Synthesis and mesomorphic characteristics of fluoroaniline derivatives with different lateral groups

Article abstract of DOI:10.1080/10426507.2012.669678

Two new homologous series of liquid crystals viz. 4-(4'-n-alkoxybenzoyloxy) -2-chlorophenylazo-4-fluorobenzenes(I) and 4-(4'-n-alkoxybenzoyloxy)-2- methylphenyl azo-4-fluorobenzenes(II) with terminal fluoro, lateral chloro(I) and methyl(II) group and central ester and azo linkages are synthesized and their mesomorphic properties are studied. Both the series are similar in molecular structure with the difference in their lateral substitutions; series I has chloro group and series II has methyl group as laterally substituted groups. All the twelve homologues of each of the series are mesogenic in nature. Series I shows nematic mesophase from the first _C1 to the last _C16 derivative synthesized; smectic mesophase is exhibited by last two viz. _C14 and _C16 derivative, where as all the members from _C1 to _C16 of series II only show nematic mesophase. The nematic mesophase shows marble texture and the smectic mesophase shows Schlirene texture of the Smectic C variety. Both the series are compared with structurally related series. Taylor and Francis Group, LLC.

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Synthesis and Mesomorphic
Characteristics of Fluoroaniline
Derivatives with Different Lateral Groups
Jayrang S. Dave a , Purvang D. Patel a & Himanshu Bhatt a
a Department of Applied Chemistry, Faculty of Technology and
Engineering , The M.S. University of Baroda , Vadodara , India
Published online: 30 Jul 2012.
To cite this article: Jayrang S. Dave , Purvang D. Patel & Himanshu Bhatt (2012) Synthesis and
Mesomorphic Characteristics of Fluoroaniline Derivatives with Different Lateral Groups, Molecular
Crystals and Liquid Crystals, 562:1, 76-84, DOI: 10.1080/10426507.2012.669678
To link to this article: http://dx.doi.org/10.1080/10426507.2012.669678
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Mol. Cryst. Liq. Cryst., Vol. 562: pp. 76–84, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/10426507.2012.669678
Synthesis and Mesomorphic Characteristics
of Fluoroaniline Derivatives with Different
Lateral Groups
JAYRANG S. DAVE, PURVANG D. PATEL,∗
AND HIMANSHU BHATT
Department of Applied Chemistry, Faculty of Technology and Engineering,
The M.S. University of Baroda, Vadodara, India
Two new homologous series of liquid crystals viz. 4-(4’-n-alkoxybenzoyloxy)-2-
chlorophenylazo-4”-fluorobenzenes(I) and 4-(4’-n-alkoxybenzoyloxy)-2-methylphenyl
azo-4”-fluorobenzenes(II) with terminal fluoro, lateral chloro(I) and methyl(II) group
and central ester and azo linkages are synthesized and their mesomorphic properties
are studied. Both the series are similar in molecular structure with the difference in their
lateral substitutions; series I has chloro group and series II has methyl group as laterally
substituted groups. All the twelve homologues of each of the series are mesogenic in
nature. Series I shows nematic mesophase from the first C1 to the last C16 derivative
synthesized; smectic mesophase is exhibited by last two viz. C14 and C16 derivative,
where as all the members from C1 to C16 of series II only show nematic mesophase. The
nematic mesophase shows marble texture and the smectic mesophase shows Schlirene
texture of the Smectic C variety. Both the series are compared with structurally related
series.
Keywords Azo and ester central linkage; chloro and methyl lateral groups; homologues
series; mesophase thermal stability; smectic C and nematic mesophase
Introduction
A number of homologous series with ester and azo central linkages have been synthesized
having different terminal and lateral groups [1–8]. Lateral substituent in central ring system
effects mesomorphic properties and play a vital role in imparting liquid crystallinity to a
potentially mesogenic compound. Central phenyl ring having lateral substitution makes
molecules broad; which play an effective role in mesogenic property of a mesogenic
compound. Studies on the effect of lateral substitution have been comparatively less ex-
plored than terminal substitution. A survey of the literature indicates that generally the
mesophase range of the mesogens having lateral substituent is less than laterally unsubsti-
tuted mesogens [9–15]. In order to establish the co-relation between chemical constitution
and mesomorphism, two new homologous series with ester and azo central linkages, fluoro
∗Address correspondence to Purvang D. Patel, Department of Applied Chemistry, Faculty of
Technology and Engineering, The M.S. University of Baroda, Vadodara, India. Tel.: +919825355636.
E-mail: pdzpatel1983@yahoo.com
76

Synthesis of Fluoroaniline Derivatives
77
terminal group and lateral chloro (Series I) and lateral methyl (Series II) groups on central
ring are synthesized and their mesomorphic properties are studied.
Experimental
4-Hydroxy benzoic acid, the appropriate n-alkyl halides, p-fluoro aniline, m-chloro phenol,
and m-cresol are of Merck grade and used as received. Solvents are dried and distilled prior
to use. Microanalyses of some of the representative compounds are performed on Perkin
Elmer Series II 2400-CHN analyzer; IR spectra are recorded on a Perkin Elmer GX-FTIR,
NMR spectra are measured on a Bruker Avance II-500 spectrometer. Liquid crystalline
properties are investigated on Leitz Laborlux 12 POL polarizing microscope provided with
a Kofler heating stage. DSC are performed on a Mettler Toledo Star SW 7.01.
1. 4-n-Alkoxy benzoic acids and 4-n-alkoxy benzoyl chlorides are synthesized by
known methods [16].
2. 2-Chloro-4-hydroxyphenylazo-4ꢀ-fluorobenzene, 2-methyl-4-hydroxyphenylazo-
4ꢀ-fluoro benzene are prepared by known method [17].
3. The series, namely 4-(4ꢀ-n-alkoxybenzoyloxy)-2-chlorophenylazo-4ꢀꢀ-fluoro-
benzenes, and 4-(4ꢀ-n-alkoxybenzoyloxy)-2-methylphenylazo-4ꢀꢀ-fluoro benzenes
are synthesized by adding dropwise a cold solution of 2-chloro-4-hydro-
xyphenylazo-4ꢀ-fluoro benzene (for series I), 2-methyl-4-hydroxyphenylazo-4ꢀ-
fluoro benzene (for series II), respectively, in dry pyridine to a cold solution of
4-n-alkoxy benzoyl chloride. The mixture is allowed to stand overnight at room
temperature. It is acidified with 1:1 cold HCl and the separated solid is filtered
and recrystallized from ethanol until constant transition temperatures are obtained.
The elemental analysis of some of the representative compounds are found to be
satisfactory. The synthetic route of the series is shown in Scheme 1.
Scheme 1. Synthetic route for series I and II.
FTIR (Nujol, KBr pellets, cm−1) :
Series I: 4-(4ꢀ-n-pentyloxybenzoyloxy)2-chlorophenylazo-4ꢀꢀ-fluorobenzenes:
2930, 1740 (–COO–), 1610(–N=N–), 1516, 1360, 1250, 890, 755, 692.

78
J. S. Dave et al.
Series I: 4-(4ꢀ-n-decyloxybenzoyloxy)2-chlorophenylazo-4ꢀꢀ-fluorobenzenes:
2944, 1731 (–COO–), 1606(–N=N–), 1504, 1319, 1264, 1041, 850, 755, 689.
1H NMR : (CDCl3, 500 MHz, δ, ppm, standard TMS)
Series I: 4-(4ꢀ-n-pentyloxybenzoyloxy)2-chlorophenylazo-4ꢀꢀ-fluorobenzenes :
δ 0.98 (3H, t, –CH3), 1.45–1.82 (m, alkyl chain),
4.06 (2H, t, –OCH2–CH2), 6.95 (1H, S, H4), 7.0 (2H, d, H5),
7.38 (2H, d, H2), 7.9 (2H, d, H1), 7.95 (2H, d, H6), 8.15 (2H, d, H3)
Series I: 4-(4ꢀ-n-decyloxybenzoyloxy)2-chlorophenylazo-4ꢀꢀ-fluorobenzenes:
δ 0.9 (3H, t, –CH3), 1.4–1.79 (m, alkyl chain),
4.05 (2H, t, -OCH2-CH2), 6.98 (1H, S, H4), 7.0 (2H, d, H5),
7.48 (2H, d, H2), 7.9 (2H, d, H1), 8.0 (2H, d, H6), 8.1 (2H, d, H3)
FTIR (Nujol, KBr pellets, cm−1):
Series II: 4-(4ꢀ-n-butyloxybenzoyloxy)2-methylphenylazo-4ꢀꢀ-fluorobenzenes:
2946, 1735 (–COO–), 1603(–N=N–), 1490, 1317, 1260, 842, 724, 689.
Series II: 4-(4ꢀ-n-heptyloxybenzoyloxy)2-methylphenylazo-4ꢀꢀ-fluorobenzenes:
2946, 1731 (–COO–), 1606(–N=N–), 1530, 1353, 1264, 890, 728, 681.
1H NMR: (CDCl3, 500 MHz, δ, ppm, standard TMS)
Series II: 4-(4ꢀ-n-butyloxybenzoyloxy)2-methylphenylazo-4ꢀꢀ-fluorobenzenes:
δ 0.9 (3H, t, –CH3), 1.5–1.8 (m, alkyl chain), 2.33 (3H, S, Ar-CH3)
4.0 (2H, t, –OCH2–CH2), 6.98 (2H, d, H4), 7.0 (2H, d, H5),
7.30 (2H, d, H2), 7.9 (2H, d, H6), 8.1 (2H, d, H1), 8.2 (2H, d, H3)
Series II: 4-(4ꢀ-n-heptyloxybenzoyloxy)2-methylphenylazo-4ꢀꢀ-fluorobenzenes:
δ 0.96 (3H, t, –CH3), 1.40–1.85 (m, alkyl chain), 2.30 (3H, S, Ar–CH3)
4.0 (2H, t, –OCH2–CH2), 6.98 (1H, S, H4), 7.1 (2H, d, H5),
7.26 (2H, d, H2), 7.93 (2H, d, H1), 7.95 (2H, d, H6), 8.1 (2H, d, H3)
Results and Discussion
In the present study, 12 homologues from each of the two homologues series viz. 4-(4ꢀ-
n-alkoxy benzoyloxy)-2-chlorophenylazo-4ꢀꢀ-fluorobenzenes (series I) and 4-(4ꢀ-n-alkoxy
benzoyloxy)-2-methy lphenylazo-4ꢀꢀ-fluorobenzenes (series II) are synthesized and their
mesomorphic properties are studied.
The general molecular structure of the series is;
All the twelve homologues of the series I are mesogens (Table 1); the nematic phase
commences from the very first derivative and remains up to the last hexadecyl derivative
synthesized while Smectic C phase commences from the tetradecyl derivative and remains
to be exhibited upto the last hexadecyl derivative synthesized. Figure 1, i.e., the plot of
transition temperatures against number of carbon atoms in alkoxy chain indicates that N–I
curve shows overall falling tendency and merges as the series is ascended; no odd–even
effect is observed in N–I curves. The Cr–M transitions show overall falling tendency with
a rising jump at decyl derivative. The nematic phase of the series shows marble texture and
the smectic phase shows schlieren texture of smectic C variety.

Synthesis of Fluoroaniline Derivatives
79
Table 1. Transition temperature ◦C of the series I. Series I: 4-(4ꢀ-n-alkoxybenzoyloxy)-2-
chlorophenylazo-4ꢀꢀ-fluorobenzenes
Transition temperatures (◦C)
R = n-alkyl group
Smectic C
Nematic
Isotropic
Methyl
Ethyl
Propyl
Butyl
Pentyl
Hexyl
Heptyl
Octyl
Decyl
Dodecyl
Tetradecyl
Hexadecyl
—
—
—
—
—
—
—
—
—
—
70
68
114
104
102
90
78
71
65
62
85
79
182
170
163
158
160
157
149
144
138
129
114
111
86
92
Figure 1. 4-(4ꢀ-n-alkoxybenzoyloxy)-2-chloro phenylazo-4ꢀꢀ-fluorobenzenes (series I).

80
J. S. Dave et al.
Table 2. Transition temperature ◦C of the series II. Series II: 4-(4ꢀ-n-alkoxybenzoyloxy)-
2-methylphenylazo-4ꢀꢀ-fluorobenzenes
Transition temperatures ◦C
R = n-alkyl group
Smectic
Nematic
Isotropic
Methyl
Ethyl
Propyl
Butyl
Pentyl
Hexyl
Heptyl
Octyl
Decyl
Dodecyl
Tetradecyl
Hexadecyl
—
—
—
—
—
—
—
—
—
—
—
—
120
122
110
92
84
78
63
67
61
72
165
158
138
140
135
131
129
128
122
117
112
98
76
68
All the 12 homologues of the series II are mesogens (Table 2); the nematic phase
commences from the very first derivative and remains upto the last hexadecyl derivative
synthesised. Figure 2, i.e., the plot of transition temperatures against number of carbon
atoms in alkoxy chain indicates that N–I curve shows overall falling tendency as the series
is ascended. Here also no odd–even effect is observed in N–I curve. The Cr–M transitions
Figure 2. 4-(4ꢀ-n-alkoxybenzoyloxy)-2-methyl phenylazo-4ꢀꢀ-fluorobenzenes (Series II).

Synthesis of Fluoroaniline Derivatives
81
Table 3. Average thermal stability ◦C
Commencement of
smectic mesophase
Series
Nematic
Smectic
I
147.19 (C1 to C16)
131.08 (C1 to C16)
189.70 (C1 to C10)
143.80 (C1 to C12)
117.09 (C1 to C14)
89.00 (C12 to C16)
–
116.80 (C8 to C16)
103.66 (C12 to C16)
88.00 (C14 to C10)
C14
–
C8
C12
C14
II
A
B
C
show overall falling tendency from methyl to hexadecyl derivative with slight rise at ethyl,
octyl, and tetradecyl derivative. Here also nematic phase of the series shows marble texture
and the smectic phase shows schlieren texture of smectic C variety.
The average thermal stabilities of series I and II are compared with structurally related
other homologous series; table 3 gives the average thermal stabilities and figure 3 gives the
molecular structures of the series in comparison. The average nematic mesophase thermal
stability of series I is 147.91◦C and series (II) is 131.08◦C similarly the average smectic
mesophase thermal stability of the series (I) is 89.0◦C; where as Series II shows only
nematic mesophase. Comparison of average mesophase thermal stability of both the series
(Table 3) shows that the nematic mesophase thermal stability of series II is lower than
that of series I. Here, the nature of lateral substituents has important implications on phase
transition temperatures and average mesophase thermal stability; series I has lateral chloro
group where as series II has lateral methyl group. Gray has also reported a system where
in lateral methyl substituent has lower thermal stability than lateral chloro substituent [18].
Comparison of series I and II with structurally related homologous series shows that all
the series in comparison are structurally more or less similar, consisting of three aromatic
cores, azo and ester central linkages. The difference between molecules of series I, II,
and A [19] is only the lateral substitution; series I has chloro group, series II has methyl
group as lateral substituent, while series A is laterally unsubstituted. The effect of the
lateral group in the central benzene ring causes disruption in the molecular packing, which
reduces the transition temperatures and melting points as well as the mesophase thermal
Figure 3. Selected homologous series for comparison.

82
J. S. Dave et al.
Table 4. Elemental analysis
Calculated
Found
H%
Series
Homologue
C%
H%
N%
C%
N%
I
I
II
II
C5
C10
C4
69.81
72.12
70.93
72.32
5.33
6.63
5.66
6.47
6.78
5.80
6.89
6.25
70.53
73.88
71.57
73.00
5.86
6.70
5.91
6.81
6.11
5.27
7.05
6.56
C7
Figure 4. Photomicrographs of the texures of representative derivatives.
Figure 5. DSC curves.

Synthesis of Fluoroaniline Derivatives
83
Table 5. DSC data
Heating
Transition
ꢀ H/
ꢀ S/
Series Member rate/◦C min−1 temperature◦C
Jg−1
J g−1 K−1
I
I
Decyl
5
5
Cr–N 87
N–I 138
Cr–Sm 70
Sm–N 86
N–I 114
Cr–N 92
N–I 140
Cr–N 72
N–I 117
48.00
1.038
80.85
2.26
0.483
41.29
0.62
0.1330
0.0025
0.2343
0.0063
0.0012
0.1133
0.0015
0.2323
0.0020
Tetradecyl
II
II
Butyl
5
5
Dodecyl
80.08
0.79
stability compared to the laterally unsubstituted analogues. Thus, introduction of chloro
group (Series I) and methyl group (Series II) in the ortho position of the azo linkage
effectively reduce both the clearing and melting points compared to those of the parent
compound (Series A). It is seen that the breadth of the molecules of the series I and II are
increased due to the presence of lateral group on the central benzene ring which decreases
both smectic and nematic thermal stabilities [20].
Series I and series B [19] has lateral chloro group on ortho position and meta position
to the azo central linkage respectively. The average nematic mesophase thermal stability of
series I is 147.91◦C and that of series B is 143.8◦C which is not marked different in series
I. However, the average smectic mesophase thermal stability of series I is 89.0◦C while that
of series B is 103.66◦C. Thus, the average smectic mesophase thermal stability of series I
is less than series B, which can be due to the difference in position of lateral chloro group.
Series I is having chloro group in the ortho position to the azo linkage whereas series B is
having chloro group in the ortho position to the ester linkage.
Similarly, Series II and series C [19] has lateral methyl group on ortho position and
meta position to the azo central linkage respectively. The average nematic mesophase
thermal stability of series II is 131.08◦C and that of series C is 117.09◦C. Thus, the average
nematic mesophase thermal stability of series II is higher than series C, which can be due
to the difference in position of lateral methyl group. Series II is having methyl group in
the ortho position to the azo linkage whereas series C is having methyl group in the ortho
position to the ester linkage.
Figure 4 shows the photomicrographs of some of the representative compounds. The
enthalpies of decyl and tetradecyl derivative of series I and butyl and dodecyl derivative of
series II are measured by DSC. The DSC data are recorded in Table 5. Figure 5 shows the
DSC curves.
Conclusion
Two new homologous series with lateral chloro(I) and lateral methyl(II) groups are syn-
thesized. The positional effect of –Cl and –CH3 lateral substituent on phase behaviour,
phase transition temperatures with respect to azo central linkage are studied. These lateral
substituents depress both melting point and clearing points of the liquid crystals. Mesogens

84
J. S. Dave et al.
with lateral substitution have reduced smectic and nematic mesophase thermal stability
than the corresponding unsubstituted homologues.
Acknowledgment
The authors thank the Head of Applied Chemistry Department, Faculty of Technology and
Engineering, The M.S. University of Baroda, Vadodara for providing research facilities.
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