Synthesis and phase transition studies of new dimer compounds connected to a 1,3-dimethylbarbituric acid core

Article abstract of DOI:10.3906/kim-1304-51

A series of dimeric unsymmetrical liquid crystals derived from heterocyclic 1,3-dimethylbarbituric acid exhibiting smectic A and nematic phase are reported. All compounds were prepared by the condensation of 4'-(R-(4- formylphenoxy)butoxy)biphenyl-4-carboxylate with 1,3-dimethylbarbituric acid in ethanol. The mesomorphic properties were investigated by DSC and POM, where the type of phase depends on the length of spacer alkoxy chains and the length of the terminal chain. While the SmA phase was observed upon the heating and cooling run when the spacer alkoxy chains carbon numbers increased (n = 6), the N phase was observed when the length of spacer alkoxy chains increased (n = 8 and 10). TUeBITAK.

Full text of DOI:10.3906/kim-1304-51

Turk J Chem
Turkish Journal of Chemistry
(2014) 38: 443 – 453
¨
http://journals.tubitak.gov.tr/chem/
˙
c
⃝ TUBITAK
doi:10.3906/kim-1304-51
Research Article
Synthesis and phase transition studies of new dimer compounds connected to a
1,3-dimethylbarbituric acid core
AbdulKarim-Talaq MOHAMMAD1,∗, Guan-Yeow YEAP2, Hasnah OSMAN2
1Chemistry Department, College of Science, Anbar University, Ramadi, Iraq
2Liquid Crystal Research Laboratory, School of Chemical Sciences, Universiti Sains Malaysia, Minden,
Penang, Malaysia
Received: 19.04.2013
•
Accepted: 28.10.2013
•
Published Online: 14.04.2014
•
Printed: 12.05.2014
Abstract: A series of dimeric unsymmetrical liquid crystals derived from heterocyclic 1,3-dimethylbarbituric acid
exhibiting smectic A and nematic phase are reported. All compounds were prepared by the condensation of 4’-(R-(4-
formylphenoxy)butoxy)biphenyl-4-carboxylate with 1,3-dimethylbarbituric acid in ethanol. The mesomorphic properties
were investigated by DSC and POM, where the type of phase depends on the length of spacer alkoxy chains and the
length of the terminal chain. While the SmA phase was observed upon the heating and cooling run when the spacer
alkoxy chains carbon numbers increased (n = 6), the N phase was observed when the length of spacer alkoxy chains
increased (n = 8 and 10).
Key words: Mesogen, Schiff’s base, pyrimidine, 1,3-dimethylbarbituric acid
1. Introduction
Liquid crystal dimers have often been regarded as a model for the semiflexible main-chain liquid crystalline
polymers, which are known to possess great application value.1 Dimeric liquid crystals are attractive because
they exhibit different properties from the corresponding low molecular mass mesogens. For example, the
transition properties of dimeric liquid crystals are known to depend on the length and parity of the flexible
spacer. Many kinds of dimeric and trimeric mesogenic molecules have been reported.2,3 In order to understand
further the physical and chemical properties of the polymers, extensive research into liquid crystal oligomers has
been carried out only to discover that these materials also exhibit unique liquid crystal properties, which are
not observed in conventional liquid crystals.1−5 Liquid crystal dimers, with 2 mesogenic groups connected by
1 flexible spacer, are the shortest of all oligomers. Various mesogenic groups, such as heterocyclic benzoxazole,
have been introduced into the system of dimers.6
In the mesophase, the presence of a heterocyclic ring in either of the 2 mesogenic groups within the
dimers can induce a different kind of intermolecular interaction; hence it would be interesting if further research
could be carried out on this subject.7,8 These significant findings on dimers have prompted researchers to
synthesize its longer counterpart with 3 mesogenic groups connected by 2 spacers, which are known as trimers
or trimesogens.9
In this paper we report our continued research on the synthesis of heterocycles containing liquid crystalline
materials.10−12 To understand the structure of the liquid crystalline property relationship we synthesized and
∗Correspondence: drmohamadtalaq@gmail.com
443

MOHAMMAD et al./Turk J Chem
characterized a series of unsymmetrical liquid crystals dimers, with these new mesogenic compounds containing
1,3-dimethylbarbituric acid moieties with an ether spacer with even parity ranging from C6 H10 to C10 H24
This is connected to biphenyl with a terminal ester moiety ranking from 6 to 16 carbons.
.
2. Experimental
2.1. Characterization
FT-IR analyses were performed on a PerkinElmer 2000-FT-IR spectrophotometer in the form of KBr pellets
and the spectra were recorded in the range of 4000–400 cm−1 . The 1 H and 13 C NMR spectra were recorded
in dimethylsulfoxide (DMSO-d6) for the title compounds at 298 K on a Bruker 400 MHz Ultrashied FT-NMR
spectrometer equipped with a 5-mm BBI inverse gradient probe. Chemicals shift was referenced to internal
tetramethylsilane (TMS). The concentration of solute molecules was 50 mg in 1.0 mL of DMSO. Standard Bruker
pulse programs13 were used throughout the experiment. The elemental (CHN) microanalyses were performed
using a PerkinElmer 2400 LS Series CHNS/O analyzer. Melting points were recorded by Gallenkamp digital
melting point.
Phase transition temperatures and associated enthalpy values were determined using a differential scan-
ning calorimeter (Elmer Pyris 1 DSC) operated at a scanning rate of ꢀ5 ◦ C min−1 on heating and cooling,
respectively. Texture observation was carried out using a Carl Zeiss Axioskop 40 optical microscope equipped
with Linkam LTS350 hot stage and TMS94 temperature controller.
2.2. Materials
The series of hexanol, octanol, decanol, dodecanol, tetradecanol, hexadecanol, α,ω-dibromoalkanes, 4-hydroxy-
benzaldehyde, 4’-hydroxybiphenyl-4-carboxylic acid, and 1,3-dimethylbarbituric acid were purchased from
Aldrich. The chemicals were used directly from the bottles without further purification. Thin-layer chro-
matography (TLC) was performed on silica-gel plates.
2.3. Synthesis
The liquid crystal dimers were synthesized according to the synthetic routes given in the Scheme. Compound
1 was synthesized via a condensation reaction between 4-hydroxybenzaldehyde with 1,6-dibromohexane, 1,8-
dibromohexane, and 1,10-dibromohexane.14 Compounds 2a–f resulted from the reaction between hydroxybip-
henyl-4-carboxyliacid and various alcohols ranging from C6 H14 O to C16 H34 O. Compounds 3a–r were prepared
from the Williamson ether synthetic reactions between compounds 1a–c and compounds 2a–f. Compounds 3a–r
were subsequently reacted with 1,3-dimethylbarbituric acid to yield the desired compounds 4a–r.
2.3.1. Synthesis of compounds 4a–r
The title compounds were synthesized according to the method described by Majumdar et al.15 A mixture of
compound 1,3-dimethylbarbituric acid (0.156 g, 0.001 mol) and hexyl 4’-(6-(4-formylphenoxy)hexyloxy)biphenyl-
4-carboxylate 3a (0.502 g, 0.001 mol) was refluxed in absolute ethanol for 3 h. The product, 4a, was obtained as
a precipitate from the hot reaction mixture. It was repeatedly washed with hot ethanol and dried in a vacuum.
444

MOHAMMAD et al./Turk J Chem
O
O
Br(CH ) Br
HO
+
2 n
OH
ROH
+
HO
R= Hexyl, Octyl, Decyl, Dodecyl, Tetradecyl and Hexadecyl
n= 6, 8 and 10
O
O
Brn(CH2)O
OR
HO
1a-c
2a-f
O
O
O
(CH2)n
O
R
O
3a-r
O
CH3
O
N
O
N
CH3
CH3
N
O
O
O
N
CH3
O
(CH2)n
O
O
R
O
4a-r
Scheme. Synthetic route towards the formation of intermediates and title compounds 4a–r.
The analytical, FT-IR, and 1 H and 13 C NMR data for the title compounds are summarized as follows:
4a Yield 82% mp 110.14 ◦ C. Anal: found for C38 H44 N2 O7 (%): C, 71.40; H, 6.80; N, 4.28. Calc (%),
C, 71.23; H, 6.92; N, 4.37. IR: υmax (KBr) (cm−1): 2980, 2864, 1760, 1650, 1588, 1250. 1 H NMR δ (ppm)
(DMSO): 8.61 (s, 1H), 6.90–8.52 (6d, C6 H5 –, 12H), 4.12 (t, 2H,J = 6.69 Hz), 4.03 (t, 2H, J = 6.27 Hz),
3.52 (t, 2H, J = 6.09 Hz), 3.28 (s, 3H), 3.14 (s, 3H), 0.82 (t, 3H). 13 C NMR δ (ppm): 174.21, 165.71, 164.89
(C=O), 161.20 (Ar–C–O), 160.07 (C=C), 115.48–141.00 (Ar–C), 60.52 (C–O–C), 22.49 (CH2), 15.04 (CH3).
4b Yield 85% mp 121.01 ◦ C. Anal: found for C40 H48 N2 O7 (%): C, 71.60; H, 7.39; N, 4.10. Calc (%),
C, 71.83; H, 7.23; N, 4.19. IR: υmax (KBr) (cm−1): 2983, 2860, 1767, 1655, 1583, 1252. 1 H NMR δ (ppm)
(DMSO): 8.60 (s, 1H), 6.94–8.57 (6d, C6 H5 –, 12H), 4.15 (t, 2H, J = 6.90 Hz), 4.00 (t, 2H,J = 6.67 Hz),
445

MOHAMMAD et al./Turk J Chem
3.50 (t, 2H, J = 6.25 Hz), 3.25 (s, 3H), 3.10 (s, 3H), 0.85 (t, 3H). 13 C NMR δ (ppm): 174.00, 164.30, 163.08
(C=O), 161.85 (Ar–C–O), 160.74 (C=C), 114.52–140.75 (Ar–C), 61.18 (C–O–C), 22.64 (CH2), 14.82 (CH3).
4c Yield 77% mp 126.60 ◦ C. Anal: found for C42 H52 N2 O7 (%): C, 72.50; H, 7.67; N, 4.14. Calc (%),
C, 72.39; H, 7.52; N, 4.02. IR: υmax (KBr) (cm−1): 2988, 2865, 1760, 1660, 1580, 1256. 1 H NMR δ (ppm)
(DMSO): 8.67 (s, 1H), 6.98–8.60 (6d, C6 H5 –, 12H), 4.10 (t, 2H, J = 6.34 Hz), 4.02 (t, 2H,J = 6.20 Hz),
3.41 (t, 2H, J = 6.60 Hz), 3.21 (s, 3H), 3.09 (s, 3H), 0.89 (t, 3H). 13 C NMR δ (ppm): 175.22, 165.70, 163.87
(C=O), 162.59 (Ar–C–O), 159.69 (C=C), 115.03–140.38 (Ar–C), 60.90 (C–O–C), 21.84 (CH2), 15.05 (CH3).
4d Yield 70% mp 134.33 ◦ C. Anal: found for C44 H56 N2 O7 (%): C, 72.76; H, 7.90; N, 3.69. Calc (%),
C, C, 72.90; H, 7.79; N, 3.86. IR: υmax (KBr) (cm−1): 2982, 2860, 1768, 1665, 1582, 1255. 1 H NMR δ (ppm)
(DMSO): 8.63 (s, 1H), 6.95–8.58 (6d, C6 H5 –, 12H), 4.17 (t, 2H, J = 6.80 Hz), 4.08 (t, 2H,J = 6.75 Hz),
3.46 (t, 2H, J = 6.08 Hz), 3.28 (s, 3H), 3.10 (s, 3H), 0.83 (t, 3H). 13 C NMR δ (ppm): 174.67, 164.27, 162.50
(C=O), 161.15 (Ar–C–O), 159.05 (C=C), 115.78–141.16 (Ar–C), 61.25 (C–O–C), 22.15 (CH2), 14.10 (CH3).
4e Yield 70% mp 140.19 ◦ C. Anal: found for C46 H60 N2 O7 (%): C, 73.29; H, 8.16; N, 3.56. Calc (%),
C, 73.37; H, 8.03; N, 3.72. IR: υmax (KBr) (cm−1): 2975, 2864, 1770 1663, 1587, 1252. 1 H NMR δ (ppm)
(DMSO): 8.60 (s, 1H), 6.91–8.60 (6d, C6 H5 –, 12H), 4.18 (t, 2H,J = 6.49 Hz), 4.04 (t, 2H,J = 6.78 Hz), 3.40
(t, 2H, J = 6.48 Hz), 3.22 (s, 3H), 3.07 (s, 3H), 0.80 (t, 3H). 13 C NMR δ (ppm): 175.11, 165.30, 163.20 (C=O),
162.08 (Ar–C–O), 160.43 (C=C), 114.33–140.59 (Ar–C), 62.76 (C–O–C), 22.64 (CH2), 15.30 (CH3).
4f Yield 85% mp 152.50 ◦ C. Anal: found for C48 H64 N2 O7 (%): C, 73.60; H, 8.13; N, 3.40. Calc (%),
C, 73.81; H, 8.26; N, 3.59. IR: υmax (KBr) (cm−1): 2984, 2869, 1761 1658, 1583, 1255. 1 H NMR δ (ppm)
(DMSO): 8.66 (s, 1H), 6.95–8.70 (6d, C6 H5 –, 12H), 4.11 (t, 2H,J = 6.79 Hz), 4.01 (t, 2H,J = 6.05 Hz), 3.46
(t, 2H, J = 6.48 Hz), 3.25 (s, 3H), 3.09 (s, 3H), 0.89 (t, 3H). 13 C NMR δ (ppm): 174.89, 164.59, 163.63 (C=O),
162.94 (Ar–C–O), 161.16 (C=C), 115.13–140.84 (Ar–C), 61.20 (C–O–C), 21.85 (CH2), 14.77 (CH3).
4g Yield 83% mp 119.70 ◦ C. Anal: found for C40 H48 N2 O7 (%): C, 71.98; H, 7.10; N, 4.30. Calc
C, 71.83; H, 7.23; N, 4.19. IR: υmax (KBr) (cm−1): 2988, 2864, 1761, 1660, 1586, 1250. 1 H NMR δ (ppm)
(DMSO): 8.70 (s, 1H), 6.90–8.52 (6d, C6 H5 –, 12H), 4.12 (t, 2H,J = 6.08 Hz), 4.04 (t, 2H,J = 6.50 Hz), 3.43
(t, 2H, J = 6.90 Hz), 3.23 (s, 3H), 3.08 (s, 3H), 0.80 (t, 3H). 13 C NMR δ (ppm): 175.07, 163.28, 162.04 (C=O),
161.20 (Ar–C–O), 160.40 (C=C), 114.19–140.87 (Ar–C), 60.47 (C–O–C), 22.64 (CH2), 15.75 (CH3).
4h Yield 83% mp 127.33 ◦ C. Anal: found for C42 H52 N2 O7 (%): C, 72.50; H, 7.34; N, 4.16. Calc
C, 72.39; H, 7.52; N, 4.02. IR: υmax (KBr) (cm−1): 2980, 2867, 1770, 1669, 1585, 1254. 1 H NMR δ (ppm)
(DMSO): 8.64 (s, 1H), 6.91–8.40 (6d, C6 H5 –, 12H), 4.10 (t, 2H,J = 6.70 Hz), 4.02 (t, 2H,J = 6.16 Hz), 3.42
(t, 2H, J = 6.68 Hz), 3.26 (s, 3H), 3.11 (s, 3H), 0.85 (t, 3H). 13 C NMR δ (ppm): 174.50, 162.17, 161.49 (C=O),
160.21 (Ar–C–O), 159.11 (C=C), 114.06–139.14 (Ar–C), 60.07 (C–O–C), 21.00 (CH2), 14.49 (CH3).
4i Yield 83% mp 143.89 ◦ C. Anal: found for C44 H56 N2 O7 (%): C, 72.71; H, 7.94; N, 3.66. Calc
C, 72.90; H, 7.79; N, 3.86. IR: υmax (KBr) (cm−1): 2989, 2864, 1763, 1650, 1581, 1257. 1 H NMR δ (ppm)
(DMSO): 8.68 (s, 1H), 6.93–8.46 (6d, C6 H5 –, 12H), 4.14 (t, 2H, J = 6.22 Hz), 4.07 (t, 2H,J = 6.74 Hz),
3.40 (t, 2H, J = 6.89 Hz), 3.20 (s, 3H), 3.03 (s, 3H), 0.85 (t, 3H). 13 C NMR δ (ppm): 174.96, 163.50, 161.78
(C=O), 161.38 (Ar–C–O), 159.88 (C=C), 115.20–140.67 (Ar–C), 61.30 (C–O–C), 22.19 (CH2), 15.78 (CH3).
4j Yield 75% mp 140.12 ◦ C. Anal: found for C46 H60 N2 O7 (%): C, 73.50; H, 8.14; N, 3.63. Calc
C, 73.37; H, 8.03; N, 3.72. IR: υmax (KBr) (cm−1): 2980, 2870, 1766, 1660, 1580, 1252. 1 H NMR δ (ppm)
446

MOHAMMAD et al./Turk J Chem
(DMSO): 8.70 (s, 1H), 6.95–8.44 (6d, C6 H5 –, 12H), 4.19 (t, 2H,J = 6.67 Hz), 4.01 (t, 2H,J = 6.05 Hz), 3.45
(t, 2H, J = 6.22 Hz), 3.18 (s, 3H), 3.06 (s, 3H), 0.89 (t, 3H). 13 C NMR δ (ppm): 175.07, 163.96, 162.03 (C=O),
161.77 (Ar–C–O), 160.14 (C=C), 115.05–140.47 (Ar–C), 60.37 (C–O–C), 22.67 (CH2), 14.20 (CH3).
4k Yield 79% mp 148.65 ◦ C. Anal: found for C48 H64 N2 O7 (%): C, 73.98; H, 8.14; N, 3.43. Calc
C, 73.81; H, 8.26; N, 3.59. IR: υmax (KBr) (cm−1): 2990, 2878, 1774, 1657, 1589, 1250. 1 H NMR δ (ppm)
(DMSO): 8.80 (s, 1H), 6.98–8.53 (6d, C6 H5 –, 12H), 4.17 (t, 2H, J = 6.89 Hz), 4.08 (t, 2H,J = 6.70 Hz),
3.40 (t, 2H, J = 6.64 Hz), 3.11 (s, 3H), 3.02 (s, 3H), 0.80 (t, 3H). 13 C NMR δ (ppm): 176.21, 165.36, 163.61
(C=O), 162.17 (Ar–C–O), 160.85 (C=C), 115.47–140.50 (Ar–C), 61.93 (C–O–C), 22.06 (CH2), 15.10 (CH3).
4l Yield 84% mp 149.50 ◦ C. Anal: found for C50 H68 N2 O7 (%): C, 74.40; H, 8.56; N, 3.24. Calc
C, 74.22; H, 8.47; N, 3.46. IR: υmax (KBr) (cm−1): 2986, 2864, 1762, 1661, 1581, 1254. 1 H NMR δ (ppm)
(DMSO): 8.85 (s, 1H), 6.93–8.59 (6d, C6 H5 –, 12H), 4.14 (t, 2H,J = 6.70 Hz), 4.02 (t, 2H,J = 6.43 Hz), 3.45
(t, 2H, J = 6.39 Hz), 3.15 (s, 3H), 3.08 (s, 3H), 0.89 (t, 3H). 13 C NMR δ (ppm): 175.14, 164.20, 162.77 (C=O),
161.05 (Ar–C–O), 160.14 (C=C), 114.02–140.38 (Ar–C), 60.16 (C–O–C), 21.69 (CH2), 14.06 (CH3).
4m Yield 80% mp 130.01 ◦ C. Anal: found for C42 H52 N2 O7 (%): C, 72.50; H, 7.29; N, 4.19. Calc
C, 72.39; H, 7.52; N, 4.02. IR: υmax (KBr) (cm−1): 2976, 2865, 1773, 1660, 1584, 1250. 1 H NMR δ (ppm)
(DMSO): 8.82 (s, 1H), 6.91–8.55 (6d, C6 H5 –, 12H), 4.11 (t, 2H,J = 6.20 Hz), 4.06 (t, 2H, J = 6.80 Hz),
3.46 (t, 2H, J = 6.85 Hz), 3.12 (s, 3H), 3.04 (s, 3H), 0.80 (t, 3H). 13 C NMR δ (ppm): 174.56, 164.49, 162.10
(C=O), 160.86 (Ar–C–O), 159.23 (C=C), 114.60–140.07 (Ar–C), 61.02 (C–O–C), 22.20 (CH2), 14.69 (CH3).
4n Yield 84% mp 142.14 ◦ C. Anal: found for C44 H56 N2 O7 (%): C, 72.73; H, 7.51; N, 3.98. Calc
C, 72.90; H, 7.79; N, 3.86. IR: υmax (KBr) (cm−1): 2984, 2872, 1770, 1653, 1578, 1257. 1 H NMR δ (ppm)
(DMSO): 8.88 (s, 1H), 6.97–8.60 (6d, C6 H5 –, 12H), 4.19 (t, 2H,J = 6.84 Hz), 4.08 (t, 2H, J = 6.29 Hz),
3.49 (t, 2H, J = 6.94 Hz), 3.15 (s, 3H), 3.08 (s, 3H), 0.78 (t, 3H). 13 C NMR δ (ppm): 175.08, 164.27, 162.84
(C=O), 160.15 (Ar–C–O), 160.97 (C=C), 115.20–141.30 (Ar–C), 62.11 (C–O–C), 22.67 (CH2), 15.38 (CH3).
4o Yield 79% mp 157.20 ◦ C. Anal: found for C46 H60 N2 O7 (%): C, 73.52; H, 8.20; N, 3.91. Calc C,
73.37; H, 8.03; N, 3.72. IR: υmax (KBr) (cm−1): 2993, 2876, 1764, 1661, 1582, 1252. 1 HNMR δ (ppm) (DMSO):
8.83 (s, 1H), 6.94–8.66 (6d, C6 H5 –, 12H), 4.12 (t, 2H,J = 6.39 Hz), 4.00 (t, 2H,J = 6.49 Hz), 3.45 (t, 2H, J
= 6.31 Hz), 3.18 (s, 3H), 3.04 (s, 3H), 0.82 (t, 3H). 13 C NMR δ (ppm): 173.48, 165.05, 162.20 (C=O), 161.06
(Ar–C–O), 160.21 (C=C), 114.50–140.67 (Ar–C), 60.80 (C–O–C), 21.05 (CH2), 14.95 (CH3).
4p Yield 77% mp 165.00 ◦ C. Anal: found for C48 H64 N2 O7 (%): C, 73.64; H, 8.40; N, 3.38. Calc
C, 73.81; H, 8.26; N, 3.59. IR: υmax (KBr) (cm−1): 2980, 2867, 1772, 1653, 1585, 1250. 1 H NMR δ (ppm)
(DMSO): 8.85 (s, 1H), 6.90–8.40 (6d, C6 H5 –, 12H), 4.11 (t, 2H, J = 6.74 Hz), 3.97 (t, 2H, J = 6.85 Hz),
3.40 (t, 2H, J = 6.63 Hz), 3.12 (s, 3H), 3.00 (s, 3H), 0.74 (t, 3H). 13 C NMR δ (ppm): 173.87, 164.96, 162.82
(C=O), 161.47 (Ar–C–O), 159.89 (C=C), 114.02–140.33 (Ar–C), 60.41 (C–O–C), 22.32 (CH2), 15.02 (CH3).
4q Yield 89% mp 172.60 ◦ C. Anal: found for C50 H68 N2 O7 (%): C, 74.06; H, 8.62; N, 3.25. Calc
C, 74.22; H, 8.47; N, 3.46. IR: υmax (KBr) (cm−1): 2986, 2871, 1765, 1660, 1580, 1250. 1 H NMR δ (ppm)
(DMSO): 8.80 (s, 1H), 6.99–8.57 (6d, C6 H5 –, 12H), 4.19 (t, 2H,J = 6.07 Hz), 4.03 (t, 2H,J = 6.39 Hz), 3.48
(t, 2H, J = 6.29 Hz), 3.23 (s, 3H), 3.08 (s, 3H), 0.83 (t, 3H). 13 C NMR δ (ppm): 174.67, 165.06, 163.26 (C=O),
162.00 (Ar–C–O), 160.28 (C=C), 115.17–141.09 (Ar–C), 61.32 (C–O–C), 21.44 (CH2), 14.92 (CH3).
447

MOHAMMAD et al./Turk J Chem
4r Yield 78% mp 183.14 ◦ C. Anal: found for C52 H72 N2 O7 (%): C, 74.86; H, 8.41; N, 3.50. Calc
C, 74.61; H, 8.67; N, 3.35. IR: υmax (KBr) (cm−1): 2990, 2884, 1775, 1666, 1579, 1255. 1 H NMR δ (ppm)
(DMSO): 8.87 (s, 1H), 6.94–8.60 (6d, C6 H5 –, 12H), 4.14 (t, 2H, J = 6.78 Hz), 4.07 (t, 2H, J = 6.56 Hz),
3.50 (t, 2H, J = 6.48 Hz), 3.26 (s, 3H), 3.10 (s, 3H), 0.89 (t, 3H). 13 C NMR δ (ppm): 175.09, 166.48, 164.37
(C=O), 162.87 (Ar–C–O), 160.40 (C=C), 115.07–140.97 (Ar–C), 61.86 (C–O–C), 22.83 (CH2), 15.60 (CH3).
3. Results and discussion
3.1. Synthesis and characterization
The condensation reaction of alkyl 4’-(R-(4-formylphenoxy)butoxy)biphenyl-4-carboxylate with 1,3-dimethylbar-
bituric acid in ethanol gave a good yield of the products (4a–r). The purity of the target compounds was checked
by TLC. Structural identification of the title compounds was achieved by employing a combination of elemental
analysis and spectroscopic techniques (FT-IR and NMR). The percentages of C, H, and N from the elemental
analysis conform to the calculated values for title compounds 4a–r.
The FT-IR data of compounds 4a–r are given in the synthetic procedures. The vibration band with the
wave numbers of 2980 cm−1 and 2864 cm−1 can be assigned to an alkyl spacer and the alkyl group attached
to one of the dimer terminals. The C=O bond gives rise to a band with a strong intensity at 1760 cm−1 . The
FT-IR data for compound 4a show a band assignable to ether C–O stretching at 1250 cm−1 in the fingerprint
region, which indicated that the alkylation reaction has taken place.
The 1 H NMR for compound 4a shows a triplet at δ 0.82 ppm, which can be attributed to the methyl
protons of the terminal alkyl chain. The 2 singlets at the region of δ 3.28 ppm and δ 3.14 ppm can be attributed
to the 2 methyl protons in the 1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione ring. The triplet assignable to
the ester O–CH2 protons can be observed at δ 4.12 ppm, while 2 triplets attributed to the methoxy protons of
the spacer are evident at δ 4.03 ppm and δ 3.52 ppm. The 12 aromatic protons of compound 4a give rise to 6
doublets with their resonances observed at δ 6.90–8.52 ppm. The singlet observed at a low field δ 8.61 ppm was
characteristic of the proton of ph–C=CH. In terms of splitting and chemical shift, the spectra of compounds
4b–r are similar to that of compound 4a.
3.2. Thermal behavior and texture observation
To characterize the liquid crystalline behavior of the new synthesized compounds 4a–4r, the phase transition
temperatures together with transition enthalpy values were determined by DSC and all the data are tabulated
in the Table.
Figure 1 shows the DSC thermograms of compounds 4k as an example. The textural observations of
the mesophase were carried out using a polarizing optical microscope POM, provided with a heating stage and
a central processor. All title compounds 4a–4r are mesomorphic regardless of the spacer alkoxy chain length
and terminal chain; however, the type of mesophase is dependent on the length of spacer alkoxy chain. The
mesophase was obtained during the heating and cooling process. These compounds exhibited a smectic phase or
nematic phase. For compounds 4a–4f (n = 6, R = 6, 8, 10, 12, 14, 16) the clearing temperatures were increased
as the carbon numbers of the terminal alkyl chains and alkoxy chain increased, T = 110.14 ◦ C < 121.01 ◦ C <
126.60 ◦ C < 134.33 ◦ C <140.19 ◦ C < 152.50 ◦ C (R = 6, 8, 10, 12, 14, 16, n = 6). The phases were identified
as smectic A. Upon the heating run the POM showed the formation of bˆatonnets that coalesced to form a focal
conic fan-shaped texture characteristic of SmA phase. Moreover, upon the heating cycle on the differential
scanning calorimetry (DSC) thermogram the peaks were observed at respective temperatures of 88.20 ◦ C (∆H
448

MOHAMMAD et al./Turk J Chem
Table. Phase transition temperatures (◦ C) and the corresponding enthalpies (J/g) of compounds 4a–r.
Transition temperature °C (corresponding enthalpy changes in kJ mol–1)
Compounds
Heating/Cooling
4a
Cr 88.20 (2.34) SmA 110.14 (42.07) I
Cr 67.02 (–39.51) SmA 104.78 (–5.89) I
4b
4c
4d
4e
4f
Cr 98.79 (6.22) SmA 121.01 (29.50) I
Cr 90.11 (–19.70) SmA 113.62 (–2.19) I
Cr 109.51 (3.86) SmA 126.60 (49.31) I
Cr 104.00 (–27.10) SmA 119.00 (–8.77) I
Cr 120.79 (1.06) SmA 134.33 (35.61) I
Cr 117.78 (–49.12) N SmA 129.04 (–8.03) I
Cr 123.98 (5.29) SmA 140.19 (51.73) I
Cr 120.50 (–64.16) SmA 133.80 (–3.22) I
Cr 136.15 (6.62) SmA 152.50 (41.38) I
Cr 135.10 (–28.20) SmA 148.11 (–0.94) I
4g
4h
4i
Cr 94.67 (5.31) N 119.70 (18.44) I
Cr 89.49 (–37.80) N 114.08 (–2.33) I
Cr 105.00 (2.77) N 127.33 (26.59) I
Cr 100.40 (–29.90) N 122.00 (–7.68) I
Cr 120.89 (4.05) N 143.89 (24.19) I
Cr 113.22 (–44.20) N 136.70 (–2.34) I
4j
Cr 122.04 (1.39) N 140.12 (26.10) I
Cr 119.72 (–16.57) N 133.89 (–7.07) I
4k
4l
Cr 126.55 (1.79) N 148.65 (31.80) I
Cr 124.11 (–15.23) N 140.93 (–4.06) I
Cr 133.00 (2.89) N 159.50 (19.59) I
Cr 128.09 (–20.66) N 154.03 (–2.30) I
4m
4n
4o
4p
4q
4r
Cr 108.78 (4.30) N 130.01 (15.04) I
Cr 105.00 (–13.41) N 125.60 (–1.34) I
Cr 119.07 (3.61) N 142.14 (17.70) I
Cr 113.11 (–20.83) N 137.50 (–2.07) I
Cr 132.42 (6.72) N 157.20 (19.20) I
Cr 127.00 (–16.92) N 149.79 (–2.49) I
Cr 138.00 (0.89) N 165.00 (20.60) I
Cr 132.11 (–15.66) N 159.93 (–2.91) I
Cr 148.88 (5.01) N 172.60 (17.71) I
Cr 146.04 (–18.30) N 168.05 (–6.70) I
Cr 157.93 (1.03) N 183.14 (19.00) I
Cr 154.76 (–19.32) N 178.00 (–4.44) I
= 2.34), 98.79 ◦ C (∆H = 6.22), 109.51 ◦ C (∆H = 3.86), 120.79 ◦ C (∆H = 1.06), 123.98◦ C (∆H = 5.29),
and 136.15 ◦ C (∆H = 6.62), which are characterized to phase transition SmA-I (Figure 2a). The temperatures
of the smectic phases shown by compounds 4a–4f were 21.94 ◦ C, 22.22 ◦ C, 17.09 ◦ C, 13.54 ◦ C, 16.21 ◦ C,
and 16.35 ◦ C. The enthalpies of the smectic–isotropic transition were in the range of 6.62–1.06 KJ mol−1 and
changed irregularly as the terminal chains increased. A typical texture described as focal–conic or Schlieren
domains was identified by POM and when cooling from isotropic liquid the coexistence of fan-shaped textures
was observed. The observed phase was assigned as a SmA phase. All observed liquid crystalline textures are
449

MOHAMMAD et al./Turk J Chem
typical according to the literature.16,17 The phase transition of I-SmA was detected by DSC through the peaks
observed upon the cooling of compounds 4a–4f (n = 6, R = 6, 8, 10, 12, 14, 16) at the respective temperatures
of 104.78 ◦ C (∆H = –5.89), 113.62 ◦ C (∆H = –2.19), 119.00 ◦ C (∆H = –8.77), 129.04 ◦ C (∆H = –8.03),
133.80 ◦ C (∆H = –3.22), and 148.11 ◦ C (∆H = –0.94). The temperatures of the smectic phases upon cooling
were 37.76 ◦ C, 23.51 ◦ C, 15.00 ◦ C, 11.26 ◦ C, 13.30 ◦ C, and 13.01 ◦ C. Likewise, the enthalpies of the phase
transition isotropic–smectic were in the range of –8.77 to –0.94 KJ mol−1 and changed irregularly as the terminal
chains increased.
Figure 1. DSC thermograms of compounds 4k.
The mesomorphic properties of compound 4g–4l (n = 8, R = 6, 8, 10, 12, 14, 16) are also given in the
Table. It can clearly be shown from the DSC differential scanning calorimetry that the clearing temperatures
increased as the carbon numbers of the terminal alkyl chains and alkoxy chain increased, T = 119.70 ◦ C <
127.33 ◦ C < 143.89 ◦ C < 140.12 ◦ C < 148.65 ◦ C < 159.50 ◦ C (R = 6, 8, 10, 12, 14, 16, n = 8), with
high enthalpy within the range of 13.80–18.44 kJ mol−1 . Moreover, the DSC thermogram was identified by
broad peaks upon the heating run at temperatures in respective compounds 4g–4l of 94.67 ◦ C (∆H = 5.31),
105.00 ◦ C (∆H = 2.77), 120.89 ◦ C (∆H = 4.05), 122.04 ◦ C (∆H = 1.39), 126.55 ◦ C (∆H = 1.79), and
133.00 ◦ C (∆H = 2.89) respectively, to phase transition of N-I. In the same behavior of compound 4a–4f, the
enthalpies changed irregularly as the terminal chains of the N-I transition increased at the range of 5.38–1.39
kJ mol−1 . The N-I phase was also characterized by POM, upon heating cycle texture showed only a Schlieren
nematic phase and the texture at the clearing temperature was typical of the nematic–isotropic transition. The
temperatures of the N-I phase were found to be 25.03 ◦ C, 22.33 ◦ C, 23.00 ◦ C, 18.08 ◦ C, 22.10 ◦ C, and 26.50
◦ C. On the other hand, the DSC thermogram upon the cooling run of compounds 4g–4l was also characterized
by broad peaks, which were assigned to the I-N phase at temperatures of 114.08 ◦ C (∆H = –2.33), 122.00 ◦ C
450

MOHAMMAD et al./Turk J Chem
(∆H = –7.68), 136.70 ◦ C (∆H = –2.34), 133.89 ◦ C (∆H = –7.07), 140.93 ◦ C (∆H = –4.06), and 154.03
◦ C (∆H = –2.30), respectively. The phase temperatures were found to be 24.59 ◦ C, 21.60 ◦ C, 23.48 ◦ C,
14.17 ◦ C, 16.82 ◦ C, and 29.94 ◦ C, while the enthalpies changed irregularly as the terminal chains increased.
A small droplet appeared and coalesced to form the classical or marble texture upon cooling under the optical
microscopy (POM), which is characteristic of a nematic phase. Figure 2b shows a nematic droplet coalesced at
157 ◦ C upon cooling for compound 4I.
Figure 2. (a) SmA fan-shaped texture at 90 ◦ C upon cooling run for compound 4a; (b) Nematic droplets coalesced at
157 ◦ C upon cooling for compound 4I.
In compounds 4m–4r (n = 10, R = 6, 8, 10, 12, 14, 16), the N-I phase was identified. Upon heating the
POM revealed the texture of the nematic phase by the presence of Schlieren texture characteristics of N phase.
In the same way, the DSC thermogram upon heating revealed the N-I phase at temperatures of 108.78 ◦ C (∆H
= 4.30), 119.07 ◦ C (∆H = 3.61), 132.42 ◦ C (∆H = 6.72), 138 ◦ C (∆H = 0.89), 148.88 ◦ C (∆H = 5.01),
and 157.93 ◦ C (∆H = 1.03). The clearing temperatures, which were also observed, increased as the carbon
numbers of the terminal alkyl chains and alkoxy chain increased, whereby T = 130.01 ◦ C, 142.14 ◦ C, 157.20
◦ C, 165.00 ◦ C, 172.60 ◦ C, and 183.14 ◦ C. This may be due to the excessive Van der Waals attractive forces
between the terminal alkyl chains or between the alkoxy chains where the melting temperatures increased from
n = 6 to 18.18 The N-I phase temperatures at the heating run were found to be 21.32 ◦ C, 23.07 ◦ C, 24.78 ◦ C,
27.00 ◦ C, 23.72 ◦ C, and 25.21 ◦ C.
The nematic phase (I-N) was also observed upon cooling for compounds 4m–4r. Upon the cooling run
the DSC thermorgam showed a broad band, which was identified to the I-N phase at temperatures of 125.60
◦ C (∆H = –1.34), 137.50 ◦ C (∆H = –2.07), 149.79 ◦ C (∆H = –2.49), 159.93 ◦ C (∆H = –2.91), 168.05 ◦ C
(∆H = –6.70), and 178.00 ◦ C (∆H = –4.44), respectively. Moreover, the phase temperatures were found to
be 20.60 ◦ C, 24.39 ◦ C, 22.79 ◦ C, 27.82 ◦ C, 22.01 ◦ C, and 23.24 ◦ C for respective compounds 4m–4r. Under
optical microscopy (POM) upon the cooling run a small droplet appeared and coalesced to form the classical
or marble texture, which is characteristic of a nematic phase.
From the result above it can clearly be shown that the type of phase depends on the length of spacer
alkoxy chains and the length of terminal chains. The SmA phase was observed upon the heating and cooling
451

MOHAMMAD et al./Turk J Chem
run when the spacer alkoxy chains’ carbon numbers increased (n = 6). The N phase was observed when the
length of spacer alkoxy chains increased (n = 8 and 10), for compounds 4g–r. In the literature, adenine and
thymine with cholesterol were prepared as thermotropic liquid crystals. In these compounds only the cholesteric
phase has been observed.18,19 However, there were several unsuccessful studies of the formation of lyotropic
liquid crystals by DNA and nucleotides20,21 and were done to prepare thermotropic liquid crystals of nucleobase
derivatives.22−24
4. Conclusion
In order to understand the effect of 1,3-dimethylbarbituric acid with the space alkoxy chain on the formation of
mesophases, new mesogenic compounds were synthesized. All synthesized compounds exhibited liquid crystal
properties when the spacer alkoxy chain (n = 6) the SmA phase was observed. However, the N phase appeared
when the alkoxyl spacer chain increased to 8 and 10.
Acknowledgments
The authors thank the University Sains Malaysia and the Malaysian Government for financing this project
through Grant No. 304/PKIMIA/3612051. One of the authors (AT Mohammad) also thanks the Chemistry
Department, College of Science, Anbar University.
References
1. Imrie, C. T.; Henderson, P. A. Colloid Interface Sci. 2008, 7, 298–311.
2. Imrie, C. T.; Luckhurst, G. R. In Handbook of Liquid Crystals, Vol. 1, D. Demus, J. W. Goodby, G. W. Gray, H.
W. Spiess, V. Vill (Eds) 801–803, Wiley-VCH, Weinheim, 1998.
3. Henderson, P. A.; Imrie, C. T. Liq. Cryst. 2005, 32, 1531–1541.
4. Tamba, M. G.; Kosata, B.; Pelz, K.; Diele, S.; Pelzl, G.; Vakhovskaya, Z.; Kresse, H.; Weissflog, W. Soft Matter
2006, 2, 60–65.
5. Pal, S. K.; Raghunathan, V. A.; Kumar, S. Liq. Cryst. 2007, 34, 135–141.
6. Liao, C. C.; Wang, C. S.; Sheu, H. S.; Lai, C. K. Tetrahedron 2008, 64, 7977–7985.
7. Matharu, A. S.; Cowling, S. J.; Wright, G. Liq. Cryst. 2007, 34, 489–506.
8. Yeap, G. Y.; Hng, T. C.; K. Mahmood, W. A.; Gorecka, E.; Takeuchi, D.; Osakada, K. Mol. Cryst. Liq. Cryst.
2008, 487, 135–152.
9. Yoshizawa, A.; Nakata, M.; Yamaguchi, A. Liq. Cryst. 2006, 33, 605–609.
10. Yeap, G. Y.; Mohammad, A. T.; Osman, H. J. Mol. Struc. 2010, 982, 33–44.
11. Yeap, G. Y.; Mohammad, A. T.; Osman, H. Mol. Cryst. Liq. Cryst. 2012, 552, 177–193.
12. Mohammad, A. T.; Osman, H.; Yeap, G. Y. Aust. J. Bas. Appl. Scien. 2011, 5, 551–554.
13. Bruker program 1D WIN-NMR (release 6.0) and 2D WIN-NMR (release 6.1).
14. Yeap, G. Y.; Hng, T. C.; Ito, M. M.; Mahmood, W. A. K.; Takeuchi, D.; Osakada, K. Mol. Cryst. Liq. Cryst.
2009, 515, 215–229.
15. Majumdar, K. C.; Mondal, S.; Pal, N.; Sinha, R. K. Tetrahedron Letters 2009, 50, 1992–1995.
16. Dierking, I. Textures of Liquid Crystals; Wiley-VCH, Weinheim, Germany, 2003.
17. Demus, D.; Richter, L. Textures of Liquid Crystals; Verlag Chemie: New York, NY, USA, 1978.
18. Collings, P. J.; Hird, M. Introduction to Liquid Crystals; Taylor & Francis Ltd: London, 1998.
452

MOHAMMAD et al./Turk J Chem
19. Itahara, T.; Sunose, M.; Kameda, T.; Ueda, T. Chem. Phys. Chem. 2002, 4, 378–379.
20. Kanie, K.; Yasuda, T.; Ujiie, S.; Kato, T. Chem. Commun. 2000, 1899–1900 and references therein.
21. Strzelecka, T. E.; Davidson, M. W.; Rill, R. L. Nature 1988, 331, 457–460.
22. Paleos, C. M.; Tsiourvas, D. Angew. Chem., Int. Ed. Engl. 1995, 107, 1839–1855.
23. Michas, J.; Paleos, C. M.; Skoulios, A.; Weber, P. Mol. Cryst. Liq. Cryst. 1994, 239, 245–255.
24. Tsiourvas, D.; Sideratou, Z.; Haralabakopoulos, A. A.; Pistolis, G.; Paleos, C. M. J. Phys. Chem. 1996, 100,
14087–14092.
453

Copyright of Turkish Journal of Chemistry is the property of Scientific and Technical
Research Council of Turkey and its content may not be copied or emailed to multiple sites or
posted to a listserv without the copyright holder's express written permission. However, users
may print, download, or email articles for individual use.