Synthesis of fluorosubstituted three ring esters and their dielectric properties

Article abstract of DOI:10.1080/15421400902817361

Laterally substituted by fluorine atoms 4-cyanophenyl 4-(4- pentylbenzoyloxy)-benzoates have been prepared and their phase transition temperatures, enthalpies and dielectric properties upon frequency were evaluated. The novel compounds exhibit a broad range of nematic mesophase, large positive dielectric anisotropy changing sign at low frequency. They are convenient components of LC mixtures for dual frequency addressing devices. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15421400902817361

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Synthesis of Fluorosubstituted
Three Ring Esters and Their
Dielectric Properties
Dorota Ziobro a , Jerzy Dziaduszek a , Marek
Filipowicz a , Roman Dąbrowski a , Joanna Czub b
Stanisław Urban b
&
a Institute of Chemistry , Military University of
Technology , Warsaw, Poland
b Institute of Physics , Jagellonian University ,
Cracow, Poland
Published online: 01 Jun 2009.
To cite this article: Dorota Ziobro , Jerzy Dziaduszek , Marek Filipowicz , Roman
Dąbrowski , Joanna Czub & Stanisław Urban (2009) Synthesis of Fluorosubstituted
Three Ring Esters and Their Dielectric Properties, Molecular Crystals and Liquid
Crystals, 502:1, 258-271, DOI: 10.1080/15421400902817361
To link to this article: http://dx.doi.org/10.1080/15421400902817361
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Mol. Cryst. Liq. Cryst., Vol. 502, pp. 258–271, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400902817361
Synthesis of Fluorosubstituted Three Ring Esters and
Their Dielectric Properties
Dorota Ziobro1, Jerzy Dziaduszek1, Marek Filipowicz1,
Roman Da˛browski1, Joanna Czub2, and Stanisław Urban2
1Institute of Chemistry, Military University of Technology,
Warsaw, Poland
2Institute of Physics, Jagellonian University, Cracow, Poland
Laterally substituted by fluorine atoms 4-cyanophenyl 4-(4-pentylbenzoyloxy)-
benzoates have been prepared and their phase transition temperatures, enthalpies
and dielectric properties upon frequency were evaluated. The novel compounds
exhibit a broad range of nematic mesophase, large positive dielectric anisotropy
changing sign at low frequency. They are convenient components of LC mixtures
for dual frequency addressing devices.
Keywords: cyano and fluorosubstituted ester; dual-frequency addressing; high positive
dielectric anisotropy; liquid crystal; nematic
1. INTRODUCTION
The applicability of liquid crystals (LC) in different electro-optical
devices depend on some important parameters, such as: wide range
of mesophase, low melting point, low viscosity, high clearing point
and sometimes large dielectric anisotropy.
The introduction of a terminal cyano group (-CN) into a molecule
results in positive anisotropy of such compounds. Among them deriva-
tives of 4-cyanophenyl 4-(4-alkylbenzoyloxy)-benzoates have wide
nematic ranges and lower melting points than 4-(4-alkoxybenzoyloxy
benzoates [1–6]. Both families show large positive dielectric anisotropy
at low frequency and it becomes negative at moderate frequency.
Therefore they are interesting as components for dual frequency LC
materials [7–9].
The work was supported by the Polish Ministry of Science and Higher Education,
grant N204 029 31=0512 and no. 765 PBS project.
Address correspondence to Dorota Ziobro, Institute of Chemistry, Military University
of Technology, Warsaw 00-908, Poland. E-mail: dziobro@wat.edu.pl
258

Synthesis of Three Ring Esters and Their Dielectric Properties
259
Liquid crystals with a fluorine atom in the lateral positions of the
molecule are interesting because they generally exhibit better proper-
ties compared with the corresponding non-substituted compounds,
such as lower ability to form smectic phases, lower threshold voltage
and biger dielectric anisotropy (De) [10].
Their dependence of the De upon frequency: at low frequencies De
reaches value ꢀ50, while at high frequencies a moderate negative
dielectric anisotropy appears and crossover (e ¼ e ) is observed at
jj
?
low frequency. In our research we continued the preparation of
nematic liquid crystalline compounds with large positive dielectric
anisotropy (De >> 0) at low frequency and having ability to become die-
lectrically negative (De < 0) at higher frequency. They are useful for
the formulation of LC mixtures for low voltage driven displays as well
as for dual frequency addressing modes. Such systems allow the LC to
be driven parallel to the applied field using a low frequency waveform
in the positive De regime, and perpendicular to it using a higher fre-
quency waveform in the negative De regime [11]. This allow to shorten
the off time for displays and other photonic devices [12–15].
In our previous paper we described the cyanophenyl esters with longer
terminal chain (octyl- and octyloxy-) and fluorine atoms substituted to
benzene rings in lateral position having moderate melting enthalpies,
which were increased with the number of fluorine atoms [6]. In
another paper we described mesomorphic and dielectric properties of
homologous series of 4-cyano-3-fluorophenyl 4-(4-alkylbenzoyloxy)-2-
fluorobenzoates [9], which exhibit a wide range of the nematic phase.
These compounds have dipole moments of polar groups (CN, COO, F)
followed with the same direction what leads to very large dielectric
anisotropy and strong decreasing the resistivity of the compounds.
According to Demus calculation [16] De > 9 involves increasing number
of ions in higher temperature region.
Based on a combination of these factors we were prepared some new
compounds belonging to the three ring esters family with the general
formulas:
where: X1 ¼ F is pending in the opposite direction to the other polar
groups X2, X3, X4 being F or H.

260
D. Ziobro et al.
The presence of fluorine atoms in lateral position of molecules
increases both values of electric permittivity constants (e and e ).
?
jj
Fluorine atom in position X1 gives imput mainly to e value, while
?
X3 and X4 to e value.
jj
2. SYNTHESIS
The routes of synthesis of compounds 1a–e and 2 are presented on
Scheme 1.
SCHEME 1 Synthetic route of compounds of the serii 1 (-CN) and 2 (-F).

Synthesis of Three Ring Esters and Their Dielectric Properties
261
Synthesis details are described in the experimental part. The charac-
teristic feature of the used method is protecting the carboxylic group in
the 4-hydroxybenzoic acid by benzyl group from benzyl isourea, which
more selectively and in mild condition and higher yield forms the ester
bond by direct treating dicyclohexyl carbodiimide [16]. The needed dicy-
clohexyl benzyl isourea is prepared easily in the presence of small
amount of cuprum chloride [17]. The compound may by additively pur-
ificated and also stored long time without decomposition in closed bottle.
The structures of the final products and intermediates were con-
firmed by IR, PMR and GC-MS(EI) (Agilent 6890 N) chromatograph
system with mass detector (Agilent MSD 5973 N) and HPLC-PDA-
MS(API-ESI) (Shimadzu Prominence LC20) chromatograph system
with diode array detector (SPD-M20A) and mass detector (LCMS-
2010EV). In the experimental part only data of mass spectroscopy
are listed, because this method gives more exact information about
structure of the compounds. The route of synthesis leads to the well
defined product without any doubts.
3. PHASE TRANSITIONS
Temperatures and enthalpies of phase transitions were measured by
SETARAM 141 DSC instrument in heating and cooling cycles with
scanning rate 2ꢁC=min. The data of temperatures and enthalpies of
phase transitions of synthesized compounds are given in Table 1.
TABLE 1 Phase Transitions Temperatures (Onset Point, from DSC
Measurment) [ꢁC] (Upper Row) and Enthalpies Transition [kJ=mol] (Lower
Row) of the Compounds of Series 1 and 2
No.
X1
X2
X3
X4
Cr
SmA
N
I
121.0
30.5
240.9
1.0
ꢂ
ꢂ
1a
H
H
H
H
–
125.0[15]
120.3
27.7
270.0[15]
222.4
1.4
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
lb
F
F
F
H
F
H
H
H
F
H
F
F
F
F
H
H
F
–
–
–
105.3
30.2
108.9
29.8
86.4
26.5
196.7
0.8
169.3
0.6
200.9
0.9
134.3
0.5
1c
Id
Ie[9]
2
H
H
–
90.3
29.6
(95.9)#
(0.4)
ꢂ
H
#monotropic phase.

262
D. Ziobro et al.
All compounds exhibit the nematic phase over a wide temperature
range. Compound with cyano group in the terminal ring and having
two fluorine atoms in position X2 and X3 (1e) has lower melting points
than compounds with fluorine atoms in position X1 and X3 (1c, 1d).
Molecules with one (1b) or without fluorine atoms in benzene terminal
rings (1a) have higher melting points than others, but show a nematic
phase over the broader temperature range, because of their high clear-
ing points. The fluorine atom in the position 2 (near carbonyl group) is
more effective for decreasing the melting point than position 3 (near
oxo group). The compound 1e shows also large range of nematic phase,
because of its low melting point. Exchanging the terminal cyano group
(1c) for a fluorine atom (2) causes lowering melting points, but also
narrowering temperature range of the nematic phase. The compound
with fluoro group in the terminal position instead of a cyano group (2)
exhibits also smectic A phase directly after melting, so it is well seen
only during cooling cycle.
4. DIELECTRIC MEASUREMENTS
Dielectric measurements were performed on the HP4192A impedance
analyzer in the frequency range of 10 kHz–30 MHz. The thickness of
the samples was 0.7 mm. In the nematic phase the samples were
oriented by a magnetic field of 0.8 T (the parallel and perpendicular
to capacitor plates). The temperature was stabilized within ꢃ0.2 K.
All measurements were carried out in the cooling runs, which some-
times led to a considerable supercooling of the N phase.
The principal permittivity components, e and e , as well as the
jj
?
relaxation processes taking part in the nematic phase of compounds
were studied for temperatures below 160ꢁC. The dipole structure of
molecules was analyzed. The relaxation times and activation barriers
characterizing the principal molecular motions were determined.
Figure 1 shows the static permittivities e and e for three compounds:
jj
?
1b, 1c, and 2. Also substance 1e was studied. However, in this case the
parallel component reached a very high value (>200), rather typical
for ferroelectric LCs. Because the substance shows a large ionic
conductivity in spite of several re-crystallization procedures, it was
assumed that the enormously large e was caused by the polarization
jj
due to free charges (so called Maxwell-Wagner effect [20]). Therefore,
additional measurements for 1e dissolved in a mixture having a
small negative dielectric anisotropy (Demus’ ester mixture), were per-
formed [21]. In this way it was possible to calculate the permittivity
components of pure 1e substance which appeared to be ꢀ60 at low

Synthesis of Three Ring Esters and Their Dielectric Properties
263
FIGURE 1 Dielectric permittivity tensor components in the nematic phase of
three substances indicated (left) and the corresponding dielectric anisotropy
(right). The shifted temperature scale is used because of very large differences
in the clearing temperatures of particular substances (compare Table 1).
temperatures [21]. Also the substance 1d exhibited very high
permittivity, e > 300, due to high ionic conductivity.
jj
The compounds studied have very high values of the dipole
moment: 7.5 D, 8.5 D, 10.2 D, and 6.8 D for 1b, 1c, 1e, and 2, respec-
tively [18]. According to the formula derived by Maier and Meier [22]
De(T) ꢀ (l2=T) ꢄ S(T), where S(T) is the order parameter (other para-
meters constituting the formula show small temperature dependence
and can be ignored). This relation can be used for discussing the data
corresponding to various substances at the same S(T) value and may
be useful for DT ¼ TNIꢅT up to ꢀ20 K, in which temperature range
the order parameter behaves similarly for different compounds [23].
For the present substances DT is very large and one can note
only that the observed trends are in qualitative agreement with the
prediction of the Maier-Meier formula (Fig. 1, right picture).
All substances exhibit the crossover frequency at which the dielec-
tric anisotropy De ¼ e ꢅe changes the sign from large positive at low
jj
?
frequencies, to negative (ꢅ2 ꢆ ꢅ5) at moderate frequencies. Figure 2
presents examples of the measured dispersion spectra.
In Figure 3 the crossover frequency fco versus temperature and ln fco
versus inverted temperature are presented which shows an activation
character of the dependence.
The extrapolation crossover frequency for compound 1b gives value
below 1 kHz at 40ꢁC.
The relaxation process observed for the parallel component of the
permittivity can nicely be described by the semicircle in the e0(e00) plot
(Cole-Cole plot)–Figure 4. This means that the relaxation process
corresponding to the molecular rotations around the short axes are

264
D. Ziobro et al.
FIGURE 2 Dispersion spectra collected for two orientations of the samples
with respect to the measuring field showing the change of the dielectric
anisotropy.
FIGURE 3 Temperature dependence of the cross-over frequency for 1b
presented in two scales.

Synthesis of Three Ring Esters and Their Dielectric Properties
265
FIGURE 4 Cole-Cole plots from the relaxation spectra in the LC phases of
three substances. For 1c at low frequencies the conductivity gives pronounced
effect.
well described by the Debye equation,
es ꢅ e
1
eꢂðxÞ ꢅ e
¼
ð1Þ
1
1 þ ixs
where es and e are the static and high frequency permittivities,
1
respectively, s is the relaxation time.
FIGURE 5 Activation plots for the nematic phase of three substances.

266
D. Ziobro et al.
The relaxation time s describes the flip-flop molecular motion
jj
around the short axis over the barrier DH ¼ R(@lns =@Tꢅ1), R is gas
jj
jj
constant – Figure 5. The slopes yield the activation barriers:
77.2 kJ=mol, 78.4 kJ=mol, and 81.6 kJ=mol (ꢃ3 kJ=mol) for 1b, 1c,
and 2, respectively, which values are comparable to that determined
by Heppke et al. [7] for substance 1a.
6. EXPERIMENTAL
3-Fluoro-4-Methoxybenzoic Acid
The 500 ml round-bottom flask was charged with magnesium turnings
(6.24 g, 260 mmol) and THF (10 ml). Then 4-bromo-2-fluoroanisole
(33.5 ml, 260 mmol) in THF (250 ml) was added dropwise and the mix-
ture was refluxed for 2 hours. After reactions completion, the mixture
was cooled to ꢅ70ꢁC on dry-ice bath, carbon dioxide was bubbled until
temperature stopped increase and the reaction mixture was allowed to
stand at room temperature overnight. Then the mixture was concen-
trated at low pressure, poured into water (100 ml), acidificated with
10% hydrochloric acid to pH ¼ 0 (ꢀ400 ml) and filtered. The crude
product was crystallized from ethanol-water (4:1, 400 ml). Yield:
32.0 g (72.4%); Mp ¼ 214–217ꢁC (Mp ¼ 208–210ꢁC [24]); GC: 96.5%;
MS: 170, 127, 99, 74, 45, 22.
2-Fluoro-4-Hydroxybenzoic Acid
A mixture of ethyl 2-fluoro-4-hydroxy benzoate (40.0 g, 217 mmol),
potassium hydroxide (50.0 ml, 0.9 mol) in water (0.1 l) and ethanol
(0.5 l) was refluxed for 6 hours. When the reaction was complete
(TLC) the reaction mixture was poured into diluted hydrochloric acid,
stirred and concentrated at low pressure. The crude product crystal-
lized from water (0.4 l). Yield: 31.5 g (90.3%); Mp ¼ 195–197ꢁC
(Mp ¼ 204–205.5ꢁC [25]); GC: 90.3%; MS: 156, 139, 127, 119, 111, 99,
92, 83, 71, 64, 57, 45, 38, 31.
3-Fluoro-4-Hydroxybenzoic Acid
40% hydroiodic acid (94.8 ml, 411 mmol) was added dropwise to acetic
anhydride (216 ml, 2.29 mol), stirred and cooled on water bath. When
the addition was complete 3-fluorometoxybenzoic acid (35.0 g,
206 mmol) was added and the reaction mixture was refluxed for 5
days. Then acetic acid was distilled off and then the solution of sodium
hydrogen sulfate was added until an iodine was reduced. The crude
product was crystallized twice from water (300 ml). Yield: 29.5 g

Synthesis of Three Ring Esters and Their Dielectric Properties
267
(91.9%); Mp ¼ 163–166ꢁC (Mp ¼ 162–163ꢁC [22]); GC: 96.4%; MS: 156,
139, 111, 83, 45, 19.
O-Benzyl N,N0-Dicyclohexylisourea
A mixture of N,N0-dicyclohexylcarbodiimide (25.0 g, 120 mmol), benzyl
alcohol (13.3 ml, 128 mmol), toluene (40 ml) and a bit of copper (I)
chloride was stirred at room temperature for 5 days. When the
reaction was complete (TLC) hexane (250 ml) was added and mixture
was passed through alumina pad. Filtrate was evaporated to dryness.
Yield: 37.0 g (97.1%); (Bp ¼ 130ꢁC=0.0001 Torr [17]).
Benzyl 3-Fluoro-4-Hydroxybenzoate
A mixture of 3-fluoro-4-hydroxybenzoic acid (25.8 g, 165 mmol), O-
benzyl N,N0-dicyclohexylisourea (49.4 g, 157 mmol) and dry THF
(200 ml) was refluxed for 6 hours. The precipitate was filtered off
and the filtrate was concentrated at low pressure. The crude product
was crystallized from ethanol (300 ml) and then from hexane=toluene
(2:1, 300 ml). Yield: 18.4 g (47.8%); Mp ¼ 89–93ꢁC; GC: 98.0%; MS: 246,
224, 201, 168, 139, 116, 91, 65, 39.
Benzyl 2-Fluoro-4-Hydroxybenzoate
Benzyl 2-fluoro-4-hydroxybenzoate was obtained similar as 3-fluoro-4-
hydroxy-benzoate by reaction of 2-fluoro-4-hydroxybenzoic acid with O-
benzyl N,N0-dicyclohexylisourea and dry THF. Yield: 26.8 g (49.1%);
Mp ¼ 139–142ꢁC, GC: 99.6%; MS: 246, 228, 201, 183, 165, 139, 111, 91,
65, 39.
Benzyl 4-(4-pentylbenzoyloxy)-3-Fluorobenzoate
A 250 ml round-bottom flask was charged with benzyl 3-fluoro-4-
hydroxybenzoate (18.3 g, 74 mmol), pyridine (12 ml, 149 mmol) and
dry dichloromethane (150 ml). The 4-pentylbenzoyl chloride (15.1 ml,
74 mmol) was dropped. The reaction mixture was stirred and refluxed
until the reaction was complete (TLC). After cooling to room tempera-
ture the reaction mixture was poured into diluted hydrochloric acid
and stirred until the precipitate of pyridine hydrochloride was dis-
solved. Phases were separated. The water phase was extracted with
dichloromethane (3 ꢇ 100 ml). The combined organic fractions were
washed with diluted hydrochloric acid (3 ꢇ 100 ml) and water (3 ꢇ
100 ml), dried over MgSO4 and concentrated in vacuum. The crude
product was purified by column chromatography (SiO2=CH2Cl2)

268
D. Ziobro et al.
obtaining colorless oil. Yield: 28.4 g (90.7%); GC: 93.7%; MS: 420, 399,
363, 355, 313, 281, 246, 207, 175, 139, 118, 91, 65, 41, 19.
Benzyl 4-(4-pentylbenzoyloxy)-2-Fluorobenzoate
Benzyl 4-(4-pentylbenzoyloxy)-2-fluorobenzoate was obtained similar as
benzyl 4-(4-pentylbenzoyloxy)-3-fluorobenzoate by reaction of benzyl 2-
fluoro-4-hydroxybenzoate and 4-pentylbenzoyl chloride with pyridine
in dry dichloromethane. Yield: 15.4 g (75.2%); GC: 99.4%; MS: 420,
401, 374, 355, 335, 313, 269, 246, 226, 207, 175, 139, 118, 91, 65, 41, 20.
Benzyl 4-(4-pentylbenzoyloxy)-Benzoate
Benzyl 4-(4-pentylbenzoyloxy)-benzoate was obtained similar as
benzyl 4-(4-pentylbenzoyloxy)-3-fluorobenzoate from benzyl 4-hydro-
xybenzoate and 4-pentylbenzoyl chloride with pyridine in dry dichlor-
omethane. Yield: 35.4 g (88.1%).
4-(4-pentylbenzoyloxy)-3-Fluorobenzoic Acid
To the solution of benzyl 4-(4-pentylbenzoyloxy)-3-fluorobenzoate
(28.5 g, 68 mmol) in THF (100 ml) 10% palladium on charcoal (1.5 g)
was added. The reaction mixture was flushed with hydrogen,
connected to gas burette filled with hydrogen and stirring was turn on.
While hydrogen was consumed the temperature was increased. When
reaction was completed (TLC), the reaction mixture was flushed with
nitrogen, catalyst was filtered off and rinsed with THF (20 ml). The fil-
trate was evaporated and the dry residue was crystallized from ethanol
(150 ml) and then from hexane=toluene (1:1, 200 ml).
Yield: 19.3 g (86.2%); Cr 180–185 N 208–213 Iso.
4-(4-pentylbenzoyloxy)-Benzoic Acid
4-(4-pentylbenzoyloxy)-benzoic acid was obtained similar as 4-(4-
pentylbenzoyloxy)-3-fluorobenzoic acid by reaction of benzyl 4-(4-
pentylbenzoyloxy)-benzoate with hydrogen and 10% palladium on
charcoal in THF.
Yield: 27.2 g (99.0%); (Cr 152 N 272 Iso [26]).
4-(4-pentylbenzoyloxy)-2-Fluorobenzoic Acid
4-(4-pentylbenzoyloxy)-2-fluorobenzoic acid was obtained similar as
4-(4-pentylbenzoyloxy)-3-fluorobenzoic acid by reaction of benzyl

Synthesis of Three Ring Esters and Their Dielectric Properties
269
4-(4-pentylbenzoyloxy)-2-fluorobenzoate with hydrogen and 10%
palladium on charcoal in THF.
Yield: 11.8 g (97.5%); Cr 107–109 N 224–225 Iso.
4-Cyano-3-Fluorophenyl 4-(4-pentylbenzoyloxy)
3-Fluorobenzoate (1c)
To the suspension of 4-(4-pentylbenzoyloxy)-3-fluorobenzoic acid
(4.8 g, 14 mmol) in dry dichloroethane (100 ml) oxalyl chloride
(1.5 ml, 17 mmol) and one drop of N,N-dimethylformamide were
added. The reaction mixture was stirred at room temperature until
the evolution of gases stopped. The excess of oxalyl chloride was
distilled off with dichloroethane (80 ml). After cooling to room
temperature, pyridine (3.5 ml, 44 mmol), 4-cyano-3-fluorophenol
(2.0 g, 14.5 mmol) and dichloromethane (80 ml) were added and
the mixture was refluxed for 6 hours. Then reaction mixture was
cooled to room temperature and poured into diluted hydrochloric
acid (100 ml). Phases were separated. The water phase was
extracted with dichloromethane (2 ꢇ 100 ml). The combined organic
fractions were washed with diluted hydrochloric acid (3 ꢇ 100 ml),
water (3 ꢇ 100 ml) and brine (100 ml), dried over MgSO4 and
concentrated at low pressure. The crude product was purified by
column chromatography (SiO2=CH2Cl2) and crystallized from
ethanol=acetone (3:1, 100 ml). Yield: 5.6 g (85.5%); HPLC: 99.1%;
MS: 448 [M-H]ꢅ, 387, 359, 329, 274, 207, 152, 136, 91.
4-Cyanophenyl 4-(4-pentylbenzoyloxy)-Benzoate (1a)
4-cyanophenyl 4-(4-pentylbenzoyloxy)-benzoate was obtained similar
as 4-cyano-3-fluorophenyl 4-(4-pentylbenzoyloxy) 3-fluorobenzoate.
Yield: 25.3 g (70.0%); HPLC: 99.1%; MS: 412 [M-H]ꢅ, 357, 319, 283,
235, 163, 118, 62.
4-Cyanophenyl 4-(4-pentylbenzoyloxy)-3-Fluorobenzoate (1b)
4-cyanophenyl 4-(4-pentylbenzoyloxy)-3-fluorobenzoate was obtained
similar as 4-cyano-3-fluorophenyl 4-(4-pentylbenzoyloxy)-3-fluoro-
benzoate.
Yield: 4.9 g (78.2%); HPLC: 99.6%; MS: 430 [M-H]ꢅ, 355, 329, 256,
235, 191, 118, 90.

270
D. Ziobro et al.
4-Cyano-3,5-Difluorophenyl 4-(4-pentylbenzoyloxy)-
3-Fluorobenzoate (1d)
4-cyano-3,5-difluorophenyl
4-(4-pentylbenzoyloxy)-3-fluorobenzoate
was obtained similar as 4-cyano-3-fluorophenyl 4-(4-pentylbenzoy-
loxy)-3-fluorobenzoate.
Yield: 5.4 g (84.8%); HPLC: 99.9%; MS: 466 [M-H]ꢅ, 417, 388, 292,
289, 221, 154, 142, 91.
4-Cyano-3-Fluorophenyl 4-(4-pentylbenzoyloxy)-
2-Fluorobenzoate (1e)
4-cyano-3-fluorophenyl 4-(4-pentylbenzoyloxy)-2-fluorobenzoate was
obtained similar as 4-cyano-3-fluorophenyl 4-(4-pentylbenzoyloxy)-3-
fluorobenzoate.
Yield: 11.7 g (94.0%); HPLC: 97.5%; MS: 472 [M-H]ꢅ, 399, 345, 293,
271, 207, 175, 113, 55.
3,4-Difluorophenyl 4-(4-pentylbenzoyloxy)-
3-Fluorobenzoate (2)
3,4-difluorophenyl 4-(4-pentylbenzoyloxy)-3-fluorobenzoate was
obtained similar as 4-cyano-3-fluorophenyl 4-(4-pentylbenzoyloxy)-
3-fluorobenzoate.
Yield: 5.3 g (82.4%); HPLC: 99.1%; MS: 441 [M-H]ꢅ, 395, 377, 329,
267, 191, 129, 91.
7. CONCLUSIONS
Laterally fluorosubstituted cyanophenyl 4-(4-pentylbenzoyloxy)
benzoates have stronger dependence of parallel electric permittivity
constant e upon frequency than analogous fluorophenyl diester. The
jj
fluorosubstitued central ring in the position 2 leads to the compounds
with the lower melting point and broader range of nematic phase than
the substitution in the position 3, but both structures are good dopant
to formulate mixtures with dual frequency addressing systems.
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