Microwave mediated solvent free synthesis of formazans catalyzed by simple ionic liquids derived from dialkylammonium salts

Article abstract of DOI:10.1039/c5ra06363a

A microwave mediated, ionic liquid catalyzed, VOC free and one pot synthesis of formazans was developed. In an alternative procedure, resin immobilized diazonium ions was used as a solid supported reaction for formazan synthesis. The efficiency of both the procedures was examined with respect to yield of product, reduction of reaction time and environmental impact. Products were obtained in a short reaction time and in moderate to high yield. This study was undertaken to find an alternative green protocol for the synthesis of formazans using ionic liquid as catalyst in aqueous media in the absence of corrosive mineral acids, buffered solutions and VOCs.

Full text of DOI:10.1039/c5ra06363a

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Microwave mediated solvent free synthesis of
Cite this: DOI: 10.1039/x0xx00000x
formazans catalyzed by simple ionic liquids derived
from tetraalkylammonium salts
Received 00th January 2012,
Accepted 00th January 2012
Pranab Jyoti Das * and Jesmin Begum.
DOI: 10.1039/x0xx00000x
A microwave mediated, ionic liquid catalyzed, VOC free and one pot
synthesis of formazans developed . In an alternative procedure, resin
immobilized diazonium ions used as a solid supported reaction for formazan
synthesis. The efficiency of both the procedures examined with respect to
yield of product , reduction of reaction time and environmental impact.
Products obtained in a short reaction time and in moderate to high yield. This
study was undertaken to find an alternative green protocol for the synthesis of
formazans using ionic liquid as catalyst in aqueous media in the absence of
corrosive mineral acids , buffered solutions and VOCs.
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Introduction
Formazan also find extensive use in analytical
Formazans are a class of high nitrogen
compounds first reported by Von Pechmann1 and
by Bamberger2. Several studies have been
reported related to establishment of their
structure, photochemical transitions, tautomer
formation and redox potential measurements.
Formazans are characterized by their prominent
πꢀπ* transitions which are sensitive to
substituents present in the phenyl rings, nature of
the solvent and acidity and basicity of the
medium3ꢀ5.
chemistry6,7 and their
thermochemical
photochemical and
properties have been
investigated8. They are reported to possess a
wide spectrum of biological activities such as
antiviral9,10, antimicrobial11,12, anti inflammatory,
analgesic13 and antifungal14 properties.
Synthetic methods for their preparation have been
reviewed earlier15 . Their synthesis is based on two
general procedures. The first is the reaction of
aryldiazonium salts with phenylhydrazones of
aldehydes in basic medium and the second is based
on coupling of aryldiazonium ions with active
methylene groups followed by Japp Klingermann
rearrangement16. However, these methods suffered
from the fact that a variety of products are obtained
depending on the temperature and basicity of the
medium. These two parameters play key roles in
Department of Chemistry, Gauhati University, Guwahati 781014, Assam,
India.
Eꢀmail: pjd23@rediffmail.com
Electronic Supplementary Information (ESI) available: [1H NMR and 13C
NMR spectra, HRMS data of all new compounds synthesized, their
methods of preparations Graphics of the reaction sequence. See
DOI: 10.1039/b000000x/
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the synthesis and requires fine control for obtaining range of ionic liquids, the salts of imidazolium,
good yields. Newer methods of synthesis are ammonium, thiazolium cations are especially
reported and notable among them are the use of popular and simple methods of their synthesis and
solidꢀliquid phase transfer catalysts17ꢀ20
,
liquidꢀ characterization have been reported38ꢀ42
.
liquid systems and crown ethers21, methods Imidazolium based IL are reported to be
reported by Tezcan et al22ꢀ25 and a green method biodegradable provided the Nꢀalkyl group has more
26
using the solid Lewis acid, BF3ꢀSiO2 . The than four carbon atoms or has a hydroxyl
commonly used method of synthesis involves three groups43.Their applicability in organic synthesis
steps, the multiplicity of steps necessarily decreases have been widely explored. However, the use of
the yield. Further since diazotization is the key step some of these IL is less attractive due to their high
which requires the use of strong mineral acids and cost . Thus it is necessary to explore possibilities of
very low temperature, use of corrosive substances preparing less expensive IL which may exhibit
and temperature control cannot be avoided. In comparable, if not better , utility as catalyst and/or
many diazocoupling reactions, acid catalyzed side solvent.
reactions of the diazonium ions is usually observed
further, acid sensitive substrates makes the
Results and discussion
synthesis even more cumbersome. Finally the use
of bases to accelerate the reaction and the necessary
effective ionic liquids for the synthesis of
use of organic solvents in the final reaction step
between diazonium ions and the phenylhydrazone
easily available dialkylamines and used them as
not only reduces yield due to insolubility of the
diazonium ions in organic solvent but also makes
reaction of aromatic aldehydes, phenylhydrazine
the procedures unacceptable from the standpoint of
During the course of our study in developing cost
formazans ,we prepared acidic ionic liquids from
catalyst for a microwave mediated four component
aromatic amines and NaNO2 for the synthesis of
green chemistry. While the only solvent free
formazans in appreciably reduced reaction time as
protocol reported by Bamonri et al27 was an
well as in high yield. Three different ionic liquids,
improvement over other procedures however, the
namely diethylammoniumhydrogensulphate, diꢀnꢀ
use of NaOH and BF3ꢀetherate prompted us to
look for better alternatives .
propylammoniumhydrogensulphate
and
diꢀnꢀ
butylammoniumhydrogensulphates were prepared
by a reported procedure47 . Earlier results indicated
a decrease in thermal stability according to the
sequence [(nꢀpropyl)2NH2]HSO4> [Et2NH2]HSO4>
[(nꢀbutyl)2NH2]HSO4 47. Since thermal stability of
the ionic liquid did not paly a significant part in the
reaction being presently studied ,we chose to use
[Et2NH2]HSO4 in all the synthesis reported here. A
trial reaction was examined using a mixture of
1:1:1 molar proportion of 4ꢀchloraniline,
benzaldehyde, phenylhydrazine , 1.2 mole of
NaNO2, 10 mol% of [Et2NH2]HSO4 and 1 mL of
deionized water. The mixture was thoroughly
ground to a homogeneous mixture. A deep red
colour developed which lead us to believe that the
Ionic liquids are recognized as environmentally
harmless media because of their low vapour
pressure, high thermal and chemical stability and
excellent solubilising characteristics. Their unique
properties and the possibility of recovery for reuse
resulted in their wide acceptance as media in many
reactions and as catalysts as well . Reports are also
available where ionic liquids have played dual role
of a solvent and a catalyst . They are also known to
influence the rate and selectivity of reactions. At
present the domain of their application have
widened attracting the attention of chemists with
widely varied research interest28ꢀ37
.
Among the
2 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C5RA06363A
four component reaction could be accomplished by
grinding method only , however, work up of the
product indicated that grinding at room temperature
gave only about 30ꢀ40% yield. Having failed to
obtain good yield, we exposed the well grounded
mixture of the reactants in the same proportion to
microwave irradiation ( 240 Watt) for 1.0 to 1.5
min and obtain the target product in 89% yield.
Microwave irradiation at 240 Watt was found to be
most suitable as increase in wattage resulting in
charring of the reaction mixture leading to poor
yield. To the best of our knowledge, acidic ionic
liquids have never been used as catalyst for the
synthesis formazans and hence this method
assumes importance. The procedure was then
generalized by using a wide variety of reactants and
yields were found to be good and reaction time
short. The yields of products were found to be
independent of the nature of substituent groups in
the carbonyl compounds and also in the aromatic
amines used. Strict control of pH and temperature
was unnecessary. Unlike previously reported
procedure, this procedure is an excellent one pot
four component synthesis of the formazan. The
reaction is shown in scheme 1
[Et2NH2]HSO4
ArꢀNH2
NaNO2
HNO2
NaHSO4
HNO2
Et2NH
ArꢀN2
ONH2Et2
H
: O:
NH2Et2
H
: NH2NHꢀPh
NH2NHꢀPh
NNHAr
NNHAr
HSO4
H2O
H
H2SO4
Et2NH
NNHAr
ArꢀN2
N=NꢀAr
[Et2NH2]HSO4
H2SO4
Et2NH
Scheme 2: Proposed mechanism of synthesis of
formazan catalyzed by ionic liquid
In addition to the use of IL as catalyst for the
synthesis of formazans, we carried out a solid
phase synthesis of formazans . In our earlier
communications we had developed a method for
immobilizing diazonium ions onto cation exchange
resin with the aim of stabilizing them and used the
diazonium ions successfully for the synthesis of
triazenes and the azo compounds44ꢀ46. In this study,
we extended the use of the immobilized diazonium
ions for the synthesis of formazans in a solid phase
reaction. In a typical solid phase procedure , the
diazonium ions from 4ꢀchloroaniline was prepared
by the conventional method using mineral acid and
NaNO2 at 0ꢀ5oC and the corresponding diazonium
ion obtained was immobilized on to an ion
exchange resin namely Amberlite IR120(Na+) .
Phenylhydrazones of benzaldehydes were prepared
separately by established procedure23,dissolved in
cyclohexane and brought into reaction with the
resin immobilized diazonium ions. The reaction
was instantaneous as observed by the change in
colour of the resin. The coloured resin was
recovered, dried and the product 1ꢀ(4ꢀchloroꢀ
phenyl)ꢀ3,5ꢀdiphenylformazan obtained by soxhlet
Ph
N
NH2
CHO
NHNH2
H
N
NaNO2, ionic liquid
N
N
+
+
microwave
R
R
R 1
240watt/ 60-90 sec
R1
Formazan
Scheme 1: One pot solvent free synthesis of formazans
using acidic ionic liquids mediated by microwave
A proposed mechanism of the synthesis of
Formazan catalyzed by ionic liquid is shown in
Scheme 2
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extraction of the resin beads using ethylacetate as procedures, products were obtained in a pure form
the solvent. Reduced pressure removal of the
solvent gave the products in moderate yield. The
procedure was then generalized by using several
combinations of different aldehydes and aromatic
amines (Scheme 3)
as indicated by TLC using prepared silicagel plates
and ethylacetate: petroleum ether ( 40ꢀ60) 1:9 as
eluent and elaborate purification procedures were
not necessary. The physical characteristics of the
products and a comparison of the two techniques
used is summarized in Table 1.
+
Table 1. Physical characteristics of formazans synthesized in
]Cl
N2
NH2
acidic IL and by solid phase synthesis procedure.
NaNO2/ HCl
0-5oC
R
P
R
Yield ( %)
in
Mp oC
+
]Cl
N2
Entry
R
R1
+
N2
SO3
P
SO Na
3
+
A*
77
69
70
66
62
72
70
65
76
72
B*
82
84
81
78
81
89
83
89
90
87
obs
173ꢀ174
160ꢀ61
199
Lit
R
Amberlite IR-120(Na+)
R
1
H
H
H
172ꢀ17421
157ꢀ5921
196ꢀ9827
153ꢀ15527
142ꢀ14323
15823
Ph
+
N2
SO3
P
2
4ꢀOCH3
N
H
Cyclohexane
N
R
+
N
N
3
H
4ꢀNO2
N
CH
NH
R
R1
R1
4
H
4ꢀCH3
H
157
Formazan
5
2ꢀCl
3ꢀCl
4ꢀBr
4ꢀ Cl
4ꢀNO2
3ꢀNO2
146
Scheme 3 Solid phase synthesis of formazan using
resin immobilized diazonium ions
6
H
157ꢀ58
190ꢀ91
120ꢀ121
234ꢀ235
176
The yield of the formazan have been found to be
moderate in case of the solid phase synthetic
procedure primarily because of strong adsorption of
the dye to the resin which resulted in incomplete
extraction with ethylacetate, whereas the IL
catalyzed four component procedure described
earlier gave excellent yield and recovery of the
product was quantitative and easy. [Et2NH2]HSO4
being soluble in water could be removed
completely from the products by several washings
with distilled water. On comparing the two
procedures used in this study it may further be
mentioned that the use of IL resulted in a one pot
solvent free synthesis while the solid phase
technique involves three steps requiring
preparations of the phenylhydrazone, preparation
of diazonium ions using corrosive mineral acids
before immobilization onto the ion exchange resin
and finally the reaction of the immobilized
diazonium ions with aldehydeꢀphenylhydrazone
were carried out in an organic solvent. In both
7
H
189ꢀ19023
11923
8
H
9
H
N
10
H
N
11
12
13
14
15
16
17
2ꢀNO2
2,4ꢀdiCl
4ꢀCH3CO
4ꢀCH3
H
H
88
70
80
68
77
72
73
80
86
90
85
82
83
75
174ꢀ175
205
N
N
N
N
N
N
N
H
214ꢀ216
153ꢀ154
179ꢀ183
180ꢀ181
203ꢀ206
H
4ꢀCl
4ꢀCH3
2ꢀCH3O
2ꢀCl
4ꢀCl
4ꢀCH3O
18
19
4ꢀ CH3
4ꢀNO2
4ꢀ NO2
4ꢀ NO2
70
90
80
90
188ꢀ190
209
N
N
* Reaction A in immobilized diazonium ions, Reaction B in ionic liquid#
# N stands for new compound
4 | J. Name., 2012, 00, 1-3
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A comparative study of the present methods using
IL and the solid phase synthesis to a few other
procedures reported in literature is summarized in
Table 2. Comparison reveals the superiority and
better environmental acceptability of the one pot
solvent free synthesis of formazans using cost
effective and easily available Ionic liquids.
Table 2: Comparison of different methods of the synthesis of
formazans
Entry
Reagents
Yield(%)
Reaction
Time steps
1-4
Obs
Figure
1: UV spectra of selected formazans in EtOH
1
2
3
4
PTC/M2CO3
/CH2Cl2, M=K, Na
45-70%
78-88%
80%
3
2
3
3
VOC
hrs
used21
BF3-SiO2
1-2
mins
Solvent
free27
Mineral acid,
NaOH,
CH3COONa
3.5 hrs
___
VOC
used23
Alkali
54-75%
Temp
and pH
control2
6
5
6
AmberliteIR120
(Na+), acid,
cyclohexane
65-74%
82-90%
1-2
hrs
3
1
This
work
VOC
used
Figure 2a
Ionic liquid
1-2
This
[Et2NH]HSO4
mins
work
Solvent
free
All formazans synthesized gave characteristics
πꢀπ* absorption in the visible region at 350 to 450
nm which on oxidation with dil HNO3 at room
temperature or with 5% KMnO4 solution, shifted
the absorption maxima to around 300 nm indicating
their conversion to tetrazolium salts48 .This was a
confirmative test for the formation of formazans as
the product. UV absorption of selected formazans
before and after oxidation shown in Figure 1 and
Figure 2a and Figure 2b respectively.
Figure 2b
Figure 2a and 2b : UV spectra of tetrazolium salt of 1-(
4-acetylphenyl)-3,5-diphenylformazan and 1-(4-Chloro-
2-nitrophenyl)-3-(4-nitrophenyl)-5-phenylformazan
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Experimental: Chemicals were purchased from solvent . Finally the products were recrystallized
Loba chieme (India) and purified by procedures from 95% (v/v) EtOH.
reported in literature49. Acidic ionic liquids
General method for synthesis of formazan in
solid phase: Resin immobilized diazonium ions
prepared from dialkylamines by a procedure
reported earlier47. Formazans obtained were
was prepared by a procedure described earlier,
confirmed by comparing their melting points with
recovered and dried44ꢀ46. The phenylhydrazone of
those reported in literature. Melting points were
the aromatic aldehydes were prepared by reported
recorded in open capillaries and are uncorrected.
methods23. The hydrazones( 1mmol) was dissolved
Products were purified by repeated column
in 50mL of cyclohexane and the solution
chromatography. All new products were
percolated through a column slurry packed with
characterized by spectroscopic methods. UVꢀvis
15g of immobilized diazonium ions. On formation
spectra were recorded in UVꢀ1800 Shimadzu UV
of the formazan dyes , the beads turned deep red.
spectrophotometer, IR spectra were recorded in
The beads were recovered , dried at room
KBr pellets in a Perkin Elmer FTꢀIR 1600
temperature and the product obtained by extraction
1
spectrophotometer and H and 13C NMR were
of the beads with ethylacetate in a soxhlet
recorded in
Bruker Bio Spin 300MHz
extraction apparatus. The products were tested for
their purity by TLC using prepared silica gel plates
and ethylacetate: petroleum ether ( 40ꢀ60) in the
ration 1:9 as the eluent . TLC indicated purity of
the product. Reduced pressure evaporation of the
products gave the formazans.
spectrometer using CDCl3 as solvent and TMS as
internal standard. Mass spectra of new compounds
were recorded in Micromass QTOF ESIꢀMS
instrument ( model HAB273) and Microwave
irradiation of reaction mixture was performed in
reactor procured from CatalystTM(India).
Experimental data of selected products:
Preparation of ionic liquids: Ionic liquids of
dialkylamines:[Et2NH2]HSO4,[(nꢀpropyl)2NH2]
HSO4 and [(nꢀisopropyl)2NH2]HSO4 were prepared
by a procedure describe earlier 47.
1-(4-nitrophenyl)-3,5-diphenylformazan(Entry
9): dark red, UV(EtOH): λmax 413(Kꢀband),
IR(KBr): ν cmꢀ1 3094(ArꢀCꢀH), 2970(NꢀH),1651
(ꢀC=Cꢀ), 1556 (ꢀNO2 ), 1415( ꢀN=Nꢀ), 1303(ꢀNO2)
1HꢀNMR(300 MHz, CDCl3): δH ppm 6.979( 1H, d
J=7.6 Hz, NH), 7.140ꢀ8.496 (m ,14H, ArꢀH) ), ,13C
NMR ( 75 MHz, CDCl3): δ ppm.114.72, 118.28,
120.43, 121.9, 123.48, 125.18, 127.99, 128.57,
132.37, 133.58, 134.31, 145.19, 150.01 HRMS (
ESI): 344.612 calc. 243. HRMS ( ESI) : 346.128(
M+) calc. 345.35.
General procedure for synthesis of formazan
using ionic liquid:
A mixture of aromatic aldehyde ( 1mmol),
phenylhydrazine (1 mmol), aromatic amine(1
mmol) and NaNO2 ( 1.2mmol) , 10 mol% of
[Et2NH2]HSO4 and 1 mL of deionized water was
ground to a homogeneous mixture. The bright
coloured mixture was exposed to microwave
irradiation ( 240 Watt) for a 1ꢀ1.5 mins. After
completion of the reaction , the solid mass obtained
was washed with water till free of ionic liquid. The
remaining solid was dissolved in ethylacetate ,
dried using anhydrous Na2SO4 and product
obtained by reduced pressure evaporation of the
1-(3-nitrophenyl)-3,5-diphenylformazan (Entry
10): dark red, UV(EtOH) : λmax 341nm (Kꢀband),
IR(KBr): ν cmꢀ1 3000 ( NꢀH str), 2369 ( CꢀH str),
1653 ( ꢀC=Cꢀ), 1548 ( ꢀNO2), 1417( ꢀN=Nꢀ), 1302 (
1
ꢀNO2), HꢀNMR ( 300 MHz, CDCl3): δH ppm
7.227 ( 1H, s, NꢀH) , 7.253ꢀ8.025 ( 14H, m, ArꢀH),
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13
13CNMR ( 75 MHz, CDCl3): δ ppm 112.30, 7.004ꢀ 8.24( 14H, m, ArꢀH), C NMR ( 75 MHz,
112.30, 113.24, 114.49, 116.98, 119.00, 126.52, CDCl3) δ ppm 146.81, 143.55, 141.76, 133.73,
128.73,129.19,129.93,138.44,139.52,143.58,145.19 129.92, 129.72, 129.38, 129.22, 127.88, 126.12,
, 145.9, HRMS ( ESI) : 346.128( M+) calc. 345.35. 124.03, 123.94, 123.56, 121.1, 115.31, 113, 20.42.
HRMS ( ESI): 344.612 calc. 243.
1-(2-nitrophenyl)-3,5-diphenylformazan (Entry
1-(4-chlorophenyl)-3-(4-methylphenyl)-5-phenyl
11): red, UV(EtOH): λmax 331.91nm(Kꢀband),
IR(KBr): ν cmꢀ1 3346(ArꢀCꢀH), 3086(NꢀH),1648
formazan (Entry 15): orange red, UV(EtOH) λmax
(ꢀC=Cꢀ), 1555(ꢀNO2 ), 1419( ꢀN=Nꢀ), 1302(ꢀNO2) 348 nm (Kꢀband), IR(KBr): ν cmꢀ1 3001( NꢀH str),
1HꢀNMR(300 MHz, CDCl3): δH ppm 6.883(1H, t, 2364 (CꢀH str), 1650 (ꢀC=Cꢀ), 1414 ( ꢀN=Nꢀ),1Hꢀ
J=7.8, J=7.5, NH), 7.759ꢀ 8.203 ( 14H, m, ArꢀH), NMR ( 300 MHz, CDCl3): δH ppm 1.798(3H, s,
13CNMR ( 75 MHz, CDCl3): δ ppm. 116.47, CH3), 6.622 (1H, s, NꢀH) 6.650ꢀ7.627 ( 13H, m,
118.49,121.01,126.19,127.25,129.02,130.04,134.49 ArꢀH), 13CNMR ( 75 MHz, CDCl3) : δ ppm
,136.34,137.02,142.16,143.9,147.84,149.34,
HRMS ( ESI): 344.612 obs , 345.35 calc.
20.13, 117.29, 118.59, 122.27, 124.65, 126.80,
127.60, 28.81,130.05,132.11,137.25,138.97,144.62,
151.12,HRMS ( ESI): 349.872 ( obs) 348.5 Calc).
1-(2,4-dichlorophenyl)-3,5-diphenylformazan
(Entry 12) : dark red, UV ( EtOH): λmax 372nm (K
band), IR(KBr): ν cmꢀ1 3276 ( CꢀH str), 3000 (Nꢀ
1-(4-chlorophenyl)-3-(2-methoxyphenyl)-5-
phenylformazan( Entry 16): dark red, UV (
H str), 1642( ꢀC=Cꢀ), 1556 ( CꢀCl), 1414 ( ꢀN=Nꢀ), EtOH): λmax 355nm ( Kꢀband), IR(KBr): ν cmꢀ1
1HꢀNMR ( 300 MHz, CDCl3) : δH ppm 7.193 ( 1H, 2923 ( NꢀH), 1651 (ꢀCꢀOꢀ), 1556( ꢀC=N), 1419( ꢀ
s, NH) 7.612ꢀ7.639 (13H, m, ArꢀH), 13C NMR N=Nꢀ), HꢀNMR ( 300 MHz, CDCl3): δH ppm
1
(CDCl3,75 MHz): 77.41 115.43, 118.95, 123.20, 3.933( 3H, d, J=13.4), 6.559( 1H, s, NꢀH), 6.587ꢀ
123.62, 128.41, 128.98, 129.47, 129.70, 130.33, 8.125(13H, m, ArꢀH) 13CNMR ( 75 MHz,
130.56, 130.78, 131.07, 133.49, 145.12, HRMS CDCl3): δ ppm 50.02, 112.72, 120.28, 126.43,
( ESI) : 369.0617 ( M+) calc.369.25.
126.80,128.28,128.99, 129.25, 129.57, 132.37,
132.58,133.31,144.19,147.58,148.79, HRMS(ESI):
349.321( M+) obs, 348.5 calc.
1-(4-acetoxyphenyl)-3,5-diphenylformazan
( Entry 13): dark red, UV ( EtOH): λmax 371 ( Kꢀ
band), IR(KBr): ν cmꢀ1 2987 ( NꢀH str), 2351 ( aro
CꢀH), 1658( ꢀCOꢀ), 1417( ꢀN=Nꢀ), HꢀNMR ( 300
MHz, CDCl3): δH ppm 6.619(1H, s, NꢀH), 7.648 ꢀ
1-(4-methoxyphenyl)-3-(2-chlorophenyl-5-
phenylformazan (Entry17): dark red, UV (
EtOH): λmax 353 ( Kꢀband), IR(KBr): ν cmꢀ1
1
7.681 (14H, m, ArꢀH), 2.524( 3H,ꢀCOCH3) 13C 2985(NꢀH), 2363 (ꢀCꢀH), 1651(CꢀO) 1599( C=N
NMR (CDCl3,75 MHz): 26.03, 112.59, 113.60, str),1415(ꢀN=Nꢀ) 1HꢀNMR ( 300 MHz, CDCl3): δH
119.87, 126.05, 127.50, 128.27, 128.50, 129.20, ppm 2.956(3H, s, OCH3), 6.925(s, NꢀH), 6.950ꢀ
130.75, 135.25, 137.18, 144.60, 151.19, 196.73 7.489( 13H, m, ArꢀH), 13CNMR( 75 MHz, CDCl3)
HRMS ( ESI) : 342.32( M+) calc.342.39.
δppm50.02,112.72,120.28,126.43,126.80, 128.28,
128.99,129.57,129.25,132.37,132.58,133.31,144.19
,147.58,148.79. HRMS ( ESI) : 376.1 calc. 376.84.
1-(4-methylphenyl)-3,5-diphenylformazan (entry
14): dark red, UV(EtOH)
λmax374(Kꢀband),
IR(KBr): ν cmꢀ12994(NꢀH),1644(ꢀC=Cꢀ), 1556(ꢀ
1-(4-methylphenyl)-3-(4-nitrophenyl)-5-phenyl
formazan ( Entry 18) : UV ( EtOH): λmax 384( Kꢀ
band), IR(KBr): ν cmꢀ1 2968( NꢀH str), 1648 ( ꢀ
1
C=Nꢀ), 1412(ꢀN=Nꢀ), HꢀNMR(300 MHz, CDCl3)
δH ppm 2.258(3H ,s), 6.625(1H, d ,J=8.4, NH),
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C=Cꢀ), 1540 ( ꢀNO2), 1410( ꢀN=Nꢀ),1301 ( ꢀNO2), benign and large scale production of formazans
1HꢀNMR ( 300 MHz, CDCl3): δH ppm 2.568( 3H,
dyes.
s, ꢀCH3), 6.625( 1H,s, NꢀH), 6.653ꢀ8.240( 13H, m,
ArꢀH), 13CNMR ( 75 MHz, CDCl3): δppm 20.42,
77.43, 113.00, 115.31, 121.10, 123.56, 123.94,
124.03, 126.12, 127.88, 129.22, 129.92, 133.73,
141.76, 143.55, 146.81. HRMS ( ESI) :360.12(
M+) obs, 359( calc).
Acknowledgements
The authors are thankful to the HOD, Department
of Chemistry, Gauhati University, for providing
laboratory facilities and Prof. A.K.Saikia , IIT,
Guwahati for instrumental facilities.
Notes and references
1-(4-nitrophenyl)-3-(4-nitrophenyl)-5-phenyl
formazan ( entry 19): red, UV ( EtOH): λmax 384
( Kꢀband), IR(KBr): ν cmꢀ1 2988( NꢀH str), 1653 (
ꢀC=Cꢀ), 1548 ( ꢀNO2), 1418( ꢀN=Nꢀ),1299 ( ꢀNO2),
1HꢀNMR ( 300 MHz, CDCl3): δH ppm 6.612( 1H,
s, NꢀH), 6.64ꢀ8.174 ( 13H, m, ArꢀH), 13CNMR
( 75 MHz, CDCl3): δ ppm 77.91, 113.66, 117.86,
121.82, 127.76, 128.43, 129.42, 130.00, 130.78,
136.08, 138.21, 147.85, 151.05, 152.08. HRMS
( ESI) : 391.21(M+ obs) 390( calc.)
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Electronic
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available:
DOI: 10.1039/b000000x/
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Table of contents
Microwave assisted solvent free one pot synthesis of formazans, catalysed by ionic liquid is
reported for the first time.
R
CHO
NHNH2
NH2
Ph
H
N
N
N
N
NaNO2/ H2O
IL/microwave
R
R1
four component
reaction
N2Cl
R1
SO3Na
ion exchange
resin
Solid phase
synthesis
R
diazonium ions
CH=NNHPh
R1
phenylhydrazones