Structural and spectral analysis of a mannich base: 3-(Morpholin-4- ylmethyl)-1,3-benzothiazole-2-thione

Article abstract of DOI:10.1007/s10870-011-0199-z

The crystal structure of 3-(morpholin-4-ylmethyl)-1,3-benzothiazole-2- thione, C₁₂H₁₄N₂OS₂, crystallizes in the monoclinic space group (P2₁/c). This benzothiazole derivative is a mannich base. Methylene group bridges the molecules of 2-mercapto benzothiazole and morpholine with an angle at the methylene bridge being 110.31(12)° [N-C-N]. The dihedral angle between the benzothiazole and morpholine planes is 70.37(5)°. The morpholine ring adopts a chair conformation. The molecular structure is stabilized by the weak C-H???S hydrogen bond in addition to the C- H???π and π???π interactions. Present study reports the conformation and hydrogen bonding interactions. Spectral analysis complement the structure analyzed. Graphical Abstract: The compound 3-(morpholin-4-ylmethyl)-1,3-benzothiazole-2-thione is a Mannich base. The crystal structure gives a picture of a methylene group bridging the molecules of 2-mercapto benzothiazole and morpholine.[Figure not available: see fulltext.]

Full text of DOI:10.1007/s10870-011-0199-z

J Chem Crystallogr (2012) 42:29–33
DOI 10.1007/s10870-011-0199-z
ORIGINAL PAPER
Structural and Spectral Analysis of a Mannich Base:
3-(Morpholin-4-ylmethyl)-1,3-Benzothiazole-2-Thione
•
•
•
S. Franklin D. Tamilvendan G. Venkatesa Prabhu
T. Balasubramanian
Received: 9 March 2011 / Accepted: 26 September 2011 / Published online: 9 November 2011
Ó Springer Science+Business Media, LLC 2011
Abstract The crystal structure of 3-(morpholin-4-ylme-
thyl)-1,3-benzothiazole-2-thione, C12H14N2OS2, crystal-
lizes in the monoclinic space group (P21/c). This
benzothiazole derivative is a mannich base. Methylene
group bridges the molecules of 2-mercapto benzothiazole
and morpholine with an angle at the methylene bridge
being 110.31(12)° [N–C–N]. The dihedral angle between
the benzothiazole and morpholine planes is 70.37(5)°. The
morpholine ring adopts a chair conformation. The molec-
ular structure is stabilized by the weak C–HÁÁÁS hydrogen
bond in addition to the C–HÁÁÁp and pÁÁÁp interactions.
Present study reports the conformation and hydrogen
bonding interactions. Spectral analysis complement the
structure analyzed.
Keywords Organic compounds Á Mannich base Á
Spectral analysis Á Crystal structure Á Hydrogen bonds
Introduction
Mannich reaction is a three-component condensation reac-
tion involving active hydrogen compound, formaldehyde
and a secondary or tertiary amine [1, 2]. It is an important
C–C bond formation reaction used widely in the synthesis of
secondary and tertiary amine derivatives [3, 4]. It is a key
step in the synthesis of many bioactive molecules [5].
Mannich base compounds have been reported as potential
biological agents. They find applications as anti-tubercular
[6], anti-malarial [7], vasorelaxing [8], anti-cancer [9] and
analgesic drugs [10]. The crystal structure of a mannich
base, 3-(morpholin-4-ylmethyl)-1,3-benzothiazole-2-thione
[MMBT], reported here is a benzothiazole derivative.
Benzothiazole derivatives are of considerable interest
for their diverse pharmaceutical uses and play an important
role in the synthesis of fused heterocyclic systems [11].
2-mercaptobenzothiazole is a heterocyclic thialato ligand
with potential S- and N- donors and it forms complexes
rich in biological activities [12, 13]. Morpholine is widely
used in organic synthesis. It is a building block in the
preparation of the antibiotic linezolid [14] and in the
anticancer agent gefitinib [15]. Its derivatives are used as
agricultural fungicides. Present study reports the crystal
structure of MMBT, in which the 2–mercaptobenzothiazole
and morpholine molecules are bridged by a methylene
group. This crystal structure has been determined to gain
further insight in its chemical and structural aspects. The
aggregation modes and the hydrogen bonding patterns have
been explored and compared with those of the related
compounds.
S. Franklin Á T. Balasubramanian (&)
Department of Physics, National Institute of Technology,
Tiruchirappalli, India
e-mail: bala@nitt.edu
Present Address:
S. Franklin
Department of Physics, Bishop Heber College,
620017 Tiruchirappalli, Tamil Nadu, India
D. Tamilvendan Á G. Venkatesa Prabhu
Department of Chemistry, National Institute of Technology,
Tiruchirappalli, India
Present Address:
D. Tamilvendan
Department of Chemistry, PRIST University,
Thanjavur, Tamil Nadu, India
123

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J Chem Crystallogr (2012) 42:29–33
Experimental
Preparation
full-matrix least-squares methods on F2 using SHELXL-97
[17]. Hydrogen atoms were located from the difference
Fourier map and their positional and isotropic displacement
parameters were refined with a riding model. Summary of
the crystal data and structure refinement for the compound
MMBT is provided in Table 1. Selected bond lengths and
angles are listed in Table 2.
4.2 g of 2-mercaptobenzothiazole was dissolved in mini-
mum 20 mL of distilled water. To this solution 2.5 mL of
formaldehyde (37%) and 2.2 mL of morpholine were
added drop by drop. The contents were stirred well at room
temperature until the solution becomes clear. The yellow
solid, obtained after 20 min, was washed with distilled
water several times and then dried in the air oven at 353 K
(Yield: 69%, mp: 122 °C). The dried product was dissolved
in 20 ml of chloroform until saturation was attained. The
filtered clear solution was then covered and kept aside for
slow evaporation. Yellow block shaped crystals of MMBT
suitable for X-ray diffraction analysis was obtained after a
week.
Elemental Analysis
The micro-elemental analysis for H, C and N has been
performed using Vario-EL element analyzer. Elemental
analysis found: C 54.09, N 10.57, H 5.34%. Calc. for
C12H14N2OS2: C 54.11, N 10.52, H 3.39%.
Spectral Studies
UV–Vis spectrum has been recorded for the compound
MMBT in the range of 190–1,100 nm using T90 UV–Vis
Spectrophotometer. The Fourier transform infrared (FTIR)
spectrum of the compound MMBT has been recorded in
the range of 400–4,000 cm-1 using KBr pellet with a
Perkin Elmer FTIR spectrophotometer at room tempera-
ture. 1H NMR spectra has been recorded on a Bruker
Advance DPX 300 MHz Ultra-Shield FTNMR Spectro-
photometer in DMSO-d6 with TMS as internal reference.
Chemical shifts are expressed in d units (ppm).
X-Ray Diffraction Studies
Single crystal X-ray diffraction data were collected on a
Bruker kappa axs APEX2 CCD diffractometer [16] using
˚
MoKa radiation (k = 0.71073 A) in the range of
2.5° \ h \ 31.7° at 273 K. The structure was solved by
direct methods using SHELXS-97 and refined by the
Table 1 Crystal data and structure refinement for MMBT
Formula
C12H14N2OS2
266.39
Formula weight
Crystal system
Space group
Cell constants
Discussion
Monoclinic
P 21/c
Structural Studies
˚
a (A)
The asymmetric unit of the crystal structure presented here
consists of one molecule of MMBT. An ORTEP-3 [18]
diagram of the crystal structure with the atom labelling
scheme is shown in Fig. 1. The bond lengths of C7–S2
8.9673(4)
˚
b (A)
9.8130(5)
˚
c (A)
14.9517(7)
a (°)
b (°)
c (°)
Volume (A )
90
˚
˚
[1.6545 (17) A] and C7–N1 [1.358 (2) A] are intermediate
between single and double bonds. This is similar to those
values observed in 2-mercaptobenzothiazole reported ear-
lier and can be attributed to the resonance between –N=C–
SH and –NH–C=S [thiol–thione tautomerism] [19, 20].
Methylene group bridges the molecules of 2-mercapto
benzothiazole and morpholine. The angle 110.31(12)° [N–
C–N] at the methylene bridge matches with 115.04(12)°,
the angle at the methylene bridge in 2-[(phenylamino)
methyl]-isoindole-1,3-dione reported by us recently [21].
The bond lengths and angles observed in the benzene ring
are within the normal range expected. The morpholine ring
adopts a chair conformation with high stability {Puckering
107.337(2)
90
3
˚
1255.92(10)
Z
4
Dcalc (Mg/m3)
l (MoKa) (mm-1
F (000)
1.409
)
0.41
560
Crystal size (mm)
0.30 9 0.20 9 0.15
17519
Reflections collected
Data/restraints/parameters
Goodness of fit on F2
Final R indices [I [ 2r(I)]
R indices (all data)
4659/0/154
1.01
R1 = 0.0461 wR2 = 0.1117
R1 = 0.0801 wR2 = 0.1304
-0.366, 0.287
CCDC 728039
˚
parameters: Q = 0.5700(19) A, h = 0.0(2)° and
-3
)
˚
(Dq)min, (Dq)max (e A
u = 270(8)° [22]}. This is similar to that of the morpho-
line rings included in compounds reported earlier [23–25].
CCDC deposition number
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J Chem Crystallogr (2012) 42:29–33
31
˚
Table 3 Hydrogen-bond geometry of MMBT (A, °)
˚
Table 2 Selected geometric parameters of MMBT (A, °)
D–HÁÁÁA
D–H
HÁÁÁA
DÁÁÁA
D–HÁÁÁA
S1–C6
1.7346 (15)
S1–C7
1.7365 (17)
1.6545 (17)
1.413 (2)
C8–H8BÁÁÁS2
0.97
0.97
2.72
2.87
3.1851 (17)
3.4431 (19)
110
119
C10–H10BÁÁÁCgi
S2–C7
O–C10
Symmetry code (i) -x, -y ? 1/2, z ? 1/2
O–C11
1.417 (3)
Cg is the centroid of the C1, C6, S1, C7, N1 ring
N2–C9
1.23 (2)
N2–C10
1.3963 (18)
122.22 (10)
92.53 (7)
S1–C7–S2
C7–S1–C6
C7–N1–C1
N1–C8–N2
C9–N2–C12
C10–O–C11
C9–N2–C8–N1
C12–N2–C8–N1
N2–C8–N1–C7
N2–C8–N1–C1
115.54 (12)
110.31 (12)
109.63 (12)
109.06 (15)
-78.19 (15)
157.90 (13)
104.44 (16)
-75.37 (17)
Two torsion angles h1 = -75.37(17)° [N2–C8–N1–C1]
and h2 = 157.90(13)° [C12–N2–C8–N1] define the posi-
tion of this ring in the molecule [26]. The benzothiazole
ring is essentially planar and makes a dihedral angle
70.37(5)° with the morpholine ring.
Fig. 2 Packing of molecules in the unit cell. (Dashed lines represent
hydrogen bonds)
The crystal packing of MMBT is stabilized by C–HÁÁÁS,
C–HÁÁÁp (Table 3) and pÁÁÁp interactions. Part of the crystal
structure of MMBT, depicting the hydrogen-bonding
interactions and the formation of hydrogen-bonded motif is
shown in Fig. 2. In MMBT, an intramolecular C–HÁÁÁS
hydrogen bond is observed which generates an S(5) motif
[27, 28]. Generally, C–HÁÁÁN intramolecular hydrogen
bonds are observed in majority of the Mannich base
Fig. 3 FTIR spectrum of MMBT with an inset for the chemical
scheme of MMBT
compounds [29–31]. However, this kind of bond is absent
in the present structure. The benzene rings at (x, y, z) and
(1 - x, -y, -z), lying in different frameworks are linked
by aromatic pÁÁÁp interactions with a centroid separation of
˚
3.5231(10) A (Fig. 2). In addition, C–HÁÁÁp interaction
(Fig. 2; Table 3) has also been observed which stabilize the
crystal packing.
Fig. 1 Molecular structure of MMBT, showing 20% probability
displacement ellipsoids
123

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J Chem Crystallogr (2012) 42:29–33
Fig. 4 1H NMR spectrum of MMBT
Acknowledgment The authors thank the SAIF at IITM, Chennai,
sponsored by DST India, for providing analytical facilities.
Spectral Studies
M.F: C12H14N2OS2, Mol wt: 266.38. Saturated compounds
containing hetero-atoms such as nitrogen, oxygen, sulphur
etc., have non-bonding electrons in addition to r electrons.
UV–Vis spectra of the solution of the compound MMBT in
ethanol registers an intense split band centered at k 285 nm
attribute to n ? p* transition of the C=S group. FTIR KBr t
in cm-1: 2948.11, 2855.88, 2814.73 (C–H aromatic),
1637.52 (C=S stretching), 1602.45 (C=C, C=N stretching),
1367.16 (C–N stretching), 1111.81 (C–N–C stretching),
1006.93 (C–O–C) 743.36 (benzene C–H out of plane bend-
ing), 603.20 (C–S stretching). FTIR spectrum of MMBT
with its chemical scheme in the inset is shown in Fig. 3. 1H
NMR (300 MHz, DMSO d6) d 2.51 (t, 4H), d 3.55 (t, 4H), d
5.17 (s, 2H), d 7.36–7.77 (m, 4H, benzyl ring) [Fig. 4].
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