Full text of DOI:10.14233/ajchem.2014.16491

Asian Journal of Chemistry; Vol. 26, No. 18 (2014), 6029-6032
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2014.16491
Synthesis of Some Substituted Formazans and bis Formazans
*
E. YILDIRIM and H. SENOZ
Department of Chemistry, Faculty of Science, Hacettepe University, Beytepe 06800, Ankara, Turkey
*Corresponding author: Tel: +90 312 2977960; E-mail: senoz@hacettepe.edu.tr
Received: 8 October 2013;
Accepted: 10 December 2013;
Published online: 1 September 2014;
AJC-15847
Novel 1-(p-aminophenyl)-3-(p-substituted phenyl)-5-phenylformazan compounds (2a-f) and 1,1'-([1,1'-biphenyl]-4,4'-yl)bis(3-(p-
substituted phenyl)-5-phenylformazan compounds (3a-f) were synthesized by diazo coupling reactions of the prepared hydrazones (1a-f)
with diazonium salts of phenylenediamine and benzidine, respectively. Novel mono-formazans were obtained with high yields under mild
reaction conditions and were crystallized from methanol. Bis-formazans were purified by flash column chromatograph over silica gel.
The structures of formazans and bis-formazans were confirmed by elemental analysis, HR-MS and their spectral behaviours were investigated
using 1H NMR, 13C NMR, FT-IR techniques. The absorption characteristics of the compounds were examined by UV-visible spectra.
Keywords: Formazan dyes, Formazan, Bis-formazan, Diazo coupling, Spectroscopy.
INTRODUCTION
EXPERIMENTAL
Formazans have attracted attention because of their
medicinal applications such as antiviral1, antifungal2, anti-
fertility3, antiinflamatory4, antitubercular5, antimicrobial6, anti-
plasmodium activity7. Oxidation of deeply coloured formazans
furnish tetrazolium salts and reduction of tetrazolium salts
easily give formazans. These compounds are used as a marker
of vitality8, because of their oxidation-reduction properties.
Tetrazolium salt/formazan systems are also used in choosing
anti-cancer drug9 and colourimetric determination of bioredu-
cibility of cells10.
The UV-visible spectra of all formazans synthesized in
this study were recorded with UV-1700 Pharma Spectropho-
tometer using 1 cm quartz cells in 10-4 mol L-1 CH2Cl2. The IR
spectra were obtained on Thermo, Nicolet IS10-FTIR spectro-
1
meter between 4000 and 400 cm-1. H NMR spectra were
recorded on a Bruker 400 MHz spectrometer using CDCl3 and
13C NMR spectra were performed 100 MHz spectrometer using
CDCl3.All the elemental analysis studies were carried out using
a LECO-CHNS- 932 elemental analyser. Melting points were
determined with an electrothermal melting point apparatus and
were uncorrected. HR-MS results of compounds were obtained
via Agilent TOF LC/MS 1200/6210.
The π-electrons in formazan compounds remarkably
enhance the formation of metal complexes which results a
bathochromic shift. Formazans and their metal complexes are
used as dyes in wool and polyamide fibers that are stable to
sunlight and water11 and they are also known as ecologically
friendly dyes12. They easily make complexation with metals
because of their polydentate ligand properties13-15. Further-
more, formazans are also used for trace element determi-
The hydrazones (1a-f) were prepared according to the
literature procedures18,19
.
General procedure for the synthesis of compounds (2a-
f): The formazans 2a-f were prepared according to the literature
procedures20-22. The hydrazones 1a-f (0.01 mol) was dissolved
in methanol (35 mL) and sodium hydroxide (1.76 g) was added
to this solution. Diazonium chloride of p-phenylenediamine
was prepared from p-phenylenediamine (1.08 g, 0.01 mol) in
concentrated HCl (2.5 mL) with sodium nitrite (0.76 g, 0.01
mol) dissolved in water (5 mL). This solution was added to
hydrazone solution at -5 °C. This mixture was stirred for 2 h
at -5 °C and stored 2 days. Compounds 2a-f were crystallized
from methanol.
nation16-17
.
The mentioned importance of formazan compounds
encouraged us to synthesize novel formazans. For this purpose,
-H, -COOCH3, -NO2, -CN, -Cl, -Br substituted benzaldehyde
phenylhydrazones were reacted with p-phenylenediamine to
obtained 1-(p-aminophenyl)-3-(p-substituted phenyl)-5-
phenylformazans (2a-f) and reacted with benzidine to obtain
1,1'-([1,1'-biphenyl]-4,4'-yl)bis(3-(p-substituted phenyl)-5-
phenylformazan derivatives (3a-f).
1-(p-Aminophenyl)-3,5-diphenylformazan (2a): (2.68
g, 85 %) was obtained as deep red crystals of m.p. 197 °C.

6030 Yildirim et al.
Asian J. Chem.
(KBr, υmax, cm-1): 3460, 3381, 3346, 3208, 3050-2950, 1624,
1601, 1506, 1431. λmax/nm (CH2Cl2): 266, 300, 490. δH 4.13
(s, 2H, NH2), 6.76 (d, J 8.0, 2H,ArH), 7.03 (t, J 8.0, 1H,ArH),
7.31-7.44 (m, 7H, ArH), 7.80 (d, J 8.0, 2H, ArH), 8.13 (d, J
8.0, 2H,ArH), 15.00 (s, 1H, NH). δC 149.73 (N-C=N), 145.09,
143.89, 140.84, 137.77, 129.45, 128.26, 127.41, 125.97,
124.33, 122.95, 114.92 (ArC). m/z (ESI) for C19H17N5: calcd.
[M + H]+: 316.1557; found: 316.1530. Anal. calc.: C 72.36, H
5.43, N 22.21 (%). Found: C 72.56, H 5,43, N 22.96 (%).
1-(p-Aminophenyl)-3-(p-methoxycarbonylphenyl)-5-
phenylformazan (2b): (2.98 g, 80 %) was obtained as deep
red crystals of m.p. 212 °C. (KBr, υmax, cm-1): 3464, 3364,
3208, 3050-2952, 1704, 1625, 1503, 1434. λmax/nm (CH2Cl2):
253, 360, 490. δH 3.93 (s, 3H, OCH3), 4.17 (s, 2H, NH2), 6.78
(d, J 8.4, 2H,ArH), 7.07 (t, J 7.2, 1H, ArH), 7.35-7.44 (m, 4H,
ArH), 7.80 (d, J 8.4, 2H, ArH), 8.08 (d, J 8.0, 2H, ArH), 8.21
(d, J 8.0, 2H,ArH), 15.26 (s, 1H, NH). δC 167.29 (C=O), 149.94
(N-C=N), 144.81, 143.53, 142.33, 139.77, 129.66, 129.43,
128.51, 125.48, 124.39, 123.56, 115.21, 115.11, 114.94 (ArC),
52.04 (OCH3). m/z (ESI) for C21H19N5O2 calcd. [M + H]+:
374.1561; found: 374.1531. Anal. calcd. : C 67.55, H 5.13, N
18.76 (%). Found: C 67.86, H 5.04, N 18.74 (%).
1-(p-Aminophenyl)-3-(p-nitrophenyl)-5-phenyl-
formazan (2c): (2.63 g, 73 %) was obtained as deep red
crystals of m.p. 231 °C. (KBr, υmax, cm-1): 3472, 3377, 3210,
3020, 1620, 1500, 1446. λmax/nm (CH2Cl2): 264, 397, 481. δH
= 4.20 (s, 2H, NH2), 6.78 (d, J 8.4, 2H, ArH), 7.10 (t, J 8.0,
1H, ArH), 7.30- 7.44 (m, 6H, ArH), 7.79 (d, J 8.4, 2H, ArH),
8.28 (d, J 8.4, 2H,ArH), 15.40 (t, 1H, NH). δC 129.53, 125.97,
125.01, 124.49, 124.13, 123.76, 115.44, 114.97 (ArC). m/z
(ESI) for C19H16N6O2 calcd. [M + H]+: 361.1408; found:
361.1337. Anal. calcd.: C 63.30, H 4.40, N 23.30 (%). Found:
C 63.04, H 4.46, N 22.95 (%).
1-(p-Aminophenyl)-3-(p-cyanophenyl)-5-phenyl-
formazan (2d): (2.79 g, 82 %) was obtained as claret red
crystals of m.p. 220 °C. (KBr, υmax, cm-1): 3476, 3377, 3212,
3030, 2207, 1628, 1487, 1451. λmax/nm (CH2Cl2): 252, 362,
484. δH 4.17 (s, 2H, NH2), 6.77 (d, J 8.5, 2H, ArH), 7.09 (t, J
7.0, 1H, ArH), 7.35-7.43 (m, 4H, ArH), 7.68 (d, J 8.5, 2H,
ArH), 7.78 (d, J 8.7, 2H, ArH), 8.24 (d, J 8.7, 2H, ArH), 15.31
(s, 1H, NH). δC 144.66 (N-C=N), 138.91, 132.13, 129.49,
125.95, 124.45, 123.90, 115.30, 114.95 (ArC), 110.13 (-CN).
m/z (ESI) for C20H16N6 calcd. [M + H]+: 341.1509; found:
341.1477. Anal. calcd.: C 70.50, H 4.70, N 24.70 (%). Found:
C 69.92, H 4.71, N 24.56 (%).
1-(p-Aminophenyl)-3-(p-chlorophenyl)-5-phenyl-
formazan (2e:) (2.34 g, 67 %) was obtained as claret red
crystals of m.p. 209 °C. (KBr, υmax, cm-1): 3468, 3354, 3211,
2920, 2853, 1625, 1511, 1470. λmax/nm (CH2Cl2): 264, 325,
387, 510. δH 4.16 (s, 2H, NH2), 7.03 (d, J 6.9, 2H, ArH), 7.05
(t, J 3.9, 1H,ArH), 7.26-7.52 (m, 6H,ArH), 7.78 (d, J 8.7, 2H,
ArH), 8.06 (d, J 8.7, 2H, ArH), 15.04 (s, 1H, NH). δC 149.90
(N-C=N), 144.94, 143.67, 139.94, 136.35, 133.18, 129.40,
128.36, 127.19, 124.38, 123.18, 114.96, 114.93 (ArC). m/z
(ESI) for C19H16ClN6 calcd. [M + H]+: 350.1167; found:
350.1123. Anal. calcd.: C 65.33, H, 4.58, N 20.06 (%). Found:
C 65.62, H 5.02, N 19.68 (%).
crystals of m.p. 207 °C. (KBr, υmax, cm-1): 3464, 3322, 3213,
3037, 1621, 1504, 1448. λmax/nm (CH2Cl2): 264, 326, 384,
508. dH 4.16 (s, 2H, NH2), 6.77 (d, J 8.7, 2H, ArH), 7.04 (t, J
6.8, 1H, ArH), 7.26-7.69 (m, 6H, ArH), 7.78 (d, J 8.5, 2H,
ArH), 8.00 (d, J 8.5, 2H, ArH), 15.05 (s, 1H, NH). δC 148.90
(N-C=N), 143.88, 142.63, 138.93, 135.80, 130.27, 128.37,
126.49, 123.36, 122.19, 120.19, 120.44, 113.95, 113.91 (ArC).
m/z (ESI) for C19H16BrN6 calcd. [M + H]+: 394.0662; found:
394.0558. Anal. calcd.: C 57.72, H 4.05, N 17.72 (%). Found:
C 57.01, H 4.19, N 17.93 (%).
General procedure for the synthesis of compounds (3a-
f): The hydrazones 1a-f (0.02 mol) was dissolved in methanol
(70 mL) and sodium hydroxide (3.52 g) was added to this
solution. Diazonium chloride of benzidine was prepared from
benzidine (1.84 g, 0.01 mol) in concentrated HCl (5 mL) with
sodium nitrite (1.52 g, 0.02 mol) in water (10 mL). This
solution was added to the hydrazone solution at -5 °C. This
mixture was stirred for 2 h at -5 °C. and stored 2 days. Each
bis formazan compounds 3a-f were purified by flash column
chromatography over silica gel. (EtOAc-hexane, 1:4)
1,1'-([1,1'-Biphenyl]-4,4'-yl)bis(3,5-diphenylformazan)
(3a): (3.05 g, 51 %) was obtained as deep red crystals of m.p.
175 °C. (KBr, υmax, cm-1): 3062, 2960, 2924, 1593, 1510, 1443.
λmax/nm(CH2Cl2): 260, 303, 501. δH 6.99 (t, J 2.4, 2H, ArH),
7.13-7.38 (m, 8H,ArH), 7.46 (m, 6H,ArH), 7.70 (m, 4H,ArH),
7.79 (d, J 8.4, 4H, ArH), 8.16 (d, J 8.4, 4H, ArH), 15.23 (s,
2H, NH ). δC 128.43, 127.88, 127.39, 127.06, 126.66, 125.92,
124.83, 118.52, 117.47 (ArC). m/z (ESI) for C38H30N8 calcd.
[M + H]+: 599.2653; found: 599.2681. Anal. calcd.: C 76.23,
H 5.05, N 18.72 (%). Found: C 76.02, H 5.71, N 18.66 (%).
1,1'-([1,1'-Biphenyl]-4,4'-yl)bis(3-(p-methoxycar-
bonylphenyl)-5-phenylformazan (3b): (4.00 g, 56 %) was
obtained as deep red crystals of m.p. 200 °C. (KBr, υmax, cm-1):
3287, 3046, 2948, 1715, 1601, 1494, 1431. λmax/nm (CH2Cl2):
251, 335, 495. δH 3.87 (s, 6H, OCH3), 7.18 (t, J 7.4, 2H,ArH),
7.31 (d, J 8.5, 4H, ArH), 7.40 (d, J 7.6, 4H, ArH), 7.56-7.64
(m, 4H, ArH), 7.70 (d, J 8.5, 4H, ArH), 8.02 (d, J 8.5, 4H,
ArH), 8.14 (d, J 8.5, 4H, ArH), 15.64 (t, 2H, NH ). δC 166.17
(-C=O), 146.28 (N-C=N), 140.84, 140.02, 139.08, 128.78,
128.50, 128.25, 127.91, 127.77, 127.11, 126.68, 126.56,
125.93, 124.36, 118.71, 117.59, 112.10 (ArC), 51.06 (OCH3).
m/z (ESI) for C42H34N8O4 calcd. [M + H]+: 715.2762; found:
715.2742. Anal. calcd.: C 70.58, H 4.79, N 15.68 (%). Found:
C 70.72, H 4.80, N 15.56 (%).
1,1'-([1,1'-Biphenyl]-4,4'-yl)bis(3-(p-nitrophenyl)-5-
phenylformazan (3c): (4.27 g, 62 %) was obtained as deep
red crystals of m.p. 168 °C. (KBr, υmax, cm-1): 3066, 3027,
2924, 1664, 1506, 1451. λmax/nm (CH2Cl2): 265, 380, 491. δH
7.35 (t, J 7.8, 2H, ArH), 7.43 (d, J 7.4, 4H, ArH), 7.52 (d, J
7.4, 4H, ArH), 7.68- 7.77 (m, 8H, ArH), 7.83 (d, J 8.4, 4H,
ArH), 8.33 (d, J 8.4, 4H, ArH), 15.88 (s, 2H, NH ). δC 146.09
(N-C=N), 128.59, 127.93, 127.19, 126.93, 126.81, 125.95,
124.89, 122.86, 118.87, 117.68 (ArC). m/z (ESI) for
C38H28N10O4 calcd. [M + H]+: 689.2376; found: 689.2356.Anal.
calcd.: C 66.27, H 4.10, N 20.34 (%). Found: C 66.92, H 4.12,
N 20.60 (%).
1,1'-([1,1'-Biphenyl]-4,4'-yl)bis(3-(p-cyanophenyl)-5-
phenylformazan (3d): (4.22 g, 65 %) was obtained as deep
red crystals of m.p. 154 °C. (KBr, υmax, cm-1): 3050, 2964,
1-(p-Aminophenyl)-3-(p-bromophenyl)-5-phenyl-
formazan (2f): (2.99 g, 76 %) was obtained as claret red

Vol. 26, No. 18 (2014)
Synthesis of Some Substituted Formazans and bis Formazans 6031
2908, 2215, 1601, 1506, 1459. λmax/nm (CH2Cl2): 248, 266,
340, 494. δH 6.99 (t, J 6.0, 2H, ArH), 7.26- 7.53 (m, 8H,ArH),
7.60- 7.76 (m, 8H, ArH), 7.83 (d, J 8.0,4H, ArH), 8.27 (d, J
8.0, 4H,ArH), 15.88 (s, 2H, NH ). δC 146.12 (N-C=N), 140.85,
140.35, 138.97, 138.37, 131.26, 128.56, 127.94, 127.16,
126.80, 125.94, 124.83, 118.80, 118.43, 117.61 (ArC), 109.46
(-CN). m/z (ESI) for C40H28N10 calcd. [M + H]+: 649.2534;
found: 649.2551. Anal. calcd.: C 74.06, H 4.35, N 21.59 (%).
Found: C 74.18, H 4.36, N 21.62 (%).
N NH
Cl
H2N
N N
CH
R
1a-f
NaOH/CH3COONa
Methanol
1,1'-([1,1'-Biphenyl]-4,4'-yl)bis(3-(p-chlorophenyl)-5-
phenylformazan (3e): (3.94 g, 59 %) was obtained as deep
red crystals of m.p. 145 °C. (KBr, υmax, cm-1): 3068, 3033,
2927, 2850, 1660, 1504, 1445. λmax/nm(CH2Cl2): 268, 314,
501. δH 7.27 (t, J 7.3, 2H, ArH), 7.36-7.49 (m, 8H, ArH), 7.54-
7.71 (m, 8H, ArH), 7.77 (d, J 6.8, 4H, ArH), 8.09 (d, J 6.8,
4H, ArH), 15.55 (s, 2H, NH ). δC 147.40 (N-C=N), 140.84,
140.39, 140.16, 135.97, 133.49, 129.82, 129.49, 129.25,
128.93, 128.54, 128.11, 127.67, 127.37, 127.06, 126.94,
119.60, 118.50, 112.92 (ArC). m/z (ESI) for C38H28Cl2N8 calcd.
[M + H]+: 668.1814; found: 668.1821. Anal. calcd.: C 68.37,
H 4.23, N 16.78 (%). Found: C 68.90, H 4.26, N, 16.62 (%).
1,1'-([1,1'-Biphenyl]-4,4'-yl)bis(3-(p-bromophenyl)-5-
phenylformazan (3f): (4.99 g, 66 %) was obtained as deep
red crystals of m.p. 161 °C. (KBr, υmax, cm-1): 3060, 3031,
2918, 2845, 1598, 1503, 1454. λmax/nm (CH2Cl2): 242, 268,
318, 501. δH 7.29 (t, J 7.7, 2H, ArH), 7.43-7.49 (m, 8H, ArH),
7.56-7.72 (m, 8H, ArH), 7.78 (d, J 8.5, 4H, ArH), 8.03 (d, J
8.5, 4H,ArH), 15.56 (s, 2H, NH ). δC 147.27 (N-C=N), 140.71,
136.25, 131.26, 129.65, 129.26, 129.02, 128.69, 127.87,
127.64, 127.43, 127.14, 126.69, 121.50, 119.32, 118.20 (ArC).
m/z (ESI) for C38H28Br2N8 calcd. [M + H]+: 757.0831; found:
757.0842. Anal. calcd.: C 60.33, H 3.73, N 14.81 (%). Found:
C 60.76, H 3.65, N 14.69 (%).
N NH
C
R
N N
NH2
-COOCH3, p-NO2, p-CN, p-Cl, p-Br
2a-f
p
R(a-f)= -H,
Fig. 1. Synthesis of formazans
N2
N
N
N2
N N
N2
N N
I
III
II
Fig. 2. Resonance structure of diazonium cation of phenylenediamine
N NH
N N
N N
Cl
Cl
CH
R
RESULTS AND DISCUSSION
1a-f
We described here the synthesis of bis-formazans. First,
we planned to obtain bis formazans from the coupling reaction
of hydrazones with diazonium salts of p-phenylenediamine
and benzidine. However, the reaction of 1a and p-phenylene-
diamine produced the mono-formazan 2a instead of bis-
formazan. (Fig. 1). Formation of 2a showed that only one of
the amino group of p-phenylenediamine has been converted
to diazonium salt. 2a was obtained from the reaction of 1a
with p-phenylenediamine even the excess amount of NaNO2
was used. Formation of mono-diazonium salt of p-phenylene-
diamine can be explained by the most probably unstable
resonance form III given in Fig. 2. This result led us to synthe-
size the novel formazans 2b-f.
NaOH/CH3COONa
Methanol
R
HN
C N
N
N
N
N
N C
NH
3a-f
R
p
-COOCH3, p-NO2, p-CN,
p
-Cl, p-Br
R(a-f)= -H,
As mentioned before, reaction of phenylenediamine with
excess NaNO2 did not give bis-diazonium salt. For this reason,
we used benzidine instead of phenylenediamine to prepare
bis-diazonium salt. When we performed the reaction of 1a
with diazonium salt of benzidine, bis formazan 3a was obtained
successfuly. This result indicated that benzidine has been easily
converted to bis diazonium salt in the case of using the same
molar ratio of benzidine and NaNO2 (1:1). This method allowed
the synthesis of novel bis formazans 3b-f by the reaction of
1b-f with bis diazonium salt of benzidine (Fig. 3).
Fig. 3. Synthesis of bis-formazans
Formazan compunds form intramoleculer hydrogen bonds
between the lone pair of N(1) and the hydrogen atom on the
N(5). So, formazans have a chelated hydrogen-bridge struc-
ture23 (Fig. 4). FT-IR spectra of the synthesized compounds
showed a weak N-H stretching band at about 3000 cm-1 and
the N-H signal of the formazan in the 1H NMR spectrum was
observed at about 15-16 ppm. These showed that the structure
has intramolecular hydrogen bonds.

6032 Yildirim et al.
Asian J. Chem.
Signals at 4.13-4.18 ppm in the 1H NMR spectra of mono-
formazans 2a-f indicate the presence of p-amino protons of
phenyl ring and intense stretching band of NH2 was also
observed at about 3400 cm-1 in its FT-IR spectra.
benzidine diazonium salt. The structures of the novel com-
pounds identified by using elemental analysis, 1H NMR, 13C
NMR, FT-IR, UV-visible techniques and LC-MS.
ACKNOWLEDGEMENTS
R5
R5
The authors thank Hacettepe University for financial
support (BAP project 011D03601006). Thanks are also due
to Assist. Prof. Dr. Habibe Tezcan and Prof. Dr. Canan
Unaleroglu for valuable advice.
N
N
N
N
N
H
R3
C
H
C
R3
N
N
N
R1
R1
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Fig. 4. Moleculer chelation and tautomerization
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Depending on the substituents, formazans have different
colours and make absorptions at different wavelengths. For
this reason, the study of UV-visible spectra of formazans is
important. Their spectra exhibit mainly four absorption bands24.
The first band observed in the wavelength range of 216-239
nm is assigned to that of π-π* transition of -C=C- bond on
phenyl moiety. The second band 240-285 nm is attributed to
the low energy π-π* transition of -C=N- bond. The third sharp
band within 300-350 nm is due to π-π* transition of -N=N-
band. The characteristic fourth broad band is generally
observed at 410-500 nm due to n-π* transitions of -N=N- band
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depending upon the structure.
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For mono-formazans 2a-f, λmax4 values were observed at
490, 481, 484, 510 and 508 nm but for bis-formazans 3a-f,
λmax4 values were observed at 495, 491, 494 and 501 nm. In all
cases, strong electron withdrawing groups such as -NO2 and
-CN shifted the characteristic fourth band of formazans
(hypsochromic effect).Any changes on the characteristic fourth
band of -Cl and -Br substituted bis-formazans were not
observed while this band shifted to higher wavelength in mono-
formazans.
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Novel mono and bis formazans have been synthesized
from easily available starting materials and under mild reaction
conditions. Mono formazans were obtained with high yields.
This method allowed for the synthesis of bis formazans from