2-Hydroxybenzoic acid esters: Synthesis, complexes with Tb(III), and their luminescence characteristics

Article abstract of DOI:10.1134/S1070427214060202

New esters of 2-hydroxybenzoic acid and 4-(4-alkoxybenzoyloxy)phenols, forming liquid crystals, were synthesized. These compounds in solution form complexes with Tb(III), exhibiting photoluminescence properties.

Full text of DOI:10.1134/S1070427214060202

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2014, Vol. 87, No. 6, pp. 787−792. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © R.V. Kondrat’eva, N.S. Novikova, S.B. Meshkova, Z.M. Topilova, P.G. Doga, 2014, published in Zhurnal Prikladnoi Khimii, 2014,
Vol. 87, No. 6, pp. 783−789.
ORGANIC SYNTHESIS AND INDUSTRIAL
ORGANIC CHEMISTRY
2
-Hydroxybenzoic Acid Esters: Synthesis, Complexes
with Tb(III), and Their Luminescence Characteristics
R. V. Kondrat’eva, N. S. Novikova, S. B. Meshkova, Z. M. Topilova, and P. G. Doga
Bogatsky Physicochemical Institute, National Academy of Sciences of Ukraine,
Lustdorfskaya Doroga 86, Odessa, 65080 Ukraine
e-mail: nadyanovikova@rambler.ru
Received February 25, 2014
Abstract—New esters of 2-hydroxybenzoic acid and 4-(4-alkoxybenzoyloxy)phenols, forming liquid crystals, were
synthesized. These compounds in solution form complexes with Tb(III), exhibiting photoluminescence properties.
DOI: 10.1134/S1070427214060202
Complexation of lanthanide ions with 2-hydroxy-
benzoic (salicylic, Sal) acid have been comprehensively
studied. Kotova et al. [1] reported both homoligand com-
RESULTS AND DISCUSSION
Intermediate 4-(4-alkoxybenzoyloxy)phenols 2 were
synthesized by the reaction of the corresponding 4-alk-
oxybenzoic acids 1 with a threefold excess of 1,4-di-
hydroxybenzene in anhydrous benzene with addition
of pyridine for binding HCl. The yield of compounds 2
was no more than 20%. An attempt was made to prepare
plexes Tb(Sal) and heteroligand complexes with neutral
3
O-donor compounds: Tb(Sal) TPPO, Tb(Sal) (TPPO) ,
3
3
2
Tb(Sal) TOPO, and Tb(Sal) (TOPO) , where TPPO is
3
3
2
triphenylphosphine oxide and ТОРО is trioctylphosphine
oxide.
4
-(4-alkoxybenzoyloxy)phenols 2 by the procedure de-
Studies of the complexes and thin films based on
them showed that these compounds are promising elec-
troluminescent materials. Complexes of lanthanides with
organic ligands are characterized by high quantum yield,
which determines wide possibilities of using them in
optoelectronics [2, 3]. It is known from published data
that liquid crystal compounds used as emission layers in
organic light-emitting diodes allow improvement of their
characteristics [4, 5].
scribed in [6], using as intermediate hydroquinone sodium
salt, but the yield in this case was about 1.5%.
It should be noted that low yield of intermediate
4-(4-alkoxybenzoyloxy)phenols 2 is a drawback of the
above-described procedure for preparing 2-hydroxy-
benzoic acid derivatives esterified at the carboxy group.
Therefore, we developed a procedure for preparing
4-(4-alkoxybenzamido)phenol 3 in a fairly good yield
(
40%) (see scheme). The structure of the intermedi-
In this study we examined the influence exerted by the
structure of new 2-hydroxybenzoic acid esters on their
mesogenic ability and complexation with lanthanides, and
also on the absorption and luminescence characteristics
of their lanthanide complexes. 2-Hydroxybenzoic acid
esters, 2-[4-(4-alkoxybenzoyloxy)phenoxycarbonyl]
phenols 5a–5d and 6, were synthesized via the scheme
shown below.
1
ate phenols 2a–2d and 3 was determined by H NMR
spectroscopy and mass spectrometry. The mass spectra
of compounds 2a–2d and 3 contain peaks of molecular
ions. The spectroscopic characteristics, yields, and melt-
ing points of the intermediate 4-(4-alkoxybenzoyloxy)
phenols 2a–2d and 4-(4-hexyloxybenzamido)phenol 3
are given in Table 1.
7
87

788
KONDRAT’EVA et al.
Scheme 1. Synthesis of 2-hydroxybenzoic acid esters.
Final products 5a–5d and 6 were synthesized by the
of 2-[4-(4-hexyloxybenzamido)phenoxycarbonyl]-
phenol 6}, the mesogenic properties disappear, and the
melting point increases.
reaction of 2-hydroxybenzoyl chloride 4, which had been
prepared in a thionyl chloride solution, with the corre-
sponding phenols 2а–2d and 3, taking into account the
protocol described in [7].
Experiments on complexation of Tb(III) ions with
compounds 5a–5d and 6 were performed in mixtures
of organic solvents (Table 3). A study by the method of
molar ratios showed that ligands 5a–5d form tris-chelates
with Tb(III). The intensity of the Tb(III) luminescence
increases in proportion to the number of carbon atom in
the terminal alkoxy group. In the Tb(III) complex with
compound 6 containing an amide group, the component
ratio is 1 : 1. Figure 1 shows the excitation and lumines-
cence spectra of Tb(III) chloride and of the Tb(III) com-
plexes with 2-[4-(4-alkoxybenzoyloxy)phenoxycarbonyl]
phenol 5а and o-hydroxybenzoic (salicylic) acid which
forms in the structure of 5a the coordination core with
the Tb(III) ion.
The structures of the final products 5a–5d and 6 were
1
determined by H NMR spectroscopy. The mass spectra
do not contain peaks of molecular ions, only fragmenta-
tion ions are detected. The spectroscopic data and yields
are given in Table 2.
The mesomorphic properties of 2-[4-(4-alkoxybenzo-
yloxy)phenoxycarbonyl]phenols 5a–5d were determined
by polarization microscopy. The phase transition tempera-
tures are given in Table 3.
As seen from Table 3, compounds 5а–5d are char-
acterized by mesomorphism typical of rod-like liquid
crystals: Homologs 5a and 5c formed an enantiotropic
nematic phase, and compounds 5b and 5d formed smectic
phases.
As seen from the excitation spectrum of the Tb(III)
complex with ligand 5а, its strongest luminescence can
be observed upon UV excitation at λ = 307 nm. The
luminescence spectrum contains bands corresponding
On introduction of an amide group into the struc-
ture of 2-hydroxybenzoic acid derivatives {preparation
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2
-HYDROXYBENZOIC ACID ESTERS
789
Table 1. Properties of 4-(4-alkoxybenzoyloxy)phenols 2a–2d and 4-(4-hexyloxybenzamido)phenol 5
Found, %/Calcu-
Mass
Yield,
%
lated, %
1
Compd.
Tm, °C
Formula spectrum,
H NMR spectrum, δ, ppm (DMSO-d , 500 MHz)
6
+
[
M ]
С
Н
N
–
C H O
329
343
371
454
2
a
25.0 103–4 73.27 7.50
3.14 7.37
20 24
4
4
4
4
10.51 s (1Н, ОН), 7.98 d (2Н, ArOН), 7.14 d (2Н,
ArOAlk), 7.05–6.86 m (2Н, ArOAlk + 2Н, ArOH),
7
3
1
.97 t (2Н, ОСН ), 1.82–1.65 m (2Н, ОСН СН ),
2
2
2
.5–1.1 m (8Н, СН ), 0.87 t (3Н, СН )
2
3
C H O
2
b
8.3 107–8 73.57 7.82
3.66 7.65
–
–
–
21 26
10.51 s (1Н, ОН), 7.98 d (2Н, ArOН), 7.14 d (2Н,
ArOAlk), 7.05–6.86 m (2Н, ArOAlk + 2Н, ArOH),
7
3
1
.97 t (2Н, ОСН ), 1.82–1.65 m (2Н, ОСН СН ),
2
2
2
.5–1.1 m (10Н, СН ), 0.86 t (3Н, СН )
2
3
C H O
2
c
20.0 102– 75.41 7.10
04 75.33 7.20
23 30
10.51 s (1Н, ОН), 7.97 d (2Н, ArOН), 7.13 d (2Н,
ArOAlk), 7.05–6.85 m (2Н, ArOAlk + 2Н, ArOH),
1
3
1
.96 t (2Н, ОСН ), 1.8–1.65 m (2Н, ОСН СН ),
2
2
2
.5–1.1 m (14Н, СН ), 0.86 t (3Н, СН )
2
3
C H O
2
d
18.0 110– 83.97 8.82
13 83.85 8.96
29 42
8.13 d (2Н, ArOAlk), 7.03 d (2Н, ArOAlk), 6.96 d
(
1
2Н,ArOH), 6.83 d (2Н, ArOH), 4.04 t (2Н, ОСН2),
1
.82–1.77 m (2Н, ОСН СН ), 1.52–1.42 m (2Н,
2 2
ОСН СН СН ), 1.40–1.20 m (24Н, СН ), 0.88 t (3Н,
2
2
2
2
СН ); solvent CDСl
3
3
C H NO
314
3
40.0 205–6 73.01 7.51 4.27
2.82 7.40 4.47
19 23
3
9.84 s (1Н, ОН), 9.20 s (1Н, NH), 7.93 d (2Н,
ArOAlk), 7.52 d (2Н, ArOН), 7.02 d (2Н, ArOAlk),
7
6
.74 d (2Н, ArOН), 4.04 t (2Н, ОСН ), 1.90–1.68 m
2
(
2Н, ОСН СН ), 1.5–1.1 m (6Н, СН ), 0.87 t (3Н,
2 2 2
СН3)
3 ×106
5
to transitions from the radiative level of terbium, D , to
4
7
sublevels of its ground state, F (j = 6, 5, 4, 3, 2). In the
j
spectrum of terbium chloride (TbCl ) at the same con-
3
centration, there is a band corresponding to the transition
5
7
2 ×106
D → F (λ = 543 nm), hypersensitive to the ligand field
4
5
effect. The intensity of this luminescence band for 5a is
2
0 times higher.
Under identical conditions of recording the spectra,
the luminescence intensity of the aqueous solution of the
Tb(III) complex with salicylic acid is 2.7 times higher
compared to the complex with 5а, which may be due
to the influence of the long conjugation chain on the
efficiency of the energy transfer from the ligand in the
excited state to the central ion.
1 ×106
λ, nm
It follows from the above data that these complexes
are characterized by strong luminescence owing to the
formation of a strong six-membered chelate ring and to
efficient intramolecular transfer of the excitation energy
from the ligand to the central ion.
Fig. 1. Excitation (λlum = 543 nm) and luminescence spectra of
1) terbium(III) chloride and terbium(III) complexes with (2) li-
gand 5а (λ = 307 nm) and (3) salicylic acid (λ = 322 nm).
(
exc
exc
–4
–3
–4
сTb = 1 × 10 , с = 1 × 10 , с = 5 × 10 M; the spectra were
5а
Sal
recorded under equal conditions. (Ilum) Luminescence intensity
and (λ) wavelength.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 6 2014

790
KONDRAT’EVA et al.
Table 2. Properties of final products 5a–5d and 2-[4-(4-hexyloxybenzamido)phenoxycarbonyl]phenol 6
Found, %/Calculated, %
Yield,
%
1
Compd.
Formula
H NMR spectrum, δ, ppm (CDCl , 500 MHz
3
С
Н
N
–
5
a
16.0
72.27
7.50
7.37
C H O 10.49 s (1Н, ОН), 8.17 d (2Н, Н-16,20), 8.10 d (1Н, Н-3), 7.60–7.54 m
27 28 6
7
2.30
(1Н, Н-5), 7.34–7.29 m (4Н, Н-9,10,12,13), 7.10–7.04 m (1Н, Н-4),
.04–6.96 m (3Н, Н-6,17,19), 4.07 t (2Н, ОСН ), 1.90–1.80 m (2Н,
7
2
ОСН СН ), 1.55–1.45 m (2Н, ОСН СН СН ), 1.45–1.25 m (6Н,
2
2
2
2
2
СН ), 0.92 t (3Н, СН )
2
3
5
b
16.0
32.0
12.0
23.0
72.60
2.71
6.67
6.54
–
–
–
C H O 10.49 s (1Н, ОН), 8.17 d (2Н, Н-16,20), 8.10 d (1Н, Н-3), 7.60–7.54 m
28 30 6
(1Н, Н-5), 7.34–7.29 m (4Н, Н-9,10,12,13), 7.10–7.04 m (Н, Н-4),
7
7
.04–6.96 m (2Н, Н-6,17,19), 4.07 t (2Н, ОСН ), 1.90–1.80 m (2Н,
2
ОСН СН ), 1.55–1.45 m (2Н, ОСН СН СН ), 1.45–1.25 m (8Н,
2
2
2
2
2
СН ), 0.92 t (3Н, СН )
2
3
5
c
73.46
3.35
6.99
6.87
C H O 10,49 s (1Н, ОН), 8.27 d (2Н, Н-16,20), 8.10 d (1Н, Н-3), 7.60–7.54 m
30 34 6
(1Н, Н-5), 7.42–7.30 m (4Н, Н-9,10,12,13), 7.19–7.09 m (1Н, Н-4),
7
7
.00–6.89 m (2Н, Н-6,17,19), 4.07 t (2Н, ОСН ), 1.90–1.80 m (2Н,
2
ОСН СН ), 1.55–1.45 m (2Н, ОСН СН СН ), 1.45–1.25 m (12Н,
2
2
2
2
2
СН ), 0.92 t (3Н, СН )
2
3
5
d
75.17
5.23
8.22
8.07
C H O 10.49 s (1Н, ОН), 8.25 d (2Н, Н-16,20), 8.10 d (1Н, Н-3), 7.60–7.54 m
36 46 6
(1Н, Н-5), 7.34–7.29 m (4Н, Н-9,10,12,13), 7.10–7.04 m (1Н, Н-4),
7
7
.04–6.96 m (2Н, Н-6,17,19), 4.07 t (2Н, ОСН ), 1.90–1.80 m (2Н,
2
ОСН СН ), 1.55–1.45 m (2Н, ОСН СН СН ), 1.45–1.25 m (24Н,
2
2
2
2
2
СН ), 0.92 t (3Н, СН )
2
3
6
72.19
2.07
6.13
6.28
3.37 C H NO 10.48 s (1Н, ОН), 8.10 d (1Н, NH), 7.95–7.7 m (5Н, Н-10,12,16,20 +
26 27 5
Н-3), 7.65–7.5 m (1Н, Н-5), 7.35–7.2 m (2Н, Н-9,13), 7.15–6.9 m
7
3.23
(
4Н, Н-4,6,17,19), 4.05 t (2Н, ОСН ), 1.95–1.75 m (2Н, ОСН СН ),
2
2
2
1
.65–1.30 m (6Н, СН ), 0.94 t (3Н, СН )
2
3
Another important characteristic of luminescent lan-
thanide complexes is their resistance to prolonged UV
The plots show the mean values from three replicate
measurements (deviation 3–5%). Comparison of these
plots shows that a mixture of methanol with benzene
(1 : 1) ensures fairly high stability of the emission in time.
irradiation. Its study for the complex Tb[Lig(5b)] shows
3
that the stability is different in different solvents (Fig. 2).
Table 3. Mesomorphism of ligands 5a–5d and 6 and luminescence characteristics of their Tb(III) complexes
Tb(III) complexes
a
Compound
n
Phase transition temperatures, °C
solvent
Tb : Lig Ilum, a arb. units, at λ = 545 nm
5
a
7
8
Cr 66.8 N 87.2 I 64.0 N 58.7 Cr
Cr 71.0 SmA 76.0 SmC 97.0 I
80
5
b
106
MeOH + PhH (1 : 1)
1 : 3
5
c
10 Cr 87.0 N 120.0 I 115.0 N 80.0 Cr
126
5
d
16
6
Cr 73.0 SmA 91.0 I
Cr 215.0 I
200
6
MeOH + ТHF (1 : 1)
1 : 1
87
a
b
(
Сr) Solid crystal, (SmA, SmС) modifications of the smectic phase, (N) nematic phase, and (I) isotropic liquid.
The values of Ilum are reduced to common experimental conditions.
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2
-HYDROXYBENZOIC ACID ESTERS
791
The data we obtained show that it is appropriate to further
study lanthanide complexes with 2-[4-(4-alkoxybenzoyl-
oxy)phenoxycarbonyl]phenols 5a–5d with the aim to
reveal their electroluminescence.
EXPERIMENTAL
τ, min
1
The Н NMR spectra of 5–10% solutions of com-
Fig. 2. Variation of the luminescence intensity Ilum of the Tb
complex with ligand 5а in the course of continuous UV irra-
pounds in CDCl or DMSO-d were recorded on a Bruker
Avance DRX 500 spectrometer operating at 500 MHz;
internal reference TMS.
3
6
–4
–3
diation. сTb = 1 × 10 , с = 1 × 10 M. Solvent: (1) metha-
5а
nol–benzene (1 : 1) and (2) methanol–tetrahydrofuran (1 : 1).
(τ) Irradiation time.
The mass spectra were taken with an MKh-1321 spec-
trometer using a direct inlet system at the ionizing electron
energy of 70 eV and ionization chamber temperature of
required volume (5 or 10 mL) with the solvents, mixed,
and left for 30 min for the complex formation.
2
20°С, and also with a VG 70-70EQ mass spectrometer
in the fast atom bombardment mode using a beam of Xe
atoms with an energy of 8 keV and m-nitrobenzyl alcohol
and polypropylene glycols as matrices.
4-Alkoxybenzoyl chlorides 1 were synthesized as
described in [8]. The yields, vacuum distillation condi-
tions, and refractive indices of the compounds obtained
are given in [9].
The phase transition temperatures were studied by po-
larization microscopy with a POLAM R-312 microscope.
2-Hydroxybenzoyl chloride 4. 1.0 g (0.007 mol) of
2
-hydroxybenzoic acid was refluxed for 13 h in 20 mL
The luminescence spectra of terbium ions (λlum
=
of thionyl chloride with the addition of 1 mL of abso-
lute dimethylformamide. The reaction behavior was
monitored by thin-layer chromatography (TLC). Excess
thionyl chloride was distilled off at reduced pressure,
and the residue was washed first with cold (2 × 10 mL)
and then with warm (2 × 15 mL) anhydrous benzene.
The compound was used in further synthesis without
additional purification.
5
45 nm) were recorded in the range 450–700 nm with
a Fluorolog FL3-22 fluorimeter (Yobin Yvon, France)
equipped with a xenon lamp and with an SDL-1 diffrac-
tion spectrometer (Leningrad Optical and Mechanical
Association, Russia) equipped with an FEU-79 pho-
tomultiplier. The luminescence of the complexes was
excited with a DRSh-250 mercury lamp. The radiation
with λ 313 and 365 nm was cut out with a UFS-1 light
filter. The solution spectra were recorded using a quartz
cell with the absorbing layer thickness of 1 cm.
4-(4-Alkoxybenzoyloxy)phenols 2a–2d (general
procedure).Asolution of 0.033 mol of appropriate 4-alk-
oxybenzoyl chloride in 20 mL of anhydrous benzene
was added dropwise over a period of 4 h to a solution
of 0.099 mol of 1,4-dihydroxybenzene in 70 mL of an-
hydrous benzene and 2.7 mL of absolute pyridine. The
mixture was stirred for 20 h at room temperature. The
reaction progress was monitored by TLC in the chlo-
roform–methanol system (10 : 1). The precipitate was
filtered off, washed with water (4 × 50 mL), and dried.
To study the complexation of Tb(III) ions with the
synthesized compounds, we prepared a 0.1 M solution
of terbium chloride by dissolution of high-purity terbium
oxide (99.988%) in hydrochloric acid (1 : 1), followed by
evaporation of the excess acid. The dry residue was dis-
solved in methanol and diluted to the required volume in
a volumetric flask. The concentration of Tb(III) ions was
determined by complexometric titration. The 0.1 M stock
solutions of reagents were prepared by dissolving their ac-
curately weighed portions in benzene or tetrahydrofuran.
The working solutions of terbium chloride and reagents
of lower concentrations were prepared by dilution of
the stock solutions. The required volume of a 0.01 M
4-(4-Hexyloxybenzamido)phenol 3. A solution
of 5.5 g (0.02 mol) of 4-hexyolxybenzoyl chloride in
10 mL of absolute chloroform was slowly added at
room temperature with stirring to a solution of 4.4 g
(0.04 mol) of p-aminophenol in 20 mL of absolute
dimethylformamide. Stirring at room temperature was
continued for 12 h. Then, the reaction mixture was
poured onto crushed ice (300 mL), and the precipitate
was filtered off, washed with cold water (2 × 200 mL),
TbCl solution was charged into a test tube, and a 0.01 M
working solution of the reagent was added to obtain the
component concentration ratio Tb : Lig equal to 1 : 3 (for
3
5
а–5d) and 1 : 1 (for 6). The mixture was brought to the
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 6 2014

792
KONDRAT’EVA et al.
and crystallized three times from alcohol in the presence
of activated carbon. Yield 2.5 g.
ions with the Tb : ligand ratio of 1 : 3. Their photolumi-
nescence increases with an increase in the length of the
terminal alkoxy group.
2
-[4-(4-Alkoxybenzoyloxy)phenoxycarbonyl]-
phenols 5a–5d and 2-[4-(4-hexyloxybenzamido)-
phenoxycarbonyl]phenol 6 (general procedure). An-
hydrous pyridine (0.005 mol) was added to a solution of
(3) The Tb(III) complex with 2-[4-(4-hexyloxynbenz-
amido)phenoxycarbonyl]phenol with the Tb : ligand ratio
of 1 : 1 is not inferior to its oxygen-containing analog in
the photoluminescence intensity.
0
.0035 mol of appropriate phenol in 15 mL of absolute
benzene. A solution of 0.005 mol of salicyl chloride in
mL of absolute benzene was added with stirring and
5
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tallized twice from 100 mL of alcohol in the presence of
activated carbon, additionally washed with cold heptane
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{
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RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 6 2014