Synthesis, characterization and corrosion inhibition potential of newly benzimidazole derivatives: Combining theoretical and experimental study

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Synthesis, Characterization and Corrosion Inhibition Potential of Newly Benzimidazole Derivatives: Combining Theoretical and Experimental Study Z. Rouifi , M. Rbaa , Ashraf S. Abousalem , F. Benhiba , T. Laabaissi , H. Oudda , B. Lakhrissi , A. Guenbour , I. Warad , A. Zarrouk PII: DOI: Reference:

S2468-0230(19)30527-9 https://doi.org/10.1016/j.surfin.2020.100442 SURFIN 100442

To appear in:

Surfaces and Interfaces

Received date: Revised date: Accepted date:

8 September 2019 5 January 2020 12 January 2020

Please cite this article as: Z. Rouifi , M. Rbaa , Ashraf S. Abousalem , F. Benhiba , T. Laabaissi , H. Oudda , B. Lakhrissi , A. Guenbour , I. Warad , A. Zarrouk , Synthesis, Characterization and Corrosion Inhibition Potential of Newly Benzimidazole Derivatives: Combining Theoretical and Experimental Study, Surfaces and Interfaces (2020), doi: https://doi.org/10.1016/j.surfin.2020.100442

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Synthesis, Characterization and Corrosion Inhibition Potential of Newly Benzimidazole Derivatives: Combining Theoretical and Experimental Study Z. Rouifia, M. Rbaab, Ashraf S. Abousalemc,d, F. Benhibaa,e, T. Laabaissia, H. Ouddaa, B. Lakhrissib, A. Guenboure, I. Waradf, A. Zarrouke a

Laboratory of Separation Processes, Faculty of Sciences, IbnTofail University, Kenitra, Morocco. Laboratoire d’Agroressources, Polymères et Génie des Procédés, Université Ibn Tofail, Faculté des Sciences, Kénitra, Morocco. c Chemistry Department, Faculty of Science, Mansoura University, El-Mansoura 35516, Egypt. d Operations Department, JOTUN, Egypt. e Laboratory of Materials, Nanotechnology and Environment, Faculty of Sciences, Mohammed V University, Av. Ibn Battouta, PO Box 1014 Agdal-Rabat, Morocco. f Department of Chemistry and Earth Sciences, PO Box 2713, Qatar University, Doha, Qatar. b

* Corresponding author. Tel.: +212 665 201 397. Fax.: +212 537 774 261. E-mail address: [email protected] (Abdelkader ZARROUK). 1

Abstract Three new heterocyclic benzimidazole derivatives and has been characterized via different spectroscopic methods ( 1H,

13

synthesized and

C NMR) and study their inhibitory

properties of three benzimidazole derivatives, namely: 2- (2- (4-chlorophenyl) -1H-benzo [d] imidazol-1-yl) -N- (p-tolyl) acetamide (CBIN-1), 2- (2- (4-chlorophenyl) -1H) benzo [d] imidazol-1-yl) -N- (3,5-dimethylphenyl) acetamide (CBIN-2) and 2- (2- (4-chlorophenyl) 1H-benzo [d] imidazol-1-yl) ) -N-phenylacetamide (CBIN-3) for carbon steel (CS) in 1 M HCl solution using electrochemical impedance spectroscopy, potentiodynamic polarization and weight loss measurements at 298 K. The experimental results show that the inhibition increases with the concentration and can reach a limit value of 95.0 % for the inhibitor CBIN-2 at 10-3M. The polarization curves show that the benzimidazole derivatives (CBIN-1, CBIN-2 and CBIN-3) are of mixed type. The increase in temperature may have a decrease in the inhibition efficacy of the compounds studied. In addition, the inhibitors obey the single layer adsorption isotherm of Langmuir. It is found that the experimental parameters confirmed those obtained by theoretical studies. Surface morphology using SEM coupled and UV-visible spectroscopy of the carbon steel treated was investigated and discussed.

Keywords: Synthesis; Corrosion inhibition; Carbon steel; DFT; Monte Carlo simulation; UVvisible spectroscopy.

2

1. Introduction Nowadays, prevention against metal corrosion becomes a necessity, given the enormous role of metals in many industrial applications. Iron and its alloys play a crucial role in almost all industries [1-3], and acidic solutions are broadly used in many industrial processes. In terms of protection, corrosion inhibitors are a full-fledged mean of minimizing against metallic corrosion, making it an easy to implement and inexpensive corrosion control method. Many Heterocyclic molecules were examined and well reported as efficient corrosion inhibitors [410].

Various authors have described that the heterocyclic compounds based on

Benzimidazole showing various applications in several fields such as analytical chemistry, Medicinal and Agrochemical [11,12]. So, the benzimidazol-2-one derivatives have attracted considerable attention during the last few decades due to their inhibition properties for metallic corrosion [13-15]. Several drugs on the market have a benzimidazole ring. These products include an anti-cancer agent Bendamustine, Benomyl (antifungal) or Rabeprazole (anti-ulcer), but there are many others with analgesic, antidiabetic or anti-inflammatory properties. In this context, the target of this work is to assess the anti-corrosive capability of newly synthesized benzimidazole derivatives, namely, 2- (2- (4-chlorophenyl) -1H-benzo [d] imidazol-1-yl) -N- (p-tolyl) acetamide (CBIN-1), 2- (2- (4-chlorophenyl) -1H) benzo [d] imidazol-1-yl) -N- (3,5-dimethylphenyl) acetamide (CBIN-2) and 2- (2- (4-chlorophenyl) 1H-benzo [d] imidazol-1-yl) ) -N-phenylacetamide (CBIN-3) on carbon steel in 1 M HCl, so we will consider through this study to gauge the effect of substitute on the inhibitory behavior. To achieve this, we used electrochemical stationary (potentiodynamic polarization) and transient (electrochemical impedance spectroscopy) and gravimetric (mass loss) techniques. These techniques allowed us to go back to the inhibitory efficiency of our inhibitors, its mode of action as well as some specific parameters related to the dissolution of 3

the metal and others related to the adsorption of the studied inhibitor to the metal surface. The surface morphology has been evaluated using SEM and UV-visible spectroscopy. More and more quantum parameters were realized by DFT and MC simulations to confirm the experimental results. 2. Experimental details 2.1. Materials In this work, we used CS samples whose chemical composition (%) is: C = 0, 37%, Mn = 0.68%, P = 0.03%, S = 0.016%, Cr =0.077%, Co = 0.09%, Ti = 0.011% Ni = 0.059%, and the rest of the iron. The samples of steel undergo, before each test, a pretreatment, which consists of polishing the surface of the sample with sandpaper of increasingly fine particle size (grade 200-400-800-1200) followed by rinsing with distilled water, degreasing with acetone, a second rinse with distilled water, and finally the sample is dried. The molar solution of hydrochloric acid is find by dilution of concentrated mother acid (commercial) density; d = 1.18 and 38% by weight of Riedel de Haen brand with water distilled. 2.2. Methods 2.2.1. Corrosion test 2.2.1.1. Gravimetric study Gravimetry is one of the oldest methods used to determine the rate of corrosion and inhibitory efficacy when using an inhibitor. Although it represents a direct method for the determination of the rate of corrosion. The steel samples have a dimension of 3cm  3cm  0.3cm . These samples are immersed in 1M hydrochloric acid HCl solution without and with the addition of the inhibitors at an ambient temperature of 298 K. The inhibitory efficiency is calculated after 6 hours of immersion, which is the average of three tests carried out under the same operating conditions for each concentration. It is determined by the following relation[16]:

4

w  %  

0 corr  corr 100 0 corr

(1)

0 and corr respectively represent the values of the corrosion rate in the absence and in the corr

presence of the inhibitor (in mg cm-2 h-1). 2.2.1.2. Electrochemical tests The electrochemical measurements are carried out involving a potentiostat / galvanostat voltalab (PGZ100), driven by a computer using the ―software voltamaster 4‖. We have used a thermo-stated electrochemical cell with three electrodes an electrode of CS in the form of a plate is used as a working electrode. This electrode is arranged facing the platinum auxiliary electrode and a saturated calomel electrode (SCE) as the reference electrode. All the tries were performed at a temperature set using a thermostat. The electrode is maintained before each measurement at its free corrosion potential for 30 minutes under aeration conditions atmospheric. The intensity-potential curves are obtained in potentiokinetic mode with a scanning speed of 0.5 mV / s and a potential range between -800 and -200 mV / SCE. The current intensity is measured in the midst the (WE) and (CE). And electrochemical impedance diagrams (EIS) were performed using a sinusoidal disturbance potential of 10 mV at a frequency between 100 kHz and 10 mHz. 2.2.2 .Surface analysis and gravimetric solution 2.2.2.1. Scanning electron microscopy (SEM) The SEM observations were made employing a JOEL JSM-5500 type device. The device has two types of detector for imaging. A secondary electron detector provides a chemical contrast image. 2.2.2.2. UV-Visible spectra UV-visible spectra were recorded in 1 M HCl at room temperature at using Jenway UVvisible (serie 67) spectrophotometer connected to a microcomputer. 5

2.2.3. Computational details 2.2.3.1. DFT calculations The functional density theory (DFT) was used to analyze the characteristics of the inhibitory / surface mechanism and to describe the structural nature and the electronic properties of the inhibitor. Indeed this method has become much popular in recent years as it can achieve similar accuracy to other methods in a short time and is less expensive (economically) from a computational point of view. In order to perform the theoretical calculations, we adjusted the DFT method (B3LYP) using the base 6-31G (d, p) implemented in Spartan Wave function [17-19]. The geometrical optimization was performed on the neutral form of inhibitors without and with considering the solvent (water) effect. 2.2.3.2. Monte Carlo Simulations (MC) Simulation The interaction and adoption behavior of the concerned inhibitors on Fe surface were explored by Monte Carlo simulations were performed on the lowest energy conformer of the inhibitors using the adsorption locater module in Materials Studio™ 2017. Since Fe (1 1 0) surface is lower in energy among the other Fe surfaces, it was selected considering its packed surface and high stability. MC simulations were performed in a simulation box of dimension (24.41 × 24.41 × 42.43 Å) with periodic boundary conditions. The simulation box consisted of six layers of Fe atoms where the first layer is the Fe slab and vacuum layer built above the surface. The effect of the aqueous solution and corrosive ions was taken into account in our investigation. Therefore, 150 H2O molecules, 15 H3O+, 15 Cl−). In the simulation study, the COMPASS force field was employed in order to adjust the atomic coordinate of the studied molecules. The adsorption energy (E ads) between the Fe surface and the inhibitor molecules is inferred from the interaction energy obtained from the energy calculations. The negative value of the interaction energy describes the binding energy of the inhibitor molecules with Fe surface [16,17]. 6

3. Results and discussion 3.1. Chemical study 3.1.1. General procedure 0.01 mol of acetamide derivatives (1) are mixed with 0.01 mol of benzimidazole (2) in 50 mL DMF in the presence of 0.03 mol of K2CO3.The reaction mixture is refluxed under magnetic agitation for 12 hours. The reaction is monitored by CCM using a hexane/ dichloromethane mixture (4:6, v/v) as eluent. The reaction mixture is concentrated in the rotary vacuum evaporator of the water tube. The resulting residue is hydrolyzed with 20 mL of NaCl saturated water, extracted with chloroform (3 × 20 mL). The organic phases are collected, washed with water saturated with NaCl, dried on anhydrous sulphate magnesium and dry concentrated in the vacuum rotary evaporator of the water trunk. The resulting crude residue is purified by silica gel column chromatography using as eluent a hexane/dichloromethane mixture (4:6, v/v), followed by recrystallization in the DMSO-EtOH mixture (5/5: v/v) scheme 1.

Scheme 1: Preparation of benzimidazole derivatives. 3.1.2. Spectral data 7

2-(2-(4-chlorophenyl)-1H-benzo[d]imidazol-1-yl)-N-(p-tolyl)acetamide (CBIN-1) 1

H NMR, δppm = 2.5268 (s, 3 H, CH3), 5.589 (s, 2 H, CH2), 6.6875-8.58 (m, 13 H, aromatic),

8.90 (s, 1 H, NH), 3.45 (s, H of trace H2O present in DMSO-d6). 13

C NMR, δppm = 14.82 (CH3), 49.87 (CH -C=O), 110.413-152.941(CH. C of aromatic)

,163.25 (CH2 -C=O). 2-(2-(4-chlorophenyl)-1H-benzo[d]imidazol-1-yl)-N-(3,5-dimethylphenyl)

acetamide

(CBIN-2) 1

H NMR, δppm = 2.5207 (s, 6 H, CH3), 4.02 (s, 2 H, CH2), 6.6871-8.5799 (m, 13 H, aromatic),

8.87 (s, 1 H, NH), 3.45 (s, H of trace H2O present in DMSO-d6). 13C NMR, δppm = 25.19 (CH3), 62.0834 (CH -C=O), 110.446-152.8481(CH. C of aromatic) ,165.33 (CH2 -C=O). 2-(2-(4-chlorophenyl)-1H-benzo[d]imidazol-1-yl)-N-phenylacetamide(CBIN-3) 1

H NMR, δppm = 5.143 (s, 2 H, CH2), 6.685-8.517 (m, 13 H, aromatic), 8.90 (s, 1 H, NH),

3.44 (s, H of trace H2O present in DMSO-d6). 13

C NMR, δppm = 46.39 (CH -C=O), 110.525-148.09(CH. C of aromatic),153.51 (CH2 -C=O).

3.2. Corrosion test 3.2.1. Gravimetric study We investigated the inhibitory efficacy of three Benzimidazole derivatives (CBIN-1, CBIN-2, and CBIN-3) at different concentrations at constant temperature after 6 hours of immersion. Corrosion rate and inhibitory efficiency are listed in Table 1. Table 1 Corrosion rates and inhibitory efficiency for different concentrations of benzimidazole derivative (CBIN-1, CBIN-2, and CBIN-3) for corrosion of CS in 1M HCl at 298 K Inhibitors HCl CBIN-1

[C] (M) 1 10-6

corr -2

-1

(mg cm h ) 1.974 0.527 8

w (%) — 73.3

θ — 0.733

CBIN-2

CBIN-3

10-5 10-4 10-3 10-6 10-5 10-4 10-3 10-6 10-5 10-4 10-3

0.372 0.255 0.133 0.379 0.287 0.188 0.119 0.549 0.397 0.309 0.196

81.1 87.1 93.3 80.8 85.5 90.5 94.0 72.1 79.9 84.3 90.1

0.811 0.871 0.933 0.808 0.855 0.905 0.940 0.721 0.799 0.843 0.901

From Table 1 we find that the rate of corrosion decreases gradually with the increase in the concentration of benzimidazole compounds. This means that the corrosion process of the CS is delayed by the addition of these inhibitors (CBIN-1, CBIN-2, and CBIN-3), while the inhibitory efficacy increases with the increase of concentration and reaches a maximum value of 94.0 % for the CBIN-2 compound after 6 hours of immersion in 1M HCl. The inhibition of corrosion can be attributed to the adsorption of the inhibitors studied at the CS/ acid solution interface. Maximum efficacy for each compound is observed at the 10 -3 M concentration and any further increase in concentration does not cause an considerable change in inhibitor performance[20].

3.2.2. Potentiodynamic polarization Polarization curves of CS in 1M HCl in the absence and presence of the three benzimidazole (CBIN-1, CBIN-2, and CBIN-3) derivatives at different concentrations and at 298 K are shown in Figure 1. Extrapolation of the Tafel straight lines to the corrosion potential allows us to determine the corrosion current density ( icorr ). The values of the electrochemical parameters relating to the study of the effect of the concentration of three benzimidazole derivatives are grouped in Table 2. In the same table are also given the values of the corresponding inhibitory efficiency. 9

1

1

0.1

0.1

0.01 0.01

i (mA/cm2)

1E-4

0.001

1E-4

1E-5 1E-6 1E-7 1E-8 -0.8

Blank solution 10-3 M of CBIN-1 10-4 M of CBIN-1 10-5 M of CBIN-1 10-6 M of CBIN-1 -0.7

-0.6

Blank solution 10-3 M of CBIN-2 10-4 M of CBIN-2 10-5 M of CBIN-2 10-6 M of CBIN-2

1E-5

1E-6

-0.5

-0.4

-0.3

1E-7 -0.8

-0.2

-0.7

-0.6

E (V/SCE)

-0.5

-0.4

-0.3

-0.2

E (V/SCE)

0.1

0.01

i (mA/cm2)

i(mA/cm2)

0.001

0.001

1E-4

1E-5

1E-6

-0.8

Blank solution 10-3 M of CBIN-3 10-4 M of CBIN-3 10-5 M of CBIN-3 10-6 M of CBIN-3 -0.7

-0.6

-0.5

-0.4

-0.3

-0.2

E(V/SCE)

Figure 1: Biasing curves of CS in 1 M HCl without and with addition of different concentrations of CBIN-1, CBIN-2, and CBIN-3 at 298 K. Table 2 Electrochemical parameters and corrosion inhibitory efficacy of steel in 1M HCl without and with addition of CBIN-1, CBIN-2, and CBIN-3 at different concentrations.

Medium

Conc (M)

-Ecorr icorr (mV vs. SCE) (µA cm-2)

ηpp (%)

Tafel slopes (mV dec-1) -βc

βa

HCl

1

457.7

551.3

114.8

102.0

—

CBIN-1

10-6 10-5 10-4 10-3 10-6 10-5 10-4 10-3

444.1 433.7 431.3 381.3 404.6 405.2 422.3 383.8

118.4 85.7 65.3 31.0 86.3 70.8 56.5 28.0

100.2 112.6 115.7 138.6 122.0 115.6 95.7 114.6

71.4 92.2 95.3 64.1 51.0 82.3 76.9 54.4

78.5 84.4 88.2 94.4 84.4 87.2 89.7 94.6

CBIN-2

10

CBIN-3

10-6 10-5 10-4 10-3

451.3 442.9 447.3 444.0

149.9 94.5 77.8 56.3

135 140.6 166.3 170.3

98.4 83.6 73.4 64.2

72.8 83.0 85.3 89.8

According to Table 2, it is well noted that the value of icorr decreases considerably with the increase of inhibitor concentration icorr reaches a value of 28.0 µA cm-2 at a concentration of 10-3 M for the inhibitor CBIN-2. This value leads to an inhibitory efficiency of 94.6%, which confirms that the CBIN-2 compound possesses an anticorrosive property. These data are consistent with the structure of these inhibitors due to the presence of certain active sites and the hetero atoms that adsorb to the metal surface, and the efficacy of its inhibitors is directly proportional to the amount of inhibitor adsorbed[21,22]. Figure 1 indicates that the cathode curves have a wide range of linearity, meaning that the Tafel law is well verified and that the hydrogen evolution reaction is under pure activation control. We find that the current density has significantly decreased for all concentrations compared to that obtained without inhibitor. As well as the addition of inhibitors CBIN-1, CBIN-2 and CBIN-3 in 1M HCl displaces the corrosion potential towards more electronegative values for all concentrations. The significant effect of these inhibitors on the anodic and cathodic slopes confirms that these compounds have a mixed character[23,24]. 3.2.3. Electrochemical impedance spectroscopy The corrosion behavior of CS in 1M HCl in the absence and in the presence of benzimidazole derivatives (CBIN-1, CBIN-2 and CBIN-3) was studied by the stationary electrochemical technique at 298 K. Corrosion potential, open circuit after 30 minutes of immersion. Nyquist diagrams of CS in uninhibited and inhibited acidic solutions containing various concentrations of CBIN-1, CBIN-2 and CBIN-3 are shown in Figure 2.

11

800

700

Blank solution -3 10 M of CBIN-1 -4 10 M of CBIN-1 -5 10 M of CBIN-1 -6 10 M of CBIN-1 fitting line

H3C O

600 N H

N

500

Cl

N

3.16 Hz

300 200

100 KHz

N H Cl

500

N

400

O

H3C

600

-Zim( cm²)

-Zim( cm²)

10 Hz

Blank solution -3 10 M of CBIN-2 -4 10 M of CBIN-2 -5 10 M of CBIN-2 -6 10 M of CBIN-2 fitting line

CH3

700

N

4 Hz

400

125 Hz 300

100 KHz

1 Hz

200

0.31 Hz

100

100

0 0

0 0

100

200

300

400

500

600

100

200

300

700

400

500

600

700

Zr ( cm²)

Zr ( cm²)

500

Blank solution -3 10 M of CBIN-3 -4 10 M of CBIN-3 -5 10 M of CBIN-3 -6 10 M of CBIN-3

H

O

400 N H

N Cl

-Zim( cm²)

300

N

1.25 Hz 10 Hz

200

100 KHz

100

0 0

100

200

300

400

500

Zr ( cm²)

Figure 2: shows the impedance diagrams of the steel/solution interface to corrosion potential in 1M HCl containing CBIN-1, CBIN-2, and CBIN-3 at different concentrations. The behavior of the impedance is generally explained using an equivalent circuit (Figure 3) including a solution resistance (Rs), the polarization resistance (Rp) and constant phase element (CPE). Rs

CPE Rp

Figure 3: The electrical circuit consistent with the experimental impedance data . Element Rs CPE-T CPE-P Rp Data File:

Freedom 12 Fixed(X) Fixed(X) Fixed(X) Fixed(X)

Value 0 0 1 0

Error N/A N/A N/A N/A

Error % N/A N/A N/A N/A

800

The CPE element is employed to take into account the depressed nature of semicircles and to provide a more precise adjustment. CPE is defined by the expression [25]: ZCPE  Q1  iw

n

(2)

Where Q named the CPE constant, n is a CPE exponent determining the phase shift which can be utilized as a gauge of roughness or heterogeneity of the surface ( 0

n

1 ), i2 = -1 defined

as an imaginary number and w is the angular frequency (w = 2πf, where f is the frequency). However, the double layer capacitances, Cdl, for a circuit comprising a CPE were determined by utilizing the next formula [26]:



Cdl  Qd R1pn



1

n

(3)

The different electrochemical impedance parameters for steel in 1M HCl in the presence of inhibitors CBIN-1, CBIN-2 and CBIN-3 are listed in Table 3. Table 3 EIS parameters and the corresponding inhibition efficiencies for CS/1.0 M HCl/benzimidazole derivatives system at 298 K. Medium

C (M)

Rs (Ω cm2)

Rp (Ω cm2)

Cdl (µF cm-2 )

Q 10-4 (µF Sn-1)

ndl

ȠEIS %

HCl

1 10-6 10-5 10-4 10-3 10-6 10-5 10-4 10-3 10-6 10-5 10-4 10-3

1.22 1.25 2.02 4.66 1.7 0.13 1.62 1.65 1.47 1.21 1.34 1.41 2.11

34.85 160.2 248.7 268.4 652.4 256.0 269.3 322.0 699.1 137.6 197.1 252.2 481.9

117.57 111.06 100.8 59.85 39.13 69.70 56.26 48.88 36.72 109.34 97.90 73.21 40.17

3.15 1.71 1.57 1.02 0.73 1.13 0.97 0.91 0.71 1.81 177 1.63 0.92

0.82 0.89 0.88 0.87 0.83 0.88 0.87 0.85 0.82 0.88 0.85 0.80 0.79

— 78.2 86.0 87.0 94.6 86.4 87.0 89.2 95.0 74.8 81.3 86.2 92.6

CBIN-1

CBIN-2

CBIN-3

13

From Figure 2 illustrates that the Nyquist diagrams geted have a single well-defined capacitive loop whose diameter increases with increasing inhibitor concentration (CBIN-1, CBIN-2, and CBIN-3), indicating an increase in the inhibitory power. This result reflects the influence of the tested inhibitors (CBIN-1, CBIN-2, and CBIN-3) on the process at the steel / HCl interface. From Table 3 we notice that the increase in concentration is accompanied by an increase in Rp and ηEIS and a decrease in Cdl [27]. Moreover, the decrease of C dl as a function of the recovery rate could be explained by the gradual replacement of the molecules on the metal surface, thus leading to the formation of an insoluble barrier film [28,29], the thickness of which is inversely proportional to the value of the capacity of the double layer which can verify equation (4). These results prove that the CBIN-2 inhibitor effectively protects the metal surface.

Cdl 

 0 e

(4)

s

Or e is the thickness of the deposit, S is the surface of the electrode  0 is the permittivity of the medium,  is the dielectric constant. 3.3. Influence of temperature and activation parameters The effect of temperature on the corrosion kinetics can help to understand the mode of the inhibitors action as well as the mechanisms involved during this corrosion. To clarify the effect of this factor on the benzimidazole compounds inhibitory potency. We plot the polarization curves of CS with and without the addition of Benzimidazole compounds (CBIN-1, CBIN-2, and CBIN-3) at a temperature range 298 K to 328 K. Figure 4 shows the effect of temperature of CS in 1M HCl medium, in the absence and in the presence of 10-3M benzimidazole compounds (CBIN-1, CBIN-2, and CBIN-3).

14

The values of the inhibitory efficiencies (  PDP %), as well as those of the parameters electrochemical associated with corrosion of CS in 1M HCl before and after addition of CBIN-1, CBN-, and CBIN-3 at different temperatures, are reported in table 4.

1

0.1

100

0.01

i (mA/cm2)

i(mA/cm2)

10

1

0.001

1E-4

0.1

0.01

1E-5

Blank solution 298 K 308 K 318 K 328 K

0.001 -800

-700

298 K of CBIN-1 308 K of CBIN-1 318 K of CBIN-1 328 K of CBIN-1

1E-6

-600

-500

-400

-300

1E-7 -0.8

-200

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.4

-0.3

-0.2

E (V/SCE)

E (mV/SCE)

1 1

0.1 0.1

0.01

i (mA/cm2)

i (mA/cm2)

0.01

0.001

1E-4

1E-5

1E-6

1E-7 -0.8

0.001

1E-4

1E-5

298 K of CBIN-2 308 K of CBIN-2 318 K of CBIN-2 328 K of CBIN-2 -0.7

-0.6

298 K of CBIN-3 308 K of CBIN-3 318 K of CBIN-3 328 K of CBIN-3

1E-6

-0.5

-0.4

-0.3

1E-7 -0.8

-0.2

-0.7

-0.6

i (V/SCE)

-0.5

E(V/SCE)

Figure 4: Biasing curves of CS in 1M HCl with addition of 10 -3 M CBIN-1, CBIN-2 and CBIN-3 at different temperatures. Table 4 Influence of temperature on electrochemical parameters of CS in 1M HCl at different concentrations of CBIN-1, CBIN-2, and CBIN-3. Medium

T (K)

-Ecorr (mV vs. SCE)

icorr (µA cm-2) 15

Tafel slopes (mV dec-1)

 PDP

1M HCl

CBIN-1

CBIN-2

CBIN-3

298 308 318 328 298 308 318 328 298 308 318 328 298 308 318 328

457.7 454.5 456.2 456.0 381.3 394.1 425.7 396.0 383.8 429.5 403.2 398.5 444.0 498.7 469.0 474.8

551.3 735.9 1152.3 1950.6 31.0 96.2 184.7 405.8 28.0 83.7 181.6 301.5 56.3 171.3 335.2 703.7

-βc 114.8 126.6 140.1 139.8 138.6 200.5 160.7 199.8 114.6 86.4 150.6 129.8 170.3 178.6 179.1 191.4

βa 102.0 95.7 93.2 98.0 64.1 54.9 79.09 87.2 54.4 82.9 146.5 72.1 64.2 189.8 95.9 101.3

(%) — — — — 94.4 86.9 84.0 79.2 94.6 88.6 84.3 84.5 89.8 77.0 71.0 64.2

According to figure 4, We note that the cathodic curves polarization, in the presence or absence of CBIN-1, CBIN-2 and CBIN-3 at a temperature range 298 to 328 K, have kept the same rhythm, which indicates that the mechanism of reducing the water on the metal surface has not been modified. Furthermore, the cathodic currents are increased with the growth of the temperature. The same behavior has been remarked in the anodic domain. The decrease interval of effectiveness between the lowest and the highest temperature does not exceed 20% for the three benzimidazole derivatives. Which confirms that these inhibitors act by adsorption to the metal surface and that they remain resistant to corrosion in this temperature range[30]. To understand more details about the corrosion process, kinetic activation parameters "activation energy Ea , enthalpy H a , and entropy Sa " were evaluated by the effect of temperature according to the law of Arrhenius and the formula alternative of the Arrhenius equation[31].

16

Figure 5 illustrates the variation of the logarithm of the corrosion current density according to the inverse of the absolute temperature. This variation of Ln (icorr )  f (1/ T ) is a right for the different concentrations without and with inhibitor. From Arrhenius's relationship, we can, therefore, calculate the energies of activation. Figure 6 clarifying the variation of the logarithm of the corrosion current density according to the inverse of the absolute temperature. This variation of Ln (icorr )  f (1/ T ) is a right for the different concentrations without and with inhibitor. From Arrhenius's relationship, we can, therefore, calculate the energies of activation the variation of Ln (icorr / T ) according to the inverse of the temperature for the acid alone and for concentration 10 -3 M of CBIN-1, CBIN-2, and CBIN-3. The rights obtained have a slope equal to (H a / R) and an ordinate originally equal to

Ln( R / Nh  Sa / R) Thanks to these rights; we can, therefore, calculate the values of H a and Sa . The values of enthalpies and entropies are listed in Table 5.

8

7

Ln (icorr)

6

5

4

Blank solution CBIN-1 CBON-2 CBIN-3

3

3.00

3.05

3.10

3.15

3.20

3.25 -1

1000/T (K )

17

3.30

3.35

3.40

Figure 5: Arrhenius plots for CS corrosion in 1 M HCl in the absence and presence of CBIN-1, CBIN-2 and CBIN-3 at 10-3 M.

2

1

Ln (icorr/T)

0

-1

Blank solution CBIN-1 CBIN-2 CBIN-3

-2

-3 3.00

3.05

3.10

3.15

3.20

1000/T ( K

3.25 -1

3.30

3.35

3.40

)

Figure 6: Transition state plot for CS corrosion in 1 M HCl in the absence and presence of CBIN-1, CBIN-2 and CBIN-3 at 10-3 M.

According to Table 5, we find that the value of the apparent activation energy Ea for 1M HCl without inhibitor (34.30 (kJ mol-1)). The analysis of data concerning the activation energy existing in Table 5 showed that the values of E a in the presence of CBIN-1, CBIN-2, and CBIN-3 are superior to that of uninhibited electrolyte. These outcomes signify retardation in corrosion rate due to a strong electrostatic effect between CBIN-1, CBIN-2, and CBIN-3 molecules and the metal surface[32]. It is observed that the values of H a are positive which suggests that the reaction is endothermic in the presence and absence of benzimidazole compounds on the surface of steel[33]. In addition, we observe an increase and a change of the sign of the entropy of activation Sa attributed to the increase of the molecular disorder during the transformation of the reagents in activated complex[34]. 18

Table 5 Activation settings of CS in 1M HCl medium without and with addition of CBIN-1, CBIN-2, and CBIN-3 at 10-3M. Medium

ΔHa (kJ mol-1) 31.70 65.57 61.89 64.51

Ea (kJ mol-1) 34.30 68.09 64.49 67.17

Blank CBIN-1 CBIN-2 CBIN-3

ΔSa (J mol-1K-1) -86.64 4.40 8.48 60.07

3.4. Adsorption isotherm To obtain more information on the mode and type of adsorption of CBIN-1, CBIN-2, and CBIN-3 on the surface of the CS, we tested the experimental data with several adsorption isotherms. Indeed, the establishment of isotherms that better describe the adsorption behavior of the corrosion inhibition is important because they provide information on the nature of the metal-solution interaction. There are several models (Langmuir, Temkin, and Frumkin, etc.) that are compared to identify the mechanism putting in play the molecules tested. In this work, the best fit was found with the adsorption isotherm of Langmuir. Figure 7 shows the calculated isotherm for benzimidazole derivatives (CBIN-1, CBIN-2, and CBIN-3). The analysis of this representation shows that inhibitors CBIN-1, CBIN-2 and CBIN-3 adsorb on the metal surface. According to the Langmuir model since the variation is linear and the regression coefficient is close to 1.

0.0014 0.0012 0.0010

Cinh/q

0.0008 0.0006 0.0004 0.0002 0.0000

CBIN-1 CBIN-2 CBIN-3

-0.0002 -0.0002

0.0000

0.0002

0.0004

0.0006

Cinh

19

0.0008

0.0010

0.0012

Figure 7: The isotherm Langmuir adsorption benzimidazole derivatives studied on the surface of CS at 298 K. The high values of adsorption equilibrium constants by the chosen adsorption model (Langmuir), the adsorption capacity of the inhibitors on the surface of the steel. Also, the

K ads value of the CBIN-2 compound is greater than those of CBIN-1 and CBIN-3. The CBIN-2 is the best recovery of the surface of steel by other inhibitors. Hence its greater effectiveness in protecting against corrosion. According to the isotherm of Langmuir the adsorption constant linked with the standard energy by the relation 5[35,36]: K ads 

*  Gads  1 exp   55.55  RT 

(5)

Table 6 Thermodynamic Parameters of adsorption of CBIN-1, CBIN-2, and CBIN-3. Inhibitors CBIN-1 CBIN-2 CBIN-3

Kads (L mol-1)

R2

320819 569962 330587

0.9999 0.9999 0.9999

 - Gads

(kJ mol-1) 41.36 42.78 41.43

 The negative signs of Gads indicate the stability of the adsorbed layer on the metal surface.  According to the literature [37], the values of Gads , close to -20 kJ / mol or less negative, are

related to electrostatic interactions between the charged molecules and the metal, while those close to -40 kJ / mol or more negative involve a transfer of charges between the molecules of  the inhibitor and the metal surface. In our case, the values of Gads for the three

Benzimidazole compounds (CBIN-1, CBIN-2, and CBIN-3) are all more negative than -40 kJ / mol, which indicate to us that it is chemical adsorption, involving the formation of coordination bonds or covalent bonds[38]. 3.5. Surface Analysis Study

20

The morphologies obtained from CS surfaces immersed in 1M HCl for 6h in the absence and in the presence of inhibitors CBIN-1, CBIN-2, and CBIN-3 (10-3M) are presented in Figure 8. The substrate surface in the acidic electrolyte as shown in figure 8A. The surface image of the CS after 6 hours immersion at 298 K in 1M HCl alone (Fig. 8-B) clearly shows that the latter is badly damaged, we can observe the presence of gray clusters and some pitting on the surface of the metal indicating that the steel has undergone almost universal corrosion over the entire surface in the absence of the inhibitor. However, in the presence of inhibitors CBIN-1, CBIN-2, and CBIN-3 (Fig. 8C,D and E), we find in the images that the surface is smooth and virtually free of corrosion products. This is due to the adsorption of the inhibitory molecules, thus forming a protective layer which limits the access of the electrolyte to the surface of the steel.

21

Figure 8: SEM analysis of CS/1.0 M HCl/CBIN-1, CBIN-2 and CBIN-3 22

3.6. UV-visible spectrometry To affirm the possibility of the formation of a complex, the UV-visible absorption spectra obtained from a solution of 1M HCl containing 10-3M of CBIN-1, CBIN-2 and CBIN-3 before immersion of CS (Figure 9) have adsorption bands between 253-352 nm. These wavelength values can be attributed to the link π - π *[39]. On the other hand, after 6 hours of CS immersion in an aggressive solution, the absorption bands λ max Displaced from 352.33 to 368.32 nm, from 354.55 to 364.32 nm and from 253.70 to 260.81 respectively, for CBIN-1, CBIN-2 and CBIN-3.This due to a complexation among the molecules and the iron ions.

3.0

 = 368.32 nm

3.0

 = 352.33 nm

2.5

2.5

 = 364.32 nm

2.0

Absorbance

2.0

Absorbance

 = 354.55 nm

1.5

1.0

CBN-1/1M HCl Fer + CBN-1/1M HCl

0.5

1.5

1.0

Fer + CBN-2/HCl 1M CBN-2/HCl 1M

0.5

0.0

0.0

-0.5

-0.5 200

400

600

800

200

1000

400

600

Wavelength (nm)

Wavelength (nm)

23

800

1000

3.0

2.5

 = 360.81 nm

Absorbance

2.0

1.5

1.0

 = 253.7 nm

0.5

CBN-3/1M HCl Fer + CBN-3/1M HCl

0.0

-0.5 200

400

600

800

1000

Wavelength (nm)

Figure 9: UV-visible spectra of the 1.0 M HCl solution in the presence of 1 mM CBIN-1, CBIN-2 and CBIN-3 inhibitors before immersion (black) and after 6 hours immersion in CS(red). 4. Quantum Chemical Studies DFT is a powerful computational tool for exploring the interactions between the inhibitor molecule and metal interface. Figure 10 the fully optimized geometries and the HOMO, LUMO diagrams of the investigated molecules in its neutral form. Analysis of the HOMO and the LUMO is very important to predict the reactive sites in the molecule structure of compounds.

24

CBIN-1 Vacuum CBIN-2 Vaccum CNB-3 Vacuum

Figure 10: Geometrical optimized structures and FMOs for the tested inhibitors at DFT level B3LYP 6.31 (d, p).

The electronic properties can be indicated from the reactivity of the tested inhibitors. It is recognized that increasing HOMO energy is coincide with an increase in the electron donation ability of organic compound. In contrast, the lower the LUMO energy is, the higher the electron affinity of the compounds. 25

The electron density of the HOMO Figure 10 is distributed mainly on the aromatic benzene ring in the molecular structure of the tested molecule. The electronic distribution of HOMO in CNB3 is higher than the other compounds [40]. The total energies, the quantum chemical descriptors HOMO and LUMO energies (EHOMO and ELUMO), energy gap (ΔE), dipole moments (μ), electronegativity (χ), the fraction of electron transferred (ΔN), in gaseous and solution phases for the neutral form of CNB molecules are summarized in Table 7.Thehigher the value of EHOMO, lower the value of ELUMO and lower the value of ΔE are often associated with high corrosion inhibition efficiency, as reported in literature. It can be seen that there is a correlation between the inhibition efficiency and the decreasing trend in E LUMO. The electrons are easily transferred from the metal surface to the LUMO orbital and forming back-bonding which strengthen the corrosion protection of the compounds. The energy gap ΔE of gaseous phase is lower than in the aqueous phase form and the global softness shows an increase which indicates that there is an increase in the reactivity of the inhibitor molecules in the gaseous form. The electronegativity and the electrophilicity are larger, suggesting an increased tendency towards acceptance of electrons. The dipole moment also shows an increase in the gaseous phase than in the water phase [37]. From the investigation by quantum chemical methods, it can be concluded that there is no obvious correlation between the experimental %IE and the trend of the quantum chemical parameters. Thus, it is beneficial to explore the action of inhibitors using molecular simulation methods, where all factors related to the solution are all considered.

26

Table 7 Quantum Chemical Parameters for the investigated inhibitors in gaseous and aqueous phase.

Inhs

Gaseous state CBIN-1 -1548.92960 CBIN-2 -1588.25040 CBIN-3 -1509.60899 Aqueous Phase CBIN-1 -1548.94586 CBIN-2 -1588.26602 CBIN-3 -1509.62542

η (eV)

σ (eV)

χ (eV)

Dipole Moment (Debye)

ELUMO (eV)

∆E (eV)

-5.95 -5.98 -6.14

-1.420 -1.420 -1.440

4.530 2.265 0.442 3.685 -0.81 4.560 2.280 0.439 3.700 -0.81 4.700 2.350 0.426 3.790 -0.81

1.47 1.24 1.29

-5.88 -5.95 -6.05

-1.260 -1.270 -1.260

4.620 2.310 0.433 3.570 -0.77 4.680 2.340 0.427 3.610 -0.77 4.790 2.395 0.418 3.655 -0.76

1.33 1.17 0.89

Total EHOMO Energy (au) (eV)

∆NFET

5. Monte Carlo Simulations Molecular Simulation is a modern tool for investigating the inhibitor interaction on a metal substrate. Thus, we use this method in the present investigation to understand the molecular interaction of inhibitors at the atomic level. The interaction of CNB-1, CNB-2 and CNB-3 on the Fe (1 1 0), MC simulation studies were carried out with consideration of the effect of all other involved species (such as H2O, H3O+, Cl− and Fe surface) which are active component of the corrosion process. The MC simulations give an appropriate configuration of the inhibitor molecules adsorbed on the surface. Figure. 11 presents the side and top views of the equilibrium adsorption configurations of surface adsorbed inhibitors in vacuum. It can be concluded that that the inhibitor molecules tend to take favorably take planar adsorption orientation on the Fe (1 1 0) surface in vacuum system. This particular orientation provided maximum surface coverage and contact of inhibitor molecules with metal surface, leaving minimum surface area to be attacked by the corrosive solution. Whereas in the presence of water Figure 12, the orientation of inhibitor molecules directed away from the Fe surface in some part of the structure moiety. Monte Carol simulations were implemented depicting the adsorption state of CNB-1, CNB-2 and 27

CNB-3 on the Fe surface. This also establishes a correlation between the theoretically-driven binding energies of the concerned inhibitor molecules with the experimentally measured

CIBN-3/Fe(110)

CIBN-2/Fe(110)

CIBN-1/Fe(110)

inhibition efficiencies [41].

Figure 11: Top and Side views of the lowest energy adosporption configuration of the benzimidazole derivatives on Fe (1 1 0) substrate obtained by Monte Carlo simulations in vacuum conditions. 28

CNB-1/Fe(110) CNB-2/Fe(110) CNB-3/Fe(110) Figure 12: Top and Side views of the lowest energy adosporption configuration of the benzimidazole derivatives on Fe (1 1 0) substrate obtained by Monte Carlo simulations in aqueous solvent.

The computed interaction energies of the adsorption systems showed that the tested inhibitors are greatly adsorbed on the Fe surface in vacuum and the aqueous solution system and the high negative value of interaction energy values is attributed to strong adsorption of the 29

molecules on the Fe surface. From the results in Table 8, it can be inferred that CNB2 has the highest interaction energy than the other studied inhibitors. The adsorption energy with the Fe surface follows the order: CNB2 > CNB1 > CNB3. The trend of adsorption of compounds did not change in vacuum or water. It can be concluded that the theoretical results agreed well with the experimental results [42].

Table 8 Output obtained from MC simulation for adsorption of inhibitors on Fe (110) surface.

Structures Fe(110)CBIN-1 – 1 Fe(110)CBIN-2 – 1 Fe(110)CBIN-3 – 1

Structures Fe(110)CBIN-1 Aq Fe(110)CBIN-2 Aq Fe(110)CBIN-3 Aq

Total energy

Adsorption energy

Rigid adsorption Deformation energy energy

CBIN-1 dEad/dNi

-89.85

-202.06

-210.53

8.48

-202.06

-114.92

-209.19

-220.93

11.74

-209.19

-70.69

-191.17

-198.25

7.08

-191.17

Total energy

Adsorption energy

Rigid adsorption energy

-1965.37

-2179.32

-2174.42

-4.90

-193.30

-8.28

-1979.85

-2175.86

-2174.28

-1.58

-220.18

-7.96

-1931.87

-2154.09

-2172.91

18.82

-183.58

-7.85

:

Deformation energy

CBIN-3 : H2O : dEad/dNi dEad/dNi

Conclusion Three new the benzimidazole derivatives were synthesized and identified by 1H and

13

C

NMR. The impact of these three heterocyclic compounds on the corrosion inhibition for carbon steel in 1 M HCl solution was investigated using experimental and theoretical techniques. The experimental results showed that the chemical structure of the benzimidazole derivatives impairs the inhibitory efficiency. The results obtained from potentiodynamic polarization data indicate that the investigated compounds are mixed type inhibitors. 30

Impedance studies were analyzed using an equivalent circuit for effects of concentration for all tested inhibitors. All benzimidazole derivatives are adsorbed on the metal surface according to Langmuir adsorption isotherm model and the corresponding values of  revealed that their adsorption mechanism on steel surface is mainly due to Gads

chemisorption. The electronic absorption spectra of UV-visible after immersion confirm complex formation of studied compounds with iron ions from CS surface Quantum chemical study confirmed the experimental results and showed that the investigated inhibitor has a strong tendency of adsorption over the metallic surface Author Statement This statement is to certify that all Authors of the article “Synthesis, Characterization and Corrosion Inhibition Potential of Newly Benzimidazole Derivatives: Combining Theoretical and Experimental Study” have been seen and approved the manuscript being submitted. We warrant that the article is the Auhor’s original work. We warrant that the article has not received prior publication and is not under consideration for publication elsewhere. No conflict of interest exists, or if such conflict exists, the exact nature must be declared. On behalf of all Co-Authors, the corresponding Author shall bear full responsibility for the submission. All Authors agree that author list is correct in its content and order and that no modification to the author list can be made without the formal approval of the Editor-in-Chief, and all Authors accept that the Editor-in-Chief’s decisions over acceptance or rejection.

No conflict of interest exists, or if such conflict exists, the exact nature must be declared.

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