Synthesis and assessment of two malonyl dihydrazide derivatives as corrosion inhibitors for carbon steel in acidic media: Experimental and theoretical studies

Article abstract of DOI:10.3390/molecules26113183

Despite the extensive use of carbon steel in all industrial sectors, particularly in the petroleum industry, its low corrosion resistance is an ongoing problem for these industries. In the current work, two malonyl dihydrazide derivatives, namely 2,2’-mal

Full text of DOI:10.3390/molecules26113183

molecules
Article
Synthesis and Assessment of Two Malonyl Dihydrazide
Derivatives as Corrosion Inhibitors for Carbon Steel in Acidic
Media: Experimental and Theoretical Studies
Saleh S. Alarfaji 1,2 , Ismat H. Ali 1,2,
*
, Mutasem Z. Bani-Fwaz 1,2 and Mahmoud A. Bedair 3,4
1
Department of Chemistry, College of Science, King Khalid University, P.O. Box 9004,
Abha 61413, Saudi Arabia; ssalarvagi@kku.edu.sa (S.S.A.); mbanifawaz@kku.edu.sa (M.Z.B.-F.)
Research Centre for Advanced Materials Science (RCAMS), King Khalid University, P.O. Box 9004,
Abha 61413, Saudi Arabia
Department of Chemistry, Faculty of Science (Men’s Campus), Al-Azhar University, Cairo 11884, Egypt;
mbedair@ub.edu.sa
2
3
4
College of Science and Arts, University of Bisha, P.O. Box 101, Al-Namas 61977, Saudi Arabia
Correspondence: ismathassanali@gmail.com
*
Abstract: Despite the extensive use of carbon steel in all industrial sectors, particularly in the
petroleum industry, its low corrosion resistance is an ongoing problem for these industries. In the
current work, two malonyl dihydrazide derivatives, namely 2,2’-malonylbis (N-phenylhydrazine-1-
carbothiamide (MBC) and N’1, N’3-bis(-2-hydroxybenzylidene) malonohydrazide (HBM),
were examined as inhibitors for the carbon steel corrosion in 1.0 M HCl. Both MBC and HBM
were characterised using thin-layer chromatography, elemental analysis, infrared spectroscopy,
and nuclear magnetic resonance techniques. The corrosion tests were performed using mass loss
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀꢁꢂꢃꢄꢅꢆ
Citation: Alarfaji, S.S.; Ali, I.H.;
Bani-Fwaz, M.Z.; Bedair, M.A.
Synthesis and Assessment of Two
Malonyl Dihydrazide Derivatives as
Corrosion Inhibitors for Carbon Steel
in Acidic Media: Experimental and
Theoretical Studies. Molecules 2021,
26, 3183. https://doi.org/
measurements, polarisation curves, and electrochemical impedance spectroscopy. It is obtained from
−5
the mass loss studies that the optimal concentration for both inhibitors is 2.0
×
10 mol/L, and the
inhibition efficiencies reached up to 90.7% and 84.5% for MBC and HBM, respectively. Electrochem-
ical impedance spectroscopy (EIS) and potentiodynamic polarisation (PDP) indicate an increased
impedance in the presence of both MBC and HBM and mixed-type inhibitors, respectively. Both
inhibitors can mitigate corrosion in the range of 298–328 K. Values of free energy changes obtained
from the Langmuir model suggest that the inhibitors suppress the corrosion process principally by
chemisorption. The computational investigations were conducted to identify the factors connected
with the anti-corrosive properties of the examined inhibitors.
10.3390/molecules26113183
Academic Editors: Han-Seung Lee,
Jitendra Kumar Singh and
Soumen Mandal
Keywords: corrosion; inhibitors; malonyl dihydrazide; Monte Carlo simulations; Fukui functions
Received: 30 April 2021
Accepted: 23 May 2021
Published: 26 May 2021
1. Introduction
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
published maps and institutional affil-
iations.
Acids have various uses in the industrial sector, such as acidification of oil and gas
wells, marinating and cleaning metallic products [1,2]. It is well-known that these acids
cause severe damage to metals and alloys. Consequently, there is an increasing need for
new techniques to suppress corrosion reactions. Chemical inhibitors are among the most
robust, inexpensive methods for hindering corrosion reactions [3–6]. Different organic
compounds, such as ionic liquids and pyrazoline derivatives, and most compounds con-
taining heteroatoms are widely exploited as corrosion inhibitors in various industries.
These heteroatoms, such as O, S, and N, help the organic compound to be adsorbed quickly
and firmly on the metal and alloy surfaces, and hence block the active sites and make a thin
layer on the surface, which hinder the path of corrosive media to the surface [7–11]. The
adsorption of the organic compound on metals or alloys is controlled by many factors, such
as the surface nature, type of the metal charge, and the inhibitor structure. Among organic
Copyright:
© 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
compounds, hydrazine compounds showed high corrosion inhibition effectiveness [12
–18].
Experimental methods are appropriate for clarifying the inhibition mechanisms and the
Molecules 2021, 26, 3183. https://doi.org/10.3390/molecules26113183
https://www.mdpi.com/journal/molecules

Molecules 2021, 26, 3183
2 of 17
corrosion behaviour of metals and alloys, but they are time-consuming and expensive.
Rapid development in theoretical chemistry and computer software and hardware pro-
vides very effective computing and graphical tools for researchers. During the past decade,
several corrosive works containing quantum chemical calculations have been published.
Such calculations are typically used to explore several properties, such as the electronic
properties of the inhibitors, the effect of the energies of the highest and the lowest occupied
molecular orbitals (HOMO and LUMO, respectively), and the gap between them [19–21]
.
Theoretical studies including both density functional theory (DFT) calculations and molec-
ular dynamic (MD) simulations on the inhibition action of some hydrazine derivatives
have been reported recently [20].
This work aims to explore the corrosion behaviour of C-steel in the presence of two mal-
onyl dihydrazide derivatives, namely, 2,2’-malonylbis(N-phenylhydrazine-1-carbothiamide),
abbreviated as MBC, and N’1, N’3-bis(-2-hydroxybenzylidene)malonohydrazide, abbre-
viated as HBM. It is well-known that the derivatives of Schiff bases are considered as
eco-friendly materials [19,20]. In addition, malonic acid is usually used as a green material
for various applications [21]. This work also aims to investigate the inhibition effect of
these two derivatives and to explain the nature of the inhibition process using the po-
tentiodynamic polarisation curves (PDP), electrochemical impedance spectroscopy (EIS),
and scanning electron microscopy (SEM). Additionally, to evaluate the adsorption affinity
of the inhibitors under study on the surface of the carbon steel, comprehensive theoretical
studies were performed using MD and DFT.
2. Results
2.1. Characterisation of the Inhibitors
The synthesis of both the thiosemicarbazide derivative (MBC) and the hydrazone
Schiff base derivative (HBM) from malonyl dihydrazide is shown in Scheme 1 according
to the published procedures [22–25]. The purity of both compounds was checked by
thin-layer chromatography (TLC) and melting point.
Scheme 1. General procedure for the synthesis of both the thiosemicarbazide derivative (1) and
hydrazone Schiff base derivative (2).
The number of NMR signals for the hydrazone Schiff base derivative (HBM) can only
be explained by assuming at least three different tautomeric isomers, as shown in Scheme 2
.

Molecules 2021, 26, 3183
3 of 17
Twenty years ago, Zhang et al. [25] confirmed the three different tautomeric isomers by
experimental and calculated spectra of NMR spectroscopy.
Scheme 2. Keto-enol tautomeric isomers of the hydrazone Schiff base.
2.2. Weight Loss Measurements
A series of mass loss experiments were performed to determine the corrosion rate
in the presence and absence of the two inhibitors under study. The corrosion rate of
carbon steel and the MBC and HBM efficiencies as corrosion inhibitors were calculated
by the weight loss method in 1.0 M HCl solutions containing various MBC and HBM
concentrations at 298 K. The values of the inhibition efficiency, IEML%, were calculated
using Equation (1) [26] and are displayed in Table 1.
CRML − CRoML
IE%ML
=
× 100
(1)
CRML
where CRML and CRMo L are corrosion rates of the carbon steel in the inhibited and unin-
hibited solutions. Obviously, from the data in Table 1, the inhibition efficiency values are
directly proportional to the MBC and HBM concentrations.

Molecules 2021, 26, 3183
4 of 17
Table 1. Mass loss results of MBC and HBM inhibitors at 298 K.
106 Concentration
mol/L
Weight Loss
(mg)
IEML
(%)
Surface Coverage
Inhibitor
(θ)
Blank
–
67.9
-
-
5.0
26.3
20.5
12.2
6.3
61.3
69.8
82.0
90.7
0.6127
0.6981
0.8203
0.9072
10.0
15.0
20.0
MBC
HBM
5.0
31.9
25.1
16.0
10.5
53.0
63.0
76.4
84.5
0.5301
0.6303
0.7664
0.8453
10.0
15.0
20.0
The highest corrosion rate and lowest inhibition efficiency are recorded at low concen-
trations of both inhibitors, MBC and HBM, and the hazards for the attack of the corrosive
media are significantly increased. When the concentrations of MBC and HBM increase by a
certain quantity, more protection is observed. The maximum inhibition efficiencies (IEML%)
were determined as 90.7% and 84.5% for MBC and HBM, respectively. The inhibitive
performance of both MBC and HBM is most likely due to the inhibitors’ adsorption on the
carbon steel surface.
2.3. Temperature Effect
Numerous mass loss experiments were conducted at the range of 298–328 K in the
presence and absence of 2.0
×
10−5 mol/L of both inhibitors. Table 2 revealed that the
corrosion rate increases for both the blank and the inhibited solutions as the temperature
increases. The IEML% drops from 90.7% to 79.4% and from 84.5% to 73.5% for MBC and
HBM respectively, as the temperature increases. These results designate that both inhibitors
could successfully suppress the corrosion reactions at relatively higher temperatures.
Results showed in Table 2 confirm that the mass loss values increase as the temperature
increases in both the blank and uninhibited solutions. Table 2 also revealed that IE% values
of both inhibitors slightly decreased as the temperature increases.
−5
Table 2. Effect of temperature on the inhibition efficiency of MBC and HBM at 2 × 10 M.
Inhibitor
Temperature
Weight Loss (mg)
IE (η%)
298
308
318
328
67.9
85.7
91.6
-
-
-
-
Blank
112.5
298
308
318
328
6.3
90.7
87.0
83.1
79.4
11.1
15.5
23.2
MBC
HBM
298
308
318
328
10.5
16.1
21.3
29.8
84.5
81.2
76.7
73.5
The mass loss values were adopted to determine the activation energy values, as shown
in Equation (2). The entropy ( S) and enthalpy ( H) changes were calculated from the
∆
∆
intercept and slope of Equation (3) and Figure 1, respectively.
Ea
ln ML = ln A −
RT
(2)

Molecules 2021, 26, 3183
5 of 17
ML
T
−∆H
kB
h
∆S
R
ln
=
+ ln
+
(3)
RT
where Ea is the activation energy of the corrosion process, kB is the Boltzmann constant,
T is the temperature in Kelvin, A is the frequency factor, and h is Planck’s constant.
-1.0
-1.5
Blank
HBM
-2.0
MBC
-2.5
-3.0
-3.5
-4.0
3.0x10-3
3.1x10-3
3.2x10-3
3.3x10-3
3.4x10-3
1/T, K-1
Figure 1. Erying model for blank, MBC and HBM.
Values of S, H, and Ea in the blank and inhibited solutions are presented in Table 3.
∆
∆
The values of activation energies in the presence of both MBC and HBM are lower than that
in the blank solution, proving that the corrosion process is more difficult after the addition
of the inhibitors. It is also clear that
∆
S and
∆H are greater than those in the blank solution.
The more significant negative sign of
∆
H in the presence of the inhibitors indicates an
exothermic nature of the corrosion process, suggesting that the ionisation of steel surface
is slow [27] in the presence of both MBC and HBM. A significant and positive value of
entropy (∆S) means that during the rate-determining step, the activated complex is formed
via an association rather than a dissociation step [28], confirming that an increase in the
disorder takes place when going from reactants to the activated complex.
Table 3. Values of activation parameters for carbon steel in 1.0 M HCl in the absence and presence of
−5
2.0 × 10 M of MBC and HBM.
Inhibitor
Ea (kJ/mol)
∆H (kJ/mol)
∆S (J/mol)
Blank
HBM
MBC
12.9
27.7
34.6
−10.3
−25.1
−40.3
175
144
122
2.4. Adsorption Isotherm Model
Both MBC and HBM are expected to be adsorbed on the carbon steel surface and,
hence, protect the metallic surface from the aggressive acidic solution’s attack. Conse-
quently, it is essential to investigate which type of adsorption (physisorption or chemisorp-
tion) plays the controlling role during the adsorption process. Generally, inhibitors are
adsorbed on metal/solution interface by the displacement of H2O molecules, as shown in
Equation (4) [3]:
inhibitor(solution) + xH2O(adsorbed) ꢀ inhibitor(adsorbed) + xH2O(solution)
(4)

Molecules 2021, 26, 3183
6 of 17
The surface coverage values were found from the mass loss measurement and ex-
amined various adsorption models, namely, Langmuir, Temkin, and Freundlich. Results
revealed that the Langmuir adsorption model fitted well (Figure 2) with a correlation
coefficient (R2) of 0.991 and 0.990 for MBC and HBM, respectively. The Langmuir equation
is shown in Equation (5) [28]:
Cinh
θ
1
Kads
=
+ Cinh
(5)
where θ is the surface coverage, Cinh is the concentration of the MBC and HBM, and Kads
is the equilibrium constant of the adsorption. The plot of the Langmuir adsorption model
(Figure 3a) gives straight lines having high Kads values, indicating that both MBC and
HBM molecules have strong interaction with the steel surface. Kads is directly related to
the standard free energy change of adsorption (∆Goads) by Equation (6) [3]:
ꢀ
ꢁ
−∆Goads
1
55.5
Kads
=
Exp
(6)
RT
where 55.5 is the molar concentration of water expressed in mol/L, R is the gas constant,
and T is the temperature in Kelvin. The values of Kads and ∆Go are shown in Table 4.
MBC
HBM
2.4x10-5
2.0x10-5
1.6x10-5
1.2x10-5
8.0x10-6
4.0x10-6
8.0x10-6
1.2x10-5
,mol/L
1.6x10-5
2.0x10-5
C
inh
Figure 2. Plot of the Langmuir model for MBC and HBM.
100
10
1
0.1
0.01
1E-3
1E-4
1E-5
1E-6
1E-7
0.1
blank
Blank
−6
0.01
1E-3
5×10 mol/L
5× 10−6 mol/L
1× 10−5 mol/L
2 × 10−6 mol/L
3× 10−6 mol/L
−5
1×10 mol/L
−5
2×10 mol/L
−5
3×10 mol/L
-800
-700
-600
-500
-400
-300
-200
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
E(mV/SCE)
E( mV/SCE)
(a)
(b)
Figure 3. Potentiodynamic polarisation curves of carbon steel in 1.0 M HCl in the presence of different concentrations of (
a)
MBC and (b) HBM.

Molecules 2021, 26, 3183
7 of 17
Table 4. Values of Kads and ∆Gads
.
Inhibitor
HBM
Kads
∆Goads (kJ/mol)
−45.1
1.7 × 105
2.5 × 105
MBC
−47.9
The free energy changes’ negative values designate that adsorption of MBC and HBM
on the carbon steel surface is spontaneous. The values of
Go are more negative than
40 kJ mol/L, indicating a chemical nature of the adsorption process. The results shown
in Table 4 demonstrate that MBC has a slightly higher negative value of
Go than that of
∆
∆
the HBM inhibitor. This fact can be ascribed to the presence of sulphur atoms in the MBC
structure. It actively boosts electron density over the whole molecular skeleton of the MBC
inhibitor, and this is one of the potential reasons for the higher efficiency of MBC than that
of HBM.
2.5. Electrochemical Measurements
2.5.1. Potentiodynamic Polarisation
Potentiodynamic polarisation plots found for carbon steel corrosion in the presence
and absence of MBC and HBM are shown in Figure 3a,b The kinetic parameters recorded
in Table 5 were obtained from Tafel curves. The percentage of inhibition efficiency (EI%PDP
for each inhibitor concentration has been determined by Equation (7):
)
icorr − icorr[inh]
IE% =
× 100
(7)
icorr
where icorr and icorr[inh] are the blank and inhibited corrosion current densities, respectively.
Table 5 exhibits that in the presence of MBC and HBM, the icorr[inh] is extremely reduced,
which indicates the formation of a protective film on the surface of the carbon steel.
Table 5. Kinetic data obtained from the PDP curves for blank, MBC, and HBM.
Concentration
−Ecorr
icorr
(µA cm
β
β
c
a
Inhibitor
θ
IE%
−2
−1
−1
(mV dec )
mol/L
(mV vs. SCE)
)
(mV dec
)
Blank
—
335
327
62
124
5.0
10
20.0
30.0
378
367
383
371
129
88
58
81
67
101
92
126
131
157
163
0.6055
0.7309
0.8226
0.9021
60.6
73.1
82.3
90.2
MBC
MBC
32
5.0
367
379
356
341
147
97
71
117
92
88
182
127
136
125
0.5504
0.7034
0.7828
0.8502
55.0
70.3
78.3
85.0
10.0
20.0
30.0
49
82
Furthermore, the values of cathodic Tafel slope (bc) and anodic Tafel slope (ba) pre-
sented in Table 5 are almost constant because the hindrance of the corrosion process is
principal as a result of the blocking of active positions on the steel surface, and hence, the
dissolution mechanism does not change in the presence of inhibitors.
Inhibitors can be divided into three classes: cathodic, anodic, cathodic, or mixed type
according to the displacement of the values of the corrosion potential in the presence and
absence of the inhibitor. When the displacement of the corrosion potential’s values is greater
than 85 mV, the inhibitor is classified as anodic or cathodic type [3]. The displacement
is less than 85 mV for both inhibitors, and thus MBC and HBM are classified as mixed-
type inhibitors. Table 5 reveals that the icorr values decrease distinctly as the inhibitor
concentration increases. This outcome confirms that both MBC and HBM can act as good

Molecules 2021, 26, 3183
8 of 17
corrosion inhibitors. The good inhibition efficiencies for both MBC and HBM are most likely
ascribed to their molecular structures, amongst other factors. In Scheme 1, it is observed
that both MBC and HBM contain benzene rings, delocalised p-electrons, N atoms, S atoms,
and electron-donating groups in their structure, helping the MBC and HBM molecules to
adhere firmly to the steel surface. Therefore, high inhibition efficiency is probable.
2.5.2. Electrochemical Impedance Spectroscopy EIS
EIS examined the capacity of MBC and HBM to inhibit the corrosion process. The Elec-
trical Equivalent Circuit (EEC) formula usually used for adjustment is shown in Figure 4
.
Outcomes are shown in Figure 5a,b. It is clear that the addition of both inhibitors power-
fully influenced the impedance response, and this effect is evident from the diameter of
semi-circles, which increased clearly.
Figure 4. Equivalent circuit model for the analysis of the electrochemical impedance spectroscopy data.
500
500
400
300
200
100
Blank
3 × 10−5 mol/L
2 × 10−5 mol/L
1 × 10−5 mol/L
5 × 10−6 mol/L
3 × 10−5 mol/L
2 × 10−5 mol/L
1 × 10−5 mol/L
5 × 10−6 mol/L
400
blank
300
200
100
0
0
0
100
200
300
400
500
600
700
800
0
100
200
300
Z
400
500
600
700
800
Zr (ohm.cm2)
2
(ohm.cm
)
r
(a)
(b)
Figure 5. Nyquist spectra for (a) MBC and (b) HBM.
The Nyquist spectra (Figure 5) exhibit slightly depressed semi-circles at medium to
high frequencies and an inductive feature at lower frequencies. The capacitive loop at
a higher frequency range suggests that carbon steel’s corrosion is mainly affected by a
charge transfer process [29]. The increase of the diameter is more noticeable as the inhibitor
concentration increases, which can be ascribed to the formation of a protective film on the
steel surface [3]. The inductive loop is ascribed to the relaxation process caused by the
adsorption of intermediate products in the presence of acid solutions and inhibitors [3,7].
It can be concluded from Table 6 that the Rct values are directly proportional to the
inhibitor’s concentrations, and in turn, the values of %IEEIS increase. Values of %IEEIS are
obtained from the Rct values of charge transfer resistance data using Equation (8) [29]:
Rct − Rct(inh)
%EIEIS
=
× 100
(8)
Rct
where Rct and Rct(inh) are the charge-transfer resistance values without and with
inhibitors, respectively.

Molecules 2021, 26, 3183
9 of 17
Table 6. Results obtained from EIS diagram for MBC and HBM.
106 × Conc.
RS,
10 × Yo
Rct
−3
Inhibitors
n
Θ
%IEEIS
(mol/L)
(Ω cm2)
µ Ω sn cm
(Ω cm2)
−1
−1
Blank
–
11.9
134.10
0.799
19.3 ± 0.7
-
-
5.0
9.5
9.6
1.5
1.7
123.40
148.70
33.22
0.801
0.827
0.866
0.835
49.4 ± 1.7
72.5 ± 3.1
111.8 ± 4.5
219.4 ± 7.8
0.6093
0.7337
0.8274
0.9120
60.9
73.4
82.7
91.2
10.0
20.0
30.0
MBC
HBM
33.01
5.0
2.7
10.0
9.9
85.72
90.12
163.6
39.83
0.887
0.750
0.791
0.862
43.1 ± 1.8
64.4 ± 2.6
82.7 ± 3.7
140.7 ± 6.3
0.5522
0.7003
0.7666
0.8628
55.2
70.0
76.7
86.3
10.0
20.0
30.0
1.4
Rs is the solution resistance, Rct is charge-transfer resistance, Yo is the capacitance, and n is the phase shift that can be explained as the
degree of the surface inhomogeneity [20].
2.6. Quantum Chemical Calculations
2.6.1. Global Reactivity Descriptors
Quantum chemical calculation can support our findings with highlights on the relation
between MBC and HBM molecular configuration and their performance as corrosion
inhibitors through various vital data. We found no virtual frequency for the optimised
MBC and HBM molecules by examining the calculated data. Figure 6 shows the most
stable configuration of MBC and HBM molecules in their neutral conditions, besides the
distribution of molecular orbital (LUMO and HOMO) maps. The calculations showed that
it varies from 1.38 to 1.40 Å for the two aromatic ring moieties for the bond distance. For the
substituted two hydroxyl groups on the aromatic rings in the HBM compound, the O-Ar
bond distance was 1.345 Å. The two N-N bond distances were 1.356 Å for MBC and 1.329
Å for the HBM. The two azo methane groups N=C in the HBM compound showed a bond
distance of 1.282 Å. The shortest bond distance was observed for the carbonyl groups C=O,
with values of 1.229 Å in MBC and 1.207 Å in HBM.
Figure 6. Optimized HOMO and LUMO structures of MBC and HBM obtained from DMol3 calculations.

Molecules 2021, 26, 3183
10 of 17
On the other hand, the most extended bond length was observed for C=S groups in
MBC (1.665 Å), facilitating its adsorption on the steel surface. The distribution of electron
clouds belongs to the HOMO, and LUMO orbitals of the MBC and HBM molecules were
located across the entire skeletons. The transfer of the electron is from MBC and HBM to
the steel surface, and so protection is mainly a result of the interaction energy between
the HOMO—inhibitor and the LUMO—steel, and vice versa. HOMO and LUMO are
functions that determine molecules’ capacity for electron-donating and accepting, respec-
tively [30–32]. Therefore, we can infer that MBC and HBM can adsorb on the steel surface
by multiple active sites, providing significant surface coverage and enhanced protection.
The different quantum chemical parameters obtained for MBC and HBM are sum-
marised in Table 7. The increase in EHOMO values shows the high electron-donating ability
of the molecule to vacant metal orbitals.
Table 7. The calculated quantum chemical parameters in eV for the neutral and protonated inhibitors at DMol3 in gas phase
and in aqueous phase.
EHOMO ELUMO
(eV) (eV)
∆E
∆Eback donation
T.E.
ε
σ
ω
χ
∆N
∆Nmax
η
IEEIS
(%)
Molecule
(eV−1
)
(eV−1
)
(eV)
(eV)
(eV)
(eV)
(eV)
(e)
(e)
(eV)
Neutral
MBC
HBM
−4.8178 −1.8514 2.9664
−5.0035 −1.6499 3.3536
−0.3708
−0.4192
−52,259.80
−31,753.34
0.2668
0.3030
0.6742
0.5964
3.7484
3.3000
3.3346
3.3267
1.2356 1.1241 1.4832 91.2
1.0953 0.9920 1.6768 86.3
MBC
HBM
−5.3499 −2.3952 2.9547
−5.2743 −1.9849 3.2894
−0.3693
−0.4112
−52,261.09
−31,755.13
0.1970
0.2497
0.6769
0.6080
5.0754
4.0049
3.8725
3.6296
1.0585 1.3106 1.4774 91.2
1.0246 1.1034 1.6447 86.3
Protonated
MBC-H2+
HBM-H2+
−10.5274 −9.4107 1.1167
−10.7963 −8.1222 2.6741
−0.1396
−0.3343
−52,266.230 0.0112
−31,769.026 0.0299
1.7910
0.7479
88.997
33.460
9.9691
9.4593
−2.65888.9273 0.5583 91.2
−0.91963.5373 1.3371 86.3
MBC-H2+
HBM-H2+
−5.9557 −4.1612 1.7945
−6.1254 −3.5374 2.5879
−0.2243
−0.3235
−52,271.259 0.0701
−31,776.083 0.1109
1.1145
0.7728
14.258
9.0196
5.0584
4.8314
1.0819 2.8188 0.8973 91.2
0.8380 1.8669 1.2940 86.3
On the contrary, the decrease in ELUMO values indicates the high tendency of the
molecule to obtain electrons from steel [30 32]. The difference between ELUMO and EHOMO
is related to the reactivity of the molecule. As the smaller is the value of E, the higher is
the molecule’s reactivity [30 32]. Regarding our results in Table 7, we can find that MBC
–
∆
–
possesses more electron-donating tendency (EHOMO) than HBM in all forms (neutral and
protonated) and phases (gas and aqueous). This tendency to donate electrons supports the
order results from the experimental studies. The MBC molecule also possesses the lowest
values of ELUMO, indicating its high ability to accept electrons from steel (back donation)
and therefore strong binding to the steel surface. The EHOMO values of the two molecules
increased upon protonation, so the protonated form can be readily adsorbed by donating
more electrons. Concerning the energy gap (
reactivity as it obtains the lowest values.
∆E), the MBC molecule overcomes HBM in
The presence of two S atoms and more conjugation in the MBC molecule increases its
adsorption ability on the steel surface. The electron back donation from steel to inhibitor
molecules was confirmed by negative values of
We found that MBC possesses higher total negative charge (
phase) than HBM ( 5.634) for the electrostatic attraction between the inhibitors and steel
surface. This high negative charge on the MBC molecule supports its high inhibition
efficiency. Based on the fraction of electrons transferred ( N) quantum parameter, posi-
tive values of N prove that electrons can follow from inhibitor molecules to the metal
∆
EBack-donation
(
∆
EBack-donation
=
−
η4 ) [33].
−
6.755—neutral form—gas
−
∆
∆

Molecules 2021, 26, 3183
11 of 17
surface [34].
∆
N of MBC is higher than HBM, suggest that the tendency of MBC molecules
to share their electrons with steel surface is more prominent than HBM molecules.
2.6.2. Local Reactivity: Fukui Functions
The best way to describe the local sites for electrophilic/nucleophilic reactivity through
the atomic charges is the local Fukui indices [35]. It enables us to identify the atomic sites
for donating or accepting electrons. Fukui functions are the derivative of chemical potential
and can be calculated for nucleophilic and electrophilic attacks by approximation method
through the following mathematical relations [36].
f (r) = (∂µ/∂ν)N
(9)
fk+ = qk(N + 1) − qk(N)
fk− = qk(N) − qk(N − 1)
(10)
(11)
where qk = atomic charge in different states (neutral (N), anionic (N + 1) or cationic (N
−
1)).
Fukui indices fk+ and fk− represent either the nucleophilic or the electrophilic sites of the
atoms. The large values of fk− are the most suitable sites to interact with electron-deficient
species. On the other hand, the large values of fk+ are the most suitable sites to interact
with electron-rich species [37]. Table 8 collects the Fukui indices for the MBC and HBM
molecules calculated from Hirshfeld atomic charges obtained from the DMol3 calculations.
As listed in Table 8, the large number of heteroatoms present in MBC molecules (S 10,
S 21, N 6, N 17, N 7, N 18, O 2, O 5, N 9, and N 20) obtain high values of fk− (0.034–0.054,
aqueous phase). These sites facilitate their interaction with a steel surface. In the HBM
molecule, we found less fk− active sites (O 24, N 7, O 25, N 6, N 8, N 9, O 2, and O 5) with
lower values (0.036–0.041, aqueous phase). This inefficiency is consistent with that of the
experimental ranking MBC > HBM inefficiency.
Table 8. The Fukui functions of studied inhibitors calculated by the DMol3 method.
MBC
HBM
Gas Phase
Aqueous Phase
Gas Phase
Aqueous Phase
Atom
Atom
f+
f−
f+
f−
f+
f−
f+
f−
∆ f
∆ f
∆ f
∆ f
C (1)
O (2)
0.028
0.035
0.01
0.018
0.041
0.008
0.018
0.041
0.042
0.041
0.01
0.029
0.063
0.012
0.019
0.019
0.037
0.022
0.02
0.042
0.041
0.01
0.029
0.063
0.012
0.02
0.022
0.037
0.019
0.019
0.01
0.033
0.024
0.041
0.012
0.024
0.041
0.05
0.009
C (1)
0.025
0.039
0.009
0.025
0.039
0.014
0.014
0.044
0.044
0.049
0.049
0.017
0.017
0.02
0.015
0.037
0.007
0.015
0.037
0.038
0.038
0.029
0.029
0.032
0.032
0.024
0.024
0.027
0.023
0.04
0.01
0.002
0.002
0.01
0.032
0.04
0.019
0.036
0.009
0.019
0.036
0.039
0.04
0.039
0.039
0.032
0.032
0.031
0.032
0.032
0.022
0.034
0.036
0.02
0.013
0.004
0.003
0.013
0.004
−0.02
−0.021
0.014
0.014
0.025
0.026
−0.009
−0.009
−0.008
0
−0.006 0.034
−0.007 O (2)
C (3)
0.002
0.01
0.012
0.033
0
C (3)
C (4)
0.012
0.032
0.04
C (4)
0.028
0.035
0.02
0.009
O (5)
−0.006 0.034
−0.007 O (5)
−0.024 N (6)
−0.031 N (7)
0.002
N (6)
−0.022 0.026
−0.024 0.019
N (7)
0.011
0.046
0.017
0.095
0.012
0.017
0.02
0.037
0.023
0.019
0.02
−0.03
0.015
0.051
0.046
0.016
0.034
0.054
0.017
0.021
0.015
0.03
−0.024 0.019
C (8)
0.036
0.035
N (8)
0.015
0.015
0.017
0.017
0.053
0.053
0.057
0.058
N (9)
−0.012 0.021
−0.013 N (9)
S (10)
C (11)
C (12)
C (13)
C (14)
C (15)
C (16)
N (17)
N (18)
C (19)
N (20)
S (21)
C (22)
C (23)
C (24)
C (25)
C (26)
C (27)
0.032
0
0.097
0.018
0.043
0.001
0
C (10)
C (11)
C (12)
C (13)
−0.002 0.021
−0.007 0.022
−0.007 0.023
−0.007 0.024
0.001
0
0.016
0.029
0.018
0.001
−0.001 C (14)
0.001
0.016
0.021
0.05
0.002
C (15)
0.026
0.048
0.026
0.029
0.029
0.026
0.048
0.026
0.02
0.003
0.008
0.022
0.041
−0.001 0.019
−0.002 C (16)
−0.024 C (17)
−0.031 C (18)
0.007
−0.015
0.01
−0.022 0.026
0.037
0.021
0.02
−0.011 0.021
0.011
0.046
0.017
0.095
0.012
0.019
0.023
0.037
0.02
−0.03
0.015
0.051
0.046
0.016
0.034
0.054
0.017
0.021
0.016
0.03
0.008
0.009
0.03
0.03
0.036
0.035
C (19)
0.021
0.036
0.034
0.022
0.033
0.041
0.04
0.009
−0.014
0.007
0
−0.009
−0.022
−0.022
−0.012 0.021
−0.013 C (20)
0.037
0.04
0.023
0.027
0.034
0.034
−0.011 0.022
0.032
0
0.097
0.018
0.043
0.001
C (21)
C (22)
0.008
0.003
0.041
0.022
−0.001 0.019
−0.002 C (23)
−0.007 0.024
−0.018 0.019
−0.018 0.018
0.001
0
0.018
0.029
0.016
0.002
O (24)
0.016
0.016
−0.001 O (25)
0.001
0.015
0.021
0.001
0
0.017
−0.002 0.021

Molecules 2021, 26, 3183
12 of 17
The identification of the active site is also confirmed by calculating the dual descriptor,
by Equation (12) [38]:
+
−
∆ f (k) = fk − fk
(12)
Positive values of
∆
f are related to nucleophilic attack but negative values of
∆
f are
related to electrophilic attack. For
∆
f > 0, the sites highly ready for nucleophilic attack are
MBC: C8, C19, S10, and S21, and HBM: N8, N9, C10, and C11. On the contrary, for ∆f < 0,
the sites highly ready for electrophilic attack are MBC: N6, N7, N17, and N18, and HBM:
N6, N7, O24, and O25.
2.7. Monte Carlo Simulations
It is imperative to study the interaction between MBC, HBM molecules, and steel
surface with Monte Carlo simulations. It was used to determine the different forms of
adsorption energy and total energy for MBC and HBM molecules, as presented in Table 9.
Table 9. The outputs and descriptors calculated by the Monte Carlo simulation for adsorption of
MBC and HBM on Fe (110) (in kcal/mol).
Neutral
Protonated
Inhibitor
MBC
HBM
MBC-H2+
HBM-H2+
−1
−6316.14
−7285.79
−6358.46
−927.33
−1197.17
7285.79
91.2
−6315.12
−6473.38
−6345.46
−127.91
−379.55
6473.38
86.3
−6181.61
−7245.47
−6318.53
−926.94
−1378.37
7245.47
91.2
−6164.68
−6416.35
−6228.34
−188.01
−629.96
6416.35
86.3
Total energy (kcal mol
)
−1
Adsorption energy (kcal mol
Rigid adsorption energy (kcal mol
)
−1
)
−1
Deformation energy (kcal mol
)
−1
(dEads/dNi) (kcal mol
Binding energy (kcal mol
IEEIS (%)
)
−1
)
The adsorption energy’s negative values for both MBC and HBM molecules either in
neutral or protonated states prove that their adsorption occurred spontaneously [39]. MBC
molecules possess higher negative values of adsorption energy (
−
7285.79 kcal mol−1
6473.38 kcal mol−1
—
—
neutral,
neutral,
−
7245.47 kcal mol−1—protonated) than HBM molecules (
−
−
6416.35 kcal mol−1—protonated), which suggested the more vital adsorption
ability and extra corrosion inhibition of MBC on the Fe (110). The high negative adsorption
energy of the protonated forms suggested that MBC and HBM molecules are still highly
effective inhibitors even after protonation. Figure 7 shows the equilibrium configuration of
MBC and HBM/Fe (110) in the presence of H2O, H3O+, and Cl−. It is clear from Figure 7
that simulations of both molecules happened through parallel orientation adsorption on
Fe (110) via heteroatoms (O, N, and S), conjugated systems of aromatic moieties, and
π
electrons. The side-by-side orientation adsorption will provide a higher blocking area and
effective interactions between all active sites in MBC and HBM molecules and Fe (110)
atoms and stimulate the inhibition effect. The large size of the MBC molecules associated
with more adsorption centres, such as the sulphur atoms, resulted in more area than the
HBM molecules.

Molecules 2021, 26, 3183
13 of 17
Figure 7. Side and top views of the most appropriate configuration for adsorption of neutral molecules on Fe (110) surface
obtained by Monte Carlo simulations in the aqueous solution.
3. Materials and Methods
3.1. Materials
The composition of the C-steel used throughout all experiments was (wt%) 0.20 C,
0.045 P, 0.30 Si, 0.53 Mn, 0.055 S, Fe balance. The corrosive solution (1.0 M HCl) was
prepared by direct dilution with double-distilled water.
Malonic diethyl ester, salicylaldehyde, phenyl isocyanate, and hydrazine hydrate
(80%) were purchased commercially from Sigma Aldrich, St. Louis MO, USA, and used
without any further purification. Absolute ethanol, DMSO, diethyl ether, and all used
solvents were purchased from Merck, Mumbai, India. The melting points were reported
on a heated stage Gallen Kamp melting point equipment (Gemini Lab, Apeldoom, Nether-
lands). Elemental C, H, N, and S analyses were carried out on a Fison EA 1108 analyser
(Shimadzu, Kyoto, Japan). The infrared (FTIR) spectra were recorded by employing a
FTIR.8300 Shimadzu Spectrophotometer (Shimadzu, Kyoto, Japan) by using KBr disc
1
in the frequency range of 4000–400 cm−1. The H NMR spectra were recorded on an
Ultra-Shield™ 500 MHz NMR Spectrometer (Shimadzu, Kyoto, Japan) using deuterated
DMSO-d6s the solvent and tetramethylsilane (TMS) as the internal standard.
3.2. Synthesis of Malonyl Dihydrazide
Malonic diethyl ester (38 mL, 40.05 g, 250.06 mmol) in 100 mL absolute ethanol was
added slowly dropwise to a stirred excess hot solution of 61 mL of hydrazine hydrate (80%)
(1002 mmol) in 100 mL absolute ethanol for 2 h. The reaction mixture was then refluxed in
a water bath for 10 h then cooled in an ice-water bath. The white solid was filtrated, rinsed
with ethanol and diethyl ether, and then dried in a desiccator over anhydrous CaCl2. Yield
was 91% (30, 227.07 mmol); mp. 154–155 ◦C (lit. 154 ◦C). Elemental analysis: C3H8N4O2,
Calc.: C 27.27%; H 6.10%; N 42.41%; found: C 27.32%; H 6.06%; N 42.37%. IR (KBr; cm−1):
3280, 3188
(2H, s, CH2), δ 4.24 (4H, s, 2NH2), δ 9.07 (2H, s, 2NH) [22].
ν(NH2), 3064 ν(NH), 2967 ν(CH), 1671 ν δ)]: δ 2.90
(C=O). 1H NMR [(DMSO-d6,

Molecules 2021, 26, 3183
14 of 17
3.3. Synthesis of 2,2’-Malonylbis(N-phenylhydrazine-1-carbothioamide) (MBC)
Phenyl isothiocyanate (2 mL, 2.26 g, 16.75 mmol) in 25 mL absolute ethanol was added
slowly dropwise to a stirred hot suspension of malonyl dihydrazide (1.10 g, 8.33 mmol)
in 25 mL absolute ethanol. The reaction mixture was then refluxed in a water bath for
8 h then cooled in an ice-water bath. The white solid was assembled and rinsed with
ethanol prior ◦to drying in an electric oven at 70 ◦C. Yield was 92.5% (3.1 g, 7.70 mmol);
◦
mp. 181–182 C (lit. 181–182 C). Elemental analysis: C17H18N6O2S2, Calc.: C 50.73%;
H 4.51%; N 20.88%; found: C 50.80%; H 4.47%; N 20.90%. IR (KBr; cm−1): 3144
ν
(NH),
3.33
10.36
3019
(2H, s, CH2),
(2H, s, 2NH) [23].
ν
(ArCH), 1671
ν
(C=O), 1349
ν
(C=S), 1511 (ArC=C). 1H NMR [(DMSO-d6,
9.64 (2H,s, 2NH), 9.84 (2H, s, 2NH), δ
δ)]:
δ
δ
7.17–7.50 (10H, m, ArH)),
δ
δ
3.4. Synthesis of N’1, N’3-bis(2-Hydroxybenzylidene)malonohydrazide (HBM)
Thin drops of glacial acetic acid were added to a solution of salicylaldehyde (3.5 mL
,
4.07 g, 33.36 mmol) in 25 mL absolute ethanol (soln. A). A suspension of malonyl dihy-
drazide (2.104 g, 15.92 mmol) was added to 25 mL of absolute ethanol (soln. B). Solution A
was added to a hot solution B with stirring over 1 h. The reaction mixture was then refluxed
in a water bath for 8 h then cooled in an ice-water bath. The white solid was obtained and
soaked with ethanol prior to drying in an electric oven at 70 ◦C. Yield was 88.6% (4.8 g,
14.10 mmol); mp. 233–235 ◦C (lit. 234–236 ◦C). Elemental analysis: C17H16N4O4, Calc.: C
60.0%; H 4.74%; N 16.46%; found: C 60.05%; H 4.69%; N 16.39%. IR (KBr; cm−1): 3748;
3271; 3062 ν(NH) + ν(OH), 2963 ν(CH), 1667 ν(C=O), 1607; 1541 ν(C=N) + Amide(II). 1H
NMR (DMSO-d6,
enol-ketone: dienol forms,
multiplets, ArH), 8.27, 8.28, 8.42 (2H, s, HC=N-NH, HC=N-NH/HC=N-N=C, HC=N-
N=C) ratio 1:1:1, 9.01, 10.01 (2H, s), 11.07, 11.41 (2H, s), 11.42, 11.49 (2H, s) and 11.88
δ):
δ
3.36, 3.61, 3.91 (2H, s, CH2), ratio 1:2:1, three tautomers, diketone:
δ
6.69–6.74, 6.85–6.93, 7.17–7.30, 7.54–7.66 (8H, 4 sets of
δ
δ
δ
δ
δ
δ
δ
(2H, s) (Ar-OH, -C-OH, =N-NH-C) [24,25].
3.5. Electrochemical Measurements
Electrochemical tests were performed using a three-electrode thermo-stated cell assem-
bly using a Gamry potentiostat/galvanostat/ZRA (model Interface 1000, Gamry, Warmin-
ster, PA, USA). A saturated calomel electrode (SCE) and platinum were used as reference
and counter electrodes, respectively. The working electrode was manufactured from
carbon steel. The electrodes were abraded with various emery papers, degreased with
acetone, rinsed with double-distilled water, and dried. All experiments were performed
at 25 ± 0.1 ◦C. The potentiodynamic curves were recorded from
−
300 to +300 mV at a
scan rate of 1 mV S−1. The open-circuit potential (OCP) was obtained after 45 min. The
electrochemical impedance spectroscopy (EIS) test was carried out using the same instru-
ment. Gamry framework software (version 6.0, Gamry, Warminster, Pennsylvania, USA)
was used for conducting the experiments. Echem Analyst Software (Gamry, Warminster,
Pennsylvania, USA) was used for plotting and fitting data. EIS measurements were carried
out in a frequency range of 10 MHz to 100 kHz with an amplitude of 5 mV peak-to-peak
using A.C. signals at relevant corrosion potential.
3.6. Computational Study
Supporting the experimental results with the computational calculations is quite
helpful to relate the inhibitory effect of the investigated compounds with their geometrical
and chemical structures. With the aids of quantum calculations, we can investigate the
active sites responsible for the corrosion inhibition mechanism. We reported a complete
geometry optimisation for MBC and HBM compounds through the ADF2020.101 and
the DMol3 module as a part of the Materials Studio software version of 2017 (Dassault
Systems Materials studio, San Diego, CA, USA). The initial optimisation and vibrational
frequencies were calculated using the ADF software (Software for Chemistry & Materials,
Amsterdam, Netherlands). Further investigations were carried out using the DMol3.

Molecules 2021, 26, 3183
15 of 17
The parameters of the DMol3 module during calculation were set as Task = Geometry
Optimisation, Functional = LDA and PWC, Basis = DND (4.4), and COSMO control for
solvent considerations. For the neutral and protonated form of MBC and HBM compounds,
EHOMO and ELUMO as basic potent descriptors as well as some other parameters derived
from them were excluded according to the following mathematical relations:
Ionization potential, I = −EHOMO electron affinity, A = −ELUMO
(13)
(14)
(15)
(16)
(I + A )
electro negativity, X = − chemical potential (µ) =
2
( I − A)
absolute hardness, η =
separation energy, ∆E = ELUMO − EHOMO
2
µ2
1
ω
electrophilicity index, ω =
nucleophilicity index, ε =
2η
fraction of electrons transferred, ∆N = [f − χinh]/[2(η Fe+ηinh)]
(17)
After the optimisation process, the adsorption of MBC and HBM molecules on the
Fe (110) surface was simulated using the adsorption locator module. The initial step is
constructing a 10
×
10
×
10 3D Fe (110) model. MBC and HBM molecules were allowed
to simulate on Fe (110) surface beside other molecules to get a close view of the experi-
mental results, such as H2O (200 molecules), H3O+ (20 molecules), and Cl (20 molecules).
−
The parameters of Monte Carlo simulations were set as: Task = Simulated annealing,
Force-field = COMPASS, Electrostatic = Ewald, and Van Der Waals = Atom-based.
4. Conclusions
This work aimed to assess two malonyl dihydrazide derivatives’ efficiency as corrosion
inhibitors for carbon steel in acidic media. The two inhibitors were studied experimentally
and theoretically for carbon steel corrosion. It is conceivable to conclude the following facts
:
O
O
O
MBC and HBM are suitable inhibitors for carbon steel corrosion in acidic media.
The PDP curves show that both MBC and HBM are mixed inhibitors.
EIS investigations proved that the addition of MBC and HBM to the corrosion medium
increases the inhibition efficacy.
O
O
O
The study of the impact of temperature on the inhibition efficiency displays that it
increases with the temperature increase.
This study revealed that the adsorption of both MBC and HBM molecules on the
carbon steel surface has a chemical nature.
The theoretical studies for both MBC and HBM have further supported the experi-
mental results.
Author Contributions: Conceptualisation, I.H.A. and S.S.A.; methodology, I.H.A.; software M.A.B.;
validation, M.A.B.; MBC and HBM molecules’ synthesis and formal analysis, M.Z.B.-F.; investigation,
M.Z.B.-F. and M.A.B.; data curation, I.H.A.; writing—original draft preparation, I.H.A.; writing—
review and editing, S.S.A.; funding acquisition, S.S.A. All authors have read and agreed to the
published version of the manuscript.
Funding: The authors extend their appreciation to the Research Center for Advanced Materials
(RCAMS) at King Khalid University, Abha, Saudi Arabia, for supporting this work through the
research groups program under Grant Number RCAMS/KKU/20/20.
Data Availability Statement: Data are available from the authors upon request.
Conflicts of Interest: The authors declare no conflict of interest.
Sample Availability: Samples of the compounds 2,2’-malonylbis(N-phenylhydrazine-1-carbothiamide)
and N’1, N’3-bis(-2-hydroxybenzylidene)malonohydrazide are available from the authors.

Molecules 2021, 26, 3183
16 of 17
References
1.
2.
3.
Njoku, D.I.; Li, Y.; Lgaz, H.; Oguzie, E.E. Dispersive adsorption of Xylopia aethiopica constituents on carbon steel in acid-chloride
medium: A combined experimental and theoretical approach. J. Mol. Liq. 2018, 249, 371–388. [CrossRef]
Gutiérrez, E.; Rodríguez, J.A.; Cruz-Borbolla, J.; Alvarado-Rodríguez, J.G.; Thangarasu, P. Development of a predictive model for
corrosion inhibition of carbon steel by imidazole and benzimidazole derivatives. Corros. Sci. 2016, 108, 23–35. [CrossRef]
Lgaz, H.; Saha, S.R.; Chaouiki, A.; Bhat, K.S.; Salghi, R.; Shubhalaxmi; Banerjee, P.; Ali, I.H.; Khan, M.I.; Chung, I.-M. Exploring
the potential role of pyrazoline derivatives in corrosion inhibition of mild steel in hydrochloric acid solution: Insights from
experimental and computational studies. Constr. Build. Mater. 2020, 233, 117320. [CrossRef]
4.
Naciri, M.; El Aoufir, Y.; Lgaz, H.; Lazrakd, F.; Ghanimi, A.; Guenboura, A.; Ali, I.H.; El Moudane, M.; Taoufik, J.; Chung, I.-M.
Exploring the potential of a new 1,2,4-triazole derivative for corrosion protection of carbon steel in HCl: A computational and
experimental evaluation. Colloids Surf. A Physicochem. Eng. Asp. 2020, 597, 124604. [CrossRef]
5.
6.
7.
Chaitra, T.K.; Mohana, K.N.S.; Tandon, H.C. Thermodynamic, electrochemical and quantum chemical evaluation of some triazole
Schiff bases as mild steel corrosion inhibitors in acid media. J. Mol. Liq. 2015, 211, 1026–1038. [CrossRef]
Cao, Z.; Tang, Y.; Cang, H.; Xu, J.; Lu, G.; Jing, W. Novel benzimidazole derivatives as corrosion inhibitors of mild steel in the
acidic media. Part II: Theoretical studies. Corros. Sci. 2014, 83, 292–298. [CrossRef]
Chafiq, M.; Chaouiki, A.; Damej, M.; Lgaz, H.; Salghi, R.; Ali, I.H.; Benmessaoud, M.; Masroor, M.; Chung, I.-M. Bolaamphiphile-
class surfactants as corrosion inhibitor model compounds against acid corrosion of mild steel. J. Mol. Liq. 2020, 309, 113070.
[CrossRef]
8.
9.
Morales-Gil, P.; Walczak, M.S.; Camargo, C.R.; Cottis, R.A.; Romero, J.M.; Lindsay, R. Corrosion inhibition of carbon-steel with
2-mercaptobenzimidazole in hydrochloric acid. Corros. Sci 2015, 101, 47–55. [CrossRef]
Zhang, T.; Cao, S.; Quan, H.; Huang, Z.; Xu, S. Synthesis and corrosion inhibition performance of alkyl triazole derivatives. Res.
Chem. Intermed. 2015, 41, 2709–2724. [CrossRef]
10. Geler, E.; Azambuja, D.S. Corrosion inhibition of copper in chloride solutions bipyrazole. Corros. Sci 2000, 42, 631–643. [CrossRef]
11. Heakal, F.E.-T.; Attia, S.K.; Rizk, S.A.; Essa, M.A.; Elkholy, A.E. Synthesis, characterisation and computational chemical study of
novel pyrazole derivatives as anticorrosion and antiscalant agents. J. Mol. Struct. 2017, 1147, 714–724. [CrossRef]
12. Ferkous, H.; Djellali, S.; Sahraoui, R.; Benguerba, Y.; Behloul, H.; Çukurovali, A. Corrosion inhibition of mild steel by 2-(2-
methoxybenzylidene) hydrazine-1-carbothioamide in hydrochloric acid solution: Experimental measurements and quantum
chemical calculations. J. Mol. Liq. 2020, 307, 11295. [CrossRef]
13. Gouda, V.K.; Sayed, S.M. Corrosion inhibition of steel by hydrazine. Corros. Sci. 1973, 13, 647–652. [CrossRef]
14. Gouda, V.K.; Shater, M.A. Corrosion inhibition of reinforcing steel using hydrazine hydrate. Corros. Sci. 1975, 15, 199–204.
[CrossRef]
15. Fouda, A.S.; El-Desoky, H.S.; Abdel-Galeil, M.A. Niclosamide and dichlorphenamide: New and effective corrosion inhibitors for
carbon steel in 1M HCl solution. SN Appl. Sci. 2021, 3, 287–299. [CrossRef]
16. Muthamma, K.; Kumari, P.; Lavanya, M. Corrosion Inhibition of Mild Steel in Acidic Media by N-[(3,4-Dimethoxyphenyl)
Methyleneamino]-4-Hydroxy-Benzamide. J. Bio Tribo Corros. 2021, 7, 10–26. [CrossRef]
17. Belghiti, M.E.; Echihi, S.; Dafali, A.; Karzazi, Y.; Bakasse, M.; Elalaoui-Elabdallaoui, H.; Olasunkanmi, L.O.; Ebenso, E.E.; Tabyaoui,
M. Computational simulation and statistical analysis on the relationship between corrosion inhibition efficiency and molecular
structure of some hydrazine derivatives in phosphoric acid on mild steel surface. Appl. Surf. Sci. 2019, 491, 707–722. [CrossRef]
18. El-Faham, A.; Osman, S.M.; Al-Lohedan, H.A.; El-Mahdy, G.A. Hydrazino-methoxy-1,3,5-triazine Derivatives’ Excellent Corrosion
Organic Inhibitors of Steel in Acidic Chloride Solution. Molecules 2016, 21, 714. [CrossRef]
19. El-Haddad, M.A.M.; Radwan, B.A.; Sliem, M.H. Highly efficient eco-friendly corrosion inhibitor for mild steel in 5 M HCl at
elevated temperatures: Experimental & molecular dynamics study. Sci. Rep. 2019, 9, 3695.
20. Chafiq, M.; Chaouiki, A.; Albayati, M.R.; Lgaz, H.; Salghi, R.; AbdelRaheem, S.K.; Ali, I.H.; Mohamed, S.K.; Chung, I.-M. Unveiled
understanding on corrosion inhibition mechanisms of hydrazone derivatives based on naproxen for mild steel in HCl: A joint
experimental/theoretical study. J. Mol. Liq. 2020, 320, 114442. [CrossRef]
21. Szlosek, D.; Currie, D. Application and Mechanism of Malonic Acid as a Green Alternative for Protein-Crosslinking. Green
Sustain. Chem. 2016, 6, 110–115. [CrossRef]
22. Weidlich, B.R. Condensation sproducte von Dihydraziden zweibasischer Säuren. Ber. Dtsch. Chem. Ges. 1906, 39, 3372–3377.
23. Uygun, Y.; Bayrak, H.; Özkan, H. Synthesis and biological activities of methylenebis-4H-1,2,4-triazole derivatives. Turk. J. Chem.
2013, 37, 812–823. [CrossRef]
24. Ranford, J.D.; Vittal, J.J.; Wang, Y.M. Dicopper(II) Complexes of the Antitumor Analogues Acylbis(salicylaldehyde hydra-
zones) and Crystal Structures of Monomeric [Cu2(1,3-propanedioyl bis(salicylaldehyde hydrazone))(H2O)2].(ClO4)2.3H2O and
Polymeric [{Cu2(1,6-hexanedioyl bis(salicylaldehydehydrazone))(C2H5OH)2}m].(ClO4)2m.m(C2H5OH). Inorg. Chem. 1998, 37,
1226–1231.
25. Zhang, C.; Rheinwald, G.; Lozan, V.; Wu, B.; Lassahn, P.-G.; Lang, H.; Janiak, C. Structural Study and Solution Integrity of
Dioxomolybdenum(VI) Complexes with Tridentate Schiff Base and Azole Ligands. Z. Anorg. Allg. Chem. 2002, 628, 1259–1268.
[CrossRef]
26. Ali, I.H.; Suleiman, M.H.A. Effect of Acid Extract of Leaves of Juniperus procera on Corrosion Inhibition of Carbon Steel in HCl
Solutions. Int. J. Electrochem. Sci 2018, 13, 3910–3922. [CrossRef]

Molecules 2021, 26, 3183
17 of 17
27. Ali, I.H.; Idris, A.M.; Suleiman, H.M.H.A. Evaluation of leaf and bark extracts of Acacia tortilis as corrosion inhibitors for mild
steel in seawater: Experimental and studies. Int. J. Electrochem. Sci. 2019, 14, 6406–6419. [CrossRef]
28. Chafiq, M.; Chaouiki, A.; Al-Hadeethi, M.R.; Ali, I.H.; Mohamed, S.K.; Toumiat, K.; Salghi, R. Naproxen-Based Hydrazones as
Effective Corrosion Inhibitors for Mild Steel in 1.0 M HCl. Coatings 2020, 10, 700. [CrossRef]
29. Lgaz, H.; Masroor, S.; Chafiq, M.; Damej, M.; Brahmia, A.; Salghi, R.; Benmessaoud, B.; Ali, I.H.; Alghamdi, M.M.; Chaouiki, A.;
et al. Evaluation of 2-mercaptobenzimidazole derivatives as corrosion inhibitors for mild steel in hydrochloric acid. Metals 2020
,
10, 357. [CrossRef]
30. Kumar, D.; Jain, N.; Jain, V.; Rai, B. Amino acids as copper corrosion inhibitors: A density functional theory approach. Appl. Surf.
Sci. 2020, 514, 145905. [CrossRef]
31. Abuelela, A.M.; Bedair, M.A.; Zoghaib, W.M.; Wilson, L.D.; Mohamed, T.A. Molecular structure and mild steel/HCl corrosion
inhibition of 4,5-Dicyanoimidazole: Vibrational, electrochemical and quantum mechanical calculations. J. Mol. Struct. 2021, 1230,
129647. [CrossRef]
32. Shokry, H. Molecular dynamics simulation and quantum chemical calculations for the adsorption of some Azo-azomethine
derivatives on mild steel. J. Mol. Struct. 2014, 1060, 80–87. [CrossRef]
33. Gómez, B.; Likhanova, V.N.; Domínguez-Aguilar, A.M.; Martínez-Palou, R.; Vela, A.; Gázquez, L.J. Quantum Chemical Study of
the Inhibitive Properties of 2-Pyridyl-Azoles. J. Phys. Chem. B 2006, 110, 8928–8934. [CrossRef]
34. Lukovits, I.; Kálmán, E.; Zucchi, F. Corrosion Inhibitors—Correlation between Electronic Structure and Efficiency. Corrosion 2001
57, 3–8. [CrossRef]
,
35. Badr, E.A.; Bedair, M.A.; Shaban, S.M. Adsorption and performance assessment of some imine derivatives as mild steel corrosion
inhibitors in 1.0 M HCl solution by chemical, electrochemical and computational methods. Mater. Chem. Phys. 2018, 219, 444–460.
[CrossRef]
36. Pearson, R.G. Chemical Hardness; Wiley-VCH Verlag GmbH: Weinheim, Germany, 1997.
37. Padmanabhan, J.; Parthasarathi, R.; Sarkar, U.; Subramanian, V.; Chattaraj, P.K. Effect of solvation on the condensed Fukui
function and the generalised philicity index. Chem. Phys. Lett. 2004, 383, 122–128. [CrossRef]
38. Morell, C.; Grand, A.; Toro-Labbé, A. New Dual Descriptor for Chemical Reactivity. J. Phys. Chem. A 2005, 109, 205–212.
[CrossRef]
39. Zhang, Q.H.; Hou, B.S.; Xu, N.; Liu, H.F.; Zhang, G.A. Two novel thiadiazole derivatives as highly efficient inhibitors for the
corrosion of mild steel in the CO2-saturated oilfield produced water. J. Taiwan Inst. Chem. Eng. 2019, 96, 588–598. [CrossRef]