2(Benzo[d]thiazol-2-ylamino)-2-(2-hydroxy-phenyl) acetonitrile derivative was prepared and characterized using thin liquid chromatography, FTIR, 1H NMR and 13C NMR. The corrosion protectiveness, kinetics, and thermodynamics of the prepared derivative as inhibitor in artificial sea water/carbon steel (CK45) system were studied. Three concentrations of the prepared inhibitor were examined, namely, 10, 100, and 1000 ppm; protection efficiencies of 23% to 73% were recorded. It was found that the experimental data obtained from polarization reading could be fitted by Langmuir isotherm and Frumkin’s isotherm; the best fit adsorption isotherm was the Frumkin adsorption isotherm. The small negative value of ΔGads indicates the spontaneity of a physical adsorption process and the stability of the adsorbed layer on the carbon steel surface. Analysis of the temperature dependence of inhibition efficiency as well as comparison of corrosion activation in absence and in presence of the inhibitors gives some insight into the possible inhibition mechanism.
Seawater is one of the most corroded and most abundant naturally occurring electrolytes, covering about 70% of the earth’s surface. The corrosively of the seawater is reflected by the fact that most of the common structural metals and alloys are attacked by this liquid or its surrounding [
Corrosion inhibition efficiency of organic compounds is related to their adsorption properties [
1) Physisorption involves electrostatic forces between ionic charges or dipoles on the adsorbed species and the electric charge at metal/solution interface. In this case, the heat of adsorption is low and therefore this type of adsorption is stable only at relatively low temperature.
2) Chemisorption involves charge sharing or charge transfer from the inhibitor molecules to the metal surface to form a coordinate type bond. In fact, electron transfer is typically for transition metals having vacant low- energy electron orbital. Chemisorption is typified by much stronger adsorption energy than physical adsorption. Such a bond is therefore more stable at higher temperatures. Molecules that contain both nitrogen and sulfur in their structure are of particular importance, since these provide an excellent inhibition in comparison to that containing only sulfur or nitrogen atoms [
1) Electrostatic interaction between charged surface of metal and the charge of the inhibitor.
2) Interaction of unshared electron pairs in the inhibitor molecule with the metal.
3) Interaction of π-electron with metal and d-A combination of the 1) - 3) types [
α-Amino nitriles have occupied an important, although often understated, position in organic chemistry ever since Strecker’s original report in 1850 on the three component reaction. Now bear his name, among aldehydes, ammonia and hydrogen cyanide [
All the chemicals and solvents which are used for the synthesis were of reagent grade and obtained commercially from British Drug House (BDH). Melting point was determined on a Gllenkamp melting point apparatus. The infrared spectra of the ligand and its complexes were recorded in the range (4000 - 400) cm−1 on a Shimadzu (8300) FTIR Spectrophotometer, using CsI pellets. Elemental analysis for carbon, hydrogen and nitrogen elements were carried out at the Euro vecter-EA3000A C. H. N. Analyzer, Al al-Bayt University (Jordan). 1HNMR and 13C-NMR spectra was recorded on a make Bruker model ultrashied 300 MHz, NMR at AhlAl-Bait University (Jordan).
A general method [
The electrolyte solution (3.5% NaCl), was prepared from reagent grade NaCl. The corrosion cell used had three electrodes, the reference electrode was a silver/silver chloride electrode., the platinum electrode was used as auxiliary electrode, and the working electrode was carbon steel specimens and the preparation procedure was as follows: thin disks with section-area of 1 cm2 were cut from the carbon steel (CK45) sheet with chemical analysis of; C (0.45), S (<0.030), Mn (0.65), Si (0.25) (wt%) and Fe (remainder). Carbon steel disks were mechanically ground down by 1200 grit abrasive SiC papers, then washed with distilled water and methanol and dried in warm and dry air flow.
The electrochemical measurement were carried out using advanced computerized potentiostatmodel Wenking MLab-200 of Bank Elektronik-Intellignt controls GmbH (Germany) and jacketed Pyrex glass cell. Polarization curves were recorded at constant sweep rate of 2 mv/s and scanning range was from −200 to + 200 mv with respect to the open circuit potential. Before each experiment, the working electrode was immersed in the test cell for 30 min until to reach steady state condition. All tests were carried out at constant temperature (within ±1˚C) by controlling the cell temperature using a cooling heating circulating water bath.
Purity of the obtained compound was examined by TLC, using chloroform and ethyl acetate (1:1) as effluent. The product color was brown yellow and the yield percentage was (83.76%) and the melting point was (70˚C - 71˚C). The reaction was clarified below:
The elemental analysis and some physical properties of the compound are in
Empirical Formula Mwt | Color | M.P. ˚C | Yield % | Elemental Analysis Calculated (Found) | |||
---|---|---|---|---|---|---|---|
C% | H% | N% | S% | ||||
C15H11N3SO 281 | yellow orange | 70 - 71 | 83.76 | 64.06 (63.87) | 3.91 (3.75) | 14.95 (14.77) | 11.39 (11.17) |
given in
Figures 4(a)-(d) show the polarization curves for carbon steel in 3.5% NaCl in present and absent of different inhibitor concentration ranging between (10 - 1000) ppm, in temperature range (298 - 323) K. Electrochemical parameters such as corrosion potential (Ecorr), cathodic and anodic Tafel slopes (bc and ba) and corrosion current density (icorr) were extracted by Tafel extrapolating the anodic and cathodic lines and are listed in
The degree of surface coverage (q) and the percentage of protection efficiency (P%) were calculated using the following equations [
C15H11N3SO | uO-H cm−1 | uN-H cm−1 | uC-H cm−1 Aliphatic | uC-H cm−1 Aromatic | dC-H cm−1 Aromatic | uC≡N Nitrile | dN-H | |
---|---|---|---|---|---|---|---|---|
3414 | 3233 | 2970 | 3062 | 752 | 2237 | 1616 |
C15H11N3SO | Aromatic Protons | Phenolic OH Proton | NH Proton | CH Proton |
---|---|---|---|---|
7.0 - 7.7 | 5.6 | 3.4 | 4.8 |
Structure | 1C | 2C | 8C | 9C | C of All Aromatic |
---|---|---|---|---|---|
117.5 | 56.5 | 155.5 | 168.5 | 120 - 130 |
where iocorr and icorr are corrosioncurrent densities in the absent and present of inhibitor, respectively. From the result in
Adsorption isotherms provide information about the interaction of the adsorption molecules with the electrode surface [
(Org(sol)) and Org(ads) are organic species dissolved in the aqueous solution and adsorbed onto the metallic surface, respectively, H2O(ads) is the water molecule adsorbed on the metallic surface and X is the size ratio respectively, the number of water molecules replaced by one organic adsorb ate. For the studied inhibitor, it was found that the experimental data obtained from polarization reading could be fitted by Langmuir isotherm and Frumkin’s isotherm. Among the tow isotherms, the best fit adsorption isotherm is the Frumkin adsorption isotherm for adsorption of inhibitor on carbon steel surface with the mean R2 value 0.9989. This means that there is an adsorption on a homogenous surface with interaction in the adsorption layer and the negative “a” value suggested that there is a decrease in the adsorption energy that is caused by the repulsive lateral force between the molecules in the adsorbed layer. The inhibitor follows Frumkin adsorption isotherm. The adsorption on a
homogenous surface with an interaction in the adsorption layer obeys Frumkin’s isotherm [
The equation of Frumkin isotherm is;
Taking log on the both sides, it becomes;
where “a” is the interaction parameter which can be positive or negative. A positive value indicates that the adsorption energy is increased by the lateral attraction between the adsorbed molecules and the negative values suggest that there is the presence of the lateral force of repulsion between the molecules in the adsorbed layer. Therefore, inhibitor after adsorption through N, O, S, atoms on the metal surface experiences lateral repulsive interactions among the N, CN, OH, S=. This also supplements that the adsorption of this inhibitor occurs via donation of electrons of N, O, S atoms to the metal.
From
The value of free energy of adsorption (ΔG)ads are calculated by using the following equation [
The various values are tabulated in the
The data in
where Rcorr is the corrosion rate A is the frequency factor and Ea* is the apparent activation energy, R is universal gas constant (8.314 J∙mol−1∙K−1).
The plot of logarithm of corrosion rate of carbon steel obtained from corrosion current densities versus the reciprocal of absolute temperature rang (293 - 323) K, give straight lines with slope of −Ea*/2.303RT as shown in
The thermodynamic parameters of carbon steel in 3.5% NaCl media in absence and in presence of inhibitor under test are given and they can be calculated using transition state Equation (11) [
where CR is the corrosion rate, Ea is the apparent activation energy, R is the universal gas constant (8.314
Temp | a | K | R2 | ΔGad/kJ∙mol−1 |
---|---|---|---|---|
293 | −0.972 | 27.352 | 0.9988 | −34.671 |
303 | −0.996 | 6.8077 | 1.0000 | −14.950 |
313 | −1.7305 | 92.683 | 0.9967 | −40.161 |
323 | −2.328 | 790.678 | 0.9999 | −47.256 |
Ө | P% | CR mm/y | WL g/m2∙d | b mV/Dec | |a| mV/Dec | icorr µA/cm2 | Ecorr mv vs. SCE | Temp. ˚C | System (3.5% NaCl) |
---|---|---|---|---|---|---|---|---|---|
- | - | 1.47 | 31.6 | 80 | 168 | 126 | −526 | 293 | Without Inhibitor |
- | - | 1.65 | 36.0 | 90 | 213 | 143 | −512 | 303 | = |
- | - | 1.75 | 37.6 | 109 | 177 | 150 | −489 | 313 | = |
- | - | 2.37 | 51.0 | 96 | 214 | 204 | −497 | 323 | = |
0.23 | 23.01 | 1.14 | 24.5 | 101 | 171 | 97 | −563 | 293 | 10 ppm Inhibitor |
0.24 | 24.47 | 1.26 | 36.0 | 109 | 189 | 108 | −484 | 303 | = |
0.26 | 26.66 | 1.28 | 27.6 | 108 | 144 | 110 | −489 | 313 | = |
0.35 | 35.29 | 1.53 | 33.0 | 117 | 135 | 132 | −468 | 323 | = |
0.36 | 56.34 | 0.64 | 13.8 | 85 | 143 | 55 | −440 | 293 | 100 ppm Inhibitor |
0.55 | 55.24 | 0.63 | 16.0 | 92 | 141 | 64 | −510 | 303 | = |
0.48 | 48.00 | 0.90 | 19.6 | 100 | 162 | 78 | −469 | 313 | = |
0.55 | 55.88 | 1.04 | 22.5 | 78 | 203 | 90 | −578 | 323 | = |
0.73 | 73.01 | 0.40 | 8.57 | 112 | 120 | 34 | −455 | 293 | 1000 ppm Inhibitor |
0.72 | 72.02 | 0.46 | 10.0 | 115 | 124 | 40 | −439 | 303 | = |
0.64 | 64.00 | 0.63 | 13.5 | 104 | 167 | 54 | −474 | 313 | = |
0.65 | 64.78 | 0.84 | 18.1 | 101 | 175 | 72 | −476 | 323 | = |
J∙mol−1∙K−1), T is temperature, A is the Arrhenius pre-exponential factor, h is the Plank’s constant (6.626176 × 1034 J∙s), N is the Avogadro’s number (6.022 × 1023 mol−1), ΔS* is the entropy of activation and ΔH* is the enthalpy of activation. The values of Ea*, ΔH* and ΔS* were calculated as shown in
Straight lines are obtained with a slope of (−ΔH*/2.303R) and an intercept of (logR/Nh + ΔS*/2.303R) from which the values of ΔH* and ΔS* were calculated. Then ΔG* calculated using the following equation:
and listed in
Analysis of the temperature dependence of inhibition efficiency as well as comparison of corrosion activation in absence and in presence of the inhibitors give some insight into the possible mechanism of inhibitor adsorption. A decrease in inhibition efficiency with rise in temperature, with analogous increase in corrosion activation energy in the presence of (100, 1000) ppm compared to its absence, is frequently interpreted as being suggestive of a physical adsorption [
Also the lower ΔH* values indicate that the inhibited corrosion reaction of carbon steel is supporting the proposed physisorption mechanism [
than association meaning that the increase in a disordering takes place on going from activated complex to reactants, which ΔS* values In absence of inhibitor is more small and negative that indicate to the association rather than of presence inhibitor [
The activation energy for corrosion reaction with using 10 ppm inhibitor was lower than in absence of inhibitor, that indicate the increasing in the ability of the corrosion rate a cording to uncompleted adsorption layer but log A values decreased with adding low inhibitor concentration.
Inhibitor Conc. | Ea* kJ∙mol−1 | ΔH* kJ∙mol−1 | ΔS*/ J∙mol−1∙K−1 | ΔG*/kJ∙mol−1 | |||
---|---|---|---|---|---|---|---|
20 C | 30 C | 40 C | 50 C | ||||
0 | 11.660 | 19.8713 | −252.70 | 93.60 | 96.15 | 98.67 | 101.20 |
10 | 7.3850 | 4.8253 | −305.30 | 93.94 | 97.15 | 100.35 | 103.56 |
100 | 13.192 | 10.6306 | −290.18 | 95.60 | 98.50 | 101.40 | 104.30 |
1000 | 20.o18 | 17.4576 | −271.20 | 96.56 | 99.26 | 101.96 | 104.66 |
2-(Benzo[d]thiazol-2-ylamino)-2-(2-hydroxy-phenyl) acetonitrile was prepared and identified successfully, then used as corrosion inhibitor. The value of icorr in case of presence of inhibitor in the three concentrations was lower than icorr in absence of inhibitor. A best protection efficiency was 73.01% in the case using 1000 ppm of the inhibitor at 293 K, and by increasing temperature, protection efficiency decreased in general; the kinetics and thermodynamic study showed that the inhibitive action took place through the physisorption of the inhibitor molecules on the carbon steel surface and that the adsorption of inhibitor on carbon steel surface obeyed Frumkin isotherm.
Abdulkareem Mohammed AliAl-Sammarraie,Khulood AbidAl-Saade,Mohammed H. A.Al-Amery, (2015) Synthesis and Characterization of Benzothiazol Derivative as a Corrosion Inhibitor for Carbon Steel in Seawater. Materials Sciences and Applications,06,681-693. doi: 10.4236/msa.2015.67070