Mesogenic 4-[4-(ω-hydroxyalkoxy)phenyl]diazenylcinnamic acids and their 4-cyanophenyl esters

Article abstract of DOI:10.1134/S1070428009020055

Homologs of a series 4-[4-(ω-hydroxyalkoxy)phenyl]diazenylcinnamic acids (C₂, C₆, C₈, C₉, C ₁₀) and their two 4-cyanophenyl esters (C₂, C₆) were synthesized. The substances obtai

Full text of DOI:10.1134/S1070428009020055

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2009, Vol. 45, No. 2, pp. 182−184. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © S.A. Kuvshinova, D.S. Fokin, V.A. Burmistrov, O.I. Koifman, 2009, published in Zhurnal Organicheskoi Khimii, 2009,
Vol. 45, No. 2, pp. 194−196.
Mesogenic 4-[4-(ω-Hydroxyalkoxy)phenyl]diazenylcinnamic Acids
and Their 4-Cyanophenyl Esters
S. A. Kuvshinovaa, D. S. Fokina, V. A. Burmistrovb, and O. I. Koifmanb
aIvanovo State University of Chemical Engineering, Ivanovo, Russia
bInstitute of Solutions Chemistry, Russian Academy of Sciences, Ivanovo, 153460 Russia
e-mail: burmistrov@isuct.ru
Received July 28, 2007
Abstract—Homologs of a series 4-[4-(ω-hydroxyalkoxy)phenyl]diazenylcinnamic acids (C2, C6, C8, C9, C10) and
their two 4-cyanophenyl esters (C2, C6) were synthesized. The substances obtained possess properties of
thermotropic nematic liquid crystals. The effect of the terminal hydroxy group of the terminal substituent on their
mesomorphous properties was analyzed.
DOI: 10.1134/S1070428009020055
In continuation of the investigation of the effect of
the hydroxy group in the terminal aliphatic substituent on
the mesomorphous properties of substances and in order
to obtain heat-resistant liquid crystals with a wide range
of mesophase existence we synthesized in the present
study 4-[4-(ω-hydroxyalkoxy)phenyl]diazenylcinnamic
acids and their 4-cyanophenyl esters.
Liquid crystalline state of a substance combines a sig-
nificant fluidity and long-range orientation order and
consequently anisotropic physical characteristics. These
qualities led to a wide application of mesogenic compounds
in versatile fields of scientific research, in engineering,
and technology [1]. The interest directed on mesogenic
molecules with chemically active and polar terminal
substituents (OH, CHO, CN, COOH) is caused by two
reasons. Firstly, they can be readily subjected to chemical
modification sharply extending the range of meso-
morphous structures. Secondly, in the mesogenes formed
by these molecules specific interactions may exist
endowing them with new characteristics [2].
Obtained phenyldiazenylcinnamic acids Ia–Ie are
crystalline substances of orange color; they were many
times recrystallized from acetic acid and ethanol (see
the scheme).
4-Cyanophenyl esters of 4-[4-(ω-hydroxyalkoxy)-
phenyl]diazenylcinnamic acids IIa and IIb are crystalline
substances of orange-red color. They were purified by
column chromatography on aluminum oxide (eluent
chloroform) and recrystallized from ethanol.
Besides a special interest attract heat-resistant liquid
crystals because of their promising application to the
analytical GLC as stationary phases for separation of
high-boiling chemical substances, in particular, 3,4- and
3,5-lutidines, p- and m-cresol, naphthalene derivatives,
polycyclic aromatic hydrocarbons, steroids, herbicides,
etc. [3].
The compounds synthesized were purified and kept
in a vacuum till the constant temperature of their phase
1
transitions and the absence in the H NMR spectra of
impurity signals.
We formerly prepared a homologous series of meso-
genic aldehydes, 4-(ω-hydroxyalkoxy)-4'-formylazo-
benzenes [4] whose significant feature was an enhanced
thermal stability and extended temperature range of the
mesophase. This effect of the terminal hydrophilic
substituent originates from the existence of supra-
molecular chain associates owing to the presence of
sufficiently strong intermolecular hydrogen bonds.
The composition and structure of compounds obtained
Ia–Ie, IIa and IIb were proved by elemental analysis
(see the table), IR and 1H NMR spectra. The parameters
of the H NMR spectra were fairly consistent with the
characteristics calculated with the use of published
data [5].
1
The temperature of phase transitions was measured
by the method of polarization thermomicroscopy and is
182

MESOGENIC 4-[4-(ω-HYDROXYALKOXY)PHENYL]DIAZENYLCINNAMIC ACIDS
183
Scheme.
HO(CH2)nO
N N
CHO
1
2
3
4
HOOCCH2COOH
Py
HO(CH2)nO
N N
Ià_Ie
CH CHCOOH
SOCl2
HO(CH2)nO
N N
CH CHCOCl
1
2
3
4
5
6
HO
CN
HO(CH2)nO
N N
IIà, IIb
n = 2 (a), 6 (b), 8 (c), 9 (d), 10 (e).
CH CHCOO
CN
compiled in the table. Theromicroscopy investigation of
4-[4-(ω-hydroxyalkoxy)phenyl]diazenylcinnamic acids
Ia–Ie showed that these compounds are high-melting,
possess a considerable stability of the mesophase and a
sufficiently wide range of its existence. Mesogenes IIa
and IIb above their melting point are melts of low viscosity.
In the polarized light schlieren-texture is observed in the
melts characteristic of nematic mesophase.
The comparison of the mesomorphous characteristics
of obtained substances Ia–Ie, IIa and IIb with those of
their structural analogs lacking the hydroxy group in the
terminal substituent which we have synthesized and
investigated earlier [6, 7] demonstrates a fairly significant
effect of the terminal hydroxy group on the phase
transition temperature. Therewith the active substituent
to a greater extent increased the temperature of the
nematic-isotrope transition than the melting point thus
leading to a considerable extension of the temperature
range of the nematic phase apparently because of the
formation of sufficiently strong intermolecular associates
bound by hydrogen bonds.
Compound Ia does not exhibit the liquid crystal
properties, evidently because the low geometrical
anisotropy of the molecule, whereas the corresponding
4-cyanophenyl ester IIa is a liquid crystal. Compounds
IIa and IIb with three aromatic rings have a significantly
higher clearing points and a wider range of the mesophase
existence than compounds Ia–Ie including two aromatic
rings. This fact is understandable from the viewpoint of
larger polarization anisotropy of compounds having three
aromatic rings.
EXPERIMENTAL
IR spectra were recorded on a spectrophotometer
1
Avtar 360PT-IR ESP from pellets with KBr. H NMR
Yield and characteristics of liquid crystalline acids HO(CH2)nOC6H4N=NC6H4CH=CHCOOH Ia–Ie and their esters
HO(CH2)nOC6H4N=NC6H4CH=CHCOOC6H4CN IIa, IIb
Phase transition
temperature, ºC
Yield, %
Found, %
H
Formula
Calculated, %
H
Compound
no.
C>N
N→I
C
N
C
N
Ia
Ib
Ic
Id
Ie
68
64
69
54
63
52
57
–
240
240
235
223
220
>300
268
65.28
68.23
69.76
70.34
70.63
67.58
70.29
5.24
6.70
7.12
7.43
7.62
4.79
5.78
8.92
7.69
7.42
6.34
6.52
10.98
9.58
C17H16N2O4 65.39
C21H24N2O4 68.48
C23H28N2O4 69.7
C24H30N2O4 70.24
C25H32N2O4 70.76
C22H19N3O4 67.87
C26H25N3O4 70.43
5.13
6.52
7.07
7.32
7.55
4.88
5,64
8.97
7.61
7.07
6.23
6.60
10.8
9.48
198
190
180
187
154
101
IIa
IIb
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 2 2009

KUVSHINOVA et al.
184
2.14 g (52%). Orange-red crystalline substance, mp
134°C. IR spectrum, ν, cm–1: 2223 (CN), 3431 (OH),
2853, 2923 (CHaliphatic), 1127–1734 (CHarom). 1H NMR
spectrum, δ, ppm: 3.84 t (2H, HOCH2), 4.31 t (2H,
CH2O), 5.1 s (1H, OH), 6.75 s, 6.55 d (1H, =CHOO),
7.93 d (1H, CH=), 7.03 d (2H, ArH1), 7.31 d (2H, ArH2),
7.70 d (2H,ArH3), 7.74 d (2H, ArH4), 7.82 d (2H,ArH5),
7.91 d (2H, ArH6).
spectra were registered on a spectrometer Bruker AC-
200 at operating frequency 200.13 MHZ from solutions
in CDCl3, chemical shifts were measured relative to TMS
with an accuracy no worse than ±0.01 ppm.
The phase transition temperatures were measured and
the textures of compounds obtained were examined on
a polarization microscope Polam P211 equipped with
a heating block. The errors in the measured phase
transition temperatures were ±0.2°C.
Likewise was prepared compound IIb.
The study was carried out under financial support of the
Program of the Department of Chemistry and Material
Science of the Russian Academy of Sciences no. 2Okh
and of the Ministry of Education and Science of the
Russian Federation (RNP 2.2.1.1.7280).
4-(ω-Hydroxyalkoxy)-4'-formylbenzenes were prepar-
ed by procedure [4]. 4-Hydroxybenzonitrile for the
synthesis of compounds IIa and IIb was obtained as
described in [8].
4-[4-(2-Hydroxyethoxy)phenyl]diazenylcinnamic
acid (Ia). A mixture of 2.7 g (10 mmol) of 4-(2-hy-
droxyethoxy)-4'-formylbenzene and 1.74 g (15 mmol) of
malonic acid was boiled in 50 ml of anhydrous pyridine
for 4 h. The reaction mixture was poured into ice water,
the precipitate was filtered off, washed with water, and
recrystallized from acetic acid and ethanol. Yield 2.12 g
(68%). Orange crystalline substance, mp 240°C. IR
spectrum, ν, cm–1: 3405 (OH), 2945, 2860 (CH), 1693
(C=O). 1H NMR spectrum, δ, ppm: 4.02 t (2H, HOCH2),
4.13 t (2H, CH2O), 7.07 d (2H,ArH1), 7.93 d (2H,ArH2),
8.00 s (4H, ArH3,4), 11.37 s (1H, COOH).
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 2 2009