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Synthesis, characterization and computational chemical study of novel pyrazole derivatives as anticorrosion and antiscalant agents
Accepted Manuscript Synthesis, characterization and computational chemical study of novel pyrazole derivatives as anticorrosion and antiscalant agents F. El-Taib Heakal, S.K. Attia, S.A. Rizk, M.A. Abou Essa, A.E. Elkholy PII:
S0022-2860(17)30927-4
DOI:
10.1016/j.molstruc.2017.07.006
Reference:
MOLSTR 24033
To appear in:
Journal of Molecular Structure
Received Date: 24 May 2017 Revised Date:
5 July 2017
Accepted Date: 6 July 2017
Please cite this article as: F. El-Taib Heakal, S.K. Attia, S.A. Rizk, M.A. Abou Essa, A.E. Elkholy, Synthesis, characterization and computational chemical study of novel pyrazole derivatives as anticorrosion and antiscalant agents, Journal of Molecular Structure (2017), doi: 10.1016/ j.molstruc.2017.07.006. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Synthesis, characterization and computational chemical study of novel pyrazole derivatives as anticorrosion and antiscalant agents F. El-Taib Heakala, S.K. Attiab, S.A. Rizkc, M.A. Abou Essaa, A.E. Elkholyb* a
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Chemistry Department, Faculty of Science, Cairo University, 12613 Giza, Egypt
b
Department of Analysis and Evaluation, Egyptian Petroleum Research Institute, 11727 Cairo, Egypt
c
Department of Chemistry, Faculty of Science, Ain Shams University, 11566 Cairo, Egypt
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Abstract
Metals corrosion and scales deposition are two serious problems of heavy burden in most
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industries. Both problems can be mitigated by adding special chemicals capable of being adsorbed on metallic surfaces as well as on scale growing crystal surfaces. Efficient materials should be rich in functional groups containing heteroatoms and/or π bonds for supporting their adsorbability on surfaces. In the present work, four novel pyrazole derivatives were synthesized and characterized for their structures using elemental analysis and spectroscopic tools. The tested compounds were fabricated by treating 2,3-diaryloxirane-2,3-dicarbonitriles with different
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nitrogen nucleophiles. The density functional theory (DFT) was then applied to explore the structural and electronic characteristics of these materials. Molecular dynamics simulation was also run to scrutinize the ability of the prepared compounds to act as corrosion inhibitors and
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antiscalant agents by adsorbing on Fe and CaSO4 surfaces.
Keywords: Corrosion inhibitors; Antiscalants; DFT; Fukui indices; Molecular dynamics; *
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Pyrazole derivatives.
Corresponding author. Tel.: +20 01115619254; 010024350142
E-mail address: [email protected]; [email protected]
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1. Introduction
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Iron-based materials are used in manufacturing the infrastructures of most industries due to their low cost and high mechanical strength [1]. Unfortunately, these materials are susceptible to corrosion attack by the action of aggressive environments in contact to them (e.g. acids and brine solutions) [2]. Corrosion phenomenon is described as the deterioration of metallic materials or their steady eating away by the effect of their aggressive environment leading to one of the main
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problems in most industries, especially petroleum and gas production [2, 3]. The basic process of metallic corrosion in aqueous solutions consists of an anodic reaction (metal dissolution) and a M(s) → M(aq)n+ + ne −
Ox(aq) + ne → Red(aq)
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cathodic reduction of any oxidant present in the electrolyte solution (e.g. H+ or O2) [4]: anodic oxidation
(1)
cathodic reduction
(2)
Corrosion inhibition based on adding special chemicals into the solution in contact to the metal of interest is among the most suitable protective methods for metallic corrosion [5].
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On the other hand, scale formation is a severe problem encountered in many industries including oil or gas production, water transport and power generation [6]. Scales are sparingly soluble salts deposited in steam generators, boilers, pipes, and other equipments used in water processes. Calcium salts (e.g. calcium sulfate) are among the most salts causing scale deposition
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[7]. Gypsum (CaSO4. 2H2O) is formed whenever calcium and sulfate ions are present together (Eq. 3 and Eq. 4). Ca2+ ions are leached from calcium containing bases such as limestone (CaCO3) and lime (CaO) used in neutralization processes or introduced with some ores such as
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dolomite [8]. Then, gypsum is converted into anhydrite (CaSO4) at high temperatures [9]. H2SO4 + CaCO3(s) + H2O → CaSO4·2H2O(s) + CO2(g)
(3)
H2SO4 + CaO(s) + H2O → CaSO4·2H2O(s)
(4)
Among the methods used for inhibiting the growth of scale crystals is the addition of chemical inhibitors, called antiscalant agents [10].
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2,3-diaryloxirane-2,3-dicarbonitriles are well known as important synthetic intermediates [11]. The reported synthetic methods for 2,3-diaryloxirane-2,3-dicarbonitriles substituted pyrazole and azole hydrazone moieties afford an important class of compounds in different fields such as agricultural and medicinal chemistry due to their broad spectrum biological activities [12] as
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well as petroleum chemistry for their broad spectrum antioxidant and anticorrosive actions [1315]. Some pyrazole derivatives were prepared and presented in this paper one of them is a chalcone compound. Chalcone compounds represent a major class of natural products widely distributed in fruits, vegetables, spices, tea and soy based foodstuff. In addition, chalcones are
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valuable intermediates in organic synthesis [14, 15], having remarkable pharmacological activities [16] and exhibiting a multitude of biological activities [17].
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Herein, four novel pyrazole derivatives are synthesized and characterized by spectroscopic methods and elemental analysis. Their structures are studied using density functional theory (DFT) method. In addition, molecular dynamics simulation was performed to investigate their efficacy as corrosion and scale inhibitors. Hitherto, DFT is the most widely used methodology for the prediction of chemical reactivity of molecules, clusters and solids. It is a successful method in providing insights into the chemical reactivity indices such as HOMO and LUMO
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energies, energy gap (∆E), chemical hardness (η), electronegativity (χ), electrophilicity (ω) and nucleophilicity (ε) [18]. DFT uses a quantum methodology that provides a cost benefit, with a relatively small machine time and good accuracy because it uses only the electron density of the molecule instead of using all electrons of the system, [19]. Recently, molecular dynamics
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simulation is used to study the interaction between organic compounds and surfaces of metals [18-23] or scales [24,25]. There is a linear correlation between binding energy and inhibition
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efficiency, where inhibition efficiency increases with binding energy [26].
2. Experiments and calculations 2.1.
Synthesis schemes
2.1.1. 3-Amino-5,5-diphenyl- 4-oxo-4,5-dihydropyrazole (I) An equimolar mixture of the starting compound (2.26-3.14 g, 0.01 mol) and hydrazine derivatives (0.01 mol) is added in 50 mL boiling ethanol (Fig. 1). The reaction mixture was refluxed for 6 h. The solid separated after cooling was filtered off, washed by petroleum ether 3
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(b.p. 40- 60 oC), dried and then recrystallized from ethanol. 2.1.2. 3,3-Diphenyl-6-oxo-1,2,7-trihydro-pyrazolo[3,4-b]pyrazine (II) A mixture of compound I (2.5 g; 0.01 mol) and ethylglycinate (1.1 mL, 0.01 mol) is added in 50
cooling was filtered off, dried and then recrystallized from dioxane.
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mL boiling ethanol (Fig. 1). The reaction mixture was refluxed for 4 h. The solid separated after
2.1.3. 1,7-Acetyl-3,3-diphenyl-6-oxo-1,2,7-trihydro-pyrazolo[3,4-b]pyrazine (III)
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An equimolar mixture of compound II (2.90 g; 0.01 mol) and chloroacetic acid (1g; 0.01 mol) is added in 20 mL phosphorous oxychloride (Fig. 1). The reaction mixture was refluxed for 2 h then poured onto ice/H2O and the formed solid was separated, filtered off, washed by petroleum
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ether (b.p. 40- 60 oC), dried and the recrystallized from toluene.
2.1.4. 3,3-Diphenyl-1,2-(methylenedicarbonyl)-6-oxo-1,2,7-trihydro-pyrazolo[3,4-b]pyrazine (IV)
An equimolar mixture of compound II (2.90 g; 0.01 mol) and diethylmalonate (2.4 mL; 0.015
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mol) is added in 50 mL boiling ethanol (Fig. 1). The reaction mixture was refluxed for 4 h. The solid that separated after cooling was filtered off, washed by petroleum ether (b.p. 40- 60 oC), dried and then recrystallized from ethanol.
pyrazine (V)
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2.1.5. 1,2-(Benzylidinemethdicarbonyl)-3,3-diphenyl-6-oxo-1,2,7-trihydro-pyrazolo[3,4-b]
An equimolar mixture of compound II (2.90 g; 0.01 mol) and diethyl benzylidine malonate (2.50
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g; 0.01 mol) is added in 50 mL boiling ethanol (Fig. 1). The reaction mixture was refluxed for 6 h. The solid that separated after cooling was filtered off, washed by petroleum ether (b.p. 40- 60 o
C), dried and then crystallized from butanol.
2.2.
Products characterization
All melting points were determined on a stuart electric melting point apparatus. Elemental analyses were carried out by Elementar Viro El Microanalysis. FT-IR spectra (KBr) were recorded on infrared spectrometer FT-IR 400D using OMNIC program. 1H-NMR spectrometry was performed using Bruker spectrophotometer at 400 MHz using TMS as internal standard and 4
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with residual signals of the deuterated solvent: δ = 7.26 ppm for CDCl3 and δ = 2.51 ppm for DMSO-d6).
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C-NMR spectra were recorded on the same spectrometer at 100 MHz and
referenced to solvent signals, δ = 77 ppm for CDCl3 and δ = 39.50 ppm for DMSO-d6.
2.3.
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Homogeneity of all synthesized compounds was checked by thin layer chromatography (TLC). Computational details
The quantum chemical computational study in this work was carried out for the fabricated compounds (II-V) using Materials Studio 6.0 (MS 6.0) software from Accelrys, Inc. DMol3
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module was used to perform the DFT calculations using Perdew and Wang LDA exchangecorrelation functional and DND basis set. The calculated parameters involved the electron density, dipole moment, Fukui indices, Frontier molecular orbitals and Mulliken atomic charges.
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Molecular dynamics (MD) simulation was carried out to illustrate the adsorption of the molecules on the surfaces of Fe and CaSO4 at the molecular level. Forcite quench module in MS 6.0 software was employed to attain many different low-energy configurations for the studied molecules adsorbed over the adsorbents surfaces using COMPASS forcefield. COMPASS stands for condensed-phase optimized molecular potentials for atomistic simulation studies and it can
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be used to optimize the structures of all components of the system of interest [27]. Fe crystal with (110) cleavage [28] and dimensions of 24.824 Å × 24.824 Å and anhydrite crystal with (001) cleavage [24] and dimensions of 34.022 Å × 34.022 Å were utilized in the MD simulation. The crystals of both adsorbents were constrained so that their atoms would not disturb all
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through the quench process. Temperature was fixed at 298 K, with NVE (microcanonical) ensemble, with a time step of 0.1 fs and simulation time of 0.5 ps. The optimized structure of each molecule was put near adsorbent surface and the simulation was run. Using the quench MD
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method as mentioned above, the lowest energetic adsorption mode of a single molecule of each compound was displayed and its corresponding binding energy was calculated. The calculated binding energy (Ebind) expresses the interaction between each molecule and Fe surface and it is calculated using the following equation [23,29]: = − ( + )
(5)
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Etot represents the total energy of the most stable orientation of each molecule over adsorbent surface. Esorbent and Esorbate represent the energies of adsorbent surface (i.e. Fe (110) or CaSO4 (001)) and the unbound molecules, respectively.
3.1.
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3. Results and discussion Structure confirmation
The 2,3-diaryloxirane-2,3-dicarbonitrile was treated with hydrazine hydrate to afford 3-amino-1substituted-5,5-diphenyl-1H-pyrazol-4(5H)-ones, compound (I). When compound (I) was
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allowed to react with ethylglycinate in boiling ethanol, pyrazolo[3,4-b]triazinone (II) is produced. Reaction of compound (II) with chloroacetic acid in the presence of phosphorous
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oxychloride yielded a fused tricyclic pyrazole derivatives (III). Compound (II) was treated with diethylmalonate to afford tricyclicdione (IV). A novel chalcone, compound (V), was synthesized via the reaction of arylidene malonate with the pyrazolo[3,4-b]triazinone, i.e. compound (II). Elemental analysis and spectroscopic analyses have confirmed the structures of the prepared compounds. All FT-IR and 1H-NMR spectra of the compound (I) are displayed as supplementary data (Figure S1-15).
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3.1.1. 3-Amino-5,5-diphenyl-4-oxo-4,5-dihydropyrazole (I)
Yield 73%, m.p. 230-232 ºC. FT-IR (KBr) spectrum (Figure S1) shows absorption bands (in cm-1) at: 3310-3270 (NH), 3052 (CHAr), 1720 (CO). The 1H-NMR (DMSO) spectrum (Figure S2) shows signals (in ppm) at: 7.38–7.56 ppm (m, 10ArH aromatic protons), 11.8 and 13.2 (s,
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acidic 3NH protons which exchanged in D2O (Figure S3)). The 13C-NMR spectrum (not shown) shows signals (δ in ppm): 112 (2C), 120.4 (2CH), 129.6 (2CH), 130.5 (CH), 131.5 (CH), 132.3
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(2CH), 134.8 (CH), 137.4 (CH), 143.4 (C), 168.0 (C), 190.2 (C). Elemental analysis; Calc.: %C 71.71, %H 5.17, %N 16.73; Found: %C 71.60, %H 5.15, %N 16.50. 3.1.2. 3,3-Diphenyl-6-oxo-1,2,7-trihydro-pyrazolo[3,4-b]pyrazine (II) Yield 70%.m.p. 164-166 ºC. FT-IR (KBr) spectrum shows absorption bands (Figure S4) at (in cm-1): 3317, 3256 (NH), 3050 (CHAr), 1668 (C=O). The 1H-NMR (DMSO) spectrum shows signals (Figure S5) in ppm at: 6.8 (s, 1H, CHpy), 7.21-7.70 (m, 10ArH aromatic protons), singlet at 6.4, 9.7 and 12.4 (s, acidic 3NH protons which exchanged in D2O (Figure S6)). Elemental analysis; Calc.: %C 70.34, %H 4.82, %N 19.31; Found: %C 70.30, %H 4.78, %N 19.28. 6
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3.1.3. 1,7-Acetyl-3,3-diphenyl-6-oxo-1,2,7-trihydro-pyrazolo[3,4-b]pyrazine (III) Yield 55%. m.p. 110-112 ºC. FT-IR (KBr) spectrum shows absorption bands (Figure S7) at (in cm-1): 1613 (C=N), 1650, 1670, 1685 (CO), 3222 (NH). The 1H-NMR (DMSO) spectrum shows
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signals (Figure S8) in ppm at: 4.50 (s, 2H, CH2), 6.2 (s, 1H, PyH), multiplet at 7.44-7.73 (m, 10ArH aromatic protons), 6.2 (s, acidic NH proton which exchanged in D2O (Figure S9)). Elemental analysis; Calc.: %C 69.09, H 4.24, N 16.96; Found: %C 69.00, H 4.19, N 16.95.
3.1.4. 3,3-Diphenyl-1,2-(methylenedicarbonyl)-6-oxo-1,2,7-trihydro-pyrazolo[3,4-b]pyrazine
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(IV)
Yield 57%. m.p. 124-126 ºC. FT-IR (KBr) spectrum shows absorption bands (Figure S10) at
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(in cm-1): 1630 (CN), 1672, 1691(CO), 3245 (NH). The 1H-NMR (DMSO) spectrum shows signals (Figure S11) at (in ppm): 4.51 (s, 2H, CH2 (CO)2), 6.7 (s, 1H, PyH), 7.44-7.83 (s, 10H, ArH aromatic protons, 12.7 (s, acidic NH proton which exchanged in D2O (Figure S12)). Elemental analysis; Calc.: %C 67.03, H 3.91, N 15.64; Found: %C 67.05, H 3.88, N 15.61.
pyrazine (V)
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3.1.5. 1,2-(Benzylidinemethdicarbonyl)-3,3-diphenyl-6-oxo-1,2,7-trihydro-pyrazolo[3,4-b]
Yield 24%. m.p. 180-182 ºC. FT-IR (KBr) spectrum shows absorption bands (Figure S13) at (in cm-1): 1630 (C=N), 1666, 1671 (CO), 3302 (NH). The 1H-NMR (DMSO) spectrum shows
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signals (Figure S14) at (in ppm): 6.8 (bs, 2H, PyH and H arylidine), 7.12-7.53 (m, 10ArH aromatic protons, 13.2 (s, acidic NH proton which exchanged in D2O (Figure S15)). Elemental
3.2.
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analysis; Calc.: %C 71.88, %H 4.14, %N 12.90; Found: %C 71.85, %H 4.15, %N 12.83. DFT study
After building the molecular structures of the synthesized compounds, they are refined to be brought to a stable geometry. This refinement process is known as optimization, and it is an iterative procedure in which the coordinated atoms are adjusted such that the energy of the structure is brought to a stationary point in which the forces on the atoms are zero. As an example, the geometry of the compound (II) is gradually optimized and its energy is continuously decreased until the fluctuations in the molecule energy are minimized (Fig. 2) 7
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which indicates that the system has reached equilibrium. Fig. 3 displays the optimized geometries of oxirane derivatives in addition to their electron densities distributed over each molecule wholly.
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Frontier molecular orbitals include the highest occupied molecular orbital (HOMO) and the highest unoccupied molecular orbital (LUMO). The regions of highest electron density (HOMO) are the sites at which electrophilic attack occurs and represent the active centers, whereas the LUMO represent the regions of nucleophilic attack [22]. HOMO and LUMO distributions are
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displayed in Fig. 4. For the compounds (II), (III) and (IV), HOMOs and LUMOs are distributed over the pyrazolo[3,4-b]pyrazine unit which indicates that this unit is the most active center for electron transfer (either donation or acceptance). Unlikely, in the compound (V), HOMO is
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distributed nearly over the whole molecule but LUMO is located over the benzilidine moiety. So, this compound can donate electrons via any of its parts but can majorly host accepted electrons through the benzilidine part. Table 1 shows that the HOMO energies for the synthesized compounds follow the order: II > V > III > IV while LUMO energies for the synthesized compounds proceeds in the order: II > IV > III > V. The energy gap between the HOMO and LUMO frontier orbitals is one of the essential characteristics of molecules which plays a
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determining role in some cases such as electric properties, electronic spectra and photochemical reactions [30]. The energy gap (∆E = ELUMO - EHOMO) [31, 32] follows the sequence: II > IV > III > V, which is similar to that for LUMO energies.
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The absolute electronegativity (χ) and the absolute chemical hardness (η) are two quantities related to the ionization potential (I) and the electron affinity (A) where [33]:
=
(6)
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=
(7)
= −
(8)
= −
(9)
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The electrophilicity index (ω) is a global reactivity concept which measures the stabilization in energy when the system acquires an additional electronic charge from the environment. The nucleophilicity index (ε) is the inverse of ω. The ω and ε indices are defined as in Eq. 10 and 11
=
!" # % &
(10)
(11)
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$=
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[18]:
The electrophilicity index follows the trend: V > III > IV > II and vice versa for nucleophilicity index. The dipole moment (µ) is an index related to the distribution of electrons in a molecule
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and is the measure of polarity in a bond [32]. µ follows the order: V > III > II > IV. The local reactivity of organic molecules can be analyzed via the Fukui index (FI). FIs involve regions of nucleophilic attack (their function is f +(r)) and regions of electrophilic attack (their function is f ̶ (r)). Fukui functions, f +(r) and f ̶ (r), are obtained from Eq. 12 and 13 [34]. %
' (() =
% ∆*
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' (() = ∆* (+*∆ (() − +* (()) (+* (() − +*∆ (())
(12) (13)
where f +(r) function measures the reactivity with respect to nucleophilic attack at the site r. The
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larger the values of f +(r), the more electrons accepted by the molecule during a nucleophilic attack. Conversely, the f ̶ (r) function measures the reactivity with respect to electrophilic attack
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at the site r. Fukui indices for the molecules (II) and (III) are distributed over pyrazolo[3,4b]pyrazine moiety the same as HOMO and LUMO distributions. As for the molecules (IV) and (V), Fukui indices are very weak and located mainly only over the carbonyl groups but f ̶ (r) is somewhat stronger for the compound V and majorly distributed over the benzilidine moiety. The Fukui function for radical attack, f 0(r), is simply the average of these two. The concept of atomic charge is a valuable tool to aid in understanding the properties of a molecule. The most common computational technique to calculate the atomic charges is Mulliken population analysis where the total electronic charges are distributed among the atoms 9
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in a molecule [35]. The Mulliken charge distribution of the synthesized compounds is presented in Table 2. It’s readily observed that hetero atoms (O and N) have the highest charge densities among all atoms. The regions of highest electron density are generally the sites at which electrophiles attack the molecule [33] and therefore O and N atoms are the most active centers in
3.3.
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these molecules. Molecular dynamics simulation
3.3.1. As corrosion inhibitors
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Generally, for a material to be effective as a corrosion inhibitor, it must be characterized by containing non-bonded electrons (free lone pairs) and/or π-electrons which facilitate electron transfer between the inhibitor and the metal [2, 36]. The synthesized compounds under study are
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rich in O and N atoms containing free lone pairs of electrons in addition to double bonds and aromatic rings containing π-electrons. The regions of the highest electron density (HOMOs) are the sites susceptible to electrophilic attack while antibonding orbitals (LUMOs) can accept electrons from Fe d-orbital [27]. Overall, excellent organic corrosion inhibitors are usually not only those donate electrons to the unoccupied metal d-orbitals but also accept free electrons from
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the metal via back-donation [27]. According to literature [22, 27] low values of the gap energy (∆E = ELUMO – EHOMO) will provide good inhibition efficiencies because the energy to remove an electron from the last occupied orbital (HOMO) of the inhibitor will be minimized and it will be easy to donate electrons to metal d-orbital and ELUMO will be minimum so that it can accept
be present.
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electrons from the filled Fe 4s2 [37]. However, one of these mechanisms may occur or both may
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MD simulation is performed for the synthesized compounds to investigate their ability to adsorb on Fe surface and the calculated binding energies (Ebind) are listed in Table 3. The values of Ebind calculated for these compounds reveal that their absolute magnitudes increase as the χ increases following the order: V > IV > III > II. In other words, the more electronegative the molecule, the better its interaction with Fe surface. These observations indicate that these compounds may act as potential inhibitors for Fe corrosion via electron transfer from metal to inhibitor where the transferred electrons are hosted in the antibonding molecular orbitals (LUMOs) and the predicted inhibition efficiency follows the order V > IV > III > II. Fig. 6 displays the adsorption modes of the prepared compounds on Fe surface where all molecules 10
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have adapted their geometries to properly adsorb on Fe surface. The pyrazolo[3,4-b]pyrazine unit is the closest moiety to Fe surface which indicates that its atoms are the main active site towards interaction with Fe surface.
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3.3.1. As antiscalant agents Controlling scaling phenomenon proceeds via the adsorption of antiscalant molecules on the growing scale crystals [38]. MD simulation is performed to study the adsorption tendency of the synthesized compounds on anhydrite (001) surface in an attempt to use them as scale inhibitors.
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MD simulation reveals that the absolute magnitudes of the calculated binding energy (Ebind) between these compounds and anhydrite (001) surface proceeds in the order: II > III > IV > V.
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Table 1 shows that II < III < IV < V in the calculated χ values. Thus, Ebind increases as χ decreases. So, these compounds may act as inhibitors for scale formation via Coulomb electrostatic interactions between the partially negatively charged functional groups of the inhibitor and the positively charged calcium ion of anhydrite and the predicted inhibition efficiency follows the order II > III > IV > V. Fig. 7 displays the adsorption modes of the prepared compounds on anhydrite surface. It’s noted that the closest parts of these molecules are
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the pyrazole and phenyl rings which may be due to the availability of free lone pairs of electrons in addition to π-electrons. Thus, these compounds can occupy the growing points of anhydrite crystals and hinder the arrival of further scaling ions, i.e. Ca2+ and SO42- [25]. Then the crystal morphology is changed and the scale crystals cannot be longer able to grow normally. This
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causes the crystals to become distorted and the internal stress of crystals increases which could result in crystal fractures [39].
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Conclusions
In this work, four novel pyrazole derivatives have been synthesized and characterized using elemental analysis and spectroscopic tools. In addition, the DFT method was employed to achieve a deep insight into their geometry and electronic properties. MD simulation has been employed to investigate the potentiality of these materials as inhibitors for both Fe corrosion and scale (CaSO4) formation. It is concluded that the tested compounds have the tendency to adsorb on Fe surface following the order: V > IV > III > II. Also, they have the tendency to adsorb on
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CaSO4 crystals and thus can deter scale formation and deposition in the following trend: II > III > IV > V.
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Carbon Steel in Produced Water, Zeitschrift für Physikalische Chemie, DOI (2017) doi: 10.1515/zpch-2017-0949.
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base derived from 2-pyridincarboxaldehyde and its Ni (II) complex, Journal of Molecular Structure, 1143 (2017) 424-430. [31] J. Fang, J. Li, Quantum chemistry study on the relationship between molecular structure and corrosion inhibition efficiency of amides, J. Mol. Struct., 593 (2002) 179-185. [32] H.M. Abd El-Lateef, M.A. Abo-Riya, A.H. Tantawy, Empirical and quantum chemical studies on the corrosion inhibition performance of some novel synthesized cationic gemini surfactants on carbon steel pipelines in acid pickling processes, Corros. Sci., 108 (2016) 94-110.
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[33] A.Y. Musa, A.A.H. Kadhum, A.B. Mohamad, A.A.B. Rahoma, H. Mesmari, Electrochemical and quantum chemical calculations on 4, 4-dimethyloxazolidine-2-thione as inhibitor for mild steel corrosion in hydrochloric acid, J. Mol. Struct., 969 (2010) 233-237. [34] X. Long, Y. Chen, J. Chen, Z. Xu, Q. Liu, Z. Du, The effect of water molecules on the thiol
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medium by 1, 12-bis (1, 2, 4-triazolyl) dodecane, Corros. Sci., 47 (2005) 447-459. [37] Y. Li, P. Zhao, Q. Liang, B. Hou, Berberine as a natural source inhibitor for mild steel in 1 M H2SO4, Appl. Surf. Sci., 252 (2005) 1245-1253.
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methods, Desalination, 304 (2012) 1-10.
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Tables
EHOMO (Ha)
ELUMO (Ha)
∆E (Ha)
∆E (eV)
I (eV)
A (eV)
χ (eV)
η (eV)
ω
ε
-0.1923
-0.0947
0.0976
2.6561
5.2332
2.5772
3.9052
1.3280
5.7419
0.1742
7.2793
-0.1987
-0.1240
0.0747
2.0329
5.4074
3.3745
4.3910
1.0164
9.4849
0.1054
8.7290
-0.2063
-0.1183
0.0880
2.3948
5.6142
3.2194
4.4168
1.1974
8.1460
0.1228
3.0498
-0.1973
-0.1399
0.0574
1.5621
5.3693
3.8072
4.5883
0.7810
13.4779
0.0742
9.1057
(II) (III) (IV) (V)
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Compound
(II)
(III)
Total charges
Atoms
Total charges
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Table 2: Mulliken total atomic charges.
Atoms
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Table 1: DFT parameters calculated for the synthesized compounds.
(IV)
Atoms
(V)
Total charges
Atoms
Total charges
-0.106
C(1)
-0.088
C(1)
-0.189
C(1)
-0.079
C(2)
0.443
C(2)
0.420
C(2)
0.465
C(2)
0.448
N(3)
-0.608
N(3)
-0.378
N(3)
-0.602
N(3)
-0.587
C(4)
0.456
C(4)
0.352
C(4)
0.498
C(4)
0.430
C(5)
0.097
C(5)
0.097
C(5)
0.114
C(5)
0.114
N(6)
-0.347
N(6)
C(7)
-0.031
C(7)
N(8)
-0.380
N(8)
N(9)
-0.476
N(9)
C(10)
-0.223
C(10)
C(11)
0.100
C(12)
-0.196
C(13)
-0.177
C(14)
-0.173
N(6)
-0.242
N(6)
-0.342
-0.024
C(7)
-0.082
C(7)
-0.012
-0.389
N(8)
-0.194
N(8)
-0.221
-0.235
N(9)
-0.160
N(9)
-0.239
-0.223
C(10)
-0.210
C(10)
-0.208
C(11)
0.093
C(11)
0.223
C(11)
0.132
C(12)
-0.197
C(12)
-0.197
C(12)
-0.200
C(13)
-0.174
C(13)
-0.159
C(13)
-0.179
C(14)
-0.169
C(14)
-0.158
C(14)
-0.171
-0.168
C(15)
-0.165
C(15)
-0.158
C(15)
-0.169
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-0.336
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C(15)
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C(1)
0.110
C(16)
0.110
C(16)
0.170
C(16)
0.056
-0.182
C(17)
-0.179
C(17)
-0.212
C(17)
-0.177
-0.176
C(18)
-0.177
C(18)
-0.168
C(18)
-0.178
-0.174
C(19)
-0.172
C(19)
-0.159
C(19)
-0.169
C(20)
-0.176
C(20)
-0.175
C(20)
-0.162
C(20)
-0.181
C(21)
-0.232
C(21)
-0.227
C(21)
-0.248
C(21)
-0.180
O(22)
-0.549
O(22)
-0.464
O(22)
-0.430
O(22)
-0.522
H(23)
0.220
H(23)
0.232
H(23)
0.185
H(23)
0.234
H(24)
0.385
H(24)
0.316
H(24)
0.397
H(24)
0.420
C(16) C(17) C(18) C(19)
16
µ (Debye)
0.329
H(25)
0.172
H(25)
0.139
H(25)
0.182
H(26)
0.378
H(26)
0.218
H(26)
0.179
H(26)
0.213
H(27)
0.174
H(27)
0.187
H(27)
0.163
H(27)
0.183
H(28)
0.215
H(28)
0.186
H(28)
0.162
H(28)
0.181
H(29)
0.183
H(29)
0.187
H(29)
0.161
H(29)
0.184
H(30)
0.180
H(30)
0.194
H(30)
0.183
H(30)
0.199
H(31)
0.181
H(31)
0.183
H(31)
0.162
H(31)
H(32)
0.198
H(32)
0.181
H(32)
0.161
H(32)
H(33)
0.181
H(33)
0.181
H(33)
0.164
H(33)
H(34)
0.178
H(34)
0.195
H(34)
0.220
H(34)
H(35)
0.178
C(35)
-0.247
C(35)
0.440
C(35)
H(36)
0.187
C(36)
0.438
C(36)
-0.581
C(36)
------
------
O(37)
-0.423
C(37)
0.437
------
------
H(38)
0.258
O(38)
-0.407
------
------
H(39)
0.244
O(39)
-0.417
------
------
------
------
H(40)
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
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H(25)
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0.182 0.179 0.179 0.202 0.410
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-0.014 0.408
O(38)
-0.495
O(39)
-0.523
0.259
C(40)
-0.180
H(41)
0.254
C(41)
0.104
------
------
C(42)
-0.195
------
------
C(43)
-0.173
------
------
C(44)
-0.152
------
------
C(45)
-0.181
------
------
C(46)
-0.146
------
------
------
H(47)
0.229
------
------
------
H(48)
0.191
------
------
------
H(49)
0.191
------
------
------
H(50)
0.194
------
------
------
H(51)
0.194
------
------
------
H(52)
0.233
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C(37)
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Table 3: The calculated binding energy for the interaction between the synthesized compounds with Fe (110) and anhydrite (001). Compound (II) (III) (IV) (V)
Ebind (kJ/mol) With Fe(110) With anhydrite(001) -119.14 -135.84 -140.88 -201.32
-868.44 -815.81 -811.72 -776.30
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Figures
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Fig. 1: Preparation scheme of the compounds under study.
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Fig. 2: Energy optimization steps of compound (II).
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(II)
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(IV)
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(III)
(V)
Fig. 3: Optimized structure (left) and electron density (right) obtained for the synthesized compounds. Color index: White = H, Grey = C, Blue = N and Red = O (vide the web version of this article).
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(II)
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(IV)
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(III)
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(V)
Fig. 4: HOMO (left) and LUMO (right) obtained for the synthesized compounds.
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DOT
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ADO
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BDO
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DMO
Fig. 5: Fukui indices obtained for the synthesized compounds: f ̶ (left), f + (middle) and f 0 (right).
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ADO
BDO
DMO
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DOT
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Fig. 6: Adsorption modes of the synthesized compounds on Fe (110).
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ADO
BDO
DMO
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DOT
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Fig. 7: Adsorption modes of the synthesized compounds on CaSO4 (001).
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Highlights Four pyrazoles were synthesized and characterized elementally and spectroscopically. DFT method was employed to fully scrutinize their structural characteristics.
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Molecular dynamics simulation is used to test their adsorbability on Fe and CaSO4.
S0022-2860(17)30927-4
DOI:
10.1016/j.molstruc.2017.07.006
Reference:
MOLSTR 24033
To appear in:
Journal of Molecular Structure
Received Date: 24 May 2017 Revised Date:
5 July 2017
Accepted Date: 6 July 2017
Please cite this article as: F. El-Taib Heakal, S.K. Attia, S.A. Rizk, M.A. Abou Essa, A.E. Elkholy, Synthesis, characterization and computational chemical study of novel pyrazole derivatives as anticorrosion and antiscalant agents, Journal of Molecular Structure (2017), doi: 10.1016/ j.molstruc.2017.07.006. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Synthesis, characterization and computational chemical study of novel pyrazole derivatives as anticorrosion and antiscalant agents F. El-Taib Heakala, S.K. Attiab, S.A. Rizkc, M.A. Abou Essaa, A.E. Elkholyb* a
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Chemistry Department, Faculty of Science, Cairo University, 12613 Giza, Egypt
b
Department of Analysis and Evaluation, Egyptian Petroleum Research Institute, 11727 Cairo, Egypt
c
Department of Chemistry, Faculty of Science, Ain Shams University, 11566 Cairo, Egypt
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Abstract
Metals corrosion and scales deposition are two serious problems of heavy burden in most
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industries. Both problems can be mitigated by adding special chemicals capable of being adsorbed on metallic surfaces as well as on scale growing crystal surfaces. Efficient materials should be rich in functional groups containing heteroatoms and/or π bonds for supporting their adsorbability on surfaces. In the present work, four novel pyrazole derivatives were synthesized and characterized for their structures using elemental analysis and spectroscopic tools. The tested compounds were fabricated by treating 2,3-diaryloxirane-2,3-dicarbonitriles with different
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nitrogen nucleophiles. The density functional theory (DFT) was then applied to explore the structural and electronic characteristics of these materials. Molecular dynamics simulation was also run to scrutinize the ability of the prepared compounds to act as corrosion inhibitors and
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antiscalant agents by adsorbing on Fe and CaSO4 surfaces.
Keywords: Corrosion inhibitors; Antiscalants; DFT; Fukui indices; Molecular dynamics; *
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Pyrazole derivatives.
Corresponding author. Tel.: +20 01115619254; 010024350142
E-mail address: [email protected]; [email protected]
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1. Introduction
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Iron-based materials are used in manufacturing the infrastructures of most industries due to their low cost and high mechanical strength [1]. Unfortunately, these materials are susceptible to corrosion attack by the action of aggressive environments in contact to them (e.g. acids and brine solutions) [2]. Corrosion phenomenon is described as the deterioration of metallic materials or their steady eating away by the effect of their aggressive environment leading to one of the main
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problems in most industries, especially petroleum and gas production [2, 3]. The basic process of metallic corrosion in aqueous solutions consists of an anodic reaction (metal dissolution) and a M(s) → M(aq)n+ + ne −
Ox(aq) + ne → Red(aq)
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cathodic reduction of any oxidant present in the electrolyte solution (e.g. H+ or O2) [4]: anodic oxidation
(1)
cathodic reduction
(2)
Corrosion inhibition based on adding special chemicals into the solution in contact to the metal of interest is among the most suitable protective methods for metallic corrosion [5].
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On the other hand, scale formation is a severe problem encountered in many industries including oil or gas production, water transport and power generation [6]. Scales are sparingly soluble salts deposited in steam generators, boilers, pipes, and other equipments used in water processes. Calcium salts (e.g. calcium sulfate) are among the most salts causing scale deposition
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[7]. Gypsum (CaSO4. 2H2O) is formed whenever calcium and sulfate ions are present together (Eq. 3 and Eq. 4). Ca2+ ions are leached from calcium containing bases such as limestone (CaCO3) and lime (CaO) used in neutralization processes or introduced with some ores such as
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dolomite [8]. Then, gypsum is converted into anhydrite (CaSO4) at high temperatures [9]. H2SO4 + CaCO3(s) + H2O → CaSO4·2H2O(s) + CO2(g)
(3)
H2SO4 + CaO(s) + H2O → CaSO4·2H2O(s)
(4)
Among the methods used for inhibiting the growth of scale crystals is the addition of chemical inhibitors, called antiscalant agents [10].
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2,3-diaryloxirane-2,3-dicarbonitriles are well known as important synthetic intermediates [11]. The reported synthetic methods for 2,3-diaryloxirane-2,3-dicarbonitriles substituted pyrazole and azole hydrazone moieties afford an important class of compounds in different fields such as agricultural and medicinal chemistry due to their broad spectrum biological activities [12] as
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well as petroleum chemistry for their broad spectrum antioxidant and anticorrosive actions [1315]. Some pyrazole derivatives were prepared and presented in this paper one of them is a chalcone compound. Chalcone compounds represent a major class of natural products widely distributed in fruits, vegetables, spices, tea and soy based foodstuff. In addition, chalcones are
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valuable intermediates in organic synthesis [14, 15], having remarkable pharmacological activities [16] and exhibiting a multitude of biological activities [17].
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Herein, four novel pyrazole derivatives are synthesized and characterized by spectroscopic methods and elemental analysis. Their structures are studied using density functional theory (DFT) method. In addition, molecular dynamics simulation was performed to investigate their efficacy as corrosion and scale inhibitors. Hitherto, DFT is the most widely used methodology for the prediction of chemical reactivity of molecules, clusters and solids. It is a successful method in providing insights into the chemical reactivity indices such as HOMO and LUMO
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energies, energy gap (∆E), chemical hardness (η), electronegativity (χ), electrophilicity (ω) and nucleophilicity (ε) [18]. DFT uses a quantum methodology that provides a cost benefit, with a relatively small machine time and good accuracy because it uses only the electron density of the molecule instead of using all electrons of the system, [19]. Recently, molecular dynamics
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simulation is used to study the interaction between organic compounds and surfaces of metals [18-23] or scales [24,25]. There is a linear correlation between binding energy and inhibition
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efficiency, where inhibition efficiency increases with binding energy [26].
2. Experiments and calculations 2.1.
Synthesis schemes
2.1.1. 3-Amino-5,5-diphenyl- 4-oxo-4,5-dihydropyrazole (I) An equimolar mixture of the starting compound (2.26-3.14 g, 0.01 mol) and hydrazine derivatives (0.01 mol) is added in 50 mL boiling ethanol (Fig. 1). The reaction mixture was refluxed for 6 h. The solid separated after cooling was filtered off, washed by petroleum ether 3
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(b.p. 40- 60 oC), dried and then recrystallized from ethanol. 2.1.2. 3,3-Diphenyl-6-oxo-1,2,7-trihydro-pyrazolo[3,4-b]pyrazine (II) A mixture of compound I (2.5 g; 0.01 mol) and ethylglycinate (1.1 mL, 0.01 mol) is added in 50
cooling was filtered off, dried and then recrystallized from dioxane.
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mL boiling ethanol (Fig. 1). The reaction mixture was refluxed for 4 h. The solid separated after
2.1.3. 1,7-Acetyl-3,3-diphenyl-6-oxo-1,2,7-trihydro-pyrazolo[3,4-b]pyrazine (III)
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An equimolar mixture of compound II (2.90 g; 0.01 mol) and chloroacetic acid (1g; 0.01 mol) is added in 20 mL phosphorous oxychloride (Fig. 1). The reaction mixture was refluxed for 2 h then poured onto ice/H2O and the formed solid was separated, filtered off, washed by petroleum
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ether (b.p. 40- 60 oC), dried and the recrystallized from toluene.
2.1.4. 3,3-Diphenyl-1,2-(methylenedicarbonyl)-6-oxo-1,2,7-trihydro-pyrazolo[3,4-b]pyrazine (IV)
An equimolar mixture of compound II (2.90 g; 0.01 mol) and diethylmalonate (2.4 mL; 0.015
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mol) is added in 50 mL boiling ethanol (Fig. 1). The reaction mixture was refluxed for 4 h. The solid that separated after cooling was filtered off, washed by petroleum ether (b.p. 40- 60 oC), dried and then recrystallized from ethanol.
pyrazine (V)
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2.1.5. 1,2-(Benzylidinemethdicarbonyl)-3,3-diphenyl-6-oxo-1,2,7-trihydro-pyrazolo[3,4-b]
An equimolar mixture of compound II (2.90 g; 0.01 mol) and diethyl benzylidine malonate (2.50
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g; 0.01 mol) is added in 50 mL boiling ethanol (Fig. 1). The reaction mixture was refluxed for 6 h. The solid that separated after cooling was filtered off, washed by petroleum ether (b.p. 40- 60 o
C), dried and then crystallized from butanol.
2.2.
Products characterization
All melting points were determined on a stuart electric melting point apparatus. Elemental analyses were carried out by Elementar Viro El Microanalysis. FT-IR spectra (KBr) were recorded on infrared spectrometer FT-IR 400D using OMNIC program. 1H-NMR spectrometry was performed using Bruker spectrophotometer at 400 MHz using TMS as internal standard and 4
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with residual signals of the deuterated solvent: δ = 7.26 ppm for CDCl3 and δ = 2.51 ppm for DMSO-d6).
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C-NMR spectra were recorded on the same spectrometer at 100 MHz and
referenced to solvent signals, δ = 77 ppm for CDCl3 and δ = 39.50 ppm for DMSO-d6.
2.3.
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Homogeneity of all synthesized compounds was checked by thin layer chromatography (TLC). Computational details
The quantum chemical computational study in this work was carried out for the fabricated compounds (II-V) using Materials Studio 6.0 (MS 6.0) software from Accelrys, Inc. DMol3
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module was used to perform the DFT calculations using Perdew and Wang LDA exchangecorrelation functional and DND basis set. The calculated parameters involved the electron density, dipole moment, Fukui indices, Frontier molecular orbitals and Mulliken atomic charges.
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Molecular dynamics (MD) simulation was carried out to illustrate the adsorption of the molecules on the surfaces of Fe and CaSO4 at the molecular level. Forcite quench module in MS 6.0 software was employed to attain many different low-energy configurations for the studied molecules adsorbed over the adsorbents surfaces using COMPASS forcefield. COMPASS stands for condensed-phase optimized molecular potentials for atomistic simulation studies and it can
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be used to optimize the structures of all components of the system of interest [27]. Fe crystal with (110) cleavage [28] and dimensions of 24.824 Å × 24.824 Å and anhydrite crystal with (001) cleavage [24] and dimensions of 34.022 Å × 34.022 Å were utilized in the MD simulation. The crystals of both adsorbents were constrained so that their atoms would not disturb all
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through the quench process. Temperature was fixed at 298 K, with NVE (microcanonical) ensemble, with a time step of 0.1 fs and simulation time of 0.5 ps. The optimized structure of each molecule was put near adsorbent surface and the simulation was run. Using the quench MD
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method as mentioned above, the lowest energetic adsorption mode of a single molecule of each compound was displayed and its corresponding binding energy was calculated. The calculated binding energy (Ebind) expresses the interaction between each molecule and Fe surface and it is calculated using the following equation [23,29]: = − ( + )
(5)
5
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Etot represents the total energy of the most stable orientation of each molecule over adsorbent surface. Esorbent and Esorbate represent the energies of adsorbent surface (i.e. Fe (110) or CaSO4 (001)) and the unbound molecules, respectively.
3.1.
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3. Results and discussion Structure confirmation
The 2,3-diaryloxirane-2,3-dicarbonitrile was treated with hydrazine hydrate to afford 3-amino-1substituted-5,5-diphenyl-1H-pyrazol-4(5H)-ones, compound (I). When compound (I) was
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allowed to react with ethylglycinate in boiling ethanol, pyrazolo[3,4-b]triazinone (II) is produced. Reaction of compound (II) with chloroacetic acid in the presence of phosphorous
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oxychloride yielded a fused tricyclic pyrazole derivatives (III). Compound (II) was treated with diethylmalonate to afford tricyclicdione (IV). A novel chalcone, compound (V), was synthesized via the reaction of arylidene malonate with the pyrazolo[3,4-b]triazinone, i.e. compound (II). Elemental analysis and spectroscopic analyses have confirmed the structures of the prepared compounds. All FT-IR and 1H-NMR spectra of the compound (I) are displayed as supplementary data (Figure S1-15).
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3.1.1. 3-Amino-5,5-diphenyl-4-oxo-4,5-dihydropyrazole (I)
Yield 73%, m.p. 230-232 ºC. FT-IR (KBr) spectrum (Figure S1) shows absorption bands (in cm-1) at: 3310-3270 (NH), 3052 (CHAr), 1720 (CO). The 1H-NMR (DMSO) spectrum (Figure S2) shows signals (in ppm) at: 7.38–7.56 ppm (m, 10ArH aromatic protons), 11.8 and 13.2 (s,
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acidic 3NH protons which exchanged in D2O (Figure S3)). The 13C-NMR spectrum (not shown) shows signals (δ in ppm): 112 (2C), 120.4 (2CH), 129.6 (2CH), 130.5 (CH), 131.5 (CH), 132.3
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(2CH), 134.8 (CH), 137.4 (CH), 143.4 (C), 168.0 (C), 190.2 (C). Elemental analysis; Calc.: %C 71.71, %H 5.17, %N 16.73; Found: %C 71.60, %H 5.15, %N 16.50. 3.1.2. 3,3-Diphenyl-6-oxo-1,2,7-trihydro-pyrazolo[3,4-b]pyrazine (II) Yield 70%.m.p. 164-166 ºC. FT-IR (KBr) spectrum shows absorption bands (Figure S4) at (in cm-1): 3317, 3256 (NH), 3050 (CHAr), 1668 (C=O). The 1H-NMR (DMSO) spectrum shows signals (Figure S5) in ppm at: 6.8 (s, 1H, CHpy), 7.21-7.70 (m, 10ArH aromatic protons), singlet at 6.4, 9.7 and 12.4 (s, acidic 3NH protons which exchanged in D2O (Figure S6)). Elemental analysis; Calc.: %C 70.34, %H 4.82, %N 19.31; Found: %C 70.30, %H 4.78, %N 19.28. 6
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3.1.3. 1,7-Acetyl-3,3-diphenyl-6-oxo-1,2,7-trihydro-pyrazolo[3,4-b]pyrazine (III) Yield 55%. m.p. 110-112 ºC. FT-IR (KBr) spectrum shows absorption bands (Figure S7) at (in cm-1): 1613 (C=N), 1650, 1670, 1685 (CO), 3222 (NH). The 1H-NMR (DMSO) spectrum shows
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signals (Figure S8) in ppm at: 4.50 (s, 2H, CH2), 6.2 (s, 1H, PyH), multiplet at 7.44-7.73 (m, 10ArH aromatic protons), 6.2 (s, acidic NH proton which exchanged in D2O (Figure S9)). Elemental analysis; Calc.: %C 69.09, H 4.24, N 16.96; Found: %C 69.00, H 4.19, N 16.95.
3.1.4. 3,3-Diphenyl-1,2-(methylenedicarbonyl)-6-oxo-1,2,7-trihydro-pyrazolo[3,4-b]pyrazine
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(IV)
Yield 57%. m.p. 124-126 ºC. FT-IR (KBr) spectrum shows absorption bands (Figure S10) at
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(in cm-1): 1630 (CN), 1672, 1691(CO), 3245 (NH). The 1H-NMR (DMSO) spectrum shows signals (Figure S11) at (in ppm): 4.51 (s, 2H, CH2 (CO)2), 6.7 (s, 1H, PyH), 7.44-7.83 (s, 10H, ArH aromatic protons, 12.7 (s, acidic NH proton which exchanged in D2O (Figure S12)). Elemental analysis; Calc.: %C 67.03, H 3.91, N 15.64; Found: %C 67.05, H 3.88, N 15.61.
pyrazine (V)
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3.1.5. 1,2-(Benzylidinemethdicarbonyl)-3,3-diphenyl-6-oxo-1,2,7-trihydro-pyrazolo[3,4-b]
Yield 24%. m.p. 180-182 ºC. FT-IR (KBr) spectrum shows absorption bands (Figure S13) at (in cm-1): 1630 (C=N), 1666, 1671 (CO), 3302 (NH). The 1H-NMR (DMSO) spectrum shows
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signals (Figure S14) at (in ppm): 6.8 (bs, 2H, PyH and H arylidine), 7.12-7.53 (m, 10ArH aromatic protons, 13.2 (s, acidic NH proton which exchanged in D2O (Figure S15)). Elemental
3.2.
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analysis; Calc.: %C 71.88, %H 4.14, %N 12.90; Found: %C 71.85, %H 4.15, %N 12.83. DFT study
After building the molecular structures of the synthesized compounds, they are refined to be brought to a stable geometry. This refinement process is known as optimization, and it is an iterative procedure in which the coordinated atoms are adjusted such that the energy of the structure is brought to a stationary point in which the forces on the atoms are zero. As an example, the geometry of the compound (II) is gradually optimized and its energy is continuously decreased until the fluctuations in the molecule energy are minimized (Fig. 2) 7
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which indicates that the system has reached equilibrium. Fig. 3 displays the optimized geometries of oxirane derivatives in addition to their electron densities distributed over each molecule wholly.
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Frontier molecular orbitals include the highest occupied molecular orbital (HOMO) and the highest unoccupied molecular orbital (LUMO). The regions of highest electron density (HOMO) are the sites at which electrophilic attack occurs and represent the active centers, whereas the LUMO represent the regions of nucleophilic attack [22]. HOMO and LUMO distributions are
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displayed in Fig. 4. For the compounds (II), (III) and (IV), HOMOs and LUMOs are distributed over the pyrazolo[3,4-b]pyrazine unit which indicates that this unit is the most active center for electron transfer (either donation or acceptance). Unlikely, in the compound (V), HOMO is
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distributed nearly over the whole molecule but LUMO is located over the benzilidine moiety. So, this compound can donate electrons via any of its parts but can majorly host accepted electrons through the benzilidine part. Table 1 shows that the HOMO energies for the synthesized compounds follow the order: II > V > III > IV while LUMO energies for the synthesized compounds proceeds in the order: II > IV > III > V. The energy gap between the HOMO and LUMO frontier orbitals is one of the essential characteristics of molecules which plays a
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determining role in some cases such as electric properties, electronic spectra and photochemical reactions [30]. The energy gap (∆E = ELUMO - EHOMO) [31, 32] follows the sequence: II > IV > III > V, which is similar to that for LUMO energies.
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The absolute electronegativity (χ) and the absolute chemical hardness (η) are two quantities related to the ionization potential (I) and the electron affinity (A) where [33]:
=
(6)
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=
(7)
= −
(8)
= −
(9)
8
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The electrophilicity index (ω) is a global reactivity concept which measures the stabilization in energy when the system acquires an additional electronic charge from the environment. The nucleophilicity index (ε) is the inverse of ω. The ω and ε indices are defined as in Eq. 10 and 11
=
!" # % &
(10)
(11)
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$=
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[18]:
The electrophilicity index follows the trend: V > III > IV > II and vice versa for nucleophilicity index. The dipole moment (µ) is an index related to the distribution of electrons in a molecule
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and is the measure of polarity in a bond [32]. µ follows the order: V > III > II > IV. The local reactivity of organic molecules can be analyzed via the Fukui index (FI). FIs involve regions of nucleophilic attack (their function is f +(r)) and regions of electrophilic attack (their function is f ̶ (r)). Fukui functions, f +(r) and f ̶ (r), are obtained from Eq. 12 and 13 [34]. %
' (() =
% ∆*
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' (() = ∆* (+*∆ (() − +* (()) (+* (() − +*∆ (())
(12) (13)
where f +(r) function measures the reactivity with respect to nucleophilic attack at the site r. The
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larger the values of f +(r), the more electrons accepted by the molecule during a nucleophilic attack. Conversely, the f ̶ (r) function measures the reactivity with respect to electrophilic attack
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at the site r. Fukui indices for the molecules (II) and (III) are distributed over pyrazolo[3,4b]pyrazine moiety the same as HOMO and LUMO distributions. As for the molecules (IV) and (V), Fukui indices are very weak and located mainly only over the carbonyl groups but f ̶ (r) is somewhat stronger for the compound V and majorly distributed over the benzilidine moiety. The Fukui function for radical attack, f 0(r), is simply the average of these two. The concept of atomic charge is a valuable tool to aid in understanding the properties of a molecule. The most common computational technique to calculate the atomic charges is Mulliken population analysis where the total electronic charges are distributed among the atoms 9
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in a molecule [35]. The Mulliken charge distribution of the synthesized compounds is presented in Table 2. It’s readily observed that hetero atoms (O and N) have the highest charge densities among all atoms. The regions of highest electron density are generally the sites at which electrophiles attack the molecule [33] and therefore O and N atoms are the most active centers in
3.3.
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these molecules. Molecular dynamics simulation
3.3.1. As corrosion inhibitors
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Generally, for a material to be effective as a corrosion inhibitor, it must be characterized by containing non-bonded electrons (free lone pairs) and/or π-electrons which facilitate electron transfer between the inhibitor and the metal [2, 36]. The synthesized compounds under study are
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rich in O and N atoms containing free lone pairs of electrons in addition to double bonds and aromatic rings containing π-electrons. The regions of the highest electron density (HOMOs) are the sites susceptible to electrophilic attack while antibonding orbitals (LUMOs) can accept electrons from Fe d-orbital [27]. Overall, excellent organic corrosion inhibitors are usually not only those donate electrons to the unoccupied metal d-orbitals but also accept free electrons from
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the metal via back-donation [27]. According to literature [22, 27] low values of the gap energy (∆E = ELUMO – EHOMO) will provide good inhibition efficiencies because the energy to remove an electron from the last occupied orbital (HOMO) of the inhibitor will be minimized and it will be easy to donate electrons to metal d-orbital and ELUMO will be minimum so that it can accept
be present.
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electrons from the filled Fe 4s2 [37]. However, one of these mechanisms may occur or both may
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MD simulation is performed for the synthesized compounds to investigate their ability to adsorb on Fe surface and the calculated binding energies (Ebind) are listed in Table 3. The values of Ebind calculated for these compounds reveal that their absolute magnitudes increase as the χ increases following the order: V > IV > III > II. In other words, the more electronegative the molecule, the better its interaction with Fe surface. These observations indicate that these compounds may act as potential inhibitors for Fe corrosion via electron transfer from metal to inhibitor where the transferred electrons are hosted in the antibonding molecular orbitals (LUMOs) and the predicted inhibition efficiency follows the order V > IV > III > II. Fig. 6 displays the adsorption modes of the prepared compounds on Fe surface where all molecules 10
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have adapted their geometries to properly adsorb on Fe surface. The pyrazolo[3,4-b]pyrazine unit is the closest moiety to Fe surface which indicates that its atoms are the main active site towards interaction with Fe surface.
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3.3.1. As antiscalant agents Controlling scaling phenomenon proceeds via the adsorption of antiscalant molecules on the growing scale crystals [38]. MD simulation is performed to study the adsorption tendency of the synthesized compounds on anhydrite (001) surface in an attempt to use them as scale inhibitors.
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MD simulation reveals that the absolute magnitudes of the calculated binding energy (Ebind) between these compounds and anhydrite (001) surface proceeds in the order: II > III > IV > V.
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Table 1 shows that II < III < IV < V in the calculated χ values. Thus, Ebind increases as χ decreases. So, these compounds may act as inhibitors for scale formation via Coulomb electrostatic interactions between the partially negatively charged functional groups of the inhibitor and the positively charged calcium ion of anhydrite and the predicted inhibition efficiency follows the order II > III > IV > V. Fig. 7 displays the adsorption modes of the prepared compounds on anhydrite surface. It’s noted that the closest parts of these molecules are
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the pyrazole and phenyl rings which may be due to the availability of free lone pairs of electrons in addition to π-electrons. Thus, these compounds can occupy the growing points of anhydrite crystals and hinder the arrival of further scaling ions, i.e. Ca2+ and SO42- [25]. Then the crystal morphology is changed and the scale crystals cannot be longer able to grow normally. This
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causes the crystals to become distorted and the internal stress of crystals increases which could result in crystal fractures [39].
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Conclusions
In this work, four novel pyrazole derivatives have been synthesized and characterized using elemental analysis and spectroscopic tools. In addition, the DFT method was employed to achieve a deep insight into their geometry and electronic properties. MD simulation has been employed to investigate the potentiality of these materials as inhibitors for both Fe corrosion and scale (CaSO4) formation. It is concluded that the tested compounds have the tendency to adsorb on Fe surface following the order: V > IV > III > II. Also, they have the tendency to adsorb on
11
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CaSO4 crystals and thus can deter scale formation and deposition in the following trend: II > III > IV > V.
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Tables
EHOMO (Ha)
ELUMO (Ha)
∆E (Ha)
∆E (eV)
I (eV)
A (eV)
χ (eV)
η (eV)
ω
ε
-0.1923
-0.0947
0.0976
2.6561
5.2332
2.5772
3.9052
1.3280
5.7419
0.1742
7.2793
-0.1987
-0.1240
0.0747
2.0329
5.4074
3.3745
4.3910
1.0164
9.4849
0.1054
8.7290
-0.2063
-0.1183
0.0880
2.3948
5.6142
3.2194
4.4168
1.1974
8.1460
0.1228
3.0498
-0.1973
-0.1399
0.0574
1.5621
5.3693
3.8072
4.5883
0.7810
13.4779
0.0742
9.1057
(II) (III) (IV) (V)
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Compound
(II)
(III)
Total charges
Atoms
Total charges
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Table 2: Mulliken total atomic charges.
Atoms
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Table 1: DFT parameters calculated for the synthesized compounds.
(IV)
Atoms
(V)
Total charges
Atoms
Total charges
-0.106
C(1)
-0.088
C(1)
-0.189
C(1)
-0.079
C(2)
0.443
C(2)
0.420
C(2)
0.465
C(2)
0.448
N(3)
-0.608
N(3)
-0.378
N(3)
-0.602
N(3)
-0.587
C(4)
0.456
C(4)
0.352
C(4)
0.498
C(4)
0.430
C(5)
0.097
C(5)
0.097
C(5)
0.114
C(5)
0.114
N(6)
-0.347
N(6)
C(7)
-0.031
C(7)
N(8)
-0.380
N(8)
N(9)
-0.476
N(9)
C(10)
-0.223
C(10)
C(11)
0.100
C(12)
-0.196
C(13)
-0.177
C(14)
-0.173
N(6)
-0.242
N(6)
-0.342
-0.024
C(7)
-0.082
C(7)
-0.012
-0.389
N(8)
-0.194
N(8)
-0.221
-0.235
N(9)
-0.160
N(9)
-0.239
-0.223
C(10)
-0.210
C(10)
-0.208
C(11)
0.093
C(11)
0.223
C(11)
0.132
C(12)
-0.197
C(12)
-0.197
C(12)
-0.200
C(13)
-0.174
C(13)
-0.159
C(13)
-0.179
C(14)
-0.169
C(14)
-0.158
C(14)
-0.171
-0.168
C(15)
-0.165
C(15)
-0.158
C(15)
-0.169
EP
-0.336
AC C
C(15)
TE D
C(1)
0.110
C(16)
0.110
C(16)
0.170
C(16)
0.056
-0.182
C(17)
-0.179
C(17)
-0.212
C(17)
-0.177
-0.176
C(18)
-0.177
C(18)
-0.168
C(18)
-0.178
-0.174
C(19)
-0.172
C(19)
-0.159
C(19)
-0.169
C(20)
-0.176
C(20)
-0.175
C(20)
-0.162
C(20)
-0.181
C(21)
-0.232
C(21)
-0.227
C(21)
-0.248
C(21)
-0.180
O(22)
-0.549
O(22)
-0.464
O(22)
-0.430
O(22)
-0.522
H(23)
0.220
H(23)
0.232
H(23)
0.185
H(23)
0.234
H(24)
0.385
H(24)
0.316
H(24)
0.397
H(24)
0.420
C(16) C(17) C(18) C(19)
16
µ (Debye)
0.329
H(25)
0.172
H(25)
0.139
H(25)
0.182
H(26)
0.378
H(26)
0.218
H(26)
0.179
H(26)
0.213
H(27)
0.174
H(27)
0.187
H(27)
0.163
H(27)
0.183
H(28)
0.215
H(28)
0.186
H(28)
0.162
H(28)
0.181
H(29)
0.183
H(29)
0.187
H(29)
0.161
H(29)
0.184
H(30)
0.180
H(30)
0.194
H(30)
0.183
H(30)
0.199
H(31)
0.181
H(31)
0.183
H(31)
0.162
H(31)
H(32)
0.198
H(32)
0.181
H(32)
0.161
H(32)
H(33)
0.181
H(33)
0.181
H(33)
0.164
H(33)
H(34)
0.178
H(34)
0.195
H(34)
0.220
H(34)
H(35)
0.178
C(35)
-0.247
C(35)
0.440
C(35)
H(36)
0.187
C(36)
0.438
C(36)
-0.581
C(36)
------
------
O(37)
-0.423
C(37)
0.437
------
------
H(38)
0.258
O(38)
-0.407
------
------
H(39)
0.244
O(39)
-0.417
------
------
------
------
H(40)
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
------
RI PT
H(25)
M AN U
ACCEPTED MANUSCRIPT
0.182 0.179 0.179 0.202 0.410
SC
-0.014 0.408
O(38)
-0.495
O(39)
-0.523
0.259
C(40)
-0.180
H(41)
0.254
C(41)
0.104
------
------
C(42)
-0.195
------
------
C(43)
-0.173
------
------
C(44)
-0.152
------
------
C(45)
-0.181
------
------
C(46)
-0.146
------
------
------
H(47)
0.229
------
------
------
H(48)
0.191
------
------
------
H(49)
0.191
------
------
------
H(50)
0.194
------
------
------
H(51)
0.194
------
------
------
H(52)
0.233
EP
TE D
C(37)
AC C
Table 3: The calculated binding energy for the interaction between the synthesized compounds with Fe (110) and anhydrite (001). Compound (II) (III) (IV) (V)
Ebind (kJ/mol) With Fe(110) With anhydrite(001) -119.14 -135.84 -140.88 -201.32
-868.44 -815.81 -811.72 -776.30
17
ACCEPTED MANUSCRIPT
TE D
M AN U
SC
RI PT
Figures
AC C
EP
Fig. 1: Preparation scheme of the compounds under study.
18
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
Fig. 2: Energy optimization steps of compound (II).
19
ACCEPTED MANUSCRIPT
RI PT
(II)
AC C
EP
(IV)
TE D
M AN U
SC
(III)
(V)
Fig. 3: Optimized structure (left) and electron density (right) obtained for the synthesized compounds. Color index: White = H, Grey = C, Blue = N and Red = O (vide the web version of this article).
20
ACCEPTED MANUSCRIPT
SC
RI PT
(II)
EP
TE D
(IV)
M AN U
(III)
AC C
(V)
Fig. 4: HOMO (left) and LUMO (right) obtained for the synthesized compounds.
21
ACCEPTED MANUSCRIPT
RI PT
DOT
M AN U
SC
ADO
AC C
BDO
EP
TE D
DMO
Fig. 5: Fukui indices obtained for the synthesized compounds: f ̶ (left), f + (middle) and f 0 (right).
22
ADO
BDO
DMO
M AN U
SC
DOT
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
Fig. 6: Adsorption modes of the synthesized compounds on Fe (110).
23
ACCEPTED MANUSCRIPT
ADO
BDO
DMO
TE D
M AN U
SC
RI PT
DOT
AC C
EP
Fig. 7: Adsorption modes of the synthesized compounds on CaSO4 (001).
24
ACCEPTED MANUSCRIPT
Highlights Four pyrazoles were synthesized and characterized elementally and spectroscopically. DFT method was employed to fully scrutinize their structural characteristics.
AC C
EP
TE D
M AN U
SC
RI PT
Molecular dynamics simulation is used to test their adsorbability on Fe and CaSO4.