Heterocyclic compounds containing the 1,2,3-triazole moiety can be synthesized through click-chemistry, which is rapid reactions with good yields allowing the synthesis of great derivatives diversity by making minor changes in the reagents. The products were obtained with good yields through a synthetic route which uses ready available nonexpensive commercial reagents and without any further purification of any product or intermediate. The carbon steel anticorrosive activity was tested through weight loss and electrochemical assays in acid media. It was observed relevant inhibition efficiency (> 90%) for inhibitors
Heterocyclic compounds have a great diversity of physical, chemistry, and biological properties which provide them a wide range of practical uses. This chemistry class is largely used in the pharmaceutical industry both in commercial products and in research and development and more recently they are gaining attention in researches for the development of new anticorrosive compounds [
Compounds containing 1,2,4-triazole moiety are widely studied as anticorrosive for copper [
Compounds containing the 1,2,3-triazole moiety can be synthesized through click-chemistry, which is rapid reactions with good yields allowing the synthesis of a great derivatives diversity by making minor changes in the reagents. The copper-catalyzed 1,3-dipolar cycloaddition reaction between an azide and an alkyne is widely used for the synthesis of compounds with the 1,2,3-triazole ring with substituents in position 4 [
The objective of the present work is the synthesis of 1,2,3-triazole derivatives (Figure
1,2,3-Triazole derivatives structures.
Reactions progress was monitored by TLC on aluminum sheets precoated with silica gel 60 (HF-254, Merck), film thickness of 0.25 mm. Nuclear magnetic resonance (1H and 13C NMR) spectra were recorded using a Varian 500 MHz instrument. For the 1H NMR spectra, chemical shifts (
All reagents and solvents used were commercially available and were employed without further purification unless specifically indicated.
FT ATR IR 3069 (C-H ar st), 2120 (N3 st), 1590 (ar C=C st), 1512 (C-NO2 ass st), 1287 (C-NO2 sym st).
FT-IR (ATR) 3436 (O-H st), 1598 (ar C=C st), 1510 (C-NO2 ass st), 1287 (C-NO2 sym st).
FT-IR (ATR) 3462 (O-H st), 3362 (N-H st), 1631 (ar C=C st), 860 (ar C-H
1H NMR (500 MHz, DMSO-
13C NMR (22.5 MHz, DMSO-
FT ATR IR 3080 (C-H ar st), 2976 (C-H aliph st), 1711 (C=O st), 1530 (C-NO2 assym st), 1343 (C-NO2 sym st), 852 (ar C-H
FT-IR (ATR) 3345 (N-H st), 2978 (C-H st), 1702 (C=O st), 1516 (ar C=C st)), 840 (ar C-H
1H NMR (500 MHz, DMSO-
13C NMR (125 MHz, DMSO-
FT ATR IR 3076 (C-H ar st), 1677 (C=O st), 1518 (C-NO2 assym st), 1341(C-NO2 sym st), 853 (ar C-H
FT-IR (ATR) 3466 (O-H st), 3326 (N-H st), 2972 (C-H st), 1517 (ar C=C st), 837 (ar C-H
1H NMR (500 MHz, DMSO-
13C NMR (125 MHz, DMSO-
Carbon steel used as specimens was cut into 3.0 cm × 1.0 cm × 1.0 cm sections and abraded with emery paper of different granulometry (320, 600, and 1000). The chemical composition ASTM 1020 carbon steel is (wt%): C (0.18%), Mn (0.30%), S (0.05%), and Fe (balance). These pieces were washed with double distilled water, degreased with acetone, and dried in air.
Triplicate specimens were immersed in a 1.0 mol L–1 HCl aqueous solution prepared from 37% HCl (purchased from Merck Co. Darmstadt, Germany) and double distilled water, in the absence and presence of corrosion inhibitors at 250 mg L–1, for a period of 24 h. After the specimens were removed, washed with water and acetone, and dried in warm air, the weight was obtained according to ASTM G31-72 [ASTM International G31-72: Standard practice for laboratory Immersion Corrosion Testing of Metals. West Conshohocken: ASTM International; 1999] (standard method) and determined using an analytical balance with a 0.1 mg precision. The efficiency of inhibition (
The gravimetric testing was also performed at different inhibitor concentrations (250–1250 mg L–1), different immersion times (4, 8, 12, 24, and 48 h), and different temperatures (25, 35, 45, and 55°C).
Electrochemical measurements were carried out in conventional three-electrode cell (100 mL) using a Microautolab III/FRA2 (Eco Chemie; Utrecht, the Netherlands) coupled to a personal computer and controlled with GPES 4.9 software (General Purpose Electrochemical System). In all cases, ASTM was used as standard method. The supporting electrolyte was the same used in loss weight and the measurements were carried out in 100 mL of nonstirred and naturally aerated electrolyte maintained at 25°C.
Carbon steel specimens with same composition used in the gravimetric weight loss measurements were cut and employed as work electrode with exposed surface area of 0.78 cm2. These carbon steel electrodes also were abraded in politriz Aropol 2V (Arotec) with emery paper of different granulometry (320, 400, 600, and 1000), washed with double distilled water, degreased with acetone, and dried in air. Saturated calomel electrode (SCE) was used as the reference electrode, and a Pt wire with large superficial area was used as the auxiliary electrode.
Work electrode in electrochemical measurements was kept in support electrolyte during 1 h to reach its stable open-circuit potential (OCP). Electrochemical impedance spectroscopy (EIS) was performed using the aforementioned potentiostat over a frequency range of 100 kHz to 10 mHz at the stable open-circuit potential with an AC wave of 10 mV (rms). Potentiodynamic polarization curves were also obtained after 1 h in the open-circuit potential and performed using a scan rate equal to 1 mV s–1 from –300 mV up to +300 mV in relation to OCP.
The synthetic inhibitors with the best inhibitory efficiency (
Synthetic route proposed to obtain triazoles compounds was presented in Scheme
Synthetic route to triazole derivatives compounds
The products were obtained using synthetic route using ready available nonexpensive commercial reagents and without any further purification of any product or intermediate. Products were obtained in good purity as observed in infrared and RMN analysis and yields of all synthetic steps were good varying between 60 and 94%.
In an electrochemical spontaneous corrosion process, when the metal interacts with electrolyte solution, both anodic and cathodic reactions occur. Corrosion mechanism of carbon steel in acid solution can happen by reaction between metallic iron and H+ producing ferrous ion (Fe2+) and hydrogen gas, shown as follows [ Fe + H [FeH [FeH Fe
The inhibition efficiency obtained from weight loss experiments with carbon steel in acid medium is presented in Table
Inhibitor efficiencies to carbon steel in 1.0 mol L–1 HCl solution containing 250 mg L–1 of commercial and proposed inhibitors after immersion for 24 h at 25°C.
| | |
---|---|---|
| 91.9 | 1.3 |
| 95.8 | 0.7 |
| 70.2 | 1.3 |
| 72.2 | 1.9 |
The data from Table
The rates of carbon steel corrosion in 1.0 mol L–1 HCl aqueous solution, in the presence and absence of the best inhibitors, in concentration range of 250–1250 mg L–1 for 24 h immersion at 25°C, as well as the efficiency results, are shown in Table
Inhibitor efficiencies and corrosion rates to carbon steel in 1.0 mol L–1 HCl solution with different concentrations of inhibitors, after immersion for 24 h at 25°C.
| | | | ||||||
---|---|---|---|---|---|---|---|---|---|
| | | | | | | | | |
| | | | | | | | | |
Blank | 12.8 | – | – | 12.8 | – | – | 12.8 | – | – |
250 | 1.0 | 91.9 | 1.3 | 0.5 | 95.8 | 0.7 | 2.2 | 72.2 | 1.9 |
500 | 0.9 | 93.4 | 0.3 | 0.4 | 96.7 | 0.3 | 1.3 | 82.9 | 1.2 |
750 | 0.7 | 94.3 | 0.8 | 0.6 | 95.5 | 5.5 | 1.3 | 83.1 | 0.9 |
1000 | 0.6 | 95.0 | 0.5 | 0.2 | 98.2 | 0.3 | 1.3 | 83.9 | 0.7 |
1250 | 0.5 | 96.2 | 0.2 | 0.1 | 99.2 | 0.2 | 0.8 | 84.1 | 0.5 |
The carbon steel corrosion rate (
The corrosion process was also investigated in different immersion time of carbon steel in 1.0 mol L–1 HCl aqueous solution in presence and absence of 500 mg L–1 of inhibitors (4, 8, 12, 24, and 48 h) at room temperature and the results of the weight loss measurements are shown in Table
Inhibitor efficiencies and corrosion rates to carbon steel in 1.0 mol L–1 HCl aqueous solution in presence and absence of the inhibitor (500 mg L−1) with different immersion times, at 25°C.
| | | | ||||
---|---|---|---|---|---|---|---|
| | | | | | | |
| | | | | | | |
4 | 16.0 | 1.7 | 89.2 | 1.5 | 0.3 | 97.9 | 0.6 |
8 | 14.7 | 1.8 | 87.5 | 1.9 | 0.3 | 97.9 | 0.2 |
12 | 14.7 | 1.6 | 88.8 | 0.7 | 0.2 | 98.7 | 0.5 |
24 | 12.8 | 0.9 | 93.4 | 0.3 | 0.4 | 96.7 | 0.3 |
48 | 14.2 | 1.6 | 88.6 | 1.2 | 0.3 | 97.9 | 0.2 |
It can be observed in Table
Corrosion rate reduction in presence of inhibitors occurs due to the formation of protective layer by inhibitor adsorption on the metallic surface. To investigate the adsorption behavior of triazole compounds, various isotherms were used and Langmuir isotherm was the best fit with the experimental data from Table
Langmuir adsorption isotherms of triazole compounds on the carbon steel surface in 1.0 mol L–1 HCl aqueous solution.
A linear correlation can be observed in Figure
Values of the
| | |||
---|---|---|---|---|
| | | | |
| 1.027 | 0.9999 | 9.25 | –33.6 |
| 0.998 | 0.9991 | 11.36 | –33.1 |
The
The effects of temperature on the corrosion of carbon steel in 1.0 mol L–1 HCl solution in absence and presence of 250 mg L–1 of inhibitors were studied during 4 h, varying temperatures (25, 35, 45, and 55°C). The corrosion rates and inhibitor efficiencies obtained in this study were presented in Table
Inhibitor efficiencies and corrosion rates to carbon steel in 1.0 mol L–1 HCl aqueous solution in absence and presence of 250 mg L–1 of inhibitors during 4 h, varying temperatures.
| | | | |
---|---|---|---|---|
| | | | |
25 | Blank | 16.0 | − | − |
| 1.7 | 89.2 | 1.5 | |
| 0.3 | 97.9 | 0.6 | |
| ||||
35 | Blank | 33.6 | − | − |
| 3.6 | 89.4 | 0.6 | |
| 0.8 | 97.6 | 1.6 | |
| ||||
45 | Blank | 66.1 | − | − |
| 5.9 | 91.1 | 0.4 | |
| 2.3 | 96.5 | 0.2 | |
| ||||
55 | Blank | 99.8 | − | − |
| 13.0 | 87.0 | 0.3 | |
| 5.4 | 94.6 | 0.3 |
Table
The apparent activation energy for carbon steel corrosion in absence and presence of 250 mg L–1 of inhibitors was determined from an Arrhenius-type plot according to
Arrhenius plots of
The apparent activation energy obtained for the corrosion process in the acid solution was 49.7 kJ mol–1 and in the acid solution in presence of
Thermodynamic parameters of corrosion inhibition process of carbon steel in 1.0 mol L–1 HCl solution in absence and presence of inhibitors.
| | | | | | |
---|---|---|---|---|---|---|
| | | | |||
blank | 50.39 | 0.9910 | 47.79 | –126.9 | 0.9918 | 2.597 |
| 52.84 | 0.9916 | 50.22 | –137.7 | 0.9840 | 2.597 |
| 76.51 | 0.9998 | 73.91 | –72.23 | 0.9971 | 2.602 |
The corrosion inhibition process also can be explained by using thermodynamic model. The adsorption heat (
Adsorption heat (
The positive values of
Figure
Potentiodynamic polarization curves of carbon steel in 1.0 mol L–1 HCl solution in absence and presence of different concentrations if inhibitor 1 (a) and inhibitor
The potentiodynamic polarization curves show the inhibitors presence caused a significant decrease in cathodic and anodic current densities. These results could be explained by the adsorption of inhibitors at the active sites of the electrode surface, which also retards the metallic dissolution and hydrogen evolution and consequently slows the corrosion process. The electrochemical parameters, i.e., the corrosion potential (
Electrochemical parameters of carbon steel in 1.0 mol L–1 HCl aqueous in absence and presence of inhibitors at different concentrations.
| | | | | | |
---|---|---|---|---|---|---|
| | | | | | |
Blank | –496.4 | 0.6055 | 180.18 | 101.74 | ||
| ||||||
| 250 | –497.6 | 0.2448 | 522.42 | 105.08 | 60 |
500 | –507.5 | 0.1157 | 369.12 | 98.09 | 81 | |
750 | –496.2 | 0.0397 | 134.92 | 78.77 | 93 | |
1000 | –492.0 | 0.0295 | 105.54 | 62.52 | 95 | |
| ||||||
| 250 | –494.7 | 0.1305 | 390.55 | 128.79 | 78 |
500 | –493.7 | 0.0414 | 132.63 | 79.09 | 93 | |
750 | –444.1 | 0.0955 | 152.75 | 45.30 | 84 | |
1000 | –495.9 | 0.0331 | 167.75 | 83.58 | 95 |
The corrosion current density (
The corrosion behavior of carbon steel in 1.0 mol L–1 HCl in the absence and presence of triazole compounds (250–1000 mg L–1) was investigated by EIS after immersion for 1 h at room temperature and Figure
Impedance data obtained from Nyquist diagram of carbon steel in 1.0 mol L–1 HCl solution without and with inhibitors at different concentrations.
| | | | | | | |
---|---|---|---|---|---|---|---|
| | | | | | | |
Blank | 0 | –0.506 | 17.344 | 3.599 | 199.53 | 45.99 | – |
| |||||||
| 250 | –0.504 | 145.12 | 3.881 | 39.81 | 27.55 | 88 |
500 | –0.514 | 261.85 | 3.928 | 19.95 | 30.46 | 93 | |
750 | –0.505 | 475.14 | 4.233 | 7.94 | 42.17 | 96 | |
1000 | –0.500 | 560.42 | 3.646 | 7.94 | 35.75 | 97 | |
| |||||||
| 250 | –0.505 | 282.00 | 3.739 | 12.59 | 44.83 | 94 |
500 | –0.509 | 313.41 | 3.295 | 12.59 | 40.34 | 94 | |
750 | –0.505 | 426.92 | 2.762 | 7.94 | 46.93 | 96 | |
1000 | –0.505 | 714.21 | 3.677 | 6.31 | 35.32 | 98 |
Nyquist diagram of carbon steel in 1.0 mol L–1 HCl solution without (a) and with inhibitors
The electrochemical impedance diagrams exhibit one depressed capacitive loop, which indicate a single time constant in the absence and presence of the inhibitors, implying two noteworthy effects: the charge transfer resistance considerably increases and
This semicircle intersection with the real axis at high frequencies produces an ohmic resistance (
From Table
The synthesis of triazoles compound following an easy, low cost, and simplified synthetic route gave good corrosion inhibitors. For this purpose, a range of 250 to 1000 mg L−1 was applied in weight loss and electrochemical assays in acid media for ASTM 1020 carbon steel. These assays showed some relevant inhibition efficiency (> 90%) for named inhibitors
For the future, our perspective is the addition of an amount of these inhibitors in commercial anticorrosive inks.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that they have no conflicts of interest.
The authors thank National Council of Technological and Scientific Development (Brazil) for research fellowship support and IFRJ and FAPERJ for the financial support.