Synthesis, spectral analysis, theoretical studies, molecular dynamic simulation and comparison of anticorrosive activity of an ester and an acid α-Hydroxyphosphonates

Article abstract of DOI:10.1016/j.molstruc.2019.06.012

Diethyl [hydroxy (phenyl) methyl] phosphonate ester (DHPMP) and [hydroxy (phenyl) methyl] phosphonate acid (HPMPA) have been synthetized and their structures were confirmed by IR, UV–Vis, ¹H, ¹³C and ³¹P NMR spectroscopies

Full text of DOI:10.1016/j.molstruc.2019.06.012

Accepted Manuscript
Synthesis, spectral analysis, theoretical studies, molecular dynamic simulation and
comparison of anticorrosive activity of an ester and an acid α-Hydroxyphosphonates
Riadh Bourzami, Louiza Ouksel, Nadjib Chafai
PII:
S0022-2860(19)30725-2
DOI:
https://doi.org/10.1016/j.molstruc.2019.06.012
MOLSTR 26654
Reference:
To appear in: Journal of Molecular Structure
Received Date: 21 March 2019
Revised Date: 3 June 2019
Accepted Date: 4 June 2019
Please cite this article as: R. Bourzami, L. Ouksel, N. Chafai, Synthesis, spectral analysis, theoretical
studies, molecular dynamic simulation and comparison of anticorrosive activity of an ester and an
acid α-Hydroxyphosphonates, Journal of Molecular Structure (2019), doi: https://doi.org/10.1016/
j.molstruc.2019.06.012.
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ACCEPTED MANUSCRIPT

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Synthesis, spectral analysis, theoretical studies, molecular
dynamic simulation and comparison of anticorrosive activity of
an ester and an acid α-Hydroxyphosphonates
1
2,*
2
Riadh Bourzami , Louiza Ouksel , Nadjib Chafai
1
Emerging Materials Research Unit, Ferhat Abbas University Sétif-1, 19000. Algeria
2
Laboratoire d’Electrochimie des Matériaux Moléculaires et des complexes (LEMMC), Département
de génie des procédés, Faculté de Technologie Université Ferhat Abbas, Sétif-1,19000. Algeria
*
E-mail: louksel2014@gmail.com
Abstract
Diethyl [hydroxy (phenyl) methyl] phosphonate ester (DHPMP) and [hydroxy (phenyl) methyl]
phosphonate acid (HPMPA) have been synthetized and their structures were confirmed by IR, UV–
1
13
31
Vis, H, C and P NMR spectroscopies. Their inhibitive capacities on the XC48 steel corrosion in
M HCl has been determined by chemical and electrochemical measurement, the weigth loss proves
1
that the adsorption of the ester or the acid on the surface of XC48 steel obeys to Langmuir isotherm,
while the polarization measurements indicate that the inhibition process is mixt, finally,
Electrochemical Impedance Spectroscopy (EIS) results show that the inhibition efficiency increased
with increasing the inhibitors concentrations. Surface topographies were carried out using the Atomic
Force Microscopy (AFM). The Density Functional Theory (DFT) using (B3LYP) method with 6-31G
(p, d) basis sets was performed to calculate some thermodynamic parameters influencing the corrosion
inhibition effect. Also, the Molecular Dynamics Simulations (MDS) was performed to simulate the
interface configuration between the inhibitors molecules and Fe (100)/H O or Fe O (110)/H O.
2
2
3
2
Keywords: α-Hydroxyphosphonate; Corrosion inhibition; AFM; DFT calculation; MD simulations.
1. INTRODUCTION
Metals may be corroded by the actions of metal heterogeneities or by several environment
modifications. Actually, about 150 million tons of iron production is destroyed annually, this loss
could be greater if there was no corrosion protection, generally, acidic aqueous solutions are the most
aggressive media for metals and alloys. Moreover, the corrosion effect can be retarded or completely
stopped by the use of inhibitors, which are compounds added in small concentrations to media.
In recent years, several organic compounds are used as inhibitors in acidic medium for steel
corrosion and their role during the process of corrosion has been studied. These inhibitors enter in the
double layer interface and replace water molecules. The heteroatoms like oxygen, nitrogen, sulfur,

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aromatic ring and phosphorus of organic compounds make a barrier between surface of the metal and
aggressive solution.
The use of organophosphorus compounds as corrosion inhibitors of metal and alloys are widely
applied owing to their low toxicity, high stability [1-9] and their adsorption on the surface of the metal
[
[
10-13]. The use of phosphonate for the protection of carbon steel in different media has been reported
14-16].
The α-hydroxyphosphonate family is a precursor for a significant variety of phosphonate
derivatives, in the tow last decades, considerable attention has been given to its antibacterial, antiviral,
anti-cancer and antioxidant properties [17-22], but few researches used α-hydroxyphosphonate as
corrosion inhibitors.
The aim of this work is the comparison of the corrosion inhibition efficiencies of an ester α-
hydroxyphosphonate form (DHPMP) and an α-hydroxyphosphonate acidic form (HPMPA) in 1M HCl
medium on metallic surfaces (XC48 steel), by means of polarization curves method, Electrochemical
Impedance Spectroscopy (EIS) and gravimetric analysis. In addition, to visualize adsorption
configurations on the Fe (100) and Fe (100)/H O, Molecular Dynamic Simulations (MDS) were also
2
performed in vacuum slab and aqueous solutions using the adsorption locator module.
The adsorption of organic molecules on metallic surfaces is influenced by the physic-chemical
properties of the inhibitors molecules, metallic surface and the external medium. For that, the Atomic
Force Microscopy (AFM) was performed and the quantum chemical parameters were calculated in gas
and aqueous phases using Density Functional Theory (DFT).
2
2
2
. EXPERIMENTAL
.1. Methods
.1.1 Gravimetric method
Gravimetric analysis is a chemical way to determine some corrosion parameters as the
2
corrosion rate and inhibition efficiency. The cleaned specimens with external surface S = 10.05 cm
were immersed by triplicate, for t = 6 h, in 1M HCl solution with various concentration C = 0, 0.1, 0.2,
.3 and 0.4 mM of phosphonate derivative at two temperatures T = 298 and T = 328K.
0
1
2
The average weight loss ∆W was calculated using the equation (1) [23]:
ꢌ
∑
(ꢃꢄꢅꢆꢇꢈꢅꢉꢃꢊꢆꢋꢅꢈ)
ꢍ
<
ꢀꢁ >ꢂ=ꢂ
Where Wbefore and Wafter are the weight of the specimen before and after immersion
respectively.
(1)
ꢎ

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The corrosion rates C , the surface coverage θ and the corresponding inhibition efficiency
RW
IE (%) obtained from gravimetric tests were calculated using the equations (2, 3 and 4) respectively
W
[
24, 25]:
ꢏꢐꢑ =ꢂ< ∆W >/ꢒꢓ
(2)
(3)
(4)
θ = (Cꢔ − Cꢐꢑ)/Cꢔ
ꢐꢑ
ꢔ
ꢐꢑ
ꢔ
IE (%) = ꢕ(C − Cꢐꢑ)/C ꢖ × 100
ꢑ
ꢐꢑ
ꢐꢑ
S is the surface, t is the time of immersion, ꢏ ꢐꢔ ꢑꢂ and ꢏꢐꢑ are corrosion rates in the absence and
presence of inhibitors, respectively.
The activation energy was deduced from Arrhenius equation (5) as follow:
Cꢐꢑ = Aexp ꢗ EꢘꢙRT
−
ꢛ
ꢜꢝꢞ
ꢟ
ꢠ
ꢣ
ꢣ
ꢚ
=>
log
=
ꢢ − ꢥ
ꢡ.ꢎꢔꢎꢐ ꢤ ꢤ
ꢍ ꢞ
ꢛꢜꢝꢍ
A is the Arrhenius constant, R is the universal gas constant and CRW1 and CRW2 are the corrosion
rates at temperatures T and T respectively.
1
2
The adsorption heat Q was computed using equation (8):
ads
ꢩꢞ
ꢩꢍ
ꢤꢍ×ꢤꢞ
ꢤꢞꢉꢤꢍ
Qꢘꢦꢧ = 2.303R ꢢlog ꢨ
ꢪ − log ꢨ
ꢪꢥ × ꢨ
ꢪ
(8)
ꢣꢉꢩꢞ
ꢣꢉꢩꢍ
Where θ and θ are surface coverage degrees at temperatures T and T respectively.
1
2
1
2
The experimental θ values at different inhibitors concentrations C were fitted using various
adsorption isotherms.
ꢛ
ꢣ
= ꢫ + c
(9)
ꢩ
ꢠꢬꢭ
K is the equilibrium constant of the inhibition adsorption.
ads
0
Kads is related to the free adsorption energy (∆G ads) following the equation (10):
ꢔ
∆
ꢮ
= −ꢲꢳꢴꢵ(55.5ꢶꢯꢰꢱ
)
(10)
ꢯꢰꢱ
2.1.2. Electrochemical method
Electrochemical measurements were carried out using a PGZ 301 voltalab 40 (data were
analyzed with Volta Master IV software) and using a three electrodes glass cell (Saturated Calomel
Electrode (SCE) as a reference, a platinum plaque as Counter Electrode (CE) and XC48 steel as a
2
Working Electrode (WE), with surface S = 0.18 cm ). The open circuit potential value (OCP) was
stabilized up to 30 min for each electrochemical measurement with a scan rate of 0.5 mV/s. Various
concentrations was used in 1M HCl as electrolyte.
The parameters, corrosion potential E , current densities i were evaluated from Tafel
corr
corr
extrapolation of the polarization curves, the corresponding inhibition efficiency IE was calculated
P
using the following equation (11) [26]:

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ꢔ
ꢔ
IE (%) = ꢕ(i
− iꢸꢹꢺꢺ)/i ꢖ × 100
(11)
ꢷ
ꢸꢹꢺꢺꢂ
ꢸꢹꢺꢺ
Where ꢻꢼꢔ
and ꢻꢼꢽꢾꢾ are the corrosion current density in the absence and presence of
ꢽꢾꢾ
inhibitors, respectively.
The Electrochemical Impedance Spectroscopy (EIS) experiments were performed at the
frequency domain from 100 kHz to 30 mHz, with an amplitude of 10 mV using alternating current
AC) at open circuit potential. The corresponding inhibition efficiency (IE ) of inhibitors was
(
EIS
calculated from the charge transfer resistance values employing the equation (12):
ꢔ
IEEIS (%) = ꢿ(R -R )/R ꣁ × 100
(12)
ꢸꣀ
ꢸꣀ
ꢸꣀ
ꢔ
Whereꢂꢲ and ꢲ are the resistance in the absence and presence of the acid respectively.
ꢼ
ꣂ
ꢼꣂ
Double layer capacitance (Cdl) values were attained at maximum frequency (fmax) and
calculated using the following equation:
Cꢦꣃ = (1/2πf꣄ꢘꣅ) × ꣆1/Rꢷ꣇
(14)
2
.2. Analysis
.2.1. Fourier transforms infrared spectroscopy FT-IR
Spectra were recorded using a FT-IR 4200 JASCO spectrometer, in the range 4000-600 cm , at
room temperature.
2
-1
2.2.2. Nuclear magnetic resonance spectroscopy NMR
Spectra were recorded at room temperature, in DMSO-d , using a Bruker AV III 300 MHz
6
spectrometer.
2.2.3. Atomic force microscopy AFM
The surface morphology was performed by AFM using an Asylum Research MFP-3D Classic
AFM instrument.
2
2
.3. Theoretical calculation
.3.1. Density Functional Theory calculation (DFT)
The full geometry optimization were performed with the Gaussian 9 program, based on density
functional theory [27], using Beck’s three parameter hybrid exchange functional [28], with 6-31G (d,
p) basis set, and Lee-Yang-Parr correlation functional (B3LYP) [29,30].
2.3.2. Molecular Dynamic Simulation (MDS)
Molecular dynamic simulations were carried out, with Materials Studio 7.0 software [31]. Fe
(
100) surface was selected for adsorption modes simulations and were performed in a simulation box
17.20 × 22.93 × 22.93 Å). The MDS was realized at 298 K, Normal Volume and Temperature (NVT)
(
ensemble, with a time step of 0.1 fs and simulation period of 50 ps using the COMPASS force field.

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The interaction energy of inhibitors on the Fe (100) surface was calculated using the following
equation (13):
Einteraction= Etotal-E(Fe + H2O)- Einh
(13)
Where Etotal is the total energy of the simulation system, EFe+H2O is the energy of iron surface
together with H O molecules and Einh is the energy of the free inhibitor molecule.
2
2
.4. Materials
The carbon steel XC48 having the chemical composition : Fe(98.098 %), C(0.418 %), F(0.777
), Mn(0.730 %), Si(0.245 %), Ni(0.079 %), S(0.019 %), P(0.016 %) and Mo(0.012 %) was cut into
%
2
cylindrical shape of dimensions (2 cm diameter x 0.6 high), with the external surface S =10.05 cm ,
after that, three cleaning steps were followed, abrading with Emery paper 800, 1200, 1500 and 2400,
washing with distilled water and rinsed with acetone.
3. RESULTS AND DISCUSSION
3.1. Synthesis
The synthesis and characterization of the ester nominated Diethyl [hydroxy (phenyl) methyl]
phosphonate (DHPMP) was reported previously [32].
The acid, nominated [Hydroxy (Phenyl) Methyl] Phosphonate Acid (HPMPA) was obtained by
hydrolysis of DHPMP with HCl 6N at 100 °C during 24 hours (Figure 1), the solvent was evaporated,
and pink solid was obtained, and washed with water and ethanol, and finally dried under vacuum. The
compound was analysed by IR and NMR spectroscopies.
3.2. FT-IR spectroscopy
The figure 2 shows IR spectrum of acid molecule, it shows a medium and broad absorption
-1
-1
band at 3250 cm due to the stretching vibration of the hydroxyl group, the band at 3013 cm is
-1
attributed to
ν(C–H) aromatic, in addition, the bands at 1624 and 1490 cm are due to ν(C=C) and
-1
ν(C–C) aromatic respectively and the band at 1163 cm due to ν(C–OH), finally, the appearance of the
-1
bands at 1233 cm of P=O, at 1021 of ν(P–O) and at 941 of ν(P–C) confirm all the obtaining of a
phosphonic acid. The absorbed frequencies characteristic of the functional groups present in the
compound and their assignments are summarized in Table 1.
3.3. NMR spectroscopy
1
3
.3.1. H NMR
1
The H NMR spectrum of HPMPA molecule is shown in Figure 3. The singlet (1H, s) signal at
.21 ppm corresponds to C-OH proton. The doublet (1H, d, J = 10.8 Hz) at 4.83 ppm corresponds to P-
5
C-H proton, the five aromatic protons CHAromatic gave a multiplet (5H, m) between (7.5 - 7.29 ppm).
Finally, the singlet at 2.5 ppm is due to deuterated DMSO-d6 residue.

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1
3
3
.3.2. C NMR
1
3
The C NMR spectrum of the HPMPA molecule is shown in Figure 4. The peak at 85.15 ppm
is attributed to the carbon of P-C-H. Peaks corresponding to aromatic carbons CHAromatic are observed
between 127-137 ppm. At the last, the peak observed around 40 ppm is due to the carbon of the
solvent.
3
1
3
.3.3. P NMR
3
1
Figure 5 shows the P-NMR spectrum of the HPMPA molecule, witch exhibits a single peak at
4.9 ppm (P = O), confirming the presence of a single type of phosphonate.
All NMR spectra confirm the hydrolysis, and declare a good purity.
2
3
.4. UV-Visible spectroscopy
The UV-Visible absorption spectrum of acid is shown in Figure 6. It comprises a strong
-1
-1
absorption band located in the ultraviolet around 270 nm (ε270 = 17626 l.mol .cm ), related to the
energy required for π-π* transition of benzene. In the visible and UV near visible domain the
compound is transparent, with cutoff wavelength 310 nm.
3.5. Theoretical calculations results
The figure 7 shows the optimized structure of the ester and the acid.
The spatial distribution of the frontier molecular orbital is shown in figure 8. The reactive
ability of the HOMO and LUMO is related to their frontier molecular orbitals [33], the energy of the
highest occupied molecular orbital (EHOMO) is directly related to electron donating ability, the
donating ability attract acceptor molecules having low-energy of empty molecular orbital, thus can
explain the adsorption of ester and acid on XC48. In return, the energy of the lowest unoccupied
molecular orbital (ELUMO) is directly related to electron affinity signifies the electron receiving
tendency.
The green and red surfaces represent the electron density difference, the red regions
show negative charge regions (electron accumulation) and the green regions show positive charge
regions (electron loss). The electron density distribution of both LUMO and HOMO are localized
principally on the benzene ring, suggesting that the benzene ring forms active sites for
adsorption on XC48.
The energy (EHOMO), the energy (ELUMO), energy gap (∆E ) and the some physic-chemical
gap
parameters (µ) of optimized molecular structures of the ester and acid have been calculated (Table 1).
It is well-known that small absolute values of the energy band gap gives good inhibition
efficiencies, the ester and the acid have ∆Egap (5.59 and 5.44 eV respectively), which entail the high

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ability to accept electrons from the d-orbital of Fe and a high stability of the Fe–DHPMP and Fe–
HPMPA complexes [34, 35]. While, the dipolar moment (µ) is a measure of the polarity of a covalent
bonds, which is associated to the distribution of electrons in molecules [36]. It is clearly seen that, the
dipolar moment increases in passing from ester to acid, also, the polarization of the molecule is
influenced by the molecule/solvent interaction [37], moreover, the large values of µ aid the adsorption.
As shown in Table 2, the low value of the overall hardness (η) and the high softness value (σ) can
produce a high inhibitory efficacy [38]. The global electrophilicity index (ω) represents the ability of
inhibitor molecules to accept electrons. According to Lukovit, if ꢀN is less than 3.6, the inhibition
efficiency increases with the increase of the electron transfer capacity to the metal surface [39]. In this
study, the ꢀN values are less than 3.6 for both ester and acid molecules, which indicate that the
electrons are transferred from the molecules to the XC48 steel.
The NBO charge analysis is performed to calculate the charge distribution over the skeleton of
the ester and the acid molecules, the table 2 shows some selected calculated NBO atomic charges, The
NBO charge analysis can give an idea of the adsorption cites [40], It is seen from table 1, that the
oxygen and some carbon atoms have negative charges, atoms negatively charged can be adsorbed on
metal surface through the acceptor–donor type reaction [41].
As noticed that the ester and the acid can promote formation of a chelate on XC48 steel surface
[
42], this result is in good agreement with the electron density distribution calculation. The positive
charge is principally centered is on phosphorus, with can be a considered as desorbed sites.
The figure 9 shows the corresponding 3D plot of the Molecular Electrostatic Potential (MEP)
generated around the ester and the acid molecules. This computational result shows that the
geometrical nucleophilic regions are located around oxygen atom of P=O bond while the electrophilic
regions are located around hydrogen atoms of O-H bonds
3.6. Corrosion results
In this part, chemical and electrochemical measurements were carried out in focus to
characterize and compare the inhibitive efficiencies of the ester and the acid. The influence of the
concentrations and the temperature on the protection of XC48 steel was studied.
3.2.1. Gravimetric results
Table 3 shows values of surface coverage θ, corrosion rate CWR and corresponding inhibition
efficiencies IE estimated from the weight loss measurements for various ester or acid concentrations.
W
The addition of 0.4 mM of the ester and acid derivatives in the aggressive medium increases
the activation energy which makes the protection process effective, also, High values of equilibrium
constants indicate that there is a strong interaction between the ester and the acid molecules and XC48

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0
steel surface [43]. Moreover, negative values of ∆G
and Q proves that the adsorption process is
ads
ads
spontaneous exothermic and proves also a good stability of the adsorbed layer on metal surface [44].
0
-1
-1
The found ∆G
values are comprise between -20 KJ.mol and -40 kJmol , those values
ads
explain the physicochemical adsorption process between ester and acid on metal surface, while highest
or lower values are related to only physical or only chemical adsorption respectively [45;46].
To study the effect of concentration and temperature on corrosion rate and inhibitory
efficiency, the curve CRW and IE (%) vs concentration at T = 298 K and T = 328 K was ploted (Figure
W
10).
It can be seen from the table 3 and Figure 10 that corrosion rate CRW decreases while inhibition
efficiency IE (%) raises with concentrations rinsing, this phenomenon can be attributed to a good
W
adsorption on the metal surface. The temperature rise has desorption effect.
Figure 11 shows that the ester and the acid adsorption on the surface of XC48 steel obeys to
Langmuir isotherm with an average correlation coefficient equal to (0.998) for both temperatures.
0
ads
K and ∆G values deduced from the Langmuir isotherm are summarized in table 3.
ads
Finally, we can resume from the weight loss method that the ester and the acid form a good
protective films on the XC48 steel surface, obtaining an augmentation in the surface coverage, also
from this method results, the inhibition efficiencies of acid form are higher than ester form, the highest
values of the inhibition effectiveness effect for the both molecules can be explained by the existence of
oxygen, phosphorus atoms and aromatic ring.
3.6.2. Electrochemical results
a. Polarization studies
TAFEL curves for XC48 steel in 1M HCl solution at various concentrations of the ester and the
acid are shown in figure 12.
The figure 12 shows that the addition of ester or acid decreases the both current densities,
anodic and cathodic, which kipping a same slope, this result demonstrates the mixed character of the
inhibition process, without modifying release of hydrogen and the anodic degradation of the metal
[
47], moreover, any significant shift of the corrosion potential is observed. Anodic values of Tafel
slope (ß ) for ester and acid indicate that these compounds do not vary the mechanism of iron
a
dissolution [48].
Electrochemical corrosion parameters, as corrosion potential Ecorr (mV/SCE), cathodic and
‒
2
anodic Tafel slopes ß and ß (mV/dec), the corrosion current density i (ꢁA.cm ) and inhibition
c
a
corr
efficiency IE (%) are given in Table 4.
p

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From the polarization method, the DHPMP and HPMPA protect well the XC48 steel surface,
this result is due to the decreasing of the icorr and increasing of inhibition efficiencies with increasing
concentrations, also acid has better results than the ester.
b. Electrochemical impedance spectroscopy
Nyquist plots for mild steel after 1 h immersion in 1M HCl solution in the absence and
presence of different concentrations of the ester and acid at 298K are given in Figure 13.
The impedance curves present one single capacitive semi-circle. These Nyquist plots are not
perfect semicircles, this may be attributed to the frequency distribution of interfacial impedance. This
behavior is a result of roughness, heterogeneity of surface and adsorption–desorption action of
inhibitive molecules on XC48 steel surface. The diameter of the semicircles in the presence of the ester
and the acid were larger than observed in blank solution (1M HCl), also, it is seen an increases with
rise of inhibitors concentrations, which may be related to the rise of surface coverage of inhibitive
molecules on XC48 steel surface.
Table 1. Electrochemical parameters and inhibition efficiency derived from impedance diagrams for
the XC48 steel at 298 K in 1M HCl without and with different concentrations of DHPMP and
HPMPA.
2
‒2
The electrochemical parameters values of R (ꢂ cm ), C (µF cm ), f (Hz) and (EEIS %) of
p
dI
max
the ester and the acid obtained from EIS are summarized in Table 5. The C values decrease while Rp
dI
values increase with increasing concentration. The increase in R values is induced by adsorption of
p
inhibitors, indicating that the exposed area decreased. By another, the decrease in C can issue from a
dI
decrease in local dielectric constant and/or an increase in the thickness of the electrical double layer,
suggesting that ester and acid inhibitors act by adsorption on the metal surface. The values of
inhibition efficiency increase with inhibitors concentration (Table 5).
Also, the electrochemical impedance spectroscopy proves that DHPMP and HPMPA have a
good inhibition effect, which: EIEIS (%) DHPMP < EIEIS (%) HPMPA.
3.7. Atomic Force Microscopy observations (AFM)
For characterizing the microstructure and to demonstrate the formation of the protective film on
XC48 steel the atomic force microscope was used. AFM images of XC48 surface before and after 6 h
of immersion in acidic solution without and with the existence of the studied inhibitors are exposed in
Figure 14.
The calculated roughness of XC48 steel in 1M HCl with and without inhibitors was
summarized in insert tables of figure 14. The value of average roughness of XC48 steel in HCl (169

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nm) was higher than that of the polished one (15.8 nm) but in presence of the ester and the acid, the
roughness is reduced to 60.7 and 30.5 nm respectively. Those observations indicate that the acid
attacks the steel surface and the adsorbed inhibitors molecules diminish the corrosion rate and surface
deterioration. Finally, we can conclude that the AFM confirms the results obtained previously.
3.8. Molecular Dynamic Simulation (MDS)
MD simulations were performed to study adsorption behaviors of the ester and the acid on Fe
(
100) and Fe O (110) surfaces (Figure 15). In order to maximize contact and increase the surface
2 3
coverage, the molecules are preferentially oriented parallel on the Fe (100) surface and perpendicular
on the Fe O (110). Phosphorus and oxygen atoms can offer electrons to the unoccupied d-orbital of
2
3
iron to form coordinate bonds (chemical interaction), and anti-bonding orbital of π-electrons in the ring
can accept electrons from the d-orbital to form dative bonds [49]. The physical interaction between the
ester or the acid and the metal surface driven by Van Der Waals dispersion forces may be attributed to
the net molecule surface attraction [50].
Table 7 indicates that the interaction energy between the inhibitor molecules and the Fe O3
2
(110) surface is less than that obtained between the inhibitor molecules and the Fe (100) surface, In
principle, the high value of binding energy is related to most rigid molecules/surface interactions [51].
This indicates that acid could have preferable performances as corrosion inhibitor than ester molecule,
a conclusion which is in total accord with the experimental results.
4. CONCLUSION
Diethyl [hydroxy (phenyl) methyl] ester phosphonate and [hydroxy (phenyl) methyl] acid
phosphonate were synthesized and their molecular structures were confirmed using, UV-vis, FTIR and
1
H NMR spectroscopies. Theoretical DFT calculations prove a good reactivity of the synthesized
molecules and predict a good adsorption on metallic surface, owing to the weak donor acceptor
interactions and conjugate π bonds. The inhibition against corrosion of XC48 steel in 1M HCl was
studied, resulting good inhibition efficiencies around 93%, but the acid presents a best effect. Also, the
surface morphologies of attacked and inhibited surfaces were followed by AFM, confirming the
previous results. The MDS were performed in focus to visualizes adsorption configurations on Fe(100)
and Fe O (110) surfaces.
2
3

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ACCEPTED MANUSCRIPT
Table 1. Selected IR frequencies and assignments of acid.
Calculated
unscaled scaled
Experimental
Assignments
ν (OH)
ν (C–H) aromatic
ν (C–C) aromatic
δ (C=C) aromatic
P=O
ν (C–OH)
ν (P–O)
ν (P–C)
3
3
1
1
1
740
250
490
624
233
3826
3173
1498
1661
1288
1034
916
3673
3046
1438
1595
1236
993
9
9
7
98
45
81
880
834
800
ν
: Elongation vibration, δ : Deformation vibration
1

ACCEPTED MANUSCRIPT
Table 2
Theoretical chemical parameters.
DHPMP
Gas Water
-29.16 -29.16 -24.88 -24.88
HPMPA
Gas Water
Theoretical parameters
Etot (KeV)
EHOMO (eV)
ELUMO (eV)
Ionization potentiel (I, eV)
Electron affinity (A, eV)
-7.15
-1.41
7.15
1.41
5.74
2.34
2.87
0.34
4.28
3.19
0.47
-6.71
-1.12
6.71
1.12
5.59
2.61
2.79
0.35
3.92
2.76
0.55
-6.47
-1.01
6.47
1.01
5.46
4.93
2.73
0.36
3.74
2.56
0.59
-6.31
-0.87
6.31
0.87
5.44
5.83
2.70
0.36
3.59
2.37
0.62
∆
E gap (eV)
Dipolar moment (ꢀ, D)
Global hardness (η, eV)
Global softness (σ, eV )
Electronegativity ( χ , eV)
Global electrophilicity(ω)
-
1
∆
N
2
I=-EHOMO, A=-ELUMO, χ =-[1/2(ELUMO+ EHOMO)], η=1/2(ELUMO- EHOMO), ω= χ /2η. σ=1/ η.
2

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Table 3
Selected calculated NBO atomic charges of DHPMP and HPMPA gas phase and in aqueous
solution.
NBO DHPMP
NBO AHPMP
Atom
Gas
2.41
Water Atom
Gas
2.37
Water
2.38
P14
O15
O16
O18
H19
H7
C20
C23
C1
2.42
P14
O15
O20
O18
H7
-1.07 -1.11
-0.86 -0.86
-0.75 -0.77
0.49
0.24
-0.11 -0.11
-0.70 -0.71
-0.23 -0.24
-0.09 -0.09
-1.06 -1.10
-0.77 -0.78
-1.01 -1.03
0.24
0.52
-0.23 -0.23
-0.09 -0.10
-0.28 -0.28
0.50
0.24
0.25
0.54
H17
C1
C4
C12
C4
3

ACCEPTED MANUSCRIPT
Table 4
Gravimetric results and some deduced thermodynamic parameters.
C
mM)
0
Thermodynamic
parameters
T = 298 K
T = 328 K
(
ꢄ
ꢄ
θ
-
CRW
IEw
Kads
∆ꢀ
θ
-
ꢅꢆꢇ IEw Kads
∆ꢀ
Ea
Qads
ꢁꢂꢃ
ꢁꢂꢃ
1,72
0.58
0.44
0.36
0.29
1.72
0.44
0.25
0.18
0.13
-
5.93
-
33.56
41.17
-
0
0
0
0
.1 0.66
.2 0.74
.3 0.79
.4 0.83
66
74
79
83
-
0.5 2.67 55
0.6 2.25 62
0.6 1.89 68
0.7 1.78 70
-9.98
2
2
.22
-34.75
-35.34
1
.81
-37.70
-38.28
43.77 -13.72
44.82 -14.38
48.68 -16.97
0
-
-
5.93
-
33.56
-
0
0
0
0
.1 0.74
.2 0.85
.3 0.89
.4 0.92
74
85
89
92
0.6 2.02 66
0.7 1.36 77
0.8 1.01 83
0.8 0.83 86
40.87 -12.73
45.03 -14.97
45.38 -15.59
.81
2.12
48.95 -19.96
-
1
-2
-1
-1
4
-1
ꢄ
-1
System unit : CRW (mg.h .mm ), IE (%), E (KJ.mol ), Q (KJ.mol ), K (10 .L.mol ), ∆ꢀ (KJ.mol ).
w
a
ads
ads
ꢁꢂꢃ
4

ACCEPTED MANUSCRIPT
Table 5
Electrochemical parameters.
C
0
‒Ecorr icorr ‒ßC
ßa
IEp
‒
71
77
81
84
‒
69
72
85
90
443
443
454
449
449
443
448
463
457
166
48
38
31
27
166
51
46
25
16
92
88
59
73
70
92
87
84
83
81
67
63
52
62
54
67
65
63
63
63
0
.1
.2
.3
.4
0
0
0
0
0
0
0
0
.1
.2
.3
.4
452
2
2
C(mM), Ecorr(mV/SCE), icorr (ꢀA/cm ), i (ꢀA/cm ), ß (mV/dec), ß (mV/dec), IE (%)
corr
C
a
p
Table 6
5

ACCEPTED MANUSCRIPT
Electrochemical parameters and inhibition efficiency derived from impedance diagrams for
the XC48 steel at 298 K in 1M HCl without and with different concentrations of DHPMP and
HPMPA.
C
Rp
19
65
73
Cdl
530
387
346
IEEIS
‒
0
.0
.1
.2
0
0
0
0
0
0
0
0
0
71
74
81
84
̶
71
73
86
.3 100 270
.4 120 209
.0
.1
.2
19
63
72
530
354
347
.3 131 243
.4 200 199
91
2
‒2
C(mM), R (ꢁ.cm ), C (ꢀF.cm ), IEEIS(%)
p
dl
Table 7
6

ACCEPTED MANUSCRIPT
Interaction energies between DHPMP, HPMPA, Fe (100)/ H O and Fe O (100)/ H O
2
2
3
2
surfaces.
Systems
EInteractio
EBinding
Fe(100)/DHPMP/H O
-4632.18
-5673.50
-3932.31
-4872.69
4632.18
5673.50
3932.31
4872.69
2
Fe(100)/HPMPA/H O
2
Fe O (100)/DHPMP/H O
2
3
2
Fe O (100)/HPMPA/H O
2
3
2
E (Kj/mol)
7

ACCEPTED MANUSCRIPT
OC H
2
5
OH
O
O
P
OH
P
OH
C H O
2
5
HCl/H O
HO
2
2
C H OH
2 5
+
1
00°C, 24 h
DHPMP
HPMPA
Fig. 1. Reaction scheme of HPMPA.
1

ACCEPTED MANUSCRIPT
100
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
4
000
3500
3000
2500
2000
1500
)
1000
50
-1
Wave number
(cm
Figure 2. FT-IR Spectrum of acid.
2

ACCEPTED MANUSCRIPT
15
12
9
6
3
0
ppm
1
Figure 3. H NMR of acid.
3

ACCEPTED MANUSCRIPT
200
150
100
ppm
50
0
1
3
Figure 4. C NMR of acid.
4

ACCEPTED MANUSCRIPT
1
50
100
50
0
-50
ppm
-100 -150 -200 -250
3
1
Figure 5. P NMR of acid.
5

ACCEPTED MANUSCRIPT
2,0
1,6
1,2
0,8
0,4
0,0
200
300
400
500
600
700
800
Longueur d'onde(nm)
Figure 6. UV-Visible spectrum of acid.
6

ACCEPTED MANUSCRIPT
(
b)
(
a)
Fig. 7. Optimized molecular structures of (a) DHPMP and (b) HPMPA.
7

ACCEPTED MANUSCRIPT
DHPMP
HPMPA
Fig. 8. Atomic orbital composition: Positive phase (green) and Negative phase (red).
8

ACCEPTED MANUSCRIPT
(
a)
(
b)
-
2
-2
-2
-2
-7,06.10 V
7,06.10 V
-6,76.10 V
6,76.10 V
Fig. 9. The total electron density mapped with electrostatic potential (a) DHPMP (b) AHPMP.
9