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Synthesis and investigations of heterocyclic compounds as corrosion inhibitors for mild steel in hydrochloric acid

Synthesis and investigations of heterocyclic compounds as corrosion inhibitors for mild steel in... The corrosion inhibition of mild steel in 0.5 M hydrochloric acid by six synthesized heterocyclic compounds was studied using weight loss measurements. The inhibition efficiency exceeded 95%. The excellent inhibitor performance was attrib- uted to the formation of protection adsorption films on the steel surface. The structures of compounds were confirmed by Fourier transform infrared and nuclear magnetic resonance analysis. The adsorption of inhibitor on steel surface followed the Langmuir adsorption isotherm. Quantum chemical calculations were also adopted to clarify the inhibition mechanism. Keywords Steel · Weight loss · FT-IR · Corrosion · Inhibition · Synthesis Introduction between the aggressive solution and metal surface hinder the dissolution of the metal and reduce corrosion damages [7, Iron and its alloys are widely used as a constructional mate- 8]. Organic inhibitors containing heteroatoms, such as N, O, rial in several industrial applications, such as petroleum, S and P, have proven practically and theoretically to act as power plants, chemical industries due to its high mechani- efficiently corrosion inhibitors in a wide range of acidic solu- cal strength, easy fabrication and low cost [1, 2]. The variety tions [9, 10]. The efficiency of these inhibitors can be attrib- of applications make steel in contact with various corrosive uted to their high polarizability and lower electronegativity; environments, such as acidic solutions during the processes so that these atoms and the functional groups can cover large of etching, acid pickling, acid descaling, acid cleaning, oil metallic surface areas and easily electrons transfer to the well acidification. [3 ]. In acidic media, steel alloys react empty orbitals of atoms [11]. In addition, nitrogen-contain- easily and converted from metallic to ionic state forming ing organic inhibitors is good anticorrosion materials for a huge economic loss. Therefore, there is a necessary need metals in hydrochloric acid, while compounds having sulfur to develop some excellent corrosion controlling methods. atoms act as good inhibitors in sulfuric acid. Compounds One of the methods is the use of corrosion inhibitors [4–6]. holding nitrogen and sulfur behave as perfect corrosion Corrosion inhibitors can be classified according to chemical inhibitors for both media [12]. The action of any inhibitor structure, method of action, etc. One of the common classes for any specific metallic alloys in sever acidic environments is organic corrosion inhibitors that obtained the highest depends on the nature of the characteristic inhibitor film importance due to their ease synthesis at relatively low cost accumulated on the metal surface and the number and nature and high protection ability. The method of prevention can of adsorption centers contributing in the adsorption process. be ascribed to the adsorption on the steel surface and imped- In general, the inhibition performance of the inhibitors hav- ing the active corrosion sites. Formation of protective layer ing different heteroatoms follows the reverse order of their electronegativities, so that in S, N, O and P, the inhibition performance followed in the order of: O < N < S < P [13]. * Anees A. Khadom The existence of organic materials in the acidic solutions aneesdr@gmail.com commonly alters the electrochemical behavior of the acidic Department of Chemistry, College of Science, University environments. In other words, it decreases the aggressive- of Diyala, Baquba City 32001, Diyala Governorate, Iraq ness of the solution. The most regularly used heterocyclic Department of Chemical Engineering, College compounds have sulfur (S), phosphorus (P), nitrogen (N) or of Engineering, University of Diyala, Baquba City 32001, oxygen (O) heteroatoms, and these effectively take part in Diyala Governorate, Iraq Vol.:(0123456789) 1 3 160 International Journal of Industrial Chemistry (2019) 10:159–173 adsorption centers. Therefore, in this study, six heterocyclic Specifications of 4‑(4‑amino‑5‑mercapto‑4H‑1,2,4‑tria‑ compounds were syntheses and selected to act as corrosion zole‑3‑yl) phenol (ATT ) inhibitors for steel in hydrochloric acid solution. −1 White crystals, m.p: 216–218  °C, FT-IR (KBr, cm ): OH (3524(, NH (3356), N–H (3144), aromatic C–H str 2 str str Experimental work (3090), C=N (1654), aromatic C=C (1505, 1409), C=S str str (1244(, Yield: 60%. The spectrum of H-NMR (400 MHz, Materials and test conditions d6-DMSO, ppm) to compound ATT appears to show the following data: δ H = 12.4 (S, 1 H, OH), 8.4 (S, 1 H, SH), All the reagents and starting materials as well as solvents 5.6–6.02 (4H, aromatic H), 5.2 (S, 2H, NH ). were purchased commercially and used without any further purification. Test sample was carbon steel which has the Specifications of 4‑amino‑5‑(4‑aminophenyl)‑4H‑1,2,4 following chemical compositions (%wt): 0.1 C, 0.335 Mn, ‑triazole‑3‑thiol (ATT ) 0.033 Si, 0.0067 S, 0.0056 P, 0.057 Al, 0.0476 Cu, 0.0201 Cr, 0.001 Co, 0.0007 Ti and the balance is F. Prior to each −1 Light gray crystals, m.p: 147–149 °C, FT-IR (KBr, cm ): measurement, the steel electrode was abraded with emery NH (3356, 3195), N–H (3137), aromatic C–H (2954), 2 str str papers with grade of 800–1500, washed ultrasonically with C=N (1647), aromatic C=C (1508, 1464), C=S (1248(, str str distilled water, acetone and alcohol, and dried under dry Yield: 63%. air. Testing electrolyte of 0.5 M HCl aqueous solution was prepared by diluting Analar Grade 37% hydrochloric acid Specifications of 4‑amino‑5‑(4‑((4‑nitrobenzylidene)amino) with ultra-pure water. All measurements were performed for phenyl)‑4H‑1,2,4‑triazole‑3‑thiol (ATT ) three times to obtain a satisfactory reproducibility. Light yellow crystals, m.p: 208–210  °C, FT-IR (KBr, Inhibitors diagnosis and measurements −1 cm): NH (3381–3287), N–H (3141), aromatic C–H 2 str str (2981), aliphatic C–H (2843), C=N (1607), aromatic str str The melting points of compounds were determined by Gal- C=C (1392), N O (1341–1516), yield: 79%. The spec- str 2 len Kamp (MFB-600) melting point apparatus. FT-IR spec- trum of H-NMR (400  MHz, d6-DMSO, ppm) show tra of compounds were recorded PERKIN ELMER SPEAC- the following data: δ H = 10.3 (S, 1 H, SH), 8.6 (S, 1H, −1 TUM-65 within the range 4000–400 cm using KBr Disk. 1 N=CH), 8–8.2 (8H, aromatic H), 4.9 (S, 2H, NH ). C- The H-NMR spectra were performed by Bruker 400 MHz NMR (400 MHz, d6-DMSO, ppm): δ C = 175 (CH=N), spectrophotometer with TMS as internal standard, and deu- 140(N–C–N), 148, 147, 140, 135, 133, 129, 127, 123, 120 terated DMSO was used as a solvent. The compounds were (Ar–CH). checked for their purity on silica gel TLC plates and the visualization of spots performed by using UV light. Specifications of 4‑amino‑5‑(4‑((4‑chlorobenzylidene) Synthesis of inhibitors amino)phenyl)‑4H‑1,2,4‑triazol‑3‑thiol (ATT ) −1 General method for the synthesis Dark gray crystals, m.p:149–151 °C, FT-IR (KBr, cm ): NH (3422–3276), N–H (3115), aromatic C–H (2942), of 4‑amino‑5‑(substituted‑phenyl)‑4H [1, 2, 4] 2 str str ‑triazole‑3‑thiols (ATT , ATT , ATT , ATT , ATT ) aliphatic C–H (2859), C=N (1610), C=C (1504), str str str 1 2 4 5 6 C–Cl (630), yield: 80%. The spectrum of H-NMR str Figure 1 shows the scheme of synthesis procedure of inhibi- 400 MHz, d6-DMSO, ppm to compound ATT appears to show the following data: δ H = 8.7 (S, 1 H, SH), 8.2 (S, 2H, tors. The compounds were synthesized by the fusion of substituted benzoic acid (0.01 mol) and thiocarbohydrazide N=CH), 7.2–8 (4H, aromatic H), 5.4 (S, 2H, NH ). C- NMR (400  MHz, d6-DMSO, ppm): δ C = 163 (CH=N), (0.015 mol), which contained in a round bottom flask and heated by a mantle until the content of the flask was melted 133(N–C–N), 141, 132, 129, 128, 127, 126, 123 (Ar–CH). [14, 15]. After cooling, the product was treated with sodium bicarbonate solution to neutralize the unreacted carboxylic Specifications of 4‑amino‑5‑(3,4‑diaminophenyl)‑4H‑1,2,4 acid, if any. It was then washed with water and collected by ‑triazole‑3‑thiole (ATT ) filtration. The completion of the reaction and the purity of −1 the compound were checked by TLC (mobile phase hex- Deep brown crystals, m.p: < 300 °C, FT-IR (KBr, cm ): ane: ethyl acetate 1:2). The product was recrystallized from NH (3363), N–H (3232), aromatic C–H (3151), 2 str str appropriate solvent to afford the title compounds. 1 3 International Journal of Industrial Chemistry (2019) 10:159–173 161 Fig. 1 Synthesis scheme of inhibitors 1 3 162 International Journal of Industrial Chemistry (2019) 10:159–173 C=N (1628), aromatic C=C (1526, 1486), C=S (1274), the resultant solution to room temperature. The resulting str str yield: 80%. yellow solid crystal 4-((4-nitrobenzylidene)amino)-5-(4- (((z)-4-nitrobenzylidene)amino)phenyl)-4H-1,2,4-tria- General method for synthesis of 4‑((4‑nitroben‑ zole-3-thiol was filtered washed and recrystallized from zylidene)amino)‑5‑(4‑ (((Z)‑4‑nitrobenzylidene)amino) appropriate solvent. The specifications of ATT3 were yel- −1 phenyl)‑4H‑1,2,4‑triazole‑3‑thiol (ATT ) low crystals, m.p:233–235 °C, FT-IR (KBr, cm ):NH 3 2 (3297), N–H (3122), aromatic C–H (2990), C=N str str str A mixture of the compound ATT (0.005 mol, 1.03 g) in (1599), C=C (1442), N O (1343–1515), yield: 79%. 2 str 2 str 15 ml of absolute ethanol with a solution of 4-nitroben- The spectrum of H-NMR (400 MHz, d6-DMSO, ppm) of zaldehyde (0.01 mol, 1.51 g) in 10 ml ethanol with five ATT appears to show the following data: δ H = 11.9 (S, drops of glacial acetic acid as a catalyst and refluxed the 1 H, SH), 8.6 (S, 2H, N=CH), 7.6–8.2 (12H, aromatic H). mixture for 13  h [16]. The completion of the reaction C-NMR (400 MHz, d6-DMSO, ppm): δC = 175 (CH=N), and the purity of the compound were checked by TLC 130(N–C–N), 147, 128, 123, 112 (Ar–CH). Figures 2, 3, (mobile phase hexane: ethyl acetate 1:2) and then cooled 4 and 5 show selected FT-IR and NMR curves of some Fig. 2 FT-IR curve of ATT Fig. 3 FT-IR curve of ATT 1 3 International Journal of Industrial Chemistry (2019) 10:159–173 163 Fig. 4 H-NMR spectra of compound ATT Fig. 5 H-NMR spectra of compound ATT 1 3 164 International Journal of Industrial Chemistry (2019) 10:159–173 Table 1 Physical property of the syntheses compounds Compound R R R R m.p. (°C) Color Molecular formula Res. solvent % Yield 1 2 3 ATT H OH H H 216–218 White C H N OS Ethanol/water 60 1 8 8 4 ATT H NH NH H >300 Deep brown C H N S Ethanol/water 81 2 2 2 8 10 6 ATT – – – – 233–235 Yellow C H N O S Ethanol/water 79 3 22 15 7 4 ATT NO – – – 208–210 Light yellow C H N O S Ethanol/water 79 4 2 15 12 6 2 ATT Cl – – – 149–151 Dark gray C H N SCl Ethanol/water 80 5 15 12 5 ATT H NH H H 147–149 Light gray C H N S Ethanol/water 63 6 2 8 9 5 Table 2 Corrosion rate of low carbon steel alloy and inhibitor effi- Results and discussion ciency of synthesis compounds corrosion in 0.5 M hydrochloric acid solution at 30 °C and 0.001 M inhibitor concentration Weight loss measurements Compounds Formula Corrosion rate Inhibitor (g m  day) efficiency Weight or mass loss technique is a very common and con- (%) ventional method for corrosion rate evaluation. It was used ATT C H N OS 24.82 69.17 in many researches as a powerful tool for metal loss estima- 1 8 8 4 ATT C H N S 25.79 67.97 tion [17–19]. Table 2 summarizes the results of weight loss 2 8 10 6 ATT C H N O S 28.17 65.02 technique of the low carbon steel alloy corrosion in 0.5 M 3 22 15 7 4 ATT C H N O S 39.92 50.43 hydrochloric acid solution at 30 °C and 0.001 M inhibitor 4 15 12 6 2 ATT C H N SCl 15.18 81.16 concentration. The values of corrosion rate were evaluated 5 15 12 5 ATT C H N S 31.86 60.43 using the following equation [20]: 6 8 9 5 weight loss (g) CR = (7) area (m )× time (day) synthesis inhibitors, while Table 1 collects the physical properties of compounds. From the corrosion rate, the percentage inhibition effi- ciency of weight loss experiments (IE) was calculated using Weight loss measurements the following equation [21]: CR − CR uninibit inhibit Rectangular test specimens, with dimensions IE = × 100 (8) CR 3 cm × 1 cm × 0.1 cm, were made from low carbon steel, uninhibit whose chemical composition as listed above. Samples were where CR and CR are the corrosion rates in the uninhibit inhibit washed with running tap water followed by distilled water, absence and presence of inhibitors, respectively. Table 2 dried with clean tissue, immersed in acetone and alcohol, shows that inhibitor efficiency ranged from 50.43 to 81.16%. dried again with clean tissue, then, kept in desiccators over ATT shows the higher performance. In order to have a clear silica gel bed until use. The dimensions of each sample were vision of ATT behavior, the effect of inhibitor concentra- measured with a vernier to second decimal of millimeter tion and temperature was studied. The results were shown in and accurately weighted to the 4th decimal of gram. The Table 3. Corrosion rate increased with increase in tempera- metal samples were completely immersed each in 500 ml ture and decrease in inhibitor concentration. While inhibitor of uninhibited and inhibited 0.5 M HCl solution contained efficiency increased with both increasing inhibitor concen- in a conical flask. They were exposed for a period of 3 h at tration and temperature. the desired temperature and inhibitor concentration. Then, the metal samples were cleaned, washed with running tap water followed by distilled water dried with clean tissue then Eec ff t of inhibitor concentration and adsorption immersed in acetone and alcohol and dried again. Weight isotherm −2 −1 losses in gm m  day (gmd) were determined in the pres- ence and absence of inhibitor. At the beginning, all inhibi- As shown in Table 3, at specific experimental temperature, tors were tested at inhibitor concentration of 0.001 M and corrosion rate of steel decreases with an increase in ATT 30 °C to select the best one. Then, the inhibitor with higher concentration. Values of inhibitor efficiency increase with efficiency was evaluated at different temperature (30–60 °C) increasing of ATT concentration approach the maximum −3 −3 −3 and inhibitor concentration of 1 × 10 , 2 × 10 , 3 × 10 , value of 95.8% at higher level of temperature and inhibitor −3 and 4 × 10  M. 1 3 International Journal of Industrial Chemistry (2019) 10:159–173 165 Table 3 Corrosion rate of low carbon steel alloy and inhibitor effi- in acidic media is commonly agreed to be adsorption on the ciency of synthesis ATT corrosion in 0.5 M hydrochloric acid solu- metal surface. This includes the assumption that the corrosion tion at different conditions reactions are prevented from occurring over the area or active Test number Inhibitor Tempera- Corrosion Inhibitor sites of the metal surface protected by adsorbed inhibitor mol- concentration ture (°C) rate (g/m . efficiency ecules, whereas these corrosion reactions occurred generally (M) day) (%) on the inhibitor-free active sites [22]. The surface coverage 1 0 20 33.99 – (ϴ = IE/100) data are very valuable in discussing the adsorp- 2 0 30 80.52 – tion features. Surface covered is related to the concentration 3 0 40 142.96 – of inhibitor at constant temperature by well-known adsorption 4 0 50 419.21 – isotherm relationships that evaluated at equilibrium condition. −3 5 1 × 10 20 9.57 71.8 The dependence of θ on the concentration of ATT concentra- −3 6 2 × 10 8.36 75.4 tion was tested graphically by fitting it to Langmuir adsorption −3 7 3 × 10 6.21 81.7 isotherm that assume a metal surface contains a fixed num- −3 8 4 × 10 5.06 85.1 ber of adsorption sites and each site took only one adsorbed −3 9 1 × 10 30 15.17 81.2 molecule. Figure 6 shows linear plots for C/ϴ versus C with −3 2 10 2 × 10 15.05 81.3 average R = 0.999 correlation coefficient, suggestion that the −3 11 3 × 10 11.23 86.1 adsorption follows the Langmuir adsorption isotherm [23]: −3 12 4 × 10 10.75 86.6 C 1 −3 16 1 × 10 40 21.27 85.1 = + C (9) −3 14 2 × 10 18.47 87.1 −3 15 3 × 10 17.66 87.7 where C is the inhibitor concentration, K adsorption equi- −3 16 4 × 10 16.83 88.3 librium constant, representing the degree of adsorption, in −3 17 1 × 10 50 22.57 94.6 other words the higher the value of K specifies that the ATT −3 18 2 × 10 20.52 95.1 molecules are strongly adsorbed on the metal surface. The −3 19 3 × 10 18.91 95.5 slops of Langmuir adsorption lines are near unity meaning −3 20 4 × 10 17.66 95.8 that each inhibitor molecules occupies one active site on the metal surface. The standard adsorption free energy (ΔG ) was calculated ads concentration. This increase in inhibitor performance with using the following equation [23]: temperature is apparently due to an increase in chemisorption ΔG 1 ads of the inhibitor. Crucial step in the action of inhibitor behavior K = exp − (10) 55.5 RT Fig. 6 Langmuir adsorption isotherms of ATT on the steel surface in 0.5 M HCl solution at different temperatures 1 3 166 International Journal of Industrial Chemistry (2019) 10:159–173 Table 4 Adsorption −1 2 −1 T (°C) K (M ) Slop R ΔG (kJ mol ) ΔH ΔS ads ads ads parameters of ATT at different −1 −1 −1 (kJ mol ) (kJ mol  K ) temperatures 20 2.5 × 10 1.09 0.99 − 28.84 79.1 0.37 30 5 × 10 1.1 0.99 − 31.57 40 17.2 × 10 1.1 1.00 − 35.84 50 47.6 × 10 1.04 1.00 − 39.71 Average value 18.1 × 10 1.08 0.99 − 33.99 where 55.5 are the concentration of water in solution increasing experimental temperature and ATT adsorbed expressed in molar, R is gas constant, and T absolute tem- according to chemical mechanism. The value of ΔH was ads perature. Table  4 shows the adsorption parameters. The obtained from Van’t Hoff equation (Eq.  11) [26] that drawn average value of standard adsorption free energy was in Fig. 7. This figure shows good linear fitting. −1 ° − 33.9  kJ  mol . The negative value of ΔG ensures the The values of adsorption thermodynamic parameters for ads spontaneous adsorption process and stability of the adsorbed inhibitor can offer valuable information about the mechanism layer on the metal surface. Commonly, value of ΔG up of corrosion inhibition. The endothermic adsorption process ads −1 to − 20 kJ mol is consistent with electrostatic interaction (ΔH > 0) is ascribed unequivocally to chemisorption, while ads between the charged molecules and the charged metal (phys- generally, an exothermic adsorption process (ΔH < 0) may ads −1 ical adsorption) while those around − 40 kJ mol or higher involve either physisorption or chemisorption or a mixture of are associated with chemical adsorption as a result of shar- both processes. In the present work; the positive sign of heat of ing or transfer of electrons from the molecules to the metal adsorption (ΔH ) indicates that the adsorption of inhibitor is ads surface to form a coordinate type of bond [24]. While other an endothermic process and the adsorption is chemisorption. researchers suggested that the range of standard adsorption This result agrees with above discussion. free energy of chemical adsorption processes for inhibitor While entropy of adsorption value (ΔS ) was obtained ads −1 in aqueous media lies between –21 and –42 kJ mol [25]. from Eq. 12 at average value of ΔG and average temperature. ads Therefore, for present work, the values of adsorption heat ΔH ads have been considered within the range of chemical adsorp- ln K =− + constant (11) RT tion. It was also observed from Table 4, limited increase in the absolute value of ΔG with an increase in temperatures, ads ΔH −ΔG ads ads indicating that the adsorption was somewhat favorable with ΔS = (12) ads Fig. 7 Van’t Hoff equation of ATT on the steel surface in 0.5 M HCl solution at different temperatures 1 3 International Journal of Industrial Chemistry (2019) 10:159–173 167 These results, which showed in Table 4, appear to contrast and acid concentration were evaluated from an Arrhenius- to that normally accepted for adsorption phenomena. It is type plot (Eq. 13) and transition state theory (Eq. 14) [34]: well known that adsorption is an exothermic with a negative sign of adsorption heat accompanied by reduction entropy CR = A exp − (13) RT of adsorption [27]. In aqueous solution, the adsorption of organic molecules commonly is accompanied by desorption ΔS ΔH RT a a of water molecules. The adsorption of organic molecules at CR = exp exp − (14) Nh R RT the metal–solution interface is a substitution adsorption pro- cess [28]. This means that each adsorbed molecule of ATT where CR is the corrosion rate, A is the Arrhenius constant, on metal surface displaces water molecules from the surface. R is the universal gas constant, h is Plank’s constant, and The thermodynamic values of ΔS are the algebraic sum ads N is Avogadro’s number. As shown in Fig.  8, plot of ln of the adsorption of ATT molecules and the desorption of (CR) versus 1/T gives straight lines with slopes of ΔE /R water molecules. Therefore, the increase in entropy is attrib- and intercept can be used for evaluating of A. While, Fig. 9 uted to the increase in solvent entropy [29, 30]. Chaitra et al. shows a liner straight lines of ln (CR/T) versus 1/T slopes [31] studied the effect of newly synthesized thiazole hydra- of ΔH /R and intercept can be used for evaluating of ΔS . a a zones on the corrosion of mild steel in 0.5 M hydrochloric Table 5 illustrates the activation parameters for steel cor- acid. Adsorption of the inhibitors followed Langmuir iso- rosion reaction acidic solution at different conditions. It therm and addition of inhibitors simultaneously decreased is clearly shown that the activation energy and enthalpy corrosion rate. vary in similar way. The activation energy and activation Tezcan et al. [32] investigated newly synthesized sulfur enthalpy for uninhibited acid were higher than inhibited one. containing Schiff base (4-((thiophene-2-ylmethylene)amino) The decrease in the value of activation energy and enthalpy benzamide) compound. Inhibition performance on mild steel appears to be unreliable. However, this may be attributed to in 1.0 M HCl solution was studied. The results showed that increase in metal surface coverage by the inhibitor molecules the highest inhibitor efficiency of 96.8%. at higher temperatures and also suggested that the formation Messali et  al. [33] studied the inhibition effect and rate of the chemisorbed layer may be greater than its rate of adsorption behavior of 4-((2,3-dichlorobenzylidene)amino)- dissolution at higher temperatures [35]. Other researchers 3-methyl-1H-,2,4-triazole-5(4H)-thione on mild steel in 1 M [36] found that some anticorrosion materials in the acidic HCl solution. The inhibitor can be adsorbed onto surface by solutions alter the kinetics of corrosion reaction by propos- both physical and chemical means obeys Langmuir adsorp- ing alternate reaction paths with lower activation energies. tion isotherm. Table 4, illustrates also that all the values of frequency factor are lower than uninhibited one, which is benefit for inhibit- Eec ff t of temperature and activation parameters ing the corrosion rate of steel. It is also well known that the increase in A raises the corrosion rate of steel [37]. Further- As shown in Table 5, at specific experimental tempera- more, at all cases, the values of E are higher than ΔH by a a a ture, corrosion rate of steel decreases with an increase value which approximately equal to RT, which confirm the in ATT concentration. The kinetics of the ATT action 5 5 thermodynamic principle of the reactions are characterized can be realized by comparing the activation parameters by following equation [38]: in the presence and absence of the inhibitor. Activation E −ΔH = RT energy (E ), enthalpy of activation (ΔH ), and entropy of a a (15) a a activation (ΔS ) for both uninhibited and inhibited 0.5 M The negative value of ΔS for both cases of absence hydrochloric acid steel corrosion at different temperatures and presence of inhibitor indicates that activated complex in the rate determining step denotes an association rather than a dissociation step, which means a decrease in disor- Table 5 Activation parameters for steel corrosion reaction in uninhib- der, takes place during the course of transition from reac- ited and inhibited 0.5 M HCl tant to the activated complex [39]. −1 −1 Khan et  al. [ 4 0] studied the inhibi - C (M) A (gmd) E (kJ mol ) ΔH (kJ mol ) ΔS a a a −1 −1 (J mol  K ) tory effect of two Schiff bases 3-(5-methoxy- 2-hydr oxybenzylideneamino)-2-(-5-me t hoxy-2-hy- 0 7.3 × 10 63.67 61.12 − 7.98 dr o xyphen y l)-2,3-dih ydr oq uinazoline-4(1H)-one − 3 5 1 × 10 1.3 × 10 23.09 20.54 − 155.22 (MMDQ), and 3-(5-nitro-2-hydroxybenzylideneamino)- − 3 5 2 × 10 1.2 × 10 23.04 20.48 − 156.21 2(5-nitro-2-hydroxyphenyl)-2,3-dihydroquinazoline- − 3 6 3 × 10 1.6 × 10 30.09 27.54 − 134.74 4(1H)-one (NNDQ) on the corrosion of mild steel in 1 M − 3 6 4 × 10 5.2 × 10 33.36 30.81 − 124.87 1 3 168 International Journal of Industrial Chemistry (2019) 10:159–173 Fig. 8 Arrhenius plots of steel in uninhibited and inhibited 0.5 M HCl Fig. 9 Transition—state plots of steel in uninhibited and inhib- ited 0.5 M HCl hydrochloric acid. The effect of temperature on the inhibi- in the inhibitor-free acid solution can be attributed to its tion process in 1 M HCl with the addition of inhibitors was chemisorption on mild steel surface. Similar results were investigated at a temperature range of 30–60 °C. Corrosion obtained by Obaid et al. [41]. The lower values of activa- rate increased with raise in temperature, and the efficien- tion energy in the presence of the inhibitors and the gen- cies of the investigated inhibitors are strongly temperature eral increase in their inhibitor efficiencies with increasing dependent. Enthalpy, entropy and enthalpy of activation temperatures are indicative of chemisorption (interaction were calculated. The result showed that Enthalpy of activa- of unshared electron pairs in the adsorbed molecule with tion for solution containing inhibitors are lower than those the metal) of these compounds on the steel surface. 1 3 International Journal of Industrial Chemistry (2019) 10:159–173 169 electronegativity scale and η is 0 eV/mol, respectively Quantum chemical and theoretical calculations Fe [46]. The fraction of electrons transferred from inhibitor to the steel surface (ΔN) was calculated and listed in Table 3. Quantum chemical calculations have been widely used to investigate reaction mechanism of inhibition process [42]. It is According to Lukovits [47], if ΔN < 3.6, the inhibition effi- ciency increased with increasing electron-donating ability also verified to be a very important tool for studying corrosion control mechanism and to obtain insight view to the inhibition at the steel surface. In this study, synthesis inhibitors were the donor of electrons, and the metal surface was the accep- mechanism of ATT inhibitor. By using of quantum chemical calculations, the structural parameters, such as HOMO (high- tor. This result supports the assertion that the adsorption of inhibitors on the steel surface can occur on the bases of est occupied molecular orbital), LUMO (lowest unoccupied molecular orbital), dipole moment (µ) and fraction of electron donor–acceptor interactions between the Л electrons of the compound and the vacant d-orbitals of the metal surface. transferred (ΔN), were calculated. The structures of inhibi- tors were optimized by ChemoOffice version 14 software. Fig- The dipole moment (µ) is also a significant factor and there is lack of agreement on the relation between µ and inhibitive ure 10 shows the optimized structures, HOMO and the LUMO structure of all synthesis inhibitors. The calculated quantum performance. Some researchers founded that a low µ value will favor accumulation of the inhibitor on metal surface and chemical properties are summarized in Table 6. As shown in Fig. 10, both the HOMO and LUMO distributions of synthesis increasing the inhibitor performance [48, 49]. While others researches suggested that a high value of dipole moment inhibitors were concentrated mainly over sulfur and nitrogen atoms. E and E characterized the electron-receiving associated with the dipole–dipole interaction of inhibitor LUMO HOMO and metal surface can enhance the adsorption on the metal and—donating capability of synthesis inhibitors. In general, a low E implies that inhibitors tend to accept electrons, surface and increasing efficiency [50, 51]. In present work, LUMO the value of µ for ATT was the lowest one among all tested while a high E refer to a strong electron donating [43]. HOMO 5 Energy gap (ΔE) specifies the chemical stability of inhibi- inhibitors that agree with the first opinion. The anodic oxi- dation behavior of steel in HCl acid can be explained by tors, and a lower energy gap value typically leads to higher adsorption on the metal surface, resulting in greater inhibition following reaction [52]: efficiencies [44]. The order of inhibition efficiency was ATT − − Fe + Cl ↔ (FeCl ) (18) ads > ATT > ATT > ATT > ATT > ATT , while the order of 5 1 2 3 6 4 − − energy gap was ATT > ATT > ATT > ATT > ATT > ATT 5 4 3 2 6 (FeCl ) ↔ (FeCl) + e (19) ads ads . The differences in orders may be attributed to close inhibi- tion efficiencies of inhibitors. As seen in Table  2, the value of + − (FeCl) → FeCl + e (20) ads ads inhibitor efficiencies were 60.43, 65.02, 67.97, and 69.17% for ATT , ATT , ATT and ATT , respectively, which is very 6 3 2 1 + 2+ − close range. However, still ATT has the lower energy gap that FeCl → Fe + Cl 5 (21) ads confirms the experimental work. The number of transferred While the cathodic hydrogen evolution reaction can be electrons (ΔN) was also calculated according to Eq. 16 [45]. written as: X − X Fe inh ΔN = (16) 2( +  ) + + Fe inh Fe + H ↔ FeH (22) ads where X and X denote the absolute electronegativity of Fe inh iron and the MLH inhibitor molecule, respectively; η and Fe − FeH + e → (FeH) (23) ads ads η denote the absolute hardness of iron and the inhibitor inh molecule, respectively. These quantities are related to elec- + − (FeH) + H + e → Fe + H (24) ads 2 tron affinity (A ) and ionization potential (I) that both related According to the structures of the synthesis inhibitors, in turn to E and E : HOMO LUMO there are the free electron pairs on N and S that able to − E + E forming **σ-bond with iron [53]. In addition, in case of I + A HOMO LUMO X = = acidic solution, electrostatic interaction is possible between 2 2 (17) the negatively charge of iron surface that may be brought − E − E HOMO LUMO I − A = = about by specific adsorption of Cl anions and the posi- 2 2 tively charged inhibitor. The essential effect of inhibitors is due to the presence of free electron pairs in the N and S Values of X and η were considered by using the val- atoms, p-electrons on the aromatic ring, type of interaction ues of I and A gained from quantum chemical calculation. with the steel surface, and metallic complexes formation. It The theoretical value of X is 7 according to Pearsons Fe 1 3 170 International Journal of Industrial Chemistry (2019) 10:159–173 Fig. 10 Optimized chemical structures of six inhibitors and HOMO–LUMO distribution is well known that steel has coordination affinity toward N and p-electrons of aromatic rings [54]. In the present case, and S bearing ligand. Therefore, adsorption on metal sur- synthesis inhibitors, there are unshared electron pairs on N face can be ascribed to coordination through heteroatoms and S, able to form σ-bond with steel. 1 3 International Journal of Industrial Chemistry (2019) 10:159–173 171 Table 6 Quantum chemical Compounds E (eV) E (eV) ΔE (eV) ΔN Dipole (debye) HOMO LUMO parameters for inhibitors ATT − 7.654 − 1.068 6.586 − 0.401 4.685 ATT − 7.186 − 2.160 5.026 − 0.462 5.691 ATT − 7.511 − 2.613 4.898 − 1.013 5.855 ATT − 7.683 − 4.574 3.109 0.115 6.942 ATT − 7.654 − 5.322 2.332 − 0.303 4.362 ATT − 7.605 − 1.068 6.537 0.407 6.124 containing tetrafluoroborate anion on MSin acidic medium. J Mol Conclusion Liq 211:105–118 3. Khadiri R, Bekkouche K, Aouniti A, Hammouti B, Benchat N, The following points can be concluded from present work: Bouachrine M, Solmaz R (2016) Gravimetric, electrochemical and quantum chemical studies of some pyridazine derivatives as corrosion inhibitors for mild steel in 1 M HCl solution. J Taiwan 1. The six inhibitors were synthesis and test successfully Inst Chem Engg 58:552–564 as corrosion inhibitors for steel in acidic solution. 4. Khadom A, Yaro A, Altaie A, Kaduim A (2009) Electro- 2. Experimental results show that the order of inhibition chemical, activations and adsorption studies for the corrosion efficiency was ATT > ATT > ATT > ATT > ATT of low carbon steel in acidic media. Port Electrochem Acta 5 1 2 3 27(2009):699–712 > ATT . 6 4 5. Musa A, Kaduim A, Abu Bakar M, Takriff M, Daud Abdul 3. The addition of ATT to the 0.5 M HCl solution at dif- Razak, Kamarudin Siti Kartom (2010) On the inhibition of mild ferent temperature and inhibitor concentration reduces steel corrosion by 4-amino-5-phenyl-4H-1, 2,4-trizole-3-thiol. corrosion of mild steel with inhibitor efficiency exceed Corros Sci 52:526–533 6. Khadom A, Musa A, Kaduim A, Abu Bakar M, Takriff M (2010) 95%. Adsorption kinetics of 4-Amino-5-Phenyl-4H-1, 2, 4-Triazole- 4. 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Corros Sci 52:3033–3341 Publisher’s Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 1 3 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png International Journal of Industrial Chemistry Springer Journals

Synthesis and investigations of heterocyclic compounds as corrosion inhibitors for mild steel in hydrochloric acid

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Springer Journals
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Copyright © 2019 by The Author(s)
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Chemistry; Industrial Chemistry/Chemical Engineering; Polymer Sciences; Nanochemistry; Environmental Chemistry
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2228-5970
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2228-5547
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10.1007/s40090-019-0181-8
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Abstract

The corrosion inhibition of mild steel in 0.5 M hydrochloric acid by six synthesized heterocyclic compounds was studied using weight loss measurements. The inhibition efficiency exceeded 95%. The excellent inhibitor performance was attrib- uted to the formation of protection adsorption films on the steel surface. The structures of compounds were confirmed by Fourier transform infrared and nuclear magnetic resonance analysis. The adsorption of inhibitor on steel surface followed the Langmuir adsorption isotherm. Quantum chemical calculations were also adopted to clarify the inhibition mechanism. Keywords Steel · Weight loss · FT-IR · Corrosion · Inhibition · Synthesis Introduction between the aggressive solution and metal surface hinder the dissolution of the metal and reduce corrosion damages [7, Iron and its alloys are widely used as a constructional mate- 8]. Organic inhibitors containing heteroatoms, such as N, O, rial in several industrial applications, such as petroleum, S and P, have proven practically and theoretically to act as power plants, chemical industries due to its high mechani- efficiently corrosion inhibitors in a wide range of acidic solu- cal strength, easy fabrication and low cost [1, 2]. The variety tions [9, 10]. The efficiency of these inhibitors can be attrib- of applications make steel in contact with various corrosive uted to their high polarizability and lower electronegativity; environments, such as acidic solutions during the processes so that these atoms and the functional groups can cover large of etching, acid pickling, acid descaling, acid cleaning, oil metallic surface areas and easily electrons transfer to the well acidification. [3 ]. In acidic media, steel alloys react empty orbitals of atoms [11]. In addition, nitrogen-contain- easily and converted from metallic to ionic state forming ing organic inhibitors is good anticorrosion materials for a huge economic loss. Therefore, there is a necessary need metals in hydrochloric acid, while compounds having sulfur to develop some excellent corrosion controlling methods. atoms act as good inhibitors in sulfuric acid. Compounds One of the methods is the use of corrosion inhibitors [4–6]. holding nitrogen and sulfur behave as perfect corrosion Corrosion inhibitors can be classified according to chemical inhibitors for both media [12]. The action of any inhibitor structure, method of action, etc. One of the common classes for any specific metallic alloys in sever acidic environments is organic corrosion inhibitors that obtained the highest depends on the nature of the characteristic inhibitor film importance due to their ease synthesis at relatively low cost accumulated on the metal surface and the number and nature and high protection ability. The method of prevention can of adsorption centers contributing in the adsorption process. be ascribed to the adsorption on the steel surface and imped- In general, the inhibition performance of the inhibitors hav- ing the active corrosion sites. Formation of protective layer ing different heteroatoms follows the reverse order of their electronegativities, so that in S, N, O and P, the inhibition performance followed in the order of: O < N < S < P [13]. * Anees A. Khadom The existence of organic materials in the acidic solutions aneesdr@gmail.com commonly alters the electrochemical behavior of the acidic Department of Chemistry, College of Science, University environments. In other words, it decreases the aggressive- of Diyala, Baquba City 32001, Diyala Governorate, Iraq ness of the solution. The most regularly used heterocyclic Department of Chemical Engineering, College compounds have sulfur (S), phosphorus (P), nitrogen (N) or of Engineering, University of Diyala, Baquba City 32001, oxygen (O) heteroatoms, and these effectively take part in Diyala Governorate, Iraq Vol.:(0123456789) 1 3 160 International Journal of Industrial Chemistry (2019) 10:159–173 adsorption centers. Therefore, in this study, six heterocyclic Specifications of 4‑(4‑amino‑5‑mercapto‑4H‑1,2,4‑tria‑ compounds were syntheses and selected to act as corrosion zole‑3‑yl) phenol (ATT ) inhibitors for steel in hydrochloric acid solution. −1 White crystals, m.p: 216–218  °C, FT-IR (KBr, cm ): OH (3524(, NH (3356), N–H (3144), aromatic C–H str 2 str str Experimental work (3090), C=N (1654), aromatic C=C (1505, 1409), C=S str str (1244(, Yield: 60%. The spectrum of H-NMR (400 MHz, Materials and test conditions d6-DMSO, ppm) to compound ATT appears to show the following data: δ H = 12.4 (S, 1 H, OH), 8.4 (S, 1 H, SH), All the reagents and starting materials as well as solvents 5.6–6.02 (4H, aromatic H), 5.2 (S, 2H, NH ). were purchased commercially and used without any further purification. Test sample was carbon steel which has the Specifications of 4‑amino‑5‑(4‑aminophenyl)‑4H‑1,2,4 following chemical compositions (%wt): 0.1 C, 0.335 Mn, ‑triazole‑3‑thiol (ATT ) 0.033 Si, 0.0067 S, 0.0056 P, 0.057 Al, 0.0476 Cu, 0.0201 Cr, 0.001 Co, 0.0007 Ti and the balance is F. Prior to each −1 Light gray crystals, m.p: 147–149 °C, FT-IR (KBr, cm ): measurement, the steel electrode was abraded with emery NH (3356, 3195), N–H (3137), aromatic C–H (2954), 2 str str papers with grade of 800–1500, washed ultrasonically with C=N (1647), aromatic C=C (1508, 1464), C=S (1248(, str str distilled water, acetone and alcohol, and dried under dry Yield: 63%. air. Testing electrolyte of 0.5 M HCl aqueous solution was prepared by diluting Analar Grade 37% hydrochloric acid Specifications of 4‑amino‑5‑(4‑((4‑nitrobenzylidene)amino) with ultra-pure water. All measurements were performed for phenyl)‑4H‑1,2,4‑triazole‑3‑thiol (ATT ) three times to obtain a satisfactory reproducibility. Light yellow crystals, m.p: 208–210  °C, FT-IR (KBr, Inhibitors diagnosis and measurements −1 cm): NH (3381–3287), N–H (3141), aromatic C–H 2 str str (2981), aliphatic C–H (2843), C=N (1607), aromatic str str The melting points of compounds were determined by Gal- C=C (1392), N O (1341–1516), yield: 79%. The spec- str 2 len Kamp (MFB-600) melting point apparatus. FT-IR spec- trum of H-NMR (400  MHz, d6-DMSO, ppm) show tra of compounds were recorded PERKIN ELMER SPEAC- the following data: δ H = 10.3 (S, 1 H, SH), 8.6 (S, 1H, −1 TUM-65 within the range 4000–400 cm using KBr Disk. 1 N=CH), 8–8.2 (8H, aromatic H), 4.9 (S, 2H, NH ). C- The H-NMR spectra were performed by Bruker 400 MHz NMR (400 MHz, d6-DMSO, ppm): δ C = 175 (CH=N), spectrophotometer with TMS as internal standard, and deu- 140(N–C–N), 148, 147, 140, 135, 133, 129, 127, 123, 120 terated DMSO was used as a solvent. The compounds were (Ar–CH). checked for their purity on silica gel TLC plates and the visualization of spots performed by using UV light. Specifications of 4‑amino‑5‑(4‑((4‑chlorobenzylidene) Synthesis of inhibitors amino)phenyl)‑4H‑1,2,4‑triazol‑3‑thiol (ATT ) −1 General method for the synthesis Dark gray crystals, m.p:149–151 °C, FT-IR (KBr, cm ): NH (3422–3276), N–H (3115), aromatic C–H (2942), of 4‑amino‑5‑(substituted‑phenyl)‑4H [1, 2, 4] 2 str str ‑triazole‑3‑thiols (ATT , ATT , ATT , ATT , ATT ) aliphatic C–H (2859), C=N (1610), C=C (1504), str str str 1 2 4 5 6 C–Cl (630), yield: 80%. The spectrum of H-NMR str Figure 1 shows the scheme of synthesis procedure of inhibi- 400 MHz, d6-DMSO, ppm to compound ATT appears to show the following data: δ H = 8.7 (S, 1 H, SH), 8.2 (S, 2H, tors. The compounds were synthesized by the fusion of substituted benzoic acid (0.01 mol) and thiocarbohydrazide N=CH), 7.2–8 (4H, aromatic H), 5.4 (S, 2H, NH ). C- NMR (400  MHz, d6-DMSO, ppm): δ C = 163 (CH=N), (0.015 mol), which contained in a round bottom flask and heated by a mantle until the content of the flask was melted 133(N–C–N), 141, 132, 129, 128, 127, 126, 123 (Ar–CH). [14, 15]. After cooling, the product was treated with sodium bicarbonate solution to neutralize the unreacted carboxylic Specifications of 4‑amino‑5‑(3,4‑diaminophenyl)‑4H‑1,2,4 acid, if any. It was then washed with water and collected by ‑triazole‑3‑thiole (ATT ) filtration. The completion of the reaction and the purity of −1 the compound were checked by TLC (mobile phase hex- Deep brown crystals, m.p: < 300 °C, FT-IR (KBr, cm ): ane: ethyl acetate 1:2). The product was recrystallized from NH (3363), N–H (3232), aromatic C–H (3151), 2 str str appropriate solvent to afford the title compounds. 1 3 International Journal of Industrial Chemistry (2019) 10:159–173 161 Fig. 1 Synthesis scheme of inhibitors 1 3 162 International Journal of Industrial Chemistry (2019) 10:159–173 C=N (1628), aromatic C=C (1526, 1486), C=S (1274), the resultant solution to room temperature. The resulting str str yield: 80%. yellow solid crystal 4-((4-nitrobenzylidene)amino)-5-(4- (((z)-4-nitrobenzylidene)amino)phenyl)-4H-1,2,4-tria- General method for synthesis of 4‑((4‑nitroben‑ zole-3-thiol was filtered washed and recrystallized from zylidene)amino)‑5‑(4‑ (((Z)‑4‑nitrobenzylidene)amino) appropriate solvent. The specifications of ATT3 were yel- −1 phenyl)‑4H‑1,2,4‑triazole‑3‑thiol (ATT ) low crystals, m.p:233–235 °C, FT-IR (KBr, cm ):NH 3 2 (3297), N–H (3122), aromatic C–H (2990), C=N str str str A mixture of the compound ATT (0.005 mol, 1.03 g) in (1599), C=C (1442), N O (1343–1515), yield: 79%. 2 str 2 str 15 ml of absolute ethanol with a solution of 4-nitroben- The spectrum of H-NMR (400 MHz, d6-DMSO, ppm) of zaldehyde (0.01 mol, 1.51 g) in 10 ml ethanol with five ATT appears to show the following data: δ H = 11.9 (S, drops of glacial acetic acid as a catalyst and refluxed the 1 H, SH), 8.6 (S, 2H, N=CH), 7.6–8.2 (12H, aromatic H). mixture for 13  h [16]. The completion of the reaction C-NMR (400 MHz, d6-DMSO, ppm): δC = 175 (CH=N), and the purity of the compound were checked by TLC 130(N–C–N), 147, 128, 123, 112 (Ar–CH). Figures 2, 3, (mobile phase hexane: ethyl acetate 1:2) and then cooled 4 and 5 show selected FT-IR and NMR curves of some Fig. 2 FT-IR curve of ATT Fig. 3 FT-IR curve of ATT 1 3 International Journal of Industrial Chemistry (2019) 10:159–173 163 Fig. 4 H-NMR spectra of compound ATT Fig. 5 H-NMR spectra of compound ATT 1 3 164 International Journal of Industrial Chemistry (2019) 10:159–173 Table 1 Physical property of the syntheses compounds Compound R R R R m.p. (°C) Color Molecular formula Res. solvent % Yield 1 2 3 ATT H OH H H 216–218 White C H N OS Ethanol/water 60 1 8 8 4 ATT H NH NH H >300 Deep brown C H N S Ethanol/water 81 2 2 2 8 10 6 ATT – – – – 233–235 Yellow C H N O S Ethanol/water 79 3 22 15 7 4 ATT NO – – – 208–210 Light yellow C H N O S Ethanol/water 79 4 2 15 12 6 2 ATT Cl – – – 149–151 Dark gray C H N SCl Ethanol/water 80 5 15 12 5 ATT H NH H H 147–149 Light gray C H N S Ethanol/water 63 6 2 8 9 5 Table 2 Corrosion rate of low carbon steel alloy and inhibitor effi- Results and discussion ciency of synthesis compounds corrosion in 0.5 M hydrochloric acid solution at 30 °C and 0.001 M inhibitor concentration Weight loss measurements Compounds Formula Corrosion rate Inhibitor (g m  day) efficiency Weight or mass loss technique is a very common and con- (%) ventional method for corrosion rate evaluation. It was used ATT C H N OS 24.82 69.17 in many researches as a powerful tool for metal loss estima- 1 8 8 4 ATT C H N S 25.79 67.97 tion [17–19]. Table 2 summarizes the results of weight loss 2 8 10 6 ATT C H N O S 28.17 65.02 technique of the low carbon steel alloy corrosion in 0.5 M 3 22 15 7 4 ATT C H N O S 39.92 50.43 hydrochloric acid solution at 30 °C and 0.001 M inhibitor 4 15 12 6 2 ATT C H N SCl 15.18 81.16 concentration. The values of corrosion rate were evaluated 5 15 12 5 ATT C H N S 31.86 60.43 using the following equation [20]: 6 8 9 5 weight loss (g) CR = (7) area (m )× time (day) synthesis inhibitors, while Table 1 collects the physical properties of compounds. From the corrosion rate, the percentage inhibition effi- ciency of weight loss experiments (IE) was calculated using Weight loss measurements the following equation [21]: CR − CR uninibit inhibit Rectangular test specimens, with dimensions IE = × 100 (8) CR 3 cm × 1 cm × 0.1 cm, were made from low carbon steel, uninhibit whose chemical composition as listed above. Samples were where CR and CR are the corrosion rates in the uninhibit inhibit washed with running tap water followed by distilled water, absence and presence of inhibitors, respectively. Table 2 dried with clean tissue, immersed in acetone and alcohol, shows that inhibitor efficiency ranged from 50.43 to 81.16%. dried again with clean tissue, then, kept in desiccators over ATT shows the higher performance. In order to have a clear silica gel bed until use. The dimensions of each sample were vision of ATT behavior, the effect of inhibitor concentra- measured with a vernier to second decimal of millimeter tion and temperature was studied. The results were shown in and accurately weighted to the 4th decimal of gram. The Table 3. Corrosion rate increased with increase in tempera- metal samples were completely immersed each in 500 ml ture and decrease in inhibitor concentration. While inhibitor of uninhibited and inhibited 0.5 M HCl solution contained efficiency increased with both increasing inhibitor concen- in a conical flask. They were exposed for a period of 3 h at tration and temperature. the desired temperature and inhibitor concentration. Then, the metal samples were cleaned, washed with running tap water followed by distilled water dried with clean tissue then Eec ff t of inhibitor concentration and adsorption immersed in acetone and alcohol and dried again. Weight isotherm −2 −1 losses in gm m  day (gmd) were determined in the pres- ence and absence of inhibitor. At the beginning, all inhibi- As shown in Table 3, at specific experimental temperature, tors were tested at inhibitor concentration of 0.001 M and corrosion rate of steel decreases with an increase in ATT 30 °C to select the best one. Then, the inhibitor with higher concentration. Values of inhibitor efficiency increase with efficiency was evaluated at different temperature (30–60 °C) increasing of ATT concentration approach the maximum −3 −3 −3 and inhibitor concentration of 1 × 10 , 2 × 10 , 3 × 10 , value of 95.8% at higher level of temperature and inhibitor −3 and 4 × 10  M. 1 3 International Journal of Industrial Chemistry (2019) 10:159–173 165 Table 3 Corrosion rate of low carbon steel alloy and inhibitor effi- in acidic media is commonly agreed to be adsorption on the ciency of synthesis ATT corrosion in 0.5 M hydrochloric acid solu- metal surface. This includes the assumption that the corrosion tion at different conditions reactions are prevented from occurring over the area or active Test number Inhibitor Tempera- Corrosion Inhibitor sites of the metal surface protected by adsorbed inhibitor mol- concentration ture (°C) rate (g/m . efficiency ecules, whereas these corrosion reactions occurred generally (M) day) (%) on the inhibitor-free active sites [22]. The surface coverage 1 0 20 33.99 – (ϴ = IE/100) data are very valuable in discussing the adsorp- 2 0 30 80.52 – tion features. Surface covered is related to the concentration 3 0 40 142.96 – of inhibitor at constant temperature by well-known adsorption 4 0 50 419.21 – isotherm relationships that evaluated at equilibrium condition. −3 5 1 × 10 20 9.57 71.8 The dependence of θ on the concentration of ATT concentra- −3 6 2 × 10 8.36 75.4 tion was tested graphically by fitting it to Langmuir adsorption −3 7 3 × 10 6.21 81.7 isotherm that assume a metal surface contains a fixed num- −3 8 4 × 10 5.06 85.1 ber of adsorption sites and each site took only one adsorbed −3 9 1 × 10 30 15.17 81.2 molecule. Figure 6 shows linear plots for C/ϴ versus C with −3 2 10 2 × 10 15.05 81.3 average R = 0.999 correlation coefficient, suggestion that the −3 11 3 × 10 11.23 86.1 adsorption follows the Langmuir adsorption isotherm [23]: −3 12 4 × 10 10.75 86.6 C 1 −3 16 1 × 10 40 21.27 85.1 = + C (9) −3 14 2 × 10 18.47 87.1 −3 15 3 × 10 17.66 87.7 where C is the inhibitor concentration, K adsorption equi- −3 16 4 × 10 16.83 88.3 librium constant, representing the degree of adsorption, in −3 17 1 × 10 50 22.57 94.6 other words the higher the value of K specifies that the ATT −3 18 2 × 10 20.52 95.1 molecules are strongly adsorbed on the metal surface. The −3 19 3 × 10 18.91 95.5 slops of Langmuir adsorption lines are near unity meaning −3 20 4 × 10 17.66 95.8 that each inhibitor molecules occupies one active site on the metal surface. The standard adsorption free energy (ΔG ) was calculated ads concentration. This increase in inhibitor performance with using the following equation [23]: temperature is apparently due to an increase in chemisorption ΔG 1 ads of the inhibitor. Crucial step in the action of inhibitor behavior K = exp − (10) 55.5 RT Fig. 6 Langmuir adsorption isotherms of ATT on the steel surface in 0.5 M HCl solution at different temperatures 1 3 166 International Journal of Industrial Chemistry (2019) 10:159–173 Table 4 Adsorption −1 2 −1 T (°C) K (M ) Slop R ΔG (kJ mol ) ΔH ΔS ads ads ads parameters of ATT at different −1 −1 −1 (kJ mol ) (kJ mol  K ) temperatures 20 2.5 × 10 1.09 0.99 − 28.84 79.1 0.37 30 5 × 10 1.1 0.99 − 31.57 40 17.2 × 10 1.1 1.00 − 35.84 50 47.6 × 10 1.04 1.00 − 39.71 Average value 18.1 × 10 1.08 0.99 − 33.99 where 55.5 are the concentration of water in solution increasing experimental temperature and ATT adsorbed expressed in molar, R is gas constant, and T absolute tem- according to chemical mechanism. The value of ΔH was ads perature. Table  4 shows the adsorption parameters. The obtained from Van’t Hoff equation (Eq.  11) [26] that drawn average value of standard adsorption free energy was in Fig. 7. This figure shows good linear fitting. −1 ° − 33.9  kJ  mol . The negative value of ΔG ensures the The values of adsorption thermodynamic parameters for ads spontaneous adsorption process and stability of the adsorbed inhibitor can offer valuable information about the mechanism layer on the metal surface. Commonly, value of ΔG up of corrosion inhibition. The endothermic adsorption process ads −1 to − 20 kJ mol is consistent with electrostatic interaction (ΔH > 0) is ascribed unequivocally to chemisorption, while ads between the charged molecules and the charged metal (phys- generally, an exothermic adsorption process (ΔH < 0) may ads −1 ical adsorption) while those around − 40 kJ mol or higher involve either physisorption or chemisorption or a mixture of are associated with chemical adsorption as a result of shar- both processes. In the present work; the positive sign of heat of ing or transfer of electrons from the molecules to the metal adsorption (ΔH ) indicates that the adsorption of inhibitor is ads surface to form a coordinate type of bond [24]. While other an endothermic process and the adsorption is chemisorption. researchers suggested that the range of standard adsorption This result agrees with above discussion. free energy of chemical adsorption processes for inhibitor While entropy of adsorption value (ΔS ) was obtained ads −1 in aqueous media lies between –21 and –42 kJ mol [25]. from Eq. 12 at average value of ΔG and average temperature. ads Therefore, for present work, the values of adsorption heat ΔH ads have been considered within the range of chemical adsorp- ln K =− + constant (11) RT tion. It was also observed from Table 4, limited increase in the absolute value of ΔG with an increase in temperatures, ads ΔH −ΔG ads ads indicating that the adsorption was somewhat favorable with ΔS = (12) ads Fig. 7 Van’t Hoff equation of ATT on the steel surface in 0.5 M HCl solution at different temperatures 1 3 International Journal of Industrial Chemistry (2019) 10:159–173 167 These results, which showed in Table 4, appear to contrast and acid concentration were evaluated from an Arrhenius- to that normally accepted for adsorption phenomena. It is type plot (Eq. 13) and transition state theory (Eq. 14) [34]: well known that adsorption is an exothermic with a negative sign of adsorption heat accompanied by reduction entropy CR = A exp − (13) RT of adsorption [27]. In aqueous solution, the adsorption of organic molecules commonly is accompanied by desorption ΔS ΔH RT a a of water molecules. The adsorption of organic molecules at CR = exp exp − (14) Nh R RT the metal–solution interface is a substitution adsorption pro- cess [28]. This means that each adsorbed molecule of ATT where CR is the corrosion rate, A is the Arrhenius constant, on metal surface displaces water molecules from the surface. R is the universal gas constant, h is Plank’s constant, and The thermodynamic values of ΔS are the algebraic sum ads N is Avogadro’s number. As shown in Fig.  8, plot of ln of the adsorption of ATT molecules and the desorption of (CR) versus 1/T gives straight lines with slopes of ΔE /R water molecules. Therefore, the increase in entropy is attrib- and intercept can be used for evaluating of A. While, Fig. 9 uted to the increase in solvent entropy [29, 30]. Chaitra et al. shows a liner straight lines of ln (CR/T) versus 1/T slopes [31] studied the effect of newly synthesized thiazole hydra- of ΔH /R and intercept can be used for evaluating of ΔS . a a zones on the corrosion of mild steel in 0.5 M hydrochloric Table 5 illustrates the activation parameters for steel cor- acid. Adsorption of the inhibitors followed Langmuir iso- rosion reaction acidic solution at different conditions. It therm and addition of inhibitors simultaneously decreased is clearly shown that the activation energy and enthalpy corrosion rate. vary in similar way. The activation energy and activation Tezcan et al. [32] investigated newly synthesized sulfur enthalpy for uninhibited acid were higher than inhibited one. containing Schiff base (4-((thiophene-2-ylmethylene)amino) The decrease in the value of activation energy and enthalpy benzamide) compound. Inhibition performance on mild steel appears to be unreliable. However, this may be attributed to in 1.0 M HCl solution was studied. The results showed that increase in metal surface coverage by the inhibitor molecules the highest inhibitor efficiency of 96.8%. at higher temperatures and also suggested that the formation Messali et  al. [33] studied the inhibition effect and rate of the chemisorbed layer may be greater than its rate of adsorption behavior of 4-((2,3-dichlorobenzylidene)amino)- dissolution at higher temperatures [35]. Other researchers 3-methyl-1H-,2,4-triazole-5(4H)-thione on mild steel in 1 M [36] found that some anticorrosion materials in the acidic HCl solution. The inhibitor can be adsorbed onto surface by solutions alter the kinetics of corrosion reaction by propos- both physical and chemical means obeys Langmuir adsorp- ing alternate reaction paths with lower activation energies. tion isotherm. Table 4, illustrates also that all the values of frequency factor are lower than uninhibited one, which is benefit for inhibit- Eec ff t of temperature and activation parameters ing the corrosion rate of steel. It is also well known that the increase in A raises the corrosion rate of steel [37]. Further- As shown in Table 5, at specific experimental tempera- more, at all cases, the values of E are higher than ΔH by a a a ture, corrosion rate of steel decreases with an increase value which approximately equal to RT, which confirm the in ATT concentration. The kinetics of the ATT action 5 5 thermodynamic principle of the reactions are characterized can be realized by comparing the activation parameters by following equation [38]: in the presence and absence of the inhibitor. Activation E −ΔH = RT energy (E ), enthalpy of activation (ΔH ), and entropy of a a (15) a a activation (ΔS ) for both uninhibited and inhibited 0.5 M The negative value of ΔS for both cases of absence hydrochloric acid steel corrosion at different temperatures and presence of inhibitor indicates that activated complex in the rate determining step denotes an association rather than a dissociation step, which means a decrease in disor- Table 5 Activation parameters for steel corrosion reaction in uninhib- der, takes place during the course of transition from reac- ited and inhibited 0.5 M HCl tant to the activated complex [39]. −1 −1 Khan et  al. [ 4 0] studied the inhibi - C (M) A (gmd) E (kJ mol ) ΔH (kJ mol ) ΔS a a a −1 −1 (J mol  K ) tory effect of two Schiff bases 3-(5-methoxy- 2-hydr oxybenzylideneamino)-2-(-5-me t hoxy-2-hy- 0 7.3 × 10 63.67 61.12 − 7.98 dr o xyphen y l)-2,3-dih ydr oq uinazoline-4(1H)-one − 3 5 1 × 10 1.3 × 10 23.09 20.54 − 155.22 (MMDQ), and 3-(5-nitro-2-hydroxybenzylideneamino)- − 3 5 2 × 10 1.2 × 10 23.04 20.48 − 156.21 2(5-nitro-2-hydroxyphenyl)-2,3-dihydroquinazoline- − 3 6 3 × 10 1.6 × 10 30.09 27.54 − 134.74 4(1H)-one (NNDQ) on the corrosion of mild steel in 1 M − 3 6 4 × 10 5.2 × 10 33.36 30.81 − 124.87 1 3 168 International Journal of Industrial Chemistry (2019) 10:159–173 Fig. 8 Arrhenius plots of steel in uninhibited and inhibited 0.5 M HCl Fig. 9 Transition—state plots of steel in uninhibited and inhib- ited 0.5 M HCl hydrochloric acid. The effect of temperature on the inhibi- in the inhibitor-free acid solution can be attributed to its tion process in 1 M HCl with the addition of inhibitors was chemisorption on mild steel surface. Similar results were investigated at a temperature range of 30–60 °C. Corrosion obtained by Obaid et al. [41]. The lower values of activa- rate increased with raise in temperature, and the efficien- tion energy in the presence of the inhibitors and the gen- cies of the investigated inhibitors are strongly temperature eral increase in their inhibitor efficiencies with increasing dependent. Enthalpy, entropy and enthalpy of activation temperatures are indicative of chemisorption (interaction were calculated. The result showed that Enthalpy of activa- of unshared electron pairs in the adsorbed molecule with tion for solution containing inhibitors are lower than those the metal) of these compounds on the steel surface. 1 3 International Journal of Industrial Chemistry (2019) 10:159–173 169 electronegativity scale and η is 0 eV/mol, respectively Quantum chemical and theoretical calculations Fe [46]. The fraction of electrons transferred from inhibitor to the steel surface (ΔN) was calculated and listed in Table 3. Quantum chemical calculations have been widely used to investigate reaction mechanism of inhibition process [42]. It is According to Lukovits [47], if ΔN < 3.6, the inhibition effi- ciency increased with increasing electron-donating ability also verified to be a very important tool for studying corrosion control mechanism and to obtain insight view to the inhibition at the steel surface. In this study, synthesis inhibitors were the donor of electrons, and the metal surface was the accep- mechanism of ATT inhibitor. By using of quantum chemical calculations, the structural parameters, such as HOMO (high- tor. This result supports the assertion that the adsorption of inhibitors on the steel surface can occur on the bases of est occupied molecular orbital), LUMO (lowest unoccupied molecular orbital), dipole moment (µ) and fraction of electron donor–acceptor interactions between the Л electrons of the compound and the vacant d-orbitals of the metal surface. transferred (ΔN), were calculated. The structures of inhibi- tors were optimized by ChemoOffice version 14 software. Fig- The dipole moment (µ) is also a significant factor and there is lack of agreement on the relation between µ and inhibitive ure 10 shows the optimized structures, HOMO and the LUMO structure of all synthesis inhibitors. The calculated quantum performance. Some researchers founded that a low µ value will favor accumulation of the inhibitor on metal surface and chemical properties are summarized in Table 6. As shown in Fig. 10, both the HOMO and LUMO distributions of synthesis increasing the inhibitor performance [48, 49]. While others researches suggested that a high value of dipole moment inhibitors were concentrated mainly over sulfur and nitrogen atoms. E and E characterized the electron-receiving associated with the dipole–dipole interaction of inhibitor LUMO HOMO and metal surface can enhance the adsorption on the metal and—donating capability of synthesis inhibitors. In general, a low E implies that inhibitors tend to accept electrons, surface and increasing efficiency [50, 51]. In present work, LUMO the value of µ for ATT was the lowest one among all tested while a high E refer to a strong electron donating [43]. HOMO 5 Energy gap (ΔE) specifies the chemical stability of inhibi- inhibitors that agree with the first opinion. The anodic oxi- dation behavior of steel in HCl acid can be explained by tors, and a lower energy gap value typically leads to higher adsorption on the metal surface, resulting in greater inhibition following reaction [52]: efficiencies [44]. The order of inhibition efficiency was ATT − − Fe + Cl ↔ (FeCl ) (18) ads > ATT > ATT > ATT > ATT > ATT , while the order of 5 1 2 3 6 4 − − energy gap was ATT > ATT > ATT > ATT > ATT > ATT 5 4 3 2 6 (FeCl ) ↔ (FeCl) + e (19) ads ads . The differences in orders may be attributed to close inhibi- tion efficiencies of inhibitors. As seen in Table  2, the value of + − (FeCl) → FeCl + e (20) ads ads inhibitor efficiencies were 60.43, 65.02, 67.97, and 69.17% for ATT , ATT , ATT and ATT , respectively, which is very 6 3 2 1 + 2+ − close range. However, still ATT has the lower energy gap that FeCl → Fe + Cl 5 (21) ads confirms the experimental work. The number of transferred While the cathodic hydrogen evolution reaction can be electrons (ΔN) was also calculated according to Eq. 16 [45]. written as: X − X Fe inh ΔN = (16) 2( +  ) + + Fe inh Fe + H ↔ FeH (22) ads where X and X denote the absolute electronegativity of Fe inh iron and the MLH inhibitor molecule, respectively; η and Fe − FeH + e → (FeH) (23) ads ads η denote the absolute hardness of iron and the inhibitor inh molecule, respectively. These quantities are related to elec- + − (FeH) + H + e → Fe + H (24) ads 2 tron affinity (A ) and ionization potential (I) that both related According to the structures of the synthesis inhibitors, in turn to E and E : HOMO LUMO there are the free electron pairs on N and S that able to − E + E forming **σ-bond with iron [53]. In addition, in case of I + A HOMO LUMO X = = acidic solution, electrostatic interaction is possible between 2 2 (17) the negatively charge of iron surface that may be brought − E − E HOMO LUMO I − A = = about by specific adsorption of Cl anions and the posi- 2 2 tively charged inhibitor. The essential effect of inhibitors is due to the presence of free electron pairs in the N and S Values of X and η were considered by using the val- atoms, p-electrons on the aromatic ring, type of interaction ues of I and A gained from quantum chemical calculation. with the steel surface, and metallic complexes formation. It The theoretical value of X is 7 according to Pearsons Fe 1 3 170 International Journal of Industrial Chemistry (2019) 10:159–173 Fig. 10 Optimized chemical structures of six inhibitors and HOMO–LUMO distribution is well known that steel has coordination affinity toward N and p-electrons of aromatic rings [54]. In the present case, and S bearing ligand. Therefore, adsorption on metal sur- synthesis inhibitors, there are unshared electron pairs on N face can be ascribed to coordination through heteroatoms and S, able to form σ-bond with steel. 1 3 International Journal of Industrial Chemistry (2019) 10:159–173 171 Table 6 Quantum chemical Compounds E (eV) E (eV) ΔE (eV) ΔN Dipole (debye) HOMO LUMO parameters for inhibitors ATT − 7.654 − 1.068 6.586 − 0.401 4.685 ATT − 7.186 − 2.160 5.026 − 0.462 5.691 ATT − 7.511 − 2.613 4.898 − 1.013 5.855 ATT − 7.683 − 4.574 3.109 0.115 6.942 ATT − 7.654 − 5.322 2.332 − 0.303 4.362 ATT − 7.605 − 1.068 6.537 0.407 6.124 containing tetrafluoroborate anion on MSin acidic medium. J Mol Conclusion Liq 211:105–118 3. Khadiri R, Bekkouche K, Aouniti A, Hammouti B, Benchat N, The following points can be concluded from present work: Bouachrine M, Solmaz R (2016) Gravimetric, electrochemical and quantum chemical studies of some pyridazine derivatives as corrosion inhibitors for mild steel in 1 M HCl solution. 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