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Molbank 2009, 2009(4), M633; doi:10.3390/M633

Short Note
4-[(1,3-Benzothiazol-2-ylimino)methyl]phenyl Dodecanoate
Sie-Tiong Ha 1,*, Teck-Ming Koh 2, Yip-Foo Win 1 and Siew-Teng Ong 1
1
Department of Chemical Science, Faculty of Science, Universiti Tunku Abdul Rahman, Jln Universiti, Bandar Barat, 31900 Kampar, Perak, Malaysia
2
Department of Science, Faculty of Engineering & Science, Universiti Tunku Abdul Rahman, Jln Genting Kelang, Setapak 53300 Kuala Lumpur, Malaysia
*
Author to whom correspondence should be addressed.
Received: 9 October 2009 / Accepted: 14 October 2009 / Published: 14 October 2009

Abstract

:
A heterocycle, 4-[(1,3-benzothiazol-2-ylimino)methyl]phenyl dodecanoate, was synthesized and its IR, 1H NMR, 13C NMR, elemental analysis and MS spectroscopic data are presented. This new compound exhibited smectic A phase.
Keywords:
4-[(1,3-benzothiazol-2-ylimino)methyl]phenyl dodecanoate; heterocyclic liquid crystal; smectic A
Schiff bases have attracted much attention ever since the discovery of the first room temperature liquid crystal, 4-methoxybenzylidene-4’-butylaniline [1]. Many kinds of heterocyclic structures, such as pyridine [2], furan [3], thiophene [4] and benzothiazole [5,6,7] have been introduced as core centre in liquid crystalline compounds. In this paper, we report the synthesis of a new Schiff base comprising the benzothiazole moiety: 4-[(1,3-benzothiazol-2-ylimino)methyl]phenyl dodecanoate. This new com­pound exhibits enantiotropic smectic A phase, as indicated by thermal (DSC) and polarizing optical microscopy studies.
In analogy to a recently published procedure [8], a solution of 2-aminobenzothiazole (6.01 g, 40 mmol) and 4-hydroxybenzaldehyde (4.88 g, 40 mmol) in absolute ethanol (60 mL) was heated under reflux for 3 h. The solvent was removed by slow evaporation and Schiff base 1 thus obtained was recrystallized from absolute ethanol. Then, Schiff base 1 (5.09 g, 20 mmol) in dimethylformamide (10 mL), was added to a solution of dodecanoic acid (4.01 g, 20 mmol) and 4-dimethylaminopyridine (1.22 g, 10 mmol) in dichloromethane (70 mL). The resulting mixture was stirred in an ice bath. To this solution, N,N’-dicyclohexylcarbodiimide (4.13 g, 20 mmol) in 10 mL of dichloromethane was added dropwise while stirring in the ice bath for 1 h. The resulting mixture was subsequently stirred at room temperature for another 3 h. Then, the reaction mixture was filtered and the excess solvent was removed from the filtrate by evaporation. Recrystallization from absolute ethanol gave the Schiff base 2 as yellow solid (44%).
Molbank 2009 m633 g001
Thermal data obtained from DSC analysis (enthalpy changes, kJ mol-1 in bracket):
Heating: Crystal 80.8 oC (45.07) Smectic A 85.6 oC (7.44) Isotropic.
Cooling: Crystal 52.7 oC (37.81) Smectic A 81.7 oC (8.17) Isotropic.
Optical photomicrograph showing fan-shaped texture of smectic A phase observed under polarizing optical microscope:
Molbank 2009 m633 g002
MS (EI): m/z = 436 (M+, 9.2%), 254 (100), 225 (8.1), 57 (4.9), 43 (6.4).
IR (KBr, cm-1): 3064, 3033 (C-H aromatic), 2922, 2851 (C-H aliphatic), 1747 (C=O ester), 1618 (C=N, imine), 1600 (C=N, thiazole), 1509 (C=C aromatic).
1H NMR (400 MHz, CDCl3): δ/ppm 0.88 (t, 3H, J = 7.0 Hz, CH3-), 1.27-1.43 (m, 16H, CH3-(CH2)8-CH2-), 1.70-1.80 (q, 2H, J = 7.3 Hz, -CH2-CH2-COO-), 2.59 (t, 2H, J = 7.6 Hz, -CH2-COO-), 7.25 (d, 2H, J = 6.8 Hz, Ar-H), 7.37 (t, 1H, J = 8.3 Hz, Ar-H), 7.48 (t, 1H, J = 8.3 Hz, Ar-H), 7.84 (d, 1H, J = 8.1 Hz, Ar-H), 7.99 (d, 1H, J = 8.1 Hz, Ar-H), 8.06 (d, 2H, J = 6.8 Hz, Ar-H), 9.05 (s, 1H, -N=CH-).
13C NMR (100 MHz, CDCl3): δ/ppm 171.7 (-COO-), 164.8 (C=N), 154.6, 151.6, 134.63, 134.6, 132.2, 131.5, 126.4, 125.1, 123.0, 122.3, 121.6 for aromatic carbons, 34.4, 31.9, 29.5, 29.4, 29.3, 29.2, 29.0, 24.8, 22.6 for methylene carbons [-COO-(CH2)10-CH3], 14.1 (-CH3).
Elemental analysis: Calculated for C26H32N2O2S: C, 71.52%, H, 7.39%, N, 6.42%; Found: C, 71.65%, H, 7.50%, N, 6.53%.

Supplementary materials

Supplementary File 1Supplementary File 2Supplementary File 3

Acknowledgements

The author (S.T. Ha) would like to thank Universiti Tunku Abdul Rahman (UTAR) for the research facilities and financial support through UTAR Research Fund (Vote No. 6200/H002). T.M. Koh would like to acknowledge UTAR for the award of the research and teaching assistantships.

References and Notes

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