2.1. Materials instruments
The substances were high purity, analytical reagent grade compounds. The British Drug Houseprovided the organic solvents. AGallenkemp melting point detector was used to find melting points (OC, uncorrected) in open capillaries (Sanyo Gallenkemp, Southborough, UK). IR spectra (KBr discs) were obtained using Fourier transform infrared spectroscopy (FTIR, plus 460 or Pye Unicam SP-1000 spectrophotometer, Pye Unicam, Cambridge, UK). 1HNMR spectra (DMSO-d6) were collected using a Bruker spectrophotometer (400 MHz for 1HNMR and 100 MHz for 13CNMR). Tetraethyl silane is used as an internal standard, while DMSO-d6 is used as the solvent. Chemical shifts are displayed in ppm. MS electrodes with the compositions and pre-treatment information described in our prior study were purchased from the AL-EZZ firm in Alexandria, Egypt. The 1 M HCl solution that is corrosive was created by diluting 37 %hydrochloric acid[36].The morphological investigation of the MS was conducted using the scanning electron microscope (SEM, JEOL, JSM5400LV).TLC on silica gel 60 F254 plates, visualization with UV light (254 nm), monitoring the reaction progress, and assessing the purity of synthesized compounds.
2.2. Inhibitor synthesis
2.2.1. Synthesis of 1-phenyl-3-methyl-5-pyrazolone2
Ethyl acetoacetate 1 (0.01 mol) and phenyl hydrazine (0.01 mol) were dissolved in ethanol (20 ml) and refluxed for one hour before the solvent was evaporated. The equivalent pyrazole 2 was produced as light yellow crystals when the solid residue crystallised from ethanol (Lit.mp 126-128 0C)[37].
2.2.2. Synthesis of4-(2-(3-methyl-5-oxo-1-phenyl-1H-pyrazol-4(5H)-ylidene) hydrazinyl)-N-(thiazol-2-yl)benzenesulfonamide 6a
In 50 mL of water, 0.1 mol of sulfathiazole 3a was suspended. Then under stirring conditions, 10 mL of 36.5% HCl was added to this solution. The mixture was progressively heated to 60 ºC until transparent. An ice bath was used to cool the solution from 0 to 5 ºC. The addition of a sodium nitrite solution (0.5 g in 5 mL water) was stirred for 5 minutes. 1-Phenyl-3-methyl-5-pyrazolone 2 (0.1 mol) was dissolved in 20 mL of (95%) ethanol and kept at 0 to 5 ºC. with sodium acetate. the diazonium salt solution was added for 10–15 minutes while being continuouslyslowly stirring to get a pure product of 4-(2-(3-methyl-5-oxo-1-phenyl-1H-pyrazol-4(5H)-ylidene) hydrazinyl)-N-(thiazol-2-yl)benzenesulfonamide6a, The precipitate that was formed was filtered, dried, and then recrystallized in 85% aqueous ethanol. solid colour of red.m.p. 145-146 °C, yield 92%. IR (KBr, cm–1):3100(NH),2911(CH-alph), 1689 (C=O),1595 (N=N),1362, 1143 (SO2) ; 1HNMR (400 MHz, DMSO-d6) δ: 2.25 (s, 3H, CH3), 6.74,7.21(2s,2H,thiazole-H),7.89 (d, 2H,AB-system), 8.01(d, 2H,AB-system),7.45-7.73 (m,5H, arom-H), 11.80,13.20 (2s,2H, 2NH changeable with D2O).13CNMR (DMSO-d6, 75 MHz)δppm):12.09(CH3),108.81,116.62,118.61,125.39,128.01(C=N),129.85,138.25,138.90,144.62, 149.15 , 156.73 (C=O),169.37 (C=N). Anal. Calcd for: C19H16N6O3S2 (440): C, 42.70; H, 3.94; N, 24.90; S, 11.40. Found: C, 42.60; H, 3.90; N, 24.80; S, 11.50 (see Figure 3 and Figure S1).
2.2.3. Synthesis of N-(4,6-dimethylpyrimidin-2-yl)-4-(2-(3-methyl-5-oxo-1-phenyl-1H-pyrazol-4(5H) -ylidene)hydrazinyl)benzenesulfonamide 6b
This compound was produced from sulfadimidine. 3b (0.1 mol) and 1-Phenyl-3-methyl-5-pyrazolone 2 (0.1 mol) in the same way that was explained for the preparation of 6a.
Orange color solid. m.p. 165-166 °C, yield 92%. IR (KBr, cm–1):3233(NH),3020(CH-arm), 2925(CH-alph), 1693(C=O), 1597 (N=N),1344, 1153 (SO2) ; 1HNMR (400 MHz, DMSO-d6) δ: 2.29 (s, 3H, CH3), 2.42 (s, 6H, 2CH3), 6.79 (s,1H,pyrimidine-H), 7.24-7.90 (m,9H, arom-H), 12.80,13.30 (2s,2H, 2NH exchangeable with D2O). 13CNMR (DMSO-d6, 75 MHz) δ (ppm):12.17(CH3-pyrazoline),23.48(CH3-yrimidine),116.07,118.39,129.56,130.47(C=N),137.81, 138.26, 144.98,147.79 (C=N), 149.26 ,154.15, 156.63 (C=O), 162.39,162.90 (C=N), 167.90 (C=N). Anal. Calcd for: C22H21N7O3S (463): C, 57.01; H, 4.57; N, 21.15; S, 6.92. Found: C, 57.00; H, 4.50; N, 21.10; S, 6.90(see Figure 4).
2.3. Preparation of metal electrode
Mild steel (MS) of the following chemical structure (wt. %): C- 0.093, P- 0.014, Si- 0.011, Mn- 0.853, Cr- 0.025, Cu- 0.012, Al- 0.032, Ni- 0.013 and Fe - In the experiments, balancing was used[38].
2.4. Gravimetric technique
Experiments were conducted on MS in 1 M HCl acid (with and without inhibitors) to measure the weight loss. The sheets utilized have the dimensions 5X 1X 0.1 cm. They were polished to variable degrees using different grades of each paper in phases. The papers that were used were 5X1X0.1 cm square. They were sequentially polished using different grades of each paper to achieve different granulation grades (SiC 1200 and 1400). The test solution was placed in a 250 ml glass vessel for each run. A clean weight was placed in an upright position and filled to the top of the jar. The plates are dried by air after being warmed. ml of the test solution rinsed and dried in ethanol. A clean weight sample of mild steel was placed in an inclined position in the jar. The specimen was removed and cleaned with distilled water to remove abrasion products after spending a day immersed in 1 M HCl (uninhibited and inhibited) with the addition of different dosages of inhibitors. The plates are then heated air dried. ethanol-washed, dried, and weighed. Thermostat-controlled experiments were conducted at constant temperatures of 298, 303, 313, and 323 K in freshly produced solutions. The corrosion rate was calculated using the weight loss[39].
2.5. Electrochemical investigations
2.5.1. Electrochemical Cell
The tests were performed using an electrochemical cell with three electrodes that has a saturated calomel electrode (SCE) as the reference electrode, a platinum wire as the counter electrode, and MS with a surface area of 1 cm2. In this study, electrochemical impedance spectroscopy, electrochemical frequency modulation, and electrochemical potentiodynamic polarization approaches have all been measured in turn. Electrochemical impedance spectroscopy (EIS) was performed using an electrode that had been submerged in the test for an hour. The EIS measurements were made at open-circuit voltage (OCV) with a small alternating voltage perturbation (10 mV) applied to the cell over the frequency range of 100 kHz to 20 mHz at 298 K.Second, electrochemical frequency modulation (EFM) was carried out using two frequencies of 2 and 5 Hz and an AC amplitude of 10 mV. Potentiodynamic polarization was also detected for anodic and cathodic polarization at a scan rate of 5 mV s-1. With the use of the Gamry 3000 potentiostat/galvanostat/ZRA and Echem Analyst 7 software, all of these methods were measured[40].
2.6. Quantum chemical calculations
Quantum chemicalcalculations of many parameters were calculated using the (DFT) method. DFT using Becke’s three parameter exchange functional (B3LYP) at the 6-311G (d, p) basis set [41] drawn in the GaussView 5.0 with Gaussian 09W program package [42]. Quantum chemical parameters such as the highest occupied molecular orbital (EHOMO), the lowest unoccupied molecular orbital (ELUMO), the energy gap (ΔE),the electron affinity EA, the ionization potential IP, the electronegativity (χ), the global hardness (η), the softness (σ), the electrophilicity index (ω), dipole moment (DM), total energy (TE), total negative charges and the fraction of electrons transferred ΔN were calculated by the following equations (1-5) [43-46].
Where χFe ≈ 7 eV[41] is taken for iron and ηFe = 0 is taken, assuming that the ionization potential, I, equal the electron affinity, A, for bulk metals where χFe and ηFe are 7 and 0 respectively [42]