Theoretical and experimental studies of structure and inhibition efficiency of imidazoline derivatives

Corrosion Science 41 (1999) 1911±1919

Theoretical and experimental studies of structure and inhibition eciency of imidazoline derivatives Daxi Wang a,*, Shuyuan Li a, Yu Ying a, Mingjun Wang a, Heming Xiao b, Zhaoxu Chen b a

School of Chemical Engineering, University of Petroleum, Changping, 102200, Beijing, Peoples Republic of China b University of Science & Technology, 210094, Nanjing, Peoples Republic of China Received 16 December 1997; accepted 31 January 1999

Abstract The purpose of this paper is to provide information on the electron con®guration of several imidazoline inhibitors by the quantum chemical calculation and to seek correlation between molecular structure and behavior of corrosion inhibition. Three imidazoline derivatives with di€erent electron-releasing substituents were designed by quantum chemical study. On the basis of calculated results, the inhibition eciency is predicted as in following order: compound III>II>I. These compounds were synthesized and measured by weight loss and electrochemical methods. Theoretical prediction is in good agreement with experimental results. Based on the theoretical and experimental results, it is concluded that electron donor group introduced, particularly, the substituent group with conjugated system, to imidazoline ring will improve corrosion inhibition eciency of imidazoline derivatives. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Imidazoline derivative; Quantum chemistry; Synthesis; Measurement; Inhibition eciency

1. Introduction Corrosion damage is frequent and very severe in oil transportation pipelines. This can not only cost very much annually for inspection, repair and replacement * Corresponding author. 0010-938X/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 0 - 9 3 8 X ( 9 9 ) 0 0 0 2 7 - X

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of corroded pipes, but also, there is danger to the public. Accordingly, it is very important to obtain a powerful corrosion inhibitor for decreasing corrosion damage and to prolong e€ective life of the pipes [1,2]. A lot of work on imidazoline inhibitors has been studied experimentally [3±5]. However, its theoretical study [6,7] is fewer relatively. Hence, it is necessary and signi®cant to research corrosion mechanism and the in¯uence of the substituent on inhibition eciency. Quantum chemical calculation has been widely used to study reaction mechanism and to interpret the experimental results as well as to resolve chemical ambiguities [8±9]. It is an approach to investigate reaction mechanism on the molecule and electronic structure level. Generally, one takes into account only the unimolecules or double-molecules reaction model to simulate the complicated reaction process [10,11]. For example, macromolecules [12] in medicine [13], bio-macromolecules [14], super-molecules system [15], etc. are usually simulated as a little ®ne molecular models. On the basis of quantum chemical method, these molecular models can be used to describe the chemical reaction processes by taking a unit or a part of the macromolecules. This calculation method has been widely used and made a great success [6±16]. It proved to be a very useful theoretical tool for studying inhibition mechanism and behavior. There are many reports on quantum chemical studies of an inhibitor. Vosta and Elicaek [17] made use of quantum study on inhibitor. Costa and Lluch [19] and other authors reported a qualitative relationship between structures and adsorption inhibitor and eciency by a quantum chemical calculation [17±22]. Zhu and Zheng [23] and others studied the inhibition mechanism of an inhibitor in an acidic medium by using quantum chemical method [23±25]. The results from these researches have been used to interpret very well some experimental phenomenon. Our paper concerns the calculation of chemical adsorption energy between imidazolines and the Fe atom by quantum chemical methods, the prediction of their inhibition eciency, and then synthesis and measurement. Similar work published in literature has not been found up to now. The purpose of this paper is to provide information for the electron con®guration of several imidazoline inhibitors by the quantum chemical calculation and to seek the relationship between molecular structure and inhibition eciency. It is anticipated that the correlation will eventually result in the design and synthesis of new inhibitors to improve inhibition eciency. In order to further understand the relationship between structure of organic compounds and corrosion inhibition, three imidazoline derivatives with a di€erent electron-releasing substituent were designed by quantum chemical study. And then they were synthesized and measured by using weight loss and electrochemical method. 2. Computation model and methods In the view of ®lm formulation mechanism, the adsorption model of the inhibitor on a metal surface can be described in following Scheme 1.

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On a microscopic state, this ®lm is the regular arrangement of the adsorbed inhibitor molecule on the metal surface. Studying the mechanism at the molecule level, we can only focus chemical adsorption of one single molecule on the Fe atom. For this reason, a model of chemical adsorption of an imidazoline molecule on a Fe atom can be simulated as Scheme 2. The chemical adsorptive power is di€erent for the compounds with di€erent substituents. Therefore, we can take into account the following model compounds (Scheme 3). Optimization calculations were carried out with the MNDO method for compounds S-I, S-II and S-III in the Scheme 3. In the calculation, the distance (RNFe) from N to Fe atom in the Scheme 2 was gradually decreased to simulate the adsorption process. The equilibrium geometry parameters were obtained by MNDO method and then were used to calculate chemical adsorption by using CNDO/2 method. 3. Calculation results and aid design 3.1. Molecular structure property We have obtained molecular geometry and charge density by MNDO calculation. It is found that the coecient of HOMO is mainly contributed by N atoms in imidazoline ring. The HOMOs are occupied by a lone pair of electrons on the N atom of the molecule. The coecients from FMOs increases in the following order: compound S-I (1.327) < S-II (1.597) < S-III (2.153). Optimized values of two C±N bond-length in the imidazoline ring are 1.421 A and 1.309 AÊ, respectively. This means that the N1±C2±N3 bond is of P-p conjugation action between P-orbital of N1 atom and p-MO of C2±N3 bond. Owing to delocalization, p-electron is easily translated to Fe atom and is more favorable for chemical adsorption of the N atom on the metal surface. The chemical absorbability increases with the introduction of the electron-releasing substituent or conjugation system, which enhanced inhibition eciency. 3.2. Chemical adsorption energy Chemical adsorption energy can be described by interaction energy between the N and Fe atom (diatomic energy: ÿENFe in quantum chemistry). The larger

Scheme 1

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Scheme 2

absolute value of ENFe, the stronger chemical adsorption. Using CNDO/2 calculation, we have obtained ÿENFe, and overlap population (QNFe) between the N atom and Fe atom. It is found that energies of adsorption states reach a minimum at RNFe=2.04 AÊ for adsorption ®nal state of compound S-I (that is, equilibrium bond lengths of N 4 Fe is 2.04 AÊ, see Table 1). That of the compound S-II and S-III is at RNFe=1.80 AÊ. The typical results are given in Table 1. Stability energy (ESTA) can be written as follows: ESTA ˆ EAS ÿ EGS Where EAS and EGS represent the intrinsic energy of adsorption state and ground state respectively. The results are listed in Table 1. As shown in Table 1, calculated absolute value of ENFe, QNFe and ESTA increase with compound S-I, S-II, S-III. The RNFe (i.e. ligand bond N 4 Fe) is 1.8 AÊ for compounds S-II as well as S-III and shorter than the compound S-I. These results show further that a substituent containing an electron-releasing group or pconjugation system results in the stronger chemical adsorption for above imidazoline derivatives. For this reason, the inhibition eciency is predicted as following order: compound S-III>S-II>S-I. 3.3. Aid design According to calculated results, we have designed three compounds: R4=hydrocarbon; R5=H(I); R5=R4(II); R5=alkyromatic hydrocarbon (III) in Scheme 3 and predicted that inhibition eciency varies in the following order:

Scheme 3

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Table 1 The typical results by CNDO/2 method Compounds

S-I S-II S-III

RNFe (AÊ)

ENFe (au.)

2.040 1.800 1.800

QNFe

ESTA (au)

N1 ±Fe

N3±Fe

N1±Fe

N3±Fe

ÿ0.4605 ÿ0.5239 ÿ0.5491

ÿ0.3394 ÿ0.5917 ÿ0.7040

0.3751 0.5307 0.5424

0.3102 0.5917 0.6226

ÿ0.2332 ÿ0.3687 ÿ0.5644

compound III>II>I. Consequently, the synthesis and measurements have been performed for these compounds. 4. Synthesis and measured results 4.1. Synthesis By using polyamine, fatty acid and alkylaromatic hydrocarbon as feedstocks, we have synthesized three imidazoline derivatives (I, II and III) and carried out IR and UV spectral analyses. Strong absorption peaks at 1600 cmÿ1 of IR and 242 nm of UV are exhibited which are attributed to the C1N bond in imidazoline ring. These results are identical with those of Ref. [26]. The spectra data indicate that objective compounds have been synthesized. Weight loss and Table 2 Corrosion inhibition e€ect from weight loss methoda Compound

No.

Corrosion rate mg/cm2/h

PIC %

I

1 2 3 1 2 3 1 2 3 1 2 3 1 2 3

0.0651 0.0635 0.0625 0.0382 0.0365 0.0347 0.1276 0.1337 0.1328 0.0208 0.0226 0.0191 0.2135 0.2240 0.2188

50.46 51.67 52.44 70.93 72.22 73.59 ± ± ± 90.49 89.67 91.27 ± ± ±

II Blank III Blank

a Corrosion medium: 5% HCL solution; inhibitor concentration: 50 ppm; temperature: 28 218C; material: A3 steel pieces.

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electrochemical polarization methods were used to evaluate the performance of the corrosion inhibitor. 4.2. Weight loss method 200 ml of 5% HCL acid is held in a 250 ml beaker. The synthesized sample with the concentration of 50 ppm is added to the beaker. Cleaned and weighed A3 steel pieces are immersed in the acid for 48 h at room temperature. The percentage inhibition corrosion (PIC) was calculated by the following equation: PIC ˆ ‰…Vo ÿ V †=Vo Š  100% Where: Vo and V represent corrosion rate in a blank test and with addition of an anticorrosion composition, respectively. The results of the corrosion inhibition test are presented in Table 2. 4.3. Polarization curve method The mixture of 5% HCL and 50 ppm inhibitor concentration was prepared. Then carbon steel A3 electrodes were inserted in the mixture for 20 min at room temperature. The solution was stirred at the rate of about 300 rpm. The corrosion rates were monitored by means of polarization method. Using US 273 A instrument ®nished the measurements and the data were automatically treated with the Model 352A program. The results are given in Table 3, which gives good agreement with weight loss method. 5. Discussion 5.1. Conjugation system and subsittent e€ect For the compound S-I, C2 atom stands in SP3 hybrid and is linked to the N atom in single bond. Because of no Pz-AO, N1±C2±N3 bond can not form p-

Table 3 PIC results of polarization curve methoda Compounds

Icorr(ma/cm2)

Vcorr (mpy)

PIC (%)

I II III Blank

126.30 91.21 17.58 360.40

116.70 84.26 16.24 332.90

65.00 75.00 95.10

a Corrosion medium: 5% HCL solution; inhibitor concentration: 50 ppm; temperature: 28 218C; material: A3 steel electrode.

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conjugation system (see Fig. 1a). Therefore, the two C±N bonds are 1.461 AÊ and 1.462 AÊ, respectively, closing to standard single bond (1.46 AÊ). For the compounds S-II and S-III, however, the C2 atom stands in SP2 hybrid and has one p-MO. Pz±AO of N atom can interact with the p-MO of C2 atom to form P-p conjugation system for N1±C2±N3 bond. Optimized N1±C2 and C2±N3 bonds are 1.421 AÊ and 1.309 AÊ, shorter than the standard single bond (1.46 AÊ) and longer than the double bond (1.28 AÊ). This implies that N1±C2±N3 bond is of a conjugation property and averages in bond length (See Fig. 1b). Owing to the conjugation system, p-electron is easily translated to d-orbital of Fe atom along to p-system. For this reason, electron-releasing substituent or conjugation system on the C2 atom will strengthen remarkably chemical adsorption of the N atom on the metal surface. Hence we can predict that the introduction of an electron releasing substituent or conjugation system to imidazoline ring will promote interaction of N with Fe atom so as to raise inhibition eciency. Fortunately, the coecients from FMOs are in following order, S-I (1.327) < S-II (1.597) < S-III (2.153). And the calculated results of ENFe, QNFe and ESTA also have the same order (see Table 1). These show important substituent e€ect. The compound S-III has strongest interaction between N and Fe atoms, while compound S-I is weakest. The electron-releasing substituent or conjugation system obviously strengthens the interaction between the N and Fe atom. Therefore, it can be predicted that inhibition eciency is improved in the following order: compound I < II < III. 5.2. Experimental results Three synthesized compounds were measured by weight loss and electrochemical methods. The averaged percentage protection of two methods was obtained. The values from two methods have the same tendency: compound I (51.54%/65%) < II (72.25%/75%) < III (90.5%/95.1%). Measured results con®rm the quantum chemical calculation. Theoretical prediction is in good agreement with experimental data.

Fig. 1. (a) Non-conjugated system; (b) PÐp conjugated system.

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6. Conclusions 1. N atoms in imidazoline ring mainly contribute the coecients of HOMO. Lone pair electrons on N atom of the molecule occupy the HOMOs. The coecients from FMOs increases in the following order: compound S-I (1.327) < S-II (1.597) < S-III (2.153). 2. N1±C2±N3 bond is of P-p conjugation property. Introduction of electron releasing substituent or conjugation system on the C2 atom will remarkably strengthen chemical adsorption of the N atom on the metal surface. 3. Strong absorption peaks at 1600 cmÿ1 of IR and 242 nm of UV are exhibited for three synthesized compounds and assigned to the C1N bond in imidazoline ring. The spectra data indicate that objective compounds have been synthesized. 4. The averaged percentage protection (PIC) measured from two methods increases in the same order: compound I (51.54%/65%) < II (72.25%/ 75%) < III (90.5%/95.1%). Theoretical prediction is veri®ed by experimental results very well. 5. Based on the theoretical and experimental results it is indicated that the electron donor substituent, particularly the substituent group with conjugated system, introduced to imidazoline ring will improve inhibition eciency.

References [1] A. Ruscher, G. Kutsan, Z. Lukacs, Studies on the Mechanisms of Corrosion Inhibition by Acetylenic Compounds in Hydrochloric Acid Solution, Corrosion Science 35 (5±8) (1993) 1425± 1430. [2] R. Zvauya, J. Dawson, Inhibition Studies in Sweet Corrosion System by a Quaternary Ammonium Compound, J. Applied Electrochemistry 24 (1994) 943±947. [3] J.X. Zheng, J.M. Zhou, Control of Corrosion by Inhibitors in Drilling Muds Containing High Concentraion of H2S, Corrosion 49 (2) (1993) 170±174. [4] Y.C. He, J. Wang, B.G. Huang, et al., The corrosion and Scaling Inhibition by Imidazloine Derivatives MC and MP in Oil®eld Produced Water for Reinjection, Oil®eld Chemistry 14 (4) (1997) 336±339. [5] J.X. Zheng, The Present Situation of Research and Application of Inhibitors in China, Corrosion & Protection 18 (3) (1997) 132±136 (China). [6] S.G. Ning, M.L. Shi, et al., The Relationship of Corrosion Inhibition Eciency on Steel in Acids with Electron Density and the Energy of Frontical Orbital of Imidazoline Derivatives, J. Chinese Society for Corrosion and Protection 10 (4) (1990) 383±390 (China). [7] V.S. Sastri, J.R. Perumareddi, Selection of Corrosion Inhibitors for Use in Sour Media, Corrosion 50 (6) (1994) 432±437. [8] D.X. Wang, H.M. Xiao, S.S. Li, Quantum Mechanical and Molecular Mechanical Studies of the Hydrolysis of Methyl Nitrate and the Solvent E€ect, J. Physical Organic Chemistry 3 (1992) 361± 366. [9] A.E. Dorigo, K.N. Houk, On the Origin of Proximity E€ects on Reactivity: A Modi®ed MM2 Model for the Rates of Acid-Catalyed Lactionizations of Hydroxy Acids, J. Am. Chem. Soc. 109 (1987) 3698±3708. [10] Michael L. McKee, A Theoretical Study of Unimolecular Reaction of Dimethyl Persuulfoxide, J. Am. Chem. Soc. 120 (1998) 3963±3969.

D. Wang et al. / Corrosion Science 41 (1999) 1911±1919

1919

[11] A.D. Becke, Density-Function Thermochemistry III: The Role of Exact Exchange, J. Chem. Phys. 98 (7) (1993) 5648±5652. [12] Daqing Gao, Yuh-Kanf Pan, et al., Theoretical Evidence for a Concerted Mechanism of the Orirane Cleavage and A-ring Formation in Oxidosqulene Cyclization, J. Am. Chem. Soc. 120 (1998) 4045±4046. [13] S.B. Rong, H.L. Jiang, Z.Q. Chi, K.X. Chen, et al., Studies on Quantitative Structure-Activity Relationship of the Stereoisomers of 3-Methyl Fentanyl Derivatives, Acta Pharmaceutica Sinica 32 (6) (1997) 420±425 (China). [14] C. Alhambra, Li Wu, et al., Walden-Inversion Enforced Transition-State Stabilization in a Protein Tyrosine Phosphatose, J. Am. Chem. Soc. 120 (1998) 3858±3866. [15] P.L. Cummins, J.E. Gready, Coupled Semiempirical Molecular Orbital and Molecular Mechanics Model (QM/MM) for Organic Molecules in Aqueous Solution, J. Computational Chemistry 18 (12) (1997) 1496±1512. [16] D.Q. Zhang, L. Yu, Z. Lu, Inhibition and PPP Quantum Chemistry Study of Benzothiazole Derivatives, J. Chinese Society for Corrosion and Protection 18 (4) (1998) 307±310 (China). [17] J. Vosta, J. Eliasek, Study on Corrosion Inhibition from Aspect of Quantum Chemistry, Corrosion Science 11 (4) (1971) 223±229. [18] R. Sayos, M. Gonzalez, J.M. Costa, On the Use of Quantum Chemical Methods as an Additional Tool in Studying Corrosion Inhibitor Substances, Corrosion Science 26 (11) (1986) 927±934. [19] J.M. Costa, J.M. Lluch, The Use of Quantum Mechanics Calculations for the Study of Corrosion Inhibitors, Corrosion Science 24 (11/12) (1984) 929±933. [20] F.B. Growcock, Inhibition of Steel Corrosion in HCL by Derivatives of Cinnamaldehyde, Part I, Corrosion Inhibition Model, Corrosion 45 (12) (1989) 1003±1007. [21] F.B. Growcock, W.W. Freinier, Inhibition of Steel Corrosion in HCL by Derivatives of Cinnamaldehyde, Part II, Structure-Activity Correlation, Corrosion 45 (12) (1989) 1007±1015. [22] Z.L. Tang, S.Z. Song, Some Aspects of Quantum Chemical Study on Organic Inhibitors, J. Chinese Society for Corrosion and Protection 15 (3) (1995) 229±236 (China). [23] Z.L. Zhu, J.X. Zheng, On the Inhibition Mechanism of Inhibitor No. 7801 in an Acidic Medium, J. Huazhong Univ. of Sci. & Tech. 23 (5) (1995) 121±124 (China). [24] P.G. Abdul-Ahad, S.H.F. Al-Madfai, Elucidation of Corrosion Inhibition Mechanism by Means of Calculated Electronic Indexes, Corrosion 45 (12) (1989) 978±980. [25] M.D. Luo, L.A. Yao, Q.Y. Wu, A Study on Correlation Between Electronic Structure and Inhibition Properties of Five-Membered Dinitrogen Heterocyclic Compounds, J. Chinese Society for Corrosion and Protection 16 (3) (1996) 195±199 (China). [26] J.X. Zheng, Z.P. Lu, F.M. Peng, Synthesis, Identi®cation and Inhibitory Property of a New Imidazoline Corrosion Inhibitor, Oil®eld Chemistry 11 (2) (1994) 163±167 (China).