Journal of Advanced Scientific Research DFT APPROACH ON CORROSION INHIBITION PERFORMANCE OF THIOSEMICARBAZONE DERIVATIVES ON METALLIC IRON

Size: px

Start display at page:

Download "Journal of Advanced Scientific Research DFT APPROACH ON CORROSION INHIBITION PERFORMANCE OF THIOSEMICARBAZONE DERIVATIVES ON METALLIC IRON"

Marianna Andrews
6 years ago
Views:

1 Rajendran et al., J Adv Sci Res, 2016, 7(1): Journal of Advanced Scientific Research Available online through ISSN Research Article DFT APPROACH ON CORROSION INHIBITION PERFORMANCE OF THIOSEMICARBAZONE DERIVATIVES ON METALLIC IRON M. Rajendran*, A. Malkiya, P. Muthupetchi, D. Devapiriam Department of chemistry, Centre for Research and Post Graduate Studies in Chemistry,N. M. S. S. Vellaichamy Nadar College, Nagamalai, Madurai , Tamilnadu, India. *Corresponding author: mrrajendran64@yahoo.com ABSTRACT Corrosion inhibition performance of three following thiosemicarbazone derivatives such as p-methylacetophenone thiosemicarbazone (TSC-1), p-methoxyacetophenone thiosemicarbazone (TSC-2) and p-aminoacetophenone thiosemicarbazone (TSC-3), on iron was evaluated by density functional theory (DFT) at the B3LYP/6-31G(d,p) level. The structural parameters that are most relevant to inhibition efficiencies, such as E HOMO, E LUMO, energy gap (ΔE), dipole moment (μ), hardness (η), softness ( ), the absolute electronegativity (χ), the electrophilicity index ( ), fraction of electrons transferred (ΔN) from thiosemicarbazone derivatives to iron and the back donation (ΔE Back-donation ) have been calculated. The local reactivity has been analyzed through the condensed Fukui function indices using condensed electron density on atoms. Keywords: Corrosion inhibition, density functional theory, Fukui function, Thiosemicarbazone 1. INTRODUCTION Heterocyclic compounds represent a potential class of corrosion inhibitors. Heterocyclic compounds containing both nitrogen and sulphur atoms are of particular importance as they often provide excellent inhibition compared to those containing only nitrogen [1-3]. The corrosion of iron and mild steel is a fundamental academic and industrial concern that has received a considerable amount of attention. To control corrosion, organic inhibitors are generally used. They protect the metal from corrosion by forming a barrier film on the metal surface. The addition of corrosion inhibitors effectively secures the metal against an acid attack by controlling metal dissolution [4, 5]. The mechanism of their action can be different, depending on the metal, the medium and the structure of the inhibitor. One possible mechanism is the adsorption of the inhibitor on the metal, which blocks the metal surface and thus does not permit the corrosion process to take place. Existing data reveal most inhibitors do act by adsorption on the metal surface through heteroatom such as nitrogen, oxygen and sulphur, double bonds, triple bonds or aromatic rings which tend to form stronger coordination bonds. Compounds with -bonds generally exhibit good inhibitive properties, the electrons for the surface interaction being provided by the π-orbitals [6]. The planarity and the lone electron pairs in the hetero atoms are important features that determine the adsorption of molecules on the metallic surface. The geometry of an inhibitor also has an important influence in determining its adsorbability at the metal-solution interface. Molecules that are planar have a greater tendency to adsorb at the metal surface than molecule that has less planar geometry [7]. The advances in computer hardware and development of related theory, molecular modeling has grown to be an effective technique to explore complex systems at molecular level. The corrosion inhibition properties can be controlled by many types of organic and inorganic compounds, but organic compounds are the more common type of corrosion inhibitors [8-10]. The most efficient inhibitors are organic compounds having π bonds in their structures. The process of corrosion inhibitor adsorption is influenced by the metal surface and the chemical structure of the organic inhibitor [11-14]. The order of corrosion efficiency of the following organic compounds are reported in literature and it is found to be p- aminoacetophenone thiosemicarbazone (TSC-3)>p-methyl acetophenone thiosemicarbazone (TSC-1)>p-methoxyacetophenone thiosemicarbazone (TSC-2). But so for no quantum chemical studies were reported on these compounds. The present work investigate elaborately the inhibition efficiency of these compounds based on theoretical studies using chemical reactivity descriptors such as energy of highest occupied molecular orbital (E HOMO ), energy of lowest unoccupied molecular orbital (E LUMO ), energy gap (ΔE), dipole moment (μ), electronegativity (χ), electron affinity (A), global hardness (η), softness (σ), ionization potential (I), the global electrophilicity (ω), the fraction of electrons transferred (ΔN), chemical potential (μ) and ΔE Back-donation [15]. Several organic compounds with hetero atoms like O, N, S, P and having multiple bonds are useful and are widely used

2 as effective corrosion inhibitors [16-20]. The organic molecules should have centres which are capable of forming coordination bonds with metal surfaces [21-23]. Stronger is the coordination bond, better is the inhibition efficiency. Their effectiveness as promising inhibitors is related to their spatial molecular structural distribution, molecular electronic structure, chemical composition, surface charge density and of course to their affinity to the individual metal surface [24-26]. 2. MATERIAL AND METHODS Density Functional Theory (DFT) methods were employed to study the inhibition efficiency of thiosemicarbazone derivatives. Among quantum chemical methods available for evaluation of corrosion inhibitors, density functional theory (DFT) has shown significant promise and appears to be adequate for pointing out the changes in electronic structure responsible for inhibitory action [27]. In DFT, the energy of the fundamental state of a polyelectronic system can be expressed as the total electronic density, and, in fact, use of electron density instead of a wave function for calculating the energy constitutes the fundamental basis of DFT [28]. Frontier molecular orbitals, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were used to predict the adsorption centers of the inhibitor molecule. For the simplest transfer of electrons, adsorption should occur at the part of the molecule where the softness, which is a local property, has the highest value. According to Koopman s theorem [32], the energies of the HOMO and the LUMO orbitals of the inhibitor molecule are related to the ionization potential and the electron affinity, respectively, by the following relationships, (1) and (2). Absolute electronegativity, χ, and absolute hardness, η, of the inhibitor molecule are [33] given by (3) and (4). The softness is the inverse of the hardness [33] (5). Electronegativity, hardness, and softness have been proved to be very useful quantities in chemical reactivity theory. When two systems, Fe and inhibitor are brought together, electrons will flow from system of lower chemical potential (inhibitor) to higher chemical potential system (Fe), until their chemical potentials become equal. I = - E HOMO (1) A = - E LUMO (2) Absolute electronegativity, and absolute hardness, η of the inhibitor molecule are given [33] = I + A/2 (3) η = I A/2 (4) The softness is the inverse of the hardness [33] = 1/η (5) The number of transferred electrons (ΔN) was also calculated by using the equation (6) given below [29] ΔN = Fe χ inh /2(η Fe + η inh ) (6) Rajendran et al., J Adv Sci Res, 2016, 7(1): Where, χ Fe, χ inh denote the absolute electronegativity of iron and inhibitor molecule, respectively, and η Fe, η inh denote the absolute hardness of iron and the inhibitor molecule, respectively. In this study for the computation of number of transferred electrons [30], we use the theoretical value of χ Fe = 7.0 ev and η Fe = 0 assuming that for a metallic bulk I = A. The absolute electrophilicity index is given by [31]. = µ 2 /2η (7) According to the definition (7), this index measures the tendency of chemical species to accept electrons. More reactive nucleophile is characterized by lower absolute electrophilicity index value and conversely more reactive electrophile is characterized by higher value. The local reactivity has been analyzed by evaluating Fukui indices (FI). The FI calculation are performed using DFT/ B3LYP/6-31G(d,p) [32]. FI are used to obtain the detail information of local reactivity [33]. The Fukui function f k is defined as the first derivative of the electronic density with respect to the number of electrons N in a constant external potential v(r) [34]. f k = ( (r)/ ( N)v(r) The Fukui functions can be written by taking the finite difference approximations as [26] f + k = q k (N+1) q k (N) (for nucleophilic attack) f - k = q k (N) - q k (N-1) (for electrophilic attack) where, q k is the gross charge of k atom i.e; the electronic density at a point r in space around the molecule. The q k (N+1), q k (N) and q k (N-1) are defined as the charge of the anionic, neutral and cationic species respectively. Here Fukui functions are obtained through the finite difference approximation using Hirschfeld population analysis (HPA) [36]. H 2 N R = CH 3 C S N NH C p-methylacetophenone thiosemicarbazone (TSC-1) R = OCH 3 p-methoxyacetophenone thiosemicarbazone (TSC-2) R = NH 2 p-aminoacetophenone thiosemicarbazone (TSC-3) Fig. 1: Chemical structure of thiosemicarbazones 3. RESULTS AND DISCUSSION The molecular structures of thiosemicarbazone derivatives were optimized with the B3LYP/6-31G(d,p) basis set without any constraint in the geometry. The chemical structures of the R

corrosion inhibitors studied are shown in fig.1.

Molecular Oribital (LUMO) of reacting species [37]. Comp. HOMO LUMO TSC-1 TSC-2 TSC-3 Fig.2: Frontier molecular orbital diagram of TSC-1, TSC-2 and TSC-3 using B3LYP/6-31G(d,p) basis set. 3.1. Mulliken atomic charges The HOMO and LUMO diagrams (fig.

Therefore, the mulliken atomic charges (Table 1) were examined to explain the inhibition approach of the molecules under investigation.

with the formation of the closely packed adsorption layer to inhibit iron ions from entering the solution.

Thiosemicarbazone derivatives have three negatively charged N-donor atoms and one S atom. The negatively charged N- donor atoms may prefer adsorption of soft iron ion.

3 corrosion inhibitors studied are shown in fig.1. According to the Frontier Molecular Orbital theory (FMO) of chemical reactivity, transition of electrons is due to interaction between Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Oribital (LUMO) of reacting species [37]. Comp. HOMO LUMO TSC-1 TSC-2 TSC-3 Fig.2: Frontier molecular orbital diagram of TSC-1, TSC-2 and TSC-3 using B3LYP/6-31G(d,p) basis set Mulliken atomic charges The HOMO and LUMO diagrams (fig.2) of the inhibitors, reflects that the electron densities were distributed homogeneously throughout the molecules. Therefore, the mulliken atomic charges (Table 1) were examined to explain the inhibition approach of the molecules under investigation. The more negative the atomic charges of the adsorbed inhibitors, the more easily the atom donates its electrons to the unoccupied orbital of the metal and adsorb preferentially on the metal surface with the formation of the closely packed adsorption layer to inhibit iron ions from entering the solution. It is clear from table 1 that Nitrogen and Sulphur atoms carrying negative charges could offer electrons to the metal surface to form a coordinate type bonds. Thiosemicarbazone derivatives have three negatively charged N-donor atoms and one S atom. The negatively charged N- donor atoms may prefer adsorption of soft iron ion. However, when -NH 2, -CH 3 and -OCH 3 groups are introduced in the six membered ring, the negative charge on the N and S are also modified. The increase of charge on the N and S atom of the thiosemicarbazone derivatives increases in this order TSC-3 > TSC-2 > TSC-1. The reason for this order of inhibition is clearly observed from the optimized structures (fig.2). From the figure 2 it is known that the electron distribution is uniform throughout the structure, when amino group is substituted at the para-position of thiosemicarbazone. Rajendran et al., J Adv Sci Res, 2016, 7(1): Table 1: Mulliken atomic charges on thiosemicarbazone derivatives of TSC-1, TSC-2 and TSC-3 obtained using B3LYP/6-31G(d,p) basis set. TSC-1 TSC-2 TSC-3 1 C C C C C C C C C C C C C C C C C C H H H H H H H H H H H H C C N C C H H H H H H C H H C N N H N N H C C H N N N H H N H H C H H N S S H C C H H H H H H S H H O However in the p-methyl and p-methoxy substituted thiosemicarbazone the electron cloud is not uniformly distributed throughout the structure, because the electron releasing power of -OCH 3 and -CH 3 is less than -NH 2 the p- methyl and p-methoxy substituted six member rings are out of the plane. The S atom in the derivatives is more favoured site for the adsorption with metal. The charges on S atom follows this order TSC-3 (S = ) > TSC-2 (S = ) > TSC-1 (S = ). The charges on the S and N atoms have a nice correlation with the corrosion inhibition efficiency investigated through the DFT method. Hence, it is understood that p-aminoacetophenone thiosemicarbazone (TSC-3) has the highest order of corrosion inhibition efficiency than p-methoxy and p-methyl thiosemicarbazone derivatives Frontier Molecular Orbitals (FMO) The interaction between the inhibitor and the metal is through the donation of the electrons from the inhibitor occupied orbital (HOMO) to the d-orbital of the metal and also through the acceptance of the electrons from d-orbital of the metal to the unoccupied orbital (LUMO) of the inhibitor

4 [38]. The binding ability of the inhibitor to the metal surface increases with increasing of the HOMO and decreasing of the LUMO energy values. Frontier molecular orbital diagram of TSC-1, TSC-2 and TSC-3 is presented in fig.2. Moreover, E LUMO indicates the ability of the molecule to accept electrons. Lower the value of E LUMO better will be the ability to accept electrons, and this will also enhance the adsorption of the inhibitor on the metal surface and therefore better inhibition efficiency. From table-2, the order of LUMO energy value for TSC-1, TSC-2 and TSC-3 is as follows: TSC-3, ev > TSC-2, ev > TSC-1, ev. From this it is clear that the order of inhibition efficiency also follows the same trend ie., TSC-3 > TSC-2 > TSC-1. Higher the value of E HOMO, better will be the inhibition efficiency. The order of E HOMO value for the three investigated species is - TSC-3, ev > TSC-2, > TSC-1, ev. The highest value of E HOMO oberserved TSC-3 indicates the better inhibition efficiency. Hence the order of inhibition efficiency based on E HOMO value is TSC-3 > TSC-2 > TSC-1. The Rajendran et al., J Adv Sci Res, 2016, 7(1): prediction made from both E LUMO & E HOMO values falls in the same line thus proving the validity of this experiment. The other parameters such as ionization potential, electronegativity, number of electron transferred and backdonation also confirms the same order Ionization energy The important global chemical parameters are summarized in table-2. Ionization energy is a fundamental descriptor of the chemical reactivity of atoms and molecules. High ionization energy indicates high stability and chemical inertness and low ionization energy indicates high reactivity of the atoms and molecules [39]. The low ionization energy value of TSC-3, shows that TSC-3 has higher inhibition efficiency compared to TSC-2 and TSC-1. From table 2 the order of ionization energy value is TSC-1, ev > TSC-2, > TSC-3, ev. Hence the order of inhibition efficiency based on ionization energy values becomes TSC-3 > TSC-2 > TSC-1. Table 2: Quantum chemical parameters for inhibitor p-methylacetophenone thiosemicarbazone (TSC-1), p- methoxyacetophenone thiosemicarbazone (TSC-2) and p-aminoacetophenone thiosemicarbazone (TSC-3), calculated using B3LYP/6-31G(d,p) basis set. Parameters TSC-1 TSC-2 TSC-3 Enthalpy of formation (au) Dipole moment (Debye) HOMO (ev) LUMO (ev) Ionization Potential (I) ev Electron affinity (A) ev Energy gap ( E) ev Hardness ( ) ev Global Softness ( ) ev Electrophilic index ( ) ev Electronegativity ( ) ev Chemical Potential (µ) ev Electronegativity Table-2 shows the order of electronegativity (χ) as TSC- 1 > TSC-2 > TSC-3. Hence the difference of electronegativity between the metal and the inhibitor is found to increase in the order TSC-1 < TSC-2 < TSC-3. According to Sanderson s electronegativity equalization principle [40] the high electronegativity and the low difference of electronegativity quickly reaches equalization and hence low reactivity is expected which in turn indicates the low inhibition efficiency. Therefore the order of inhibition efficiency is TSC-3 > TSC-2 > TSC-1, which supports our earlier predictions Number of electrons transferred The number of electrons transferred (ΔN) was calculated and are tabulated in table-3. Values of ΔN show that the inhibition efficiency resulting from electron donation agrees with Lukovit s study [41]. If ΔN < 3.6, the inhibition efficiency increases by increasing the electron-donating ability of these inhibitors to donate electrons to the metal surface and it increases in the following order TSC-3 > TSC-2 > TSC-1. Thus, the highest fraction of electrons transferred is associated with TSC-3 which is considered to be the best inhibitor. While the least fraction of electron transferred is associated with the inhibitor TSC-1 which indicates its least inhibition efficiency Back-donation In table-3, ΔE Back-donation values calculated for the inhibitors, TSC-1, TSC-2 and TSC-3 are listed. According to Gomeze et al [42], during the presence of charge transfer the back-donation of charges is the negative of hardness (-η/4) which governing the interaction between the inhibitor

5 molecule and the metal surface. ΔE Back-donation implies that η > 0 and ΔE Back-donation < 0 the charge transfer to a molecule, followed by a back-donation from a molecule is energetically favoured [43]. Table 3: The number of electron transferred ( N) and E Back- donation (ev) values calculated for inhibitors TSC-1, TSC- 2 and TSC-3 using B3LYP/6-31G(d,p) basis set. Parameters TSC-1 TSC-2 TSC-3 transferred electron fraction ( N) E Back donation (ev) Rajendran et al., J Adv Sci Res, 2016, 7(1): Table 4: Electron donating ( - ) and electron accepting ( + ) powers and net electrophilicity ± calculated for inhibitors TSC-1, TSC-2 and TSC-3 using B3LYP/6-31G(d,p) basis set. Property TSC-1 TSC-2 TSC-3 - ev ev ± ev Table 5: Fukui indices for electrophilic and nucleophilic attacks in inhibitors calculated usingt B3LYP/6-31G(d,p) level theory; maxima in bold p-methylacetophenone thiosemicarbazone (TSC-1) p-methoxyacetophenone thiosemicarbazone (TSC-2) p-aminoacetophenone thiosemicarbazone (TSC-3) Positions symbols f + f - Positions symbols f + f - Positions symbols f + f - 1 C C C C C C C C C C C C C C C C C C H H H H H H H H H H H H C C N C C H H H H H H C H H C N N H N N H C C H N N N H H N H H C H H N S S H C C H H H H H H S H H O There is general consensus by several authors that the more negatively charged a heteroatom is the more it can be adsorbed on the metal surface through the donor acceptor type reaction [44]. It is important to consider the situation corresponding to a molecule that is going to receive a certain amount of charge at some centre and is going back to donate a certain amount of charge through the same centre or another one [42]. The electron donating ( - ) and electron accepting ( + ) powers and net electrophilicity ( ) of the inhibitor molecules calculated with B3LYP/6-31G(d,p) basis set, are presented in table-4. It follows that a larger + value corresponds to a better capability of accepting charge, whereas a smaller value

6 of - value of a system makes it a better electron donor. Based on the electron donating and accepting powers of TSC-1, TSC-2 and TSC-3 presented in the table 3, the order of corrosion inhibition is in the order cited below TSC-3 > TSC- 2 > TSC Local chemical reactivity The energy levels of frontier orbitals indicate the tendency of inhibitors to form bonds with the metal surface [45]. Further study on the spatial distribution of the electron density of inhibitor, ie the local concentration and local depletion of electron charge density allows us to determine whether the inhibitor undergo electrophilicity or nucleophilicity reactions [46]. To examine the local reactivity behavior the condensed fukui function indices were calculated and are summarized in table-5. According to Parr and Yang larger the value of fukui functions greater will be the reactivity. Hence higher the value of condensed fukui function, the more reactive is the particular atomic centre in the molecule [47]. The highest value of f k+ for TSC-1, TSC-2 and TSC-3 occurs at N16, N16 and N19 respectively, indicating their preferred site for nucleophilic attack. Based on the f k - values obtained the sites S23, S23 and S26 are found to be the most reactive site for the electrophilic attack in the thiosemicarbazides TSC-1, TSC-2 and TSC-3 respectively. 4. CONCLUSION Using the DFT/B3LYP/6-31G(d,p) level theory, the corrosion inhibitor efficiencies of three thiosemicarbazone derivatives (TSC-1, TSC-2 & TSC-3) were investigated and it lead to the following conclusions. Quantum chemical parameters such as E HOMO, E LUMO, energy gap (ΔE), hardness (η), softness ( ) electron affinity (E), ionization potential (I), the absolute electronegativity ( ), the fraction of electron transferred (ΔN), electrophilicity index ( ) and the backdonation (ΔE Back-donation ) were calculated. Analysis of the data obtained for each parameter mentioned above shows that the the inhibition efficiency of thiosemicarbazone derivatives is in the following order TSC-3 > TSC-2 > TSC-1. From the order Rajendran et al., J Adv Sci Res, 2016, 7(1): cited above, it is clear that, TSC-3 has the highest inhibition efficiency among all the three thiosemicarbazone. Fukui function reveals the nuclophilic and elctrophilic attacking sites of the inhibitors. 5. REFERENCES 1. Granes SL, Rosales BM, Oviedo C, Zerbino JO, Corros. Sci., 1992; 33: Raicheva SN, Aleksiev BV, Sokolov EJ, Corros. Sci., 1993; 34: Subramaniam G, Balasubramaniam K, Shridhar P, Corros. Sci., 1990; 30: Schmitt G, Br. Corros. J 1984; 19: Quraishi M, Sharma H, J. Appl. Electrochem., 2005; 35: Fekry AM, Ameer MA, Int. J. Hyd. Eng., 2010; 35: Liu P, Fang X, Tang Y, Sun C, Yao C, Materials Sci and Appl., 2011; 2: Ravari FA, Dadgarinezhad A, Shekhshoaei I, G.U. J. Sci., 2009; 22: Ebadi M, Basirun WJ, Khaledi H, Mohd Ali H, Chem. Cen. J., 2012; 6: Antonijevic MM, Petrovic MB, Int. J. Electrochem. Sci., 2008; 3: Lagrenee M, Mernari B, Bouanis M, Traisnel M, Bentiss F, Corros Sci., 2000; 44: Bentiss F, Lagrenee M, Traisnel M, Hornez JC, Corrs Sci.,1999; 41: El-Sayed, Sherif M, Applied surface science, 2006; 252: Subramanian R, Lakshminarayanan V, Corros. Sci., 2002; 44: Dandia A, Gupta SL, Sudheer A, Quraishi MA, J. Mater. Environ. Sci., 2012; 3: Hasanov R, Sadıkoglu M, Bilgic S., Appl. Surf. Sci. 2007; 253: Bentiss F, Traisnel M, Gengembre L, Lagrenee MA, Appl. Surf. Sci. 1999; 152: Ouchrif A, Zegmout M, Hammouti B, El-Kadiri S, Ramdani A., Appl. Surf. Sci. 2005; 252: Sherif ESM. Appl. Surf. Sci., 2006; 252: Liu B, Xi H, Li Z, Xia Q., Appl. Surf. Sci. 2012; 258: Khaled KF, Electrochim Acta., 2010; 55:

Quantum Chemical Studies on the Inhibiting Effect of Bipyrazoles on Steel Corrosion in HCl

ISS: 0973-4945; CODE ECJHAO E- Chemistry http://www.e-journals.net 2010, 7(2), 419-424 Quantum Chemical Studies on the Inhibiting Effect of Bipyrazoles on Steel Corrosion in HCl K. LAAREJ, M. BOUACHRIE