Synthesis, structural characterization, theoretical studies and corrosion inhibition of a new pyrrole derivative:1-(1-benzyl-4-(4-chlorophenyl)-2,5-dimethyl-1H-pyrrol-3-yl)ethanone

Article abstract of DOI:10.1016/j.molstruc.2019.03.095

A new penta-substitued pyrrole derivative 1-(1-benzyl-4-(4-chlorophenyl)-2,5-dimethyl-1H-pyrrol-3-yl)ethanonewas synthesized in one pot four-component coupling reaction catalyzed by natural hydroxyapatite (Ca₅(PO₄)₃OH). The structure of the title compound was studied using diverse spectroscopic techniques such as ¹H and ¹³C NMR and FT-IR and confirmedby single-crystal X-ray diffraction. Computation studies using density functional theory (DFT) method at B3LYP/6-311 + G(d,p) in gas phase and polarizable continuum model have been performed to predict the spectral and geometrical data of the compound. Good correlations, higher than 99%, were found between the experimental and predicted spectroscopic data. Furthermore, the closest contacts between active atoms of the compound were obtained through Hirshfeld surface analysis along with the electrostatic potential surfaces (EPS) investigations. The electrochemical study showed a good inhibition efficiency of this compound on the steel S300 surface by blocking the active sites.

Full text of DOI:10.1016/j.molstruc.2019.03.095

Accepted Manuscript
Synthesis, structural characterization, theoretical studies and corrosion inhibition of
a new pyrrole derivative:1-(1-benzyl-4-(4-chlorophenyl)-2,5-dimethyl-1H-pyrrol-3-
yl)ethanone
Abdelhadi Louroubi, Abdallah Nayad, Ali Hasnaoui, Ismail Hdoufane, Rachid Idouhli,
Mohamed Saadi, Lahcen El Ammari, Abouelfida Abdessalam, Moha Berraho, Larbi El
Firdoussi, Mustapha Ait Ali
PII:
S0022-2860(19)30381-3
DOI:
https://doi.org/10.1016/j.molstruc.2019.03.095
MOLSTR 26364
Reference:
To appear in: Journal of Molecular Structure
Received Date: 16 January 2019
Revised Date: 19 March 2019
Accepted Date: 29 March 2019
Please cite this article as: A. Louroubi, A. Nayad, A. Hasnaoui, I. Hdoufane, R. Idouhli, M.
Saadi, L. El Ammari, A. Abdessalam, M. Berraho, L. El Firdoussi, M.A. Ali, Synthesis, structural
characterization, theoretical studies and corrosion inhibition of a new pyrrole derivative:1-(1-benzyl-4-(4-
chlorophenyl)-2,5-dimethyl-1H-pyrrol-3-yl)ethanone, Journal of Molecular Structure (2019), doi: https://
doi.org/10.1016/j.molstruc.2019.03.095.
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ACCEPTED MANUSCRIPT
Synthesis, structural characterization, theoretical studies and
corrosion inhibition ofa new pyrrole derivative:1-(1-benzyl-4-(4-
chlorophenyl)-2,5-dimethyl-1H-pyrrol-3-yl)ethanone
Abdelhadi Louroubi1, Abdallah Nayad1, Ali Hasnaoui1, Ismail Hdoufane2, Rachid Idouhli3,
Mohamed Saadi4, Lahcen El Ammari4, Abouelfida Abdessalam3, Moha Berraho5, Larbi El
Firdoussi1 and Mustapha Ait Ali1,*
1Equipe de Chimie de Coordination et Catalyse, Département de Chimie, Université Cadi
Ayyad, Faculté des Sciences Semlalia, B.P 2390, 40001 Marrakech, Morocco,
2Laboratoire de Chimie Moléculaire, Faculté des Sciences Semlalia, Université Cadi Ayyad
BP 2390, Marrakech, Morocco
3Physical-Chemistry of Materials and Environment Laboratory, Faculty of Sciences Semlalia,
Cadi Ayyad University, Marrakech, Morocco
4
Laboratoire de Chimie Appliquée des Matériaux, Centres des Sciences des Matériaux,
Faculty of Sciences, Mohammed V University in Rabat, Avenue Ibn Battouta, BP 1014,
Rabat, Morocco.
5Laboratoire de Chimie des Substances Naturelles,"Unité Associé au CNRST
(URAC16)"Faculté des Sciences Semlalia, BP 2390 Bd My Abdellah, Université Cadi
Ayyad40000 Marrakech, Morocco
*Corresponding authors: aitali@uca.ac.ma
Abstract
A new penta-substitued pyrrole derivative 1-(1-benzyl-4-(4-chlorophenyl)-2,5-
dimethyl-1H-pyrrol-3-yl)ethanonewas synthesized in one pot four-component coupling
reaction catalyzed by natural hydroxyapatite (Ca5(PO4)3OH). The structure of the title
1
13
compound was studied using diverse spectroscopic techniques such as H and C NMR and
FT-IR and confirmedby single-crystal X-ray diffraction. Computation studies using density
functional theory (DFT) method at B3LYP/6-311+G(d,p) in gas phase and polarizable
continuum model have been performed to predict the spectral and geometrical data of the
compound. Good correlations,higher than 99%, were found between the experimental and
predicted spectroscopic data. Furthermore,the closest contacts between active atoms of the
compound were obtained through Hirshfeld surface analysis along with the electrostatic
potential surfaces (EPS) investigations. The electrochemical study showed a good inhibition
efficiency of this compound on the steel S300 surface by blocking the active sites.
Keywords: Pyrrole; X-ray structure; DFT; Hirshfeld Surface; corrosion inhibition.
1

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1. Introduction
Nowadays, several researches are oriented in sustainable processes involving atom
efficient routes, waste of energy, avoiding toxic solvents, and using bio or chemo catalysis [1–
3]. For this purpose, multi-component reactions (MCRs) [4,5] allowing the synthesis in one-
pot procedure of molecules by three or more starting materials, are gaining a huge impact in
chemistry especially in organic synthesis [6]. Among the diversity of scaffolds synthesized by
MCRs, pyrroles moieties are largely described in the literature [2,7,8]. Moreover, pyrroles
derivatives exhibit good biological activities such as antibacterial, antioxidant and
anticancer[9–11]. In addition, these compounds are used in material science as building
blocks of semiconducting materials, polymers and solar cells [12–14]. However, few studies
were performed using pyrroles derivatives as synthetic inhibitors against corrosion in
aggressive media[15–17].
Density-functional theory (DFT) is one of the most popular quantum mechanical
methods for computational treatments of chemical systems and processes[18–22]. Based only
on fundamental physical constants, DFT calculation is used in inorganic and organic
chemistry [23], to explain the structure, energy and molecular characteristics of compounds.
Applied in pyrroles derivatives, it allows the investigation of the prediction of vibrational
frequencies [24–26].
In the present study, we report the synthesis and characterization of a poly-
substitutedpyrrole obtained by one potmulti-component reaction, conducted in solvent free
and catalyzed by natural hydroxyapatite (Scheme 1). The structure was characterized using
1
various experimentalspectroscopic methods including H NMR, 13C NMR, FT-IR and
confirmed by single crystal X-ray diffraction.Furthermore, DFT calculations have been
carried out at the B3LYP/6-311+G(d,p) in gas phase and polarizable continuum model (by
considering IEF-PCM formalism) to predict the corresponding spectroscopic data and Z-
matrix coordinates for the titled compound. Hirshfeld surface and fingerprint plots were used
to understand the interactions and their quantitative contributions of the crystal structure. In
addition, the inhibitory effect was studied for steel S300 in HCl 1M solution using
potentiodynamic polarization analysis.
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Scheme 1. Synthesis of 1-(1-benzyl-4-(4-chlorophenyl)-2,5-dimethyl-1H-pyrrol-3-
yl)ethanone
2. Material and methods
2.1 Spectral data measurements
The reagents and solvents used in the experiments were purchased from commercial
sources. Liquid chromatography was performed on silica gel (Merck 60, 220-440 mesh). The
reaction mixtures were monitored on a trace Shimadzu chromatograph equipped with an FID
detector. GC parameters for capillary columns TG-5MS (30 m x 0.25 mm): injector 230°C;
detector 250 °C; oven 40 °C for 2 min then 40 °C min-1 until 280 °C for 12 min; column
pressure 42.9 kPa, gas flow 20 mL.min-1. For MS detection, the ionization was performed on
an ISQ LT single quadruple mass spectrometer in positive EI modes using a mass scan range
of 50 to 400 Da. NMR studies were performed using CDCl3 as solvent on a Bruker Avance
300 spectrometer, and chemical shifts are given in ppm relative to external TMS. Infrared
(IR) spectrum was recorded using KBr pellets on a VERTEX 70 in the range 4000-400 cm-1
region.
2.2 Synthesis
The synthetic step of the studied compound was illustrated in Scheme 1. A mixture of
acetylacetone (0.25g, 2.5mmol), benzylamine (0.27g, 2.5 mmol), p-Chlorobenzaldehyde
(0.35g, 2.5 mmol), nitroethane, (0.40g, 5.3 mmol) and hydroxyapatite Ca5(PO4)3OH (0.02g,
0.39 mmol) was stirred at 60 °C during 24h. After cooling to room temperature, the crude
product was diluted with water (5 mL) and extracted with ethylacetate (3 х 5 mL). The
obtained organic layers were collected, dried over Na2SO4 and the solvent was removed under
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reduced pressure. The residue was purified by column chromatography over silica gel (Merk
60, 220-440 mesh) using a mixture of hexane/ethylacetate (95/5:v/v) as eluent.
Recrystallization from ethylacetate afforded the product (C21H20NOCl) in 67% yield (0.566g,
1.68mmol) as colorless block.
C21H20NOCl: EI-MS (positive mode) m/z = 337.1 (18%)[M]+.,m/z=322.1 (17%) [M-
+
CH3]+, m/z=211.1 (5%) [M-ClC6H4-CH3]+, m/z=91.1 [C7H7 ] (100%); FT-IR (cm-1, KBr):
υ(Csp2-H) 3027, υ(C-C) of benzene rings 1577, υ(C=C) of pyrrole ring 1514.
1H NMR (300
MHz, CDCl3); δ (ppm): 1.95 (s, 3H), 2.01 (s, 3H), 2.49 (s, 3H), 5.13 (s, 2H), 6.97-7.40 (m,
13
9H). C NMR (75 MHz, CDCl3); δ (ppm):10.29 (CH3), 11.76 (CH3), 31.18 (CH3), 46.98
(CH2), 121.11 (C), 121.61 (C), 125.65 (2CH), 126.24 (C),127.55 (CH), 128.39 (2CH),128.98
(2CH), 131.89 (2CH), 132.58 (C),134.50 (C), 135.63 (C), 136.66 (C), 196.85 (C=O).
2.3X-ray crystallography
Structural examinations of the title compound were performed employing APEX III
Bruker, 2016 diffractometer equipped with Cu-Kα radiation (λ = 1.5418 Å) at 173 K. The
structure was solved by direct methods and successive Fourier difference synthesis using
SHELXS-2014 [27], and refined by full matrix least square procedure on F2 with anisotropic
thermal parameters. The positions of non-hydrogen atoms were refined anisotropically by
SHELXL-2014 [28]. Hydrogen atoms were placed in chemically acceptable positions. The
ORTEP of the compound was generated using ORTEP3 [29] software package and packing
diagram was generated using Mercury software [30]. A total of 221 parameters was refined
with 3360 unique reflections which covered the residuals to R1 0.039. Crystallographic data
have been deposited with the Cambridge Crystallographic Data Centre as supplementary
publication number CCDC 1849255 for PDMF. Copies of the data can be obtained free of
charge via http://www. ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336
033: or by e-mail: deposit@ccdc.cam.ac.uk.
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Table 1.
Crystallographic and structure refinement parameters of the title compound.
Crystal data
Chemical formula
Mr
C21H20ClNO
337.83
Crystal system, space group
Temperature (K)
a, b, c (Å)
Orthorhombic, P212121
173
5.3365 (4), 15.6832 (12), 20.9890 (16)
1756.6 (2)
V (Å3)
Z
4
Radiation type
Cu Kα
1.96
µ (mm−1)
Crystal size (mm)
Description
0.36 × 0.27 × 0.20
Block
Color
Colorless
1.277
Dx,g cm-3
Diffractometer
Absorption correction
Tmin, Tmax
Bruker D8 VENTURE Super DUO
Multi-scan (SADABS; Krause et al., 2015)
0.416, 0.746
No. of measured, independent and
Observed [I> 2σ(I)] reflections
Rint
36671, 3360, 3008
0.087
(sinθ/λ)max (Å−1)
R[F2> 2σ(F2)], wR(F2), S
No. Of reflections
No. Of parameters
Theta_min
0.611
0.033, 0.085, 1.05
3360
221
3.5
Theta_max
70.3
H-atomtreatment
H-atom parameters constrained
0.17−0.21
ꢀρmax, ꢀρmin (e Å−3)
2.4 Computational studies
The Gaussian 09 program package has been used for all computational
investigations[31]. The 3D structure geometry optimization and vibrational frequency
calculations of the title compound have been performed in the gas phase applying DFT
method. The assignments of all atoms are performed using Becke’s three-parameter hybrid
functional and the correlation functional of Lee, Yang, and Parr (B3LYP) level [32,33] with
the 6-311+G(d,p) basis. GIAO at B3LYP/6-311++G(d,p) level of DFT has been applied to
calculate 1H et 13C NMR isotropic chemical shifts in CDCl3 solvent.
2.5 Hirshfeld surface calculations
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The Hirshfeld surface (HF) analysis is a powerful graphic tool attempting to quantify
the interplay between molecules in the crystal as well as between atoms in the molecule by
partitioning the crystal electron density into molecular fragments [34]. For a better
comprehension of the intermolecular interactions and the electrostatic molecular potential in
the crystal structure, HF surface analysis with their associated two-dimensional fingerprint
plots were obtained using the Crystal Explorer 17.5 package[35]. The HF is then defined
within the crystal and the proximity of its nearest neighbors. For this purpose, the normalized
contact distance dnorm combining the distances from the HF surface to the nearest nucleus
inside (di) and outside the surface (de) is mapped in the surface over a fixed color using a red-
white-blue coloring scheme. The red regions, attributed to shorter Van Der Waals interactions
radii, are due to a negative value of dnorm while long interatomic contacts appeared as blue one
with a positive dnorm. In addition, the absence of contact is showed by a white color with zero
dnormvalue[36]. From the 2D-fingerprint plots, all major interactions are given with a
percentage of contribution of each contact to the total HF area and the colors in the map are
white if no occurrence, blue for some occurrence and green for frequent occurrence [37].
2.6 Electrochemical analysis
The electrochemical tests of the corrosion behavior of steel S300 with following
chemical composition (wt): (Fe (98.55 %), C (0.15 %), Mn (1.25 %), and Si (0.05 %)) in 1M
HCl acid were conducted using a PGZ100 potentiostat. The instrument was connected to a
jacketed glass cell coupled to the bath thermostat (20 ±1 °C). Platinum electrode (2 cm2) and
silver-silver chloride electrode (Ag/AgCl) have been used as auxiliary and reference
electrodes, respectively. Before each experiment, the working electrode (0.76 cm2) has been
polished with emery paper SiC of grades 500, 1200 and 2000. Then, the electrode was washed
and immersed in acidic solution. The potentiodynamic polarization curves have been
performed in the potential range -0.8 V to -0.2 V at a scanning rate up to 1 mV/sec. All
measurements were taken on the working electrode immersed in test solution of HCl 1M for
30 min to achieve the steady state open-circuit potential.
3. Results and discussion
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3.1. Single crystal X-ray structural analysis of the title compound.
The structure and geometry of the title compound in the solid state is established by
single crystal X-ray structural analysis. This compound crystallizes in the orthorhombic
system with P212121 space group and one molecule in the asymmetric unit. The molecular
structure of the title compound is illustrated in Fig.1 and the packing diagram is displayed in
Fig.2. Crystal data collection and structure refinement details are summarized in Table 1. The
pyrrole ring system is approximately planar, with the dihedral angles between the two
attached systems (chlorophenyl and benzyl) are 57.16(14)(°) and 84.06(13)(°), respectively.
There is an intramolecular C—H···O hydrogen bond involving a carbonyl atomO1,
and the H atom of the C18of the methyl group forming a S(6) ring motif. In the crystal,
molecules are linked by pairs of C-Cl···π interactions, forming inversion dimers (Table 2 and
Fig. 3). There are no others significant intermolecular interactions.
Table 2
Hydrogen-bond geometry (Å,°).Cg is the centroid of the C1/C2–C14 ring.
D—H…A
D—H
0.98
H
···
2.37
3.693
A
D
···
A
D—H···
A
3.000(4)
4.746(3)
121
C18-H18···O1
C1-Cl···Cgi
1.740
117.09
Symmetry code (i): -x, y+1/2, -z+1/2
Fig. 1. The molecular structure of the title compound, with the atom labelling.
Displacement ellipsoids are drawn at the 30% probability level. The intramolecular C—H···O
hydrogen bonds shown as a dashed line (see Table 2).
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Fig.2. A view of the crystal packing of the title compound.
Fig. 3. A partial view of the crystal packing of the title compound, showing the C—
Cl···π Interactions as dashed lines (see Table 2; Cl atoms involved are shown as balls).
3.2. Theoretical structure
The geometry optimization of the synthesized compound was carried out by DFT method
at B3LYP/6-311+(d,p) basis set in gas phase. The predicted bond lengths, bond angles and
dihedral angles were compared with the experimental values and the results of some
significant structural parameters are given in Table 3. The superposition of the optimized and
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the X-ray structure shows an excellent agreement between the calculated geometric
parameters and the crystallographic data (Fig. 4). Furthermore, this agreement is confirmed
by a good correlation between X-ray data and the calculated geometric parameters. Hence, a
correlation coefficient of 99.64% is found between bond length of the optimized structure and
the X-ray one in gas phase. Similarly, good agreements are obtained between calculated
angles and torsion angles in gas phase with the experimental ones with correlation coefficients
of 98.79 % and 99.92 %, respectively.
Fig.4. Superposition of the X-Ray (green) and the optimized (yellow) structure
of the compound.
Table 3.
Bond lengths (Å) and bond angles (º) of compound 1 and the experimental data.
Label
DFT
Bond lengths (Å)
1.763
XRD
C1 Cl1
N1 C6
C5 C6
C6 C16
N1 C7
C7 C8
N1 C17
C17 C18
C17 C19
C19 C20
C20 O1
C20 C21
1.741(3)
1.385(3)
1.366(3)
1.497(3)
1.462(3)
1.510(3)
1.361(3)
1.494(4)
1.386(3)
1.471(3)
1.226(3)
1.506(4)
1.392
1.377
1.495
1.456
1.523
1.375
1.498
1.395
1.476
1.221
1.525
Bond angles (°)
107.9
N1 C6 C5
107.9(2)
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N1 C7 C8
N1 C6 C16
C18 C17 C19
O1 C20 C21
Cl1 C1 C14
O1 C20 C19
C18 C17 N1
N1 C17 C19
Cl1 C1 C2
C16 C6 C5
C6 N1 C7
C6 N1 C17
C17 C19 C20
115.1
121.9
132.1
118.6
119.5
121.2
120.3
107.5
119.5
130.1
124.6
110.1
127.9
113.5(2)
121.3(2)
130.7(2)
119.3(2)
119.4(2)
121.7(2)
121.4(2)
107.9(2)
119.4(2)
130.6(2)
124.2(2)
110.1(2)
123.9(2)
Dihedralangles
-179.9
177.1
Cl1 C1 C2 C3
C4 C5 C6 N1
C8 C7 N1 C6
C18 C17 N1 C6
C7 N1 C6 C5
-180.0(2)
168.0(2)
-86.9(3)
176.5(3)
178.2(2)
-91.8
178.3
175.6
3.3.Frontier molecular orbitals analysis
Contour plots of some selected molecular orbitals (MOs) of the compound were carried
out using the B3LYP/6-311+G(d, p) level. The MOs distributions of the HOMO-2, HOMO-1,
HOMO, LUMO, LUMO+1 and LUMO+2 (see Fig. 5) and their energies level are calculated
to be -6.726, -6.565, -5.893, -1.083, -0.904 and -0.889, respectively. Furthermore, the higher
energy occupied molecular orbital (HOMO) to the low-lying virtual orbital (LUMO) band gab
energy is 4.81 eV. These results confirm the stability of the synthesized molecule. In addition,
the HOMO orbital is mainly localized on the pyrrole moiety, slightly localized on the methyl
groups along with the p-chlorophenyl ring. The HOMO-1 is delocalized over the pyrrole ring,
ketone function and the p-chlorophenyl ring. The HOMO-2 is localized on the p-chlorophenyl
ring but slightly delocalized over pyrrole moiety and ketone function. On the other hand, the
LUMO orbital is localized on the carbonyl with slight delocalization over pyrrole ring, the p-
chlorophenyl ring and the C-phenyl ring attached with the nitrogen atom of pyrrole moiety.
The LUMO+1 is mainly localized over the phenyl group and having a slight localization over
the p-chlorophenyl ring. The LUMO+2 orbitals were settled across the p-chlorophenyl ring
along with a smaller localization over the phenyl group.
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HOMO
HOMO-1
HOMO-2
LUMO
LUMO+1
LUMO+2
Fig. 5. Contour plots of some selected MOs of the compound.
3.4.Vibration spectra
The theoretical FT-IRspectrum of the titled compound was calculated at the B3LYP/6-
311+G(d,p) level of theory. The scaled vibration modes are obtained at the same level of
theory and scaled with a factor of 0.9613 factor [38]. It is observed that the stretching
vibration modes of C-H of aromatic (υ(Csp2-H)) are located at 3027 cm-1, which coincide well
with the corresponding scaled vibrational frequencies at 3029 cm-1. For the carbonyl group
(
υ(C=O)), having conjugation with pyrrolic moiety, it is observed at 1638 cm-1 while the
corresponding scaled one correlates well at 1636 cm-1. The main observed vibrational modes
and their corresponding calculated and scaled ones are presented in Table 4 and the
experimental FT-IR spectrum is shown in figure 6.
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Fig. 6. Experimental FT-IR spectrum of the titled compound.
Table 4.
Experimental and theoretical vibrational wavenumbers (cm-1) of the studied compound at
B3LYP/6-311+G(d,p) level and their assignments.
Assignments
Experimental values
Calculated DFT/6311+G(d.p)
Cal
3151
1702
Scal
3027
1638
3029
1636
υ(Csp2-H)
υ(C=O)
1625
1644
1562
1580
1577
1514
υ(C=C) of benzene rings
1545
1604
1485
1542
υ(C=C) of pyrrole ring
υ : stretching
3.5.NMR Study
1H and 13C NMR chemical shifts of the title compound were computed at the B3LYP/6-
311++G(d,p) within GIAO approach in solvent phase (Table 6). The solvent effects on the
chemical shift values are considered by using IEF-PCM formalism, for which, CDCl3 is used
as a selected solvent. Very good correlations were obtained between the predicted and
1
13
experimental H and C NMR chemical shifts. Hence, correlations coefficients of 99.97 %
and 99.67 % are obtained between the predicted and experimental of both NMR chemical
shifts, respectively (Fig. 7).
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Table 5.
Experimental and theoretical 1H and 13C NMR shifts (ppm) for the title compound.
13C NMR chemical shifts
1H NMR chemical shifts
Atom
Experimental Calculated
Atom
Experimental Calculated
(ppm)
(CDCl3)
(ppm)
(CDCl3)
DFT/B3LYP
(ppm)
DFT/B3LY
P (ppm)
C-1
C-2
136.66
128.98
131.89
134.50
121.61
126.24
46.98
138.88
127.09
130.82
135.09
119.64
124.58
42.43
H-2
H-3
7.32
7.40
5.13
6.97
7.28
7.24
7.33
7.29
7.22
7.00
1.95
2.01
2.49
7.22
7.22
4.86
6.80
7.30
7.11
7.27
7.14
7.09
7.14
1.98
2.12
2.27
C-3
H-7
C-4
H-9
C-5
H-10
H-11
H-12
H-13
H-14
H-15
H-16
H-18
H-21
C-6
C-7
C-8
135.63
125.65
128.39
127.55
128.39
125.65
128.98
131.89
10.29
134.83
125.05
127.68
126.31
128.21
123.53
127.32
132.99
4.06
C-9
C-10
C-11
C-12
C-13
C-14
C-15
C-16
C-17
C-18
C-19
C-20
C-21
132.58
11.76
133.71
5.52
121.11
196.85
31.18
120.52
198.37
27.66
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Fig. 7. Correlation curves between predicted and experimental chemical shifts for compound.
13C NMR (left) and 1H NMR (right).
3.6.Hirshfeld surface studies
The HF surface analysis (Fig. 8, left) and EPS (Fig. 8, right) reveal the presence of
intermolecular interactions (inter-contacts) in the crystalline environment of the titled
compound. The red spots over HF surface indicates the interactions that involves hydrogen
bonding (Fig. 8, (left)). In ESP, the negative electrostatic potential appears in the red region
(hydrogen acceptors), and the positive electrostatic potential (hydrogen donor) appears in
blue. The intercontacts over HF surface are quantified using 2D fingerprint plots. The major
intercontacts contributions of the titled compound are found between H···H (52.9%), Cl···H
(8.3%), and H···Cl (5.3%) (Fig. 9). Other intercontacts (e.g, C···C, H···O, Cl···C, C···O,
C···N) show contribution rates less than 3.8%.
Fig. 8. dnorm (left) and EPS (right) mapped on the HF surface for visualizing the
intermolecular contacts.
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Fig. 9. Fingerprint plots of the highest interactions of the title compound. di corresponds to the
closest internal distance from a given point of HF surface, and de to the closest external
contacts (i.e., external distance).
3.7.Corrosion measurement
Corrosion is defined as the chemical or electrochemical reaction between a metal and its
environment causing the deterioration of physical proprieties of materials [39]. The use of
organic compounds as inhibitors is one of the greatest methods in order to get a good
corrosion protection. In the current work, experimental studies for establishing the current
density using polarization curves measurements were performed for the title compound. The
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ACCEPTED MANUSCRIPT
curves presented in Fig. 10 illustrate the cathodic and anodic polarization of steelS300 in 1M
HCl solution without and with inhibitor at 20 °C. The corresponding electrochemical
parameters such as corrosion potential (Ecorr), corrosion current density (icorr), anodic and
cathodic Tafel slopes (ba, bc) and inhibition efficiency (η%) were determined by Tafel
extrapolating and the values are summarized in Table 6.
The inhibition efficiency is calculated using the following equation:
′
ꢂ
ꢆꢂ
ꢃꢄꢅꢅ
ꢃꢄꢅꢅ x100
(1)
ꢀ ꢁ
η % =
′
ꢂ
ꢃꢄꢅꢅ
Where ꢇ'corr and ꢇcorr are the corrosion current densities without and with inhibitor,
respectively.
Fig. 10. Polarization curves of steel S300 in 1M HCl without and with inhibitor in 10-3 M.
Fig. 10 shows that the presence of inhibitor shifts the cathodic branches to the lower
values of current densities without changing in the anodic branches. Moreover, the values of
corrosion potential shifted to the cathodic domain. It’s well known that, when the corrosion
potential (Ecorr) shift to more than ±85 mV compared to the blank one, the inhibitor can be
16

ACCEPTED MANUSCRIPT
considered as anodic or cathodic type. However, when the shift is less than 85 mV, it can be
considered as mixed-type [40,41].
From Table 6, it can be seen that the addition of 10-3 M of inhibitor decreased clearly
the corrosion current density compared to the blank. The cathodic and anodic slopes
decreased. The displacement in cathodic branches and the corrosion potential to the cathodic
domain, observed at 36 mV, demonstrate that the hydrogen evolution reaction was
dominantly inhibited. These results explain that the adsorption of inhibitor molecule onto the
steel S300 surface acts as mixed type with cathodic predominance. The adsorption of the
molecule of inhibitor onto the steel S300 surface can take place by the heteroatoms and π-
bonding/retrodonation blocking the active site [42,43].
Table 6.
Polarization parameters for steel S300 in 1M HCl in the presence and absence of inhibitor.
Ecorr
(mV vs.
Ag/AgCl))
icorr
(mA/cm2)
ba
bc
η
(%)
Conc.
(mol/L)
(mV/dec)
(mV/dec)
Blank
10-3
-379
-415
0.683
0.146
77
65
-142
-157
---
78.6
4. Conclusion
In this study, we report the preparation of a pyrrole derivative in one-pot
multicomponent solvent free reaction catalyzed by natural hydroxyapatite in an excellent
yield. The structure of the compound was elucidated by FT-IR, 1H NMR,13C NMR and X-ray
diffraction techniques. Computational study using DFT approach was employed to predict the
structural and spectroscopic proprieties for a comparative study with experimental values.
Further, the Hirshfeld surface analysis showed that H···H interactions are the most dominant
constituting more than 50% of all interactions. The results obtained from electrochemical
experiments suggested the good inhibition efficiency of the organic component for steel S300
corrosion in 1M HCl.
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Highlights
•
•
•
•
•
•
Pyrrole derivative was characterized by FT-IR spectroscopy and X-ray diffraction.
The optimized geometry of the compound was computed by DFT method.
C−H⋯O and C—Cl···π interactions consolidate the 3D stacking of the compound.
HOMO-LUMO energy gaps, EPS analyses were investigated.
The contributions for the crystal packing were determined with Hirshfeld surface.
Corrosion inhibition was measured for the title compound.