Synthesis, spectral analysis, anti-corrosive activity and theoretical study of an aromatic hydrazone derivative

Article abstract of DOI:10.1016/j.molstruc.2018.12.073

An aromatic hydrazone derivative; namely (E)-1-(3-nitrobenzylidene)-2-(p-tolyl)hydrazine (E-NBPTH) has been synthesized by condensation of an aromatic hydrazine with an aromatic aldehyde in methanol at reflux. The molecular structure of E-NBPTH has been i

Full text of DOI:10.1016/j.molstruc.2018.12.073

Accepted Manuscript
Synthesis, spectral analysis, anti-corrosive activity and theoretical study of an
aromatic hydrazone derivative
Nadjib Chafai, Salah Chafaa, Khalissa Benbouguerra, Abdelkader Hellal, Mouna
Mehri
PII:
S0022-2860(18)31506-0
DOI:
https://doi.org/10.1016/j.molstruc.2018.12.073
MOLSTR 26010
Reference:
To appear in: Journal of Molecular Structure
Received Date: 2 September 2018
Revised Date: 16 December 2018
Accepted Date: 18 December 2018
Please cite this article as: N. Chafai, S. Chafaa, K. Benbouguerra, A. Hellal, M. Mehri, Synthesis,
spectral analysis, anti-corrosive activity and theoretical study of an aromatic hydrazone derivative,
Journal of Molecular Structure (2019), doi: https://doi.org/10.1016/j.molstruc.2018.12.073.
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NH2
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H3C
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Synthesis, spectral analysis, anti-corrosive activity and theoretical study of
an aromatic hydrazone derivative
Nadjib Chafai1, *, Salah Chafaa1, Khalissa Benbouguerra1, Abdelkader Hellal1,2, Mouna
Mehri1.
1Laboratory of Electrochemistry of Molecular Materials and Complex (LEMMC). Department of
Process Engineering, Faculty of Technology, University Ferhat ABBAS Setif-1, El-Mabouda campus,
19000 Sétif, Algeria
2Department of Science and Material, Faculty of Science and Technology, University Djilali
Bounaama Khmis Miliana
Abstract
An aromatic hydrazone derivative; namely (E)-1-(3-nitrobenzylidene)-2-(p-tolyl)hydrazine
(E-NBPTH) has been synthesized by condensation of an aromatic hydrazine with an aromatic
aldehyde in methanol at reflux. The molecular structure of E-NBPTH has been identified and
1
analyzed by spectroscopic methods such as UV-vis, IR, H NMR and 13C NMR. The
corrosion inhibition behavior of the prepared molecule in 0.5M H2SO4 was investigated by
gravimetric, electrochemical and theoretical methods. According to the polarization study, the
E-NBPTH acts as a mixed type of inhibitor. The adsorption of E-NBPTH on the iron surface
follows the Langmuir isotherm. The optimized molecular structure and some quantum
chemical parameters of the synthesized compound have been calculated using the density
functional method (DFT). The results obtained from theoretical study are well support the
experimental results.
Keywords: Hydrazone;– Synthesis; Spectral analysis;– Corrosion inhibition; Adsorption;
DFT.
*Corresponding author. Tel.: +213664208212. E-mail address: n.chafai@univ-setif.dz or
nadjib82@gmail.com
1

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1. Introduction
Hydrazone derivatives are an important and highly active class of organic molecules, which
are offer a wide range of applications such as the development of new anti-corrosive agents
[1
̶
3] and anti-cancer drugs [4
̶ 7]. The high activity of hydrazones may be related to the
presence of the N
̶
N and C=N bonds in their molecular structures.
Since long time, corrosion is considered a major problem in the industrial field and it causes
losses of millions of dollars annually. To this effect, several techniques were developed and
employed to remedy this problem, especially, the use of the organic inhibitors which is
considered one of the most applied and effective techniques [8, 9]. Recently, many researches
in the corrosion field prove that several hydrazones and their derivatives are reported as useful
corrosion inhibitors for diverse metals and alloys in various media [10–14]. In this context
several works have been published involving the development of the synthetic methods of
these molecules in order to improve their yields [15 ̶ 17].
Generally, the inhibition activity of the organic inhibitors is related to the presence of different
heteroatoms and aromatic rings in their molecular structure [18]. In the other hand, this
activity is associated to the physicochemical and electronic characteristics of the inhibitor
molecule [19, 20]. During the past 20 years, the quantum chemical calculations using DFT
method are become an effective approach to determine a correlation between the corrosion
inhibitory efficiency and some quantum chemical parameters [21-24]. Also, the DFT
calculations are extensively used to study the various biological activities of the bioactive
molecules [25
in the corrosion inhibition studies in order to comprehend the interactions between inhibitor
molecules and metallic surfaces [28 31].
̶ 27]. Additionally, molecular dynamics simulations (MDS) are widely utilized
̶
In the present work, we interest on the synthesis and spectroscopic analysis of an aromatic
hydrazone derivative namely; namely (E)-1-(3-nitrobenzylidene)-2-(p-tolyl)hydrazine (E-
NBPTH). On the other hand, the anti-corrosive activity of the synthesized molecule has been
evaluated in sulfuric acid medium using gravimetric measurements, potentiodynamic
polarization curves and electrochemical impedance spectroscopy (EIS). The influence of the
immersion time and temperature on the inhibition efficiency of the synthesized molecule has
been investigated. Additionally, the DFT calculations were effected to correlate experimental
results. Also, the molecular dynamics simulations (MDS) were applied to study the
interactions between inhibitor molecule and the Fe (110) surface.
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2. Experimental
2.1. Materials and reagents
All the reagents used for the hydrazone derivative synthesis and the sulfuric acid (98%)
employed in corrosion study were purchased from Sigma-Aldrich and used without further
purification. Moreover, in the corrosion experiments the employed specimens and working
electrode were prepared from XC48 carbon steel with the following chemical composition
(wt.%): C(%)= 0.418, Mn(%)= 0.730, Mo(%) = 0.012, P(%)= 0.016, S(%)= 0.019, Si(%)=
0.245, Ni(%)= 0.079, F(%)= 0.777 and Fe(%)= 98.09873. Before each corrosion test the
surface of carbon steel was successively cleaned with various grades of SiC abrasive papers,
washed with bi-distilled water and dried.
2.2. Spectroscopic details
The UV–Vis spectrum of the synthesized compound was run in DMSO solution on a Jasco V-
650 UV-Vis spectrometer in the region of 190–900 nm. Also, the FT-IR spectrum of the
synthesized molecule was realized in solid state at room temperature using the JASCO 4000
FTIR spectrometer and the measured vibrational frequencies are recorded in the range of 600–
4000 cm-1. In addition, the NMR spectra were obtained on a Bruker Advance 300 NMR
spectrometer operating at 300 MHz for 1H NMR and 13C NMR in CDCl3 as a solvent.
2.3. Synthesis of the studied hydrazone
The studied hydrazone derivative; namely (E)-1-(3-nitrobenzylidene)-2-(p-tolyl)hydrazine (E-
NBPTH), was synthesized by the condensation of (4-methylphenyl)hydrazine (0.1247 g, 1
mmol) with 3-nitrobenzaldehyde (0.1527 g, 1 mmol) under methanol reflux for 4 h (Fig. 1).
The formed yellow precipitate was filtered, washed with methanol and dried. The obtained
final product is a pure yellow powder which is passed later to the spectroscopic
characterization.
2.4. Corrosion inhibition tests
2.4.1. Weight loss tests
All the carbon steel specimens used in weight loss tests are cylindrical forms of 9.43 cm2 of
area. Firstly, all specimens were weighed before the immersion in the tested solutions. Then,
each specimen was immersed at constant temperature in 0.5M H2SO4 solutions in absence and
in presence of various concentration of E-NBPTH for an immersion time of 24h. After the
expiration of the immersion time the specimens were recuperated from the tested solutions
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rinsed with bi-distilled water and dried at room temperature. Finally, the dried specimens
were weighed for a second time and the obtained mass values were used to calculate the
corrosion rate (ꢀꢁꢂꢃꢃ), surface coverage (ꢄ) and inhibition efficiency (ꢅꢆ (%)), employing the
following equations:
∆ꢊ
ꢋ×ꢌ
ꢊ ꢎꢊ
ꢍ
ꢏ
ꢀꢇꢈꢉꢉ
ꢄ = ꢐ
=
=
(1)
(2)
ꢋ×ꢌ
ꢔ
ꢎꢐ
ꢑꢒꢓꢓ
ꢑꢒꢓꢓ
ꢔ
ꢐ
ꢑꢒꢓꢓ
ꢔ
ꢎꢐ
ꢅꢆ(%) = ꢐ
× 100
(3)
ꢕꢖꢗꢗ
ꢕꢖꢗꢗ
ꢔ
ꢐ
ꢕꢖꢗꢗ
where:
W1: The mass of specimen before immersion in the tested solution.
W2: The mass of specimen after immersion in the tested solution.
S: The surface area of the specimen.
t: The immersion time of each test.
ꢘꢜꢙꢚꢛꢛ : The corrosion rate in the absence of E-NBPTH.
ꢘꢙꢚꢛꢛ : The corrosion rate in the presence of E-NBPTH.
2.4.2. Electrochemical tests
A conventional cell containing three-electrode system was applied to realize all the
electrochemical measurements. In these tests, the glass carbon is used as auxiliary electrode, a
saturated calomel electrode (SCE) was employed as reference electrode and a XC48 carbon
steel was used as working electrode. An electrochemical workstation PGZ 310 Voltalab40
was used to realize all the electrochemical tests. Also, the Voltamaster 4 standard software
was utilized to plot the obtained experimental data. The employed potential range for the
potentiodynamic polarization tests is varied from –800 to –200 (mV/SCE) and the applying
scan rate is 0.5 mV s-1. From the obtained polarization data we can calculate the inhibition
efficiency (Ep (%)) by applying the following formula [32]:
°
ꢟ
ꢎꢟ
ꢕꢖꢗꢗꢣ × 100
(4)
ꢕꢖꢗꢗ(ꢠꢡꢢ)
( )
ꢅꢝ % = ꢞ
ꢟ
ꢕꢖꢗꢗ(ꢠꢡꢢ)
where ꢤꢁ°ꢂꢃꢃ and icorr(inh) indicate the corrosion current densities in the absence and presence of
E-NBPTH, respectively.
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In this study, to realize the electrochemical impedance spectroscopy (EIS) tests, we chose the
amplitude signal perturbation of 5 mV AC sine wave and varying the frequency region from
100 kHz to 10 mHz. From the obtained EIS data we can determine the inhibition efficiency
( )
(ꢅꢥ % ) by employing the following formula [32]:
°
ꢧ ꢎꢧ
ꢨꢩ × 100
(5)
ꢨ
( )
ꢅꢥ % = ꢦ
°
ꢧ
ꢨ
where ꢪꢫ° and ꢪꢫ indicate the charge transfer resistances in the absence and presence E-
NBPTH, respectively.
2.5. DFT calculations and MDS details
2.5.1. DFT calculations
The Gaussian 09W program package was used to perform all quantum chemical calculations
[33]. The molecular structure of E-NBPTH was geometrically optimized employing DFT
method with B3LYP hybrid functional at 6-31G (d,p) basis set [34, 35]. Also, at the optimal
structure of E-NBPTH, the vibrational frequencies have been calculated using the
DFT/B3LYP method with 6-31G (d,p) basis set. Moreover, the quantum chemical parameters
such as the energy gap (ꢀEGAP), dipole momentum (µ), global hardness (η), global softness
(σ), absolute electronegativity (χ), electrophilicity index (ω) and fraction of transferred
electrons (ꢀN) are determined using the calculated values of the highest occupied molecular
orbital energy (EHOMO) and lowest unoccupied molecular orbital energy (ELUMO). All the
precedent parameters are calculated using the following equations [36, 37]:
∆ꢅꢬꢐꢫ = ꢅꢭꢮꢯꢰ − ꢅꢱꢰꢯꢰ
(6)
ꢎꢳ
ꢹ
ꢲ = ꢳ
(7)
ꢴꢵꢶꢷ
ꢸꢷꢶꢷ
ꢺ = ꢼꢻ
(8)
(9)
ꢽ = ꢎ(ꢳ
ꢾꢳ
)
ꢸꢷꢶꢷ
ꢴꢵꢶꢷ
ꢹ
ꢏ
ꢿ = ꣀꢹꢼ
(10)
(11)
ꣀ
ꢎꣀ
ꢠꢡꢢ
ꣂꣃ
Δꣁ = ꣄ (
)꣆
ꢹ ꢼ ꢾ ꢼ
ꣂꣅ
ꢠꢡꢢ
where:
χFe and χinh represent the absolute electronegativity of iron and E-NBPTH, respectively.
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ηFe and ηinh represent the absolute hardness of iron and E-NBPTH, respectively.
Generally, we use the theoretical values of χFe = 7.0 eV and ηFe = 0 to calculate the fraction of
transferred electrons [38].
2.5.1. MDS details
In this study, the molecular dynamics simulations (MDS) have been realized by using the
Materials Studio 7.0 software [39]. Firstly, the Fe(110) surface was chosen to simulate the
adsorption of E-NBPTH on the iron surface. Moreover, the selected dimensions of the
simulation box are (17.20 Å × 22.93 Å × 22.93 Å), employing the periodic boundary
conditions. Also, this simulation box includes the Fe slab, the water slab containing E-
NBPTH molecule and a vacuum slab. Then, the molecular geometry of E-NBPTH and the
Fe(110) surface are optimized by minimization of energy. Finally, the COMPASS force field
model was applied to perform the MDS at 298K, NVT ensemble and using a time step of 0.1
fs with a simulation period of 50 ps.
3. Results and discussion
3.1. Spectral analysis
The examination of the obtained UV-vis spectrum of E-NBPTH recorded in DMSO at room
temperature indicates the presence of an absorption bands in ultraviolet domain. The spectrum
of E-NBPTH shows band at 364.48 nm attributed to n→π* transitions produced by the imine
group (C=N) of the synthesized hydrazone. Moreover, the band situated at 304.75 nm is
attributed to n→π* transitions originated by the nitro group (NO2).
The inspection of the experimental and theoretical infrared spectra of E-NBPTH allows
selecting the vibration frequencies of the characteristic functional groups of E-NBPTH (Table
1). In addition, we used a scaling factor of 0.9614 to scale the calculated frequencies [40].
Consequently, we observe that the scaling theoretical frequencies are in good accordance with
the experimental frequencies (Fig. 2). So, the analysis of the obtained IR experimental
spectrum shows the presence of the following characteristic peaks:
The observed peak at 3307 cm-1 could be attributed the N
peak appeared at 3079 cm-1 can be referred to the stretching vibration of aromatic C
Moreover, the less intense broad peak appeared at 2986 cm-1 is assigned to the stretching
vibration of aliphatic C H bonds. The presence of peaks within the range of 1665
2000 cm-1
H bond (overtone patterns). The
̶
H stretching vibration. A weak
H bonds.
̶
̶
̶
is mostly due to the bending vibration of the aromatic C
̶
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characteristic peak of the synthesized hydrazone is observed as a very intense peak at 1521
cm-1, which is assigned to the stretching vibration of the imine group (C=N). In addition, the
stretching vibration of the aromatic nitro group (Ar
1349 cm-1. The peaks with medium intensities obtained within the region 1200-1290 cm-1 can
be referred to the stretching vibration of C N band. The detected peaks in the region 1020-
1180 cm-1 could be assigned to the stretching vibration of the N
N bond. The peak appeared
at 914 cm-1 can be referred to the N
O bond vibration. The intense thin peak located at 815
cm-1 may be due to C N band vibration. The peak situated at 734 cm-1 may be attributed to
the out of plane bending vibrations of C H group. Additionally, the N H out of plane bending
̶ NO2) was appeared as an intense peak at
̶
̶
̶
̶
̶
̶
vibrations were also observed at 674 cm-1.
1
The examination of the obtained H NMR spectrum for the synthesized molecule allows
determining the main characteristic signals, such as the singular signal appeared at 2.33 ppm
is attributed to the three protons of
CHAr ) are assigned to the signals observed in the region of 7.05-8.12 ppm. Moreover, the
observed singular signal at 8.43 ppm may be referred to the proton of NH group. The proton
of aliphatic =CH group is appeared as a singular signal at 7.67 ppm. On the other hand, the
̶ CH3 group. Also, the characteristic aromatic protons ( ̶
̶
̶
̶
interpretation of the 13C NMR spectrum of E-NBPTH indicates the presence of the
characteristic signals of the carbons present in its molecular structure. For example, the
observed signal at 20.65 ppm is attributed to the carbon of
carbon of imine group ( C=N) is appeared at 141.64 ppm. The aromatic carbon related to the
nitro group ( CAr NO2) is observed at 148.72 ppm. The other aromatic carbons signals are
̶ CH3 group. The signal of the
̶
̶
̶
observed in the zone of 113.04-137.48 ppm.
3.2. Anti-corrosive activity
3.2.1. Weight loss tests
Table 2 summarizes the obtained results from weight loss tests, such as mass loss, corrosion
rate, surface coverage rate and inhibition efficiency in the absence and in the presence of E-
NBPTH at different concentrations. From the presented results in Table 2 and Fig. 3(a), we
can observe that the mass loss and the corrosion rate decrease by increasing the concentration
of E-NBPTH while the recovery rate and the inhibition efficiency increase by augmentation
the concentration of the investigated molecule. This behavior can be attributed to the
formation of a protective layer of the E-NBPTH molecules on the metallic surface and
therefore retarding the attack of the carbon steel surface by sulfuric acid.
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In addition, the obtained results of the effect of temperature on the corrosion rate and the
inhibition efficiency are regrouped in Table 3 and presented by Fig. 3(b). So, we can be seen
that the corrosion rate increases by increasing the temperature while the inhibition efficiency
decreases by increasing of the temperature. This phenomenon is due to exothermicity of the
adsorption process of the E-NBPTH molecules on the iron surface, this proves without a
doubt that the protection mechanism occurs through the adsorption of E-NBPTH on the iron
surface.
3.2.2. Activation energy
Generally, the Arrhenius plots are used to determine the activation energy (Ea) by plotting the
variation of the logarithm of the corrosion rate as a function of the inverse of the temperature
in absence and in presence of an inhibitor. In this study, the following relations are used to
plot the Arrhenius lines in the absence and in the presence of E-NBPTH at 10-3M [41]:
꣍
ꢎꢳ
꣌
꣇꣈ (ꢀ꣉ꢁꢂꢃꢃ) = ꣇꣈ (꣊꣋) + ꢦꢧ ꣎ ꢩ
(12)
꣇꣈ (ꢀꢇꢈꢉꢉ) = ꣇꣈ (꣊) + ꢦꢎꢧꢳ꣎ ꢩ
(13)
꣌
where :
ꢀ꣉ꢁꢂꢃꢃ and ꢀꢁꢂꢃꢃ : are the corrosion rates in the absence and in the presence of E-NBPTH,
respectively.
꣊′ and ꣊ : are the Arrhenius pre-exponential constants in the absence and in the presence of E-
NBPTH, respectively.
ꢅ꣏ and ꢅ꣏′ : are the activation energies in the absence and in the presence of E-NBPTH,
respectively (J mole-1).
R: is the gas constant (8.314 J mole-1 K).
T : is the temperature (K).
Fig. 4 shows that the obtained Arrhenius plots in absence and in presence of E-NBPTH are
good straight lines. From the slopes of these straight lines we can determine the values of the
activation energy in absence (ꢅ꣏′ = 17.179 kJ/mol) and in presence of the investigated
inhibitor at 10-3M (ꢅ꣏ = 43.05 kJ/mol). We observe that the obtained value of the activation
energy in the presence of E-NBPTH is higher than that obtained in the absence of E-
NBPTH, which indicates the inhibiting behavior of the synthesized inhibitor. Consequently,
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for this type of inhibitors the elevation of temperature after the addition of the inhibitor to the
corrosive medium decreases the inhibition efficiency.
3.2.3. Checking of the adsorption isotherm
The adsorption isotherms are largely used to explicate the mechanism of corrosion inhibitors
by determination of the interactions nature between inhibiting molecules and metallic atoms.
Generally, according on the type of these interactions, we can distinguish two types of
adsorption: physisorption and chemisorption. In our case, the inhibitive action of E-NBPTH
may be related to the adsorption of its molecules on the carbon steel surface and forming a
protective layer.
In this context, to test the adsorption isotherm followed by our system, we plot the linear
regression of the graphic relation between C/θ and C at 25°C (Fig. 5). Fig. 5 shows that a
good straight line was obtained with a correlation coefficient almost equal to 1 (0.99989),
indicating that the adsorption of E-NBPTH follows Langmuir adsorption isotherm (Eq. (14)).
Also, this result indicates the formation of a mono-layer of E-NBPTH molecules on the iron
surface without lateral interactions between the adsorbed molecules.
꣐
꣑
ꢻ
=
+ ꣕
(14)
꣒
꣌꣓꣔
where C and Kads are the E-NBPTH concentration (M) and the adsorption equilibrium
constant (M−1). The Kads value can be determined from the intercept line on the C/θ axis. The
high value of Kads (Kads =14.149 103 M-1) indicates a strong interactions between the adsorbed
molecules and the iron surface [42], which are attributed to the presence of some heteroatoms
(O and N) in the molecular structure of E-NBPTH. On the other hand, the obtained value of
Kads is used to calculate the standard free energy of adsorption (∆꣖꣗꣉꣘꣙) by using the following
relation:
∆꣖꣏꣉꣚꣛ = −ꢪ꣜ ln(55.5꣝꣏꣚꣛
)
(15)
where R indicates the gas constant (8.314 J K-1 mol-1), T represent the absolute temperature
(K) and the value 55.5 represent the water concentration in the solution (M).
The calculated value of ∆꣖꣗꣉꣘꣙ for the adsorption of E-NBPTH on the iron surface is –39.33
kJ/mol. Generally, the negative sign of ∆꣖꣗꣉꣘꣙ indicates the spontaneity of the adsorption
process of E-NBPTH onto the iron surface, which means the presence of strong interactions
between the inhibitor molecules and the carbon steel surface [43]. In addition, the obtained
value of ∆꣖꣗꣉꣘꣙ is almost equal to –40 kJ/mol, this indicates that the adsorption of E-NBPTH
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on the carbon steel surface is made by means of chemical adsorption by formation of the
coordination and covalent bonds [44, 45].
3.2.4. Polarization curves tests
The obtained results of the concentration effect of E-NBPTH on the polarization curves are
summarized in Table 4 and presented in Fig. 6. From the Fig. 6, we can see that in presence of
the E-NBPTH at different concentrations, the anodic and cathodic branches of the
polarization curves are displaced towards the low currents with an identical degree. This
phenomenon indicates that the synthesized hydrazone acts as a mixed-type inhibitor by
controlling both the cathodic and anodic reactions without modifying the cathodic release of
hydrogen and the anodic degradation of the metal [46]. Also, Table 4 shows that the
increasing of the E-NBPTH concentration decreases the obtained values of icorr. Accordingly,
the inhibition efficiency increases with augmentation of the inhibitor concentration and
reaches its maximum value at 10-3 M, which indicates that the inhibiting power of the
investigated hydrazone probably associated to the its adsorption on the iron surface, which is
lead to the formation of a protective barrier film. Consequently, the corroding area on the
metal surface is reduced which leads to the diminution of the anodic dissolution of XC48
carbon steel and to the obstruction of the cathodic hydrogen liberation.
3.2.5. EIS tests
The influence of the E-NBPTH concentration on the Nyquist plot of the studied carbon steel
in 0.5M H2SO4 solution is showed in Fig. 7. Also, the electrochemical parameters determined
from the Nyquist data, such as charge transfer resistance (Rct,) double layer capacitance (CdI),
solution resistance (Rs) and inhibition efficiency (Ez (%)) are grouped in Table 5. From the
results presented in Fig. 7 and Table 5 we observe that the augmentation of the inhibitor
concentration increases the Rct values and decreases the Cdl values. The augmentation of the
Rct is probably related to the formation of a protective layer on the carbon steel surface.
Further, the diminution of the Cdl values is probably associated to the augmentation of the
width of the electrical double layer, signifying that the E-NBPTH protect the carbon steel
against corrosion by adsorption of its molecules on the iron surface [47, 48]. On the other
hand, we clearly observe from Fig. 7 that the all obtained Nyquist plots are almost semi-
circles with similar shapes. This indicates that the addition of E-NBPTH does not cause any
change to the corrosion mechanism [49]. In addition, the diameter of the Nyquist plot
augmented with the augmentation of the E-NBPTH concentration, indicating that the charge
transfer process controls the corrosion of carbon steel in the studied aggressive medium [50].
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Also, we can note from Fig. 7 that the Nyquist graphs are not perfect semicircles, which are
attributed to the frequency dispersion produced by the roughness of the surface and chemical
composition of XC48 carbon steel [51].
To evaluate the inhibition power of the studied inhibitor, we conducted a comparative study
of the inhibition efficiency of E-NBPTH and some inhibitors reported in previous studies.
We observe from the Table 6 that the E-NBPTH presents the better efficiency compared to
the selected compounds obtained in previous works [21, 52, 53]. Also, the inspection of the
molecular structures of the studied inhibitor and the three compounds selected for the
comparison (Table 6), indicates that the good inhibitive activity of the examined inhibitor can
be related to the presence of the hydrazone group (C=N ̶ N) in the molecular structure of E-
NBPTH. In addition, the presence of the NO2 group can improve the inhibition efficiency of
E-NBPTH. For example, we observe that the inhibition activity of our inhibitor is higher than
of inhibitor studied in reference [21]; this may be due to the presence of the hydrazone group
in the molecular structure of E-NBPTH.
3.3. Computational study
In general, the inhibition efficiency of an inhibitor is associated to its electronic structure,
especially some calculated quantum chemical parameters such as the EHOMO, the ELUMO, the
ꢀEGAP, dipole momentum (µ), η, σ, χ, ω and ꢀN. Also, the obtained values of these
parameters for the studied inhibitor are grouped in Table 7. All of these parameters were
calculated at the optimal geometry of E-NBPTH (Fig. 8(a)). From the Fig. 8(a), which
represents the optimized molecular structure of E-NBPTH with atomic Mulliken charges, we
observe that the most negative atoms are the N12 (-0.543), the O9 (-0.400), the O8 (-0.396)
and the N11 (-0.241), which are probably the active sits of adsorption [28]. Consequently,
these atoms (O and N atoms) can share their electron pairs with the d-orbitals of the iron
surface to form coordination bonds [54].
The chemical reactivity of the inhibitive molecules and the interactions between them or other
species can be quantified by their frontier molecular orbitals (HOMO and LUMO) and energy
gap [55]. Generally, the elevated values of the EHOMO are related to the electrons donor
capacity of a molecule [56], whereas the least values of the ELUMO are associated to the
capacity of the molecule to receive electrons [57]. Also, the elevated value of EHOMO shows
the electrons transfer tendency of a molecule to a suitable acceptor which assists the
adsorption of the inhibitive molecules on the iron surface, whereas the low value of ELUMO
indicates an efficient adsorption process [58, 59]. The Fig. 8(b) illustrates that the electron
11

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density of the HOMO orbital is almost dispersed on the all molecular structure of the E-
NBPTH, thus increasing the contribution capacity of studied hydrazone. Moreover, the
negligible HOMO density on the N ̶ O2 group is related to the high electronegativity of the
oxygen atoms which have greater affinity to keep their pairs of electrons. Meanwhile, Fig.
8(c) shows that the electron density allocation of LUMO orbital is centralized mostly on the
nitrogen atoms of the hydrazone group (N
̶ N=C) and aromatic ring who wears the nitro group
(Ar NO2), which indicates that the nitrogen atoms may be as the active centers for adsorption
̶
of E-NBPTH on iron surface. Additionally, from the optimized molecular structure of E-
NBPTH we observe that the tow aromatic rings are a plane conjugated structure, which
indicates that the inhibitor molecules are adsorbed on the iron surface in flat mode basing on
the π back bonding [60].
Generally, to measure the stability of a molecule we need to calculate its energy gap (ꢀEGAP),
which is an essential parameter that influences the reaction of an inhibitor. Also, ꢀEGAP
describes the reactivity of the inhibitive molecules towards the metallic surface. For the
studied inhibitor, the obtained low value of ꢀEGAP reveals the elevated inhibition efficiency of
E-NBPTH by improving the reactivity of the molecule, which eases the adsorption of the
investigated inhibitor on iron surface [61].
In literature, several works show that the corrosion inhibitive activity of an inhibitor can be
estimated by the dipole moment (µ), which is related to the polarity of the inhibitive molecule
[62]. Table 7 indicates that the calculated value of the dipole moment (µinh= 5.102 Debye) for
the investigated molecule is greater than that of H2O (꣞꣟ ꣠= 1.88 Debye), this high value of µ
ꢏ
leads to electrons transfer from the E-NBPTH molecules to the iron surface. Also, the
interactions between the E-NBPTH molecules and iron surface are increased with increasing
dipole moment value [63].
Global hardness and softness are two other important quantum parameters can be used to
estimate the reactivity and stability of the inhibitive molecules. In addition, the resistance of a
molecule against deformation or polarization of its electron cloud is measured by the global
hardness. Generally, a good corrosion inhibitor is characterized by the small value of global
hardness and the elevated value of the softness [64]. From the Table 7, we observe clearly that
the E-NBPTH has a low value of the hardness and an elevated value of the softness, which
proves the high inhibition efficiency of the investigated hydrazone. On the other hand, the
capability of an inhibitor to take electrons can be illustrated by the electrophilicity index (ω)
and the inhibition efficiency augments with the diminution of the ω.
12

ACCEPTED MANUSCRIPT
Also, the fraction of transferred electrons (ꢀN) is an indication of the donating ability of
electrons from the inhibitive molecules to an appropriate metallic surface. Therefore, the
increasing of the ꢀN increases the electrons contribution capability of an inhibitor at the
metallic surface, which ameliorates its inhibitive activity. The positive value of ꢀN indicates
that the ability of an inhibitor to donate electrons to the metallic surface is great; while the
negative value of ꢀN illustrates that the capability to give electrons to an appropriate metal is
low [65]. From the Table 7 we observe that the obtained value of ꢀN is positive and less than
3.6. So, in accordance with the Lukovits et al. study [66], the corrosion inhibitive activity of
E-NBPTH is enhanced by increasing of its ability to donate electrons, which indicates the
formation of an adsorbed inhibitive layer at the iron surface and appearance of coordinate
bonds between the inhibitive molecules and the iron atoms.
Generally, the active canters responsible for electrophilic and nucleophilic reactions can be
determined by interpretation of the molecular electrostatic potential (MEP) maps, which is
associated to the electronic density of a molecule. Fig. 8(d) represents the calculated 3D and
2D MEP maps of E-NBPTH. So, the examination of this figure displays that the red and
yellow colors represent the negative zones of the MEP associated to the electrophilic
reactions, whereas the blue color represents the positive zones related to the nucleophilic
reactions. Furthermore, the studied hydrazone derivative has four potential centers (O9, O8,
N11 and N12) effective for the electrophilic reactions. Also, the aromatic rings present in the
molecular structure of E-NBPTH are considered as negative zones.
3.4. Molecular dynamic simulations (MDS) study
Recently, the interactions between the inhibitive molecules and the iron surface can be
understood and interpreted by using the molecular dynamic simulations (MDS). Fig. 9
illustrates the equilibrium configuration of E-NBPTH on the Fe (110) surface in a vacuum
slab. We can observe clearly from the Fig. 9 that the E-NBPTH adsorbs on the Fe (110)
surface with a horizontal mode between the rigid hydrazone molecular structure and iron
surface, which confirms the strong interactions between the E-NBPTH and iron atoms. From
the optimized molecular structure of E-NBPTH, we can say that the adsorption on Fe (110)
surface is made by the involvement of the electrons of oxygen, nitrogen and the benzene rings
of E-NBPTH with the electrons of iron (chemical adsorption). In addition, the physical
adsorption between the E-NBPTH molecules and the iron surface produced by the Van der
Waals dispersion forces can also participate to attract the inhibitive molecules towards the
iron surface [67]. The obtained value of adsorption energy (−133.289 kcal/mol) shows that
13

ACCEPTED MANUSCRIPT
the E-NBPTH has negative adsorption energy, which indicates the spontaneity of the
adsorption process. Also, the obtained high value of binding energy (133.289 kcal/mol) is
attributed to a better and more stable adsorption process.
4. Conclusions
An aromatic hydrazone derivative (E-NBPTH) has been synthesized and its molecular
structure is analyzed by using UV-vis, IR, 1H NMR and 13C NMR spectroscopic methods. On
the other hand, the anti-corrosive activity of E-NBPTH has been evaluated for the corrosion
of the XC48 carbon steel in a 0.5 M H2SO4 solution by using the electrochemical methods, the
quantum chemical calculations and the molecular dynamic simulations. In this context,
several conclusions were drawn. Firstly, the synthesized hydrazone is a good inhibitor for the
protection of the XC48 carbon steel against corrosion in a 0.5 M H2SO4 solution and the
elevation of the E-NBPTH concentration increases its inhibitive activity. In addition, the E-
NBPTH acts as mixed inhibitor by controlling the anodic and cathodic reactions. Also, the
presence the investigated inhibitor increases the Rct and reduces Cdl values. Also, the E-
NBPTH is chemically adsorbed on the carbon steel surface according the Langmuir
adsorption isotherm. The obtained value of ∆꣖꣗꣉꣘꣙ shows the spontaneity of the adsorption
process and strong interactions are formed between the inhibitor molecules and the iron
surface. Finally, the obtained experimental results are in good agreement and are well
supported by the theoretical study such as quantum chemical calculations and Molecular
dynamics simulations.
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Figures Captions:
Fig. 1. Synthetic rout of the studied hydrazone.
Fig. 2. Correlation diagram between the theoretical and experimental wavenumbers of E-
NBPTH.
Fig. 3. Influence of E-NBPTH concentration (a) and temperature (b) on corrosion rate and
inhibition efficiency.
Fig. 4. The calculated Arrhenius straight lines for the corrosion of the XC48 carbon steel in
0.5M H2SO4 solution in presence and absence of 10-3M of E-NBPTH.
Fig. 5. Langmuir adsorption isotherm of XC48 carbon steel in 0.5M H2SO4 solution in
presence of E-NBPTH at 25°C.
Fig. 6. Potentiodynamic polarization curves obtained for the XC48 carbon steel electrode in
0.5M H2SO4 solution in presence of various concentrations of E-NBPTH at 25°C.
Fig. 7. Nyqusit plots for XC48 carbon steel in 0.5M H2SO4 solution in absence and in
presence of various concentrations of E-NBPTH at 25°C.
Fig. 8. Optimized structure with atomic Mulliken charges, HOMO and LUMO frontier
orbitals and MEP map of E-NBPTH.
Fig. 9. Side and top views of the simulated most stable configuration for the adsorption of E-
NBPTH on Fe (110) surface.
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Tables Captions:
Table 1
Experimental and theoretical values of wavenumber for the selected vibrations of E-NBPTH.
Table 2
Obtained results from weight loss tests for the corrosion of XC48 carbon steel in 0.5M H2SO4
solutions in absence and presence of different concentrations of E-NBPTH at 25°C.
Table 3
Effect of temperature on the corrosion rate and inhibition efficiency after 24h of immersion in
the electrolytic solution in presence of 10-3M of E-NBPTH.
Table 4
Electrochemical parameters obtained from the polarization curves of the XC48 carbon steel in
0.5M H2SO4 solution in absence and presence of various concentrations of E-NBPTH at
25°C.
Table 5
Electrochemical parameters obtained from EIS data of the XC48 carbon steel in 0.5M H2SO4
solution in absence and presence of various concentrations of E-NBPTH at 25°C.
Table 6
Comparison of the inhibition efficiency at the optimal concentration of E-NBPTH with the
literature data as corrosion inhibitors in acidic medium
Table 7
Calculated quantum chemical parameters of E-NBPTH using DFT/B3LYP 6-31G (d,p)
method.
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Table 1
Experimental and theoretical values of wavenumber for the selected vibrations of E-NBPTH.
Assignment
Vibrational frequency (cm-1)
Experimental Theoretical
Unscaled
Scaled
3366
3063
2919
1552
1343
1253
1146
929
3307
3079
2986
1521
1349
1254
1151
914
3502
3187
3037
1615
1397
1304
1196
967
ν(N
ν(C
ν(C
̶
̶
̶
H)
H)Ar
H)Alph
ν(C=N)
ν(NO2)
ν(C
ν(N
ν(N
δ(C
δ(N
̶
̶
̶
N)
N)
O)
H)
H)
734
779
748
̶
̶
674
691
664
ν: stretching, δ : out of plane bending

ACCEPTED MANUSCRIPT
Table 2
Obtained results from weight loss tests for the corrosion of XC48 carbon steel in 0.5M H2SO4
solutions in absence and presence of different concentrations of E-NBPTH at 25°C.
C (M)
Blank
10–6
W1 (g)
W2 (g)
Acorr (g/cm2h)
Ew (%)
∆W (g)
ꢀ
13.71110 13.61837 0.092730 0.0004097296
–
–
13.82486 13.79853 0.026330 0.0001163222 0.7161 71.61
13.76012 13.73957 0.020550 0.0000908006 0.7784 77.84
13.79221 13.77559 0.016620 0.0000734358 0.8208 82.08
13.76608 13.75358 0.012500 0.0000552315 0.8652 86.52
10–5
10–4
10–3

ACCEPTED MANUSCRIPT
Table 3
Effect of temperature on the corrosion rate and inhibition efficiency after 24h of immersion in
the electrolytic solution in presence of 10-3M of E-NBPTH.
T (°C) W1 (g)
W2 (g)
ꢀW (g) A°corr (g/cm2h) Acorr (g/cm2h) Ew (%)
13.76608 13.75358
13.74857 13.72517
13.78861 13.75085
13.69898 13.63678
0.01250 0.0004097296
0.02340 0.0005840421
0.03776 0.0006438611
0.06220 0.0008002601
0.0000552315 86.52
0.0001033934 82.30
0.0001668431 74.09
0.0002748321 65.66
25
35
45
55

ACCEPTED MANUSCRIPT
Table 4
Electrochemical parameters obtained from the polarization curves of the XC48 carbon steel in
0.5M H2SO4 solution in absence and presence of various concentrations of E-NBPTH at
25°C.
C (M)
Blank
10-6
Ecorr (mV/SCE) Icorr (mA/cm2) βa (mV/dec.) βc (mV/dec.) EP (%)
– 480.5
– 472.6
– 472.9
– 470.1
– 473.2
0.8192
0.2289
0.1778
0.1541
0.1054
81.6
59.4
54.9
41.2
37.2
– 152.2
– 125.1
– 120.4
– 107.1
– 47.9
–
72.06
78.30
81.19
87.13
10-5
10-4
10-3

ACCEPTED MANUSCRIPT
Table 5
Electrochemical parameters obtained from EIS data of the XC48 carbon steel in 0.5M H2SO4
solution in absence and presence of various concentrations of E-NBPTH at 25°C.
C (M)
Blank
10-6
Rct (ꢁ cm2) CdI (µF cm-2)
Rs (ꢁ cm2)
1.926
Ez (%)
–
19.22
64.35
91.38
102.0
141.4
2069.0
955.4
870.7
623.5
560.3
2.067
70.13
78.96
81.16
86.41
10-5
2.086
10-4
2.131
10-3
2.354

ACCEPTED MANUSCRIPT
Table 6
Comparison of the inhibition efficiency at the optimal concentration of E-NBPTH with the
literature data as corrosion inhibitors in acidic medium
Inhibitor
Ew (%) Ep (%) Ez (%)
Ref.
O
H
N+
N
N
O-
86.52
85.83
85.60
87.13
86.26
84.36
86.41 This work
H3C
N
CH3
CH3
N
83.65
72.83
[21]
[52]
F
N
N
N
N
O
N+
O-
N
N
83.00
84.00
83.00
[53]