Synthesis and thermal properties for 4-(4-alkoxyphenoxycarbonyl)phenyl 3-alkoxy-2-X-benzoates

Article abstract of DOI:10.1080/15421400590957071

Some derivatives of 4-(4-alkoxyphenoxycarbonyl)phenyl 3-alkoxy-2-X- benzoates (X=F, Cl, Br, or CF₃) were synthesized by means of an ortho-directed lithiation followed by an electrophilic aromatic substitution reaction, as a key step, and their

Full text of DOI:10.1080/15421400590957071

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Synthesis and Thermal
Properties for 4-(4-
Alkoxyphenoxycarbonyl)phenyl
3-Alkoxy-2-X-benzoates
Hiroaki Okamoto a , Yuki Morita a , Yoichi Segawa a &
Shunsuke Takenaka a
a Department of Advanced Materials Science and
Engineering , Faculty of Engineering, Yamaguchi
University , Ube, Yamaguchi, Japan
Published online: 31 Aug 2006.
To cite this article: Hiroaki Okamoto , Yuki Morita , Yoichi Segawa &
Shunsuke Takenaka (2005) Synthesis and Thermal Properties for 4-(4-
Alkoxyphenoxycarbonyl)phenyl 3-Alkoxy-2-X-benzoates, Molecular Crystals and Liquid
Crystals, 439:1, 221/[2087]-227/[2093], DOI: 10.1080/15421400590957071
To link to this article: http://dx.doi.org/10.1080/15421400590957071
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Mol. Cryst. Liq. Cryst., Vol. 439, pp. 221=[2087]–227=[2093], 2005
Copyright # Taylor & Francis Inc.
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400590957071
Synthesis and Thermal Properties for
4-(4-Alkoxyphenoxycarbonyl)phenyl
3-Alkoxy-2-X-benzoates
Hiroaki Okamoto
Yuki Morita
Yoichi Segawa
Shunsuke Takenaka
Department of Advanced Materials Science and Engineering, Faculty
of Engineering, Yamaguchi University, Ube, Yamaguchi, Japan
Some derivatives of 4-(4-alkoxyphenoxycarbonyl)phenyl 3-alkoxy-2-X-benzoates
(X¼F, Cl, Br, or CF3) were synthesized by means of an ortho-directed lithiation
followed by an electrophilic aromatic substitution reaction, as a key step, and their
thermal properties of liquid crystals were examined. These results are discussed in
terms of molecular structure and electrostatic effects.
Keywords: binary phase diagram; lateral substituent; liquid crystals; nematic phase;
synthesis
INTRODUCTION
It has been well known that the linearity of the molecular shape is one
of important factors in exhibiting liquid crystal (LC) properties.
Therefore, the introduction of the lateral substituent to the LC
molecule is avoided in practical LC materials, though it sometimes
modifies the phase sequence as well as dielectric anisotropy [1–3].
Recently, we revealed that the LC molecules with the lateral alkoxy
substituent exhibit a smectic A (SmA) and=or smectic C (SmC) proper-
ties, and mentioned the conformational effect of the lateral alkoxy
group on mesomorphic properties [4–7]. However, the influence of
This work is partially supported by Electric Technology Research Foundation of
Chugoku.
Address correspondence to Hiroaki Okamoto, Department of Advanced Materials
Science and Engineering, Faculty of Engineering, Yamaguchi University, Tokiwadai
2557, Ube, Yamaguchi 755-8611, Japan. E-mail: oka-moto@po.cc.yamaguchi-u.ac.jp
221=[2087]

222=[2088]
H. Okamoto et al.
the lateral substituent on mesomorphic properties is not yet clear.
Accordingly, compounds 1–5 were synthesized to study the effect of
the lateral substituents on mesomorphic properties, shown below.
EXPERIMENTALS
Method
The transition temperatures and latent heats were determined using a
Seiko SSC-5200 DSC, where indium (99.9%) was used as a calibration
standard (mp¼156.6ꢀC, 28.4 J=g). The DSC thermogram was operated
at a heating or cooling rate of 5ꢀC minꢁ1. The mesophases were char-
acterized by a Nikon POH polarizing microscope fitted with a Mettler
thermo-control system (FP-900). 1H NMR spectra were measured
using a JEOL EX-270 spectrometer, where TMS was used as an inter-
nal standard. IR spectra were recorded with a Horiba FT-200 infrared
spectrometer. The purity was checked by HPLC.
MATERIALS
Compounds 1–5 (Figure 1) were synthesized in a moderate yield
according to Schemes 1–3, where an ortho-directed lithiation and
subsequent electrophilic aromatic substitution reaction, as a key step.
For the synthesis of compounds 1 and 5, treatment of 2-X-n-hexyloxy-
benzene (X¼F or CF3) with a equivalent of n-butyllithium afforded an
aryllithium species, which was quenched with carbon dioxide to give
the corresponding carboxylic acid on acidification in a moderate yield
(Scheme 1). In these reactions, the fluoro subustituent is indispensable
for the directing group of the ortho-lithiations.
For compounds 2–4, treatment of 3-methoxymethoxybenzyl alcohol,
prepared by methoxymethylation of ethyl 3-hydroxybenzoate and the
FIGURE 1 Chemical structures for compounds 1–7.

Synthesis and LC Properties for 3-Alkoxy-2-X-benzoates
223=[2089]
SCHEME 1 Synthesis for 3-alkoxy-2-X-benzoic acid (X ¼ F or CF3). Reagent
and conditions: (a) C6H13Br, K2CO3, 3-Pentanone, reflux; (b) BuLi, THF, ꢀ78ꢁC
ꢁC then CO2.
subsequent reduction of the ester, with 2 equivalents of n-buthyl-
lithium gave the ortho-lithiated aryllithium species. The species was
quenched with hexachloroethane [8] for 2 or 1,2-dibromoethane [9]
for 3 and 4, to give the corresponding benzyl alcohol in a moderate
yield. In all the cases shown in scheme 1 and 2, the lithiations with
n-buthillithium follwed by the electrophilic aromatic substitution
reaction were carried out at low temperature (ꢀ78ꢁC). Subsequent
functional group conversions, such as oxidation, deprotection, alky-
lation etc, on the benzyl alcohols, gave the desired carboxylic acids,
as shown in Scheme 2.
Compounds 1–5 were prepared by an esterification of the
corresponding carboxylic acids and phenols. The spectra data for 1–5
are summarized in Ref. [10].
Compounds 6 and 7s were prepared by the conventional methods
described in our earlier paper [4].
SCHEME 2 Synthesis for 3-alkoxy-2-X-benzoic acid (X¼Cl, Br or CN).
Reagent and conditions: (a) MOMCl, NaH, THF (95%); (b) LiAlH4, THF
(90%); (c) 2BuLi, THF, ꢀ78ꢁC then hexachloroethane (X¼Cl; 70%) or
1,2-dibromoethane (X¼Br; 58%); (d) KMnO4, H2O, acetone (X¼Cl; 75%,
X¼Br; 66%); (e) H2SO4, EtOH, (X¼Cl; 87%, X¼Br; 62%); (f) C6H13Br,
K2CO3 (X¼Cl; 70%, X¼Br; 77%); (g) CuCN, DMF (54%); (h) NaOH aq., EtOH
(X¼Cl; 65%, X¼Br; 69%, X¼CN; 45%). MOM; Methoxymethyl group.

224=[2090]
H. Okamoto et al.
SCHEME 3 Synthesis for compounds 1–7.
RESULTS AND DISCUSSION
Transition temperatures and latent heats for 1–7 are summarized in
Table 1.
Compounds 1, 2, and 5 show a nematic (N) phase with a schlieren
and homeotropic textures under a homogeneous and homogeneous
alignment glass surfaces, respectively, in a cooling process. The N–I
(isotropic) transition temperatures for 1, 2, and 5 are determined to
be 55, 64, and 25ꢁC, respectively. Compounds 3 and 4, on the other
hand, are non-mesogenic even in a rapid cooling process.
TABLE 1 Transition Temperatures and Latent Heats for Compounds 1–7
Compound
Transition temperature (ꢁC)
Latent heat (kJ=mol)
m
6
n
C
N
I
mp
N–I
1
2
3a
3b
4
6
. 63
. 68
. 67
. 80
. 128
. 59
. 67
. 79
. 76
(. 55)
(. 64)
[. 57]
–
.
.
.
.
.
.
.
.
.
46.3
34.8
30.5
48.5
35.1
33.7
45.3
58.8
36.5
0.4
ꢂ2
14
6
–
5
(. 25)
. 84
. 81
[. 22]
0.5
0.8
1.3
1
1
6aꢂ
6bꢂ
14
5
1
7ꢂ
5
C, N, and I indicate crystal, nematic, and isotropic phases, respectively.
Parentheses and brackets indicate a monotropic and virtual transitions, respectively.
ꢂ1, See ref. [6]; ꢂ2, The latent heat could not be detected by a DSC thermogram on
rapid cooling process.

Synthesis and LC Properties for 3-Alkoxy-2-X-benzoates
225=[2091]
In order to determine the LC properties for 3 and 4, the binary phase
diagrams for the mixtures of 3 and 4-octyloxyphenyl 4-octyloxybenzoate
(8), and 4 and 4-(4-hexyloxyphenoxycarbonyl)phenyl 4-cyano-3-heptylox-
ybenzoates (9) were examined and are shown in Figure 2. The N–I
transition temperature decreases gradually with increasing the concen-
tration of 3a, and a virtual N–I transition temperature for 3a was
estimated to be 57ꢁC as shown in Figure 2(a). The smectic C (SmC)–N
transition temperature, on the other hand, steeply decreases with
increasing the concentration of 3a and could not be observed at more
than 30 mol% of 3a. As can be seen from Figure 3(b), SmC–smectic A
(SmA) and SmA–N or I transition temperatures decrease steeply with
increasing the concentration of 4, indicating mesomorphic properties
for 4 are extremely low.
The effective order of the substituent (X) for the N–I phase transition
temperature is expressed as follows.
T
N–I; CH3 (6)>Cl (2)>Br (3)>F (1)>CF3 (5)>H (7), CN (4)
FIGURE 2 Binary phase diagrams for the mixtures; (a) 4-octyloxyphenyl
4-octyloxybenzoate (8) (left) and 3a (right), and (b) 4-(4-hexyloxyphenoxycar-
bonyl)phenyl 4-cyano-3-heptyloxybenzoates (9) (left) and 4 (right). ꢁ; N–I,
4
4; SmA–I, ; SmC–N or SmA, &; C–SmC, N, SmA, or I. Phase transitions
below a melting point are a monotropic transition.

226=[2092]
H. Okamoto et al.
FIGURE 3 Plots of N–I transition temperature vs. breadth of LC core for
4
1;
ꢁ
, 2; &, 3; 4, 4; , 6; ~, and 7; &.
The N–I transition temperatures and virtual ones for 1–4, 6, and 7
are plotted against the breadth of the LC cores, which are optimized by
a semi-empirical molecular calculation (MOPAC) with an AM1 method
[12] as shown in Figure 3.
The N–I transition temperatures for 1–4 show a good correlation
with the breadth of the LC core, though those for 6 and 7 are separated
from the correlation.
These results indicate that the N–I transition temperatures are
influenced by not only geometrical effect, such as the breadth of the
LC core, but also electrostatic one.
Further examination is now underway.
REFERENCES
[1] Weissflog, W. (1998). In: Handbook of Liquid Crystals, Demus, D., Goodby, J. W.,
Gray, G. W., Spiess, H.-W., & Vill, V. (Eds.), Wiley-VCH: Weinheim, Vol. 2B.
[2] Tschierske, C. (1998). J. Mater. Chem., 8, 1485.
[3] Hird, M., Goodby, J. W., Gough, N., & Toyne, K. J. (2001). J. Mater. Chem., 11,
2732.
[4] Okamoto, H., Umeda, A., & Takenaka, S. (1998). Mol. Cry st. Liq. Cryst., 317, 111.
Phase sequence and transition temperature for 9 are C 116 SmC 117 N 118 I (ꢁC).
[5] Wu, J., Okamoto, H., & Takenaka, S. (2001). Chem. Lett., 116.
[6] Wu, J., Okamoto, H., & Takenaka, S. (2001). Chem. Lett., 330.
[7] Wu, J., Okamoto, H., Morita, Y., & Takenaka, S. (2001). Bull. Chem. Soc. Jpn, 74,
2437.
[8] Winkle, M. R. & Ronald, R. C. (1982). J. Org. Chem., 47, 2101.
[9] Ronald R. C. & Winkle, M. R. (1983). Tetrahedron Lett., 39, 2031.
[10] Spectra data for 1: IR (KBr disc); n ¼1726.0 cmꢀ1
,
1H NMR (CDCl3); d¼0.91 (6H, t,
J¼7.0 Hz), 1.32–1.52 (12H, m), 1.79 (2H, quin., J¼6.5 Hz), 1.85 (2H, qui.,

Synthesis and LC Properties for 3-Alkoxy-2-X-benzoates
227=[2093]
J¼6.5 Hz), 3.96 (2H, t, J¼6.5 Hz), 4.07 (2H, t, J¼6.5 Hz), 6.92 (2H, d, J¼9.0 Hz),
7.12 (2H, d, J¼9.0 Hz), 7.18–7.20 (2H, m), 7.38 (2H, d, J¼8.5 Hz), 7.62 (1H, m), and
8.27 (2H, d, J¼8.5 Hz) ppm.
Spectra data for 2: IR (KBr disc) n ¼1735.6 and 1741.4 cmꢀ1
,
1H NMR (CDCl3);
d¼0.91 (6H, t, J¼7.0 Hz), 1.32–1.52 (12H, m), 1.79 (2H, quin., J¼6.5 Hz), 1.85
(2H, qui., J¼6.5 Hz), 3.96 (2H, t, J¼6.5 Hz), 4.07 (2H, t, J¼6.5 Hz), 6.92 (2H, d,
J¼9.0 Hz), 7.12 (2H, d, J¼9.0 Hz), 7.18–7.20 (2H, m), 7.38 (2H, d, J¼8.5 Hz),
7.62 (1H, m), and 8.27 (2H, d, J¼8.5 Hz) ppm.
Spectra data for 3a: IR (KBr disc) n ¼1739.5 cmꢀ1, 1H NMR (CDCl3); d¼0.91 (3H, t,
J¼6.0 Hz), 0.92 (3H, t, J¼6.0 Hz), 1.32–1.59 (12H, m), 1.79 (2H, qui., J¼6.5 Hz),
1.86 (2H, qui., J¼6.5 Hz), 3.96 (2H, t, J¼6.5 Hz), 4.08 (2H, t, J¼6.5 Hz), 6.93
(2H, d, J¼8.0 Hz), 7.07 (1H, dd, J¼8.0, 1.5 Hz), 7.12 (2H, d, J¼8.0 Hz), 7.37 (1H,
t, J¼8.0 Hz), 7.42 (2H, d, J¼8.0 Hz), 7.48 (1H, dd, J¼8.0, 1.5 Hz), and 8.27 (2H,
d, J¼8.0 Hz) ppm.
Spectra data for 4a: IR (KBr disc) n ¼1689.3 and 2227 cmꢀ1
,
1H NMR (CDCl3);
d¼0.90 (3H, t, J¼6.5 Hz), 1.31–1.57 (6H, m), 1.43 (3H, t, J¼7.0 Hz), 1.86 (2H,
qui., J¼6.5 Hz), 4.12 (2H, t, J¼6.5 Hz), 4.44 (2H, q, J¼7.0 Hz), 7.19 (1H, dd,
J¼8.0, 1.5 Hz), and 7.54–7.65 (2H, m) ppm.
Spectra data for 5: IR (KBr disc); n ¼1731.8 and 1756.8 cmꢀ1
,
1H NMR (CDCl3);
d ¼ 0.88 (3H, t, J¼7.0Hz), 0.92 (3H, t, J¼7.0 Hz), 1.24–1.54 (12H, m), 1.79 (2H,
qui., J¼7.0 Hz), 1.85 (2H, qui., J¼7.0Hz), 3.96 (2H, J¼6.5Hz), 4.10 (2H, J¼7.0 Hz),
Hz), 6.94 (2H, d, J¼8.0 Hz), 7.12 (2H, d, J¼8.0Hz), 7.32 (1H, t, J¼8.0 Hz), 7.37 (2H, d,
J¼9.0 Hz), 7.87 (1H, d, J¼8.0 Hz), 8.23 (1H, d, J¼8.0 Hz), and 8.30 (2H, d, J¼9.0 Hz)
ppm.
[11] Demus, D., Demus, H., & Zaschke, H. (1976). Flu¨ssige Kristalle in Tabellen, VEB
Deutscher Verlag fu¨r Grundstoff Industrie, Leipzig. Phase sequence and transition
temperature for 8 are C 63 SmC 72 N 90 I (ꢁC).
[12] Dewar, M. J. S., Zoebisch, E. G., Healy, E. F., & Steward, J. J. P. (1985). J. Am.
Chem. Soc., 107, 3903.