Synthesis, crystallographic and spectral studies of 3-(4-(Phenylamino) Phenylamino)Cyclohex-2-Enone

Article abstract of DOI:10.1007/s10870-009-9664-3

The title compound, 3-(4-(phenylamino)phenylamino)cyclohex-2-enone, β-enaminone of 1,3-cyclohexanedione and p-amino diphenylamine (C ₁₈H₁₈N₂O) was prepared and characterized by ¹H-NMR, ¹³C-NMR, Elemental analysis and IR spectroscopy as well as single crystal X-ray diffraction. These results indicate the predominance of the keto-enol tautomerism. Molecular conformation around the central disubstituted benzene ring is affected by the tautomerism and two steric effects between side molecular groups and mono substituted benzene ring. Electron delocalizations due to these effects have been observed in the molecular structure, the structure being stabilized by some intermolecular hydrogen bonds.

Full text of DOI:10.1007/s10870-009-9664-3

J Chem Crystallogr (2010) 40:376–380
DOI 10.1007/s10870-009-9664-3
ORIGINAL PAPER
Synthesis, Crystallographic and Spectral Studies
of 3-(4-(Phenylamino) Phenylamino)Cyclohex-2-Enone
•
•
•
¨
Mahir Timur Gu¨lten Kavak Hu¨lya S¸enoz
_
Semra Ide Nazan Tunoglu
•
˘
Received: 23 February 2009 / Accepted: 31 October 2009 / Published online: 14 November 2009
Ó Springer Science+Business Media, LLC 2009
Abstract The title compound, 3-(4-(phenylamino)phe-
nylamino)cyclohex-2-enone, b-enaminone of 1,3-cyclo-
hexanedione and p-amino diphenylamine (C18H18N2O)
due to intramolecular hydrogen bonding. Because of the
significant reactivity of the conjugated N–C=C–C=O
system, b-enaminones are used as important intermedi-
ates in synthetic organic chemistry for the preparation
of a large number of heterocyclic compounds [1–8].
b-Enaminones have a wide variety of applications in med-
icine, biochemistry, coordination chemistry and photonic
technologies [9–11]. Some b-enaminones are pharmaco-
logically active and exhibit anticonvulsant activity [12–
15].
1
was prepared and characterized by H-NMR, 13C-NMR,
Elemental analysis and IR spectroscopy as well as single
crystal X-ray diffraction. These results indicate the pre-
dominance of the keto-enol tautomerism. Molecular con-
formation around the central disubstituted benzene ring is
affected by the tautomerism and two steric effects between
side molecular groups and mono substituted benzene ring.
Electron delocalizations due to these effects have been
observed in the molecular structure, the structure being
stabilized by some intermolecular hydrogen bonds.
Despite the importance of b-enaminones as valuable
biologically active compounds, their synthesis has received
to date little attention. Among them, the most simple and
straightforward conventional method is the azeotropic
removal of water by refluxing an amine and 1,3-diketone in
aromatic solvents. The other methods used for this trans-
formation with various activators such as microwave irra-
diation, the reaction catalyzed by NaAuCl, bismuth(III)
trifluoroacetate, Lanthanum trichloride have been reported
[16–20]. b-Enaminones, derived from cyclic 1,3-dicar-
bonyl compounds, are significantly more stable than acy-
clic analogs.
Keywords Schiff base Á b-Enaminone Á
Cyclohexanedione Á Crystal structure Á
Spectroscopic studies Á Tautomerism
Introduction
b-Enaminones are a class of enamines which are more
stable than the enamines of monocarbonyl compounds
When a 1,3-diketone is used in Schiff base synthesis, a
more stable b-enaminone derivative is formed by means
of isomerization. A keto-enol tautomerism (A ꢀ B) is
observed when only one carbonyl group of 1,3-diketone
forms the corresponding ketoimine because of added con-
jugation, which covers the three carbons of hexane ring.
The ketoimine is then converted to b-enaminone form
which is stabilized both by the formation of intermolecular
hydrogen bonding and resonance [21, 22].
˘
¨
M. Timur (&) Á H. S¸enoz Á N. Tunoglu
Faculty of Science, Department of Chemistry, Hacettepe
University, 06800 Beytepe-Ankara, Turkey
e-mail: mahirtimur@gmail.com
G. Kavak
Faculty of Science and Art, Department of Physics, Dicle
University, 21280 Diyarbakır, Turkey
We report here the structure of an b-enaminone, which
was obtained by condensation of a diketone, 1,3-cyclo-
hexanedione, and a primary amine, p-amino diphenylamine
(Scheme 1).
_
S. Ide
Faculty of Engineering, Department of Physics Engineering,
Hacettepe University, 06800 Beytepe-Ankara, Turkey
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J Chem Crystallogr (2010) 40:376–380
377
Scheme 1 The reaction of 1,3-cyclohexanedione and p-amino diphenylamine to yield 3-(4-(phenylamino) phenylamino)cyclohex-2-enone
Scheme 2 The other possible
structures of the reaction
product given in Scheme 1
Fig. 1 Molecular structure of
the 3-(4-(phenylamino)
phenylamino)cyclohex-2-enone,
showing 50% probability
displacement ellipsoids
The ketoamine, iminoenol and ketoimin form (Schiff
base) are the three tautomeric forms of b-enaminones
(Scheme 2). However, the enaminone form is generally
favored because of increased resonance between sp3-
nitrogen and the carbonyl group [23, 24]. b-enaminones
show double-bond stereoisomerism. Previous NMR spec-
troscopic and X-ray crystallographic studies have shown
that enaminones exist as either the E-s-E-s-E or as mixture
of both conformations, depending on the C-2 substituent
the Z-s-Z-s-E conformations [25]. The E and Z forms of
Solvents and all reagents were technical grade and were
purified and dried by distillation from appropriate desiccant
when necessary. Concentration of solutions after reactions
and extractions were achieved using a rotary evaporator at
reduced pressure.
Analytical and preparative thin layer chromatography
(TLC) was performed on silica gel HF-254 (Merck). Col-
umn chromatography was carried out by using 70–230
mesh silica gel (0.063–0.2 min, Merck).
1
enaminones can easily be identified by means of H-NMR
Method
spectroscopy. The N–H signal of the Z isomer appears at
9–13 ppm while the same signal for the E isomer appears
at 4–8 ppm due to strong intermolecular hydrogen bonding
[26].
The structures of the compounds in this study were deter-
mined by the instruments mentioned below.
All melting points were measured in sealed tubes using
an electrothermal digital melting point apparatus (Gal-
lenkamp) and were uncorrected. The investigation of
vibrational properties of the b-enaminone was carried out
on a Mattson 1000 Model FT-IR Spectrometer within the
range of 4000–400 cm-1. The IR sample was prepared as
The molecular structure and crystallographic numbering
order of the atoms of 3-(4-(phenylamino) phenylami-
no)cyclohex-2-enone are shown in Fig. 1.
1
Experimental
KBr pellet. H-NMR, 13C-NMR were recorded on a reso-
lution fourier transform Bruker WH-400 NMR spectrom-
eter with tetramethylsilane as an internal standard.
Chemical shifts were reported in ppm relative to the sol-
vent peak. Signals were designated as follows: s, singlet; d,
doublet; t, triplet; q, quartet; m, multiplet. Elemental
Material
All starting compounds and solvents for synthesis were
purchased from Across, Aldrich, Sigma and E. Merck.
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J Chem Crystallogr (2010) 40:376–380
microanalyses of the separated solid chelates for C, H, N,
were performed with a Elementar Analysensysteme GmbH
vario MICRO CHNS analyser.
13C-NMR (DMSO-d6); dppm, 97,55 (C-2 vinyl carbon
atom); 163.33 (C-3 vinyl carbon atom); 195.68 (C-1 car-
bonyl carbon atom).
Elemental Analysis calculated (found): C, 77.67 (77.38);
H, 6.52 (6.49); N, 10.06 (9.94); O, 5.75 (6.19).
Synthesis
A mixture of 10 mmol (1.12 g) 1,3-cyclohexanedione and
10 mmol (1.84 g) p-amino-diphenylamine were refluxed in
100 mL benzene using a Dean-Stark apparatus until all
water was completely separated. The removal of water is
very important because of the back hydrolysis of the
enaminone. Benzene was evaporated and the precipitate
was extracted with ethanol. The crude product was purified
by silica gel column chromatography using a mixture of n-
hexane/ethyl acetate mixture as eluent. The product was
recrystallized twice from ethanol and obtained as pure
crystals. Yield: 58%, mp. 207–208 °C.
Crystallographic Studies
A summary of the key crystallographic information is
given in Table 1. A suitable single-crystal was selected and
mounted on an Enraf–Nonius CAD-4 diffractometer. The
Table 2 Some geometrical parameters of 3-(4-(phenylamino)phe-
nylamino) cyclohex-2-enone
˚
Bond lengths (A)
O–C1
1.253(2)
1.399(2)
1.401(2)
1.344(2)
1.428(2)
1.376(2)
1.369(2)
1.502(2)
1.392(3)
1.394(2)
1.388(3)
1.392(2)
1.414(3)
1.391(2)
N2–C10
N2–C13
Spectroscopic Studies
N1–C3
IR (KBr, cm-1); t(N–H) 3282 s and 3212 m, t(Ar–H)
3030 m, t(C–H) 2995 m and 2946 s and 2860 m, t(C=O
and C=C of enamine) 1680–1490 s and broad, t(C–N)
1370–1252 s. 1H-NMR (CDCl3); d ppm, 7.30–7.40 (m, 4H,
NH–Ph-NH); 7.00–7.10 (m, 5H, Ph-NH); 5.95 (s, 1H,
enamine NH); 5.75 (s, 1H, PhNHPh); 5.50 (s, 1H, vinylic
CH); 2.50 (t, 2H, CH2); 2.40 (t, 2 H, CH2); 2.00(m, 2 H,
CH2).
N1–C7
C8–C7
C3–C2
C3–C4
C10–C11
C10–C9
C13–C14
C13–C18
C1–C2
C7–C12
Table 1 Crystal data and details of the structure determination of
3-(4-(phenylamino) phenylamino)cyclohex-2-enone
Bond angles (°)
C10–N2–C13
C3–N1–C7
N1–C3–C2
C11–C10–C9
C11–C10–N2
C9–C10–N2
C14–C13–C18
C14–C13–N2
C18–C13–N2
C3–C2–C1
C8–C7–C12
C8–C7–N1
C12–C7–N1
O–C1–C2
127.02(16)
126.40(15)
124.49(16)
117.83(17)
118.10(16)
123.99(17)
118.13(18)
123.84(16)
118.01(17)
122.19(17)
118.72(16)
119.87(15)
121.31(16)
122.08(17)
Crystal formula
Formula weight
Crystal dimensions (mm)
Temp (K)
C18H18N2O
278.34
0.56 9 0.58 9 0.6
291(2)
Crystal system
Space group
Monoclinic
P21/c
˚
a (A)
9.823(1)
15.625(1)
10.841(1)
116.440(8)
4; 1.24
˚
b (A)
˚
c (A)
b (°)
Z; Dcalc (g cm-1
Range of h (°)
)
2.5/26.3
0.078
l (MoKa) (mm-1
)
Reflections collected
Reflections used in refinement
No. of refined parameters
R/Rw values
3,195
Torsion angles (°)
C7–N1–C3–C2
C13–N2–C10–C9
C10–N2–C13–C14
C3–N1–C7–C12
C3–C2–C1–O
N2–C13–C14–C15
3,019
-7.8(3)
31.8(3)
203
0.0590/0.1503
1.0880
17.3(3)
GOF
-48.6(3)
-172.09(18)
178.34(18)
Final shift
0.000
-3
)
˚
(Dq)min, (Dq)max (e A
0.550, -0.452
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J Chem Crystallogr (2010) 40:376–380
379
structure was solved by direct methods with SHELXS-97
and refined by least squares on F2obs with SHELXL-97 [27].
All the hydrogen atoms were located from difference
Fourier map and they were refined using riding model.
Some geometrical parameters (bond lengths, bond
angles and torsion angles) can be seen in Table 2.
conjugation of the NH group with two adjacent phenyl
groups. The two phenyl groups also absorb at different
fields. The five protons of the phenyl group attached to only
one NH group appear upfield in comparison to other aro-
matic group, probably due to the influence of two NH
groups attached at para positions of the later phenyl group.
The lone C-2 vinyl hydrogen for the b-enaminone com-
pound appeared as a singlet at 5.50 ppm, with an integral
area equivalent to one hydrogen. The 13C NMR results also
supported the b-enaminone structure by the observation of
signals in the region of 195.68 (C-1 carbonyl carbon atom),
163.33 (C-3 vinyl carbon atom), and 97.55 (C-2 vinyl
carbon atom).
Results and Discussion
The title compound is an enaminone rather than an imi-
noenol or a ketoimine. In the IR spectrum of this com-
pound, an intense broad band appears at 1,490–1,680 cm-1
due to normal carbonyl absorption, the broadness probably
arising from the interference of the conjugated C=C
absorption of the enamine moiety and the intermolecular
hydrogen bonding of the carbonyl moiety. The two bands
at 3282 and 3212 cm-1 arise from the stretching vibrations
of N–H group attached to the conjugated carbonyl group,
whereas the absorptions in the region 1,370–1,252 cm-1
are due to C–N stretching of the aromatic amino groups.
Appearance of the later absorption at shorter wavelengths
than the corresponding absorption of aliphatic amines is
due to the fact that the force constant of the C–N bond is
increased by the resonance with the ring [28].
The ketoamine (enaminone) form of our compound is
distinguished from the ketoimino form by the presence of a
single vinylic proton and a single amine proton at d: 5.50
and 5.75 ppm, respectively.
Elemental analysis is in agreement with the formulae of
the b-enaminone.
The discussion related with the crystallographic struc-
ture can be given by the following explanations.
The mean planes of the six-membered rings are twisted
with respect to each other in order to minimize the steric
hinderance (H2ÁÁÁH12 and H9ÁÁÁH14). Indeed, they make an
angle of 48.80(6)° and 43.02(6) between the cyclohexa-
none ring and the phenyl rings and between the two phenyl
rings, respectively. The conformation of the molecule can
be also affected by the intermolecular hydrogen bonds in
Fig. 2. Geometrical details of these hydrogen bonds were
given in Table 3. With the help of these donor–acceptor
relationship, It can be said that, trans-keto form may be
seen in the molecular conformation and this intermolecular
tautomeric form may cause thermal and photochromic
According to literature data reported for compounds
1
containing the b-enaminone structure [29, 30], the H and
13C NMR data of the prepared b-enaminone compound,
clearly possessed the appropriate signals needed to identify
these compound unambiguously. In the 1H NMR spectrum,
the NH group between two phenyls appears at d: 5.95,
while the NH of the enaminone group absorbs at d: 5.75.
The downfield shifting in the former case arises due to the
Fig. 2 Packing diagram
showing molecular orientation
and hydrogen bonded chains
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J Chem Crystallogr (2010) 40:376–380
˚
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Table 3 Hydrogen bonding geometry (A, °) for 3-(4-(phenylami-
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˚
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CCDC-657271 contains the supplementary crystallo-
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Acknowledgments This work was supported financially by Hacet-
tepe University (Research Center Office/Projects No: 01.02.602.002
and 05A601009).
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