Synthesis of 4-alkoxy-2-substituted-benzenethiols and their application to thermotropic liquid crystals

Article abstract of DOI:10.1246/bcsj.75.175

A new synthetic method of 4-alkoxy-2-X-benzenethiols (X = H, halogens, CH₃) has been established. In order to confirm the validity as a component of liquid crystal materials, some derivatives of S-(4-alkoxy-2-X-phenyl) 4-R-thiobenzoates (R = C_nH_2n+₁O, CN, NO₂, X = halogens, CH₃) were prepared. Most of the thioesters exhibit a nematic phase, while the lateral substituents (X) tend to reduce the mesophase thermal stability as well as the melting point. The effect of lateral substituents on the mesomorphic properties is discussed.

Full text of DOI:10.1246/bcsj.75.175

Bull. Chem.
Soc. Jpn.
75
1
© 2002 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 75, 175–179 (2002)
175
The Chemical
Society of Ja-
pan
The Chemical
Society of Ja-
pan
AM
1
Synthesis of 4-Alkoxy-2-substituted-benzenethiols and Their Application
to Thermotropic Liquid Crystals
LC Properties of Thioesters
H. Okamoto et al.
15
2002
175
Hiroaki Okamoto,* Jianwei Wu, Yuki Morita, and Shunsuke Takenaka
Department of Advanced Materials Science and Engineering, Faculty of Engineering, Yamaguchi University,
Tokiwadai 2-16-1, Ube, Yamaguchi, 755-8611
179
BCSJA8
0009-2673
01220
7
(Received July 5, 2001)
5
2001
9
25
2001
A new synthetic method of 4-alkoxy-2-X-benzenethiols (X = H, halogens, CH3) has been established. In order to
confirm the validity as a component of liquid crystal materials, some derivatives of S-(4-alkoxy-2-X-phenyl) 4-R-
thiobenzoates (R = CnH2n+1O, CN, NO2, X = halogens, CH3) were prepared. Most of the thioesters exhibit a nematic
phase, while the lateral substituents (X) tend to reduce the mesophase thermal stability as well as the melting point. The
effect of lateral substituents on the mesomorphic properties is discussed.
2.1
5.6.9
Benzenethiols are one of the important components of liq-
uid crystal (LC) molecules, and LC materials incorporating a
thioester linkage have been developed.1–6 The thioester link-
age is also given much attention as the core of chiral LC mate-
rials.7–9 Thioester compounds are known to have excellent me-
somorphic properties compared with the corresponding ester
ones, since the thioester linkage is superior in linearity and
longitudinal length to the ester one.10
For example, 1,4-benzenebis(S-4-alkoxyphenyl carbothio-
ate),2 S-phenyl thiobenzoates,2–6 and S-(4-biphenylyl)
thiobenzoates7 with alkyl and/or alkoxy groups at both termi-
nal positions show a higher nematic–isotropic (N–I) transition
temperature and a wider mesomorphic range than the corre-
sponding ester compounds.
The introduction of a lateral substituent is one of the con-
ventional methods for changing and improving the LC proper-
ties such as the dielectric constant, refractive index, and transi-
tion temperature. In the case of benzenethiol compounds, the
introduction of a lateral substituent is not very easy because of
high chemical reactivity around the sulfur moiety. As far as we
know, therefore, thioester LC materials involving lateral sub-
stituents at the S-phenyl ring have not been developed.
Fig. 1. Chemical structures of compounds 1–5.
Recently, we successfully prepared LC materials having 3-
DSC thermogram was operated at a heating or cooling rate of 5
°C/min. The mesophases were characterized by a Nikon POH po-
larizing microscope fitted with a Mettler thermo-control system
fluoro- and 3-methyl-thiocyanatobenzenes.11
During the process, we found that thiocyanato compounds
can be successfully converted to the corresponding thiols by
the reaction of LiAlH4 or NaBH4 in high yield, suggesting that
4-thiocyanato-3-X-phenols are convenient intermediates for
the synthesis of 4-alkoxy-2-X-benzenethiols.
In this paper we wish to show the synthesis of 4-alkoxy-2-
X-benzenethiols (Fig. 1) and its application to LC materials.
The LC properties are discussed in terms of the geometrical
and electrostatic nature of the molecules.
1
(FP-900). H NMR spectra were measured using a JEOL EX-270
spectrometer, where tetramethylsilane was used as an internal
standard. IR spectra were recorded with a Horiba FT-200 infrared
spectrometer. The purity was checked by HPLC and elementary
analysis. Molecular parameters were estimated by a semi-empiri-
cal molecular orbital method (MOPAC 97).
Materials. The synthetic scheme for 1–5 is shown in Fig. 2.
3-Fluoro-4-thiocyanatophenol: The thiocyanation of phe-
nols was carried out according to a method described in our earlier
paper.11 After a solution of N-chlorosuccinimide (15.49 g, 116
mmol) and ammonium thiocyanate (8.8 g, 116 mmol) in methanol
(150 mL) was stirred at 0 °C for 2 h, 3-fluorophenol (6.5 g, 57.8
mmol) in methanol (50 mL) was added dropwise, and the mixture
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 (mp 156.6 °C, 28.4 J/g). The

176 Bull. Chem. Soc. Jpn., 75, No. 1 (2002)
LC Properties of Thioesters
Fig. 2. Synthetic scheme of (S-4-alkoxy-2-X-phenyl) 4-R-thiobenzoates (1–5).
was stirred at 0 °C for 24 h. To the reaction mixture, a 20% aque-
ous solution of sodium hydrogencarbonate (200 mL) was added,
and the precipitates were filtered off. Half of the solvent of the fil-
trate was evaporated in vacuo, and the residue was extracted twice
with ether (50 mL). The combined ether layer was washed with
water and dried over anhydrous sodium sulfate. After removing
the solvent, the residue was purified by column chromatography
on silica gel using chloroform as an eluent. The product was re-
crystallized from a mixed solvent of ether–hexane to give 3-fluo-
ro-4-thiocyanatophenol as colorless needles; yield 20%; mp 66–
68 °C; IR (KBr) 2171 (CN) and 3290 cm−1 (OH); 1H NMR δ 6.38
(1H, br), 6.68–6.74 (2H, m), 7.45 (1H, t, J = 8.6 Hz).
3-Chloro-4-thiocyanatophenol: Colorless powder; yield
17%; mp 86–88 °C. 1H NMR δ 6.16 (1H, br.), 6.82 (1H, dd, J =
8.6, 2.6 Hz), 7.01 (1H, d, J = 2.6 Hz), 7.54 (1H, d, J = 8.6 Hz).
3-Bromo-4-thiocyanatophenol: Pale yellow powder; yield
20%; mp 88–90 °C. 1H NMR δ 6.21 (1H, br.), 6.87 (1H, dd, J =
8.9, 2.6 Hz), 7.18 (1H, d, J = 2.6 Hz), 7.56 (1H, d, J = 8.9 Hz).
3-Methyl-4-thiocyanatophenol: Colorless needles; yield
50%; mp 72–74 °C. 1H NMR δ 2.47 (3H, s), 5.89 (1H, br.), 6.70
(1H, dd, J = 8.5, 3.0 Hz), 6.79 (1H, d, J = 3.0 Hz), 7.45 (1H, t, J
= 8.5 Hz).
6.3 Hz), 6.71–6.78 (2H, m), 7.50 (1H, t, J = 8.6 Hz).
2-Fluoro-4-hexyloxyphenyl Thiocyanate: 1H NMR δ 0.91
(3H, t, J = 6.6 Hz), 1.30–1.44 (6H, m), 1.79 (2H, quin., J = 6.9
Hz), 3.96 (2H, t, J = 6.3 Hz), 6.71–6.78 (2H, m), 7.50 (1H, t, J =
8.6 Hz).
2-Chloro-4-octyloxyphenyl Thiocyanate:
Colorless oil;
yield 67%. 1H NMR δ 0.89 (3H, t, J = 6.9 Hz), 1.29–1.45 (10H,
m), 1.79 (2H, quin., J = 7.0 Hz), 3.93 (2H, t, J = 6.6 Hz), 6.87
(1H, dd, J = 8.9, 2.6 Hz), 7.03 (1H, d, J = 2.6 Hz), 7.59 (1H, d,
J = 8.9 Hz).
2-Bromo-4-octyloxyphenyl Thiocyanate:
Colorless oil;
yield 67%. 1H NMR δ 0.89 (3H, t, J = 6.8 Hz), 1.29–1.46 (10H,
m), 1.78 (2H, quin., J = 6.7 Hz), 3.95 (2H, t, J = 6.7 Hz), 6.92
(1H, dd, J = 8.9, 2.6 Hz), 7.15 (1H, d, J = 2.6 Hz), 7.61 (1H, d, J
= 8.9 Hz).
2-Methyl-4-octyloxyphenyl Thiocyanate:
Colorless oil;
yield 62%. 1H NMR δ 0.89 (3H, t, J = 6.6 Hz), 1.29–1.47 (10H,
m), 1.78 (2H, quin., J = 6.8 Hz), 2.34 (3H, s), 3.95 (2H, t, J = 6.6
Hz), 6.76 (1H, dd, J = 8.6, 2.6 Hz), 6.84 (1H, d, J = 2.9 Hz), 7.52
(1H, d, J = 8.6 Hz).
4-Octyloxyphenyl Thiocyanate: Colorless oil; yield 35%.
1H NMR δ 0.89 (3H, t, J = 6.8 Hz), 1.29–1.46 (10H, m), 1.79
(2H, quin., J = 6.9 Hz), 3.96 (2H, t, J = 6.7 Hz), 6.93 (2H, d, J =
8.9 Hz), 7.48 (2H, d, J = 8.9 Hz).
2-Fluoro-4-octyloxyphenyl Thiocyanate:
2-Fluoro-4-hy-
droxy-thiocyanatobenzene (0.88 g, 5.22 mmol), triphenylphos-
phine (1.78 g, 6.79 mmol), and octanol (0.82 g, 6.30 mmol) were
dissolved in dry THF (10 mL), and diethyl azodicarboxylate
(DEAD, 40% in toluene, 2.95 g, 6.78 mmol) was added to the so-
lution at 0 °C under a nitrogen atmosphere. After the reaction
mixture was brought to room temperature, stirring was continued
for 12 h. The reaction mixture was poured into water and extract-
ed with toluene. The organic layer was washed with water and
dried over anhydrous sodium sulfate. After removing the toluene,
ether was added to the residue and diethyl hydrazodicarboxylate
separated out was filtered off. After removing the solvent, the res-
idue was purified by column chromatography on silica gel using
petroleum ether–chloroform (2 : 1) as an eluent, giving 2-fluoro-4-
octyloxyphenyl thiocyanate as a colorless oil; 0.91 g, yield 62%;
2-Fluoro-4-octyloxybenzenethiol: To a solution of 2-fluoro-
4-octyloxy-thiocyanatobenzene (0.33 g, 1.17 mmol) in ethanol
(5 mL), sodium borohydride (0.11 g, 2.91 mmol) was added drop-
wise at 0 °C. After stirring for 2 h, water (4 mL) was slowly added
to the reaction mixture. The ethanol was removed by evaporation
and the residue was extracted with ether twice. The combined
ether layer was dried over anhydrous sodium sulfate. After re-
moving ether, the product was obtained as a colorless oil. Because
the oily material easily became dark under atmospheric condi-
tions, it was reacted with the acids without further purification;
yield 0.29 g (96%); IR (KBr) 2600 cm−1 (SH).
2-Chloro-4-octyloxy-, 2-bromo-4-octyloxy-, 2-methyl-4-octyl-
oxybenzenethiols were obtained similarly.
S-(4-Octyloxyphenyl) 4-Butoxythiobenzoate (1b): 1b was
obtained by the reaction of 4-butoxybenzoyl chloride and 4-octyl-
1
IR (KBr) 2158 cm−1 (CN); H NMR δ 0.91 (3H, t, J = 6.6 Hz),
1.30–1.44 (10H, m), 1.79 (2H, quin, J = 6.9 Hz), 3.96 (2H, t, J =

H. Okamoto et al.
Bull. Chem. Soc. Jpn., 75, No. 1 (2002) 177
(2H, d, J = 8.6 Hz).
S-(2-Fluoro-4-octyloxyphenyl) 4-Nitrothiobenzoate (2j):
1H NMR δ 0.90 (3H, t, J = 6.3 Hz), 1.30–1.55 (10H, m), 1.79
(2H, quin., J = 6.8 Hz), 3.99 (2H, t, J = 6.5 Hz), 6.78 (2H, d, J =
8.8 Hz), 7.35 (1H, t, J = 7.7 Hz), 8.20 (2H, d, J = 8.9 Hz), 8.34
(2H, d, J = 8.9 Hz).
S-(2-Chloro-4-octyloxyphenyl) 4-Butoxythiobenzoate (3a):
1H NMR δ 0.89 (3H, t, J = 6.6 Hz), 0.98 (3H, t, J = 7.0 Hz),
1.29–1.54 (12H, m), 1.74–1.86 (4H, m), 3.97 (2H, t, J = 6.6 Hz),
4.03 (2H, t, J = 6.6 Hz), 6.86 (1H, dd, J = 8.9, 2.6 Hz), 6.93 (2H,
d, J = 8.9 Hz), 7.09 (1H, d, J = 2.6 Hz), 7.44 (1H, d, J = 8.9 Hz),
8.00 (2H, d, J = 8.8 Hz).
S-(2-Chloro-4-octyloxyphenyl) 4-Octyloxythiobenzoate (3b):
1H NMR δ 0.90 (6H, t, J = 6.6 Hz), 1.29–1.49 (20H, m), 1.72–
1.86 (4H, m), 3.97 (2H, t, J = 6.6 Hz), 4.02 (2H, t, J = 6.6 Hz),
6.86 (1H, dd, J = 8.9, 2.6 Hz), 6.93 (2H, d, J = 8.8 Hz), 7.09 (1H,
d, J = 2.6 Hz), 7.44 (1H, d, J = 8.9 Hz), 8.00 (2H, d, J = 8.8 Hz).
S-(2-Bromo-4-octyloxyphenyl) 4-Butoxythiobenzoate (4a):
1H NMR δ 0.89 (3H, t, J = 6.6 Hz), 0.98 (3H, t, J = 7.1 Hz),
1.29–1.57 (12H, m), 1.74–1.86 (4H, m), 3.97 (2H, t, J = 6.6 Hz),
4.03 (2H, t, J = 6.6 Hz), 6.90 (1H, dd, J = 8.8, 2.6 Hz), 6.95 (2H,
d, J = 8.9 Hz), 7.27 (1H, d, J = 2.6 Hz), 7.47 (1H, d, J = 8.8 Hz),
and 8.00 (2H, d, J = 8.9 Hz).
oxybenzenethiol according to the conventional method. IR (KBr)
1670 cm−1 (CwO); 1H NMR δ 0.89 (3H, t, J = 6.6 Hz), 0.98 (3H,
t, J = 7.0 Hz), 1.29–1.54 (12H, m), 1.74–1.86 (4H, m), 3.97 (2H,
t, J = 6.6 Hz), 4.02 (2H, t, J = 6.6 Hz), 6.92 (2H, d, J = 8.8 Hz),
6.96 (2H, d, J = 8.9 Hz), 7.38 (2H, d, J = 8.8 Hz), 7.98 (2H, d, J
= 8.9 Hz). Found: C, 72.43; H, 8.27%. Calcd for C25H34O3S: C,
72.21; H, 8.09%.
Compounds 1c–5b were prepared by the similar manner.
S-(4-Octyloxyphenyl) 4-Hexyloxythiobenzoate (1c):
NMR δ 0.89 (6H, t, J = 6.6 Hz), 1.29–1.50 (16H, m), 1.74–1.86
(4H, m), 3.98 (2H, t, J = 6.7 Hz), 4.02 (2H, t, J = 6.6 Hz), 6.92
(2H, d, J = 8.8 Hz), 6.96 (2H, d, J = 8.9 Hz), 7.38 (2H, d, J = 8.8
Hz), 7.98 (2H, d, J = 8.9 Hz).
1H
S-(4-Octyloxyphenyl) 4-Octyloxythiobenzoate (1d):
1H
NMR δ 0.89 (6H, t, J = 6.6 Hz), 1.29–1.50 (20H, m), 1.74–1.84
(4H, m), 3.98 (2H, t, J = 6.6 Hz), 4.02 (2H, t, J = 6.6 Hz), 6.92
(2H, d, J = 8.8 Hz), 6.96 (2H, d, J = 8.9 Hz), 7.38 (2H, d, J = 8.8
Hz), 7.98 (2H, d, J = 8.9 Hz).
S-(2-Fluoro-4-hexyloxyphenyl) 4-Ethoxythiobenzoate (2a):
1H NMR δ 0.89 (3H, t, J = 6.6 Hz), 1.24–1.40 (6H, m), 1.45 (3H,
t, J = 6.6 Hz), 1.74–1.85 (4H, m), 3.95 (2H, t, J = 6.6 Hz), 4.10
(2H, q, J = 6.8 Hz), 6.72–6.78 (2H, m), 6.92 (2H, d, J = 8.9 Hz),
7.34 (1H, t, J = 7.7 Hz), 7.99 (2H, d, J = 8.9 Hz).
S-(2-Fluoro-4-hexyloxyphenyl) 4-Hexyoxythiobenzoate (2b):
1H NMR δ 0.89 (6H, t, J = 6.6 Hz), 1.29–1.52 (12H, m), 1.74–
1.86 (4H, m), 3.95 (2H, t, J = 6.6 Hz), 4.02 (2H, t, J = 6.6 Hz),
6.72–6.78 (2H, m), 6.92 (2H, d, J = 8.8 Hz), 7.34 (1H, t, J = 8.0
Hz), and 7.97 (2H, d, J = 8.9 Hz).
S-(2-Fluoro-4-hexyloxyphenyl) 4-Cyanothiobenzoate (2c):
1H NMR δ 0.90 (3H, t, J = 6.6 Hz), 1.29–1.49 (6H, m), 1.81 (2H,
quin., J = 6.9 Hz), 3.99 (2H, t, J = 6.6 Hz), 6.78 (2H, d, J = 8.6
Hz), 7.34 (1H, t, J = 8.1 Hz), 7.81 (2H, d, J = 8.9 Hz), 8.10 (2H,
d, J = 7.7 Hz).
S-(2-Fluoro-4-octyloxyphenyl) 4-Ethoxythiobenzoate (2d):
1H NMR δ 0.89 (3H, t, J = 6.5 Hz), 1.24–1.40 (10H, m), 1.45
(3H, t, J = 6.7 Hz), 1.74–1.85 (4H, m), 3.95 (2H, t, J = 6.6 Hz),
4.10 (2H, q, J = 6.9 Hz), 6.72–6.78 (2H, m), 6.92 (2H, d, J = 8.8
Hz), 7.34 (1H, t, J = 7.6 Hz), 7.99 (2H, d, J = 8.9 Hz).
S-(2-Fluoro-4-octyloxyphenyl) 4-Butoxythiobenzoate (2e):
1H NMR δ 0.89 (3H, t, J = 6.5 Hz), 0.98 (3H, t, J = 7.2 Hz),
1.29–1.54 (12H, m), 1.74–1.86 (4H, m), 3.97 (2H, t, J = 6.6 Hz),
4.03 (2H, t, J = 6.6 Hz), 6.72–6.78 (2H, m), 6.92 (2H, d, J = 8.9
Hz), 7.34 (1H, t, J = 7.9 Hz), 7.97 (2H, d, J = 8.9 Hz).
S-(2-Fluoro-4-octyloxyphenyl) 4-Hexyloxythiobenzoate (2f):
1H NMR δ 0.89 (6H, t, J = 6.6 Hz), 1.29–1.50 (16H, m), 1.74–
1.86 (4H, m), 3.95 (2H, t, J = 6.7 Hz), 4.03 (2H, t, J = 6.6 Hz),
6.72–6.78 (2H, m), 6.92 (2H, d, J = 8.9 Hz), 7.34 (1H, t, J = 7.9
Hz), 7.97 (2H, d, J = 8.9 Hz).
S-(2-Bromo-4-octyloxyphenyl) 4-Octyloxythiobenzoate (4b):
1H NMR δ 0.90 (6H, t, J = 6.6 Hz), 1.29–1.50 (20H, m), 1.74–
1.86 (4H, m), 3.97 (2H, t, J = 6.6 Hz), 4.04 (2H, t, J = 6.6 Hz),
6.90 (1H, dd, J = 8.8, 2.6 Hz), 6.95 (2H, d, J = 8.9 Hz), 7.27 (1H,
d, J = 2.6 Hz), 7.47 (1H, d, J = 8.9 Hz), 8.00 (2H, d, J = 8.9 Hz).
S-(2-Methyl-4-octyloxyphenyl) 4-Butoxythiobenzoate (5a):
1H NMR δ 0.89 (3H, t, J = 6.6 Hz), 0.98 (3H, t, J = 6.6 Hz),
1.29–1.49 (12H, m), 1.74–1.84 (4H, m), 3.97 (2H, t, J = 6.6 Hz),
4.04 (2H, t, J = 6.6 Hz), 6.76 (1H, dd, J = 8.9, 2.6 Hz), 6.89 (1H,
d, J = 2.6 Hz), 6.93 (2H, d, J = 8.8 Hz), 7.34 (1H, d, J = 8.9 Hz),
8.01 (2H, d, J = 8.8 Hz).
S-(2-Methyl-4-octyloxyphenyl) 4-Octyloxythiobenzoate (5b):
1H NMR δ 0.90 (6H, t, J = 6.6 Hz), 1.29–1.47 (20H, m), 1.74–
1.84 (4H, m), 2.34 (3H, s), 3.95 (2H, t, J = 6.6 Hz), 4.03 (2H, t, J
= 6.6 Hz), 6.76 (1H, dd, J = 8.9, 2.6 Hz), 6.89 (1H, d, J = 2.6
Hz), 6.93 (2H, d, J = 8.8 Hz), 7.34 (1H, d, J = 8.9 Hz), 8.01 (2H,
d, J = 8.8 Hz).
Results and Discussion
Syntheses. 4-Alkoxybenzenethiols have been prepared
through several steps from phenols.2 These synthetic methods
are not necessarily convenient for the preparation of substitut-
ed benzenethiols, since the scheme involves drastic reaction
conditions. Therefore, we attempted to prepare 4-alkoxy-2-X-
benzenethiols according to the scheme in Fig. 2. Usually, the
thiocyanation of phenol has been achieved by the reaction of
chlorine and lead(Ⅱ) thiocyanate.12
We found that the reaction of 3-substituted (X) phenols with
N-chlorosuccinimide and ammonium thiocyanate gives 3-X-4-
thiocyanatophenols. Under such conditions, thiocyanation se-
lectively occurs only at the 4 position of the phenols. The thio-
cyanation appears to be sensitive to the electrostatic nature of
the substituents, X. That is, an electron-donating substituent,
such as a methyl group gives a better yield than the electron-
withdrawing ones, such as halogens.
S-(2-Fluoro-4-octyloxyphenyl) 4-Octyloxythiobenzoate (2g):
1H NMR δ 0.89 (6H, t, J = 6.6 Hz), 1.29–1.54 (20H, m), 1.74–
1.86 (4H, m), 3.94 (2H, t, J = 6.6 Hz), 4.02 (2H, t, J = 6.6 Hz),
6.72–6.78 (2H, m), 6.92 (2H, d, J = 8.9 Hz), 7.34 (1H, t, J = 7.9
Hz), 7.97 (2H, d, J = 8.9 Hz).
S-(2-Fluoro-4-octyloxyphenyl) 4-Decyloxythiobenzoate (2h):
1H NMR δ 0.89 (6H, t, J = 6.6 Hz), 1.29–1.54 (24H, m), 1.74–
1.86 (4H, m), 3.94 (2H, t, J = 6.6 Hz), 4.02 (2H, t, J = 6.6 Hz),
6.72–6.78 (2H, m), 6.92 (2H, d, J = 8.9 Hz), 7.34 (1H, t, J = 7.9
Hz), 7.97 (2H, d, J = 8.8 Hz).
S-(2-Fluoro-4-octyloxyphenyl) 4-Cyanothiobenzoate (2i):
1H NMR δ 0.90 (3H, t, J = 6.5 Hz), 1.30–1.48 (10H, m), 1.81
(2H, quin., J = 6.9 Hz), 3.99 (2H, t, J = 6.6 Hz), 6.78 (2H, d, J =
8.7 Hz), 7.34 (1H, t, J = 8.2 Hz), 7.81 (2H, d, J = 8.6 Hz), 8.10
The alkylation of phenol is usually achieved by Williamson
synthesis with alkyl halides under the presence of anhydrous
potassium carbonate. In the cases of 3-X-4-thiocyanatophe-

178 Bull. Chem. Soc. Jpn., 75, No. 1 (2002)
Table 1. Thermal Properties for Compounds 1–5
LC Properties of Thioesters
Transition temperatures
Latent heats
/kJ mol−1
C–N N–I
Compounds
/°C
N
No
1a*1
1b
1c
1d
1e
2a
2b
2c
2d
2e
2f
X
R
Rꢀ
C
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
I
H
H
H
H
H
F
F
F
F
F
F
F
F
F
F
C2H5O
C4H9O
C6H13O
C8H17O
C8H17
C8H17
C8H17
C8H17
81
60
58
O
O
O
O
O
O
O
(O
(O
O
O
O
O
(O
—
(O
O
(O
O
107
105
105
102
99
79
74
74)
75)
72
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
40.1
35.4
40.5
1.7
1.7
2.6
59*2
64*3
78
C10H21O C8H17
C2H5O
C6H13O
NC
C2H5O
C4H9O
C6H13O
C8H17O
C10H21O C8H17
NC
O2N
C4H9O
C8H17O
C4H9O
C8H17O
C4H9O
C8H17O
C6H13
C6H13
C6H13
C8H17
C8H17
C8H17
C8H17
45.2
38.0
36.3
47.7
43.1
32.7
44.6
45.6
40.4
35.1
43.2
50.6
42.8
46.2
42.0
39.9
1.7
1.7
1.0
1.7
1.6
1.6
1.9
2.0
0.9
—
2.2
2.6
1.8
2.0
1.7
1.8
57
101
78
48
42
44
62
79
71
55
43
53
34
53
29
72
74
73
72)
2g
2h
2i
C8H17
C8H17
C8H17
C8H17
C8H17
C8H17
C8H17
C8H17
2j
3a
3b
4a
4b
5a
5b
Cl
Cl
Br
Br
CH3
CH3
40)
44
29)
35
49)
49
(O
O
C, N, and I indicate crystal, nematic, and isotropic liquid phases, respectively. Values
in parentheses indicate a monotoropic transition temperature.
*1 Transition temperatures of 1a were cited from Ref. 5.
*2 A transition at 59 °C is a C–Sm C transition. An Sm C–N transition was observed
at 68.2 °C (∆H = 0.8 kJ mol−1).
*3 Transition temperatures of 1e were cited from Ref. 2. Our observation indicated
that a transition at 59 °C is a C–Smectic C transition, and this compound undergoes an
Sm C–N transition at 74 °C.
nols, a similar reaction causes of decomposition of the thio-
usual schlieren texture. The transition temperatures and latent
heats are summarized in Table 1. The average N–I transition
temperature for the hydrogen compounds (1a–1e) is 104 °C,
which is slightly higher than that for the corresponding ester
compounds (91 °C).14 The introduction of a lateral fluorine
atom reduces the N–I transition temperature, 73 °C on average
for 2d–2h. Generally, the effect of the lateral substituent on
the mesomorphic properties has been interpreted in both geo-
metrical and electrostatic terms. The substitution of a fluorine
atom at the lateral position, for example, slightly increases the
breadth around the substituent, since the C–F bond (1.36 Å) is
longer than the C–H one (1.10 Å), and the van der Waals radi-
us for fluorine is larger than hydrogen. The effective order for
the N–I transition temperature decreases by the order of H > F
> Cl = CH3 > Br. The N–I transition temperatures for some
members are plotted against the breadths calculated by MO-
PAC in Fig. 3. The breadths are the distance between the lon-
gitudinal axis of the phenyl ring and the center of the atom or
the group.The N–I transition temperatures for S-(4-pentylphen-
yl) 4-decyloxy-2-X-thiobenzoates (X = H, F, or Cl) are also
plotted in the Figure.15 Both compounds show a similar fea-
ture. The features quite resemble that for 4-octyloxy-3-X-bi-
phenyl-4ꢀ-carboxylic acids (X = H, F, Cl, Br, I, CH3, and
NO2).16
cyanato group. Because a 1H NMR examination of the crude
products suggested the presence of two alkyl groups, we as-
sumed that the decomposition of the thiocyanato group and S-
alkylation occurred simultaneously under the conditions.
In this work, therefore, alkylation of the hydroxy group was
achieved by the Mitsunobu reaction,13 and the objective mate-
rials were obtained by mild conditions. For the reaction, the
synthetic yield seems to be almost independent of the electro-
static nature of the substituent.
The thiocyanatobenzene compounds were quantitatively
converted to the corresponding benzenethiols by the reaction
of LiAlH4. We confirmed that this reaction also occurs by
NaBH4. Because the benzenethiols were less stable under an
atmospheric condition, these were reacted with the benzoyl
chloride without further purification.
Thermal Properties. S-Phenyl thiobenzoates having
alkyl and alkoxy groups at both terminal positions are reported
to exhibit nematic (N), smectic A and C phases (Sm A and C,
respectively), and for some members also to exhibit smectic
phases having a higher order of the molecular arrangement.2
Compounds 1d and 1e also show an Sm C phase having a bro-
ken focal conic fan and schlieren textures under homogeneous
and homeotropic alignments, respectively. Most of the materi-
als having a lateral substituent show an N phase exhibiting a
Generally, the reduction of the N–I transition temperature

H. Okamoto et al.
Bull. Chem. Soc. Jpn., 75, No. 1 (2002) 179
Conclusion
A new synthetic pathway of 4-alkoxy-2-X-benzenethiols
was established; the materials incorporating this moiety show
LC properties, and the lateral substituent slightly lowers the
N–I transition temperature. These compounds are expected to
be useful for LC devices.
References
1
(1966).
2
M. S. Newmann and H. A. Karnes, J. Org. Chem., 54, 4100
M. E. Neubert, B. Ziemnicka-Merchant, M. R. Jirousek, S.
J. Laskos, J. D. Leonhardt, and R. B. Sharma, Mol. Cryst. Liq.
Cryst., 154, 209 (1988).
3
M. E. Neubert, R. E. Cline, M. J. Zawaski, and P. J.
Wildman, Mol. Cryst. Liq. Cryst., 76, 43 (1981).
R. M. Reynolds, C. Maze, and E. Oppenheim, Mol. Cryst.
Liq. Cryst., 36, 41 (1976).
4
5
(1976).
6
Y. B. Kim and M. Seno, Mol. Cryst. Liq. Cryst., 36, 293
Fig. 3. Plots of N–I transition temperatures vs molecular
breadth*1 around the substituent estimated by a semi-em-
pirical molecular orbital calculation (see text). (ꢀ) S-(4-
butoxy-2-X-phenyl) 4-octyloxythiobenzoates (X = H, F,
Cl, Br, CH3), (ꢁ) S-(4-octyloxy-2-X-phenyl) 4-octylox-
ythiobenzoates (X = H, F, Cl, Br, CH3), (ꢂ) S-(4-pen-
tylphenyl) 4-decyloxy-2-X-thiobenzoates (X = H, F, Cl).
*1 see text.
M. E. Neubert, R. E. Cline, M. J. Zawaski, P. J. Wildman,
and A. Ekachai, Mol. Cryst. Liq. Cryst., 76, 43 (1981).
M. E. Neubert and I. G. Shennouda, Mol. Cryst. Liq.
Cryst., 205, 29 (1991).
7
8
M. E. Neubert, S. S. Keast, M. C. Ezenyilimba, C. A.
Hanlon, and W. C. Jones, Mol. Cryst. Liq. Cryst., 237, 193 (1993).
9
L. Valerie, I. Noel, J. Glles, and Nguyen Huu Tinh, Liq.
Cryst., 26, 361 (1999).
10 H. Kelker and R. Hatz, “Handbook of Liquid Crystals,”
Verlag Chemie GmbH, Weinhaim p55 (1984).
11 H. Okamoto, V. F. Petrov, and S. Takenaka, Liq. Cryst., 26,
691 (1999).
12 R. G. R. Bacon and R. G. Guy, J. Chem. Soc., 1960, 318.
13 O. Mitsunobu, Synthesis, 1, 1 (1981).
14 D. Demus, H. Demus, and H. Zaschke, “Flüssige Kristalle
in Tabellen,” VEB Deutscher Verlag für Grundstoff Industrie,
Leipzig (1976).
15 M. E. Neubert, S. S. Keast, Y. Dixon-Polverine, F.
Herlinger, M. R. Jirousek, K. Leung, K. Murray, and J. Rambler,
Mol. Cryst. Liq. Cryst., 250, 109 (1994).
16 W. H. de Jeu and J. van der Veen, Mol. Cryst. Liq. Cryst.,
40, 1 (1977).
17 C. Tschierske, J. Mater. Chem., 8, 1485 (1998).
18 G. W. Gray and B. Jones, J. Chem. Soc., 1954, 683.
19 G. W. Gray and B. Jones, J. Chem. Soc., 1955, 236.
has been interpreted in terms of an increased molecular
breadth around the substituent. In the present compounds the
increase in the torsional angle between two phenyl rings due to
a steric hindrance between the substituent and the carbonyl ox-
ygen of the benzoate ring must be taken into consideration.
For the effect of lateral substituents on the mesomorphic
properties, the relative importance of the dipole has also been
pointed out.17 In 6-alkoxy-5-X-naphthalene-2-carboxylic acid
systems, for example, the substituents, such as halogens, are
known to enhance the N–I transition temperature.18,19 For the
phenomena, it has been postulated that the increased dipole
arising from the substituent causes an enhancement of the N–I
transition temperature.17 In the present cases, the change in the
molecular geometry rather than the dipole is responsible for
the reduction of the N–I transition temperature.