(2S,3R)-2-((1-(4-amionophenyl) ethylidene)amino)-3-hydroxybutanoic acid as a novel and eco-friendly corrosion inhibitor for the carbon steel (X56) used in Iraq’s oil installations

Herein, the successful a novel corrosion inhibitor ((2S,3R)-2-((1-(4-amionophenyl) ethylidene) amino)-3-hydroxybutanoic acid compound (S1) was synthesized by the condensation reaction of equimolar of the 4-amino acetophenone with threonine amino acid. 1H NMR, 13C NMR, C.H.N., and FTIR techniques were used to confirm the structure of the S1 inhibitor. The impacts of S1 inhibitor was tested on the carbon steel (x56) in 0.5 N hydrochloric acid solution at 298.15 K. The electrochemical measurements were accomplished such as open circuit potential (OCP) and polarization scan, the results were confirmed the S1 as an excellent inhibitor and act as a mixed inhibitor to control on both the anodic and cathodic reaction to retarding the corrosion process by blocking the active sites on the surface electrode. These data were proved by the FE-SEM images and mapping spectra, it was seen the protective layer clearly on the surface.


Introduction
Corrosion is the process that converts metal into a chemically stable configuration like hydroxide, oxide, and sulfide [1]. This process happens with the gradual destruction of the materials via an electrochemical reaction chemical or chemical with their environment [2][3][4] . The metal parts used in industry are subject to rapid corrosion, which greatly increases both scheduled and unplanned maintenance costs [5,6]. Corrosion-resistant steel has attracted great interest in industrial application as a way to reduce costs associated with product failure [7]. As the increased corrosion resistance of the metals extends the life of metal parts and thus reduces replacement and maintenance costs [8]. For that, no cost-effective process has been developed to produce highly corrosion-resistant metals for use in the manufacture of steel products [9]. Corrosion in the oil industries is one of the central and dangerous constraints that accompany these industries, starting from the extraction of crude oil and ending with the stages of the use of its derivatives, through purification, refining, manufacturing, and transportation, and storage operations.
Refinery equipment and metallic constructions in oil refineries and petrochemical mills are in contact with the ore oils and fuel and products of petroleum, solvents, soil, atmosphere, and water [10][11][12]. The acidic solutions are the most corrosive mediums and used in conserve, acid cleaning, sediment boiler, and oil well industries [7,13,14]. The essential criteria adopted in selecting the appropriate inhibitors depend mainly on the type of acid, concentration, and temperature. Some organic derivatives of amino acids were investigated by researchers as corrosion inhibitors for the carbon steel in acidic solutions such as hydrochloric acid [15][16][17].
The inhibition process occurs via the electrostatic interactions molecules and the interaction between unshared electron pairs of hetero-atoms and vacant d-orbital of iron surface atoms [18,19]. The non-toxic of various amino acid derivatives as threonine has led to their use as corrosion inhibitors due to the presence of electrons and heterogeneous atoms as well as aromatic rings in their structures that absorb or form an insoluble metal compound on the surface of the metal [20][21][22]. So, the present work aims to study the inhibition effect of (2S,3R)-2-((1-(4-amionophenyl) ethylidene)amino ) -3-hydroxybutanoic acid on the corrosion of carbon steel type X56 in 0.5 N HCl aerated solution. The chemical structure of the corrosion inhibitor used in this study, as shown in Fig. 1.  The Carbon steel ( X56) coupon was taken from Iraq's oil refine fields and had the compositions of the following elements, as shown in Table.1. The optical emission spectroscopy type PMI MASTER PRO2 used to reveal the chemical structures of the MS specimen. The appropriate sample was prepared with dimensions ( 1 cm × 1 cm ) and thickness (0.4 cm). All carbon steel (X56) specimens polished like a mirror by using the emery papers at different sizes and finally by the soft cloth with diamond past as lubricating oil. To prepare the working carbon steel electrode, it was covered with an epoxy resin, for that the exposed area 1 cm2 to contact with the electrolyte solution [23].   (10,30, and 50 ) ppm in 0.5 N HCl aggressive aerated acidic media.

2:2: Synthesis of corrosion inhibitor
A novel (2S,3R)-2-((1-(4-amionophenyl) ethylidene)amino ) -3-hydroxybutanoic acid compound ( S1 ) was synthesized by the condensation reaction of equimolar from the 4-amino acetophenone (1mmol) with threonine amino acid (1mmol) in 25 mL mixture of absolute ethanol and sodium hydroxide [24]. The mixture was reflexed for 55 0 C for 10 h under magnetic stirred to give a yellow color, this is the first identify to formation the Schiff base. Moreover, the progress of the reaction was followed up by the thin film chromatography ( TLC ). The solution obtained was evaporated under 25 0 C. The solid obtained was washed several times with absolute ethanol, and then recrystallized by utilized the deionized water-ethanol mixture ( 1:3). The S1 compound (product yield 86%) was prepared to record the melting point in the range 199-201 0 C. To estimate the purity of the S1 compound, 1 H NMR, 13 C NMR ,C.H.N., and FTIR measurements were used to the characterized structure of the ((2S,3R)-2-((1-(4-amionophenyl) ethylidene)amino ) -3-hydroxybutanoic acid corrosion inhibitor.

2:3: Electrochemical measurement
The corrosion cell was constructed with carbon steel (X56) as the working electrode to study the inhibitory effects of (2S,3R)-2-((1-(4-amionophenyl) ethylidene)-3hydroxybutanoic compound on the corrosion of the carbon steel (X56) when exposed to the aerated hydrochloric acidic solution (0.5 N) in the 303.15 K. The Calomel and Platinum electrodes were used as a reference and auxiliary electrodes, respectively.
All of them were placed in corrosion electrochemical cell in the same time and connected with the M-lab Potentiostat/Galvanostat device ( BANK ELETRONIC company, Germany) to measure the polarization curves and estimated the parameters of corrosion process such as the corrosion current density (icorr), corrosion potential (Ecorr.), anodic and cathodic Tafel slopes (ߚ , ߚ ), respectively, and the corrosion rate at the polarized carbon steel (X56) working electrode.

2:4: Characterization techniques
Carbon steel (X56) specimens were characterized by the field emission scanning electron microscope (FESEM) ZEISS Gemini type 500 (ZEISS, Germany LTD. company ) at the accelerating voltage (0.02 -30 ) k and the magnification of image (50 -2,000,000). Firstly, the carbon steel (X56) sample ( exposed area ~ 1.8 cm2) was The FESEM images were taken to study the morphology of carbon steel surface in with and without the inhibitor. EDS ( energy dispersive spectroscopy ) spectrums were determined to identify the compositions of the chemical elements at the same conditions of the aggressive electrolyte solution. It is necessary before each image was recorded, the samples were washed with deionized water and dried in a desiccator for one hour.

Scheme.1:
The suggested mechanism of the S1 corrosion inhibitor.     working electrode with interval time in 0.5 normal hydrochloric acid solution in the absence and the presence of S1 corrosion inhibitor at the 289.15 K. It can be seen that the curve of OCP drifts towards more negative values and which led to a short step. This behavior was studied by the West and co-workers [21,26], which denotes the collapse of the oxide film formed in the air before immersion displays on the working electrode surface, as shown in the following equation :  Moreover, in the presence of the S1 inhibitor, the OCP potential values shifted towards a more positive direction, especially in a high concentration of inhibitor (50 ppm). This happening can be interpreted in the idea of the formation of the protective film on the surface carbon steel (X56). For that, at a high concentration established of the steady iron -complexes alongside nitrogen atoms [27]. As cited in the OCP electrochemical measurements, there is attention was taken to the stability of the OCP value before the polarization scan was recorded. To know more  10 about the kinetics of the corrosion reaction, which includes both the anodic and cathodic reactions that happen on the X56 working electrode surface, the carbon steel sample was immersed in the 0.5 N hydrochloric acid solution in the absence and presence of the S1 inhibitor at 289.15 K. The information obtained from the potentiodynamic scan are shown in Fig.6. The full parameters of the polarization curves such as the corrosion potential, corrosion current density, Tafel constants, the corrosion rate, and inhibition efficiency are tabulated in Table. 2. It can be observed that the corrosion potentials (E corr ) shifted to a more negative with the S1 corrosion inhibitor, this result has affirmed the influence of the S1 compound as an organic inhibitor in retarding the E corr by the adsorption process and hence blocking the active area sites on the X56 surface electrode. From Table.2, the corrosion current density The slightly changed an anodic slope constant (b a ) which demonstrates interference in the mechanism of corrosion reaction in the presence of S1 inhibitor. These data indicate that the corrosion inhibitor (S1) acts as a mixed type inhibitor with main control on the cathodic reaction by retarding the evolution of hydrogen via the blocking effect of the active sites.  The values of P% were increased with increasing the concentration of S1 inhibitor in the corrosive HCl solution, as shown in Table 2. This it might interpret that the corrosion inhibitor S1 is a good inhibitor, especially at a high concentration to control the corrosion process and leads to an increase in the inhibition efficiency values. This behavior is consistent with decreasing the corrosion rate from 266.3 to 69.04 mpy. The FE-SEM technique was used to characterize the surface of the carbon steel X56 in 0.5 hydrochloric acids aerated solution in the presence of an S1 inhibitor at 298.15 K, as shown in Fig. 7 a,b, and c. The surface of the electrode seems to have sustained less damage in the aggressive HCl solution, due to the disappearance of the cracking and pitting with the formation of the pale grey thin film (Fe 3 C film) [21,28]. There is emphasized on the protective film layer ( Fig. 7 a) on the X56 surface electrode and this an improvement in the integrity of the carbon steel surface. Moreover, the mapping results have given the composition of the analysis of the elements of the protective layer, it seems that the elements as carbon, oxygen, nitrogen, and iron are present, as displayed in Fig 7 b and c. For that, the aggressive attack seems less severe in the presence of an S1 compound as a corrosion inhibitor.

4: Conclusion
In the present work, we successfully to synthesis a novel corrosion inhibitor (2S,3R)-2-((1-(4-amionophenyl) ethylidene)amino ) -3-hydroxybutanoic acid compound (S1 ) via condensation reaction of equimolar of the 4-amino acetophenone with threonine amino acid. 1 H NMR, 13 C NMR ,C.H.N., and FTIR techniques were used to confirm the structure of the S1 inhibitor. The carbon steel type x56 was used as a working electrode to test the S1 inhibitor in 0.5 N hydrochloric acid solution at 298.15 K. The electrochemical measurements were achieved such as open circuit potential and polarization scan, the results were affirmed the S1 as an excellent inhibitor and act as a mixed inhibitor to control on both the anodic and cathodic reaction to retarding the corrosion process by blocking the active sites on the surface electrode. These data were proved by the FE-SEM images and mapping spectra, it was seen the protective layer clearly on the surface.