REGULAR ARTICLE

Corrosion inhibition, adsorption and thermodynamic propertiesof 2-aminopyridine derivatives on the corrosion of carbon steelin sulfuric acid solution

TARIK ATTARa,b,* , FATIHA NOUALIc, ZAHIRA KIBOUc,d, ABBES BENCHADLIa,

BOULANOUAR MESSAOUDIa,b, ESMA CHOUKCHOU-BRAHAMa and

NOUREDDINE CHOUKCHOU-BRAHAMc

aLaboratory of ToxicoMed, University of Abou Bekr Belkaid, B.P.119, 13000 Tlemcen, AlgeriabHigher School of Applied Sciences, P.O. Box 165 RP, 13000 Tlemcen, AlgeriacLaboratoire de Catalyse et Synthese en Chimie Organique, Faculte des Sciences, Universite de Tlemcen,

B.P. 119, 13000 Tlemcen, AlgeriadFaculte des Sciences et de la Technologie, Universite de Ain Temouchent, B.P. 284,

46000 Ain Temouchent, Algeria

E-mail: att_tarik@yahoo.fr; t.attar@essa-tlemcen.dz

MS received 24 March 2021; revised 23 June 2021; accepted 24 June 2021

Abstract. Corrosion inhibition of carbon steel in sulfuric acid solution was performed by three synthesized

products named 2-(butylamino)-4-phenylnicotinonitrile (BAPN), 2-(propylamino)-4-phenylnicotinonitrile,

and 2-(methylamino)-4-phenylnicotinonitrile using weight-loss method and scanning electron microscopy

(SEM). The temperature impact on the inhibition mechanism of the synthesized inhibitors of the carbon steel

surface was investigated at various temperatures (20–50 �C) where the inhibitive efficiency diminished with

increasing temperatures. The maximum IE of 97.45% was achieved at a temperature of 20 �C, the con-

centration of BAPN inhibitor of 5910-4 M, and H2SO4 acid concentration of 0.5 M. The adsorption of

inhibitors studied onto the carbon steel surface obeys the Langmuir adsorption isotherm. The SEM surface

analysis showed the formation of a protective organic film on the steel surface. The quantum chemical

calculations (DFT) supported the experimental results and showed that the inhibition efficiency also depends

on the structure of the inhibitor.

Keywords. Corrosion inhibition; 2-Aminopyridine derivatives; Carbon steel; Weight loss; DFT; SEM.

1. Introduction

In the chemical industry, carbon steel is the dominant

metal material because of its wide use and various

applications thanks to its low price and exceptional

mechanical and physical properties.1 The wastes and

residues of the metallic component damage in relation

to corrosion are countless. This includes cracks, time

loss and production arrest, structural and mechanical

damage, pollution, economic problems, and also large-

scale ecological damage.2 Hence, these negative

effects can be minimized or eliminated using diverse

techniques to protect the metal surface from aggres-

sive environments. Sulfuric acid is one of the strong

inorganic acid used in various industrial processes,

such as steel manufacturing, acid pickling, acid

descaling, gasoline, ion exchange resins regenerating,

sulfonation agents, cellulose fibers, sugar bleaching,

paper bleaching, pharmaceuticals, fertilizers, automo-

bile batteries, amino acid intermediates, water treat-

ment, coloring agents, oil well acidizing and acid

cleaning. The use of corrosion inhibitors is the most

practical alternative to block the active sites and

enhance the adsorption process, thus decreasing the

dissolution rate and extending the equipment life

span.3 The study of corrosion processes and their

inhibition by organic compounds is a very large field

of research. The corrosion inhibition using organic

*For correspondence

Supplementary Information: The online version contains supplementary material available at https://doi.org/10.1007/s12039-021-01971-w.

J. Chem. Sci. (2021) 133:109 � Indian Academy of Sciences

https://doi.org/10.1007/s12039-021-01971-wSadhana(0123456789().,-volV)FT3](0123456789().,-volV)

compounds is mainly because of the physical or

chemical adsorption resulting from the interaction of

the inhibitor’s polar centers with active sites on the

metal surface.4–6 They act through the adsorption

mechanism on the surface of alloys of these molecules

that form a barrier against corrosive solutions.7,8 On

the other hand, many syntheses of heterocyclic com-

pounds have nitrogen or oxygen; in addition to con-

jugated pi-system have been synthesized by our

research group.9–12 Application of pyridine derivatives

as corrosion inhibitors can be found in literature.

3-imino-4-methyl-2-(pyridin-3-ylhydrazono)pentanen-

itrile, 4-(3,4-dichlorophenyl)-2,6-dimethyl-1,2-dihy-

dropyridine-3,5-dicarbonitrile, 1,4-diamino-5-cyano-

2-(4-methoxyphenyl)-6-oxo-1,6-dihydropyridine-3-

carboxylic acid and ethyl 4-amino-5-cyano-2-(di-

cyanomethylene)-6-phenyl-1,2-dihydropyridine-3-car-

boxylate have been applied as corrosion inhibitors for

carbon steel in 2 M HCl, giving only about 69.5, 74.8,

82.1 and 91.0% inhibition efficiencies respectively at

1910-4 M.13 The corrosion inhibition efficiencies of

2-amino-6-methoxy-4-phenylpyridine-3,5-dicarboni-

trile, 2-amino-6-methoxy-4-(4-methyl-phenyl) pyr-

idine-3,5-dicarbonitrile and 2-amino-6-methoxy-4-(4-

methoxylphenyl) pyridine-3,5-dicarbonitrile have

been reported to inhibit mild steel corrosion in 1 M

HCl to the tune of 88, 95 and 97% efficiency respec-

tively at 1.6910-3 M concentration.14 Also, 6-(2,4-

dihydroxyphenyl)-4-phenyl-2-(phenylamino)nicoti-

nonitrile (DPPN), 6-(2,4-dihydroxyphenyl)-2-((4-hy-

droxyphenyl)amino)-4-phenylnicotinonitrile (DHPN)

and 6-(2,4-dihydroxyphenyl)-2-((4-methoxyphenyl)

amino)-4-phenylnicotinonitrile (DMPN) for mild steel

corrosion in 1 M HCl have been estimated to be 94.02,

95.42 and 97.18%, respectively at 20.20910-5 M

concentration of the inhibitors and 25 �C.15 The

present investigation is an attempt to explore three

novel inhibitors: 2-(butylamino)-4-phenylnicotinoni-

trile, 2-(propylamino)-4-phenylnicotinonitrile and

2-(methylamino)-4-phenylnicotinonitrile. They are

easily synthesizable, non-toxic and biologically

important,16 best suited for the development of non-

toxic inhibitors, and for an enhanced inhibition effi-

ciency at lower concentrations and at higher temper-

atures by introducing more heteroatoms (nitrogen) for

the mitigation of carbon steel corrosion. It was con-

sidered worthwhile to test these inhibitors for studying

the corrosion inhibition performance of carbon steel in

0.5 M H2SO4 solution by weight loss and surface

analysis. In addition, quantum chemical calculations

using density functional theory (DFT) were performed

to estimate theoretically the reactivity parameters of

the inhibitor.

2. Experimental

2.1 Spaceman preparation and weight lossmeasurements

Carbon steel samples used as test materials contain: C:

0.37%, Mn: 0.68%, Cu: 0.16%, Cr: 0.077%, Ni:

0.059%, Si: 0.023%, S: 0.016%, Ti: 0.011%, Co:

0.009% and the balance being Fe. Prior to tests, the

carbon steel material was abraded using a series of

emery paper sheets (from 600 to 1200 grains) to be

finally washed with water and acetone (99%, Sigma-

Aldrich, Germany). The solution of 0.5 M H2SO4 was

prepared by dilution of sulfuric acid (98%, Merck,

Germany) with distilled water. Various concentrations

of inhibitors (1910-6 to 5910-4 M) in 0.5 M H2SO4

solution were used at different temperatures which

were 293, 303, 313 and 323 K. The investigated

samples were washed with distilled water, acetone

then dried and weighed. All measurements were done

in triplicate, and the mean value of the weight loss was

reported and recorded. The corrosion rate ‘CR’ and the

inhibitor efficiency were calculated via the following

equations Eqs. 1 and 2:17,18

CR ¼ w

S� tð1Þ

where w denotes the weight loss (mg), S represents

the sample area (cm-2) and t symbolizes the immer-

sion time (h-1). The corrosion inhibition efficiency

(IE%) and the surface coverage (h) were calculated

from the CR values:

IE (% ) ¼ CR� CRInh

CR� 100 ð2Þ

where CR and CRinh denote the obtained corrosion

rates in the absence and presence of the inhibitor.

2.2 Characterization of carbon steel surface

Scanning electron microscopy (SEM) and TM1000

Hitachi Tabletop Microscope were used to investi-

gate the sample’s surface immersed in sulfuric acid,

and the presence and absence of corrosion inhibitors

for 24 h.

2.3 Computational studies

The effectiveness of inhibitors can be related to their

molecular electronic and spatial molecular structures.

The present work was; therefore, extended to establish

109 Page 2 of 10 J. Chem. Sci. (2021) 133:109

the effectiveness of three novel compounds as corro-

sion inhibitors using the tools of density functional

theory. DFT method at the B3LYP/6-31G* level of

theory was employed to test the inhibitor quantum

chemical calculations using the Gaussian-09 suit of

program. The values of the highest molecular orbitals

(EHOMO) and lowest occupied molecular orbitals

(ELUMO) were calculated. Other parameters, such as

electronegativity (v), global hardness (g), the affinity

of electrons (EA), and the ionization potential (IP)were determined by Koopmans’ theorem.19 The

HOMO energy is related to the ionization potential

(IP = -EHOMO) whereas the LUMO energy is linked

to the electron affinity (EA = -ELUMO).20 The energy

gap (DE) was determined as:21

DE ¼ ELUMO � E HOMO ð3ÞUsing electron affinity (EA) and ionization potential

(IP), the electronegativity (v) and the global hardness

(g) may be calculated as:22

v ¼ 1=2 IPþ EAð Þ ð4Þ

g ¼ 1=2 IP� EAð Þ ð5ÞThe number of transferred electrons (DN) was cal-

culated as:23

DN ¼ vFe � vInhð Þ=2 gFe þ gInhð Þ ð6Þwhere vFe and vInh are the absolute electronegativitiesof iron and the inhibitor, gFe and gInh are the absolute

hardness of iron and the inhibitor, respectively.

The theoretical values (v=7.0 eV mol-1 and g=0 eVmol-1) for iron were obtained from the literature.24

The value of the charges back-donation was calcu-

lated using the following expression:25

DEback�donation ¼ �g=4 ð7ÞThe charges transferred to the molecule, are ener-

getically favored when g[ 0 and DEback-donation\0.

3. Results and Discussion

3.1 Effect of concentration and temperatureon inhibition efficiency

The temperature can change the interactions between

the carbon steel and the sulfuric acid in the absence

and presence of the inhibitors. All the three inhibitors,

that is, BANP, PANP and MPAN are found highly

efficient for the corrosion inhibition of carbon steel.

On varying the concentration of the inhibitors used, a

change in the inhibition efficiency and the surface

coverage was observed as shown in Table 1. An

obvious increase was observed in the surface coverage

and the percentage inhibition with increasing con-

centrations of the inhibitors indicating the inhibitor

adsorption on the metal surface. The inhibition effi-

ciency obtained at optimum concentrations at 293 K

were 97.45, 95.43 and 91.73% for BAPN, PAPN and

MAPN, respectively. The inhibition efficiency

decreases as the temperature increases. This indicates

that the desorption of the adsorbed inhibitor due to the

enhanced solution agitation by higher rates of hydro-

gen gas evolution at elevated temperature is possible

and may cause the ability of the inhibitor to be

adsorbed on the carbon steel surface to reduce.26

BAPN (80.56%) shows a good inhibitor against cor-

rosion compared to other inhibitors. This inhibitory

power is more remarkable in a concentration of

1910-6 M. It is worthy of mentioning that the tests

were repeated three times to ensure reproducibility,

and the obtained results are the mean value (Table 1).

The evaluated inaccuracy did not exceed 5%.

3.2 Effect of immersion timeon inhibition efficiency

The immersion time is another important parameter

which ascertains the inhibitive effect on the metallic

surfaces. In order to study the effect of the immersion

time on the corrosion behavior of carbon steel, the

Table 1. Inhibition efficiency IE(%) and surface coveragefrom weight loss measurement for carbon steel corrosion in0.5 M H2SO4 without and with the addition of differentconcentrations of BAPN, PAPN and MAPN at differenttemperatures.

T (K) C (M) IE(%) h IE(%) h IE(%) hBAPN PAPN MAPN

293 1910-6 80.56 0.80 68.77 0.68 64.36 0.645910-6 87.51 0.87 78.58 0.78 76.74 0.761910-5 93.15 0.93 86.37 0.86 84.97 0.845910-4 97.45 0.97 95.43 0.95 91.73 0.91

303 1910-6 66.76 0.66 52.66 0.52 48.55 0.485910-6 75.38 0.75 63.75 0.63 58.31 0.581910-5 81.67 0.81 72.34 0.72 65.67 0.655910-4 93.64 0.93 85.28 0.85 80.96 0.80

313 1910-6 47.46 0.47 35.02 0.35 27.99 0.275910-6 60.16 0.60 42.95 0.42 35.92 0.351910-5 62.66 0.62 54.23 0.54 54.87 0.545910-4 81.49 0.81 76.09 0.76 73.94 0.73

323 1910-6 21.67 0.21 15.95 0.15 12.97 0.125910-6 27.97 0.27 21.89 0.21 28.59 0.281910-5 34.06 0.34 26.13 0.26 24.54 0.245910-4 47.42 0.47 45.02 0.45 41.17 0.41

J. Chem. Sci. (2021) 133:109 Page 3 of 10 109

inhibition efficiencies of three inhibitors were obtained

after 1, 2, 3, 6 and 24 h of immersion in 0.5 M H2SO4

solution at 303 K temperature as given in Table S1, SI.

From Table S1 (Supplementary Information), the

inhibition efficiency increases with an immersion time

from 1 to 6 h, thereafter it remains almost stable from

6 to 24 h. On the other hand, the IE(%) is higher 97%

for all inhibitors used from 6 h. The BAPN (93.64%)

shows a good inhibitor since its inhibitory ability

reached a maximum value from 3 hours immersion

compared to other inhibitors PAPN (85.28%) and

MAPN (80.96%). This behavior could be attributed to

the adsorptive layer of inhibitors that rests upon the

immersion time.27 The inhibitive film on the steel

surface firstly reaches a more compact and uniform

condition during a prolonging immersion time (3–6 h),

while the adsorptive film is in a saturated state within

6–24 h.

3.3 Activation parameters of the corrosionprocess

The corrosion rates evaluated at different temperatures

in the absence and presence of inhibitors were used to

calculate the activation energy (Ea), activation

enthalpy (DHa), and activation entropy (DSact) of themetal dissolution.

The activation energy values were calculated using

the Arrhenius equation Eq. 8:28

CR ¼ k exp �Ea=RT

� �ð8Þ

where CR is the corrosion rate, k is a constant, R is the

gas constant (R = 8.314 J�mol-1�K-1) and T is the

temperature, K.

The values of Ea (Table S2, Supplementary Infor-

mation)) for carbon steel in sulfuric acid without and

with different concentrations of inhibitors were

obtained from the slope of the ln(CR) plot versus 1/T

(Figure S1, Supplementary Information). The activa-

tion enthalpy values DHa and activation entropy DSacan be calculated by the slope (-DHa/R) and intercept

[(ln(R/Nh)?(DSa/R)] of the above plot ln(CR/T) vs. 1/T (Figure S2, Supplementary Information), using the

following transition state equation (9).29

ln CR=Tð Þ ¼ ln R=Nhð Þ þ DSa=Rð Þ½ � � DHa=RTð Þð9Þ

where N is Avogadro number, h is Plank’s constant.

The data (Table S2, SI) show that the activation

energies for the carbon steel corrosion in 0.5 M H2SO4

in the presence of different inhibitors and their

concentrations are higher than that of free acid. The

activation energy values indicate that they are more

important than the activation enthalpy values. This

result shows that the corrosion process must have

involved a gaseous reaction. The increase in DHa with

an increase in the concentration of the inhibitor for

carbon steel corrosion reveals that the decrease in

carbon steel corrosion rate is mainly controlled by

kinetic parameters of activation. The DHa positive

values in the absence and presence of the inhibitor

reflect the endothermic nature of a metal dissolution

process, suggesting the slow dissolution of carbon

steel.30

The higher values of free Gibbs energy (DGa) of the

process in the inhibitors presence when compared to

that in its absence is attributed to its physisorption,

while the opposite one is the case with chemisorptions.

The DGa[ 0 means a non-spontaneous corrosion

reaction which increases with increasing the inhibitor

concentration.31 With the concentration increase, the

free energy of activation increases, which is ascribed

to the formation of an unstable activated complex in

the rate-determining transition state. The entropy of

activation values are less negative for inhibited solu-

tions than that for the uninhibited solutions. This

suggests that an increase in randomness occurred

while moving from reactants to the activated complex.

3.4 Adsorption isotherms

Information on the interaction between the carbon

steel surface and the inhibitor compound can be pro-

vided by the adsorption isotherm. The adsorption of

inhibitor molecules at the metal solution interface

reduces the corrosion rate which is considered as a

substitution adsorption process where an organic

compound from the aqueous media moves the water

molecules associated with the surface (H2Oads).

OrgSol þ nH2Oads $ Orgads þ nH2O

where ‘n’ is the number of water molecules replaced

by the adsorption of one inhibitor molecule.

The inhibiting strength of the three investigated

organic compounds on the carbon steel corrosion in

0.5 M H2SO4 solution is based on their adsorption onto

the steel surface. The adsorption depends on the

chemical structure of the inhibitor and the chemical

composition of the steel, the type of the aggressive

acid, the pH value, the temperature and the exposure

time.

The isotherms of Temkin, Langmuir, Freundlich

and Frumkin were tested for fitting data and the best

109 Page 4 of 10 J. Chem. Sci. (2021) 133:109

results were found for Langmuir isotherm (Figure S3,

Supplementary Information), which can be expressed

in the following way:32

C=h ¼ 1=Kads þ C ð10Þwhere C denotes the concentration of inhibitors in

mol.L-1, h symbolizes surface coverage and

Kads represents the adsorption equilibrium constant.

The linear regression coefficient (R2) is almost

equal to 1, indicating that the adsorbed molecules

occupy only one site. The Kads value as obtained from

the intercept of the isotherm is given in Table 2. The

free energy of adsorption DGads can be calculated

from the following equation Eq. 11:33

DGads ¼ �RT ln 55:5 Kadsð Þ ð11Þwhere R is the universal gas constant (J mol-1 K-1), T

is the absolute temperature (K) and the constant value

of 55.5 is the concentration of water in solution (mol

L-1).

The adsorption enthalpy (DHads) can be calculated

using Van’t Hoff equation Eq. 12:34

lnðKadsÞ ¼ �ðDHads=RTÞ þ constant ð12ÞFigure 1 shows that there is a linear relationship

between ln(Kads) and 1/T, thus the value of DHads is

calculated according to Equation (5) and listed in

Table 2. The following equation was employed to

calculate the adsorption entropy (DSads):35

DGads ¼ DHads � TDSads ð13ÞThe obtained values for DSads are shown in Table 2.The adsorption equilibrium constants for all inhi-

bitors are positive, showing the feasibility of the

adsorption of the inhibitors to the carbon steel surface.

This result confirms the trend obtained with the inhi-

bitor which has better inhibition efficiency:36 The

adsorption equilibrium constant decreases with the

temperature rise.37 This indicates that at a higher

temperature, the adsorbed inhibitor tends to desorb

back from the metal surface.38 The negative value of

the free energy adsorption revealed the spontaneity of

its process.39 The thermodynamic parameters for the

inhibitors adsorption can furnish precious information

about the mechanism of corrosion inhibition. An

exothermic adsorption process DHads\0 may imply

either chemisorption or physisorption or a mixture of

both processes. The endothermic adsorption process

DHads[0 is assigned unequivocally to chemisorp-

tion.33 Based on the results of this study, the calculated

free energy and enthalpy of the adsorption values for

Table 2 The values of Kads, DHads, DSads and DGads forcarbon steel in the absence and presence of an optimum

concentration of inhibitors in 0.5 M H2SO4 at differentstudied temperatures.

ProductsT(K) R2

Kads

(104 L/mol) DHads (kJ/mol)DSads

(J/mol K) DGads (kJ/mol)

BAPN 293 1 233.828 -67.35 -74.58 -45.50303 0.999 90.542 -74.88 -44.67313 0.999 49.185 -72.85 -44.55323 0.999 16.437 -75.30 -43.03

PAPN 293 1 118.166 -63.86 -68.34 -43.84303 0.999 48.661 -68.52 -43.10313 0.999 28.693 -66.18 -43.15323 0.999 9.354 -69.18 -41.52

MAPN 293 1 96.846 -57.58 -49.45 -43.36303 0.999 42.023 -49.90 -42.73313 0.999 21.114 -49.52 -42.35323 0.999 10.641 -49.50 -41.86

3.1 3.2 3.3 3.411

12

13

14

15

BAPN PAPN MAPN

Ln (K

ads) (

L/m

ol)

1000/T (K-1)

Figure 1. ln(Kads) versus 1/T for adsorption BAPN,PAPN and MAPN on carbon steel surface

J. Chem. Sci. (2021) 133:109 Page 5 of 10 109

the three studied inhibitors show that the adsorption

mechanism is not completely chemical or physical and

that a combination of physisorption and chemisorption

exists between the inhibitor and the metal surface. The

negative values obtained for changes in the adsorption

entropy confirm that there is an association of the

inhibitor’s molecules.

3.5 Scanning electron microscope

In this examination, we used a scanning electron

microscope (SEM) in order to characterize the surface

state of the steel before and after immersion in sulfuric

acid. Figure 2 shows the SEM images of the carbon

steel samples after 24 h of immersion in 0.5 M H2SO4

solution without and with the addition of 5910-4 M of

the inhibitors produced (BAPN, PAPN and MAPN) at

a temperature of 30 �C. We noticed that the surface of

the carbon steel after 24 h of immersion in the cor-

rosive solution alone (Figure 2.b) was aggressively

damaged. This clearly shows that the steel has

undergone a strong dissolution in the absence of the

inhibitor, unlike the steel surface (Figure 2.a) which

appears smooth with few lines resulting from polish-

ing. It is very clear from Figure 2 (c, d and e) that the

addition of the three inhibitors, studied in sulfuric acid,

stops the dissolution and consequently the corrosion of

carbon steel. This difference in appearance is attrib-

uted to the formation of a protective adherent layer on

the surface of the steel in the presence of these

inhibitors.40,41 This protects the steel surface against

the aggressions of the corrosive environment. These

results are in agreement with the inhibition efficiency

obtained from the weight loss measurement.

3.6 Theoretical calculations

The electronic properties of the inhibitors were studied

by density function theory (DFT)- B3LYP/6-31G*.

Optimized structure, HOMO and LUMO were inves-

tigated for three molecules and displayed in Figure 3.

The investigated parameters energy of the frontier

molecular electrons, the global hardness, the gap

energy, the back-donation and the number of trans-

ferred electrons were displayed in Table 3. The high

values of HOMO energy tend to donate electrons to an

appropriate acceptor molecule of low empty molecular

orbital energy. The inhibitor does not only donate

electrons to the unoccupied orbital of the metal ion but

can also receive electrons from the metal, forming a

feedback bond, considered as an excellent inhibitor.

From Table 3 that by increasing the length of the alkyl

Figure 2. SEM images of carbon steel specimens corroded in 0.5 M sulfuric acid solution: before immersion (a), theabsence (b) and presence of BAPN (c) PAPN (d) and MAPN (e) at their optimum concentration.

109 Page 6 of 10 J. Chem. Sci. (2021) 133:109

chain (methyl, propyl and butyl), the EHOMO becomes

larger and larger, indicating the increased capability of

the electron donor of the molecule. By increasing the

length of the alkyl chain, ELUMO also has an increasing

trend, which shows that the capability of the electron

acceptor will weaken.42 The EHOMO values of the

molecules studied increase in the following order:

BAPN[PAPN[MAPN, which means that BAPN has

the highest inhibition efficiency and the best inhibition

performance, which agrees well with the experimental

measurement.43

In our case, the lower values of the global hardness (g)are pronounced to be a better corrosion inhibitor.44 The

gap energy levels of the molecules were another

important factor that should be considered. The order of

DEgap values MAPN[PAPN[BAPN is in good

agreement with that of experimental inhibition effi-

ciency MAPN\PAPN\BAPN. In the literature, the

lower the DEgap values are, the higher the inhibition

efficiency will be.45,46

If DN\3.6, the inhibition efficiency increases by

increasing the electron-donating ability of these inhi-

bitors to donate electrons to the metal surface.47 The

results indicate that DN values correlate strongly with

experimental inhibition efficiencies. This is in good

agreement with the experimental observations. In a

simple model of charge transfer for donation and back

donation of charges, an electronic back donation pro-

cess can occur as a result of the interaction between

the inhibiting molecule and the metal surface. The

energy of the back-donation involves that when (g[0)

and DEBack-donation\0, the charge transfer to a

HOMO Molecular structure LUMO

BAPN

PAPN

MAPN

Figure 3. Optimized structure, HOMO and LUMO orbitals for BAPN, PAPN and MAPN molecules using DFT approach

Table 3. Calculated quantum chemical parameters of the studied inhibitors with carbon steelin 0.5 M H2SO4, using the DFT method and weightloss.

SubstrateHOMO(eV) LUMO (eV)

g(eV) DEgap (eV)

DEback-donation

(eV)DN(eV)

IE(%)

BAPN -5.88 -1.51 2.17 4.37 -0.54 0.76 97.45PAPN -5.90 -1.52 2.19 4.38 -0.55 0.75 95.43MAPN -5.95 -1.54 2.23 4.41 -0.56 0.73 91.73

J. Chem. Sci. (2021) 133:109 Page 7 of 10 109

molecule, followed by a back-donation from the

molecule, is energetically favored.48

3.7 Mechanism of inhibition

The inhibition effect of 2-Aminopyridine derivatives

towards the corrosion of carbon steel in 0.5 M H2SO4

solution may be attributed to the adsorption of these

compounds at the metal-solution interface. From the

obtained experimental and theoretical results, we

suggest the adsorption mechanism presented in Fig-

ure 4. As all three inhibitors BAPN, PAPN, and

MAPN possess nitrogen atoms, they can be protonated

easily. During the inhibition process, the inhibitors get

protonated in solution and become positively charged

as well as the metal surface in the acid media. Sulfate

ions are specifically adsorbed onto the metal and cre-

ate an excess of negative charge on its surface.49 This

favours the adsorption of protonated BAPN on the

surface through electrostatic attraction and hence

reduces the dissolution of iron (physical adsorption).

In addition, the inhibitors were chemically adsorbed

onto the carbon steel surface by donor/acceptor inter-

action amongst free electron pairs of heteroatoms and

the vacant d-orbital of iron atoms of the surface.

Moreover, this type of electron transfer causes

excessive accumulation of negative charge on the

electron-rich metallic surface which renders it to

transfer its electrons to the vacant p* (anti-bonding)

molecular orbitals of the inhibitors through retro-do-

nation.50 In summary, the adsorption of 2-Aminopy-

ridine derivatives on the carbon steel surface is

comprehensive and includes both physisorption and

chemisorption.

4. Conclusions

The three organic compounds BAPN, PAPN and

MAPN showed a good inhibition efficiency against

carbon steel corrosion in an acidic sulfuric solution.

The inhibition efficiency was found to increase with

the rise of the concentration of the inhibitor and lower

with the temperature rise. The BAPN is the highest

one in inhibiting the steel corrosion which returns to

the latter that possesses a higher electronic cloud and

which enhances the adsorption propensity on the steel

surface. The Langmuir isotherm was found to be the

best isotherm describing the adsorption behaviors on

the steel interface. The results of the adsorption iso-

therm revealed that the three organic compounds

behaved as a mixed type of adsorption. SEM pictures

exposed that the inhibitors were adsorbed on the metal

surface and formed a film that protected the carbon

steel surface. The efficiency of the inhibitors obtained

from the weight loss method and density functional

theory are in good agreement.

Acknowledgements

The authors wish to thank Directorate-General for Scientific

Research and Technological Development (DGRSDT) and

the University of Tlemcen for their financial support.

References

1. Abeng F E, Ikpi M E, Anadebe V C and Emori W 2020Metolazone compound as corrosion inhibitor for api 5lx–52 steel in hydrochloric acid solution Bull. Chem.Soc. Ethiop. 34 407

N

N

NH

Fe2+ Fe2+Fe2+Fe2+ Fe2+

SO42-SO4

2-SO42-

e-e-e- e-e-

SO42-

Fe FeSO4

2-SO42-

ChemisorptionPhysisorptionReterodonation

Figure 4. The suggested mechanism of 2-(butylamino)-4-phenylnicotinonitrile for carbon steel in sulfuric acid solution

109 Page 8 of 10 J. Chem. Sci. (2021) 133:109

2. Nwanonenyi S C, Obasi H C, Chukwujike I C,Chidiebere M A and Oguzie E E 2019 Inhibition ofcarbon steel corrosion in 1 M H2SO4 using soy polymerand polyvinylpyrrolidone Chem. Afr. 2 277

3. Chakravarthy M P, Mohana K N and Pradeep Kumar CB 2014 Corrosion inhibition effect and adsorptionbehaviour of nicotinamide derivatives on mild steel inhydrochloric acid solution Int. J. Ind. Chem. 5 1

4. Popova A, Christov M and Vasilev A 2015 Mono- anddicationic benzothiazolic quaternary ammonium bro-mides as mild steel corrosion inhibitors. Part III:influence of the temperature on the inhibition processCorros. Sci. 94 70

5. Ostapenko G I, Gloukhov P A and Bunev A S 2014Document investigation of 2-cyclohexenylcycl- ohex-anone as steel corrosion inhibitor and surfactant inhydrochloric acid Corros. Sci. 82 265

6. Ozcan M, Toffoli D, Ustunel H and Dehri T 2014Insights into surface-adsorbat interactions in corrosioninhibition processes at the molecular level Corros. Sci.80 482

7. Al-Amiery A, Kassim F, Kadhum A and Mohamad A2016 Synthesis and characterization of a novel eco-friendly corrosion inhibition for mild steel in 1 Mhydrochloric acid Sci. Rep. 6 1

8. Al-Amiery A A, Kadhum A A, Alobaidy A A and AbuBakar M 2014 Novel corrosion inhibitor for mild steelin HCl Materials 7 662

9. Mehiaoui N, Kibou Z, Gallavardin T, Leleu S, FranckX, Mendes R F, et al. 2021 Novel bis-(3-cyano-2-pyridones) derivatives: synthesis and fluorescent prop-erties Res. Chem. Intermed. 2021 1

10. Mehiaoui N, Kibou Z, Berrichi A and Choukchou-Braham N 2020 Novel synthesis of 3-cyano-2-pyridonesderivatives catalyzed by Au–Co/TiO2 Res. Chem.Intermed. 46 5263

11. Kibou Z, Cheikh N, Choukchou-Braham N andVillemin D 2016 A rapid synthesis of highly function-alized 2-pyridones and 2- aminopyridines via a micro-wave-assisted multicomponent reaction J. Mater.Environ. Sci. 7 3061

12. Kibou Z, Cheikh N, Choukchou-Braham N, Villemin Dand Lohier J-F 2016 Easy Solventless Synthesis of newmono and bis amino5Hchromeno[3,4-c] pyridin-5-onederivatives from cyanoenaminocoumarin Tetrahedron72 1653

13. Abd El-Maksoud S A and Fouda A S 2005 Somepyridine derivatives as corrosion inhibitors for carbonsteel in acidic medium Mater. Chem. Phys. 93 84

14. Ansari K R, Quraishi M A and Singh A 2015 Corrosioninhibition of mild steel in hydrochloric acid by somepyridine derivatives: an experimental and puantumchemical study J. Ind. Eng. Chem. 25 89

15. Verma C, Olasunkanmi L O, Quadri T W, Sherif E andEbenso E 2018 Gravimetric, electrochemical, surfacemorphology, DFT, and Monte Carlo simulation studieson three N-substituted 2-aminopyridine derivatives ascorrosion inhibitors of mild steel in acidic medium J.Phys. Chem. C 122 11870

16. Nouali F, Kibou Z, Boukoussa B, Choukchou-BrahamN, Bengueddach A, Villemin D and Hamacha R 2020Efficient multicomponent synthesis of 2-aminopyridines

catalysed by basic mesoporous materials Res. Chem.Intermed. 46 3179

17. Attar T, Benchadli A and Choukchou-Braham E 2019Corrosion inhibition of carbon steel in perchloric acidby potassium iodide Int. J. Adv. Chem. 7 35

18. Attar T, Larabi L and Harek Y 2014 Inhibition effect ofpotassium iodide on the corrosion of carbon steel (XC38) in acidic medium Int. J. Adv. Chem. 2 139

19. Danaee I, Ramesh K S, Rashv Aveic M and Vijayan M2020 Electrochemical and quantum chemical studies oncorrosion inhibition performance of 2,2’-(2-Hydrox-yethylimino)bis[N-(alphaalpha-dimethylphenethyl)-N-methylacetamide] on mild steel corrosion in 1M HClsolution J. Mater. Res. 23 1

20. Pearson R 1988 Absolute electronegativity and hard-ness: application to inorganic chemistry Inorg. Chem.27 734

21. Benhadria N, Messaoudi B and Attar T 2020 The studyof the correlation between the detection limit and theenergy stability of two antimony complexes by meansof conceptual DFT M. J. Chem. 22 111

22. Attar T, Messaoudi B and Benhadria N 2020 DFTtheoretical study of some thiosemicarbazide derivativeswith copper Chem. Chem. Technol. 14 20

23. Musa A Y, Kadhum A A, Mohamed A B and Takriff MS 2011 Molecular dynamics and quantum chemicalcalculation studies on 4,4-dimethyl-3-thiosemicarbazideas corrosion inhibitor in 2.5 M H2SO4 Mater. Chem.Phys. 129 660

24. Alaoui K, El Kacimi Y and Galai M 2020 Newtriazepine carboxylate derivatives: correlation betweencorrosion inhibition property and chemical structure Int.J. Ind. Chem. 11 23

25. Guo L, Safi Z S, Kaya S and Shi W 2018 Anticorrosiveeffects of some thiophene derivatives against the corro-sion of iron: a computational study Front. Chem. 6 1

26. Ait Addi B 2020 Tin corrosion inhibition by molybdateions in 0.2 M maleic acid solution: electrochemical andsurface analytical study Mediterr. J. Chem. 10 465

27. Li X H, Deng S D and Fu H 2012 Inhibition of thecorrosion of steel in HCl, H2SO4 solutions by bambooleaf extract Corros. Sci. 62 163

28. Khadom A A and Abd A N 2018 Xanthium strumariumleaves extracts as a friendly corrosion inhibitor of lowcarbon steel in hydrochloric acid: kinetics and mathe-matical studies S. Afr. J. Chem. Eng. 25 13

29. Mobin M, Zehra S and Aslam R 2016 L-Phenylalaninemethyl ester hydrochloride as a green corrosioninhibitor for mild steel in hydrochloric acid solutionand the effect of surfactant additive RSC Adv. 6 5890

30. Abdel-Gaber A M, Rahal H T and Beqai F T 2020Eucalyptus leaf extract as a ecofriendly corrosioninhibitor for mild steel in sulfuric and phosphoric acidsolutions Int. J. Ind. Chem. 11 1

31. Benchadli A, Attar T and Choukchou-Braham E 2019Inhibition of carbon steel corrosion in perchloric acidsolution by povidone iodine Phys. Chem. Res. 7 837

32. Dagdag O, Safi Z, Hsissou R, Erramli H, ElBouchti M,Wazzan N, et al. 2019 Epoxy pre-polymers as new andeffective materials for corrosion inhibition of carbonsteel in acidic medium: computational and experimentalstudies Sci. Rep. 9 1

J. Chem. Sci. (2021) 133:109 Page 9 of 10 109

33. Attar T, Larabi L and Harek Y 2014 The inhibitioneffect of potassium iodide on the corrosion of pure ironin sulfuric acid Adv. Chem. 2014 1

34. Grudic V, Boskovic I, Radonjic D, Jacimovic Z andKnezevic B 2019 The electrochemical behavior of Alalloys in NaCl solution in the presence of pyrazolederivative IJCCE 38 127

35. Akinbulumo O A, Odejobi O J and Odekanle E L 2020Thermodynamics and adsorption study of the corrosioninhibition of mild steel by Euphorbia heterophyllaL. extract in 1.5 M HCl Res. Mater. 5 100074

36. Dohare P, Quraishi M A and Obot I B 2018 A combinedelectrochemical and theoretical study of pyridine-basedSchiff bases as novel corrosion inhibitors for mild steelin hydrochloric acid medium J. Chem. Sci. 130 8

37. Attar T, Benchadli A, Mellal T, Dali Youcef B andChoukchou-Braham E 2021 Use of experimentaldesigns to evaluate the influence of methyl green dyeas a corrosion inhibitor for carbon steel in perchloricacid M. J. Chem. 23 60

38. Attar T, Benchadli A, Messaoudi B, Benhadria N andChoukchou-Braham E 2020 Experimental and theoret-ical studies of eosin Y dye as corrosion inhibitors forcarbon steel in perchloric acid solution Bull. Chem.React. Eng. 15 454

39. Negm A M, Fouda A S, Abdelwahab S M, Teraze A Yand Shalof R 2019 Cooling system pipeline corrosionbehavior after reusing of reverse osmosis reject plantwater as feed water source Egypt. J. Chem. 62 257

40. Gao H, Xie N, Zhang J, Sun J, Zhang J and Jin Z 2020Synthesis and application of carboxyethylthiosuccinicacid by thiolene click reaction: as a novel rust removerwith corrosion inhibition properties J. Chem. Sci. 13256

41. Al-Amiery A, Taghried A S, Alazawi K F, Shaker L M,Kadhum A A and Takriff M S 2020 Quantum chemicalelucidation on corrosion inhibition efficiency of Schiffbase: DFT investigations supported by weight loss andSEM techniques Int. J. Low-Carbon Technol. 15 202

42. Guocai T and Weizhong Z (2020) Theoretical study ofthe structure and property of ionic liquids as corrosion

inhibitor, density functional theory calculations, SergioRicardo De Lazaro, Luis Henrique Da Silveira Lacerdaand Renan Augusto Pontes Ribeiro IntechOpen,doi:https://doi.org/10.5772/intechopen.92768

43. Mashuga M E, Olasunkanmi L, Adekunle A S, Yesu-dass S, Kabanda M M and Ebenso E E 2015 Adsorption,thermodynamic and quantum chemical studies of1-hexyl-3-methyl-imidazolium based ionic liquids ascorrosion inhibitors for mild steel in HCl Mater. 8 3607

44. Elshafie A M, Gad E M and Abdel Halim A 2018Theoretical approach for the performance of 4-mer-capto-1-alkylpyridin-1-ium bromide as corrosion inhi-bitors using DFT Egypt. J. Pet. 27 695

45. Abd El-Lateef H M 2015 Experimental and computa-tional investigation on the corrosion inhibition charac-teristics of mild steel by some novel synthesized iminesin hydrochloric acid solutions Corros. Sci. 92 104

46. Akbas E, Celik S, Ergan E and Levent A 2019Synthesis, characterization, quantum chemical studiesand electrochemical performance of new 4,7-dihydrote-trazolo[1,5-a]pyrimidine derivatives J. Chem. Sci. 13130

47. Arrousse N, Salim R, Al Houari G, El Hajjaji F, ZarroukA, Rais Z, et al. 2020 Experimental and theoreticalinsights on the adsorption and inhibition mechanism of(2E)-2-(acetylamino)-3-(4-nitrophenyl) prop-2-enoicacid and 4-nitrobenzaldehyde on mild steel corrosionJ. Chem. Sci. 132 112

48. Ansari K R and Quraishi M A 2015 Experimental andcomputational studies of naphthyridine derivatives ascorrosion inhibitor for N80 steel in 15% hydrochloricacid Phys. E 69 322

49. Zhou Y, Guo L, Zhang S, Kaya S, Luo X and Xiang B2017 Corrosion control of mild steel in 0.1 M H2SO4 -solution by benzimidazole and its derivatives: anexperimental and theoretical study RSC Adv. 7 23961

50. Chandrabhan V, Quraishi M A and Neeraj Kumar G2018 2-(4-{[4-Methyl-6-(1-methyl-1H-1,3-benzodiazol-2-yl)-2-propyl-1H-1,3-benzodiazol-1-yl] methyl} phe-nyl) benzoic acid as green corrosion inhibitor for mildsteel in 1M hydrochloric acid Ain. Shams Eng. J. 9 1225

109 Page 10 of 10 J. Chem. Sci. (2021) 133:109