Structural studies of 1-phenyl-2,3-dimethyl-5-oxo-1,2-dihydro-1H-pyrazol-4- ammonium 2[(2-carboxyphenyl) disulfanyl]benzoate

Article abstract of DOI:10.1016/j.molstruc.2012.04.065

Reaction of 4-aminoantipyrine with 2-mercaptobenzoic acid afforded a proton transfer derivative, 1-phenyl-2,3-dimethyl-5-oxo-1,2-dihydro-1H-pyrazol-4- ammonium 2[(2-carboxyphenyl) disulfanyl]benzoate, (HAAP⁺? HTBA^-), via the oxidation of 2-mercaptobenzoic acid into 2,2′-dithiobis(benzoic acid). The compound has been characterized on the basis of elemental analysis, IR, ¹H and ¹³C NMR and mass spectral data. The infrared spectrum suggests the existence of an ion-pair compound, which is further established by the single crystal X-ray analysis to be an extended 1D supramolecular chain network extending along 'b' cell direction. The compound shows good thermal stability.

Full text of DOI:10.1016/j.molstruc.2012.04.065

Journal of Molecular Structure 1021 (2012) 147–152
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Structural studies of 1-phenyl-2,3-dimethyl-5-oxo-1,2-dihydro-1H-pyrazol-4-
ammonium 2[(2-carboxyphenyl) disulfanyl]benzoate
b
a
Shiji Fazil a, Reena Ravindran a, , A. Sarau Devi , B.K. Bijili
⇑
a Department of Chemistry, S.N. College for Women, Kollam, Kerala 691 001, India
b Department of Chemistry, S.N. College, Kollam, Kerala 691 001, India
h i g h l i g h t s
"
"
"
"
"
The reaction between 4-aminoantipyrine and 2-mercaptobenzoic acid resulted in a proton transfer salt.
This compound crystallize in the space group P-1.
The ion-pair units are interlinked by hydrogen bonds forming a ID supramolecular network.
Spectral studies (IR, NMR, Mass) confirm the formation of proton transfer salt.
The compound shows thermal stability upto 260 °C.
a r t i c l e i n f o
a b s t r a c t
Article history:
Reaction of 4-aminoantipyrine with 2-mercaptobenzoic acid afforded a proton transfer derivative, 1-phe-
nyl-2,3-dimethyl-5-oxo-1,2-dihydro-1H-pyrazol-4-ammonium 2[(2-carboxyphenyl) disulfanyl]benzo-
ate, (HAAP+ꢀHTBAꢁ), via the oxidation of 2-mercaptobenzoic acid into 2,20-dithiobis(benzoic acid). The
compound has been characterized on the basis of elemental analysis, IR, 1H and 13C NMR and mass spec-
tral data. The infrared spectrum suggests the existence of an ion-pair compound, which is further estab-
lished by the single crystal X-ray analysis to be an extended 1D supramolecular chain network extending
along ‘b’ cell direction. The compound shows good thermal stability.
Received 23 January 2012
Received in revised form 20 April 2012
Accepted 20 April 2012
Available online 28 April 2012
Keywords:
Proton transfer
Aminoantipyrine
Mercaptobenzoic acid
Ion-pair
Ó 2012 Elsevier B.V. All rights reserved.
Crystal structure
Thermal study
1. Introduction
crystal packing motifs due to NAHꢀ ꢀ ꢀO and OAHꢀ ꢀ ꢀO hydrogen
bonded interactions in the self-assembly of various amines with
Among the pyrazolone derivatives, 4-aminoantipyrine (AAP)
has been used commonly as reagents in biological [1], pharmaco-
logical [2], clinical [3], and analytical applications [4]. Other deriv-
atives of AAP such as schiff bases have been extensively
investigated and utilized to construct metal-antipyrine networks
in crystal engineering [5]. AAP offers both donor and acceptor sites
for hydrogen bonding through amino N atom and keto O atom
respectively. These non-covalent interactions play an important
role in determining the potential applications of its analogues in
material science [6] and pharmaceutical industry [7]. Recent re-
search efforts have shown fascinating molecular topologies and
carboxylic acids [8,9]. Similar non-covalent interactions leading
to supramolecular networks are observed in the self-assembly of
4-aminoantipyrine with salicylic acid [10]. The crystal structure
of the resulting compound showed charge assisted hydrogen bond
interactions between protonated aminoantipyrine and a deproto-
nated salicylate anion. This observation prompted us to investigate
the interactions between 4-aminoantipyrine and 2-mercaptoben-
zoic acid (MBA).
Herein, we report our results concerning the spectral and ther-
mal studies along with single crystal X-ray analysis of the proton
transfer salt, 1-phenyl-2,3-dimethyl-5-oxo-1,2-dihydro-1H-pyra-
zol-4-ammonium
2[(2-carboxyphenyl)
disulfanyl]benzoate,
(HAAP+ꢀHTBAꢁ), obtained during the reaction of 4-aminoantipyrine
⇑
Corresponding author. Tel.: +91 471 3044123.
E-mail address: reena1234@gmail.com (R. Ravindran).
with 2-mercaptobenzoic acid.
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.04.065

148
S. Fazil et al. / Journal of Molecular Structure 1021 (2012) 147–152
2. Experimental
3. Results and discussion
2.1. Materials and physical measurements
3.1. Single crystal structure of (HAAP+ꢀHTBAꢁ)
4-Aminoantipyrine (Merck) and 2-mercaptobenzoic acid (Sig-
ma–Aldrich) were of reagent grade and used as such. Microanalysis
was carried out using a Vario EL III elemental analyzer. Infra red
spectrum was recorded on a Perkin Elmer FT-IR instrument as
KBr pellet in the range 4000–400 cmꢁ1. The 1H NMR and 13C
NMR were recorded using Bruker DRX-500 MHz with DMSO as sol-
vent. DART-MS was recorded on a Jeol-AccuToF JMS-T100LC mass
spectrometer having a DART (Direct Analysis in Real time) source.
The thermal studies were recorded on a Mettler TG-50 thermobal-
ance with a heating rate of 20 °C/min. in nitrogen atmosphere. The
single crystal X-ray data-collection of the compound was carried
out using Bruker Axs kappa apex 2 CCD diffractometer.
In the present study, during the 1:2 stoichiometric reaction of
4-aminoantipyrine with 2-mercaptobenzoic acid, the acid is first
oxidized to 2,20-dithiobis(benzoic acid), (H2TBA) [12], which subse-
quently undergoes proton transfer to 4-aminoantipyrine to form
an ion-pair compound, (HAAP+ꢀHTBAꢁ). The flexible conformation
and variable degree of deprotonation of the dibasic acid (H2TBA)
is known to have formed cocrystals, with few bases, in which the
acid–base pairs are held together by charge assisted hydrogen
bonds [13].
The compound, (HAAP+ꢀHTBAꢁ), crystallizes in the space group
P-1. The crystal structure reveals the formation of a 1:1 proton
transfer compound, held together by a hydrogen bond. Here proton
transfer takes place from the carboxyl group at C1 of the dibasic
acid, (H2TBA) to the amino group of the base, (AAP). The asymmet-
ric unit of the compound thus contains 4-ammonium antipyrine,
(HAAP+) as the cation and monocarboxylate of 2,20-dithiobis(ben-
zoic acid), (HTBAꢁ) as the anion (Fig. 1). This is a redetermination
of a similar crystalline structure isolated during the direct reaction
of 4-aminoantipyrine with 2,20-dithiobis(benzoic acid) [14].
In the crystal of (HAAP+ꢀHTBAꢁ) obtained according to Scheme 1,
the pyrazolone ring and phenyl ring are in gauche orientation
along the N1AC15 bond. This is reflected from the dihedral angles
C23/N1/C15/C20 = ꢁ66.0(3)° and C16/C15/N1/N2 = ꢁ65.6(3)°. Pro-
tonation of the amino group usually leads to the elongation of the
CAN bond [15]. This is found true in the case of 4-ammonium anti-
pyrine cation also. The CAN distance [C22AN3 = 1.4270(19) Å] is
longer than the CAN distance of neutral AAP (1.3960 Å) [10,16].
This lengthening is observed when the amine N atom of AAP ac-
cepts a H atom from the carboxyl group of acid. All other bond
length and bond angle values (Table 2) are consistent with those
of other reported structure of AAP derivatives.
The anion moiety of the ion-pair is also non-planar. The S1AS2
bond length is 2.0502(6) Å and agrees with the literature value of
other disulfides [17]. The dihedral angle value C2/S1/S2/
C9 = 83.03(8)° shows that the aryl substituents on the two sulfur
atoms are in an approximate perpendicular disposition with re-
spect to each other [12]. The COOH and COOA groups are essen-
tially coplanar with the respective aromatic ring. The benzene
ring with COOH group is tilted more from the plane defined by
the S1AS2 axis and the respective ring C atoms [S1/S2/C9/
C10 = ꢁ16.12(15)°] than the other ring with COOA group [S1/S2/
C2/C3 = ꢁ11.23(15)°]
2.2. Synthetic procedure
Refluxing 4-aminoantipyrine (0.203 g, 1 mmol) and 2-mercapto
benzoic acid (0.308 g, 2 mmol) in 50% ethanol–water mixture for
15 h, followed by partial room temperature evaporation of the sol-
vent, resulted in the separation of brown colored blocks of the
compound, (HAAP+ꢀHTBAꢁ) with m.p. 224–225 °C (Scheme 1).
The elemental analysis data for the compound, Found(Calcd):
C,58.91(58.92); H,4.5(4.55); N,08.15(08.25); S,12.61(12.58) agrees
with the empirical formula C25 H23 N3 O5 S2.
2.3. Crystal structure determination of (HAAP+ꢀHTBAꢁ)
Single crystal suitable for diffraction was obtained by slow
evaporation of a solution of the compound in ethanol–water mix-
ture. The brown crystal of the compound having appropriate
dimensions of 0.30 mm ꢂ 0.20 mm ꢂ 0.20 mm was mounted on a
fine-focus sealed tube for X-ray crystallographic study. A Bruker
Axs-kappa apex 2 CCD diffractometer equipped with a graphite
monochromated Mo K
measurement of data.
a (k = 0.71073) radiation was used for the
The structure was solved by direct methods and refined by full
matrix least squares on F2 (SHELXL 97) program package [11].
Molecular graphics employed include ORTEP 3 and Mercury 2.3.
The hydrogen-atoms potentially involved in hydrogen bonding
interactions were located from difference electron density maps.
The positions of all H atoms were identified from a difference elec-
tron density peak and were fixed geometrically during refinement.
The title compound crystallizes in triclinic P-1 with
There are two short non-bonded Sꢀ ꢀ ꢀO contacts also
[S1ꢀ ꢀ ꢀO1 = 2.647 Å and S2ꢀ ꢀ ꢀO3 = 2.665 Å] between sulfur atoms
of disulphide linkage and oxygen atoms of COOH and COOA
groups. The proton transfer from the carboxyl group at C1 to the
neighboring amino group of pyrazolone moiety makes the CAC
bond joining the COOA group [C1AC7 = 1.493(2) Å ] to be slightly
longer than that joining the COOH group [C8AC14 = 1.472(2) Å].
a = 9.6289(2) Å,
b = 10.2473(2) Å,
c = 13.7889(5) Å
and
V = 1203.12(6) A3.
The crystallographic XRD data is given in Table 1. Full Crystallo-
graphic data (cif file) relating to the crystal structure have been
deposited with the Cambridge Crystallographic Data Center as
CCDC 764774.
Scheme 1.

S. Fazil et al. / Journal of Molecular Structure 1021 (2012) 147–152
149
Table 1
Table 2
Summary of crystal data and structure refinement for (HAAP+ꢀHTBAꢁ).
Selected bond lengths (Å) and torsional angles (°) of
(HAAP+ꢀHTBAꢁ).
Empirical formula
C25H23N3O5S2
C(1)AC(7)
C(2)AS(1)
C(7)AO(1)
C(7)AO(2)
C(8)AC(14)
C(9)AS(2)
C(15)AN(1)
C(22)AN(3)
1.493(2)
1.7839(16)
1.227(2)
1.276(2)
1.472(2)
1.7868(17)
1.418(2)
1.4270(19)
2.0502(6)
ꢁ66.0(3)
Formula weight
Temperature
Wavelength
Crystal system, space
group
Unit cell dimensions
509.58
293(2) K
0.71073 A
Triclinic, P-1
a = 9.6289(2) Å
b = 10.2473(2) Å
c = 13.7889(5) Å
1203.12(6)°A3
2, 1.407 Mg/m3
0.264 mmꢁ1
a
= 99.803(2)°
b = 92.0030(10)°
= 115.3080(10)°
c
S(1)AS(2)
Volume
C(20)AC(15)AN(1)AC(23)
C(16)AC(15)AN(1)AN(2)
C(3)AC(2)AS(1)AS(2)
C(1)AC(2)AS(1)AS(2)
C(10)AC(9)AS(2)AS(1)
C(8)AC(9)AS(2)AS(1)
C(2)AS(1)AS(2)AC(9)
Z, Calculated density
Absorption coefficient
F(000)
Crystal size
Theta range for data
collection
ꢁ65.6(3)
ꢁ11.23(15)
170.20(11)
ꢁ16.12(15)
164.77(12)
83.03(8)
532
0.30 ꢂ 0.20 ꢂ 0.20 mm
2.25–29.95°
Limiting indices
ꢁ13ÜhÜ13, ꢁ14ÜkÜ14,
ꢁ19ÜlÜ19
Reflections collected/
unique
Completeness to
theta = 25.00
29812/6936 [R (int) = 0.0294]
Table 3
99.9%
Hydrogen bond interactions in (HAAP+ꢀHTBAꢁ) (Å and °).
Absorption correction
Semi-empirical from
equivalents
0.951 and 0.902
DAHꢀ ꢀ ꢀA
d(DAH)
(Å)
d(Hꢀ ꢀ ꢀA)
d(Dꢀ ꢀ ꢀA)
<(DHA)
(°)
(Å)
(Å)
Max. and min.
transmission
Refinement method
N(3)AH(3A)ꢀ ꢀ ꢀO(1)
0.89
1.97
1.99
1.67
1.71
2.8268(19)
2.8552(18)
2.5527(18)
2.5188(18)
160.7
164.5
170.7
168.0
N(3)AH(3B)ꢀ ꢀ ꢀO(3)#1 0.89
N(3)AH(3C)ꢀ ꢀ ꢀO(2)#2 0.89
O(4)AH(4A)ꢀ ꢀ ꢀO(5)#3 0.82
Full-matrix least-squares on
F2
Data/restraints/
parameters
6936/0/320
Symmetry transformations used to generate equivalent atoms: #1 x,y + 1,z #2
ꢁx + 1,ꢁy + 1, ꢁz #3 x,yꢁ1,z
Goodness-of-fit on F2
Final R indices
[I > 2sigma(I)]
R indices (all data)
Largest diff. peak and
hole
1.034
R1 = 0.0444, wR2 = 0.1130
R1 = 0.0685, wR2 = 0.127
0.335 and ꢁ0.193 e Aꢁ3
tend along the ‘b’ cell direction by means of N3AH3BꢀO3 and
O4AH4BꢀO5 interactions forming R22ð9Þ motifs (Fig. 2). These
non-covalent interactions thus form an extended ID supramolecu-
lar chain network. Adjacent chains in the crystal structure are held
together by van der Waals forces.
Fig. 1. ORTEP diagram of HAAP+ꢀHTBAꢁ.
The cation and anion moieties of (HAAP+ꢀHTBAꢁ) are held to-
gether by N3AH3AꢀO1 hydrogen bond (Fig. 1). The presence of
NHþ3 is the source of extensive hydrogen bonds in the lattice (Ta-
ble 3). Two adjacent inversion related antiparallel ion-pairs are fur-
ther connected by a pair of N3AH3CꢀO2 interactions forming a
centro-symmetric tetramer. These NAHꢀO interactions thereby
create a R44 (12) motif. The centro-symmetric tetramers then ex-
Fig. 2. Hydrogen bond interactions in (HAAP+ꢀHTBAꢁ).

150
S. Fazil et al. / Journal of Molecular Structure 1021 (2012) 147–152
Fig. 3. IR spectrum of (HAAP+ꢀHTBAꢁ).
Fig. 4. 1H NMR spectrum of (HAAP+ꢀHTBAꢁ).
3.2. Spectral studies of (HAAP+ꢀHTBAꢁ)
and symmetric stretching of NAH bonds are observed at 1608
and 1492 cmꢁ1 respectively [23].
The IR spectrum of the compound, (HAAP+ꢀHTBAꢁ), is character-
A strong band at 1295 cmꢁ1 is assigned to
m(CAN)– m(CAS) and
ized by a very strong carbonyl stretching peak at 1664 cmꢁ1
,
m
(SAS) of the anion is observed at 649 and 549 cmꢁ1 respectively
(Fig. 3). It is assigned to the C@O stretch of pyrazole ring which
superimposes with the C@O stretch of the carboxylic groups of
the acid moiety [18]. A broad band centered at 3231 cmꢁ1 is as-
signed to the stretching of the hydrogen bonded OAH of the COOH
group [19]. The OAH bonding frequency appears at 1436 cmꢁ1. The
in-plane and out-of-plane stretching modes of OAH are observed
[24,25].
The 1H NMR spectra of the compound, HAAP+ꢀHTBAꢁ in DMSO
(Fig. 4) display two signals of equal intensity at 2.103 ppm (3H)
and 2.746 ppm (3H), corresponding to the protons of CACH3 and
NACH3 groups respectively [26]. The aromatic protons give a group
of multi signals at 7.222–8.045 ppm (13H). The ammonium pro-
tons ðNHþ3 Þ which are involved in extensive hydrogen bonding is
observed as a weak broad band at 10.262 ppm [27] whereas the
proton of the COOH group is detected at 12.647 ppm [28].
at 1261 cmꢁ1 and 992 cmꢁ1 respectively.
A strong peak at
1582 cmꢁ1 corresponds to the presence of an ionized carboxylate
group. It is further confirmed by the appearance of a weak band
at 1372 cmꢁ1 due to the symmetrical stretching of COOA [20].
The medium broad band at 1887 cmꢁ1 is characteristic of the
1,2-disubstituted benzene rings in the compound. Another intense
peak at 749 cmꢁ1 supports this observation [21]. In the title com-
pound, NHþ3 is the source of extensive hydrogen bonding. This is
confirmed by the broad ammonium band at 3075 cmꢁ1 along with
weak bands at 2639 cmꢁ1 and 2486 cmꢁ1 [22]. The asymmetric
The 13C NMR spectrum of the compound, (HAAP+ꢀHTBAꢁ) in
DMSO (Fig. 5) display the signals corresponding to the different
non-equivalent carbons at different values of chemical shift, d.
The methyl carbon atoms of the pyrazol ring appear at
d
9.82 ppm (N–CH3) and 38.18 ppm (CACH3). Aryl carbon atoms
are observed in the region 119–138 ppm [24]. The carbonyl group
of pyrazol ring appears at 161.32 ppm [24]. Due to charge density

S. Fazil et al. / Journal of Molecular Structure 1021 (2012) 147–152
151
Fig. 5. 13C NMR spectrum of (HAAP+ꢀHTBAꢁ).
differences, the carboxylic acid and carboxylate functional groups
4. Conclusion
are having slightly different chemical shift values. The peak at
167.59 ppm corresponds to the carbon atom of carboxylate group
[29] and that of carboxylic acid is observed at 170.12 ppm [30].
The mass spectrum of the compound shows a well-defined par-
ent peak at m/z = 509, with a relative intensity of 40%. The base
peak at m/z = 204 is attributed to the cation moiety, C11H14N3O,
and the peak at m/z = 305 with a relative intensity of 38% is attrib-
uted to the anion moiety, C14H9O4S2. These observations support
the formation of the proton-transfer salt, (HAAP+ꢀHTBAꢁ).
Structural studies of the newly synthesized 1-phenyl-2,3-di-
methyl-5-oxo-1,2-dihydro-1H-pyrazol-4-ammonium 2[2-carbo-
xyphenyldisulfanyl]benzoate was carried out. Single crystal X-ray
analysis of the compound shows the formation of a proton transfer
salt, (HAAP+ꢀHTBAꢁ). IR, 1H and 13C NMR and Mass spectral data
supports the formation of the proton transfer salt. The compound
is thermally stable up to 260 °C and then undergoes single stage
decomposition. The cation and anion moieties of (HAAP+ꢀHTBAꢁ)
are held together by various hydrogen bond interactions leading
to a 1D chain structure.
3.3. Thermal study of (HAAP+ꢀHTBAꢁ)
Acknowledgments
In order to examine the thermal stability of the new compound,
the thermogravimetric analysis of (HAAP+ꢀHTBAꢁ) and its parent
components, AAP and MBA, were carried out in the temperature
range 0–600 °C in nitrogen atmosphere. Comparison of the ther-
mograms revealed that (HAAP+ꢀHTBAꢁ) is relatively more stable
than AAP and MBA (Fig. 6). The thermal decomposition of
(HAAP+ꢀHTBAꢁ) commences at 260 °C and continues, without the
formation of any thermally stable intermediate, till heating ends
at 600 °C. This one step weight loss process confirms that the title
compound is a neutral salt, with a remarkably stable hydrogen
bonded framework, as evidenced by single crystal X-ray structure
[31].
The authors are thankful to SAIF, IIT Madras for the Single Crys-
tal XRD result and SAIF, Cochin University of Science and Technol-
ogy, Kochi, India for elemental analysis, IR and NMR studies.
Financial aid in the form of research fellowship from University
of Kerala (for S.F.), UGC, New Delhi (for A.S.D.) and CSIR, New Delhi
(for B.K.B.) is greatly acknowledged.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the
online
version,
at
http://dx.doi.org/10.1016/
j.molstruc.2012.04.065.
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