Synthesis, characterization and dielectric properties of new 5-(4-hydroxyphenyl)-10,15,20-tri-4-[2-(3-pentadecylphenoxy)ethoxy]phenyl porphyrin and their Ni, Co and Cu complexes

Article abstract of DOI:10.21577/0103-5053.20160261

New asymmetric cardanol-based porphyrins, free-base and coordinated with Ni, Co and Cu, were synthesized and completely characterized as A3B type. Such porphyrins were obtained aiming improved solubility in polar solvents due insertion of an -OH phenolic group. Their thermal and dielectric properties were also evaluated. Changes in the synthetic route reduced the reaction time and improved the yields of the aldehyde precursor obtainment. Electronic absorption spectra of the new porphyrins in CH₂Cl₂, EtOH and acetone, indicated a decrease in the ε (molar absorptivity) values with increasing solvent polarity, except for the nickel complex which, in acetone, showed a slight increase of 2percent in the ε value. The dielectric measurements showed that the conductivity (σ) and the loss tangent (tan δ) increased with frequency, but the permittivity (ε′) decreased. The results showed that the coordination of the porphyrin promoted a significant change in thermal and dielectric properties, specially for to the Ni-complex compound, which presented the best dielectric properties with interesting values of permittivity and loss tangent at 100 MHz (19.46 and 0.011 a.u., respectively).

Full text of DOI:10.21577/0103-5053.20160261

http://dx.doi.org/10.21577/0103-5053.20160261
J. Braz. Chem. Soc., Vol. 28, No. 6, 1063-1073, 2017.
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Article
Synthesis, Characterization and Dielectric Properties of New 5-(4-Hydroxyphenyl)-
10,15,20-tri-4-[2-(3-pentadecylphenoxy)ethoxy]phenyl porphyrin and Their Ni, Co
and Cu Complexes
João P. F. Mota,*,a Antônio E. da Costa Júnior,a Viviane G. P. Ribeiro,a Samuel G. Sampaio,a
Nayane M. A. Lima,a Fernando L. F. da Silva,a Claudenilson S. Clemente,a
Giuseppe Mele,b Diego Lomonacoa and Selma E. Mazzettoa
aLaboratório de Produtos e Tecnologia em Processos (LPT), Departamento de Química Orgânica e Inorgânica,
Universidade Federal do Ceará, Campus do Pici, 60440-900 Fortaleza-CE, Brazil
bDepartment of Engineering for Innovation, University of Salento, Lecce, Italy
New asymmetric cardanol-based porphyrins, free-base and coordinated with Ni, Co and Cu,
were synthesized and completely characterized asA3B type. Such porphyrins were obtained aiming
improved solubility in polar solvents due insertion of an −OH phenolic group. Their thermal and
dielectric properties were also evaluated. Changes in the synthetic route reduced the reaction time
and improved the yields of the aldehyde precursor obtainment. Electronic absorption spectra of the
new porphyrins in CH2Cl2, EtOH and acetone, indicated a decrease in the ε (molar absorptivity)
values with increasing solvent polarity, except for the nickel complex which, in acetone, showed
a slight increase of 2% in the ε value. The dielectric measurements showed that the conductivity
(σ) and the loss tangent (tan δ) increased with frequency, but the permittivity (ε’) decreased. The
results showed that the coordination of the porphyrin promoted a significant change in thermal
and dielectric properties, specially for to the Ni-complex compound, which presented the best
dielectric properties with interesting values of permittivity and loss tangent at 100 MHz (19.46
and 0.011 a.u., respectively).
Keywords: asymmetric porphyrins, cardanol, dielectric properties
Introduction
porphyrins has grown exponentially in order to control
their electronic and thermal properties.4 The addition
of substituents at the meso positions and metal ions in
the center of porphyrins can improve the electrical and
magnetic properties, protecting against auto-oxidation and
reducing the formation of dimers. However, these structural
modifications can promote, in some cases, a significant
decrease in their planarity.5
A simple way to obtain porphyrins is the acid
catalyzed condensation reaction of pyrrole with specific
aldehyde, followed by oxidation of the porphyrinogen.
This procedure, originally developed by Rothemund,6
has been refined by Adler-Longo,7-9 due to the addition
of metal salts to the reaction. Despite the modest yields,
the relative simplicity of this method has become suited
for preparation of large amounts of tetraarylporphyrins.
Higher yields and milder reaction conditions using
Lewis acid (TFA or BF3) as catalyst were obtained by
Lindsey et al.10 More recently, substituted asymmetrical
porphyrins (A3B, A2B2, etc.) were obtained via mixed
Porphyrins are relatively planar aromatic system
consisting of four pyrrole type rings joined by four
methynic carbons. They have attracted scientists from many
areas due to their biological importance, their fascinating
physical, chemical, and spectroscopic properties.1 These
compounds have a high electron density due to its
18 π-electrons delocalized on the macrocyclic ring, which
are responsible for their spectroscopic characteristics.2
Porphyrin and its derivatives play multiple roles in nature,
such as energy transfer and light absorption in a wide range
of the electromagnetic spectrum. Such features are of great
interest to the industry of optoelectronic components, such
as solar cells, due to its ability to act as photosensitizers
when irradiated under visible light.3 Thus, this is certainly
one of the most promising areas of application for these
compounds. The structural modeling and synthesis of new
*e-mail: jpfmota@yahoo.com.br

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Synthesis, Characterization and Dielectric Properties of New 5-(4-Hydroxyphenyl)
J. Braz. Chem. Soc.
aldehyde condensations, using a mixture of two different
aldehydes as starting materials.11-13
initial temperature of degradation at 352 °C (Tonset) and
other parameters as the final and the half decomposition
temperature (Tendset and T*, respectively), the residual
mass and the numbers of degradation stages were also
evaluated.22 The dielectric properties, like the loss tangent
(tan δ), permittivity (ε’) and conductivity (σ) are the
most important parameters to determine the suitability
for electronics applications.23,24 According to Lukichev,25
materials presenting high dielectric constant associated
with low loss tangent have important applications in
microelectronics. The measurements showed that 4b have
good dielectric permittivity (ca. 20 a.u.) and 4d had the
lowest permittivity (ca. 6 a.u.). These results suggest that
the metal promoted a significant change in thermal and
electrical properties of the asymmetric porphyrin.
Asymmetric porphyrins are molecules that exhibit
some advantages over the symmetric porphyrins (A4)
like: reduced aggregation, groups that allows the use of a
wide range of solvents, and presence of dipole moment,
which may facilitate the electron injection into the TiO2
conduction band.14 In addition, asymmetric porphyrins have
been synthesized seeking a better efficacy in photodynamic
therapy (PDT), since the cellular affinity depends on
amphiphilic character, that is, dependent on the structural
arrangement of groups hydrophilic (phenolic −OH or
carboxylic −COOH) and hydrophobic (alkyl or aryl chains)
meso-substituents in macrocycle.15,16
Some studies mention the synthesis of porphyrins
using cardanol as starting material,17-19 which provides
interesting lipophilic properties, besides being a substance
derived from a renewable raw material, the cashew nut
shell liquid (CNSL).20 Cardanol is a phenolic lipid and
the main constituent of the CNSL, a dark oil obtained
as a by product from industrial processing of the cashew
nut (Anacardium occidentale L.).21 It is known that the
presence of an alkyl chain or an aryl substituents in
porphyrins are important, not just for increase solubility
in organic solvents and influence the aggregation of these
materials, but also to modify its chemical characteristics and
photophysical properties.11 Here, we report the synthesis
and characterization of novel asymmetric cardanol-based
A3B porphyrins 4a-d (4a: metal-free, 4b: Ni, 4c: Co,
4d: Cu) as well as the study of their thermal and dielectric
properties. Scheme 1 shows the steps and reagents used in
the preparation of asymmetric porphyrins.
Results and Discussion
Synthesis
The synthesis of porphyrins starting from cardanol
are mentioned by many papers since 2004,26-29 and they
employed a procedure which consists in producing
an aldehyde derivative as precursor. Normally, this
precursor is compound 3 (4-[2-(3-pentadecylphenoxy)
ethoxy] benzaldehyde), obtained by a reaction between
compound 2 (1-(2-bromoethoxy)-3-pentadecylbenzene)
and 4-hydroxybenzaldehyde in acetone using anhydrous
potassium carbonate (K2CO3) as base, stirred for 24 h and
with 40% yield.
In this study, it was found that the replacement of the
base, K2CO3, by KOH, promoted a decrease on the yield
(about 25%), that can be associated with the deprotonation
of acetone present in the reaction as solvent.30 A new
reaction procedure using DMF as solvent and KOH as base
at 100 °C, provided a better yield (62%) of compound 3 in
From the thermogravimetric analysis (TGA) it was
possible to determine that the thermal stabilities of the
porphyrins 4a-d, in inert atmosphere, was in the following
order: 4a > 4d > 4c > 4b. In TGA, the porphyrin 4a showed
Scheme 1. Synthesis of asymmetric porphyrin 4a A3B type from cardanol, where (a) KOH, dibromoethane, 70 °C, 6 hours; (b) KOH, DMF, 100 °C,
6 hours; (c) 4-hydroxybenzaldehyde, CHCl3, BF3, DDQ, 1 hour; (d) acetate metal salts (Ni, 4b; Co, 4c; and Cu, 4d), chloroform/DMF, 3 hours, 90 °C.

Vol. 28, No. 6, 2017
Mota et al.
1065
only 6 hours of reaction. Based on the result of this new
procedure, it is possible to conclude that the DMF is not
affected by a strong base.
For free base porphyrin 4a, the characteristic chemical
shift of pyrrole N−H located into the porphyrin ring is
located at −2.73 ppm. If we assume equivalence 1 for the
peak at 8.84 ppm which was assigned to 8H (β-pyrrolic), the
integration of the other peaks can be related to the following
hydrogens: peak at 4.48-4.54 ppm to 12H (O−(CH2)2−O),
at 2.64 ppm to 6H (Ph−CH2), at 0.88 ppm to 9H (CH3) and
peak at 5.29 ppm to 1H (Ph−OH). These peaks indicated
that the porphyrin 4a is an asymmetric compound of A3B
type. After formation of complexes (4b-d), the signal
peak at −2.73 ppm disappeared, since the hydrogen atom
in the N−H bond is replaced by a metal ion.33 In some
paramagnetic metalloporphyrins the signals may be broad
due to the hyperfine electron-nuclear interactions and by
relaxation processes.11 Figure 1 shows that compounds 4c
(cobalt porphyrin) and 4d (copper porphyrin) presented this
phenomenon, thus indicating the paramagnetic character
of these metals. 13C NMR data to 4a showed signals that
confirm the presence of alkyl (13.85-35.83 ppm), ethers
(66.22 ppm) and aromatic groups (111.37-158.45 ppm).
Similar signals were observed for metalloporphyrins 4b-d
(Figure S1). The results indicated that compounds 4a-d
were obtained with good purity, which was confirmed
by mass spectrometry (MALDI-TOF, Figure S2) and
elemental analysis. The m/z for the molecular ion presented
the following values: 1669.938 (4a), 1726.860 (4b),
1726.907 (4c) and 1731.889 (4d).
Characterization
The chemical structures of the asymmetric porphyrin 4a
and its metal complexes 4b-d(A3B type) were characterized
1
using H and 13C nuclear magnetic resonance (NMR),
matrix-assisted laser desorption ionization-time of flight
mass spectrometry (MALDI-TOF-MS), elemental analysis,
UV-visible absorption, Fourier transform infrared (FTIR)
and fluorescence emission spectroscopy. The FTIR data are
listed in Table 1, which were consistent with the proposed
structures of the corresponding compounds. For compound
4a, the absorption bands at 3319 and 967 cm-1 are assigned
to the N−H stretching and in plane bending vibrations of
the pyrrole group, respectively.2 These absorption bands
disappeared in the spectra of metal complexes (4b-d),
since the hydrogen atom of the N−H bond is replaced by
a metal ion to form N−M bond, and a new metal-sensitive
absorption band appeared at ca. 1000 cm-1, which further
confirmed the formation of metal complexes.31 Moreover,
the presence of aliphatic groups in porphyrins 4a-d, are
also evident by the presence of absorbance peaks at 2923
and 2852 cm-1, which are characteristic of asymmetric and
symmetric νC−H modes, respectively.17 In addition, the
compounds exhibit absorption bands of the phenyl groups
at ca. 1610 cm-1, assigned to the C=C stretching vibration.32
Electronic absorption and luminescence spectra
Table 1. FTIR data to asymmetric porphyrins and its vibrations mode
Electronic absorption spectra of porphyrins 4a-d in
CH2Cl2, EtOH and acetone (Figure 2), show one intense
band in the near-ultraviolet region of the spectrum (Soret
or B band) and absorption bands at higher wavelengths
in the visible region (Q bands). The free base porphyrin
4a have four Q bands denoted as IV, III, II, and I,32 while
the metallated porphyrins presented one (4b and 4c) or
two Q bands (4d) due to the increase of symmetry of
the complexes.34 Characteristic Q and B (Soret) bands of
metalloporphyrins are determined by transitions of the
π-electrons between two higher occupied and two lower
unoccupied orbitals.35 Nevertheless, the changes in the
molecular structure and the effect of the solvent may alter
the spectra of the porphyrins.36 The molar absorptivity
coefficient values (ε) of Soret band of the porphyrins 4a-d
are shown in Table 2, and the results indicated a decrease
in the values of ε with increasing solvent polarity, except
for the nickel porphyrin (4b), in which there was a slight
increase of 2% at the ε obtained in acetone. The low
values of the molar absorptivity coefficient (Table 2) of
the compounds in ethanol clearly indicate the formation of
in cm-1 (KBr)
Vibration
mode
4a
4b
4c
4d
3319
2923
2852
1607
1349
1245
967
−
−
−
νN−H
2923
2852
1608
1353
1246
−
2923
2852
1608
1351
1246
−
2923
2852
1608
1345
1245
−
νC−H (Ar)
νC−H (Ali)
νC−C (Ar)
νC−N
νAr−O−C
δ N−H
1004
1001
999
N−M
The 1H NMR and 13C NMR spectra were in accordance
with the assigned structures and presented all the expected
signals for asymmetrical meso-substituted porphyrins
derived from cardanol. The signals obtained in CDCl3
(1H NMR, Figure 1) for 4a-dexhibited the spectral signatures
of the porphyrin core and signals typical of the peripheral
cardanol units, such as the singlet at 1.26 ppm corresponding
to the 72 protons of the aliphatic groups (−CH2−).

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J. Braz. Chem. Soc.
Figure 1. 1H NMR (300 MHz, CDCl3) of asymmetric porphyrins 4a-d.

Vol. 28, No. 6, 2017
Mota et al.
1067
Figure 2. Electronic absorption spectra of porphyrins 4a-d, in the following concentrations: 4a 1.5 × 10-6 M; 4b 8.0 × 10-6 M; 4c 8.0 × 10-6 M and
4d 2.5 × 10-6 M.
Table 2. Molar absorptivity coefficient (ε) of asymmetric porphyrins 4a-d in different organic solvents at 25 °C
Dichloromethane
Acetone
ε / (105 L mol-1 cm-1)
Ethanol
ε / (105 L mol-1 cm-1)
Sample
λ
max / nm
ε / (105 L mol-1 cm-1)
λ
max / nm
418
λ
max / nm
4a
4b
4c
4d
421
417
414
418
5.542
1.181
1.060
3.986
4.170
1.215
1.012
3.965
419
1.523
0.391
0.325
0.909
416
415
414
432
415
415
aggregated species, due to, probably, the poor solubility in
this solvent, evidenced by decrease in the intensity of the
absorption bands (hypochromic effect).
Therefore, these asymmetric porphyrins 4a-d allowed
us to work with a greater variety of solvents, including
acetone. This significant change on the solubility of
these porphyrins probably occurs due to the presence of
the hydroxyl group at the macrocyclic structure, which
promotes a better interaction and affinity to polar solvents.
Fluorescence emission spectroscopy of porphyrin 4a
and metalloporphyrins 4b, 4c and 4d were investigated
in dichloromethane (10-5 M) at room temperature. The
emission spectrum of the porphyrin 4a showed two bands
in the red region, one intense at 658 nm (ca. 5 × 107) and a
lower one at 715 nm (ca. 1 × 107) after excitation at 421 nm
Specifically for compound 4c, we observe the
formation of J-aggregates that showed a red-shifted
absorption band at 432 nm.37 This phenomenon indicated
that the molecules of compound 4c have side-by-side
interactions in an ethanolic solution. Usually, porphyrins
derived from cardanol have good solubility in solvents
with low polarity such as chloroform (µ = 1.04),
dichloromethane (µ = 1.60) and THF (µ = 1.75), but they
are insoluble in polar solvents like acetone (µ = 2.88).

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Synthesis, Characterization and Dielectric Properties of New 5-(4-Hydroxyphenyl)
J. Braz. Chem. Soc.
(Figure 3A). This spectral behavior was similar to other
meso-porphyrins and indicates that these compounds can be
used in optoelectronic systems working in the red spectral
region, for example as catalyst, solar cells, OLEDs (organic
light-emitting diode) and photodynamic therapy.38,39 The
fluorescence emission was attributed to the transition from
the excited singlet state S1/S2 to the ground state S0 (S2 → S0,
S1 → S0). The spectra of the complexes 4b-d showed a
very weak fluorescence band, and when 4b is excited at
421 nm, this band appeared at 651 nm with intensity about
2 × 103 a.u. (Figure 3B). The decrease in the emission band
intensity to porphyrins 4b-d probably occurred due to the
heavy atom effect, where the presence of atoms with higher
atomic numbers increases the probability of non-radiative
transitions.40,41 The excitation spectrum of 4a (Figure 4)
showed bands responsible for emission with major
wavelength at 658 nm. Comparing the excitation spectrum
with the absorption spectrum is possible to observe
that the emission happened from the absorption of the
Soret and Q bands.
Figure 4. Excitation spectrum of the porphyrin 4a with emission band
in 658 nm.
atmosphere (N2) using a temperature range between
25 and 900 °C. In general, the results showed that the
order of observed thermal stabilities of the porphyrins
4a-d were: 4a > 4d > 4c > 4b. Thus, we verified that
porphyrin 4a has the best thermal properties, probably
due to the absence of metal coordinated to the center of
the macrocycle, that can act as promoter of degradation
process. Table 3 summarizes the decomposition range
and maximum temperature values, as well as the weight
loss of the main stages of degradation and the residual
weight. The decomposition of the compounds 4a, 4c and
4d occurred in two different stages, while the porphyrin
4b presented three stages.
The first stage of degradation was attributed to the
loss of the peripheral chains of cardanol attached to the
macrocyclic ring of the porphyrins and the second was
associated to the degradation of the macrocycle ring
4a-d.2 Metalloporphyrins showed initial temperature of
degradation lower than the free asymmetric porphyrin 4a.
Similar results was reported by Antina et al.,42 which
related the decrease in thermal stability of porphyrins
to changes in the aromaticity and π-polarization of the
macrocyclic system, due to the presence of the metal ion.
Clemente et al.17 showed that the thermal degradation
of the symmetric porphyrin, derived from cardanol,
started at 250 °C (Tonset). This information indicated
Figure 3. Fluorescence emission spectra of the free base porphyrin 4a (A)
and the complex 4b, 4c and 4d (B) with a concentration of 10-5 M in
CH2Cl2.
Thermal stability
In order to evaluate the thermal stability of the
compounds 4a-d, TGA studies were carried out in inert
Table 3. Thermogravimetric parameters of the two first stages of degradation in N2 atmosphere
First stage
Second stage
Sample
Range
temperature / °C
Range
temperature / °C
Tmax / °C
Weight loss / %
Tmax / °C
Weight loss / %
Residue / %
4a
4b
4c
4d
352-468
161-342
166-454
328-477
434
300
428
451
64.13
46.24
50.16
49.39
468-702
342-477
454-581
477-658
640
454
520
586
34.19
29.25
47.11
40.09
1.68
4.24
2.73
10.52

Vol. 28, No. 6, 2017
Mota et al.
1069
that the asymmetric porphyrin 4a is more thermally
stable than its symmetric porphyrin analogue, due to
the thermal decomposition of 4a started only at 352 °C.
Therefore, these porphyrins are suitable for applications
in technological areas that require luminescent compounds
(red region) and elevated thermal stability, like OLEDs
and solar cells.43 During the second stage of thermal
degradation, all samples showed gradual mass loss
between 29.25 and 47.11% in the temperature range of
342 to 702 °C.
from the decrease in polarization of the molecules across
electric field. When comparing the dielectric permittivity
values of the analyzed molecules, we can see that the
porphyrin 4b had the highest permittivity (ca. 20 a.u.),
while 4d porphyrin had the lowest (ca. 6 a.u.). These
results indicated that the compound 4b is more susceptible
to polarization, since higher permittivity values are
resulted from the dipole generation. The decrease in the
dielectric permittivity value with increasing frequency can
be attributed to dipole relaxation phenomenon in which
the dipoles at low frequencies follow the frequency of
the applied field.46 However, with the increase frequency,
the oscillations in the dipoles cannot follow the applied
field and tend to disappear due to the limited time for its
polarization.47
Dielectric properties
Dielectric permittivity (ε’) is a measure that shows the
ability of materials to store energy and have their dipoles
oriented when subjected to an alternating electric field.
This capacity is associated with the electric susceptibility
of these compounds. The extent of the polarization is
directly related to the nature of the material, shape and
their structures. Therefore, if the electrical properties
(dielectric permittivity) are known, it is possible to predict
the influence of an electric field in the polarization of the
material studied.
The dielectric permittivity and dielectric loss tangent
(tan δ) of porphyrins 4a-d were obtained at room
temperature using the following relationship:44,45
Z = 1 / iwεC0 = 1 / iw(ε’ + iε’’)C0
(1)
where ε’ and ε’’ are the real (permittivity) and imaginary
parts (dielectric loss) of the dielectric function, respectively.
C0 (C0 = ε0A / d) is the empty cell capacitance, where, A
is the electrode area, d is the thickness sample, ε0 is the
permittivity of free space (ε0 = 8.854 × 10-12 F m-1) and w
(w = 2πf) is the angular frequency. The components of the
complex dielectric function was derived using the relations,
Figure 5. Dielectric permittivity with frequency to porphyrins 4a-d at
room temperature.
Dielectric loss tangent is characterized by the loss of
energy due to the movement and orientation of electric
dipoles of the material, where compounds that have
low dielectric loss are considered suitable for use in
microelectronics.48 The dielectric loss tangent (tan δ,
Figure 6) was determined as a function of frequency and
the results obtained for compounds 4a-d indicated that
this parameter increases proportionally with the frequency.
In general, the compounds showed low loss tangent and
exhibited dispersion for high values in ca. 100 kHz.
Porphyrin 4b showed the best dielectric characteristics,
since it combines a high value of dielectric permittivity
(19.46 at 100 kHz) and a low dielectric loss tangent (0.011
at 100 kHz).
ε’ = C / C0 and ε’’ = −iσ / wC
(2)
where C is the capacitance and σ is the conductivity. The
imaginary part of the dielectric function can be calculated as
ε’’ = ε’tan δ. This expression determines the dielectric loss.
It was observed a small decrease in the dielectric
permittivity for all asymmetric porphyrins (4a-d),
when the applied frequency was increased (Figure 5).
At frequencies greater than 1 MHz it was observed that
the values practically did not change. The values of
dielectric permittivity at low frequencies can be assigned
to different types of polarization, such as dipole or
electronic.42 According to the data, it was observed that
this slight decrease in dielectric permittivity resulted
The results in Table 4 shows that when a metal ion was
added in the center of asymmetric porphyrin, the dielectric
properties were significantly altered.23 The increase in the
dielectric permittivity (ε’) of the 4b porphyrin (about three
times), compared with the free porphyrin 4a (permittivity

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Synthesis, Characterization and Dielectric Properties of New 5-(4-Hydroxyphenyl)
J. Braz. Chem. Soc.
permittivity and low loss tangent. This study indicates that
the coordination of the porphyrin nucleus with a metal
promoted a significant change in thermal and electrical
properties of these compounds.
Experimental
Reagents
All the starting reagents used in this work were
purchased from Sigma-Aldrich Chemical,Vetec, Dynamics,
Synth and Acros Organic, and used as received. Solvents
were previously distilled before their use.
Figure 6. Frequency dependence of the dielectric loss tangent at room
temperature.
Analyses
6.96), is a proof of this influence. Another important
parameter of the dielectric properties is the conductivity (σ),
and it is associated with migration of charge carriers.49 The
conductivity in alternating current (σac) of the asymmetric
porphyrins at room temperature was determined as
described by Deger et al.50 The porphyrin coordinated
with nickel (4b) had the highest conductivity values at
all frequencies: 1.3 × 10-8 Sm-1 (1 kHz), 2.8 × 10-8 Sm-1
(10 kHz), 1.9 × 10-7 Sm-1 (100 kHz) and 4.6 × 10-6 Sm-1
(1 MHz). For other porphyrins, the maximum conductivities
were observed in 1 MHz to 4a (8.6 × 10-7 Sm-1),
4c (1.6 × 10-6 Sm-1) and 4d (6.7 × 10-7 Sm-1), respectively.
These conductivities indicated that the compounds studied
have low polarization when subjected to an external electric
field.
UV-Vis: analyses were performed on a Varian Cary
5000 spectrophotometer, where the spectrum was obtained
using quartz cells of 1.0 cm optical path (CHCl3) in the
following concentration: 4a 1.5 × 10-6 M, 4b 8.0 × 10-6 M,
4c 8.0 × 10-6 M and 4d 2.5 × 10-6 M. FTIR: spectra
were obtained using a PerkinElmer Spectrum One
spectrophotometer, and the samples were prepared as
1
pellets (KBr). H NMR and 13C NMR: was obtained in
a nuclear magnetic resonance Bruker Avance DPX 300
spectrometer, operating at 300 (1H) and 75 MHz (13C)
(CDCl3). TGA/DTA: the thermal stability of the samples
was evaluated by thermogravimetric analysis It was used
an equipment Mettler Toledo TGA/SDTA 851e. The
decomposition analyses were performed under nitrogen
atmosphere in a constant flow of 50 mL min-1, with
heating rate of 10.0 °C min-1, sample mass of 5.0 mg and
a temperature program from 25 to 900 °C. MS: samples
were analyzed on a Bruker Microflex LT (MaldiTof) using
alphacyano, and dichloromethane as a matrix and 5% TFA
as mobile phase. Elemental analysis (CNH): the percentual
composition of the samples was analyzed on a PerkinElmer
2400 Series II. Dielectric measurements: the samples were
shaped in a cylinder, with metal bases (Al). They were
pressed by two electrodes connected in order to perform
capacitance measurements, dielectric loss, impedance
real and imaginary. Measurements were made at room
Conclusions
The novel metal-free porphyrin 4a and their metallated
analogs 4b-d, were successfully synthesized and
characterized like asymmetric porphyrins A3B type.
The results of TGA/DTA (differential thermal analysis)
analysis showed that the metalloporphyrins have lower
initial temperature of degradation (4b, 4c and 4d)
compared to free asymmetric porphyrin (4a). The dielectric
measurements indicates that the asymmetric porphyrins 4b
have good dielectric properties, due to its better dielectric
Table 4. Values of the dielectric properties to asymmetric porphyrins at room temperature
1 kHz
10 kHz
100 kHz
1 MHz
Compound
ε’
tan δ
0.007
0.073
0.014
0.008
ε’
tan δ
0.003
0.016
0.011
0.008
ε’
tan δ
0.007
0.011
0.012
0.007
ε’
tan δ
0.015
0.026
0.020
0.012
4a
4b
4c
4d
6.96
20.36
9.65
5.97
6.87
19.66
9.43
5.86
6.80
19.46
9.30
5.81
6.73
19.10
9.12
5.75

Vol. 28, No. 6, 2017
Mota et al.
1071
temperature in atmospheric air through a precisionAgilent
4294A impedance analyzer connected to a microcomputer
in the 1 Hz-10 MHz frequency range.
35.83 (Ph−CH2), 66.22 (O−(CH2)2−O), 111.37-158.45
(C-aromatic); FTIR (KBr) ν / cm-1 3436, 3319, 2923,
2852, 1607, 1583, 1509, 1448, 1245, 1158, 1071, 967;
UV-Vis (CH2Cl2) λmax / nm 421, 516, 557, 592, 649; MS
(MALDI-TOF) m/z, for C113H144N4O7 [M+], observed:
1669.938; required: 1670.375; elemental analysis (CNH)
for C113H144N4O7, observed: C 81.29, N 3.65, H 8.76%;
required: C 81.25, N 3.35, H 8.69%.
Synthesis of the asymmetric porphyrins
Cardanol precursors of the porphyrins
Hydrogenated cardanol (1) was obtained in our
laboratory through chromatographic separation of the
constituents of CNSL followed by hydrogenation.51 The
compound 1-(2-bromoethoxy)-3-pentadecylbenzene (2)
derived from 1, was prepared and characterized by FTIR,
Metalloporphyrins (4b-d)
4a (0.06 mmol) and acetate metal salts (0.60 mmol,
Ni, 4b; Co, 4c; and Cu, 4d) were added in a mix of the
chloroform/DMF (20 mL of each) for 3 hours at 90 °C.
The product was purified by chromatography in a silica
gel column using dichloromethane as eluent, and the
product collected in the first fraction eluted corresponding
to compounds 4b-d. The metalloporphyrins were
recrystallized with a mix of ethanol/hexane.
1
and H NMR according to the procedure previously
described.52
Aldehyde (3)
Compound 4-[2-(3-pentadecylphenoxy)ethoxy]
benzaldehyde (3) was obtained by a mix of 2 (3.0 g,
7.30 mmol) and 4-hydroxybenzaldehyde (1.3 g,
10.90 mmol) using KOH (1.3 g, 23.30 mmol) as base in
50 mL of DMF. The system was maintained in stirring at
100 °C for 6 h, and the progress of reaction was carried
out by thin layer chromatography (TLC). The reaction
mixture was subjected to a pretreatment by means of a
liquid-liquid partition with distilled water (200 mL) and
ethyl acetate (200 mL). The organic phase was dried with
anhydrous Na2SO4, concentrated and purified in column
chromatography with silica gel having as eluent hexane/
ethyl acetate (95:5). The compound 3 was obtained in 62%
yield (2.0 g), molecular weight 452.67 g mol-1 (C30H44O3).
4b
Yield 89%. 1H NMR (300 MHz, CDCl3) d 0.88 (t, 9H,
J 6.3 Hz, CH3), 1.26 (s, 72H, CH2−(CH2)12−CH3), 1.64 (m,
6H, Ph−CH2−CH2), 2.64 (t, 6H, J 7.5 Hz, Ph−CH2), 4.55 (d,
12H, J 4.8 Hz, O−(CH2)2−O), 6.84-7.95 (28H, Ph−H), 8.77
(s, 8H, H-β pyrrolic); 13C NMR (75 MHz, CDCl3) d 14.08
(CH3), 22.66 (CH2−CH3), 29.36-31.90 (CH2−(CH2)13−CH3),
36.06 (Ph−CH2), 66.88 (O−(CH2)2−O), 111.67-158.73
(C-aromatic); FTIR (KBr) ν / cm-1 3432, 2923, 2852,
1608, 1584, 1507, 1448, 1246, 1158, 1074, 1004; UV-Vis
(CH2Cl2) λmax / nm 416, 529; MS (MALDI-TOF) m/z,
for C113H142N4O7Ni [M+], observed: 1726.860; required:
1727.054; elemental analysis (CNH) for C113H142N4O7Ni,
observed: C 79.56, N 2.21, H 9.38%; required: C 78.59,
N 3.24, H 8.29%.
Metal-free porphyrin (4a)
The free base 5-(4-hydroxyphenyl)-10,15,20-tri-4-[2-
(3-pentadecylphenoxy)ethoxy]phenyl porphyrin (4a) was
obtained by a mix of the pyrrole (0.88 mmol), 3 (0.88 mmol),
4-hydroxybenzaldehyde (0.22 mmol), NaCl (16.25 mmol),
BF3 (0.22 mmol) and DDQ (0.50 mmol) in chloroform/
ethanol (50 mL, ethanol 0.8%) at room temperature
for 1 hour. The crude was packaged in a silica column
chromatography and eluted with solvents of increasing
polarity: dichloromethane, dichloromethane/ethanol
(9:1). The asymmetric free base porphyrins (4a) were
obtained in the second fraction eluted and the compound
was recrystallized with ethanol/hexane. 4a: yield 26%.
1H NMR (300 MHz, CDCl3) d −2.73 (s, 2H, N−H), 0.88
(t, 9H, J 6.5 Hz, CH3), 1.26 (s, 72H, CH2−(CH2)12−CH3),
1.67 (m, 6H, Ph−CH2−CH2), 2.64 (t, 6H, J 8.0 Hz,
Ph−CH2), 4.52 (d, 12H, J 4.5 Hz, O−(CH2)2−O), 5.29 (s,
1H, Ph−OH), 6.85-8.09 (28H, Ph−H), 8.84 (s, 8H, H-β
pyrrolic); 13C NMR (75 MHz, CDCl3) d 13.85 (CH3),
22.42 (CH2−CH3), 29.43-31.66 (CH2−(CH2)13−CH3),
4c
Yield 79%. 1H NMR (300 MHz, CDCl3) d 0.87 (t, 9H,
J 5.4 Hz, CH3), 1.25 (s, 72H, CH2−(CH2)12−CH3), 1.53
(broad signal, 6H, Ph−CH2−CH2), 2.66 (broad signal, 6H,
Ph−CH2), 4.53 (broad signal, 12H, O−(CH2)2−O), 6.89-
8.16 (broad signals, 28H, Ph−H), 8.67 (broad signal, 8H,
H-β pyrrolic); 13C NMR (75 MHz, CDCl3) d 13.69 (CH3),
22.27 (CH2−CH3), 28.96-31.51 (CH2−(CH2)13−CH3),
35.78 (Ph−CH2), 67.41 (O−(CH2)2−O), 111.48-158.44
(C-aromatic); FTIR (KBr) ν / cm-1 3436, 2923, 2852,
1608, 1583, 1507, 1449, 1246, 1158, 1073, 1001; UV-Vis
(CHCl3) λmax / nm 414, 530; MS (MALDI-TOF) m/z, for
C113H142N4O7Co [M+], observed: 1726.907; [M+] required:
1727.298; elemental analysis (CNH) for C113H142N4O7Co,
observed: C 77.77, N 3.39, H 8.45%; required: C 78.57,
N 3.24, H 8.29%.

1072
Synthesis, Characterization and Dielectric Properties of New 5-(4-Hydroxyphenyl)
J. Braz. Chem. Soc.
4d
M. G.; J. Heterocycl. Chem. 1968, 5, 669.
Yield 83%. 1H NMR (300 MHz, CDCl3) d 0.88 (t, 9H,
10. Lindsey, J. S.; Schreiman, I. C.; Hsu, H. C.; Kearney, P. C.;
Marguerettaz, A. N.; J. Org. Chem. 1987, 52, 827.
11. Guo, Y.-C.; Xiao, W.; Mele, G.; Martina, F.; Margapoti, E.;
Mazzetto, S. E.; Vasapollo, G.; J. Porphyrins Phthalocyanines
2006, 10, 1071.
J 6.0 Hz, CH3), 1.26 (s, 72H, CH2−(CH2)12−CH3), 1.64
(broad signal, 6H, Ph−CH2−CH2), 2.62 (broad signal,
6H, Ph−CH2), 4.46 (broad signal, 12H, O−(CH2)2−O),
6.86 (broad signal, 6H, H-aromatic); 13C NMR (75 MHz,
CDCl3) d 14.10 (CH3), 22.66 (CH2−CH3), 29.36-
31.89 (CH2−(CH2)12−CH2), 36.07 (Ph−CH2), 66.45
(O−(CH2)2−O), 111.61-158.70 (C-aromatic); FTIR (KBr)
ν / cm-1 3434, 2923, 2852, 1608, 1583, 1504, 1447, 1245,
1158, 1072, 999; UV-Vis (CHCl3) λmax / nm 418, 542,
578; MS (MALDI-TOF) m/z, for C113H142N4O7Cu [M+],
observed: 1731.889; required: 1731.896; elemental analysis
(CNH) for C113H142N4O7Cu, observed: C 78.28, N 3.47, H
8.41%; required: C 78.37, N 3.23, H 8.26%.
12. Zhuang, C.; Tang, X.; Wang, D.; Xia, A.; Lian, W.; Shi,Y.; Shi,
T.; J. Serb. Chem. Soc. 2009, 74, 1097.
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Y.; Zanoni, M. V. B.; Assis, M. D.; J. Braz. Chem. Soc. 2000,
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Supplementary Information
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Supplementary information is available free of charge
at http://jbcs.org.br as PDF file.
17. Clemente, C. S.; Ribeiro, V. G. P.; Sousa, J. E. A.; Maia, F. J.
N.; Barreto,A. C. H.;Andrade, N. F.; Denardin, J. C.; Mele, G.;
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Acknowledgments
18. Sandrino, B.; Clemente, S. C.; Oliveira, T. M. B. F.; Ribeiro, F.
W. P.; Pavinatto, F. J.; Mazzetto, S. E.; Neto, P. L.; Correia, N.
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The authors would like to thank the support from CAPES
and CNPq (PVE 401359/2014-0 and 402566/2013-0),
Almonds Company in Brazil by providing cashew nuts,
CENAUREMN (Centro Nordestino de Aplicação e Uso
da Ressonância Magnética Nuclear, Brazil) for the NMR
analyses
20. Attanasi, O. A.; Mele, G.; Filippone, P.; Mazzetto, S. E.;
Vasapollo, G.; Arkivoc 2009, viii, 69.
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Submitted: June 6, 2016
Published online: September 26, 2016