Synthesis and Mesomorphic Properties of a Novel Ester Homologous Series: 4-(4'- n -Alkoxy Benzoyloxy) Benzyl Cinnamates

Article abstract of DOI:10.1080/15421406.2014.915627

A novel homologous series 4-(4'-n-alkoxy benzoyloxy) benzyl cinnamates was synthesized and studied with a view to understanding and establishing the relationships between mesomorphism and molecular structure. The novel series consists of eleven members with the commencement of mesomorphism from the pentyloxy homologue onwards to the hexadecyl homologue. The remaining homologues are nonmesomorphic. All the mesomorphic homologues exhibit smectogenic mesomorphism in addition to nematogenic mesomorphism for a definite temperature range in an enantiotropic manner, except for the pentyloxy homologue, which exhibits only a nematogenic mesophase in an enantiotropic manner without the formation of a smectic phase. The texture of the nematic mesophase is of the threaded or Schlieren type and the smectic mesophase is of the type A or C texture, as determined by a miscibility method. Transition temperatures were observed through an optical polarizing microscope equipped with a heating stage. The transition curves of a phase diagram predominantly behave in a normal manner, but partly deviated from normal behavior with the exhibition of an odd-even effect. Analytical and spectral data confirms the molecular structures of all homologues. The mesomorphic behavior of the present series is compared with other structurally similar known series. The mesomorphic temperatures vary between 106°C and 180°C. The mesophase length varies between 33°C to 53°C. Thus, the novel series is predominantly nematogenic and partly smectogenic with relatively high transition temperatures and is of a high melting type. The average thermal stabilities for smectic and nematic phases are 144.1°C and 171.4°C, respectively.

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Synthesis and Mesomorphic Properties of
a Novel Ester Homologous Series: 4-(4′-
n-Alkoxy Benzoyloxy) Benzyl Cinnamates
H. Brijesh Patela & A. V. Doshib
a Huntsman, Baroda Textile Effects Pvt. Ltd, Umraya village, Taluka
Padra, Vadodara, Gujarat, India
b Dr. K. N. Modi University, Newai, Dist. Tonk, Rajasthan, India
Published online: 15 Jan 2015.
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To cite this article: H. Brijesh Patel & A. V. Doshi (2015) Synthesis and Mesomorphic Properties of a
Novel Ester Homologous Series: 4-(4′-n-Alkoxy Benzoyloxy) Benzyl Cinnamates, Molecular Crystals and
Liquid Crystals, 606:1, 56-65, DOI: 10.1080/15421406.2014.915627
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Mol. Cryst. Liq. Cryst., Vol. 606: pp. 56–65, 2015
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2014.915627
Synthesis and Mesomorphic Properties of a Novel
Ester Homologous Series: 4-(4ꢀ-n-Alkoxy
Benzoyloxy) Benzyl Cinnamates
H. BRIJESH PATEL1 AND A. V. DOSHI2,∗
1Huntsman, Baroda Textile Effects Pvt. Ltd, Umraya village, Taluka Padra,
Vadodara, Gujarat, India
2Dr. K. N. Modi University, Newai, Dist. Tonk, Rajasthan, India
A novel homologous series 4-(4ꢀ-n-alkoxy benzoyloxy) benzyl cinnamates was syn-
thesized and studied with a view to understanding and establishing the relationships
between mesomorphism and molecular structure. The novel series consists of eleven
members with the commencement of mesomorphism from the pentyloxy homologue on-
wards to the hexadecyl homologue. The remaining homologues are nonmesomorphic.
All the mesomorphic homologues exhibit smectogenic mesomorphism in addition to ne-
matogenic mesomorphism for a definite temperature range in an enantiotropic manner,
except for the pentyloxy homologue, which exhibits only a nematogenic mesophase in
an enantiotropic manner without the formation of a smectic phase. The texture of the
nematic mesophase is of the threaded or Schlieren type and the smectic mesophase is of
the type A or C texture, as determined by a miscibility method. Transition temperatures
were observed through an optical polarizing microscope equipped with a heating stage.
The transition curves of a phase diagram predominantly behave in a normal manner,
but partly deviated from normal behavior with the exhibition of an odd–even effect.
Analytical and spectral data confirms the molecular structures of all homologues. The
mesomorphic behavior of the present series is compared with other structurally similar
known series. The mesomorphic temperatures vary between 106◦C and 180◦C. The
mesophase length varies between 33◦C to 53◦C. Thus, the novel series is predominantly
nematogenic and partly smectogenic with relatively high transition temperatures and is
of a high melting type. The average thermal stabilities for smectic and nematic phases
are 144.1◦C and 171.4◦C, respectively.
Keywords Enantiotropy; liquid crystals; mesomorphism; nematic; smectic
Introduction
The phenomenon of mesomorphism is not exhibited by all substances, but some substances,
whose molecular structure generates favorable magnitudes of molecular rigidity and flex-
ibility [1–3] to enable and maintain their molecular arrangement in a two-dimensional
array in a floating condition, either in a layered manner by lamellar molecular packing
in their crystal lattices or through a statistically parallel orientational order of molecules,
can exhibit mesomorphic behavior. Cinnamic acids with an n-alkoxy terminal group and
∗Address correspondence to A. V. Doshi, Dr. K. N. Modi University, Plot No. INS-1, RIICo
Industrial Area Ph-II, Newai, Dist, Tonk, Rajasthan 304 021, India. Tel: 9898345428. E-mail:
research@dknmu.org
56

Properties of a Novel Ester Homologous Series
57
their ester derivatives [4,5] acquire suitable magnitudes of anisotropic forces of inter-
molecular attractions [6,7], as a consequence of favorable molecular rigidity and flexibility
they can exhibit mesomorphism. Thus, the proposed investigation is planned to synthe-
size novel ester derivatives consisting of three phenyl rings bridged through COO and
CH CH COO CH2− central groups with a left n-alkoxy (–OR) terminal end group
without any lateral or right terminal end group [8]. Hence, linear, lath-like molecules have
sufficient end to end lateral intermolecular attractions to cause or to induce mesomorphism
depending upon the molecular structure.
Experimental
Synthesis
4-Hydroxy benzoic acid was alkylated with appropriate alkylating agents (R–X) to prepare
4-n-alkoxy benzoic acids (A) by the modified method of Dave and Vora [9]. Component (B)
viz. 4-hydroxy benzyl cinnamate was prepared by a usual established method [10,11] (m.p
150◦C, yield 80%). Components A were converted to their acid chlorides using dry thionyl
chloride. The acid chlorides were then condensed with a component B in dry cold pyridine
[12,13] to prepare final ester derivatives of the novel homologous series. Final products
were individually decomposed, filtered, washed, dried, and purified by EtOH until constant
transition temperatures were obtained. The synthetic route to the novel homologous series
is shown in scheme-1. 4-Hydroxy benzoic acid, 4-hydroxy cinnamic acid, benzyl alcohol,
alkyl halides, MeOH, EtOH, KOH, toluene, sulfuric acid, thionyl chloride, and pyridine
required for synthesis were used as received, except solvents, which were dried and purified
prior to use.
Characterization
Some selected members of the present novel series were characterized by elemental anal-
1
ysis, infra red spectra, HNMR spectra, and mass spectra. Microanalysis was performed
1
using a Perkin-Elmer PE 2400 CHN analyzer, HNMR spectra were recorded on Bruker
spectrometer using DMSO solvent. Infrared spectra were recorded on a Perkin-Elmer spec-
trum GX spectrometer. Transition temperatures and the textures of the smectic and nematic
mesophases as determined by a miscibility method were characterized by an optical polar-
izing microscope equipped with a heating stage. Thermodynamic quantity enthalpy change
(ꢀH) and entropy change (ꢀS = ꢀ ꢀH/T) are qualitatively discussed.
Analytical Data (Table 1)
Spectral Data
1HNMR in ppm for the decyloxy derivative: 1.23 (Long alkyl chain),
1.71 ( CH2 CH2
O
of C10H21), 3.31 ( OCH2 of
OC10H21 group), 3.9
( COO CH2 C6H5), 6.3 and 6.83 (p-substituted phenyl ring), 7.85 (mono-substituted
phenyl ring), 4.00 (trans CH CH group).
1HNMR in ppm for the dodecyloxy derivative: 1.34 (Long alkyl chain),
1.72 ( CH2 CH2
O
of C14H29), 3.3 ( OCH2 of
OC12H25 group), 3.92

58
H. B. Patel and A. V. Doshi
Scheme 1. Synthetic route to the series.
( COO CH2 C6H5), 6.3 and 6.9 (p-substituted phenyl ring), 7.8 (mono-substituted
phenyl ring), 4.1 (trans CH CH group).
IR in cm−1 for the hexyloxy derivative: 696 and 733 (mono-substituted phenyl ring),
891 (p-substituted phenyl ring), 1200 (ether linkage of C6H13O C6H4), 1168, 1256,
1605 ( COO ester group), 934 (trans CH CH group).
IR in cm−1 for the tetradecyloxy derivative: 695 and 732 (mono-substituted phenyl
ring), 889 (p-substituted phenyl ring), 1198 (ether linkage of C14H29O C6H4), 1169,
1258, 1606 ( COO ester group), 939 (trans CH CH group).
Mass Spectra
Mass spectra for the butoxy derivative: Molecular formula C27H26O5; Calculated Molecular
weight 430. Practical mass observed by Mass spectroscopy 430.
Texture of Nematic and Smectic Phase by Miscibility Method
Pentyloxy derivative → Threaded nematic
Hexadecyloxy derivative → Schlieren nematic and smectic C
Octyloxy derivative → Threaded nematic and smectic A

Properties of a Novel Ester Homologous Series
59
Figure 1. Phase behavior of series.
Results and Discussion
4-Hydroxy-benzyl cinnamate is nonmesomorphic, but on condensing with 4-n-alkxoy ben-
zoic acids through their corresponding acid chlorides mesomorphic homologues are gen-
erated. The novel homologous series contains eleven members. The methyl to butyl ho-
mologues of the series are nonmesomorphic, while the pentyl to hexadecyl derivatives are
mesomorphic. All the mesomorphic homologues, except for the pentyloxy homologue ex-
hibit smectogenic and subsequently nematogenic character in enantiotropic manner, while
only the pentyloxy homologue exhibits nematogenic character without the formation of a
smectogenic mesophase. A phase diagram (Fig. 1) of the series is plotted for the transi-
tion temperatures (Table 2) as determined by an optical polarizing microscope equipped

60
H. B. Patel and A. V. Doshi
Table 1. Elemental analysis for methoxy, ethoxy, and propoxy derivatives
Elements % found (% calculated)
Sr. No.
Molecular formula
C
H
1
2
3
C24H20O5
C25H22O5
C26H24O5
74.35 (74.22)
74.51 (74.62)
74.98 (75.00)
5.26 (5.15)
5.31 (5.47)
5.79 (5.76)
with a heating stage, against the number of carbon atoms present in n-alkoxy chain of
the n-alkoxy terminal end group. Smooth curves are drawn by linking like or related
points for the solid–mesomorphic, solid–smectic, smectic–nematic, nematic–isotropic,
or solid–isotropic transition points. Thus, the phase diagram consists of three transition
curves viz. solid–mesomorphic or isotropic, smectic–nematic and nematic–isotropic. The
solid–isotropic or mesomorphic transition curve follows a zigzag path of rising and falling
values in the usual established manner. The smectic–nematic and nematic–isotropic transi-
tion curves adopt a partly descending tendency in a normal manner, but they deviate from
normal behavior for very few members of the series. The nematic–isotropic transition curve
exhibits an odd–even effect, while the smectic–nematic transition curve does not show an
odd–even effect because the smectic mesophase is exhibited by the even numbered homo-
logue derivatives. The nematic–isotropic transition curves for the odd and even members
were extrapolated [14,15] to determine latent ability of propoxy and butoxy homologues
to show mesomorphic behavior and to magnify odd–even effect for the nematic transition
curve. The odd–even effect disappears from and beyond the octyloxy homologue. Analyt-
ical and spectral data of homologues matches with their molecular structures. The smectic
mesophase length varies between 10◦C to 37◦C and nematic mesophase length varies be-
tween 12◦C to 45◦C. The average thermal stabilities for the smectic and nematic phases are
144.1◦C and 171.4◦C, respectively. The mesomorphic properties of the homologues vary
Table 2. Transition temperatures of series in ◦C
Transition temperature in ◦C
Compound no.
n-alkyl group ( CnH2n+1) (n)
Sm
Nm
Isotropic
1
2
3
4
5
6
7
8
1
2
3
4
5
6
8
10
—
—
—
—
—
140.0
119.0
106.0
109.0
109.0
148.0
—
—
—
—
135.0
154.0
129.0
134.0
146.0
140.0
162.0
210.0
190.0
200.0
158.0
180.0
173.0
169.0
157.0
168.0
152.0
201.0
9
10
11
12
14
16
Sm: Smectic
Nm: Nematic

Properties of a Novel Ester Homologous Series
61
from homologue to homologue of the series under discussion. The series is predominantly
nematogenic and partly smectogenic and of a high melting type.
The esterification process through acid chloride formation breaks the hydrogen bond-
ing between two molecules of the 4-n-alkoxy benzoic acids and dimerization disappears.
Nonmesomorphicity of the methoxy to butoxy homologues is attributed to their shorter
n-alkyl chain, which normally strengthens intermolecular attractions to raise the crystalliz-
ing tendency of a substance, without formation of lamellar packing of molecules in their
crystal lattices. Thus, such molecular packing is unable to withstand exposed thermal vibra-
tions, and undergo abrupt breaking of their crystal lattices which, suddenly transform into
isotropic liquid from solid crystalline state, at melting temperature with the absence of any
sort of two-dimensional order in a floating condition. The molecules are randomly oriented
in all possible directions with high order of disorder or entropy (ꢀs = ꢀH/T). Exhibition
of a smectogenic and/or a nematogenic mesophase or mesophases by the pentyloxy to
hexadecyloxy homologues is attributed to the disalignment of molecules at an angle less
than 90◦ under observation through a hot stage polarizing microscope adopting either a
sliding-layered or statistically parallel orientational-ordered arrangement of the molecules
in a floating condition under the influence of heat. As heat is applied to a sample, the
intermolecular attractive forces are weakened and as a consequence of favorable molecular
rigidity and flexibility, the molecules under examination adopt sliding-layered arrangement
due to the lamellar packing of molecules in their crystal lattices, which results in the appear-
ance of a smectogenic mesophase from the hexyloxy to hexadecyloxy homologues. The
pentyloxy homologue does not facilitate smectogenic behavior which is due to the absence
of lamellar packing in their crystal lattices and hence, molecular arrangement adopts only
a statistically parallel orientational order of molecules in floating condition. The nonmeso-
morphicity of the propoxy and butoxy homologues was examined by extrapolating the
nematic–isotropic transition curves for odd (third) and even (fourth) homologues. The ex-
trapolated transition curve for the propoxy homologue indicates 165◦C as latent transition
temperature (LTT) showing latent ability of the propoxy homologue to exhibit the nematic
mesophase monotropically in an irreversible manner below its isotropic temperature. How-
ever, it is not realizable due to its high crystallizing tendency. The extrapolated transition
curve for smectic and nematic merges into the isotropic point of 158◦C for the butoxy
homologue, which indicates that neither monotropic, nor enantiotropic nematic or smectic
mesophase is possible to emerge. Moreover, extrapolated transition curves magnify the
odd–even effect. The odd–even effect diminishes as the series is ascended and merges into
each other at the octyloxy homologue. This odd–even effect disappears from and beyond
the octyloxy homologue because the longer n-alkyl may coil or bend or flex or couple to
lie with major axis of the core structure and follows as a single curve. Variations in meso-
morphic properties from homologue to homologue in present or same series is attributed
to the progressive addition of methylene units. Relatively higher transition temperatures of
homologues and high degrees of mesomorphism may be attributed to the presence of the
multiple bond in the vinyl cinnamate central group, and linear lath-like molecular geome-
try, which enhances molecular rigidity and flexibility, inducing higher thermal stability to
maintain two dimensional array of molecules in a floating condition. Thus, the presently
investigated novel series is predominantly nematogenic and partly smectogenic. The me-
somorphic properties of the present series-1 are compared with other structurally similar
known series X [16] and Y [17] as shown in Fig. 2.
Homologous series 1, X and Y have structural similarities and differences are clearly
shown in Fig. 2. Mesomorphic behavior of the three series of homologues and the de-
gree of mesomorphism will differ on the basis of differing molecular structure as a

62
H. B. Patel and A. V. Doshi
Figure 2. Structurally similar homologous series.
consequence of changing molecular rigidity and flexibility affecting magnitudes of inter-
molecular anisotropic forces of attractions. Table 3 as mentioned below shows the average
thermal stability for smectic and nematic phases, the commencement of the smectic and
nematic mesophases, and the group efficiency order.
Table 3 shows the mesomorphic behavior of the presently investigated novel homol-
ogous series 1 and series X and Y chosen for the comparative study. Series 1 and X
are structurally similar for RO C6H4 COO C6H4 CH CH COO CH2–, whereas
they differ from series Y from a central bridge linking the two phenyl rings by the
CH CH unit from the common molecular part. The rest of the molecular part con-
tained by series 1 is the aromatic phenyl ring while series X and Y contain commonly
the CH2 CH2 CH2 CH2 CH3. Thus, the uncommon parts from series 1, X, and Y
cause differences in magnitudes of intermolecular anisotropic forces of lateral and ter-
minal attractions as a consequence of differing magnitudes of molecular rigidity and
flexibility [12,13]. All the homologous of series 1, X, and Y exhibit smectic and then
nematic mesophases, for definite temperature length, but their phase lengths are differ-
ent due to their minor structural variation for the same homologue from series to se-
ries. Thermal stabilities for smectic and nematic of series 1 are more than for series X,
but are less than for series Y. The relatively higher value of thermal stabilities of se-
ries 1 than series X is attributed to the additional phenyl ring substituted in place of
the CH2 CH2 CH2 CH2 CH3 terminal chain, and of series X bonded to a middle
common CH CH COO CH2– unit. The difference of molecular rigidity induced by
the aromatic phenyl ring of series 1 being more than the molecular flexibility induced
by CH2 CH2 CH2 CH2 CH3 terminal chain. Conversely, the molecular flexibility
Table 3. Average thermal stability in ◦C
Series→
Series 1
Series X
Series Y
smectic-nematic Or
smectic-isotropic
commencement of smectic
phase
144.1 (C6 C16) C6 93.2 (C8 C14) C8 179.6 (C7 C14) C7
nematic-isotropic
commencement of nematic
phase
171.4 (C5 C16) C5 136.4 (C6 C14) C6 190.3 (C3 C14) C3

Properties of a Novel Ester Homologous Series
63
induced by CH2 CH2 CH2 CH2 CH3 chain in the case of series Y exceeds the in-
termolecular attraction of the central bridge CH CH COO in place of central bridge
COO of series 1. Thus, the central bridge which is CH CH COO in case of
homologous series Y and carboxylate COO in the case of series 1 and X under compar-
ison are closely similar to each other. Both these central bridges are comparable, though
the vinyl carboxylate CH CH COO has a greater length and causes more noncopla-
narity due to a twist obtained as the oxygen atoms of the vinyl carboxylate group bump
into the nonbonded adjacent hydrogen atoms of the aromatic rings. On account of these
differences, the intermolecular lateral and terminal attractions of a homologous series Y
exceeded those of homologous series 1 and X. Hence, smectic and nematic thermal sta-
bilities of series Y are higher than series 1 and X. Earliest commencement of the nematic
mesophase formation in case of series Y as compared to series 1 and X is related to the
order of magnitudes of the anisotropic forces of intermolecular attractions caused by the
varying molecular length to breadth ratio, and hence the variation of the ratio of the molec-
ular polarity to polarizability. Alternation of transition temperatures, odd–even effect, and
variations of mesomorphic properties from series to series for the same homologue or ho-
mologue to homologue in the same series is attributed to the changing methylene unit of end
group.
Conclusions
• Group efficiency order derived on the basis of thermal stabilities for smectic and
nematic mesophase formation is as under.
Smectic:
CH CH COO CH2 (CH2)4 CH3 >
with
CH CH COO
CH CH COO CH2 C6H5 >
with
COO
CH CH COO CH2 (CH2)4 CH3
with
COO
Nematic:
CH CH COO CH2 (CH2)4 CH3 >
with
CH CH COO
CH CH COO CH2 C6H5 >
CH CH COO CH2 (CH2)4 CH3
• Group efficiency order derived on the basis of early commencement of smectic and
nematic is as under.

64
H. B. Patel and A. V. Doshi
Smectic:
CH CH COO CH2 C6H5 >
with
COO
CH CH COO CH2 (CH2)4 CH3 >
with
CH CH COO
CH CH COO CH2 (CH2)4 CH3
with
COO
Nematic:
CH CH COO CH2 (CH2)4 CH3 >
with
CH CH COO
CH CH COOx CH2 C6H5 >
with
COO
CH CH COO CH2 (CH2)4 CH3
with
COO
• The novel homologous series is predominantly nematogenic and partly smectogenic
with considerable mesomorphic phaselength and higher-ordered melting type.
• Mesomorphism exhibition of a substance is very sensitive and susceptible to minute
change in the molecular structure.
• Suitable magnitudes of molecular rigidity and flexibility play an important role in
inducing mesomorphism in a substance.
• Variations in mesomorphism from homologue to homologue in the same series is
due to the sequential addition of methylene unit or units, to the n-alkyl chain of a
left n-alkoxy end group.
• Absence of lamellar packing of molecules in the crystal lattices hinders the smecto-
genic property.
Acknowledgements
Authors acknowledge thanks to the Green Circle Inc. Lab for research facilities ser-
vices as and when needed. Authors also thank Dr. N. N. Vyas, Dr. Vipul Patel, and
Dr. M. L. Chauhan for their valuable helping hand and microscopic facility. Thanks are due
to the Sophisticated Analytical Instrumentation Facility, Punjab University, Chandigarh,
for analytical services.
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