Synthesis and characterization  of Substituted Schiff Base from Benzene-1,4-Diamine: Study of Biological Activity and Corrosion Inhibitor Effect

doi:10.21203/rs.3.rs-5147441/v1

This work includes a simple condensation reaction between aromatic amine " 2,5-dimethyl-benzene-1,4-diamine" or "2,3,5,6-tetramethyl-benzene-1,4-diamine with a carbonyl compound (pyridine-2-carboxaldehyde") to produce a new ligand. The produced ligands (L1a, L2a) were underwent to reduction reactions using (NaBH4) at room temperature to produce the new ligands" 2,5-dimethyl-N,N'-bis-pyridin-2-ylmethyl-benzene-1,4-diamine" (L1b) and "2,3,5,6-tetramethyl-N,N'-bis-pyridin-2-ylmethyl-benzene-1,4-diamine "(L2b). All ligands (L1a-L2b) are characterized by 1H-13C NMR, FT.IR, mass spectrometry, and elemental microanalysis. The ligands (L1b, L2b) effectiveness was examined as corrosion inhibitors and gave good results. In another application, activity of ligands was studied against two bacterial types E. coli (Gram-) and Staph. (Gram+) in comparison with the drug used Chloramphenicol. The ligands (L1a and L1b) showed a highest inhibition, but the ligands) L2a andL2b (did not show any inhibition effect at 25and50 Conc.(μg/ml)

Biological sciences/Biochemistry

Physical sciences/Chemistry

anti-microbic

Carbon Steel

Corrosion

Polarization

NaBH4

Pyridine-2-yl ring is a 6-membered ring heterocyclic compound whose structure comprises five C atoms besides one N atom. [1] Many synthetic applications of ligand pyridine-2-yl and their analogous compounds, where they regarded as the forerunners for producing special corrosion inhibitors [2,3]. They were described broadly in various areas of chemistry such as coordination chemistry [4,5], organic chemistry [5,6], and industrial chemistry [7] . as a class of organic compounds, Schiff bases have significant applications in pharmaceutical sector. They show biological applications including antibacterial [8-10] Ligands of the 2-pyridyl ring are extremely important because of their robust chelating ability and unexpected architecture. Compounds of pyridine-2-yl and complexes exhibited extremely high thermal stability [12,11]. Schiff bases are made by reacting of aromatic amino acids with carbonyl compounds. They act as effective and economically corrosion inhibitors, especially in hydrochloric acid due to their ability to be adsorbed on the metal surface[13]. Hydrochloric acid is employed to investigate the corrosion of carbon steel alloys due to its applications in cleaning and oil well stimulation. Preventing metals corrosion process cannot completely accomplished, but adding chemical inhibitors can control its rate. [15]. Carbon steel is used in many industrial and military applications. Therefore, protecting this metal in aqueous solutions is economically and environmentally important. The use of inhibitors is an effective way to diminish the carbon steel corrosion [16]

Chemicals were provided by various companies including Sigma-Aldrich, VWR Chemicals, Acros Organics, Fisher Scientific, and Thomas Baker and used directly with no more purification. Elemental microanalysis of the prepared compounds was conducted at the University of Leeds. FTIR spectra were recorded using Perkin-Elmer FTIR spectrometer. The Ultimate 3000 spectrometer was utilized to run the Mass spectroscopic measurements. ¹H and ¹³C NMR spectral data of the samples were obtained employing a Bruker DPX 300 MHz NMR spectrometer.

3.1. Synthesis of "2,5-dimethyl-N,N'-bis-pyridin-2-ylmethylene-benzene-1,4-diamine "(L1a)

pyridine-2-carbaldehyde (9.3 mmol,1 g) was dissolved in methanol (30 mL), then it was slowly added with stirring to as solution of 2,5-dimethyl-benzene-1,4-diamine (4.66 mmol,0.635 g) in methanol (40 mL). The produced mixture was refluxed at 70°C for 3hrs. The solvent was then eliminated by vacuum, yielding a yellow-brown solid product [17]. The product was washed tree times with 4 ml of acetone, and then dried under vacuum, resulting in “2,5-dimethyl-N,N'-bis-pyridin-2-ylmethylene-benzene-1, 4-diamine” with yield (0.79 g), 53.88% and melting point (M.P.) = 172.9 ^oC (Scheme 1).

¹H NMR (300 MHz, DMSO-d₆) δ: 8.74 (dd, J = 6, and 3 Hz, 2H, py-6); 8.55 (s, 2H, methylene); 8.21 (d, J = 6 Hz, 2H, py-3); 8.00 (td, J = 6, and 3Hz, 2H, py-4); 7.56 (m, 2H, py-5); 7.12 (s, 2H, phenyl); 2.35 (s, 6H, methyl). ¹³C NMR (75 MHz, DMSO-d₆) δ: 159.15, 154.24, 149.63, 147.55, 137.01, 130.74, 125.48, 121.12, 119.43, and 17.17. FT-IR (solid state): = 3051 (w), 3006 (w), 2976 (w), 2905 (w), 1625 (m), 1582 (m), 1563 (m), 1434 (m), and 774 (s) cm^-1. ESI-MS: m/z 315.16{M+H}⁺, calculated (314.15). Elemental microanalysis: C 75.80, H 5.80, and N 18.00 (%), calculated for C₂₀H₁₈N₄: C 76.41; H 5.77; and N 17.82 (%).

3.2 Synthesis of the ligand" 2,5-dimethyl-N,N'-bis-pyridin-2-ylmethyl-benzene-1,4-diamine" (L1b)

A solution of NaOH (78 mmol,3g) was gradually added to (4.7 mmol, 1.5 g) compound (L1a) in (300 mL) of methanol at the ambient temperature. The obtained mixture was stirred for 10hrs. After the reaction was ended, the solvent was eliminated using vacuum. This material was then dissolved in (300 mL) of deionized water, with the addition of 1 M hydrochloric acid solution (HCl). Next, the reaction pH was set to 10 utilizing an aqueous solution of NaOH. As a result of these steps, the compound was separated from the alkaline solution through sedimentation, then filtration and washing with deionized water (4 times, 100 mL each time) were performed and finally dried under vacuum[17]. This process yielded (0.93 g ) 61.22%, of L1b, and M.P.=155 °C. (Scheme 1).

¹H NMR (DMSO-d₆) δ= 8.74 (dd, J = 6, and 3 Hz, 2H, py-6); 8.55 (s, 2H, methylene); 8.21 (d, J = 6 Hz, 2H, py-3); 8.00 (td, J = 6, and 3Hz, 2H, py-4); 7.56 (m, 2H, py-5); 7.12 (s, 2H, phenyl); 2.35 (s, 6H, methyl). ¹³C NMR (75 MHz, DMSO-d₆) δ: 159.15, 154.24, 149.63, 147.55, 137.01, 130.74, 125.48, 121.12, 119.43, and 17.17. FT. IR (solid state): = 3051 (w), 3006 (w), 2976 (w), 2905 (w), 1625 (m), 1582 (m), 1563 (m), 1434 (m), and 774 (s) cm^-1. ESI-MS: m/z 315.16{M+H}⁺, calculated (314.15). Elemental microanalysis: C 75.80; H 5.80; and N 18.00 (%), calculated for C₂₀H₁₈N₄: C 76.41; H 5.77; and N 17.82 (%).

3.3 Synthesis of the ligand" 2,3,5,6-tetramethyl-N,N'-bis-pyridin-2-ylmethylene-benzene-1,4-diamine" (L2a) pyridine-2-carbaldehyde (9.3 mmol, 1g) in methanol (30mL) was added dropwise to a stirred solution of "2,3,5,6-tetramethyl-benzene-1,4- Diamine"(4.67 mmol, 0.7663 g) in methanol (40 mL). This mixture was refluxed for 3hrs at 70°C. After the reaction was ended, the solvent was eliminated using vacuum, resulting in a yellow-brown solid material[17]. This resulted product was then washed (for three times) by acetone (3 ml), and then dried under vacuum, yielding 1.02 g of ligand (L2a), 63.86% and M.p= 243 °C. Scheme 2 shows synthesis ligand L2a.

¹H NMR (300 MHz, DMSO-d₆) δ: 8.75 (d, J = 3 Hz, 2H, py-6); 8.35 (d, J = 6 Hz, 2H, py-3); 7.90 (t, J = 9, and 6Hz, 2H, py-4), 7.45 (m, 2H, py-5); 7.28 (s, 2H, methylene), and 1.69 (s, 12H, methyl). ¹³C NMR (75 MHz, DMSO-d₆) δ: 163.80, 154.67, 149.63, 147.27, 136.69, 125.20, 123.47, 121.18, and 15.01. FT. IR (solid state): = 3078 (w), 3050 (w), 2985 (w), 2955 (w), 2903 (w), 1633 (s), 1583 (m), 1562 (m), 1436 (m), 1401(s), and 776 (s) cm^-1. ESI-MS: m/z 343.1939{M+H}⁺, calculated (342.18). Elemental microanalysis: C 76.93; H 6.56; and N 16.23 (%), calculated for C₂₂H₂₂N₄: C 77.16; H 6.48; and N 16.36 (%).

3.4 Synthesis of " 2,3,5,6-tetramethyl-N,N'-bis-pyridin-2-ylmethyl-benzene-1,4-diamine" (L2b)

Sodium borohydride (3 g,78 mmol) was slowly mixed with a solution of ligand L2 (1 g, 2.9 mmol) in methanol(300 mL) at the ambient temperature with stirring. The resulted mixture was kept stirred for 10 hrs. A Vacuum was utilized to remove the solvent. The obtained powder-solid material was dissolved in deionized water (250 mL), and a solution (HCl, 1M) was then added. A Solution of ( NaOH 2M) was then added to raise the pH of the reaction resulting in a precipitated ligand. the produced ligand was filtered and washed four times by deionized water (100 mL) before it was left to dry by vacuum[17]. Yield: (0.71 g, 70.22 %) of (L2b) and m.p= 111.5ºC. Scheme 2 shows synthesis of ligands (L2a and L2b). ¹H NMR (300 MHz, DMSO-d₆) δ: 8.56 (d, J= 3 Hz, 2H, py-6), 7.80 (td, J= 9, and 6 Hz, 2H, py-4), 7.47 (d, J= 9 Hz, 2H, py-3), 7.31 (m, 2H, py-5): 4.16 (s, 2H, amine), 3.99 (s, 4H, -CH₂-), and 2.17 (s, 12H, -CH₃). ¹³C NMR (75 MHz, DMSO-d₆) δ: 159.41, 148.77, 141.08, 136.52, 127.51, 122.09, 122.00, 54.43, and 17.78. FT-IR (solid state): (cm^-1) 3356 (m), 3054 (w), 3007 (w), 2943 (w), 2900 (w), 2794 (w), 1593(m), 1567(m), 1435(s), 1419 (s), 1370(m), 1093(m), and 758 (s). ESI-MS: m/z 347.22 {M+H}⁺ (calc. 346.22). Microanalysis: C 74.72; H 7.27; N 16.09 (%), calculated for C₂₂H₂₆N₄: C 76.27; H 7.56; N 16.17 (%).

Electrochemical measurement technology was used to evaluate the effect of inhibitors on the corrosion rate of carbon steel in acidic media. The experimental system was set up using an electrochemical cell, in which three electrodes were inserted: a working electrode, a reference electrode, and an auxiliary electrode. [18,19] The open circuit voltage of the working electrode was measured after a stabilization period to reach an equilibrium state. Next, a variable voltage was applied to the working electrode, typically between ±200 mV.

An agar (38 gm) were dissolved in of distilled water (1000 mL) with continuous stirring over the fire until the substance dissolved completely. Then, the mixture was put on an autoclave at a temperature of 120°C for 10 minutes. After that, the mixture was left until the temperature decreased and poured into dishes. Upon the agar solidifies in the dish, holes were made in the middle of the dish. 2wills were made a bacterial suspension and compare the spore with 5 using the Sweep. By the spreading process, the bacteria was distributed over the medium in four directions. In one of the two holes, prepared compounds were placed with concentrations (25, 50, 100), and in the other hole, the antibiotic was placed with a certain concentration. The media were then placed in the incubator for 18-24 hours at a temperature of 37°C[20]. The work was conducted at the University of Wasit, College of Science.

Characterization

The ligand (L1a) was synthesized by a simple condensation reaction between" 2,5-dimethyl-benzene-1,4-diamine and pyridine-2-carbaldehyde" [17]. ¹H NMR spectrum displays the vanishing of the aldehyde signal at δ 9.98 (Fig. 1) and the signal of amine at δ 3.92 [22,23]. The¹³C NMR spectrum displays the vanishing of the (-CHO) group signal at δ 193.62 (Fig. 2), and presence of the imine signal at δ 159.15 [24,25]. FT-IR spectrum (Fig. 3) displays the presence of two bands located at 1582 and 1563 cm^-1, which are belong to imine group [26,2]. The mass spectrum of L1a displays a high intensity signal at 315 m/z {M+H}⁺ (Fig.4).

The ligand (L1b) was prepared by the reduction reaction of (L1a) using NaBH4. The ¹H NMR spectrum of ligand (L1b) illustrates the vanishing of the imine group (-HC=N-) signal at δ 8.55. The spectrum also displays the presence of triplet signal at δ 4.91 and double signal at δ 4.33 ppm , which are attributed to the (-N-H), and (-CH₂-) groups, respectively (Fig.5) [20]. The ¹³C NMR spectrum displays a new signal at δ 49.41, which is assigned to (-CH₂-) moiety and vanishing of the signal of imine moiety signal at δ 159.15 (Fig.6) [21]. The FT. IR spectrum apparently displays the change in bands compared to those of (L1a) ligand. The vanishing of bands at 1582, and 1563 cm^-1, which belong to the(-HC=N-) moiety in (L1a) [25, 26]. Moreover, the spectrum also displays the existence of a new band at 3382 cm^-1, which indicates the generation of (-N-H) (Fig.7)[22]. These findings designate that Schiff base was reduced and a new compound with a secondary amine moiety was formed. Finally, the mass spectrum of ligand (L1b) exhibits a high intensity signal at 319 m/z {M+H}⁺, which refers to the molecular weight of the new ligand plus one proton. (Fig.8(

The ligands (L2a and L2b) were characterized in part (2). Data of their spectra are shown in the support file.

Corrosion study

Electrochemical measurement technology was used to assess the inhibitors impact on the corrosion rate of carbon steel in acidic media. The current generated by the reaction was recorded at each level of applied voltage. The data were analyzed using polarization curves, where Tafel slopes were extracted for both anodic and cathodic current. These data were utilized to determine the corrosion current density (icorr) for both samples of carbon steel in the presence and absence of the inhibitors. Based on the obtained results, the protection efficiency of the inhibitors was calculated using the appropriate equation, which led to an evaluation of their effectiveness in reducing the corrosion rate. [27,20]. Figs (9-10) signify the polarization curves for the compounds (L1a, L1b, L2a, and L2b), along with a blank hydrochloric acid solution. Furthermore, the constituents of the carbon steel utilized as the working electrode are summarized in Table1.

Table 1: Corrosion parameters for blank and compound in HCl solutions, and compounds (L1a-L2b)

Comp.	Temp.	E corr.	I corr.	I corr./ r	Resis.	Anodic β	Cathodic β	Corr. rate,	IE%
Blank	293	-0.527	227.2	4.544E-4	96.84	0.104	0.099	2.230	-
Blank	303	-0.529	262.0	5.239E-4	88.06	0.106	0.106	2.571	-
L1a	293	-0.597	36.67	7.334E-5	1553	0.204	0.369	0.360	84
L1a	303	-0.627	39.26	7.853E-5	1817	0.262	0.440	0.385	85
L2a	293	-0.637	19.04	3.807E-5	2145	0.146	0.263	0.187	92
L2a	303	-0.651	20.98	4.196E-5	2205	0.177	0.267	0.206	92
L1b	293	-0.632	37.69	7.539E-5	1706	0.227	0.426	0.370	83
L1b	303	-0.671	38.65	7.729E-5	1683	0.263	0.347	0.379	85
L2b	293	-0.764	18.42	3.684E-5	2657	0.198	0.261	0.181	92
L2b	303	-0.814	22.28	4.456E-5	2298	0.281	0.203	0.219	91

I corrosion(μA); I corrosion per surface area( A/cm²); Anodic β Tafel constant, V/decade; Cathodic β Tafel constant( V/decade); Corrosion rate(mm/year); (IE%) inhibition efficiency

Fig. (9-10) show a polar curves that are measuring the corrosion of ligands in HCl (0.1M) at different temperatures while they were being subjected to the polarization. Chemical molecules containing four nitrogen atoms are found to act as effective inhibitors. These organic compounds adsorbed onto the metallic surface and hence decrease the corrosion rate. It has been demonstrated that the adsorption process is primarily influenced by the physicochemical characteristics of the inhibitor such as the active groups, density of the electron at the donor atom, orbital features, π bonds, the presence of benzene rings, and the electronic structure of the compound.

The finding disclosed that these chemicals inhibit the corrosion of carbon steel in HCl through adsorption on the active spots of anode and cathode without altering the underlying corrosion mechanism. This suggests that the deposited inhibitors restrict the active surface sites, and sub consequently decreasing the area available for metal dissolution processes. While an increase in temperature did not significantly affect the corrosion inhibition of compound Lb, the reduction of this compound notably influenced the corrosion rate (CR) and the efficiency percent (%E) due to the transformation of the -N=C group into NH-CH. The corrosion inhibition attributed to Schiff bases can be linked to their molecular structure, which contain π electrons of the C-N group and π electrons of the aromatic ring.

Antibacterial activity

An antiseptic steel borer was utilized to dig the wells in the agar media for every plate. The ligands were dissolved in DMSO to prepare the test solution. Utilizing a micropipette, the wells were then filled with the prepared solution. The incubation time of the plates was 24 and the Petri plates were kept at 37°C. The effect of the prepared compounds on two types of bacteria: Escherichia coli (Gram-) and Staphylococcus aureus(Gram+). The compounds L1a, L2a, L1b, and L2b showed an activity at concentration of 100 (μg/ml) against Staphylococcus aureus. While L1a and L2a showed an inhibition activity at a concentration of 25-100(μg/ml) against both of Staphylococcus aureus and

E.coli. On the other hand, the compounds L1b and L2b did not show any inhibition with concentrations of 25,50, 100(μg/ml) against E. coil While did not showed an inhibition activity at a concentration of 25-50(μg/ml) against of Staphylococcus aureus and . Overall, these results reflect the bioactivity of the compounds in inhibiting of bacterial growth. Table2 shows the inhibition activity of the compounds at different concentrations.

Table 2: Inhibition zone diameter (mm)

Comp.	E.coli				Staphylococcus aureus
Comp.	Conc.25(μg/ml)		Conc.50(μg/ml)	Conc.100(μg/ml)	Conc.25(μg/ml)	Conc.50(μg/ml)	Conc.100(μg/ml)
L1a	20mm		20mm	22mm	21mm	23mm	27mm
L1b	10mm		10mm	11mm	15mm	17mm	23mm
L2a	-------		-----	-----	-----	---	20mm
L2b	-------		------	------	-----	----	20mm
Chloramphenicol		10			15

In this study, four compounds were prepared via two condensation reactions. The compounds were then exposed to reduction reaction by NaBH4. Their chemical structures were confirmed by ¹H- ¹³CNMR, Mass, CHN, and FT-IR spectroscopy. It was proven that the four prepared compounds possess high corrosion inhibitor values. Due to the presence of methyl groups, the effectiveness of these compounds as inhibitors of two types of bacteria (Staphylococcus aureus and E. coli) was demonstrated. All compounds showed a high effectiveness against the bacteria Staphylococcus aureus at a concentration of 100 micrometers, and good effectiveness for the two compounds L2a and L1a against E.coli. This indicates that the prepared compounds have a potential activity as corrosion inhibitors besides antimicrobial applications.

Competing interests

The authors declare no competing interests.

Author contributions

S.H. developed the study's concept and design, conducted the experiments, and wrote the manuscript, H.D. assisted in the design, collected and analyzed data, and contributed to the writing, while M.L. provided analysis support, reviewed the manuscript for intellectual content, and coordinated the project.

Funding Declaration

The author personally funded this research and manuscript preparation. There were no external sources of funding.

Data availability

All data generated through this study are included in this manuscript and the Supplementary data file.

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Schemes 1 and 2 are available in the Supplementary Files section

No competing interests reported.

Synthesis and characterization of Substituted Schiff Base from Benzene-1,4-Diamine: Study of Biological Activity and Corrosion Inhibitor Effect

Status:

Version 1

Abstract

Figures

1. Introduction

2. Experimental

3. Synthesis of new ligands

4. Measured of corrosion

5. Study of anti-amicrobic

6. Results and discussion

Conclusion

Declarations

References

Schemes

Additional Declarations

Supplementary Files

Status:

Version 1