1-Phenyl-3-(quinolin-5-yl)urea as a host for distinction of phthalic acid and terephthalic acid

Article abstract of DOI:10.1007/s12039-013-0376-z

Co-crystals of 1-phenyl-3-(quinolin-5-yl)urea (1) with terephthalic acid, adipic acid; and salts of 1 with phthalic acid, p-toluenesulphonic acids are prepared and structurally characterized. The reaction of phthalic acid and p-toluenesulphonic acid resul

Full text of DOI:10.1007/s12039-013-0376-z

c
J. Chem. Sci. Vol. 125, No. 2, March 2013, pp. 267–273. ꢀ Indian Academy of Sciences.
1-Phenyl-3-(quinolin-5-yl)urea as a host for distinction of phthalic acid
and terephthalic acid
DIPJYOTI KALITA and JUBARAJ B BARUAH∗
Department of Chemistry, Indian Institute of Technology Guwahati, North Guwahati 781 039, India
e-mail: juba@iitg.ernet.in
MS received 21 January 2012; revised 26 July 2012; accepted 2 August 2012
Abstract. Co-crystals of 1-phenyl-3-(quinolin-5-yl)urea (1) with terephthalic acid, adipic acid; and salts of
1 with phthalic acid, p-toluenesulphonic acids are prepared and structurally characterized. The reaction of
phthalic acid and p-toluenesulphonic acid resulted in protonation of the host 1, whereas the terephthalic acid
and adipic acid interact with 1, led to cocrystals with the host 1 through hydrogen bond interactions. The
hydrogen bonds that appears in the urea taps of the host molecules 1 are lost while formation of salts; in such
cases anions interacts with the urea portion of the host, while in the co-crystals the hydrogen bonded urea taps
are retained. The salts are yellow in colour while the co-crystals are colourless; thereby the positional isomer
phthalic acid can be distinguished from the terephthalic acid.
Keywords. 1-Phenyl-3-(quinolin-5-yl)urea; hydrogen bond; co-crystal; salt; visual distinction.
1. Introduction
of two positional isomers phthalic acid and terephthalic
acid by this host.
The anion recognition property of urea derivatives are
well-known in both in solid and in solution state.1–5
Hosts having urea motif are useful for selective bind-
ing of carboxylic acids such as dibutylmalonic acid.6
Owing to their versatile biological applications, design
and synthesis of hosts for selective binding of car-
boxylic acids have gained interest in recent time.7–12
There are several examples of hosts for dicarboxylic
acids and their binding properties are explored in
details.13–22 Troger’s base analogues have been reported
to recognize dicarboxylic acids with different chain
lengths.23–28 Recently, it is shown that dicarboxylic
acids form salts and co-crystals with pyridine hosts
depending on the orientation of the acid groups.29–35
Further to this conformational change in dicarboxylic
acid by hosts have practical applications in memory
devices.36,37 Binding of the carboxylic acids to nitro-
gen containing hosts have great diversity37,38 and upon
such binding also leads to changes in the physical pro-
perties from the parent compounds.38 We have shown
that urea derivative 1-phenyl-3-(quinolin-5-yl)urea (1)
is a good host in recognizing the cis and trans unsatu-
rated acids.39 In this report, we discuss structural fea-
tures of salt and cocrystals of 1 with rigid and flexible
carboxylic acids (scheme 1) and about visual distinction
2. Experimental
2.1 Synthesis of 1-phenyl-3-(quinolin-5-yl)urea (1)
5-Aminoquinoline (0.721 g, 5 mmol) was dissolved
in dry dichloromethane (10 mL) and to this solu-
tion another solution of phenylisocyanate (0.54 mL,
5 mmol) in dichloromethane was added drop-wise and
the mixture was stirred at room temperature for 3 h.
The product formed was filtered and recrystallized from
methanol. Yield: 78%. IR (KBr, cm−1): 3280 (s), 3062
(m), 1641 (s), 1599 (s), 1557 (s), 1493 (s), 1449 (m),
1315 (m), 1249 (s), 1091 (w), 799 (m), 748 (m), 694
(m). 1HNMR (DMSO-d6, 400 MHz, ppm): 8.8 (3H, m),
8.4 (1H, d, J = 8.8 Hz), 8.0 (1H, d, J = 7.2 Hz), 7.6 (2H,
m), 7.4 (3H, m), 7.2 (2H, m), 7.0 (1H, t, J = 7.2 Hz). 13C
NMR(DMSO-d6, 100 MHz, ppm): 118.3, 118.9, 121.4,
121.9, 122.7, 124.5, 129.5, 130.1, 130.8, 135.4, 140.2,
148.8, 150.9, 153.5. LC-MS [M + 1]: 264.13.
2.2 Synthesis of the salts and co-crystals of 1
The compound 1 and the dicarboxylic acids (1:1) were
dissolved in aqueous methanol. Slow evaporation of the
solution results in colourless crystals of the co-crystals
whereas in case of salts yellow coloured crystals were
observed.
∗For correspondence
267

268
Dipjyoti Kalita and Jubaraj B Baruah
1-phenyl-3-(quinolin-5-yl)urea (1)
3
2
4
5
Scheme 1. The host and its salts and cocrystals.
2.2a Salt of 1 with phthalic acid: Isolated Yield: 2.2d p-Tolunesulphonate salt of 1: The compound
69%. IR (KBr, cm−1): 3444 (w), 2924 (w), 1695 (s), 1 and p-tolunesulphonic acids (1:1) were dissolved in
1587 (m), 1535 (m), 1406 (m), 1284 (s), 1072 (m), aqueous methanol. Slow evaporation of the solution
737 (m). 1HNMR (DMSO-d6, 400 MHz, ppm): 9.0 (1H, results in yellow coloured crystals of salt 5. Isolated
s), 8.9 (2H, m), 8.5 (1H, d, J = 7.6 Hz), 8.0 (2H, m), yield: 64%. IR (KBr, cm−1): 3291 (w), 2922 (w), 1708
7.6 (5H, m), 7.5 (3H, m), 7.3 (2H, d, J = 7.6 Hz), 7.0 (s), 1637 (m), 1600 (m), 1539 (s), 1417 (m), 1366 (m),
(1H, d, J = 6.8 Hz). UV-vis {methanol, nm(ε)} 320 (1.3 1212 (s), 1165 (m), 1126 (m), 1033 (m), 1009 (m), 795
× 104 cm−1mol−1); 400 (6 × 103 cm−1mol−1).
(m). 1HNMR (DMSO-d6, 400 MHz, ppm): 9.4 (1H, s),
9.2 (2H, m), 8.2 (1H, d, J = 7.6 Hz), 8.0 (2H, m), 7.8
(1H, d, J = 8.0 Hz), 7.5 (5H, m), 7.3 (2H, m), 7.1 (2H,
d, J = 7.6 Hz), 7.0 (1H, t, J = 7.2 Hz), 2.2 (3H, s).
2.2b Co-crystal of 1 with terephthalic acid: Isolated
Yield: 67%. IR (KBr, cm−1): 3444 (w), 3266 (s),
2925(w), 1698 (s), 1637 (s), 1599 (s), 1562 (s), 1496
1
(m), 1275 (s), 1253 (m), 807 (m), 729 (m). HNMR
2.3 X-ray crystallographic studies
(DMSO-d6, 400 MHz, ppm): 9.0 (1H, s), 8.9 (2H, m),
8.5 (1H, d, J = 8.8 Hz), 8.0 (5H, m), 7.7 (2H, m), 7.6
(1H, m), 7.5 (2H, d, J = 7.6 Hz), 7.3 (2H, t, J = 7.2 Hz),
7.0 (1H, t, J = 7.2 Hz). UV-vis {methanol, nm(ε)} 320
(1.6 × 104 cm−1mol−1).
Diffraction data for compounds were collected at 296 K
with Mo Kα radiation (λ = 0.71073 Å) using a Bruker
Nonius SMART APEX CCD diffractometer equipped
with graphite monochromator and Apex CD camera.
The SMART software was used for data collection and
2.2c Co-crystal of 1 with adipic acid: Isolated Yield: also for indexing the reflections and determining the
74%. IR (KBr, cm−1): 3436 (w), 3270 (s), 2945 (w), unit cell parameters. Data reduction and cell refine-
1716 (s), 1639 (s), 1598 (s), 1561 (s), 1496 (m), 1258 ment were performed using SAINT software and the
(m), 1173 (m), 805 (m). 1HNMR (DMSO-d6, 400 MHz, space groups of these crystals were determined from
ppm): 9.0 (1H, s), 8.9 (2H, m), 8.5 (1H, d, J = 8.4 Hz), systematic absences by XPREP and further justified by
8.0 (1H, d, J = 6.8 Hz), 7.7 (2H, m), 7.6 (1H, m), 7.5 the refinement results. The structures were solved by
(2H, d, J = 8.0 Hz), 7.3 (2H, t, J = 8.0 Hz), 7.0 (1H, t, direct methods and refined by full-matrix least-square
J = 7.2 Hz), 2.2 (2H, m), 1.5 (2H, m).
calculations using SHELXTL software. All the non-H

Distinction of positional isomers
269

270
Dipjyoti Kalita and Jubaraj B Baruah
atoms were refined in the anisotropic approximation it acts as acceptor for hydrogen bonding and breaks the
against F2 of all reflections. The H-atoms attached to
heteroatoms in these crystals were located in the differ-
ence Fourier synthesis maps, and refined with isotropic
displacement coefficients. The locations of acidic pro-
tons were justified by difference Fourier synthesis map
and in the refinement these were allowed for as riding
atoms. The Crystallographic parameters of the salts and
cocrystals are listed in table 1.
urea taps. The role of electron withdrawing groups in
retaining urea taps in lattice was studied earlier41 and
it has been shown that the orientation of the aromatic
groups of urea can be controlled by the urea carboxylate
interactions.42
Terephthalic acid forms a colourless co-crystal (3)
with host 1. The co-crystal 3 crystallizes in the mono-
clinic P21/c space group where the terephthalic acid
molecule lies on an inversion centre with only half
of the molecule contained in the crystallographic
asymmetric unit (figure 2a). The urea tap motif of
the host molecule is maintained in the co-crystal
(N2-H2N····O1, N3-H3N····O1). Another intermolecu-
lar hydrogen bonding between the quinoline N atom
and the carboxylic acid (O2-H2····N1) forms a bridge
between two host molecules as shown in figure 2b. The
hydrogen bond parameters are shown in table 3. In this
case the terephthalic acids molecules are not capable
of intra-molecular hydrogen bond it does not affect the
urea taps and prefers to adopt a linear arrangement.
The pair of positional isomer namely phthalic acid
and terephthalic acid can also be distinguished by virtue
of their colour arising from the formation of salt and
co-crystal. Phthalic acids forms a yellow coloured salt
whereas terephthalic acid forms a colourless co-crystal.
The quinoline derivatives generally show n–π* transi-
tion.43 Upon protonation non-bonding electrons are no
longer available; energy of these levels goes beneath
the π-level. This helps in generating new transition
π–π* transition and this transition occurs at a higher
wavelength (400 nm) due to narrowing of energy among
3. Results and discussion
Phthalic acid forms a yellow coloured salt (2) with
host 1. The salt 2 crystallizes in the orthorhombic Pbcn
space group with one protonated cation of 1 and a
phthalate anion in the asymmetric unit (figure 1a). The
urea tap motif is not observed in the structure of this
salt, instead two hydrogen bond between the oxygen
atom of the phthalate anion and the urea nitrogen atom
is observed (N2-H2N····O4, N3-H3N····O5) (table 2).
Another intermolecular hydrogen bond between the
protonated nitrogen atom of the quinoline ring and the
carboxylate group of phthalate anion (N1-H1N····O2)
is also present in the crystal structure (figure 1b). The
urea derivatives generally form planar urea tap motif
and such motifs can be broken down by the presence of
guest molecules or anions which may lead to the break-
down of the well-organized urea tap motifs.40 In this
particular case there is strong intra-molecular hydrogen
bond interactions in the anion makes a cyclic structure
within the anion and this moiety binds to the host and
(a)
(b)
Figure 1. (a) Asymmetric unit of 2 (ORTEP diagram drawn in 50% probability ellipsoid).
(b) Hydrogen bonding network in 2.
Table 2. Hydrogen bond distances and angles for compound 2.
D-H····A
dD−H (Å)
dH····A (Å)
dD····A (Å)
<D–H···· A (◦)
N(1)-H(1N)····O(2) [x, −y, −1/2 + z]
N(2)-H(2N)····O(4) [−x, y, 1/2 − z]
N(3)-H(3N)····O(5) [−x, y, 1/2 − z]
O(3)-H(4A)····O(4)
1.05(3)
0.86
0.86
1.68(3)
2.16
2.14
2.714(2)
3.015(3)
2.970(3)
2.367(3)
168(2)
177
163
1.25(4)
1.12(4)
174(4)

Distinction of positional isomers
271
(a)
(b)
Figure 2. (a) Asymmetric unit of 3 (ORTEP diagram drawn in 50% probability ellipsoid).
(b) Hydrogen bonding network in 3.
Table 3. Hydrogen bond distances and angles for compound 3.
D-H····A
dD−H (Å)
dH····A (Å)
dD····A (Å)
<D–H····A(◦)
N(2)-H(2N)····O(1) [x, −1 + y, z]
N(3)-H(3N)····O(1) [x, −1 + y, z]
O(2)-H(2A)····N(1) [x, 3/2 − y, 1/2 + z]
0.86
0.86
0.82
2.10
1.98
1.89
2.864(1)
2.779(2)
2.697(2)
148
155
168
(a)
(b)
Figure 3. (a) Asymmetric unit of 4. (ORTEP diagram drawn in 50% probability ellipsoid).
(b) Hydrogen bonding network in 4.
Table 4. Hydrogen bond distances and angles for compound 4.
D-H····A
dD−H (Å)
dH····A (Å)
dD····A (Å)
<D–H····A(◦)
N(2)-H(2N)····O(1) [x, −1 + y, z]
N(3)-H(3N)····O(1) [x, −1 + y, z]
O(3)-H(3A)····N(1) [x, 3/2 − y, 1/2 + z]
0.85(2)
0.90(3)
0.82
2.10(2)
1.98(3)
1.92
2.870(3)
2.798(4)
2.707(5)
150(2)
150(2)
162
(a)
(b)
Figure 4. (a) Asymmetric unit of 5. (b) Short range interactions in 5.

272
Dipjyoti Kalita and Jubaraj B Baruah
the bonding and anti bonding π-orbitals. In order to states by phthalic acid and p-toluenesulphonic acids are
confirm that this change in absorbance is from the reasonable and follow a predictive trend.
host part, we have also studied the UV-visible spec-
tra of the phthalic acid and terephthalic acid. Phthalic
acid absorbs at 273 nm and on addition of base such
as triethyl amine, no absorbance in the visible region
4. Conclusion
is observed. Similarly, in the case of terephthalic acid
which absorbs at 285 nm, no absorbance at the visible
region is observed on addition of triethyl amine. Hence,
the yellow colour of the salts is only because of the
protonated form of the host 1.
The host 1 forms a colourless co-crystal with adipic
acid (4). The co-crystal 4 crystallizes in the space group
monoclinic P21/c with half of the adipic acid molecule
and a molecule of host 1 in the crystallographic asym-
metric unit (figure 3). The co-crystal 4 forms an
analogous structure with the other co-crystals by main-
taining the urea tap hydrogen bonding interaction (N2-
H2N····O1, N3-H3N····O1) (table 4). The carboxylic
acid group of adipic acid form hydrogen bonds with
the quinoline N atom (O3-H3····N1). The hydrogen
bonded self-assembly of the co-crystal is shown in
figure 3.
The present study thus shows that the host 1 is good for
distinguishing two positional isomers of dicarboxylic
acid namely phthalic acid and terephthalic acid. The
protonation of quinoline unit allows the system to lose
the self-assembling process by two N–H and one car-
bonyl oxygen of urea group of two neighbouring urea
derivatives. These results also support the reasons pro-
vided on support of strong intra-molecular hydrogen
bond interactions in visual distinction of maleic acid
from fumeric acid by the same host.39 The tereph-
thalic acid being an industrially important substrate for
polyester fibres and plastics, contamination of phthalic
acid in such material is unwanted.44 But the contami-
nant of terephthalic acid could be phthalic acid due
to synthetic procedures, thus the presence of latter as
impurity can be easily found out by using host 1 as an
indicator.
The salt 5 crystallizes in the space group mono-
clinic C2/c and exists as a Zꢁ = 1 structure with a
total of two molecules in the crystallographic asym-
metric unit (Zꢁꢁ = 2). The asymmetric unit consists
of a p-tolunesulphonate anion and a protonated 1
cation. In this structure also the urea tap motif
is not observed, instead the urea H atoms are
involved in an intermolecular hydrogen bond with
the O atom of the p-tolunesulphonate anion (dD−H···A
(Å), N2-H2N···O2, 2.904(2); N3-H3N···O4, 3.050(2)
and <D-H···A (◦), <N2-H2N···O2, 167(2); <N3-
H3N···O4, 153(1)). Another oxygen atom O3 of the p-
tolunesulphonate anion forms a hydrogen bond with the
protonated quinoline nitrogen atom (dD−H···A (Å), N1-
H1N···O3, 2.698(2) and <N1-H1N···O3, 156(2)). The
asymmetric unit of 5 is shown in figure 4a along with
the short range interactions in figure 4b.
The p-tolunesulphonate salt 5 shows a sharp peak
at 1212 cm−1 characterestic of the p-tolunesulphonate
anion. It may be mentioned that the type of supramole-
cular assembly formed by combination of carboxylic
acids with pyridine depends on the difference in
pKa values of each counterpart.31 But in the case of
acid–base complexes with similar pKa values, the
amount of proton transfer in the solid state is not a pre-
dictable parameter as a continuum exists between the
two extremes.32 The terephthalic acid, phthalic acid,
adipic acid and p-toluenesulphonic acids have pKa1
values 3.51, 2.98, 4.42, and 2.8, respectively. Thus, in
the cases of the salt formation in solid and solution
Supplementary materials
The CIF data are deposited to Cambridge Crystallo-
graphic Database, CCDC Nos. are 854224-854226.
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