
8.0
10.0
72
65
64
70
64
60
58
55
56
55
66
55
65
70
80
75
80
85
80
75
75
80
85
90
78
68
60
75
68
64
60
58
62
60
70
58
9
10
11
12
Thiophene
2-Naphthol
2-NO2 thiophene
1-NO2-2-naphthol
which then interacts with the substrate to afford the corresponding nitro aromatic
compound as shown in Scheme 2 (path I).
However, in the case of decarboxylative nitration of a,b-unsaturated carboxylic
acids, the mechanism is explained through the conversion of the chloroiminium ion
into the nitroiminium ion in the presence of NaNO2. The nitroiminium cation thus
formed converts a,b-unsaturated carboxylic acids into a nitroolefin derivative
through a decarboxylation step as shown in path II of Scheme 2.
The reaction times for most of the studied reactions under conventional method
are in the range of 8 to 10 h. In the past few decades, ultrasonic-assisted reactions have
received the attention of chemists with a view to save energy and improve the environ-
mental friendliness of the reaction protocols.[35–38] When the reactions are conducted
in the sonicator, nitration of aromatic compounds and decarboxylative nitration of
a, b-unsaturated carboxylic acids underwent smoothly under present experimental
conditions, which can be seen from the data presented in Table 2. The pioneering work
Table 2. Decarboxylative nitration of a,b-unsaturated acids using TCICA=DMF and NaNO2
(isolated yields)
Conventional
RT (h) Yield (%)
Sonication
No.
Cinnamic acid (CA)
Product
RT (h)
Yield (%)
1
2
3
4
5
6
7
8
CA
b-Nitro styrene
8.0
8.5
8.0
8.5
9.0
8.5
8.5
8.0
7.5
10.0
10.0
9.5
72
62
66
65
64
60
66
66
76
64
60
58
65
75
70
70
85
85
80
70
60
95
85
85
75
65
70
70
68
64
72
68
80
65
65
62
2-Cl CA
4-Cl CA
4Br CA
2-Me CA
2-OMe CA
4-Me CA
4-OMe CA
4-OH CA
4-NO2 CA
CRA
2-Cl b-nitro styrene
4-Cl b-nitro styrene
4-Br b-nitro styrene
2-Me b-nitro styrene
2-OMe b-nitro styrene
4-Me b-nitro styrene
4-OMe b-nitro styrene
4-OH b-nitro styrene
4-NO2 b-nitro styrene
1-Nitro ethene
9
10
11
12
AA
1-Nitro propene

TCICA/DMF/NaNO2 NITRATION
5
Scheme 2. Mechanism of nitration reactions using TCICA=DMF reagent.
of Mason and Suslick on ultrasonics has emerged as boon to chemists to use ultrasonics
as a green reaction tool to achieve organic synthesis.[36,37] Under sonication, reaction
times reduced amazingly from 8 to 10 h under conventional methods to 60 to 90 min.
Such dramatic sonocatalysis could be attributed to cavitation phenomenon as explained
earlier.[35–38] The use of ultrasound in liquid-phase chemical reactions provides specific
activation based on acoustic cavitation, a physical phenomenon. Cavitation is a process
in which mechanical activation destroys the attractive forces of molecules in the liquid
phase. During sonication the growth and collapse of cavitation bubbles occur violently
under the influence of the rarefaction and compression pressure cycles of ultrasound.
Collapsing cavities attain high temperatures and pressures, which are responsible for
activation of molecules; cavitation efficiently directs the energy by straining the mol-
ecule, reshaping the potential energy surface.
EXPERIMENTAL
All the chemicals were purchased from Aldrich or Arcos Organics and used
without further purification. Analytical thin-layer chromatography (TLC) was

6
M. S. KUMAR ET AL.
carried out using Merck aluminum-backed 0.2-mm silica-gel 60 F-254 plates. Column
chromatography was conducted using Merck silica gel 60 (230–400 mesh). Perkin–
Elmer FT-IR and Varian VNMRS 400-MHz spectrometers were used for recording
1
infrared (IR) and H NMR spectra. Chemical shifts are reported as values in ppm
relative to CHCl3 (7.26), and tetramethylsilane (TMS) was used as internal standard.
A Buchi B-545 capillary melting-point apparatus is used for the determination of
melting points. Melting points reported herein are uncorrected. Mass spectra were
obtained on a ZAB-HS mass spectrometer using electrospray ionization (ESI).
Preparation of TCICA=DMF Reagent
Method of preparation of TCICA=DMF reagent and its characterization is
similar to the one described in our recent publication.[34] This reagent was always
prepared fresh prior to use in the decarboxylative nitration reaction. One mol of each
reactant (viz., TCCA and DMF) was added to CH2Cl2 solvent in a round-bottomed
flask and stirred for about 2–3 h at room temperature.
Conventional Procedure for Synthesis of Nitro Compounds Using
TCICA=DMF Reagent
To 0.01 mol phenol (as a typical example for aromatic compounds), about
0.01 mol of TCICA=DMF reagent and sodium nitrite (1 g) were added with CH2Cl2
or acetonitrile (25 mL) in a previously cleaned round-bottom flask and stirred under
reflux condition about 8 to 10 h. The completion of the reaction was checked by
TLC. After completion the reaction mixture was washed with NaHCO3 solution
and then treated with ethyl acetate. The organic layer was separated, dried over
anhydrous MgSO4, evaporated under vacuum, and purified with column chromato-
graphy using ethyl acetate–hexane as eluent to get pure product 4-nitro phenol as
yellow powder (mp 111–113 °C) in 85% yield, IR (KBr) (nmax=cmꢀ1): 3331, 1614,
1592, 1500, 1346; 1H NMR (300 MHz, CDCl3): d 9.95 (s 1H, OH), 6.95 (d 2H, J ¼ 8
Hz), 8.15 (d 2H, J ¼ 8 Hz); 13C NMR (75 MHz, CDCl3) d115.6, 126.4, 141.4, 161.8;
m=z ¼ 139.
Ultrasonically Assisted Synthesis of Nitro Compounds Using
TCICA=DMF Reagent with Sodium Nitrite
The reaction mixture containing centimolar molar organic substrate,
[TCICA=DMF] reagent, and sodium nitrite were added to the CH2Cl2 or acetonitrile
in a clean round-bottomed flask clamped in an ultrasonic bath with a frequency of
33 kHz and 100 W electric power rating and stirred for about 1.0 to 1.5 h. After
completion, the reaction mixture was treated with NaHCO3 solution, followed by
the addition of ethyl acetate. The separation and purification procedure is almost
the same as the previous procedure.
CONCLUSIONS
In summary, the authors have developed a safe method for nitration of aro-
matic compounds and decarboxylative nitration of a,b-unsaturated acids using

TCICA/DMF/NaNO2 NITRATION
7
[TCICA=DMF] adduct in the presence of NaNO2 under mineral-acid-free
conditions. This reaction is very useful both from economical and environmental
points of view, displaying the advantages of (i) operational simplicity, (ii) mild
reaction conditions, (iii) avoidance of organic solvents and toxic and expensive
reagents, (iv) short reaction times, and (v) high product yields.
ACKNOWLEDGMENTS
The authors thank Osmania University authorities and the chemistry head and
principal of Nizam College, T. Navaneeth Rao, for constant encouragement and
support.
FUNDING
The authors thank the University Grants Commission, New Delhi, for
financial support in the form of Rajiv Gandhi Postdoc Fellowship awarded to
M. Venkateswarlu.
SUPPLEMENTAL MATERIAL
Spectroscopic results of certain compounds; IR spectra of TCICA, DMF, and
(TCICA-DMF) adduct; and NMR and mass spectral data of certain isolated
products for this article can be accessed on the publisher’s website.
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