1,3-Bis(ethyl-amino)-2-nitro-benzene, 1,3-bis-(n-octylamino)-2-nitro- benzene and 4-ethylamino-2-methyl-1H-benz-imid-azole

Article abstract of DOI:10.1107/S0108270108008275

1,3-Bis(ethyl-amino)-2-nitro-benzene, C10H15N3O2, (I), and 1,3-bis-(n-octylamino)-2-nitro-benzene, C22H39N3O2, (II), are the first structurally characterized 1,3-bis-(n-alkyl-amino)-2-nitro-benzenes. Both mol-ecules are bis-ected though the nitro N atom and the 2-C and 5-C atoms of the ring by twofold rotation axes. Both display intra-molecular N - H...O hydrogen bonds between the amine and nitro groups, but no inter-molecular hydrogen bonding. The nearly planar mol-ecules pack into flat layers ca 3.4 A apart that inter-act by hydro-phobic inter-actions involving the n-alkyl groups rather than by π-π inter-actions between the rings. The intra- and inter-molecular inter-actions in these mol-ecules are of inter-est in understanding the physical properties of polymers made from them. Upon heating in the presence of anhydrous potassium carbonate in dimethyl-acetamide, (I) and (II) cyclize with formal loss of hydrogen peroxide to form substituted benzimidazoles. Thus, 4-ethylamino-2-methyl-1H-benzimidazole, C10H13N3, (III), was obtained from (I) under these reaction conditions. Compound (III) contains two independent mol-ecules with no imposed inter-nal symmetry. The mol-ecules are linked into chains via N - H...N hydrogen bonds involving the imidazole rings, while the ethylamino groups do not participate in any hydrogen bonding. This is the first reported structure of a benzimidazole derivative with 4-amino and 2-alkyl substituents.

Full text of DOI:10.1107/S0108270108008275

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
strong inter- and intrachain hydrogen-bonding interactions,
which arise from the presence of secondary amine groups
ortho to an aryl nitro group in the polymer repeat unit. As an
extension of this study, we have prepared two more series of
polyamines by the reactions of homologous aliphatic diamines
with 2,6-difluoronitrobenzene and 2,4-difluoronitrobenzene,
details of which will be published elsewhere. As a precursor to
the polymer syntheses, model compounds were synthesized
from aliphatic diamines and the isomeric difluorides
mentioned above. We report herein the detailed structural
characterization of the secondary diamines 1,3-bis(ethylam-
ino)-2-nitrobenzene, (I), and 1,3-bis(n-octylamino)-2-nitro-
benzene, (II), derived from 2,6-difluoronitrobenzene. These
compounds were synthesized successfully at a reaction
temperature of 393 K in dimethylacetamide (DMAC), in the
presence of excess anhydrous potassium carbonate and
toluene. These reactions failed to yield the desired compounds
when the reaction temperature exceeded 403 K. In order to
understand this, the reaction mixture was analyzed periodi-
cally by gas chromatography and mass spectroscopy (GC/MS)
with increasing reaction temperatures. These studies suggest
that the desired diamines, which form quantitatively at or
below 403 K, undergo further transformations as the
temperature is gradually increased. 4-Ethylamino-2-methyl-
1H-benzimidazole, (III), was obtained from (I) during this
process. Benzimidazole derivative (III) is the only product
that could be unequivocally identified by GC/MS analyses.
However, the presence of a number of other organic products,
probably oligomeric in nature, was evident during the purifi-
cation of (III) using column chromatography. Compound (II)
underwent a similar reaction to yield 2-heptyl-4-(n-octyl-
amino)-1H-benzimidazole. However, in spite of repeated
attempts, we were unable to obtain crystals of appropriate
quality.
ISSN 0108-2701
1,3-Bis(ethylamino)-2-nitrobenzene,
1,3-bis(n-octylamino)-2-nitrobenzene
and 4-ethylamino-2-methyl-1H-benz-
imidazole
Christopher P. Walczak,a Matthew M. Yonkey,a Philip J.
Squattrito,a* Dillip K. Mohantya* and Kristin Kirschbaumb
aDepartment of Chemistry, Central Michigan University, Mount Pleasant, MI 48859,
USA, and bDepartment of Chemistry, University of Toledo, Toledo, OH 43606, USA
Correspondence e-mail: p.squattrito@cmich.edu, mohan1dk@cmich.edu
Received 26 February 2008
Accepted 26 March 2008
Online 9 April 2008
1,3-Bis(ethylamino)-2-nitrobenzene, C10H15N3O2, (I), and 1,3-
bis(n-octylamino)-2-nitrobenzene, C22H39N3O2, (II), are the
first structurally characterized 1,3-bis(n-alkylamino)-2-nitro-
benzenes. Both molecules are bisected though the nitro N
atom and the 2-C and 5-C atoms of the ring by twofold
rotation axes. Both display intramolecular N—Hꢀ ꢀ ꢀO
hydrogen bonds between the amine and nitro groups, but no
intermolecular hydrogen bonding. The nearly planar mol-
˚
ecules pack into flat layers ca 3.4 A apart that interact by
hydrophobic interactions involving the n-alkyl groups rather
than by ꢀ–ꢀ interactions between the rings. The intra- and
intermolecular interactions in these molecules are of interest
in understanding the physical properties of polymers made
from them. Upon heating in the presence of anhydrous
potassium carbonate in dimethylacetamide, (I) and (II) cyclize
with formal loss of hydrogen peroxide to form substituted
benzimidazoles. Thus, 4-ethylamino-2-methyl-1H-benzimida-
zole, C10H13N3, (III), was obtained from (I) under these
reaction conditions. Compound (III) contains two indepen-
dent molecules with no imposed internal symmetry. The
molecules are linked into chains via N—Hꢀ ꢀ ꢀN hydrogen
bonds involving the imidazole rings, while the ethylamino
groups do not participate in any hydrogen bonding. This is the
first reported structure of a benzimidazole derivative with
4-amino and 2-alkyl substituents.
Comment
This report is part of our continuing work on polyamines. In
our earlier studies (Teng et al., 2006), polyamines were
synthesized by the reactions of homologous aliphatic diamines
with 1,5-difluoro-2,4-dinitrobenzene. These polymers are only
soluble in concentrated mineral acids, including sulfuric, nitric
and perchloric acids, at room temperature. This excellent
solvent resistance is believed to be due to the existence of
Molecules of (I) are bisected by a twofold rotation axis that
contains atoms N1, C1, C4 and H4 (Fig. 1). The H atoms on the
N atoms of the ethylamino groups participate in strong
intramolecular hydrogen bonds with the O atoms of the
adjacent nitro group (Table 1). This pattern has been observed
previously in molecules with primary amine groups on both
sides of a nitro group (Ammon et al., 1982). A search of the
o248 # 2008 International Union of Crystallography
doi:10.1107/S0108270108008275
Acta Cryst. (2008). C64, o248–o251

organic compounds
Figure 3
The molecular structure of (II), showing the atom-labeling scheme.
Displacement ellipsoids are drawn at the 50% probability level and H
atoms are shown as small spheres of arbitrary radii. Dashed lines indicate
hydrogen bonds. The asymmetric unit consists of one-half of the molecule
and unlabeled atoms are related to labeled atoms by the symmetry
Figure 1
The molecular structure of (I), showing the atom-labeling scheme.
Displacement ellipsoids are drawn at the 50% probability level and H
atoms are shown as small spheres of arbitrary radii. Dashed lines indicate
hydrogen bonds. The asymmetric unit consists of one-half of the molecule
and unlabeled atoms are related to labeled atoms by the symmetry
1
operator (ꢃx; y; ꢃz þ ).
2
3
2
3
2
operator (ꢃx þ ; y; ꢃz þ ).
Figure 4
A single layer of molecules of (II), viewed along the a axis. Note the
absence of intermolecular N—Hꢀ ꢀ ꢀO hydrogen bonding.
zigzag anti conformation and the essentially planar molecules
pack in flat layers parallel to (301) with no intermolecular N—
Hꢀ ꢀ ꢀO hydrogen bonding (Fig. 4). Similar to (I), the layers are
˚
separated by about 3.4 A, but the rings are not face-to-face.
Rather, the dominant interaction is between the hydrophobic
octyl chains. This preference for interactions between long
alkyl chains over those between phenyl rings has also been
noted in N-(n-decyl)-4-nitroaniline (Yonkey et al., 2008). The
absence of intermolecular hydrogen bonding between the
amine and nitro groups in the monomers, though under-
standable given the strong intramolecular interactions, does
raise questions about what may be taking place in the poly-
mers. We do note, however, that there are examples of aryl
nitro compounds with ortho secondary amines in which the
amine participates in simultaneous intra- and intermolecular
N—Hꢀ ꢀ ꢀO hydrogen bonds (Panunto et al., 1987).
Figure 2
A single layer of molecules of (I), viewed along the c axis. Note the
absence of intermolecular N—Hꢀ ꢀ ꢀO hydrogen bonding.
Cambridge Structural Database (CSD, Version 5.29 plus
update of January 2008; Allen, 2002) revealed no prior reports
of 1,3-bis(n-alkylamino)-2-nitrobenzene structures, so this
would appear to be the first example involving secondary
amines. The ethyl groups adopt an anti conformation (C2—
N2—C5—C6 torsion angle ca 180ꢁ), with the result that the
molecules are essentially planar. The molecules pack into flat
layers parallel to (103) (Fig. 2). It should be noted that there
are no intermolecular hydrogen bonds involving the amine H
atoms. The packing is thus dominated by hydrophobic inter-
actions. Interestingly, although the interlayer spacing (ca
Compound (III) is formed from (I) by an internal cycliza-
tion in which a new bond is formed between the ꢁ-C atom of
one of the ethyl groups and the nitro N atom. In the process,
the two ꢁ-H atoms and both nitro O atoms are lost. The
presence of a peak of 34 a.m.u. in the mass spectrum suggests
the possibility of hydrogen peroxide as the decomposition
product. Structurally, (III) occurs as two independent mol-
ecules that occupy general positions and do not differ signif-
icantly in conformation (Fig. 5). The molecules are essentially
planar, with a dihedral angle of 57.25 (1)ꢁ between them. In
both molecules, the amine N atom is most displaced from the
˚
˚
3.4 A) is short enough for strong ꢀ–ꢀ interactions, the layers
least-squares plane of the non-H atoms, viz. by 0.124 (1) A for
˚
atom N12 and by 0.057 (1) A for atom N22. Similar to what is
are actually shifted so that the rings are not over one another.
Molecules of (II) are very similar to those of (I), being also
bisected through the nitro group and ring by a twofold axis
(Fig. 3) and displaying the same intramolecular N—Hꢀ ꢀ ꢀO
hydrogen bonding (Table 2). The n-octyl groups are in the
found in benzimidazole itself (Vijayan et al., 2006), the mol-
ecules in (III) are linked by N—Hꢀ ꢀ ꢀN hydrogen bonds
between the protonated and unprotonated N atoms of the
imidazole rings of adjacent molecules into chains running
ꢂ
Acta Cryst. (2008). C64, o248–o251
Walczak et al.
C10H15N3O2, C22H39N3O2 and C10H13N3 o249

organic compounds
reduced pressure, and the solvents from the dark-red filtrate were
removed under high vacuum to yield a bright-red solid residue. The
crude product was dissolved in hexane (15 ml), transferred to a
separating funnel and washed repeatedly with deionized water. The
organic layer was collected, dried over anhydrous magnesium sulfate
and filtered, and the filtrate was evaporated using a rotary evaporator
to yield a bright-red solid. Crystals suitable for X-ray diffraction were
obtained by recrystallization from hexane. Analysis for compound
(I): yield 65%; m.p. 336–338 K; 1H NMR (400 MHz, CDCl3): ꢂ 8.6 (s,
2H), 7.1 (m, 1H), 5.9 (d, 2H), 3.2 (m, 3H), 1.3 (t, 6H); 13C NMR
(CDCl3): ꢂ 148.51, 137.06, 121.01, 98.01, 38.34, 14.42; IR (KBr, ꢃ >
1400 cmꢃ1): 3347, 2980, 2860, 1582, 1515, 1472; MS (m/z) (% base
peak): 209 (85), 174 (100), 132 (72.5), 147 (55). Analysis for
compound (II): yield 70%; m.p. 343–345 K; 1H NMR (400 MHz,
CDCl3): ꢂ 8.7 (t, 2H), 7.1 (t, 1H), 5.8 (d, 2H), 3.2 (m, 4H), 1.7 (m, 4H),
1.3 (m, 20H), 0.9 (t, 6H); 13C NMR (CDCl3): ꢂ 148.69, 136.99, 97.88,
43.76, 32.02, 29.51, 29.42, 28.99, 27.40, 22.86, 14.31; IR (KBr, ꢃ >
1400 cmꢃ1): 3343, 2957, 2926, 2850, 1583, 1515, 1471; MS (m/z) (%
base peak): 377 (63.2), 342 (97.7), 244 (40.3), 232 (43.7), 134 (100).
Compound (III) was synthesized from (I) (prepared as described
above) by taking the red solution obtained after azeoptropic removal
of water and heating it to 433 K for 24 h. During this time, the color
gradually turned dark brown. The reaction solution was then diluted
with dichloromethane (30 ml). The resulting heterogeneous mixture
was filtered through Celite at reduced pressure and solvents were
removed under high vacuum. The crude product was dissolved in
dichloromethane (15 ml), transferred to a separating funnel and
washed repeatedly with deionized water. The organic layer was
collected, dried over anhydrous magnesium sulfate and filtered, and
the filtrate was evaporated using a rotary evaporator to yield a dark-
brown solid. The crude product was eluted on a neutral alumina
column using dichloromethane–ethyl acetate (70:30 v/v) to obtain the
desired compound, viz. (III). The blue–green solid was recrystallized
from hexane. Analysis for compound (III): yield: 15%; m.p. 432–
434 K; 1H NMR (400 MHz, CDCl3): ꢂ 7.1 (m, 1H), 6.7 (m, 1H), 6.3 (m,
1H), 3.3 (q, 2H), 2.6 (s, 3H), 1.3 (t, 3H); 13C NMR (CDCl3): ꢂ 148.24,
139.90, 134.53, 131.55, 124.02, 101.55, 99.67, 38.39, 30.00, 15.06; IR
(KBr, ꢃ > 1400 cmꢃ1): 3366, 2961, 1607, 1540, 1422; MS (m/z) (% base
peak): 175 (38), 132 (38), 160 (100).
Figure 5
A packing diagram for (III), showing the atom-labeling scheme.
Displacement ellipsoids are drawn at the 50% probability level and H
atoms are shown as small spheres of arbitrary radii. The asymmetric unit
consists of two independent molecules. N—Hꢀ ꢀ ꢀN hydrogen bonds
(dashed lines) involving the imidazole rings link the molecules into chains
running parallel to the a axis. There are no hydrogen bonds involving the
amine N atoms.
parallel to the a axis. The amine groups do not participate in
any N—Hꢀ ꢀ ꢀN hydrogen bonds. Benzimidazole crystallizes in
a noncentrosymmetric space group and is of interest as a
potential nonlinear optical material (Vijayan et al., 2006).
However, in spite of the similar hydrogen bonding, (III)
crystallizes in a centrosymmetric space group. The presence of
intermolecular hydrogen bonds in (III) is reflected in the
significantly higher melting point compared with (I) and (II).
A search of the CSD found no benzimidazole derivatives with
alkyl groups in the 4-position and an R group in the 2-position,
making this the first structurally characterized example.
Compound (I)
Crystal data
Experimental
3
˚
C10H15N3O2
Mr = 209.25
V = 523.61 (10) A
Z = 2
Compounds (I) and (II) were prepared by similar routes. Anhydrous
potassium carbonate (1.0943 g, 0.008 mol) and a solution of ethyl-
amine (1.0805 g, 0.0240 mol; 70% in water) or octylamine (0.7284 g,
0.006 mol) in dimethylacetamide (DMAC, 8 ml) were combined in a
100 ml three-necked round-bottomed flask fitted with a nitrogen
inlet, a thermometer, a magnetic stirring bar and a Dean–Stark trap
with a condenser. To the stirred solution was added 2,6-difluoro-
nitrobenzene (0.4342 g, 0.0027 mol) in DMAC (5 ml) was added.
Additional DMAC (8 ml) was used to wash the transfer container
and this was added to the reaction mixture, followed by the addition
of toluene (20 ml). The color of the reaction mixture turned bright
red when the temperature reached 343 K. The temperature of the
reaction mixture was raised to 393 K, and the reaction was allowed to
continue at this temperature for 3 h. Water, the by-product of the
reaction, was removed via azeotropic distillation with toluene. On
completion of the reaction, the reaction mixture was allowed to cool
to room temperature and diluted with dichloromethane (30 ml). The
resulting heterogeneous mixture was filtered through Celite at
Monoclinic, P2=n
Mo Kꢁ radiation
ꢅ = 0.10 mmꢃ1
T = 140 (2) K
0.40 ꢄ 0.06 ꢄ 0.03 mm
˚
a = 5.0425 (6) A
˚
b = 9.2564 (10) A
˚
c = 11.4901 (13) A
ꢄ = 102.492 (2)ꢁ
Data collection
Bruker SMART 6000 CCD area-
detector diffractometer
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
Tmin = 0.77, Tmax = 1.00
3016 measured reflections
1017 independent reflections
919 reflections with I > 2ꢆ(I)
Rint = 0.055
(expected range = 0.768–0.997)
Refinement
R[F2 > 2ꢆ(F2)] = 0.046
wR(F2) = 0.121
S = 1.15
100 parameters
All H-atom parameters refined
ꢃ3
˚
Áꢇmax = 0.31 e A
ꢃ3
˚
1017 reflections
Áꢇmin = ꢃ0.16 e A
ꢂ
o250 Walczak et al. C10H15N3O2, C22H39N3O2 and C10H13N3
Acta Cryst. (2008). C64, o248–o251

organic compounds
Table 1
Hydrogen-bond geometry (A, ) for (I).
Table 2
Hydrogen-bond geometry (A, ) for (II).
ꢁ
ꢁ
˚
˚
D—Hꢀ ꢀ ꢀA
D—H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D—Hꢀ ꢀ ꢀA
D—Hꢀ ꢀ ꢀA
D—H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D—Hꢀ ꢀ ꢀA
N2—H2ꢀ ꢀ ꢀO1
0.85 (2)
1.91 (2)
2.566 (1)
133 (2)
N2—H2ꢀ ꢀ ꢀO1
0.844 (18)
1.910 (18)
2.570 (1)
134 (2)
Table 3
Hydrogen-bond geometry (A, ) for (III).
ꢁ
˚
Compound (II)
D—Hꢀ ꢀ ꢀA
D—H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D—Hꢀ ꢀ ꢀA
Crystal data
3
˚
C22H39N3O2
Mr = 377.56
V = 2121.0 (3) A
Z = 4
N11—H11ꢀ ꢀ ꢀN23
0.945 (17)
0.950 (17)
1.896 (18)
1.946 (17)
2.8293 (14)
2.8761 (15)
169.2 (15)
165.9 (15)
N21—H21ꢀ ꢀ ꢀN13i
Monoclinic, C2=c
a = 21.5603 (16) A
Mo Kꢁ radiation
ꢅ = 0.08 mmꢃ1
T = 140 (1) K
0.38 ꢄ 0.19 ꢄ 0.03 mm
Symmetry code: (i) x þ 1; y; z.
˚
˚
b = 9.1066 (7) A
˚
c = 12.6778 (10) A
All H atoms were located in difference Fourier syntheses and were
˚
refined isotropically [C—H = 0.915 (17)–1.030 (14) A].
ꢄ = 121.560 (2)ꢁ
For all compounds, data collection: SMART (Bruker, 2003); cell
refinement: SAINT-Plus (Bruker, 2003); data reduction: SAINT-
Plus; program(s) used to solve structure: SHELXTL (Version 6.10;
Sheldrick, 2008); program(s) used to refine structure: SHELXTL;
molecular graphics: CrystalMaker (Palmer, 2006); software used to
prepare material for publication: SHELXTL and local programs.
Data collection
Bruker SMART 6000 CCD area-
detector diffractometer
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
Tmin = 0.841, Tmax = 1.000
8645 measured reflections
2568 independent reflections
2012 reflections with I > 2ꢆ(I)
Rint = 0.022
(expected range = 0.839–0.998)
DKM acknowledges financial support for this project from
the Research Excellence Fund of Michigan and the Presi-
dent’s Bridge to Commercialization Grant, and sabbatical
support from Central Michigan University. The authors thank
the College of Arts and Sciences of the University of Toledo
and the Ohio Board of Regents for generous financial support
of the X-ray diffraction facility.
Refinement
R[F2 > 2ꢆ(F2)] = 0.054
wR(F2) = 0.149
S = 1.06
202 parameters
All H-atom parameters refined
ꢃ3
˚
Áꢇmax = 0.43 e A
ꢃ3
˚
2568 reflections
Áꢇmin = ꢃ0.28 e A
Compound (III)
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: SK3210). Services for accessing these data are
described at the back of the journal.
Crystal data
3
˚
V = 1886.47 (10) A
Z = 8
C10H13N3
Mr = 175.23
Monoclinic, P21=n
Mo Kꢁ radiation
ꢅ = 0.08 mmꢃ1
T = 140 (2) K
0.36 ꢄ 0.30 ꢄ 0.30 mm
˚
a = 9.6166 (3) A
References
˚
b = 16.2072 (5) A
Allen, F. H. (2002). Acta Cryst. B58, 380–388.
Ammon, H. L., Bhattacharjee, S. K. & Holden, J. R. (1982). Acta Cryst. B38,
1851–1854.
˚
c = 12.1236 (3) A
ꢄ = 93.278 (1)ꢁ
Bruker (2003). SMART (Version 5.630) and SAINT-Plus (Version 6.45A).
Bruker AXS Inc., Madison, Wisconsin, USA.
Data collection
Palmer, D. (2006). CrystalMaker. Version 7.2.3. CrystalMaker Software Ltd,
Yarnton, England.
Panunto, T. W., Urbanczyk-Lipkowska, Z., Johnson, R. & Etter, M. C. (1987).
J. Am. Chem. Soc. 109, 7786–7797.
Bruker SMART 6000 CCD area-
detector diffractometer
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
Tmin = 0.893, Tmax = 1.000
19605 measured reflections
4120 independent reflections
3759 reflections with I > 2ꢆ(I)
Rint = 0.019
¨
Sheldrick, G. M. (1996). SADABS. University of Gottingen, Germany.
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122.
Teng, Y. H., Kaminski, G., Zhang, Z., Sharma, A. & Mohanty, D. K. (2006).
Polymer, 47, 4004–4011.
Vijayan, N., Bhagavannarayana, G., Kanagasekaran, T., Ramesh Babu, R.,
Gopalakrishnan, R. & Ramasamy, P. (2006). Cryst. Res. Technol. 41, 784–
789.
(expected range = 0.873–0.977)
Refinement
R[F2 > 2ꢆ(F2)] = 0.044
wR(F2) = 0.118
S = 1.09
339 parameters
All H-atom parameters refined
ꢃ3
˚
Áꢇmax = 0.30 e A
Yonkey, M. M., Walczak, C. P., Squattrito, P. J., Mohanty, D. K. & Kirschbaum,
K. (2008). Acta Cryst. E64, o549.
ꢃ3
˚
4120 reflections
Áꢇmin = ꢃ0.24 e A
ꢂ
Acta Cryst. (2008). C64, o248–o251
Walczak et al.
C10H15N3O2, C22H39N3O2 and C10H13N3 o251