Synthesis and evaluation of new long alkyl side chain acetamide, isoxazolidine and isoxazoline derivatives as corrosion inhibitors

2-(Alkylsulfanyl)-N-(pyridin-2-yl) acetamide derivatives were synthesized via amidation reaction of acyl chlorides bearing S atom in the long chain with 2-aminopyridine. Derivatives of isoxazolidine and isoxazoline were synthesized through 1,3-dipolar cycloaddition reactions with three different long chain alkenes containing O or S as hetero atoms and C,N-diphenyl nitrone or benzonitrile-N-oxide, respectively. Synthesized compounds were characterized with their FT-IR, ¹H NMR spectra and then their physical properties and corrosion prevention efficiencies were investigated. All compounds were tested with steel coupons in acidic medium by gravimetric method, and also some of them were tested with steel stripe in paraffin based mineral oil medium via standard method. Acidic test was done with a medium concentration of 2 M HCl for 20 h at room temperature. Mineral oil was used and the test in this medium was done at 60 °C constant temperature but varying time from 42 to 63 h. The best inhibition was generally obtained at 50 ppm inhibitor concentration in the acidic medium. All tested inhibitors except two of them in oil medium also showed promising inhibition efficiencies.     

Theoretical elucidation on corrosion inhibition efficiency of 11-cyano undecanoic acid phenylamide derivatives: DFT study

The inhibition effects of 11-cyano undecanoic acid phenylamide derivatives against corrosion are studied by means of density functional approach B3LYP/6-311G(d,p) calculations. The efficiencies of corrosion inhibitors and the molecular structure relate to some parameters, such as E _HOMO, E _LUMO, the energy gap between E _LUMO and E _HOMO (ΔE = E _LUMO ? E _HOMO), dipole moments (μ), and other parameters, including electronegativity (χ), global hardness (η), softness (ρ), chemical potential (μ_c) and the fraction of electrons transferred from the inhibitor molecule to metallic atom (ΔN). The computed quantum chemical properties indicate good correlation with experimental corrosion inhibition efficiencies of 11-cyano undecanoic acid phenylamide derivatives. A good correlation between the substituent type and inhibition efficiency of inhibitors through the application of Hammett relationship is obtained. The linear correlation is also found between the Hammett parameters and calculated molecular orbital energies.     

Effect of alkyl chain length on inhibition performance of imidazoline derivatives investigated by molecular dynamics simulation

In this article, the inhibition efficiency of imidazoline derivatives with different alkyl chain was investigated from aspect of diffusion using molecular dynamics method. The diffusion coefficient of three corrosive ions in the inhibitor membrane was proposed to evaluate the inhibition efficiency, and three related parameters, fractional free volume of membrane, interaction energy between membrane and particle, mobility of inhibitor membrane, were also discussed to illuminate the diffusion performance of corrosive particles in inhibitor membrane at length. These researches provide one more reasonable theoretical method to evaluate the inhibition efficiency, and may have important significance for the filtration of inhibitor.     

Molecular dynamics and density functional theory study on relationship between structure of imidazoline derivatives and inhibition performance

The inhibition performance of two imidazoline derivatives, 3-ethylamino-2-undecyl imidazoline (EUI) and chloride-3-ethylamino-3-(2,3-two hydroxyl) propyl-2-undecyl imidazoline sodium phosphate(CEPIP), for Q235 steel in CO₂ saturated solution at 298 K have been tested by weight loss experiment and electrochemical techniques. The adsorption behavior of the two inhibitors on Fe surface has been studied using molecular dynamics (MD) method and density functional theory. The results indicated that the two imidazoline derivatives could both adsorb on the Fe surface firmly through the imidazoline ring and heteroatoms, the two inhibitors both have excellent corrosion inhibition performance.     

Theoretical study of corrosion inhibition of amides and thiosemicarbazones

An examination of quantum chemical and corrosion inhibition studies were carried out to investigate whether any clear links exist between the results of quantum chemical calculations and the experimental efficiencies of urea (U), thiourea (TU), acetamide (A), thioacetamide (TA), semicarbazide (SC), thiosemicarbazide (TSC), methoxybenzaldehydethiosemicarbazone (MBTSC), 2-acetylpyridine-(4phenyl) thiosemicarbazone (2AP4PTSC), 2-acetylpyridine-(4-methyl) thiosemicarbazone (2AP4MTSC), benzointhiosemicarbazone (BZOTSC) and benzilthiosemicarbazone (BZITSC) being corrosion inhibitors. The quantum chemical calculations have been performed by using DFT, ab-initio molecular orbital and semi-empirical methods for some amides and thiosemicarbozone derivatives being corrosion inhibitors. The highest occupied molecular orbital energy (E_HOMO), lowest unoccupied molecular orbital energy (E_LUMO), the energy gap between E_HOMO and E_LUMO (ΔE_HOMO-LUMO), dipole moments (μ), charges on the C, O, N, S atoms, the total energies of the molecules and the polarizabilities 〈α〉, the coefficients of the development of the MO over the atomic orbital (AO) corresponding to the between atoms which a new bond is established have been calculated.The results of quantum chemical calculations and experimental efficiencies of inhibitors were subjected to correlation analysis. We have reached the conclusion that the synthesis of better corrosion inhibitors can be achieved by controlling all electronic properties and parameters of a selected group of molecules.     

Influence of the alkyl chain length of 2 amino 5 alkyl 1,3,4 thiadiazole compounds on the corrosion inhibition of steel immersed in sulfuric acid solutions

The corrosion inhibition efficiency of 2 amino 5 alkyl 1,3,4 thiadiazole compounds with different alkyl chain lengths, namely: 2 ethyl, 3 n propyl, 5 n penthyl, 7 hepthyl, 11 undecyl and 13 tridecyl, was evaluated in the system steel/1 M H₂SO₄. These compounds were synthesized, characterized by FT-IR and NMR spectroscopy analysis and evaluated using electrochemical impedance spectroscopy and SEM analysis. The results showed that the inhibition mechanism involves blockage of the steel surface by the inhibitor molecules by a Langmuir-type adsorption process and that the alkyl chain length plays an important role in the inhibition efficiency of the synthesized inhibitors.     

Theoretical investigation of corrosion inhibition effect of imidazole and its derivatives on mild steel using cluster model

Interaction energies of imidazole and its seven derivatives on the surface of mild steel were calculated via a cluster model by using quantum chemical calculations at density functional theory level. The mild steel surface and its adsorption sites were considered as some clusters taken from two-layered (0 0 1) planes and the quantum chemical calculations which were carried out consist of adsorption of the inhibitor molecules on the surface of these clusters. It is shown that 90% of inhibition variations of the imidazole derivatives are described by considering perpendicular interaction of the inhibitors by iron atom in the mild steel unit cell.     

Theoretical evaluation of the inhibition properties of two thiophene derivatives on corrosion of carbon steel in acidic media

The density functional theory at the B3LYP/6‐311G++(d,p) basis set level calculations were performed on two thiophene derivatives used as corrosion inhibitors, namely 2‐methylthiophene and 2‐(aminomethyl)thiophene, to investigate the correlation between its molecular structure and the corresponding inhibition efficiency (IE%). Quantum chemical parameters such as the highest occupied molecular orbital energy (E_HOMO), the lowest unoccupied molecular orbital energy (E_LUMO), energy gap (ΔE), dipole moment (µ), electronegativity (χ), hardness (η), and the fraction of electrons transferred from the inhibitor molecule to the metal surface (ΔN), have been calculated. A good correlation between the theoretical data and the experimental results was found.     

Theoretical considerations on the supposed linear relationship between concrete resistivity and corrosion rate of steel reinforcement

Traditionally, the assessment of service life of steel reinforced concrete structures has been focused on the prediction of the time required to achieve a transition from passive to active corrosion rather than to accurately estimate the subsequent corrosion rates. However, the propagation period, i.e. the time during which the reinforcing steel is actively corroding, may add significantly to the service life. Consequently, ignoring the propagation period may prove to be a conservative approach. On the other hand the prediction of the corrosion rate may result in a very complex task in view of the electrochemical nature of corrosion and the numerous parameters involved. In order to account for the various influences an essentially empirical model has been introduced in which the electrolytic resistivity of the concrete environment serves as the major parameter. This model will be discussed for carbonation‐induced corrosion based on the commonly accepted theory of aqueous corrosion. An alternative model for microcell corrosion is proposed which is based on the commonly accepted view that anodic and cathodic sites are microscopic and their locations change randomly with time. In line with this view electrolytic resistivity can be incorporated and thus may play a significant role in the kinetics of the corrosion process. For a wide range of corrosion current densities the relationship between corrosion current density, log(i_corr), and concrete resistance, log(R_con), can then be approximated by an almost ideal linear relationship. Assuming a fixed geometrical arrangement of anodic and cathodic sites on the steel surface, this linear relationship is also valid for concrete resistivity, ρ_con. However, from the theoretical treatment of the electrochemical processes underlying reinforcement corrosion it becomes evident that a linear relationship between corrosion current density and concrete resistivity does not necessarily imply that concrete resistance is dominating the overall corrosion cell resistance. In most cases a significant portion of the driving voltage of the corrosion cell will be consumed by the transfer of electrical charge involved in cathodic reactions, i.e. cathodic activation control will dominate.     

A study of the inhibition of iron corrosion by imidazole and its derivatives self-assembled films

The self-assembled (SA) films of imidazole and its derivatives were prepared on the iron surface. The protection abilities of these films against iron corrosion in 0.5 M H₂SO₄ solution were investigated using electrochemical impedance spectroscopy (EIS) and polarization techniques. The results of EIS and polarization curves demonstrated that films of the imidazole and its derivatives were able to protect iron from corrosion effectively. XPS was also used for the surface analysis, the results from XPS confirmed the adsorption of imidazole derivatives on the iron surface by monitoring the functional group peaks of the compounds.     

Theoretical study of benzimidazole and its derivatives and their potential activity as corrosion inhibitors

A theoretical study of benzimidazole (BI) and two of its derivatives namely 2-methylbenzimidazole (2-CH₃BI) and 2-mercaptobenzimidazole (2-SHBI) recently used as corrosion inhibitors for mild steel in 1 M HCl was undertaken by considering Density Functional Theory (DFT) at the B3LYP/6-311G++(d,p) level. The properties most relevant to their potential action as corrosion inhibitors has been calculated in the neutral and protonated form: E_HOMO, E_LUMO, energy gap (ΔE), dipole moment (μ), electronegativity (χ), global hardness (η) and the fraction of electrons transferred from the inhibitor molecule to the metallic atom (ΔN). The theoretical results are in agreement with the experimental data.     

Surface active and thermodynamic properties of some surfactants derived from locally linear and heavy alkyl benzene in relation to corrosion inhibition efficiency

Linear and heavy alkyl benzene (HAB) were sulfonated with fuming sulfuric acid (oleum) and the sulfonated products were esterified with tri and poly ethanolamine (d = 4 and 6). The prepared three esters from each series were quaternized with n‐butyl bromide. The resulted six quaternized ester of linear and HAB sulfonate were named as (L1Q, L2Q, L3Q, H1Q, H2Q, and H3Q). The surface and thermodynamic properties of these compounds have been investigated. From the data obtained, it was found that surface tension and surface active properties for the HAB derivatives were better than which obtained from linear alkyl benzene (LAB) derivatives. From the results obtained from the surface activity, the best performance compound from each group was selected to study the corrosion inhibition efficiency of them relative to the surface activity. The obtained results show that the LAB derivative L3Q exhibited inhibition efficiency (93.1%) at 1000 ppm but H3Q exhibited (97%) at 600 ppm. The diversity of the resulted data obtained was discussed in the light of chemical structure of the alkyl benzene sulfonate.     

On the relationship between corrosion inhibiting effect and molecular structure of 2,5-bis(n-pyridyl)-1,3,4-thiadiazole derivatives in acidic media: Ac impedance and DFT studies

The inhibition properties of 2,5-bis(n-pyridyl)-1,3,4-thiadiazoles (n-PTH) on corrosion of mild steel in different acidic media (1 M HCl, 0.5 M H₂SO₄ and 1 M HClO₄) were analyzed by electrochemical impedance spectroscopy (EIS). The n-PTH derivatives exhibit good inhibition properties in different acidic solutions and the calculated values of revealed that the adsorption mechanism of n-PTH on steel surface is mainly due to chemisorption. While in 1 M HClO₄, both 2-PTH and 4-PTH isomers stimulate the corrosion process especially at low concentrations. Quantum chemical calculations using the density functional theory (DFT) were performed on n-PTH derivatives to determine the relationship between molecular structure and their inhibition efficiencies. The results of the quantum chemical calculations and experimental inhibition efficiency were subjected to correlation analysis and indicate that the inhibition effects of n-PTH may be explained in terms of electronic properties.     

Free and Wilson correlation between the molecular structure of some imidazolines and their corrosion inhibiting properties

In deaerated media containing hydrogen sulfide, the inhibition of the corrosion of N 80 steel by a homologous series of imidazolines was measured potentiokinetically. The data obtained were correlated to the structure of these molecules by means of Free and Wilson relationships. These correlations, allowed the behaviour of some derivatives to be predicted successfully.     

Impact of gamma-ray-pre-irradiation on the efficiency of corrosion inhibition of some novel polymeric surfactants

The effect of gamma-ray-pre-irradiation on the efficiency of two types of polymeric surfactants, (I and II) as corrosion inhibitors for 304 stainless steel in 2 M hydrochloric acid solution was examined. The inhibition efficiency of the undertaken additives was evaluated using both chemical and electrochemical techniques. The chemical structure of the two polymeric surfactants is illustrated as follows: where MA=maleic anhydride; BP=block polymer of polyoxy ethylene-polyoxy propylene (M.Wt=5000 g mol⁻¹).The obtained corrosion data, indicated that the corrosion inhibition efficiency of the inhibitor (II) was obviously not affected by gamma-ray-irradiation, meanwhile the efficiency of the inhibitor (I) demonstrated a remarkable decrease. Scanning electron microscope (SEM) was used to examine the surface morphology of stainless steel samples after immersion in 2 M HCl solution in absence and presence of the inhibitors at concentration of 400 ppm before and after exposure to gamma-ray-radiation up to a total does of 100 kGy.     

2-Amino-5-(4-pyridinyl)-1,3,4-thiadiazole monolayers on copper surface: Observation of the relationship between its corrosion inhibition and adsorption structure

Corrosion inhibition behavior of 2-amino-5-(4-pyridinyl)-1,3,4-thiadiazole (4-APTD) monolayers on copper surface were investigated by electrochemical impedance spectroscopy (EIS), electrochemical polarization measurement and surface-enhanced Raman scattering (SERS) experiment. The EIS mechanism of the copper surface with 4-APTD monolayers fitted to the mode of R(Q(R(QR))). The electrochemical polarization measurements indicated high inhibition efficiency of about 90.4%. SERS results suggested that 4-APTD molecules anchored at copper surface in a tilted orientation directly via N³ and N¹² atoms. The transition adsorption states of 4-APTD on the copper surface were observed as the potential applied from 0 to −1.6 V vs. SCE.     

Effect of temperature on the inhibition of the acid corrosion of steel by benzimidazole derivatives

The effect of 2-mercaptobenzimidazole (inh. I) and 2-mercapto-5-methylbenzimidazole (inh. II) on the corrosion of mild steel in 1M solutions of sulphuric acid has been investigated in relation to the concentration of the inhibitor as well as temperature by various monitoring corrosion techniques. The results obtained revealed that these compounds are good inhibitors. All the impedance diagrams gave semicircles for both inhibitors indicating that the corrosion of mild steel is controlled by a charge transfer process and the presence of either inhibitor does not alter the mechanism of the dissolution of mild steel. In general, both inhibitors efficiencies increased with increasing the inhibitors concentration at all temperatures used. On the other hand, inhibitors efficiencies were almost constant with increasing the temperature at concentrations 5 × 10⁻⁴ M, 1 × 10⁻³ M and 5 × 10⁻³ M. The best performance was noticed in case of (inh. II) especially at the concentration 5 × 10⁻³ M. Adsorption of both inhibitors was found to follow Langmuir, Flory-Huggins isotherms and kinetic-thermodynamic model. The binding constants “K” were calculated for both inhibitors. On increasing the temperature, the value of “K” increased in both cases indicative of stronger binding of the inhibitor molecule to the mild steel surface and hence higher inhibition efficiency at higher temperatures. The activation energy of the corrosion reaction decreases with increasing the concentration of (inh. I) or (inh. II). The adsorption of both inhibitors on the surface of mild steel is probably chemisorbed on the electrode surface. The thermodynamic parameters were calculated. Mass loss measurements revealed that both inhibitors exhibit maximum inhibition efficiency with increasing the concentration and temperature which confirm the data obtained from AC impedance. DC polarization data reveals that, both inhibitors does not alter the mechanism of anodic behaviour of mild steel and they behave as mixed type inhibitors. Again both inhibitors exhibit maximum inhibition efficiency with increasing the concentration and temperature which confirm the data obtained from AC impedance.     

2,5-Bis(n-methoxyphenyl)-1,3,4-oxadiazoles used as corrosion inhibitors in acidic media: correlation between inhibition efficiency and chemical structure

The efficiency of 2,5-bis(n-methoxyphenyl)-1,3,4-oxadiazoles (n-MOX), as corrosion inhibitors for mild steel in 1 M HCl and 0.5 M H₂SO₄ have been determined by weight loss measurements and electrochemical studies. The results showed that these inhibitors revealed a good corrosion inhibition even at very low concentrations. Comparison of results among those obtained by the studied oxadiazoles showed that 2-MOX was the best inhibitor. It is found to behave better in 1 M HCl than in 0.5 M H₂SO₄. Polarisation curves indicate that 2-MOX is a mixed inhibitor in 1 M HCl, but in 0.5 M H₂SO₄, the inhibition mode of 2-MOX depends on the electrode potential and acts essentially as a cathodic inhibitor. The inhibition efficiency slightly increases with temperature in the range from 25 to 60 °C, the associated activation energy have been determined. The addition of 2-MOX leads to decrease this activation energy. The adsorption of 2-MOX on the mild steel surface in both acidic media follows a Langmuir isotherm model. Significant correlations are obtained between inhibition efficiency with the calculated chemical indexes, indicating that variation of inhibition with structure of the inhibitors may be explained in terms of electronic properties.     

Effect of the molecular structure of some quinones on their corrosion inhibiting action

The molecular characteristics obtained by quantum chemical self‐consistent field (SCF) calculations of a series of quinones are correlated with the experimentally determined inhibitor efficiency for mild steel corrosion in neutral aqueous medium. It was established that the decrease of the ionization potential and the increase of the dipole moment of the quinone molecules favor the higher protective effect. The electron density and the geometric molecular structure have also been computed and are discussed in view of the corrosion inhibition.