Synthesis, Characterization and Corrosion Protective Efficiency of 2[2-Oxo-phenyl hydrazinyl ethyl] benzamide on Mild Steel in Sulphuric Acid Medium

2[2-Oxo-phenyl hydrazinyl ether] benzamide (2BA) was synthesized, characterized and tested effective for corrosion inhibition of mild steel in 1 N H2SO4 solution using galvanodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. Polarization resistances calculated from the EIS measurements are in good agreement with those obtained from alternating current (AC) polarization measurements. The mild steel samples were also analyzed by Scanning Electron Microscopy (SEM). The result showed that 2BA is an excellent inhibitor for mild steel in acid medium. The inhibition was assumed to occur via adsorption of the inhibitor molecule on the metal surface. In the 303-323K temperature range, the 2BA adsorption follows Langmuir isotherm model. The protection efficiency increases with increasing the inhibitor concentration in the range of 250-1000 ppm but slightly decreases with increasing temperature.


Introduction
It is generally assumed that corrosion inhibition performed by chemical compound added to the electrolyte is to be attributed almost as a first stage, to the adsorption of the additives (ions or neutral polar molecules) to the metal/solution interface.The nature and the surface charge of the metal, the type of corrosion media and molecular structure of the inhibitor influence its adsorption in acid corrosion.The inhibitor adsorption may determine a structural change of the double layer, thus it reduces the rate of the electrochemical partial reaction, the anodic metal dissolution and the cathodic hydrogen ions reduction.The theoretical consideration of a correlation between the molecules structure of organic compounds and their ability to adsorb on the metal surface and hence to inhibit the corrosion process is aimed at in a series of the studies [1][2][3] .
The action of such inhibitors is a specific interaction between certain functionalities and the metal surface.Hetero atoms such as nitrogen, oxygen and sulphur, play a crucial role therein owing to their free electron pairs [4][5] .Compounds with π bonds also generally exhibit good inhibitive properties, the electrons for the surface interaction being provided by the πorbital.Both features obviously can be combined within the same molecule, which may then give rise to particularly potent inhibitors.Schiff bases-the condensation product of an amine and a ketone or aldehyde and with R 2 C=NR' as general formula are known example of this category and have been investigated for the inhibition of acid corrosion of mild steel 6-7 aluminum 8 and copper 9 and of neutral halide corrosion of copper [10][11][12] .The explanation lies in the presence of unoccupied π*-orbital in the Schiff base molecule, which enable electron back donation from the transition metal d-orbitals and stabilize the existing metal inhibitor bond [6][7] .The aim of this work is to investigate the role played by newly synthesized 2[2-oxo-2phenyl hydrazinyl ethyl] benzamide on the corrosion behavior on mild steel in 1 N H 2 SO 4 .In view of this, 2[2-oxo-2phenyl hydrazinyl ethyl] benzamide (2BA) was synthesized and characterized using IR and NMR analysis techniques.The inhibitive action of 2BA on the corrosion behavior of mild steel in 1 N H 2 SO 4 solution at three levels of concentration and at three different temperatures was measured.Corrosion inhibition was investigated using electrochemical technique (Polarization and EIS) and weight loss measurements.

Experimental
2[2-Oxo-2-phenyl hydrazinyl ethyl] benzamide was synthesized in the laboratory using well established methods and characterized by spectral analysis method.The IR spectra (in KBr pellets) were recorded on a Nicolet-Protege 460 spectrometer. 1H NMR spectra were recorded on a 300 MHzDPX300 spectrometer.

Synthesis
In the laboratory, 2[2-oxo-phenyl hyrazinyl ethyl] benzamide (2BA) was synthesized from ester of hippuric acid using the following procedure: A mixture of 0.01(mol) ester of hippuric acid, 0.01 (mol) of phenyl hydrazine, 0.2 mL of glacial acetic acid and 25 mL of absolute ethanol was refluxed for 24 h.The crystalline product thus obtained was filtered, washed, dried and recrystalized in methanol.The yield of crystals was 83% and their melting point was 178-179 °C.The required intermediates were prepared using reported procedures 13 .Their purity was monitored by TLC and its structure was established by spectral measurements.

Weight loss measurements
Weight loss measurements were carried out by weighing the mild steel specimens before and after immersion in 100 cm 3 acid solution for different time intervals in the absence and presence of various concentrations of compound at different temperatures.The inhibition efficiency (%) of the inhibitor was calculated by Equation 1: Where, W o and W are weight losses without and with inhibitor.
The corrosion rate of mild steel was calculated using 10 Equation 2 6 10 45 .3  ADT Where, W = weight loss (g), D = Density of mild steel specimen (g cm -3 ), A = Area of the coupon (cm 2 ), T = exposure time (h).

Polarization measurements
A conventional three-electrode system consisting of mild steel as working electrode, platinum foil as counter electrode and saturated calomel as reference electrode, was used for the polarization measurement.The anodic and cathodic polarization values were measured under galvanostatic condition in the range of 0 to ± 200 µA.
The percentage inhibition efficiency (% IE) was calculated using the equation 3: Where, Iº coor and I corr are the corrosion current densities in the absence and presence of inhibitor.

Electrochemical impedance spectroscopy studies (EIS)
Impedance spectroscopy measurements were carried out in the frequency, ranging from 42 Hz to 5 MHz using LCR HI-Tester (H10K1 3532-50).

SEM and FT-IR studies
The surface morphology of the steel samples was investigated after anodic polarization using SEM technique (JSM 840 Jeol).FT-IR spectra (in KBr pellets) were recorded on a nicolet protege 460 spectrophotometer.

Characterization of 2[2-Oxo phenyl hydrazinyl ether] benzamide
Ester of hippuric acid (4) on treatment with phenyl-hydrazine in ethanol containing trace of glacial acetic acid as catalyst, yielded

Weight loss measurements
The values of percentage inhibition (%IE) and corrosion rate (µ corr ) obtained from weight loss method at different concentrations of inhibitor and at different temperatures are summarized in Table 1.It has been found that 2BA compound inhibits the corrosion of mild steel in 1 N H 2 SO 4 solution at different concentrations used in this study i.e. 250, 500, 1000 ppm.It has also been observed from Figure 1 that the inhibition efficiency of the mild steel increases with the increase in concentration of 2BA compound.The variation of inhibition efficiency with solution temperatures for various inhibitor concentrations are shown in Figure 2.
It can be seen that inhibition efficiency obtained at different concentrations of inhibitor causes a significant decrease with an increase in temperature from 303 K to 323 K while inhibition efficiency of the inhibitor increases with increase in the concentration.This behavior could be attributed due to strong interaction of compound with the metal surface that results in the adsorption of inhibitor molecules [15][16][17] .The lone pair of electron on the nitrogen will coordinate with the metal atoms of active sites.The presence of higher electron density of carbonyl group in 2BA causes stronger interaction with metal surface.Functional graphs such as -NH-, -N=N-and -C=N-, having π bonds, are found in inhibitor which inhibit corrosion of metal by interaction with the electrode surface through electron sharing to increase adsorption and hence higher inhibition of corrosion [18][19][20] .

Polarization measurement
Anodic and cathodic potentiodyamic polarization curve of mild steel in 1 N H 2 SO 4 at 303 K in the absence and presence of 2BA compound of various concentrations associated with electrochemical parameters and % inhibition efficiency (%IE) is shown in Figure 3. Corrosion current density (I corr ), Corrosion potential (E corr ), Tafel slopes (β a and β c ), surface coverage and %IE are given in Table 2.The result shows that I corr values decrease with increase in the concentrations of inhibitors and least I corr was obtained at 1000 ppm of the inhibitors.The value of tafel slope shows that the corrosion inhibition efficiency may be due to the control of hydrogen evolution reaction.From the polarization curves of 2BA, there is a simpler shift of both the anodic and cathodic curves towards lower current density region.The degree of surface coverage (θ) was determined using 21 the Equation 4: Where, Iº corr and I corr are the corrosion current densities in the absence and presence of inhibitor respectively.
The degree of coverage 'θ' was found to increase with increase in the concentration of additive and decrease with the increase in the temperature.

Electrochemical impedance measurements
The experimental results of EIS measurements obtained for the corrosion of mild steel without and with inhibitor are summarized in Table 3. Figure 4 shows the complex impedance plots for mild steel in 1 N H 2 SO 4 with and without various concentration of 2BA at 303 K.

Thermodynamic parameters
In order to understand the mechanism of corrosion inhibition, the adsorption behavior of the organic adsorbate on the steel surface must be known.The degree of surface coverage (θ) for Synthesis, Characterization and Corrosion Protective Efficiency study 337 different concentration of inhibitor has been evaluated from galvanodynamic polarization measurements.The data were tested graphically by fitting to various isotherms.A straight line was obtained on plotting log (θ/1-θ) against log C, suggesting that the adsorption of the compound on mild steel surface follows Langmuir adsorption isotherm model 22 (Figure 5).

Adsorption isotherm
The inhibition efficiency of 2BA compound is determined by their adorability on the surface of the corroding metal.Where mono layer adsorption occurs on the steel surface, the Langmuir adsorption isotherm 22 may be expressed by equation 5: Where T is temperature, A is independent constant, C is inhibitor concentration, R is gas constant, ∆H is heat of adsorption and θ is surface coverage by the inhibitor molecule.Figure 6 shows the Plot of log θ/(1-θ) versus (1/T) at different additive concentrations.The slope of the linear parts of curves is equal to -∆H/2.303R from which the average heat of adsorption, ∆H were calculated at different concentration of inhibitor and are given in Table 4.The negative valves of ∆H reflect the exothermic behavior of 2BA compound on the metal surface.

Activation energy
The activation energy of the corrosion process can be calculated using the Equation 7: Where E a is the activation energy, A is the frequency factor, T is the absolute temperature, R is the gas constant and K is the rate of metal dissolution reaction 16 .
The values for the compound studied are listed in Table 4.This result agrees with the order of IE.The activation energy is higher in the presence of additives than in its absence.During the corrosion reaction mechanism, the charge transfer is blocked with adsorption of 2BA molecules to the metal surface, causing the increase in the activation energy [23][24] .The higher values of E a are good evidence for the chemisorption mechanism of 2BA compound on the steel surface.

Morphological investigation
Microstructural studies of mild steel in 1 N H 2 SO 4 in absence and presence of a certain concentration of compound at 303K were performed and illustrated in the Figures.It is clear that the corrosion attack was more pronounced in the absence and presence of low inhibitor concentration (500 ppm) of the studied inhibitors at 303 K temperature (Figure 8a, 8b), while the film formed on the metal surface becomes more protective with increase of inhibitor concentration (1000 ppm) at 303K (Figure 8c).This is attributed to the involvement of compounds in the interaction with the active sites of metal surface.This results in enhanced surface coverage of the metal so that there is a contact between metal and the aggressive medium.

IR Studies
The compound formed on the corroded steel specimens after polarization were scrapped, collected and subjected to FT-IR spectral studies.The involvement of NH group, C=C and C=O in interaction reaction with metal surface atom could be proved by the respective IR spectra.The shift in the adsorption peaks from NH (3231-3229) C=CAr (3005-3002) C=O (1745-1741) C=C (763-760) further the intensity of the peaks stretching frequency is decreased which implies that the shift peaks in this compound is coordinated to Fe +2 resulting in the formation of a Fe +2 inhibitor complex on the metal surface.

Conclusion
2BA compound inhibits the corrosion of mild steel in 1 N H 2 SO 4 .The inhibition efficiency increases by increasing the inhibitor concentration.Polarization measurement shows that the 2BA studied act as mixed type inhibitors.AC impedance plots of mild steel show that polarization resistance increases with increase in inhibitor concentration.The adsorption of 2BA molecules on the metal surface from 1 N H 2 SO 4 solution obeys Langmuir adsorption isotherm.The negative sign of ∆H ads indicates that the adsorption process is spontaneous and exothermic.SEM examination of the electrode surface confirmed the existence of such adsorbed film.

Figure 1 .
Figure 1.Variation of inhibition efficiency as a function of inhibitor concentration at different temperatures in 1 N H 2 SO 4 .

Figure 2 .
Figure 2. Variation of inhibition efficiency as a function of temperature for various inhibitor concentrations in 1 N H 2 SO 4 .

Figure 3 .
Figure 3. Galvanostatic polarization curve for different inhibitor concentrations in 1 N H 2 SO 4 at 303 K.

Figure 4 .
Figure 4. Nyquist plot for different inhibitor concentrations in 1 N H 2 SO 4 .

Figure 7 .
Figure 7. Variation of corrosion current with temperature in 1 N H 2 SO 4 .

Figure 8
(a, b, c).SEM images (2000x) at different concentration of inhibitor in 1 N H 2 SO 4 .

Table 1 .
Corrosion parameters obtained from weight loss measurements for various inhibitor concentrations at different temperatures in 1 N H 2 SO 4 .

Table 2 .
Corrosion parameters obtained from polarization measurements for various inhibitor concentrations at different temperatures in 1 N H 2 SO 4 .

Table 3 .
Impedance parameters obtained using electrochemical impedance method in 1 N H 2 SO 4 at 303 K

Table 4 .
Activation parameters at various inhibitor concentrations in 1 N H 2 SO 4 .