Synthesis, Characterization of New Polytriazole Derivatives from Polyacryloyl chloride and Theoretical with Corrosion Inhibitor Study for Stainless steel in acidic medium

 

Amaal S. Sadiq¹, Entesar O. Al-Tamimi²

¹Department of Chemistry, College of Science for Woman, University of Baghdad,

Al-Jadiriya, Baghdad, Iraq.

²Department of Chemistry, College of Science, University of Baghdad, Al-Jadiriya, Baghdad, Iraq.

 

ABSTRACT:

The purpose of the study is to synthesize and characterize a new polytriazole derivative from polyacryloyl chloried, first reaction of polyacryloyl chloride with hydrazine hydrate in the presence of DMF as a solvent to obtained acid hydrazide (1) than reacted with different amide to give poly 1,2,4-triazole derivatives(1a-1c). Newly synthesized compounds were characterized by spectral methods [¹³C-NMR, ¹H-NMR, and FTIR] and calculated some of its physical properties. Also, we worked theoretical study involving calculated the geometric configurations, total energy, dipole moment etc..,. In addition, the inhibition effect of the synthesized compounds (1a-1c) on corrosion of stainless steel in 1M HCl were studied by method of weight loss. The results of weight loss measurements showed that corrosion inhibition efficiency by increasing the concentration of organic inhibitors for stainless steel in 1M HCl solution at 30^oC.

 

 

 

1. INTRODUCTION:

Polymers have come to play an important and ubiquitous function in everyday life-from plastics and elastomers, on the one hand, to natural biopolymers such as DNA and proteins, on the other hand. The study of polymer science starts with an understanding of the processes by which these materials are synthesized¹. The critical polymer may have many reactions in order to obtain a large number of polymer varieties that have added good physical properties and high thermal stability². Triazole ring is a typical heterocyclic compound it can be prepared with the Pellizzari reaction,³. The synthesis of substituted triazole derivatives showed a significant numerical increase, according to literature surveys, triazole derivatives are used in a wide range of biological activities⁴, Same as: anti-bacterial⁵, anti-inflammatory⁶, anti-convulsant⁷, anti-tumor⁸, analgesic⁹, enzyme inhibitor¹⁰.

 

Triazoles were been shown to have some desirable characteristics, such as oxidative/reductive conditions, resistance to metabolic degradation and good stability to acidic/basic hydrolysis¹¹. Heteroatom derivatives with high electron density, known to be adsorption centers, are effective as corrosion inhibitors. A number of researchers have developed a new series of polytriazoles with a variety of structures, some of which possess not only excellent processability, but also good mechanical properties and thermal stability¹². Planarity and a lone pair of electrons present on heteroatomes are important construct features that decide the adsorption of these molecules on the metal surface. Continuing work on the development corrosion inhibitors for acidic solutions containing N atom¹³. In this Paper, we describe the synthesis of various polytriazoles, which contain different groups and have been used as corrosion inhibitors for against Stainless steel in hydrochloric solution by weight loss process.

 

2. EXPERIMENTAL:

2.1. Materials and physical measurements:

All starting materials and solvents have been collected from Sigma-Aldrich and Fluka was used without further purification. (Melting points) were measured on Gallen Kamp capillary melting point apparatus and were uncorrected. Completion of reaction and purity of all compounds are checked on aluminum coated TLC plates 60 F245 (E. Merck) using ethyl acetate and hexane as the mobile phase and imagined under iodine vapor. FT-IR measurements were recorded on Shimadzu model (FTIR-8400S). (¹HNMR and ¹³CNMR) spectra were obtained with Bruker spectrophotometer model ultra-shield at 400 MHz in DMSO solution with the TMS as internal standard.

 

2.2. Synthesis of the organic compounds:

2.2.1. Synthesis of polyhydrazide¹⁴.

A mixture of poly acryloyl chloride (0.01mole) and hydrazine hydrate (0.01mole, 99%) in 15ml of Dimethyl formamide (DMF) was refluxed for 7 hours. The solvent was then evaporated and the liquid was cooled and filtered. Separate precipitate was purified by dissolving in DMSO and recipitating from acetone. The physical properties of synthesized compound is given in Table (1).

 

2.2.2 Synthesis of polytriazole derivatives¹⁵

Polyhydrazide (0.01mole) was dissolved in DMSO, added to this solution different amide (0.01mole) and stirred to obtain a clear solution, followed by (8-14) reflux, evaporated of the resulting reaction . The reaction mixture was then cooled at room temperature and poured into ice cold water to precipitate. The resulting substance was then recrystallized with DMSO, and recipitating from acetone, ethanol, water. The physical properties of synthesized compounds (1a-1c) are given in Table (1).

 

Table1: The physical properties of all compounds

No. of comp.	Structure	Chemical formula	Color	Molecular weight	Softing Point C0	Yield%
1		C3H6N2	White	70	257-272	90
1a		C10H9N3O	Light yellow	187	200-217	69
1b		C10H9N3	yellow	171	129-141	72
1c		C9H8N4	white	172	152-166	78

 

3. MATERIALS AND METHODS OF WEIGHT LOSS:

3.1. Preparation HCl solution:

The analytical level of 37% HCl with a molecular weight of 36.5 g/mol was used for the preparation of an acide electrolyte. The acid was combined with double distilled water to make 1 M HCl solution. For each collection of freshly prepared tests, 1M HCl solutions were used to prevent any contamination.

 

3.2. Preparation of specimens:

The sheet of stainless steel used has the composition percentages (0.045% P, 2.00% Mn, 0.08% C, 0.03% S, 16.00-18.00% Cr, 2.00-3.00% Mo, 0.75% Si, 0.01% N, 10.00-14.00 Ni, and the remainder iron 31.004-38.005%). Specimens were cut for use as coating substrates to size (2.5 cm in diameter), using a method of cutting machismo (wire cut), the open side was gridded and mechanically polished using a grinding wheel tool. All specimens were grinded and polished using a series of grits of increasing fineness (500 to1500) to the surface finish, the specimen was degreased with acetone and washed indistilled water finally with ethanol and stored inside desiccators before being used in corrosion studies.

 

3.3. Weight loss measurements:

In the case of experiment weight loss, five glass containers with a capacity of (100ml) containing (1M HCl). The first beaker was functioning as blank, while each of the other four beaker contained various concentration inhibitors, all of which were placed at room temperature (about 30C°), the specimens were initially weighed in an analytical balance, then suspended and completely immersed in the experimental solutions. After every immersion of 24 hours, the specimens were removed from the container, cleaned with emery papers, washed in doubled distilled water degreased with acetone, dried and reweighed. Weight loss allowed calculation of the mean corrosion rate (mg cm^-2h^-1). The corrosion rate of mild steel was determined using the relation¹⁶

 

 

∆m: mass loss

S: the area

t: immersion period

 

The percentage inhibition efficiency (IE%) was calculated using the relationship¹⁷.

 

 

Where Wcorr and Wcorr (inh) are the corrosion rates of mild steel in the absence and presence of inhibitor

 

 

4. RESULTS AND DISCUSSION:

4.1. Synthesis:

Scheme 1 included the synthesis of polytriazole derivatives. Characterization data for all compounds (1a–1c) are given in the experimental section. All newly synthesized compounds provided a satisfactory analysis of the proposed structures, confirmed on the basis of FTIR, ¹HNMR and ¹³CNMR data.

 

Scheme1: The chemical steps for the synthesis of compounds (1, 1a-1c).

 

4.2. FT-IR spectra:

The FTIR spectra of compound (1) has significant characteristic stretching vibration bands corresponding to the (C = O) amide band at 1674cm^-1, (–NH) at 3265cm^-1 and (NH2) at 3242,3286 cm^-1, while the FTIR spectra of compounds (1a-1c) have important characteristic stretching vibration bands corresponding to the (C = O) amide band which are disappeared and the stretching vibration bands corresponding to the (C = N) imine band that appear¹⁸, see Table 2.

 

4.3. NMR Spectra:

The ¹HNMR and ¹³CNMR spectra of compounds (1a and 1b) are listed in Table 3¹⁹.

 

Table 2: FT-IR Spectral data of synthesized compounds (1a-1c) in cm^-1

Comp. No.	n C-H Aromatic	n C-H aliphatic	n C=N	n C=C Aromatic	n NH
1a	3058	2952,2875	1641	1598.1498	3396
1b	3055,3029	2964,2931	1635	1575, 1488	3307
1c	3105,3043	2947,2812	1637	1595	3365

 

Table (3) ¹HNMR and ¹³CNMR data of compounds (1a and 1b) in ppm.

Compd. No.	Compound structure	1HNMR data in ppm	13C-NMR data in ppm
1a		d1.86(t,-CH2-CH-), d2.6-2.86(m,-H2-CH-), d 6.84-7.89(m, 4H, ArH), d 8.45 (s, 1H, NH), d 1.92(s, 1H, OH)	C1=38.34; C2=29.54; C3=171.48; C4=160.50; C5=116.48; C6=127.68; C7=123.92; C8=133.48; C9=117.69; C10=149.53
1b		d1.65(t,-CH2-CH-),d 1.98-2.98(m,-H2-CH-), d 7.45-7.72(m, 5H, ArH), d 9.06(s, 1H, NH)	C1=27.68; C2=34.38; C3=169.92; C4=191.52; C5=132.42; C6=126.87; C7= 127.70; C8=130.85

 

4.4. Weight loss:

This research focuses on the study of the effects of compounds (1a-1c) for corrosion inhibition in (1 M HCl) solution with the addition different concentration for 24 hours immersion at 30C°. Corrosion rate and inhibition efficiency results from measurements of weight loss at different concentrations of suggested inhibitors depicted in Figure 1 and summarized in Table 4.]. These values indicate that mild steel corrosion is minimized by the presence of suggested inhibitors in (1 M HCl) at all concentrations used in this study. However, there is a significant decrease in the weight of the mild steel specimen after 24 hours without the use of an inhibitor. This could be explained by the adsorption of organic compounds on a mild steel surface that hinders the corrosion environment. The inhibitive activity of the inhibitor may be partly due to the presence of heteroatoms, aromatic rings that have high electron density in the polytriazole derivative structure and the capacity to create a protective film on the metal corroding layer²⁰.

 

Figure 1: Effect of inhibitor concentration on the efficiencies of stainless steel obtained at 30^oC in 1M HCl containing different concentrations of suggested inhibitors

 

Adsorption isotherm is very useful for determining the properties of an adsorption inhibitor. Values of surface coverage measured by weight loss scales have been used to fit the isothermal curves of Langmuir. The properties of Langmuir isothermal adsorption are expressed in the equation (3)²¹.

 

K_{ads: is the equilibrium constant of the adsorption process}

 

According to the Langmuir isotherm, the values of the Kads can be calculated from the intercepts of the straight line of plotting C/θ versus C (see Figure 2,3), K_adsiis related to the standard free energy of adsorption ∆G^o_ads, with the following equation:

 

(The value 55.5) is the molar concentration of water in the solution in (1M).

 

Table 4: Corrosion rate, inhibition efficiency, surface coverage (θ) and standard free energy of adsorption for mild steel in 1M HCl by using weight loss measurements

 

 

Figure 2: Langmuir adsorption isotherm plot for mild steel in (1M HCl) solution in the presence of various concentrations of inhibitor (1a)

 

Figure 3: Langmuir adsorption isotherm plot for mild steel in (1M HCl) solution in the presence of various concentrations of inhibitor (1b)

 

From Table 4, standard free adsorption energy values are negative to imply that the adsorption processes of all suggested inhibitors (B1-B6) were spontaneous processes on a mild steel surface after 24 h immersion at 30^oC. Standard free adsorption energy values are negative to imply that the adsorption processes of all suggested inhibitors (1a-1c) were spontaneous processes on a mild steel surface after 24 h immersion at 30^oC.It makes sense for a remarkable relationship between the indicated inhibitors and the metal sheet. Here, the adsorbed molecule moves closer to the surface of the metal, making electrons overlap with the surface atoms that cause physisorption for the suggested inhibitors^22,23.

 

5. Theoretical Details:

Quantum chemical calculations are potential tools to show wide spectrum of application to develop and design organic corrosion inhibitor systems in the field of corrosion phenomenon. Different levels of quantum chemical calculations can be provided very useful correlation between corrosion inhibition efficiency and molecular structure of organic inhibitor. Reactivity of the inhibitor molecules largely effect by natural of molecular structure and electronic configuration of frontier molecular orbitals (HOMO and LUMO). HOMO. Both frontier molecular orbitals of molecule form coordinate bonds with the proper orbitals in the electronic system of metal. Therefore, the adsorption process is achieved by organic inhibitor molecules on the surface of metal. The higher energy of the frontier molecular orbital (HOMO) and lower frontier molecular orbital (LUMO) show high inhibition efficiency of organic inhibitor^24,25. In addition to frontier molecular orbitals, energy gap is an energetic factor to predict chemical reactivity of the organic molecule of inhibitor. When the energy gap has low value that reflects on chemical reactivity of the organic molecule to be higher. In this case, the adsorption process of organic molecule is highly occurred on the metal surface. From this point, some quantum energetic parameters were calculated for organic molecular models and listed in Table 5.

 

All the theoretical quantum calculations were performed for suggested inhibitors (1a) and (1b) using more geometrical stable conformations in the gas phase at 25ºC (see Figure 4). It is seen from energetically stable conformation of the molecules that all the molecules are almost non-planar geometry. It suggests that all the molecules have its way and orientation to reach mild steel surface through active atoms. Thus, the high in inhibition efficiency of the all suggested inhibitors can be build up by their different geometric configurations.

 

Table 5: Quantum chemical parameters of the studied potytriazole derivatives as corrosion inhibitors.

Inhibitors EHOMO ELUMO DE I A χ η S DN Dipole moment  (eV) (eV) (eV) (eV) (eV) (eV-1) (D)
(1a) -8.8914 -0.4960 8.3954 8.8914 0.4960 4.6937 4.1977 0.2382 0.5494 1.83	(1b) -9.0936 -0.5426 8.5510 9.0936 0.5426 4.8181 4.2755 0.2338 0.5103 4.40
aI = ‒EHOMO,	bA = ‒ELUMO

 

Figure 4: More geometrical stable conformations of suggested inhibitors (1a-1b) with PM3 method.

 

The PM3 HOMO and LUMO isosurfaces plots for suggested inhibitors (1a-1b) are shown in Figure 4. On the base of the presence of N atoms in suggesting inhibitors, the repartition density of the HOMO and LUMO is preferentially localized on N of (-N-N=) and (-NH-C=N-) groups of all molecular modeling systems. Table 5 also shows different dipole moments for suggested inhibitors (1a-1b). The values of dipole moment can be attributed to the non-uniform distributions of positive and negative charges on the various atoms, which could be related to improving the dipole–dipole interaction of organic molecules and mild steel surface. Electrostatic potential maps for suggested inhibitors (1a-1b) are depicted in Figure 6. This Figure shows the non-uniform distribution of electron density and concentration of negative charges on N atoms of           (-N-N=), (N=N-NH) moieties for all molecules, which reflect the different values of the calculated dipole moments (see Table 5).

 

 

Fig. 5: The frontier molecular orbital density distributions (HOMO and LUMO) for suggested inhibitors (1a-1b) by using PM3 method.

 

Figure 6: Electrostatic potential maps for suggested inhibitors (a1-1b) by using PM3 method.

 

Theoretical calculations were determined of the electron transfer fraction (DN) from the suggested organic molecules into the mild steel surface. The ionization potential and electron affinity of the inhibitor molecules could be calculated by using of Koopmans’ theorem²⁶. It states that, ionization potential (I), as I = –E_HOMO and electron affinity (A) as A = –E_LUMO. The calculated I and A of the suggested inhibitors are used to predict the absolute electronegativity (χ) and global hardness (η) of the suggested organic molecules, as follows:

 

 

The electron transfer fraction (DN) is calculated by the Pearson’s method [27-29] for transferring electrons from the organic molecule into the metal surface. The value of (DN) is calculated according to Eq. (7):

 

In order to predict the fraction of electrons, ΔN, a theoretical value for the absolute electronegativity of bulk metal iron can be used χ_Fe»7eV³⁰, whereas the global hardness of η_Fe »0, with regarding that a metallic bulk I=A³¹, since they are softer compares with the neutral metallic atoms. When DN > 0 the process of electron transfer from the organic molecule into the metallic surface can be occurred, and vice versa if        ΔN< 0³². Softness (S=1/η)³³ is another important parameter to elucidate chemical reactivity of the molecule.

 

In this work, the values of ΔN are positive that indicates that all suggested inhibitors (1a-1b) are donating electrons and have abilities to form adsorption thin film on mild steel surface. Inspection of Table 5 reveals that softness is a parameter to predict the chemical reactivity of the molecules. The molecule that have adsorption features can be related with the inhibitor molecule softness. The particular donor-accepter interaction can be considered for mild steel as a soft acid and organic inhibitor molecules as soft bases⁴³. Thus, soft-soft interaction is the prevalent factor for the adsorption of inhibitor molecule. It can be seen from Table 5 that the calculated softness values of the inhibitors are decreasing in the order of (1a) > (1b), which confirm a good adsorption capability of (1a) on the metal surface with a smallest energy gap.

 

5. CONCLUSION:

The inhibition efficiency of synthesized polytriazole derivatives was investigated for stainless steel corrosion in 1 M HCl solution. The weight loss methods were made use of for the studies. The polytriazole derivative are found to be a good anti-corrosive agent for stainless steel against 1 M HCl corrosion, inhibition efficacy improved with an increased concentration of inhibitors. Anti-corrosive activity is mainly due to the adsorption of polymer on the surface of the stainless steel, adsorption free energy values showed the physisorption effect (1a-1c) and provided useful information to describe the interaction between the metal surface and the organic molecules. Finally, we worked on theoretical experiments in order to compare them with experimental results, there is a good agreement between theoretical and experimental results.

 

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Received on 13.01.2020           Modified on 13.03.2020

Accepted on 05.04.2020         © RJPT All right reserved