Synthesis of liquid-crystalline 4,4 '-dodecyloxybenzoyloxybenzoyl-4-oxy-2- hydroxybenzaldehyde and related azomethine

Article abstract of DOI:10.1134/S1070363211090192

4,4′-Dodecyloxybenzoyloxybenzoyl-4-hydroxy-2-hydroxybenzaldehyde and the related linear azomethine, the intermediates at the formation of iron(III)-containing complexes, were synthesized. These compounds were characterized by thin layer chromatography, elemental analysis, IR, NMR spectroscopy, mass spectrometry, and by the data of differential scanning calorimetry. The aldehyde and the azomethine show mesomorphic properties.

Full text of DOI:10.1134/S1070363211090192

ISSN 1070-3632, Russian Journal of General Chemistry, 2011, Vol. 81, No. 9, pp. 1853–1858. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © U.V. Chervonova, M.S. Gruzdev, A.M. Kolker, 2011, published in Zhurnal Obshchei Khimii, 2011, Vol. 81, No. 9, pp. 1515–1520.
Synthesis of Liquid-Crystalline
4,4 '-Dodecyloxybenzoyloxybenzoyl-4-oxy-2-
hydroxybenzaldehyde and Related Azomethine
U. V. Chervonova, M. S. Gruzdev, and A. M. Kolker
Institute of Solution Chemistry, Russian Academy of Sciences, ul. Academicheskaya 1, Ivanovo, 153045 Russia
e-mail: gms@isc-ras.ru
Received August 3, 2010
Abstract—4,4'-Dodecyloxybenzoyloxybenzoyl-4-hydroxy-2-hydroxybenzaldehyde and the related linear
azomethine, the intermediates at the formation of iron(III)-containing complexes, were synthesized. These
compounds were characterized by thin layer chromatography, elemental analysis, IR, NMR spectroscopy, mass
spectrometry, and by the data of differential scanning calorimetry. The aldehyde and the azomethine show
mesomorphic properties.
DOI: 10.1134/S1070363211090192
The published methods of synthesis of alkyloxy-
benzoic acids esters [1–5] have both advantages and
disadvantages. The classic way of esterification
consists in the synthesis of acid halide through reaction
of the acid with a halogenating reagent like SOCl2,
POCl , and PCl , followed by acylation of the phenol
angular molecular structure exhibiting mesophases of
various types [7, 8]. They are mostly the resorcinol
derivatives, symmetrical relative to the central unit
[2, 9]. A large number of bridging groups like azo-
methine, azo-, and ether moieties are used in the design
and synthesis of these compounds with p-alkoxy-
terminated chains.
3
5
fragment and elongation of the molecule in the
environment or in the presence of an organic base [1].
This method has several disadvantages, one of which
is the occurrence of side reactions accompanied by the
tarring of the products that significantly reduces the
yield and increases the cost of purifying the
synthesized compounds. Since the early 90-ies pub-
lications have appeared on the possible formation of
the ester fragment by the interaction of the carboxy
and phenol groups in the presence of dicyclohexyl-
carbodiimide in the medium of methylene chloride,
chloroform or N,N-dimethylformamide (DMF) with
catalytic amounts of dimethylaminopyridine [2]. The
latter method allows obtaining materials of high purity
in a high yield, and also gives an opportunity to use
this method for setting and removing the protecting
group for the controlled grow of the organic molecule
in the size and length. A major shortcoming of this
method is the use of expensive palladium on activated
carbon and hydrogen for the debenzylation by
hydrogenolysis.
We present here the results on the synthesis and
study of mesomorphic behavior of asymmetric
tridentante azomethine, 4,4'-dodecyloxybenzoyloxy-
benzoyl-4-salicylidene-N'-ethyl-N-ethylenediamine and
its precursor, 4,4-dodecyloxybenzoyloxybenzoyl-4-
hydroxy-2-hydroxybenzaldehyde.
Synthesis of 4,4'-dodecyloxybenzoyloxybenzoyl-4-
hydroxy-2-hydroxybenzaldehyde IV was carried out
through the reactions of intermediate products shown
in Scheme 1. Benzyl 4-hydroxybenzoate (I) acting as a
protection block in the esterification reaction was
obtained in the first stage by alkylation of the carboxy
group of p-hydroxybenzoic acid with benzyl bromide
in a medium of water-free DMF [10]. Latter on, ester I
was used for elongation of the chain of the p-
dodecyloxybenzoic ester II [2] removing the
protection by the cleavage of benzyl group in the form
of toluene (debenzylation by hydrogenolysis).
From the obtained p-dodecyloxybenzoyloxy-
benzoic ester III aldehyde IV was synthesized. The
formation of Schiff base V occurred as a result of
The widespread use of mesomorphic materials [6]
gave an impetus to the study of compounds with an
1
853

1
854
CHERVONOVA et al.
Scheme 1.
CH Cl
2
O
HO
+
OH
2
5°C, 12 h
2
Na CO3
DMF
O
HO
O−СH2
I
O
N,N'-dicyclohexylcarbodiimide,
4
-dimethylaminopyridine,
C12H25O
25°C, 24 h
OH
O
C H O
O
1
2 25
O
O−СH2
II
1
,4-dioxane, 5% Pd/C
4
0°C
H2
O
C H O
O
1
2 25
O
OH
III
O
N,N'-dicyclohexylcarbodiimide,
HO
4
-dimethylaminopyridine,
2
CH Cl2
H
2
5°C, 24 h
OH
O
C H O
O
O
1
2 25
O
O
IV
H
OH
EtOH
C H
H N
N
H
CH3
2
6
6
O
C H O
O
O
1
2 25
O
CH=N
N
CH3
H
V
OH
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 9 2011

SYNTHESIS OF LIQUID-CRYSTALLINE
1855
Fig. 1. Time-of-flight mass spectrum of the Schiff base.
reaction of the aldehyde group of compound IV with
the amino group of N-ethylethylendiamine in a
benzene–ethanol mixed solvent [11].
position of the fragment ions. It should be noted that
the fragmentation of molecule V occurs mainly at the
bonds of the ester groups with
defragmentation of the fragments.
a
uniform
For a detailed study of the azomethine structure a
mass-spectrometric investigation of a sample of 4,4'-
dodecyloxybenzoyloxybenzoyl-4-salicylidene-N'-ethyl-
N-ethylenediamine was performed. The mass spectra
were recorded using the MALDI–TOF method. Figure 1
shows the time-of-flight mass spectrum of compound V.
Phase behavior. We confirmed the liquid-
crystalline behavior of the substances in the study by
thermal polarization microscopy and differential
scanning calorimetry (see the table). The data of two
methods are in good agreement.
Scheme 2 reflects the main directions of the
characteristic fragmentation of compound V and the
presence of its molecular ion, as well as the com-
As the initial liquid-crystalline compound was used
p-dodecyloxybenzoic acid, from which was obtained
p-dodecyloxybenzoyloxybenzoic acid III, which also
Scheme 2.
4
09.55
M+Na] 432.54
[M+K] 448.64
[
1
85.32
2
89.44
[
M+Na] 208.31
[
M+Na] 312.43 381.54
[
M+K] 224.41
[
M+Na] 404.53
M+K] 420.63
517.65
[M+Na] 540.64
[
M+K] 328.53
[
O
[M+K] 556.74
H C
5 12
O
O
O
2
CH2 H C
2
O
H
C
2
C
N
HN
CH3
H
1
[
[
69.33
M+Na] 192.32
M+K] 208.42
OH
2
[
[
61.43
M+Na] 284.42
M+K] 300.52
393.55
[
M+Na] 416.54
2
[
[
73.44
M+Na] 296.43
M+K] 312.53
[M+K] 432.64
530.67
[M+Na] 553.66
M+Na] 448.54
601.76
[M+Na] 624.75
[M+K] 640.85
425.55
[
[
M+K] 569.76
[
M+K] 464.64
3
[
[
05.44
M+Na] 328.43
M+K] 344.53
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 9 2011

1
856
CHERVONOVA et al.
The phase transition temperatures according to the dif-
ferential scanning calorimetry (DSC) in the heating cycle
transition to isotropic phase at 219.57°C with sub-
sequent repetition upon cooling.
T
phase1
,
ΔH
1
,
T
phase2
,
ΔH
2
–1
,
T
iso
,
ΔHiso
,
Compound
The compounds obtained were characterized by
thin-layer chromatography, elemental analysis, IR,
NMR spectroscopy, mass spectrometry, and by the
data of differential scanning calorimetry. The final
aldehyde and the azomethine obtained from it show
liquid-crystalline phase behavior.
–
1
–1
°
С
J g
°С
J g
°С
J g
С
С
C
26
33
37
Н
34
Н
38
H
48
O
5
O
7
N
2
(III) 125.14 54.04 212.72 9.01 220.5 15.86
a
a
(IV) 112.04 64.4 163.39 (4.47) 172.76 (4.47)
(V) 88.67 8.38 110.12 0.69 219.57 117.54
O
6
a
In parentheses the total area of two peaks is shown.
EXPERIMENTAL
exhibits the mesomorphic properties (see the table) [2].
These results suggest that increasing the length of the
molecule while maintaining its ability to form dimers
by hydrogen bonds between the terminal carboxy or
aldehyde groups should not lead to changes in the
liquid-crystal properties. At the introduction of
protective group to the carboxy group the substance
loses mesomorphic phase transitions and only a low-
temperature crystal–melt transition occurs. Indeed, in
the cycle of first heating of aldehyde IV at 105°C a
transition was registered of the crystal to the
mesophase which existed in the temperature range
All reagents and solvents were of chemically pure
grade and were used without further purification. IR
spectra of compounds were recorded on a Bruker
–
1
Vertex 80V device in the regions of 7500–370 cm
–
1
and 670–190 cm from pellets with KBr. The NMR
1
13
spectral studies on the nuclei H (500.17 MHz) and C
125.76 MHz) were performed on a Bruker Avance-
00 instrument. Elemental analyses of crystalline
(
5
compounds were carried out on a FlashEA 1112
analyzer. Mass spectra were recorded using the
MALDI–TOF method on a Bruker Daltonics Ultraflex
mass-spectrometer in the positive ion mode using
reflection option, the matrix was 2,5-dihydroxybenzoic
acid. Thin layer chromatography was performed on the
chromatographic plates PolyGRAM, Sil G/UV 254,
eluent chloroform. Termopolarization microscopy was
performed on a MIN-8 microscope with a heating plate
of the original design.
1
05–120°C (Fig. 2).
At 125°C an increase of mesomorphic spherulites
in the mesophase occurs, presumably of A-smectics,
which at 140°C transforms into the nematic phase. The
transition to the isotropic phase was fixed at 155°C. A
scheme of the phase behavior is as follows: Cr 105 M1
1
20 SmA 140 N 155 I in the cycle of heating. In the
Benzyl p-hydroxybenzoate (I). Samples of p-
hydroxybenzoic acid (15 g, 0.109 mol) and anhydrous
Na CO (11.55 g, 0.109 mol) were dissolved in DMF
cooling cycle the reverse is true: I 152 SmA 110 N 138
M 85 Cr. The latter observation allows to assert that
1
2
3
compound IV is an enantiotropic liquid crystal.
(
100 ml). At stirring benzyl chloride (12.54 ml,
For azomethine V two mesophases are typical in
the heating cycle, at 88.67 and 110.12°C, and the
0.109 mol) was added and the reaction mixture was
stirred for 12 h at room temperature. The solution was
Т
phase1
2
nd heating
Т
phase2 iso
Т
Т
Т
iso
phase1
1
st cooling
Т
phase1
Т, °C
Fig. 2. DSC curves of 4,4'-dodecyloxybenzoyloxybenzoyl-4-hydroxy-2-hydroxybenzaldehyde in the heating and cooling cycles.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 9 2011

SYNTHESIS OF LIQUID-CRYSTALLINE
1857
then mixed with 200 ml of distilled water, extracted
with diethyl ether (5×25 ml), the combined organic
extracts were washed with water (3×25 ml) and NaCl
solution (20 ml). The organic layer was dried over
anhydrous Na SO and concentrated in a vacuum. The
Pd/C (2.7 g) was added, and the mixture was stirred at
40°C under hydrogen for 1 h. The reaction mixture
was filtered and the solvent was distilled in a vacuum.
The resulting product was recrystallized from a
mixture of 1,4-dioxane–petroleum ether (bp 60–80°C).
Yield 92% (9.9 g), mp 220.5°C. IR spectrum of III, ν,
2
4
residue was purified by recrystallization from a
CH Cl –hexane (1:6) mixture. Yield 93.7% (23.04 g),
–
1
cm : 3070, 2972 s (aromatic C–H), 2851 s
[(CH ) CH ), 1732 s (C=O), 1688 s [C(O)O], 1261,
2
2
mp 121°C. Found, %: C 73.06, H 5.71, O 21.23.
C H O . Calculated, %: C 73.67, H 5.3, O 21.03. IR
2
n
3
1470 s (symmetric vibrations of aromatic ring), 1292,
1
4
12
3
–
1
1
spectrum, ν, cm : 3497.43 m (intramolecular hyd-
1161 s [Alk–P–OC(Ph)]. H NMR spectrum (CDCl ,
3
rogen bond), 3388.42 s (OH), 3091.40, 3027.06 s
TMS), δ, ppm: 0.86–0.90 t (3H,CH ), 1.26–1.51 m
3
(
aromatic C–H), 2948.44 s (CH ), 1685.05 s (C=O),
(18H, 9CH ), 1.79–1.86 q (2H, PhOCH CH ), 4.03–
2
2
2
2
1
605.45, 1585.28 s (aromatic C–H), 856.02 s (sym-
metric vibrations of 1,4-disubstituted aromatic ring),
31.10, 697.73 s (symmetric vibrations of mono-
4.06 t (2H, PhOCH ), 6.97–6.99 d (2H, PhH), 7.32–
2
7.35 d (2H, PhH), 8.13–8.15 d (2H, PhH), 8.18–8.21 d
(2H, Ph–H). Found, %: C 73.61, H 8.3. C H O .
7
2
6
34
5
1
substituted aromatic ring). H NMR spectrum (DMSO-
Calculated, %: C 73.21, H 8.03.
d , TMS), δ, ppm: 5.28 s (2H, CH ), 6.83 d (2H, H–
6
2
13
Ph), 7.4 m (5H, H–Ph'), 7.82 d (2H, H–Ph). C NMR
4,4-Dodecyloxybenzoyloxybenzoyl-4-hydroxy-2-
hydroxybenzaldehyde (IV). Weighed samples of
compounds III (6 g, 0.014 mol) and 2,4-dihydroxy-
benzaldehyde (1.94 g, 0.014 mol) were dissolved in
spectrum (DMSO-d , TMS), δ , ppm: 66.60, 113.96,
6
C
1
21.27, 127.88, 132.41, 135.5, 165.30. Mass spectrum,
+
m/z: (M 228.24), 228 [M ].
1
00 ml of CH Cl . Then a sample of dicyclohexyl-
2 2
Benzyl p-dodecyloxybenzoyloxybenzoate (II). A
mixture of compound I (6.7 g, 0.029 mol), 4-
dodecyloxybenzoic acid (9 g, 0.029 mol), catalytic
amount of dimethylaminopyridine, and water-free
CH Cl (100 ml) was stirred for 10 min, 6.66 g
carbodiimide (3.52 g, 0.017 mol) was added. The
mixture was stirred until complete dissolution of the
components, and then a catalytic amount of dimethyl-
aminopyridine was added. The reaction mixture was
stirred for 24 h. The precipitated urea was filtered off
on a glass frit. The solvent was distilled off on a rotary
evaporator. The resulting yellowish solid residue was
purified by chromatography on silica gel, eluent
chloroform. The product was recrystallized from
acetonitrile. Yield 6.18 g (80.46%), mp 172.76°C. IR
spectrum, ν, cm : 3450 s (intramolecular hydrogen
bond), 3099, 3053 s (aromatic C–H), 2956–2850 s
[(CH ) –CH ], 2771–2625 w (CHO), 1731 s (C=O),
1415, 1393 s (Ph–CHO), 1285–1149 s [Alk–P–
OC (Ph)], 829–795 s (symmetric vibrations of 1,4-
2
2
(
0.032 mol) of dicyclohexylcarbodiimide was added
and the mixture was stirred for 24 h at room tem-
perature. The precipitate was filtered off, the filtrate
was washed successively with 5% of acetic acid (2×
2
5 ml), 5% solution of NaOH (2×25 ml) and water
(
3×25 ml), dried over anhydrous Na SO . The solvent
2
4
–
1
was distilled off on a rotary evaporator. The resulting
yellowish solid residue was purified by chromato-
graphy on silica gel, eluent chloroform. The product
was recrystallized from a chloroform–acetonitrile
mixture. Yield 86% (13.1 g), mp 62–63°C. IR spec-
2 n 3
–
1
1
trum, ν, cm : 2918 s (aromatic C–H), 2851 s [(CH ) –
disubstituted aromatic ring). H NMR spectrum
2
n
CH ], 1732 s (C=O), 1470 s (symmetrical vibrations of
aromatic ring), 1292 s [Alk–C–O–C(Ph)]. H NMR
(CDCl , TMS) δ, ppm: 0.91 t (3H, CH ), 1.28 m (18H,
3
3
3
1
CH Alk), 1.85 t (2H, CH ), 4.06 t (2H,OCH Alk), 6.95
2
2
2
spectrum (CDCl , TMS), δ, ppm: 0.86–0.90 t (3H,
3
m (4H, H–Ph), 7.01 d (2H, H–Ph), 7.62 d (2H, H–Ph),
8.15 d (2H, H–Ph), 8.26 d (2H, H–Ph), 9.9 s (1H,
CH ), 1.27–1.50 m (18H, 9CH ), 1.78–1.85 q (2H,
3
2
1
3
PhOCH CH ) 4.02–4.06 m (2H, PhOCH ), 5.38 s (2H,
2
2
2
PhCOH), 11.29 s (1H, PhOH). C NMR spectrum
OCH Ph), 6.96–6.98 d (2H, PhH), 7.28–7.30 d (2H,
2
(
CDCl , TMS), δ , ppm: 13.66, 14.65, 21.73, 22.72,
3 C
PhH), 7.35–7.46 m (5H, Ph–H), 8.12–8.16 m (4H, Ph–
H). Found, %: C 76.65, H 7.94. C H O . Calculated,
2
1
1
8.64, 69.4, 110.19, 113.37, 114.7, 115.08, 118.66,
20.81, 126.10, 131.31, 131.81, 132.62, 133.11, 134.38,
35.66, 155.74, 157.52, 163.19, 163.44, 164.24,
33
40
5
%: C 76.71, H 7.80.
p-Dodecyloxybenzoyloxybenzoic acid (III). A
weighed sample of compound II (13.1 g, 0.025 mol)
194.79, 196.21. Mass spectrum, m/z: (M 546.65), 545
+
[M ]. Found, %: C 71.54, H 7.83, O 20.63. C33N O .
38 7
was dissolved in 1,4-dioxane (100 ml), a catalyst 5%
Calculated, %: C 72.51, H 7.01, O 20.48.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 9 2011

1
858
CHERVONOVA et al.
4,4'-Dodecyloxybenzoyloxybenzoyl-4-salicylidene-
ACKNOWLEDGMENTS
N'-ethyl-N-ethylenediamine (V). A sample of com-
pound IV (0.45 g, 0.82 mmol) at permanent stirring
was dissolved in a mixture of 30 ml of ethyl alcohol
and 20 ml of benzene. An alcohol solution (10 ml) of
N-ethylethylenediamine (0.07 g, 0.82 mmol) was
added, and azeotrope (alcohol–benzene–water) was
distilled off from the reaction mixture with the Dean–
Stark trap. The reaction mixture was stirred for 2 h,
and the solvent was distilled off in a vacuum of a
water-jet pump. The product was recrystallized from
an acetone–chloroform mixture. Yield 0.38 g (75%),
This work was financially supported by the grant of
the President of Russian Federation, no. MK-1625.2009.3.
The authors are grateful to Yu.G. Gorbunova
(Institute of Organic and Inorganic Chemistry,
Moscow) for the help in mass-spectrometric studies
and to O.B. Agapova (Ivanovo State University) for
performing thermomicroscopy.
REFERENCES
1
. Weigand–Hilgetag, Organisch-Chemische Experimenti-
erkunst, Suvorov, N.N., Ed., Moscow: Khimiya, 1968.
–
1
mp 219°C. IR spectrum, ν, cm : 3320 s (OH, NH),
3
1
1
068 w (aromatic C–H), 2921–2848 s [(CH ) –CH ],
729 s (C=O), 1639 s (CH=N bending), 1605 (Ar),
250 s (in-plane bending vibrations of 1,2,4-
2. Shreenivasa Murthy, H.N. and Sadashiva, B.K., Liquid
Crystals, 2004, vol. 31, no. 10, p. 1347.
2
n
3
3
. Murray, A. and Williams, D.L., Organic Syntheses with
Isotopes, Moscow: Inostrannaya Literatura, part 1,
substituted aromatic ring), 1166 s (C–O–C), 1100 w
Alk–C–OC(Ph)], 891–846 s (out-of-plane bending
1
961.
[
1
4. Bredfield, A.E. and Jones, B., J. Chem. Soc., 1929, part 2,
vibrations of 1,2,4-substituted aromatic ring). H NMR
spectrum [(CD ) CO, TMS], δ, ppm: 0.88 s (3H, CH ),
1
p. 2660.
3
2
3
5. Jones, B., J. Chem. Soc., 1935, part 2, p. 1874.
.09 t (3H, CH ), 1.29 m (8H, CH Alk), 1.49 s (2H,
3 2
6
. Deng-Ke, Yang and Shin Tson, Wu, Fundamentals of
Liquid Crystal Devices, Chichester: John Wiley & Sons,
2006.
CH ), 1.77 t (1H, NH), 2.70 t (2H, CH NH), 3.34 d
2
2
(
2H, =N–CH ), 4.03 q (2H, OCH Alk), 4.15 d (2H,
2 2
OCH CH Alk), 6.87 m (2H, H–Ph), 6.95 m (2H, H–
Ph), 7.11 d (2H, H–Ph), 7.32 d (2H, H–Ph), 7.79 d
7. Pelzl, G., Diele, S., and Weissflog, W., Adv. Mater.,
999, vol. 11, p. 707.
2
2
1
8
. Sadashiva, B.K., Raghunathan, V.A., and Pratibha, R.,
(
9
1H, CH=N), 7.89 (m, 1H, H–Ph), 8.13 (d, 2H, H–Ph),
.9 s (1H, Ph–COH). C NMR spectrum [(CD ) CO,
3 2
1
3
Ferroelectrics, 2000, vol. 243, p. 249.
9
. Shreenivasa Murthy, H.N. and Sadashiva, B.K., Liquid
Crystals, 2002, vol. 29, p. 1223.
TMS], δ , ppm: 14.90, 26.69, 39.80, 44.08, 49.38,
C
6
8.82, 115.68, 122.75, 129.97, 133.06. Mass spectrum,
1
0. Denieul, M.P., Laursen, B., Hazell, R., and Skrydstrup, T.,
+
m/z: (M 616.79), 618.73 [M ]. Found, %: C 72.57, H
J. Org. Chem., 2000, vol. 65, p. 6052.
7
7
.94, N 4.43, O 15.06. C H N O . Calculated, %: C
37 48 2 6
2.05, H 7.84, N 4.54, O 15.56.
11. Saghatforoush, L.A., Aminkhani, A., and Chalabian, F.,
Transition Met. Chem., 2009, vol. 34, p. 899.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 9 2011