Hydrazino-methoxy-1,3,5-triazine derivatives' excellent corrosion organic inhibitors of steel in acidic chloride solution

Article abstract of DOI:10.3390/molecules21060714

The corrosion inhibition performance of 2-hydrazino-4,6-dimethoxy-1,3,5-tirazine (DMeHT), 2,4-dihydrazino-6-methoxy-1,3,5-triaizine (DHMeT), and 2,4,6-tridydrazino-1,3,5-triaizne (TH₃ ) on steel corrosion in acidic media was examined using electrochemical techniques. The results showed 2,4-Ddihydrazino-6-methoxy-1,3,5-triaizine (DHMeT) gave the best corrosion protection performance among the other hydrazino derivatives even at a low concentration of 25 ppm (95%). The number of hydrazino groups play an important role in the corrosion inhibition, where the two hydrazine groups increased the electrostatic interactions between the protonated tested compounds, the negatively charged steel surface resulted from the adsorption of the chloride anions, and the presence of the methoxy group made the compound more reliable for formation of film protection on the surface of steel through the lone pair of oxygen atoms. Electrochemical Impedance Spectroscopy (EIS) measurements suggested that the corrosion process of steel in presence of the hydrazino-s-triazine derivatives (TH3 , DMeHT and DHMeT) were being controlled by the charge transfer reaction. Polarization curves indicated that the examined TH₃ , DMeHT and DHMeT behaved as mixed type inhibitors.

Full text of DOI:10.3390/molecules21060714

molecules
Article
Hydrazino-methoxy-1,3,5-triazine Derivatives’
Excellent Corrosion Organic Inhibitors of Steel in
Acidic Chloride Solution
Ayman El-Faham 1,2,*, Sameh M. Osman 1,3, Hamad A. Al-Lohedan 1,4 and Gamal A. El-Mahdy 4,5,
*
1
Department of Chemistry, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451,
Saudi Arabia; smahmoud@ksu.edu.sa (S.M.O.); hlohedan@ksu.edu.sa (H.A.A.-L.)
Chemistry Department, Faculty of Science, Alexandria University, P.O. Box 426, Ibrahimia,
2
Alexandria 12321, Egypt
3
Advanced Materials Research Chair, Department of Chemistry, College of Science, King Saud University,
P.O. Box 2455, Riyadh 11451, Saudi Arabia
Surfactants Research Chair, Department of Chemistry, College of Science, King Saud University,
Riyadh 11451, Saudi Arabia
Chemistry Department, Faculty of Science, Helwan University, Helwan 11795, Egypt
Correspondence: aymanel_faham@hotmail.com (A.E.-F.); Gamalmah2000@yahoo.com (G.A.E.-M.);
Tel.: +966-114673195 (A.E.-F.)
4
5
*
Academic Editor: Wim Dehaen
Received: 29 April 2016; Accepted: 27 May 2016; Published: 1 June 2016
Abstract: The corrosion inhibition performance of 2-hydrazino-4,6-dimethoxy-1,3,5-tirazine
(DMeHT), 2,4-dihydrazino-6-methoxy-1,3,5-triaizine (DHMeT), and 2,4,6-tridydrazino-1,3,5-triaizne
(TH3) on steel corrosion in acidic media was examined using electrochemical techniques. The results
showed 2,4-Ddihydrazino-6-methoxy-1,3,5-triaizine (DHMeT) gave the best corrosion protection
performance among the other hydrazino derivatives even at a low concentration of 25 ppm (95%).
The number of hydrazino groups play an important role in the corrosion inhibition, where the two
hydrazine groups increased the electrostatic interactions between the protonated tested compounds,
the negatively charged steel surface resulted from the adsorption of the chloride anions, and the
presence of the methoxy group made the compound more reliable for formation of film protection
on the surface of steel through the lone pair of oxygen atoms. Electrochemical Impedance
Spectroscopy (EIS) measurements suggested that the corrosion process of steel in presence of the
hydrazino-s-triazine derivatives (TH3, DMeHT and DHMeT) were being controlled by the charge
transfer reaction. Polarization curves indicated that the examined TH3, DMeHT and DHMeT behaved
as mixed type inhibitors.
Keywords: s-triazine; hydrazine derivatives; organic corrosion inhibitor; steel; polarization; EIS;
adsorption
1. Introduction
The study of the corrosion phenomena of steel in acidic solution has become predominantly
important because of the huge applications in the industry. Organic inhibitors normally inhibit the
corrosion of steel by creating a film on the surface of the steel. The efficacy of the inhibitors is dependent
on the molecular structure, the chemical composition, and their attractions to the surface of the steel.
The efficiency of these compounds are influenced by their electronic structure, aromatic character and
the type of functional groups [1–4].
In recent years, heterocyclic compounds have been extensively studied as organic corrosion
inhibitors of steel in acidic solution. Recently, 1,2,4-and 1,2,3-triazole derivatives were reported as a
Molecules 2016, 21, 714; doi:10.3390/molecules21060714
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new class of heterocyclic compounds with promising results as organic corrosion inhibitors of steel in
1 M HCl [5–16].
1,3,5-Triazine (s-triazine) derivatives are another class of heterocyclic compounds and have an
excellent potential for the formation of non-covalent bonds, which involve either their nitrogen
lone-pairs, their heteroaromatic p-electrons or their σ-backbones [17–22]. Recently reported as organic
promising corrosion inhibitors of steel in 1 M hydrochloric acid [23], the reported data showed that
the corrosion inhibition effect depends on the electronic nature of the groups attached to the triazine
moiety [23–26].
Recently, we reported novel s-triazine derivatives as promising organic inhibitors (Figure 1) [27],
and the reported results for electrochemical process revealed that, as the nitrogen content increased in
the terminal chain, the effeciency for the corrosion protection of steel in acidic solution increased.
Figure 1. Structure of the new s-triazine derivatives as promising organic corrosion inhibitors.
Herein, we report easily prepared compounds with relatively low molecular weight and cheaper
materials than the reported ones for triazine deriavtives [23–27] to stress the flexibility and the effect of
the number of hydrazino groups along with the methoxy groups that directly attached to the triazine
ring for corrosion inhibition of steel in acidic media.
2. Results and Discusions
2.1. Synthesis of the Hydrazino-triazine Derivatives
2,4,6-Trichloro-1,3,5-triazine (cyanuric chloride )
1 has been known for a long time as an excellent
starting material for the synthesis of multitopic molecules [28]. The unique feature of cyanuric chloride
is the ability to replace each chlorine atom by any nucleophilic reagent under control of the reaction
temperature (Figure 2) [29].
Figure 2. Synthesis of trisubstituted s-triazine derivatives from cyanuric chloride.
˝
In this work, cyanuric chloride
intermediate 2,4-dichloro-6-methoxy-1,3,5-triazine (DCMeT,
The NMR spectrum (1H-NMR and 13C-NMR) was in good agreement with the reported data [30].
The dichloro derivative (DCMeT) was reacted with hydrazine hydrate using ultrasonic
1
was first reacted with methanol at 25 C for 30 min to afford the
2) in high yield and purity (Scheme 1).
2
˝
irradiation at 60 C in acetonitrile as a solvent to afford the product DHMeT
was in a good agreement with the reported data (Scheme 1) [31].
3; the spectral data

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Scheme 1. Synthesis of hydrazino-s-triazine derivatives.
The dimethoxy derivatives DMeCT
4
were prepared in the same way for prepation of
2
with a
˝
longer reaction time of reaction and heating in methanol for 4 h at 50 C to afford the chloro-dimethoxy
˝
4 [32]. Reaction of 4 with hydrazine hydrate using ultrasonic irradiation at 60 C
derivatives DMeCT
afforded the expected product DMeHT 5 in an excellent yield and purity.
The trihydrazino TH3 was prepared from the reaction of cyanuric chloride
hydrate. The reaction was first performed at 0 ˝C and warmed up to 25 ˝C and finally sonicated at
6
1 with hydrazine
˝
60 C to afford the product in high yield and purity (Scheme 1). The structure of DMeHT
3, DHMeT 5,
and TH3
6
were confirmed by NMR (1H and 13C) spectrum and elemental analysis, and were in
accordance with the reported data [33,34].
2.2. Potentiodynamic Polarization Measurements
Cathodic and anodic polarization curves of steel in 1 M HCl solution containing different
concentrations of TH3 ( ), DMeHT ( ) and DHMeT ( ) are shown in Figures 3–5, respectively.
6
5
3
The presence of TH3, DMeHT and DHMeT lowered the current density of the the anodic and cathodic
curves compared with the blank solution. The results may be attributed to adsorption of TH3, DMeHT
and DHMeT on the steel surface, and hence inhibited the continuation of the corrosion process.
This suggests that the TH3, DMeHT and DHMeT suppressed the anodic and cathodic reactions by
increasing the energy barrier for both processes [35].
Figure 3. Influence of TH3 concentrations on polarization plots of steel electrode in 1 M HCl solution.

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Figure 4. Influence of DMeHT concentrations on polarization plots of steel electrode in 1 M HCl solution.
Figure 5. Influence of DHMeT concentrations on polarization plots of steel electrode in 1 M HCl solution.
As observed from Table 1, the number of hydrazine groups have a great effect on the corrosion
inhibition. At high concentrations (250 ppm), the three tested compounds DHMeT, DHMeT, and TH3
have almost the same effect (97.8, 95.2, and 97.8, respectively). While at low concentration (25 ppm
and 50 ppm), the dihydrazino DHMeT derivative has the best effect (95.1 and 96.6, respectively). This
indicates that the hydrazine groups play an important role in the inhibition efficiency, where the two
hydrazine groups increased the electrostatic interactions between the protonated tested compounds
and the negatively charged steel surfaces that resulted from the adsorption of the chloride anions, and
the presence of the methoxy group makes the compound more reliable for formation of film protection
on the surface of steel through the lone pair of oxygen atoms, while increasing the hydrazine group
does not improve the efficiency at low concentration as shown in Table 1.
All estimated electrochemical parameters obtained from the extrapolation of the polarization
curves are listed in Table 1 for TH3, DMeHT and DHMeT. The tested material was labeled as a cathodic
or anodic type if the shift in Ecorr is >85 mV with respect to Ecorr of the blank solution [36]. In addition,
the tested material is known as a mixed type inhibitor if the shift in Ecorr is <85. It is the clear that the
shift in Ecorr values is less than 85 mV, suggesting that TH3, DMeHT and DHMeT can be classified as a
mixed type of inhibitor [37
can be given as [39–41]:
,38]. The inhibition efficiency (IE%) that was calculated from polarization
IE% “ r1 ´ picorr(inh){icorr(uninh)qs ˆ 100 (1)
where icorr(uninh) and icor(inh) are corrosion current density values in the uninhibited and inhibited
solution, respectively. It can be concluded that the higher the TH3, DMeHT and DHMeT concentrations,
the higher the values of IE. The results can be attributed to more adsorption of the inhibitor on

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steel surface. The diminution of the Icorr values confirms that the TH3, DMeHT and DHMeT block
the active sites on the steel surface via adsorption of the inhibitor. The predominant corrosion
current density value decreased by increasing the inhibitor concentration, showing that TH3,
DMeHT and DHMeT have corrosion protection performance for the steel corrosion in the acidic
chloride-containing environment.
Table 1. Effect of TH3, DMeHT and DHMeT concentrations on the inhibition efficiency of steel
calculated by electrochemical methods.
Polarization Method
EIS Method
Compd.
Conc.
(ppm)
Ba
(mV)
Bc
icorr
Rct
Ohm
Cdl
Ecorr (V)
(mV)
IE%
IE%
µA/cm2
(µF/cm2)
Blank
69
120
´0.3955
839
1.80
334
_____
____
25
50
150
250
53
54
49
50
119
117
140
111
´0.3583
´0.3534
´0.3489
´0.3587
36
32
22
19
95.6
96.1
97.3
98.0
43.0
54.0
66.5
84.0
110
100
95.0
93.0
95.1
96.6
97.2
97.8
DHMeT; 3
DMeHT; 5
TH3; 6
25
50
150
250
56
55
58
53
164
160
111
118
´0.3398
´0.3498
´0.3735
´0.3667
59
56
50
34
92.9
93.3
94.0
95.9
33.0
29.0
35.8
37.7
118
108
102
98
92.8
93.7
94.0
95.2
25
50
150
250
62
61
43
47
230
227
70
´0.3370
-0.3380
-0.3616
-0.3480
124
120
51
85.0
85.6
93.9
97.7
11.6
13.2
30.0
83.0
128
122
114
94.0
84.4
86.0
94.0
97.8
121
19
2.3. Electrochemical Impedance Spectroscopy (EIS)
Nyquist curves for steel in acidic chloride solution containing different concentrations of TH3,
DMeHT and DHMeT are shown in Figures 6–8, respectively. A single capacitive loop has been observed
with an increased diameter with increasing TH3, DMeHT and DHMeT concentration. The data shown
in Figures 6–8 were fitted by an equivalent circuit (EC) comprised of solution resistance (Rs), charge
transfer resistance (Rct) in parallel with double layer capacitance (Cdl) as shown in Figure 9 [42]. It is
composed of (Rs), (Cdl) and (Rct). The values of them are listed in Table 1 for TH3, DMeHT and
DHMeT. It is clear that the Rct values are highly dependent upon the concentration of the tested
materials and increase with the increase in TH3, DMeHT and DHMeT concentrations.
Figure 6. Nyquist plots of steel electrode obtained in 1 M HCl solution and containing various
concentrations of TH3.

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Figure 7. Nyquist plots of steel electrode obtained in 1 M HCl solution and containing various
concentrations of DMeHT.
Figure 8. Nyquist plots of steel electrode obtained in 1 M HCl solution and containing various
concentrations of DHMeT.
Figure 9. The equivalent used in fitting the electrochemical impedance spectroscopy (EIS) data.
The formation of inhibitive films on the steel/solution interface led to an increase in the values of
Rct. The replacement of pre-adsorbed water molecules (high dielectric constant) on the steel surface by
adsorption of TH3, DMeHT and DHMeT molecules (with lower dielectric constant) is accompanied by
a decrease in the Cdl values. IE% was estimated from the values of Rct(uninh) in the uninhibited solution
and Rct(inh) in the inhibited solution as follows [43–45]:
IE% “ r1 ´ pRct(uninh){Rct(inh)qs ˆ 100
(2)
It is clear that the values of IE% increased significantly in the presence of TH3, DMeHT and
DHMeT, suggesting the protection performance of the tested materials towards the corrosion of steel

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in the acidic chloride solution. The results can be attributed to an adsorption of TH3, DMeHT and
DHMeT molecules on the active sites of steel surface, which, in turn, enhanced the high protection
performance. It is obvious from the results that the TH3, DMeHT and DHMeT inhibited the corrosion
ability of steel in the acidic chloride-containing environment even at low concentrations. The calculated
values of IE presented in Table 1 follow the same trend as those obtained from the polarization results.
The results of IE% obtained from potentiodynamics and EIS measurements are in good agreement
with that reported previously for increasing the IE% with an increase in the triazole derivities [15,46].
2.4. Adsorption Isotherm
Investigating the adsorption isotherms models is very important for determining the type of
interactions of the tested materials with the exposed surface [47]. The experimental data were fitted to
the various isotherms [48–52]. The best fit to the collected data of the tested materials is the Langmuir
adsorption isotherm (Figure 10), which was described as [53]:
C(inh){θ “ 1/Kads ` C(inh)
(3)
where C(inh) is the inhibitor concentration, Kads is the adsorption equilibrium constant and
θ
is the
surface coverage. Plotting of C(inh)/θ vs. C(inh) exhibited a linear relationship as depicted in Figure 10a–c
for TH3, DMeHT and DHMeT, respectively. The results indicate that the adsorption of TH3, DMeHT
and DHMeT on the steel surface follows the Langm˝uir adsorption isotherm. The constant Kads is
related to the standard free energy of adsorption (∆G ads) by the following equation [54,55]:
˝
∆G ads “ ´RT(ln 55.5Kads)
(4)
where R is the gas constant (8.314 J
¨
mol´1
¨
K
´1) and T is the absolute temperature (K). It was
established that the existence of electrostatic interaction between charged metal surface and
cha˝rged organic molecules in the bulk of the solution may be at˝tributed to a small value of
´1
´1
∆G ads ď ´20 kJ¨ mol (physical adsorption). The high value of ∆G ads ě ´40 kJ¨ mol involves
charge sharing or charge transfer between the metal surface and organic molecules to form a coordinate
type of bond (chemical adsorption) [56
,
57]. The calculated values of
∆
G˝ads for TH3, DMeHT and
DHMeT are 34.33, 35.89 and 37.86 kJ
suggested that the adsorption process of the TH3, DMeHT and DHMeT on the steel surface can be
labeled as complex interactions, which includes both physical and chemical adsorption [58].
´
´
´
¨
mol´1, respectively. The estimated values of G˝ads
∆
Figure 10. Langmuir adsorption plot of steel in 0.1 M HCl solution containing different concentrations
of: (a) TH3; (b) DMeHT; (c) DHMeT.

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The estimated values of
∆
G˝ads suggested that the adsorption process of the TH3, DMeHT and
DHMeT on the steel surface can be labeled as complex interactions, which includes both physical and
chemical adsorption [59].
The physical adsorption of the hydrazino-s-triazine derivatives occurred between the protonated
tested compounds, and the negatively charged steel surface resulted from the adsorption of the chloride
anions via electrostatic interactions as shown in Figure 11a, whereas the unshared electron pairs of the
nitrogen atoms of the hydrazine group and the triazine ring shared with the empty d-orbital of iron
atoms on the steel surface and enhanced the chemical adsorption (Figure 11b). In addition, electron
donor-acceptor interactions may also arise between the π-electrons of imine (C=N) groups of 1,3,5
triazine rings and the empty d-orbital of iron atoms (Figure 11c). The adsorption˝and stability of the
adsorbed layer on the steel surface may be attributed to the negative value of ∆G ads [59].
Figure 11. Proposed schematic representation of the adsorption of the hydrazino-1,3,5-triazines on
steel in 1.0 M HCl solution: (
3. Experimental Section
3.1. Materials and Methods
a) physical adsorption; (b) chemical adsorption. (c) chemical adsorption.
Cyanuric chloride and hydrazine hydrates (80%) were pruchased from Aldrich (Sigma-Aldrich
Chemie GmbH, 82024 Taufkirchen, Germany). The solvents used were of HPLC reagent grade. Melting
points were determined with a Mel-Temp apparatus and are uncorrected (Sigma-Aldrich Chemie
GmbH). The 1H-NMR and 13C-NMR spectra were recorded on a JEOL 400 MHz spectrometer (JEOL,
Ltd., Tokyo, Japan), and the chemical shift values were reported in
were performed on a Perkin-Elmer 2400 elemental analyzer (PerkinElmer, Inc., 940 Winter Street,
Waltham, MA, USA), and the values found were within 0.3% of the theoretical values. The ultrasonic
δ units (ppm). Elemental analyses
˘
bath was purchased from Selecta (Barcelona, Spain). The purity of the compounds was checked by TLC
on silica gel-protected aluminum sheets (Type 60 GF254, Merck, Massachusetts, MA, USA). Tests were
performed with steel rods of the following composition (wt %): 0.14% C, 0.57% Mn, 0.21% P, 0.15% S, 0.37%
Si, 0.06% V, 0.03% Ni, 0.03% Cr and the remainder Fe. The method of electrode preparation of the working
electrode, the reference and the counter electrode are the same as used previously in our studies [27].
The chemical composition, the method of electrode preparation of the working electrode,
the reference and the counter electrode are the same as used previously in our studies [27].
3.2. Electrochemical Measurements
All electrochemical experiments were conducted through the Solartron 1470E system
(Potentiostat/Galvanostat) (Indiana, IN, USA) with Solartron 1455A as Frequency Response Analyzer
(FRA). Polarization studies were carried out at 1 mV/s scan rate. EIS measurements were executed

Molecules 2016, 21, 714
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within the frequency domain 10 kHz to 0.01 Hz using a sine wave of 10 mV amplitude peak to peak.
EIS measurements were conducted after 1 h immersion in 1 M HCl solution containing different
concentrations of the investigated inhibitors.
3.3. Synthesis of 2,4-Dichloro-6-methoxy-1,3,5-triazine (DCMeT, 2)
The product was prepared using the reported method [30] and obtained from CH2Cl2/hexane
as a white solid in 98% yield; mp 87–88 ˝C (Lit. [30]; mp 86–87 ˝C). 1H-NMR (CDCl3)
OCH3). 13C-NMR (100 MHz, CDCl3) δ 54.8 (OCH3), 168.9, 171.4 (C=N, triazine).
δ 3.99 (s, 3H,
3.4. Synthesis of 2-Chloro-4,6-dimethoxy-1,3,5-triazine (DMeCT, 4)
The product was prepared using the reported method [32] and obtained from CH2Cl2/hexane
as a white solid in 96% yield; mp 73–75 ˝C [Lit. [32] mp 76–78 ˝C). 1H-NMR (CDCl3)
2OCH3). 13C-NMR (100 MHz, CDCl3) δ 54.6 (OCH3), 167.8, 170.2 (triazine moiety).
δ 3.98 (s, 6H,
3.5. General Method for the Synthesis of Hydrazine-1,3,5-triazine Derivatives
Solution of hydrazine hydrate (20 mL, 80%) in acetonitrile (20 mL) was added to a solution of the
chloro derivatives (20 mmol, CC , DCMeT , or DMeCT ) in 50 mL acetonitrile at room temperature.
1
2
4
The reaction mixture was sonicated at 60 ˝C for 1 h. The excess solvent and hydrazine hydrate was
removed under reduced pressure, and excess of diethyl ether was added to give a slightly pink colored
solid which on drying converted to white solid. The solid was collected by filtration, washed with
diethyl ether (2 ˆ 50 mL), and finally dried under vacuum to give a pure product in yield 95%–98%.
2,4-Dihydrazino-6-methoxy-1,3,5-triazine (DHMeT,
3
). The product was obtained as a white solid in
1
yield 95%; mp >240 ˝C. [Lit. [31] 93% yield). IR (KBr, cm´1): 3296, 3199, 1584, 1548, 1497. H-NMR
(D2O-drop TFA) ppm:
Calcd for C4H9N7O (171.09): C, 28.07; H, 5.30; N, 57.28; found: C, 28.21; H, 5.41; N, 57.43.
δ δ 64.1, 162.3, 162.9. Anal.
3.65 (s, 3H, OCH3); 13C-NMR (D2O-drop TFA) ppm:
2-Hydrazino-4,6-dimethoxy-1,3,5-triazine (DMeHT,
5
). The product obtained as a white solid in yield
1
96%; m.p 165 ˝C (dec). IR (KBr, cm´1): 3296, 3199, 1584, 1548, 1497. H-NMR (400 MHz, D2O-TFA)
δ
3.89 (s, 3H) ppm. 13C-NMR (100 MHz, D2O-TFA)
C5H9N5O2 (171.16): C, 35.09; H, 5.30; N, 40.92; found: C, 35.22; H, 5.37; N, 41.02.
δ 65.9, 66.1, 162.5, 163.8 ppm. Anal. Calcd for
˝
2,4,6-Trihydrazino-1,3,5-triazine (TH3, 6). The product obtained as a white solid in yield 95%; mp >240 C.
[Lit. [33] 93%). IR (KBr, cm´1): 3346, 3299, 1580, 1565, 1498. Anal. Calcd for C3H9N9 (171.16): C, 21.05;
H, 5.30; N, 73.65; found: C, 21.31; H, 5.42; N, 73.90.
4. Conclusions
The three hydrazino-s-triazine derivatives TH3 6, DMeHT 5 and DHMeT 3 are easily prepared
from very cheap commercial starting materials and have remarkable protection performance on the
corrosion of steel in acidic chloride solution. The number of hydrazine group play an important
role in the corrosion inhibition efficiency, where the two hydrazine groups increased the electrostatic
interactions between the protonated tested compounds and the negatively charged steel surface that
resulted from the adsorption of the chloride anions, and the presence of the methoxy group made the
compound more reliable for formation of film protection on the surface of steel through the lone pair
of oxygen atoms, while increasing the hydrazine group does not improve the efficiency, especially
at low concentration (25 ppm and 50 ppm). Polarization curves indicated that the examined TH3,
DMeHT and DHMeT were labeled as mixed type corrosion inhibitors. The adsorption of TH3, DMeHT
and DHMeT onto the steel surface occurred through the nitrogen lone-pairs or its heteroaromatic
p-electrons. The protection performance of tested compounds was increased with increasing the
number of the hydrazine units in the ring, Dihydrazino derivatives DHMeT showed the best corrosion
protection performance among the other hydrazino derivatives even at a low concentration of 25 ppm

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(95%) The adsorption of TH3, DMeHT and DHMeT on the steel surface obeys the Langmuir adsorption
isotherm. The calculated values of IE follow the same trend as those obtained from the polarization
results.The adsorptions of TH3, DMeHT and DHMeT on the steel surface can be explained as complex
interactions (both physical and chemical adsorption).
Acknowledgments: The authors thank the Deanship of Scientific Research at King Saud University for funding
this work through the Prolific Research Group Program (PRG-1437-33; Saudi Arabia).
Author Contributions: The work was designed by A. El-Faham, G. A. El-Mahdy, and H. A. Al-Lohedan. The main
part of this work was carried out by A. El-Faham and S. Osman. The corrosion studies and the analysis of data
were carried out by A. El-Faham and G. A. El-Mahdy. All authors read and approved the final manuscript.
Conflicts of Interest: The authors declare no conflict of interest.
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Sample Availability: Samples of the compounds TH3, DmeHT, and DHMeT are available from the authors.
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