Synthesis and Evaluation of Liquid Crystal Behavior of a Novel Homologous Series: 4-(4′-n-Alkoxy benzoyloxy) Phenylazo-2″, 6″-dimethylbenzenes

Article abstract of DOI:10.1080/15421406.2014.884395

A novel homologous series entitled 4-(4′-n-alkoxy benzoyloxy) phenyl azo 2^″, 6^″-dimethyl benzenes consisting of 12 members is reported. Liquid crystal behavior as a nematogenic mesophase commences from the pentyloxy homologue monotropically and then continues enantiotropically until the last hexadecyloxy homologue without exhibition of any smectogenic behavior. An odd-even effect is observed for nematic-isotropic transition curve of the phase diagram. The textures of the nematic mesophase are of the threaded or Schlieren type. Analytical and spectral data support the molecular structure of the homologues. Transition temperatures of the novel homologues were determined by an optical polarizing microscopy. Liquid crystal properties of a novel homologous series are compared with other known homologous series. The average thermal stability for the nematic phase is 77.1°C.

Full text of DOI:10.1080/15421406.2014.884395

This article was downloaded by: [Northeastern University]
On: 11 January 2015, At: 14:00
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Molecular Crystals and Liquid Crystals
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/gmcl20
Synthesis and Evaluation of Liquid
Crystal Behavior of a Novel Homologous
Series: 4-(4′-n-Alkoxy benzoyloxy)
Phenylazo-2″, 6″-dimethylbenzenes
V. C. Kotadiyaa, M. D. Khunta & U. C. Bhoyaa
a Department of Chemistry, Saurashtra University, Rajkot, Gujarat,
India
Published online: 15 Dec 2014.
Click for updates
To cite this article: V. C. Kotadiya, M. D. Khunt & U. C. Bhoya (2014) Synthesis and Evaluation
of Liquid Crystal Behavior of a Novel Homologous Series: 4-(4′-n-Alkoxy benzoyloxy)
Phenylazo-2″, 6″-dimethylbenzenes, Molecular Crystals and Liquid Crystals, 605:1, 52-60, DOI:
10.1080/15421406.2014.884395
To link to this article: http://dx.doi.org/10.1080/15421406.2014.884395
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &

Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Mol. Cryst. Liq. Cryst., Vol. 605: pp. 52–60, 2014
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2014.884395
Synthesis and Evaluation of Liquid Crystal Behavior
of a Novel Homologous Series: 4-(4ꢀ-n-Alkoxy
benzoyloxy) Phenylazo-2ꢀꢀ, 6ꢀꢀ-dimethylbenzenes
V. C. KOTADIYA, M. D. KHUNT, AND U. C. BHOYA∗
Department of Chemistry, Saurashtra University, Rajkot, Gujarat, India
A novel homologous series entitled 4-(4ꢀ-n-alkoxy benzoyloxy) phenyl azo 2ꢀꢀ, 6ꢀꢀ-
dimethyl benzenes consisting of 12 members is reported. Liquid crystal behavior as
a nematogenic mesophase commences from the pentyloxy homologue monotropically
and then continues enantiotropically until the last hexadecyloxy homologue without
exhibition of any smectogenic behavior. An odd-even effect is observed for nematic-
isotropic transition curve of the phase diagram. The textures of the nematic mesophase
are of the threaded or Schlieren type. Analytical and spectral data support the molecu-
lar structure of the homologues. Transition temperatures of the novel homologues were
determined by an optical polarizing microscopy. Liquid crystal properties of a novel
homologous series are compared with other known homologous series. The average
thermal stability for the nematic phase is 77.1◦C.
Keyword Liquid crystal; mesogen; monotropy; nematic; smectic
Introduction
Suitable molecular rigidity from the rigid core of a molecule and the flexibility from units
such as the terminal alkyl chains [1–3] play an important role in generating favorable
magnitudes of anisotropic forces of intermolecular attractions, which induces liquid crystal
properties [4] in a substance. Thus, liquid crystalline behavior of a substance is directly
related to its molecular structure, that is, molecular shape, size, aromaticity, polarity and
polarizability, and position of functional groups. The structure of the novel molecules re-
ported here consist of three phenyl rings bridged through COO and N N functional
groups which act as the rigid core and the left n-alkoxy ( OR) terminal end group on first
phenyl ring as well as the two lateral methyl groups substituted at ortho position of the
N N on third phenyl ring act as a flexible units of the molecule. Thus, liquid crystal
behavior of a molecule can be correlated with its molecular structure.
Experimental
Synthesis
4-Hydroxy benzoic acid was alkylated by suitable alkylating agent by the modified method
Dave and Vora [5]. The azodye, 4-hydroxy phenyl azo 2ꢀ, 6ꢀ dimethyl benzene was prepared
∗Address correspondence to U. C. Bhoya, Department of Chemistry, Saurashtra University,
Rajkot-360005, Gujarat, India; E-mail: drucbhoya@sauuni.ernet.in
Color versions of one or more of the figures in the article can be found online at
www.tandfonline.com/gmcl.
52

Azoesters with Lateral Methyl Groups
53
Table 1. Elemental analysis for (1) Ethyloxy (2) Pentyloxy (3) Heptyloxy derivatives
Elements %Found
H
Elements %Calculated
Molecular
formula
Sr. no.
C
N
C
H
N
1
2
3
C23H22N2O3
C26H28N2O3
C28H32N2O3
73.72
74.90
75.61
5.95
6.81
7.22
7.40
6.70
6.22
73.78
74.97
75.65
5.92
6.78
7.26
7.48
6.73
6.30
by the well-known method of diazotization [6]. 4-n-Alkoxy benzoic acids were converted to
the corresponding acid chlorides using freshly distilled thionyl chloride and condensed with
an ice cold solution of azodye in pyridine [7]. The final azoester products were individually
decomposed in 1:1 hydrochloric acid aqueous solution, filtered, washed, dried, and purified
until a homologue gave constant transition temperatures.
4-Hydroxy benzoic acid, alkyl halides, KOH, thionyl chloride, methanol, ethanol,
pyridine, 2, 6, dimethyl aniline, and phenol were used as received except solvents which
were dried and purified prior to use. The synthetic route to the azoester homologue is shown
in Scheme 1.
Characterization
Selected member of a series were characterized by elemental analysis (Table 1), 1HNMR
spectroscopy, infrared spectroscopy, mass spectrometry, and textural identification. Micro-
analysis was performed using a EuroEA Elemental Analyzer. IR spectra were recorded on
Shimadzu FTIR-8400 spectrometer, 1HNMR spectra were recorded on Bruker spectrometer
using DMSO-d6 as the solvent and mass spectra were recorded on Shimadzu GC-MS Model
No. QP-2010 instrument. The type of textures of liquid crystal phases were determined by
a miscibility process, and liquid crystal properties were determined by optical polarizing
microscopy equipped with heating stage.
Analytical Data
Elemental Analysis (Table 1).
Spectral Data
NMR in ppm for the Hexayloxy Derivative. 0.873–0.908 (t, 3H, CH3 of OC6H13
group), 1.31–1.45 (6H, m, polymethylene group of OC6H13), 1.74–1.77 (t, 2H,
CH2 CH2 O ), 2.317 (6H, s, CH3 of phenyl ring). 4.08–4.12 (t, 2H, CH2-O-),
7.12–8.12 (m, 11H, substituted phenyl ring). The NMR data are consistent with the molec-
ular structure.
NMR in ppm for the Octyloxy Derivative. 0.87–0.88 (t, 3H,-CH3 of
OC8H17
group), 1.27–1.45 (10H, m, polymethylene group of OC8H17), 1.72–1.79 (t,
2H, CH2 CH2 O ), 2.31 (6H, s, CH3 of phenyl ring). 4.08–4.11 (t, 2H, CH2 O ),
7.12–8.11 (m, 11H, substituted phenyl ring). The NMR data are consistent with the molec-
ular structure.

54
V. C. Kotadiya et al.
Scheme 1. Synthetic route to the series.
IR in cm−1 for the Hexadecyloxy Derivative. 636 (polymethylene ( CH2-)n group of
OC16H33), 740, 771 (para & ortho substituted phenyl ring), 835 (1,6 disubstituted phenyl
ring), 1170 (>C=O group), 1259 ( COO ester group), 1606 ( N N Str.), 1753 (C
O, Str. of COO group), 2847, 2916 (Aromatic phenyl ring). The IR data are consistent
with the molecular structure.

Azoesters with Lateral Methyl Groups
55
Table 2. Transition temperatures in ◦C of series-1
Transition temperature in ◦C
n-Alkyl group
Compound no.
n = CnH2n+1
Sm
N
Isotropic
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
10
12
14
16
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
104.0
111.2
102.0
100.0
82.3
83.2
78.3
79.7
76.6
—
(71.9)
80.6
51.5
60.3
49.8
57.9
59.7
86.9
10
11
12
74.0
71.3
130.0
() indicate monotropy.
Sm—Smectic, N—Nematic.
IR in cm−1 for the Dodecyloxy Derivative. 650 (polymethylene ( CH2
)
group of
n
OC12H24), 742, 761 (para & ortho substituted phenyl ring), 840 (1,6 disubstituted phenyl
ring), 1175 (>C O group), 1026, 1261 ( COO ester group), 1606 ( N N Str.), 1730
(C O, Str. of COO– group), 2845, 2937 (Aromatic phenyl ring). The IR data are consis-
tent with the molecular structure.
Mass Spectra of the Decyloxy Derivative. m/z (rel. int.%): 486 (M)+
Mass Spectra of the Tetradecyloxy Derivative. m/z (rel. int.%): 542 (M)+
Texture Determination by Miscibility Method.
• Hexyloxy homologue: Threaded nematic
• Tetradecyloxy homologue: Schlieren nematic
Result and Discussion
The azodye, 4-hydroxy phenyl azo-2ꢀ,6ꢀdimethyl benzene(M.P. 144.5◦C) is nonmesomor-
phic, but on condensing it with dimerized n-alkoxy benzoic acids through their acid
chlorides, mesomorphic derivatives of a novel homologous series 4-(4ꢀ-n-alkoxy benzoy-
loxy)phenylazo 2ꢀꢀ,6ꢀꢀ-dimethyl benzenes are generated. Nemetogenic mesophase formation
commences from the pentyloxy homologue monotropically and then enantiotropically from
the hexyloxy to hexadecyloxy homologue without exhibition of a smectogenic mesophase
even in the monotropic condition. Transition temperatures (Table 2) of the novel homo-
logues, as determined by an optical polarizing microscope with heating stage, are plotted
versus the number of carbon atoms present in n-alkyl chain of left n-alkoxy terminal end
group, to give a phase diagram showing phase behavior (Fig. 1). The solid-isotropic or
nematic transition curve follows a zigzag path of rising and falling values and behaves in a

56
V. C. Kotadiya et al.
Figure 1. Phase behavior of series.
normal manner. The nematic-isotropic transition curve slightly rises and then descends as
the series is ascended up to the tetradecyloxy homologue and then drastically ascends for the
hexadecyloxy homologue. Thus, the nematic-isotropic transition curve behaves in a usual
established manner up to the tetadecyloxy homologue and then a somewhat unexpected be-
havior is shown by the hexadecyloxy homologue. The nematic-isotropic transition curve is
extrapolated [8], following the trend of a nematic-isotropic transition curve for third [odd]
and fourth (even) nonmesomorphic members of the novel homologous series to predict
their latent ability to exhibit mesomorphism. The predicted latent transition temperature
(LTT) for the propoxy and butoxy homologues are below their melting points at 61.5◦C and
82.0◦C respectively. An odd–even effect is observed for nematic-isotropic transition curve
and the effect is magnified by extrapolating the nematic-isotropic transition curve. Meso-
morphic (nematic) phase length varies from 11.6◦C to 43.1◦C. The average thermal stability
(Table 3) is 77.1◦C. The series under discussion is nematogenic only with lower ordered
melting type and without exhibition of smectic character. The odd–even effect diminishes
and disappears from and beyond the nonyloxy homologue. Mesomorphic properties vary
from homologue to homologue in the same novel series.
Table 3. Average thermal stability in ◦C
Series
[1]
[X]
[Y]
Smectic—nematic
or
114.0
C10–C16
—
—
—
—
Smectic-isotropic
commencement of
smectic phase
Nematic-isotropic
Commencement of
nematic phase
C10
77.1
[C6–C14]
C5
113.0
[C10–C16]
C3
138.54
[C1–C8]
C1

Azoesters with Lateral Methyl Groups
57
The disappearance of dimerisation of 4-n-alkoxy benzoic acids is attributed to the
breaking of hydrogen bonding by the esterification process. Addition of a phenyl ring linking
through a N N central bridge to a 4-n-alkoxy acid (via acid chloride) increases the
molecular rigidity and aromaticity, and the two methyl groups increase molecular flexibility
and length to breadth ratio; which enables liquid crystal properties as a consequence of
suitable magnitudes of anisotropic forces of intermolecular attractions from the pentyloxy to
hexadecyloxy homologues. However, liquid crystal properties are not induced for methoxy
to butoxy homologues because of the absence of suitable magnitudes of anisotropic forces
of intermolecular attractions in terms of a high tendency towards the crystal state. Relatively
shorter n-alkyl chain lengths from methyl to n-butyl induces lower molecular flexibility and
higher crystallizing tendency in a molecule which hinders disalignment of molecules at an
angle less than 90 degrees. Molecules from pentyloxy to hexadecyloxy homologues disalign
at an angle of less than 90 degree for a definite range of temperature against the externally
exposed thermal vibrations and float on the surface with a statistically parallel orientational
order for aparticular temperaturerangewithsuitablemagnitudes ofanisotropicforces ofend
to end intermolecular attractions. Thus, the nematic mesophase formation is exhibited by
the pentyloxy to hexadecyloxy homologues of the present series. Absence of smectogenic
behavior of the present series is attributed to the absence of lamellar packing [4,9] of
molecules in their crystal lattices due to inadequate ability of intermolecular attractions
to maintain a sliding layered arrangement of molecules in a floating condition under the
influence of heat by resultant molecular polarity and polarizability. An odd-even effect
of alternation of transition temperatures as well as changing mesomorphic behavior from
homologue to homologue in the present series are attributed to the sequential change in
the number of methylene units in the n-alkoxy terminal end group. The disappearance
of the odd–even effect for higher homologues from and beyond the nonyl homologue is
attributed to the flexing, bending, coiling, or coupling of n-alkyl chain with major axis of
the core. The mesomorphic nematogenic phase length varies from a minimum of 11.6◦C
at the tetradecyloxy homologue to a maximum of 43.1◦C at the hexadecyloxy homologue.
Thus, present novel series is predominantly nematogenic without exhibition of smectogenic
character. The average thermal stability for nematic of the series is 77.1◦C. Thus, series is
considered as low melting type and medium ranged liquid crystallinity. The mesomorphic
properties of the present series-1 are compared with the structurally similar other known
homologous series X [10] and Y [11] shown in Fig. 2.
The average thermal stabilities and other information for series-1 and series-X and
series-Y chosen for comparison are shown in Table 3.
Table 3 shows the thermal stabilities for the smectic phase and/or the nematic phase,
the commencement of the nematic and/or the smectic mesophase for the novel series-1,
and series-X and series-Y chosen for comparing mesomorphic properties. Homologous
series-1, series-X, and series-Y (Fig. 2) are identical with respect to their molecular rigidity
formed by three phenyl rings bonded through COO and N N central bridges as
well as left handed flexible n-alkoxy (–OR) terminal end group for the same homologue
from series to series. However, they differ with respect to the presence or absence of methyl
groups substituted at different positions with respect to the N N or COO functional
groups and the changing n-alkoxy terminal end group from homologue to homologue in the
same series. Thus, series-1, series-X, and series-Y are identically similar in their molecular
rigidity but differ in their molecular flexibility. The generation of mesomorphic properties
and the degree of mesomorphism depend upon the combined effects of the magnitudes of
molecular rigidity and flexibility. Therefore, observed variations in mesomorphic behavior
of series-1, series-X, and series-Y can be attributed and correlated with the variation of

58
V. C. Kotadiya et al.
Figure 2. Structurally similar homologous series.
molecular structures (Fig. 2). Homologous series-1 and series-X are isomeric with each
other containing two methyl groups with identical molecular rigidity but with different
molecular flexibility caused by two methyl groups linked at different position of same
(i.e., ortho position to N N ) and different phenyl rings. Steric hindrance to protect the
N N central group by two methyl groups in series-1 is relatively more as compared to
series-X. Moreover the length to breadth ratio and hence the ratio of the molecular polarity to
polarizability varies between series-1 and series-X. Thus, polarizability is the predominant
factor out of two opposing effects [9] concerning anisotropic forces of intermolecular
attractions [4] for series-Y as compared to series-1. Hence, series-1 shows only the nematic
mesophase while, series-Y additionally shows a smectic mesophase. Homologous series-1
and series-X show only the nematogenic mesophase without the exhibition of a smectic
phase, but their commencement of nematic mesophase formation differs (series-1 from fifth
and series-X from third member), which indicates difference in magnitudes of anisotropic
forces of intermolecular attractions. Absence of smectogenic character in isomeric series-1
and series-X indicates the absence of lamellar packing of molecules in their crystal lattices
due to inappropriate magnitudes of anisotropic forces disturbing an extent of molecular
coplanarity and hinders layered arrangement of molecules perpendicular to the plane of a
surface in floating condition to form smectic mesophase. Intermolecular adhesive end to
end forces are sufficient to maintain a statistically parallel orientational order of molecules
in floating condition from very first member of a series-Y and the same nematogenic
mesophase commences relatively late from fifth and third member of a series-1 and series-
X respectively due to poorer end to end attractions. The variations in mesomorphic behavior
from homologue to homologue in the same series and series to series for same homologue
are attributed to the sequentially added methylene unit and the changing position of the
same functional groups [12] respectively. The increasing order of thermal stability for the
nematic phase is attributed to the energy stored by a molecule (ꢀH) based on the combined

Azoesters with Lateral Methyl Groups
59
effect of molecular rigidity and flexibility to stabilize the mesophase formed within definite
range of temperature.
Conclusions
The following conclusions are drawn for the novel homologous series.
1. The novel homologous series is only nematogenic without exhibition of any smec-
togenic property.
2. The novel homologous series is a relatively low melting type with considerable
mesophase length.
3. Group efficiency order derived on the basis of thermal stability for nematic is,
Series − Y > Series − X > Series − 1
4. Group efficiency order derived on the basis of early commencement of nematic
phase is, Series − Y > Series − X > Series − 1
5. Group efficiency order derived on the basis of thermal stability
and the early commencement of smectic mesophase is as under.
Series − Y > Series − X > Series − 1
6. Liquid crystal property in a substance is induced only by favorable and suitable
magnitudes of molecular rigidity and flexibility.
7. Mesomorphic behavior of a series from homologue in the same series varies with
the sequentially added methylene unit, keeping right terminal or lateral end group
unchanged.
8. Mesomorphic behavior for the same homologue from series to series depend upon
(i) varying right sided lateral or/and terminal end group or groups or (ii) varying
position of the same functional group or groups present on right side of isomeric
series, keeping n-alkyl chain of left n-alkoxy group unchanged.
9. Suitable magnitude of molecular rigidity and flexibility, that is, molecular structure
has direct relation to induce liquid crystal property in a substance or fittest molecular
rigidity and flexibility operates liquid crystal behavior of a substance with respect
to its molecular structure.
Acknowledgments
Authors acknowledge thankfulness to the Department of Chemistry (DST-FIST Funded
& UGC-SAP Sponsored) Saurashtra University, Rajkot, for research work. Authors are
also thankful to Dr. A.V. Doshi, Ex. Principal M.V.M. Science and Home Science College
Rajkot, for his important co-operation during present investigation as and when required.
Also thanks are due to the National Facility for Drug Discovery through New Chemical
Entities (NCE’s), for analysis of samples.
References
[1] Marcos, M., Lomenta, A., Serrano, J. L., & Ezcurra, A. (1992). Adv. Mater., 4, 285.
[2] Hird, M., Toyne, K. J., & Gray, G. W. (1993). Liq. Cryst., 14, 741.
[3] Hird, M., Toyne, K. J., Gray, G. W., Day, S. E., & Mc Donnell, D. G. (1993). Liq. Cryst., 15,
123.
[4] (a) Gray, G. W., & Windsor, P. A. (1974). Liq. Cryst. Plastic Cryst., Vol. 1, Chapter 4, Ellis
Horwood: Chichester, UK. (b) Gray, G. W. (1962). Molecular Structure and the Properties of
Liquid Crystal, Academic Press: London.

60
V. C. Kotadiya et al.
[5] Dave, J. S., & Vora, R. A. (1970). Liquid Crystal and Ordered Fluids, Plenum Press: New York,
477.
[6] Furniss, B. S., Hannaford, A. J., Smith, P. W. G. & Tatchell, A. R. (1989). Vogel’s Text Book of
Practical Organic Chemistry, 4th ed., Longman Publisher Pvt. Ltd.: Singapore.
[7] Doshi, A. V., & Ganatra, K. J. (1999). Proc. Ind. Acad. Sci. (Chem. Sci.), 4, 11, 562. (b) Bhoya,
U. C., Vyas, N. N., & Doshi, A. V. (2012). Mol. Cryst. Liq. Cryst., 552, 104.
[8] (a) Doshi, A. V., & Lohar, J. M. (1993). Ind. Acad. Sci. Chem. Sci., 105(3), 209. (b) Travadi, J.
J., Bhoya, U. C., & Doshi, A. V. (2012). Mol. Cryst. Liq. Cry., 552, 10.
[9] (a) Patel, V. R., & Doshi, A. V. (2010). Der Pharma Chemica., 2(6), 429. (b) Cauhan, M. L., &
Doshi, A. V. (2007). J. Ind. Chem. Soc., 84(8), 774. (c) Bhoya, U. C., & Doshi, A. V. (2011).
Der Pharma Chemica., 3(2), 135. (d) Makwana, N. G., & Doshi, A. V. (2006). Acta Ciencia
Indica Chem., 32(4), 391. (e) Prajapati, H. R., & Doshi, A. V. (2009). J. Ind. Chem. Soc., 86(5),
470.
[10] Ganatra K. J., & Doshi, A. V. (2000). J. Inst. Chemist (Ind.), 72(2), 61.
[11] Ganatra K. J., & Doshi, A. V. (2005). J. Ind. Chem. Soc., 82(5), 466.
[12] (a) Suthar, D. M., & Doshi, A. V. (2013). Mol. Cryst. Liq. Cry., 571(1), 1. (b) Chuhan, H. N., &
Doshi, A. V. (2013). Mol. Cryst. Liq. Cry., 570(1), 12.