Synthesis and Rust Preventing Properties of Dodecyl Succinate

Article pubs.acs.org/IECR

Synthesis and Rust Preventing Properties of Dodecyl Succinate Derivatives Containing Triazole Groups Seung-Yeob Baek,† Young-Wun Kim,*,† Seung-Hyun Yoo,† Keunwoo Chung,† Nam-Kyun Kim,† and Joon-Seop Kim*,‡ †

Green Chemistry Research Division, Surfactant & Lubricant Research Team, KRICT, Daejeon 305-600, South Korea Department of Polymer Science & Engineering and BK21 Education Center of Mold Technology for Advanced Materials & Parts, Chosun University, Gwangju 501-759, South Korea

‡

ABSTRACT: Green corrosion inhibitors, n-dodecyl succinate derivatives containing one (HSE) or two triazole groups (DSE), were prepared by three step reactions, that is, nucleophilic substitution reaction, click coupling reaction, and esterification reaction. The characterization results obtained from 1H NMR, FT-IR, and elemental analysis indicated that the succinate derivatives were synthesized successfully. The rust preventing properties of the final products were also investigated using both ASTM D665 and weight loss methods. It was found that the strength of rust-preventing property due to the presence of succinate derivatives in paraffin oil was largely determined by the concentration of alkyl chains, not by their length or by the types of functional groups.

1. INTRODUCTION Mild steel has been used widely in industry as a material for reaction vessels, storage tanks, and so forth. However, the exposure of steel to a humid environment causes a surface degradation, that is, corrosion, and, thus, causes heavy losses on the economy and potential problems of safety in the work place.1 We usually use lubricants as metal working fluids introduced to reduce friction between moving parts. In addition, the lubricants can also be used to prevent corrosion since the integral part of most lubricants is rust prevention. The layer of a lubricant on the steel surface can provide sufficient protection against a corrosive attack on the metal surface. In the gas, oil, and petrochemical industries, the corrosion of steel in an oil medium or an acidic medium is a major concern since the corresponding industries require distillation, hydrogenation, desulfurization processes, and utilize vacuum containers and/or catalytic reactors. Even in a closed oil container, condensed water can be found inside, which is due to the temperature change, and this condensed water, even though the amount of which is relatively small, can cause corrosion. Then, this corrosion can accelerate oil degradation, resulting in oxidation, hydrolysis, acid build-up, wear debris, additive interaction, colloidal phenomena, microbial attack, ingression of dust, soot, and unburned fuel.2 As expected, the corrosion of metal becomes more severe in an acidic medium, and, thus, in the chemical industries, corrosion inhibitors have been used extensively to reduce the acid corrosion damage on the metal surface by decreasing corrosion rates of the metal or an alloy.3,4 The corrosion inhibitors can be either inorganic or organic materials. Since some of inorganic inhibitors are known to be a hazard to health and environmental pollutants,5,6 the use of organic inhibitors is in greater demand. In the case of the organic inhibitors, they adsorb at a metal/solution interface and inhibit the corrosion on the metal surface. Most of the effective organic corrosion inhibitors contain multiple bonds and heteroatoms such as © 2012 American Chemical Society

oxygen, nitrogen, sulfur, which make the inhibitors adsorb on the metal surface.7−9 Such kinds of organic inhibitors are, for example, benzaldehydes,10 furans,11,12 isoxazolidines,13 triazoles,14−17 pyridines,18 thiadiazole,19 oxadiazoles,20 and imidazolines.21−24 Recently, environmental regulations on industrial consumption and development of new corrosion inhibitors have become stricter. Thus, natural products (e.g., biomass based, nontoxic, and environmental-friendly products) have gained much attention to the development of “green corrosion inhibitors” that have high inhibition efficiency. In recent years, the need for developing fine chemicals based on bioproducts as raw materials is increasing because of the depletion of oil resources and the sustained effort to prepare eco-friendly materials and find a way to decrease greenhouse gas emissions. Thus, now we face a transition from the existing petrochemical industry to the new renewable energy industry that is pushing for sustainable, green growth. As a result, the proportion of the green energy and biotechnology industries is growing, and the development of alternative bioindustrial processes that can replace the petroleum-based chemical processes becomes an urgent task around the world. Since biobased alkyl succinate is manufactured using biomass feedstocks as raw materials, it is cost-competitive, compared to petroleum-based ones, and has great potential to become a higher value-added general-purpose chemical material. Especially, the alkyl succinate is highly biodegradable and, thus, has the advantage of possible applications such as in environmentally friendly products. For past five years, our group has been working on the preparation and modification of biobased alkyl succinate and has obtained very positive results. In this work, we studied succinate as a starting material for a green Received: Revised: Accepted: Published: 9669

February 6, 2012 June 15, 2012 June 26, 2012 June 26, 2012 dx.doi.org/10.1021/ie300316f | Ind. Eng. Chem. Res. 2012, 51, 9669−9678

Industrial & Engineering Chemistry Research

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2.2. Synthesis. n-Dodecyl succinate derivatives containing alkyl triazole were synthesized through three steps as shown in Scheme 2. As the first step, the alkyl (R′) azide (Az) derivatives

corrosion inhibitor. We chose long alkyl succinic anhydride, that is, n-dodecyl (C12) succinic anhydride, to synthesize several new environmental-friendly inhibitors, that is, dodecyl succinate esters containing either only one alkyl (R′) triazole group or two alkyl triazole groups (HSE-C12-Tz-R′ and DSEC12-Tz-R′, whose chemical structures are shown in Scheme 1)

Scheme 2. Synthetic Route of n-Dodecyl Succinate Derivatives Containing One Triazole Group (HSE-C12-TzR′) or Two Triazole Groups (DSE-C12-Tz-R′)

Scheme 1. Chemical Structures of HSE-C12-Tz-R′ and DSEC12-Tz-R′

and conducted a preliminary study on their rust preventing properties. At this point, it should be mentioned that since the main purpose of the present work is to investigate the rustpreventing properties of final products, we used commercially available dodecyl succinic anhydride, instead of one obtained from biomass, as a starting material because the former has high purity and, thus makes data interpretation easier.

(Az-R′) were prepared by a substitution reaction of sodium azide to three alkyl halides (octyl- (C8), dodecyl- (C12), and octadecyl (C18) chloride). As the second step, the triazole alcohol compounds (C2OH-Tz-R′) were synthesized by a click coupling reaction between alkyl azide and propargyl alcohol. As the third step, the final target products of n-dodecyl succinate derivatives containing only one triazole group (HSE-C12-TzR′) were prepared by the reaction between n-dodecyl succinic anhydride and C2OH-Tz-R′. Dodecyl succinate derivatives containing two triazole groups (DSE-C12-Tz-R′) were also prepared by an esterification reaction of dodecyl succinic anhydride with two equivalent amounts of C2OH-Tz-R′. Since we had used the same method to prepare either Az-R′ or C2OH-Tz-R′ or HSE-C12-Tz-R′ or DSE-C12-Tz-R′, as an example, here we give a detailed synthesis procedure of only one compound of each series (e.g., containing octyl as R′) below. In addition, as a control system, we also used an alkyl succinate derivative, having dodecyl and octyl alkyl chains, DSE-C12-C8, and its synthesis procedure was reported elsewhere.28 2.2.1. Synthesis of Alkyl Azide. Octyl azide (Az-C8) was prepared as follows: n-Octyl chloride (10 g, 67 mmol) (C8) and sodium azide (5.25 g, 81 mmol) were placed in a 100 mL three-neck round-bottom flask. Then, 80 mL of dimethylformamide (DMF) was added to the reaction flask to make homogeneous solution. The homogeneous solution was kept at 60 °C for 24 h under a nitrogen atmosphere. The conversion of reactants to products was checked using GC chromatography at room temperature; the products were separated using a mixture of ethyl acetate/water (1/1 v/v). The organic phase containing the products was dried with MgSO4 and was filtered. Subsequently, the ethyl acetate was evaporated to obtain yellowish liquid, that is, Az-C8 (10.2 g, 98% yield). The NMR, FT-IR, GC, and elemental analysis results of each compound of Az-R′ are given below. The elemental analysis results are in good agreement with the calculated values based on the chemical formula of Az-R′. Octyl Azide (Az-C8). 1H NMR (δ, ppm): 3.25 (m, 2H), 1.60 (m, 2H), 1.40−1.13 (m, 10H), 0.88 (t, 3H). FT-IR (ν, cm−1): 2960, 2929, 2859, 2095, 1466, 1350, 1262.

2. EXPERIMENTAL SECTION 2.1. Materials Used and Characterization. For the synthesis of dodecyl succinate derivatives containing alkyl triazole group, n-octyl chloride (Aldrich, 99%), n-dodecyl chloride (Aldrich, 97%), n-octadecyl chloride (Aldrich, 96%), sodium azide (Aldrich, 99.5%), propargyl alcohol (Aldrich, 99%), copper(I) bromide (Aldrich, 98%), n-dodecyl succinic anhydride (TCI, 95%), p-toluenesulfonic acid monohydrate (Junsei, 99%), toluene (SK Chemical, LP grade), ethyl acetate (SK Chemical, LP grade), and magnesium sulfate anhydrous (Daejung, 99%) were used. The 1H NMR spectra of the products in CDCl3 were obtained using a Bruker DPX-300 spectrometer with standard pulse sequences operating at 300 MHz; tetramethylsilane (TMS) was used as the internal standard. The FT-IR spectra of the products were measured using a Bio-RAD FTS165 spectrometer. The ring-opening reactions of n-dodecyl succinic anhydride with triazole alcohol were monitored using an Agilent Technologies 7890A gas chromatograph after silylation.25−27 An Agilent Technologies HP-1 capillary column with dimensions of 0.32 mm (inner diameter) × 30 m (length) × 0.25 μm (film thickness) was used for the separation of products. The temperature was increased from 50 to 320 °C at a heating rate of 10 °C/min. The split ratio was 1:50, and helium was used as the carrier gas at a flow rate of 1 mL/min. The injector and detector temperatures were 250 and 300 °C, respectively. The melting temperatures of the products were determined using a PerkinElmer JADE DSC under a constant stream of N2 at atmospheric pressure. The heating rate was 5 °C/min. For the study on the surface morphology of steel disk after corrosion process, a Philips XL30SFEG SEM was utilized. Also, the elemental analysis of steel disk after the corrosion process was carried out by an energy-dispersive X-ray spectroscopy (EDX) method, using a Bruker AXS XFlash Detector 4010. 9670

dx.doi.org/10.1021/ie300316f | Ind. Eng. Chem. Res. 2012, 51, 9669−9678


Article

39 mmol) were placed in a 250 mL three-neck round-bottom flask without solvent. Then, the reaction mixture was kept at 80 °C for 10 h, resulting in an appearance of a green solid product, that is, mainly HSE-C12-Tz-C8 (17.2 g, 97% yield). At this time, it should be mentioned that according to the GC results, less than 5% of product was found to be DSE-C12-Tz-C8. The NMR, FT-IR, GC, and elemental analysis results of each HSE-C12-Tz-R′ are given below. Again, the elemental analysis results are in good agreement with the calculated values based on the chemical formula of HSE-C12-Tz-R′. HSE-C12-Tz-C8. 1H NMR (δ, ppm): 7.65 (m, 1H), 5.24 (m, 2H), 4.35 (m, 2H), 2.85 (m, 1H), 2.72 (m, 1H), 2.51 (m, 1H), 1.90 (m, 4H), 1.56−1.08 (m, 22H), 0.88 (t, 6H). FT-IR (ν, cm−1): 3146, 2925, 2856, 1740 (ester CO), 1466, 1165. Elemental analysis (%): C = 67.58, H = 10.30, N = 8.77, O = 13.35 (calculated for C27H49N3O4: C = 67.60, H = 10.30, N = 8.76, O = 13.34). HSE-C12-Tz-C12. 1H NMR (δ, ppm): 7.66 (m, 1H), 5.24 (m, 2H), 4.34 (m, 2H), 2.88 (m, 1H), 2.71 (m, 1H), 2.52 (m, 1H), 1.90 (m, 4H), 1.56−1.08 (m, 30H), 0.88 (t, 6H). FT-IR (ν, cm−1): 3146, 2925, 2856, 1740 (ester CO), 1466, 1165. Elemental analysis (%): C = 69.53, H = 10.72, N = 7.83, O = 11.92 (calculated for C31H57N3O4: C = 69.49, H = 10.72, N = 7.84, O = 11.94). HSE-C12-Tz-C18. 1H NMR (δ, ppm): 7.64 (m, 1H), 5.24 (m, 2H), 4.34 (m, 2H), 2.86 (m, 1H), 2.70 (m, 1H), 2.53 (m, 1H), 1.90 (m, 4H), 1.56−1.08 (m, 42H), 0.88 (t, 6H). FT-IR (ν, cm−1): 3150, 2921, 2852, 1736 (ester CO), 1466, 1165. Elemental analysis (%): C = 71.69, H = 11.22, N = 6.78, O = 10.31 (calculated for C37H69N3O4: C = 71.68, H = 11.22, N = 6.78, O = 10.32). 2.2.4. Synthesis of n-Dodecyl Succinate Containing Two Triazole Groups. At this point, it should be mentioned that the synthesis of HSE derivatives requires a relatively mild condition, for example, low temperature. On the other hand, the synthesis of DSE derivatives needs a catalyst (i.e., p-toluene sulfonic acid) for the condensation reaction. n-Dodecyl succinate containing two octyl triazoles (DSE-C12-Tz-C8) was synthesized as follows: n-Dodecyl succinic anhydride (10 g, 37 mmol) and C2OH-Tz-C8 (16.4 g, 78 mmol) were placed in a 250 mL three-neck round-bottom flask equipped with a Dean−Stark apparatus and a condenser. After the addition of toluene (120 mL) to the reactants, the solution was stirred, and, then, a catalyst, that is, p-toluene sulfonic acid (0.7 g, 3.7 mmol), was added slowly to the solution. The reaction mixture was kept at 130 °C for 10 h. The water evolved was removed using the Dean−Stark apparatus. When the reaction was complete, the solution was cooled to room temperature, and the reaction mixtures were purified using ethyl acetate/water (1/1 v/v) and neutralized with aqueous Na2CO3 solution. The organic phase was dried with MgSO4, filtered, and then ethyl acetate was evaporated to obtain a green solid product, that is, mainly DSE-C12-Tz-C8 (24.4 g, 98% yield). At this time, it should be mentioned that according to the GC results, less than 1% of product was found to be HSE-C12-Tz-C8. The NMR, FT-IR, GC, and elemental analysis results of each DSE-C12-Tz-R′ are given below, and one can find that the elemental analysis results are in good agreement with the calculated values based on the chemical formula.

GC (min): 9.9. Elemental analysis (%): C = 61.91, H = 11.05, N = 27.04 (calculated for C8H17N3: C = 61.89, H = 11.04, N = 27.07). Dodecyl Azide (Az-C12). 1H NMR (δ, ppm): 3.25 (m, 2H), 1.60 (m, 2H), 1.40−1.13 (m, 18H), 0.88 (t, 3H). FT-IR (ν, cm−1): 2960, 2929, 2859, 2095, 1466, 1350, 1262. GC (min): 15.1. Elemental analysis (%): C = 68.21, H = 11.92, N = 19.87 (calculated for C12H25N3: C = 68.20, H = 11.92, N = 19.88). Octadecyl Azide (Az-C18). 1H NMR (δ, ppm): 3.25 (m, 2H), 1.60 (m, 2H), 1.40−1.13 (m, 30H), 0.88 (t, 3H). FT-IR (ν, cm−1): 2960, 2929, 2859, 2095, 1466, 1350, 1262. GC (min): 21.1. Elemental analysis (%): C = 73.19, H = 12.61, N = 14.20 (calculated for C18H37N3: C = 73.16, H = 12.62, N = 14.22). 2.2.2. Synthesis of 4-Hydroxymethyl-N-alkyl 1,2,3-triazole. 4-Hydroxymethyl-N-octyl 1,2,3-triazole (C2OH-Tz-C8) was synthesized as follows: Az-C8 (10 g, 64 mmol) and copper(I) bromide (1.83 g, 1.28 mmol) were placed in a 100 mL threeneck round-bottom flask containing DMF (80 mL), and the solution was stirred. To the solution, propargyl alcohol (4.0 g, 71 mmol) was added slowly. The reaction solution was kept at 40 °C for 8 h. Then, the solution was cooled to room temperature and purified using a mixture of ethyl acetate/water (1/1 v/v). The organic phase was treated with MgSO4 to remove water, filtered, and the ethyl acetate was evaporated to obtain a green solid product, that is, C2OH-Tz-C8 (3.4 g, 99% yield). The NMR, FT-IR, GC and elemental analysis results of each C2OH-Tz-R′ are given below. Again, the elemental analysis results are in good agreement with the calculated values based on the chemical formula of C2OH-Tz-R′. C2OH-Tz-C8. 1H NMR (δ, ppm): 7.65 (m, 1H), 4.79 (m, 2H), 4.34 (m, 2H), 3.97 (m, 1H), 1.90 (m, 2H), 1.43−1.16 (m, 10H), 0.88 (t, 3H). FT-IR (ν, cm−1): 3400, 3130, 3079, 2925, 2852, 1462, 1223, 1150, 1015. GC (min): 18.4. Elemental analysis (%): C = 62.50, H = 10.02, N = 19.90, O = 7.58 (calculated for C11H21N3O: C = 62.52, H = 10.02, N = 19.89, O = 7.57). C2OH-Tz-C12. 1H NMR (δ, ppm): 7.56 (m, 1H), 4.78 (m, 2H), 4.34 (m, 2H), 2.96 (m, 1H), 1.90 (m, 2H), 1.43−1.16 (m, 18H), 0.88 (t, 3H). FT-IR (ν, cm−1): 3388, 3130, 3079, 2921, 2848, 1462, 1219, 1146, 1007. GC (min): 22.2. Elemental analysis (%): C = 67.38, H = 10.93, N = 15.70, O = 5.99 (calculated for C15H29N3O: C = 67.37, H = 10.93, N = 15.71, O = 5.98). C2OH-Tz-C18. 1H NMR (δ, ppm): 7.65 (m, 1H), 4.79 (m, 2H), 4.34 (m, 2H), 2.96 (m, 1H), 1.90 (m, 2H), 1.43−1.16 (m, 30H), 0.88 (t, 3H). FT-IR (ν, cm−1): 3400, 3130, 3079, 2925, 2852, 1462, 1223, 1150, 1015. GC (min): 26.8. Elemental analysis (%): C = 71.73, H = 11.75, N = 11.96, O = 4.56 (calculated for C21H41N3O: C = 71.74, H = 11.75, N = 11.95, O = 4.55). 2.2.3. Synthesis of n-Dodecyl Succinate Containing One Alkyl Triazole Group. n-Dodecyl succinate containing one octyl triazole (HSE-C12-Tz-C8) was made as follows: n-Dodecyl succinic anhydride (10.0 g, 37 mmol) and C2OH-Tz-C8 (8.2 g, 9671



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DSE-C12-Tz-C8. 1H NMR (δ, ppm): 7.59 (m, 2H), 5.21 (m, 4H), 4.34 (m, 4H), 2.80 (m, 1H), 2.69 (m, 1H), 2.48 (m, 1H), 1.90 (m, 6H), 1.56−11.08 (m, 40H), 0.88 (t, 9H). FT-IR (ν, cm−1): 3141, 2925, 2856, 1736 (ester CO), 1466, 1161, 1049. Elemental analysis (%): C = 67.85, H = 10.17, N = 12.48, O = 9.50 (calculated for C38H68N6O4: C = 67.82, H = 10.18, N = 12.49, O = 9.51). DSE-C12-Tz-C12. 1H NMR (δ, ppm): 7.50 (m, 2H), 5.12 (m, 4H), 4.28 (m, 4H), 2.75 (m, 1H), 2.61 (m, 1H), 2.40 (m, 1H), 1.83 (m, 6H), 1.56−11.08 (m, 56H), 0.81 (t, 9H). FT-IR (ν, cm−1): 3142, 2925, 2852, 1736 (ester CO), 1466, 1161, 1053. Elemental analysis (%): C = 70.33, H = 10.78, N = 10.72, O = 8.16 (calculated for C46H84N6O4: C = 70.36, H = 10.78, N = 10.70, O = 8.15). DSE-C12-Tz-C18. 1H NMR (δ, ppm): 7.55 (m, 2H), 5.17 (m, 4H), 4.32 (m, 4H), 2.79 (m, 1H), 2.66 (m, 1H), 2.43 (m, 1H), 1.90 (m, 6H), 1.56−11.08 (m, 68H), 0.81 (t, 9H). FT-IR (ν, cm−1): 3139, 2921, 2856, 1736 (ester CO), 1466, 1165, 1057. Elemental analysis (%): C = 73.03, H = 11.43, N = 8.82, O = 6.71 (calculated for C58H108N6O4: C = 73.06, H = 11.42, N = 8.81, O = 6.71). 2.3. Rust Preventing Property Measurements. 2.3.1. ASTM D665 Method. The rust preventing characteristics of paraffin oil containing synthetic seawater and ester derivative inhibitors were evaluated using an ASTM D665 method.29 A detailed procedure of a typical test method is described as follows. The rod-type specimens of mild steel (its composition (wt %) was Fe = 94.0, C = 4.1, O = 1.1, Mn = 0.36, Al = 0.3, Si = 0.19) were prepared under the ASTM D665 procedure. To eliminate impurities on the steel surface and make the uniform steel surface, the steel specimens were rotated using a motor at a speed of 950 rpm to make the smooth surface using 60, 120, 180, 320, 400, 600, and 800-grit sandpapers. Then, the rod specimens were washed with acetone and hexane, and dried and stored in a desiccator. A mixture of 300 mL of the paraffin oil containing various amounts of inhibitors and 30 mL of the synthetic seawater was stirred at 60 °C, in which a cylindrical steel test rod was immersed completely for 24 h, and the composition of salts in the synthetic seawater, prepared in accordance with the description in ASTM D665, was as follows: NaCl = 24. 54 g/L, MgCl2·6H2O = 11.10 g/L, Na2SO4 = 4.09 g/L, CaCl2 = 1.16 g/L, KCl = 0.69 g/L, NaHCO3 = 0.20 g/L, KBr = 0.10 g/L. After 24 h, the rust on the test rod surface was evaluated. The rusting rate was classified as follows: “Pass”, when the test rod was rust-free; “light”, when the test rod had not more than six rust spots, each of which was less than 1 mm in diameter; “moderate”, when the rusting was more severe than that mentioned above for the “light” but confined to less than 5% of the surface area of the test rod; “severe”, when the rust on the test rod surface covered more than 5% of the surface area. 2.3.2. Weight Loss Method. The surface of disk-type specimens of mild steel, the dimension of which was 25 mm (diameter) × 1 mm (thickness), was smoothed with 120, 180, 320, 400, 600, 800, and 1500-grit sandpapers in order, washed with acetone and hexane, and dried and kept in a desiccator. After the weights of the specimens were measured accurately, the specimens were immersed in the solution of synthetic seawater and paraffin oil containing various amounts of inhibitors for 24 h. Then, the specimens were taken out,

rinsed thoroughly with distilled water, dried, and weighed again accurately. Three parallel experiments were performed for each test. An average weight loss (W) in grams was calculated using the following equation: W = W1 − W2

(1)

where W1 and W2 are the average weights of specimens before and after the immersion, respectively. Corrosion inhibition efficiency (η %) was calculated using the following equation: η% = [(W1 − W )/W1] × 100%

(2)

A corrosion rate (CR) (mm/year) was calculated using the following equation: CR = K × W /(A × d × t )

(3)

where A is the surface area of specimens (in the present work, A = 4.91 cm2), d is the density of iron (7.86 g/cm3), and t is the immersion time, that is, 24 h. K (= 8.76 × 104) is the conversion constant that enabled expressing CR in mm/year, when t, A, W, and d values are expressed in the quoted units.30

3. RESULTS AND DISCUSSION 3.1. Synthesis of Dodecyl Succinate Derivatives Containing Alkyl Triazoles. The n-dodecyl succinate derivatives containing triazole (HSE-C12-Tz-R′ and DSEC12-Tz-R′) were synthesized by three step reactions, that is, (1) nucleophilic substitution reaction of sodium azide to alkyl halide, (2) click coupling reaction between alkyl azide (Az-R) and propargyl alcohol, and (3) esterification reaction between dodecyl succinic anhydride and triazole alcohol (C2OH-Tz-R′). To confirm the chemical structures of the HSE-C12-Tz-R′ and DSE-C12-Tz-R′, 1H NMR, FT-IR techniques were utilized. For the convenience of readers, only some of the 1H NMR and FTIR spectra are discussed below. The 1H NMR and FT-IR spectra of the HSE-C12-Tz-C8 and DSE-C12-Tz-C8 are seen in Figures 1 and 2, respectively. According to the 1H NMR spectra of the HSE-C12-Tz-C8, it is seen that while NMR peaks at δ = 4.79 ppm (s, 2H, −CH2OH) and δ = 3.97 ppm (s, 1H, CH2OH) of C2OH-Tz-C8 disappear, a new peak appears at δ = 5.24 ppm (s, 2H, −CCH2OC(O)−). In addition, a peak at δ = 3.18 ppm (s, 1H, the protons of the methylene of dodecyl succinic anhydride) shifts to δ = 2.71 ppm (t, 1H, −CHCHH−C(O) −O−) and 2.52 ppm (t, 1H, −CHCHH−C(O) −O−) after a ring-opening reaction. In the case of the FT-IR spectra of the HSE-C12-Tz-C8, IR bands at ν = 1805 cm−1 and 1780 cm−1 for anhydride carbonyl of dodecyl succinic anhydride and at ν = 3400 cm−1 for primary alcohol disappear, but IR bands appear at ν = 1740 cm−1 for ester carbonyl and at ν = 3300−2700 cm−1 for free carboxylic acid, indicating a successful ring-opening reaction. These results indicate that the HSE-C12-Tz-C8 has been synthesized successfully by the reaction between dodecyl succinic anhydride and triazole alcohol. In the case of the 1H NMR of the DSEC12-Tz-C8, it is seen that while NMR peaks at δ = 4.79 ppm (s, 2H, −CH2OH) and 3.97 ppm (s, 1H, CH2OH) of C2OHTz-C8 disappear, new peaks appear at δ = 5.21 ppm (s, 2H, −CCH2OC(O)−). In addition, a peak at δ = 3.18 ppm (s, 1H, the protons of the methylene of dodecyl succinic anhydride) shifts to δ = 2.69 ppm (t, 1H, −CHCHH−C( O)O−) and 2.48 ppm (t, 1H, −CHCHH−C(O) −O−) after the completion of a ring-opening reaction. In the case of the FT-IR spectra of the DSE-C12-Tz-C8 in Figure 2, IR bands at ν = 1805 cm−1 and 1780 cm−1 for anhydride carbonyl of 9672



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Again, these results suggest that the DSE-C12-Tz-C8 has been synthesized successfully by the reaction between triazole alcohol and dodecyl succinic anhydride. The yields, color, total acid numbers (TAN), and solubilities of the HSE and DSE derivatives are listed in Table 1. The high Table 1. Yield, Color, TAN, and Solubility of HSE and DSE Derivatives ester derivatives

yield (%)

color

TAN (mg KOH/g)

solubility @ 300 ppm

HSE-C12-Tz-C8 HSE-C12-Tz-C12 HSE-C12-Tz-C18

97 98 96

green brown brown

128.8 (120)a 108.2 (108) 99.0 (92.6)

soluble soluble soluble

DSE-C12-Tz-C8 DSE-C12-Tz-C12 DSE-C12-Tz-C18

98 98 97

green green green

1.0 (0) 0.9 (0) 0.4 (0)

soluble soluble soluble

a

The value in parentheses indicates the calculated amount of KOH in milligrams to neutralize the acid groups of one gram sample.

yield percentages of the derivatives suggest that the synthesis procedure mentioned above is very effective in the preparation of the HSE and DSE derivatives. Naturally, with increasing alkyl chain length, the molecular weight of the derivatives increases, and, thus, the mole of the HSE derivatives, especially the amount of acid groups, per unit weight of sample decreases, leading to decreasing TAN. In the present work, it is seen that the TAN decreases with increasing alkyl chain length, and that the TANs for the HSE derivatives are similar to the calculated amount of KOH in milligrams to neutralize the acid groups of one gram of HSE derivatives completely. It should also be noted that the DSE derivatives that should not have any acid group theoretically show very small TANs. However, the values are too small to be considered as meaningful values that affect the physical properties of the DSE derivatives strongly. The small differences between TANs and the calculated amount of KOH for HSE and DSE derivatives suggest that the ringopening reaction and esterification reaction are very effective to prepare decent HSE and DSE derivatives. At this point, it should be mentioned that the HSE and DSE derivatives should be soluble in paraffin oil, at least to some extent, to show the rust preventing property in paraffin oil. Thus, the solubility of the derivatives in paraffin oil should be evaluated. In the present study, it is observed that all derivatives are soluble in paraffin oil at the concentration of 300 ppm, indicating that the ester derivatives can be used as corrosion inhibitors in oil. 3.2. Rust Preventing Property Measurements. 3.2.1. ASTM D665 Method. Shown in Figure 3 are the images of the steel surface after 24 h immersion of steel in the mixed solution of seawater/paraffin oil containing various amounts of ester derivatives; the brief summary of rusting rates obtained from the images is listed in Table 2. The results obtained from DSE-C12-C8 (ref 28) are also included in Figure 3 and Table 2. Table 2 indicates that the addition of the ester derivatives to paraffin oil reduces the rusting rate of the steel significantly, indicating that the ester derivatives act as corrosion inhibitors. With increasing concentration, the ester derivatives show better corrosion inhibition. Especially, above 150 ppm, the HSE and DSE derivatives act as effective corrosion inhibitors. In addition, the rusting rates of HSE-C12-Tz-R′ derivatives are slightly better than those of corresponding DSE-C12-Tz-R′ derivatives. This implies that for the corrosion inhibition the presence of

Figure 1. NMR spectra of (A) dodecyl succinic anhydride, (B) C2OH-Tz-C8, (C) HSE-C12-Tz-C8, and (D) DSE-C12-Tz-C8.

Figure 2. FT-IR spectra of (A) dodecyl succinic anhydride, (B) C2OH-Tz-C8, (C) HSE-C12-Tz-C8, and (D) DSE-C12-Tz-C8.

dodecyl succinic anhydride and at ν = 3400 cm−1 for a primary alcohol disappear, but an IR band at ν = 1736 cm−1 of ester carbonyl appears, indicating a successful ring-opening reaction. 9673



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noting that, since the molecular weight of HSE is smaller than that of corresponding DSE, at the same concentration, a mole of HSE derivatives in the solution is larger than that of DSE derivatives, and, thus, the molar ratios of the HSE derivative to the corresponding DSE derivative are in the range of 1.40− 1.54, depending on the alkyl chain length. As expected, increasing amount of ester derivatives would enhance corrosion inhibition, which might be what we observed here. It should also be noted that the numbers of alkyl chains per HSE and DSE molecules are two and three, respectively, that is, the number ratio of chains is 0.67. These two facts mentioned above indicate that at the same concentration, the numbers of alkyl chains of HSE and DSE derivatives are similar to each other. Thus, when we replace an HSE with a corresponding DSE, we indeed change three factors at the same time: (1) functional groups (i.e., from one carboxylic acid and triazole to two triazoles), (2) molecular weight (e.g., from 619 g/mol for HSE-C12-Tz-C18 to 952 g/mol for DSE-C12-Tz-C18), (3) number of alkyl chains (i.e., from two to three). Thus, one should keep this molar ratio effect in mind when one interprets the data. In addition, the increasing length of alkyl chain of triazole also increases the molecular weight and hydrophobicity of the ester derivatives. Thus, when one interprets the data, one has to consider these factors simultaneously. In Table 2, it is also seen that with increasing alkyl chain length, the rusting rate becomes worse, even though the longer alkyl chain might be more hydrophobic. This might be because the molecular weight of ester derivatives increases with increasing alkyl chain length, which decreases the amount of ester derivatives in the solution to keep the same concentration. In addition, the longer alkyl chain might disrupt the constitution of the close packed protective layer at the metal−water interface, compared to the shorter alkyl chain. This weakens the rust preventing properties. 3.2.2. Weight Loss Method. The inhibition efficiency of the corrosion inhibitor for mild steel can also be calculated using a weight loss method. Listed in Table 3 are the percentages of inhibition efficiency (η %) and corrosion rates (CR) obtained from the measurements of weight loss of mild steel in a mixture of seawater and paraffin oil containing different amounts of ester derivatives. As expected, with increasing amount of inhibitor, the η % increases but the CR decreases, and, with increasing alkyl chain length of ester derivatives, the η % decreases but the CR increases. In addition, when the alkyl chain length is the same, the η % and CR values of HSE derivatives are slightly larger and smaller, respectively, compared to those of DSE derivatives. Again, this is due to the differences in functional groups and molecular weights of the HSE and DSE derivatives. Table 3 also indicates that above 150 ppm, both the HSE and the DSE derivatives act as very effective inhibitors; especially, the η % and CR values are very

Figure 3. Images of steel surface after 24 h immersion of the steel in a mixture of synthetic seawater and paraffin oil containing various amounts of HSE and DSE derivatives. The data for DSE-C12-C8 were obtained from ref 28.

carboxylic acid groups with one triazole is slightly better than the presence of two triazoles. This can be understood: According to the works by Suzuki et al. and Tsuji et al., the mixture of a corrosion inhibitor containing tertiary amine and an inhibitor containing carboxylic acid shows a better inhibition property than an individual inhibitor does.31,32 The same explanation may be applicable here. The nitrogen of triazole can exchange electrons with those of steel in the course of anodic dissolution, leading to the formation of physisorbed species. These species now interfere with an electrochemical reaction and form a protective layer on the steel surface, making the corrosion kinetic slow down. At this point, it should also be mentioned that the nitrogen of triazole has a basic character, and, thus, the physisorption on the steel surface makes pH at the interface higher. When the inhibitor contains carboxylic acid, the carboxylic acid can react with corrosion products, which increases the protective layer thickness. This leads to slightly better corrosion inhibition. In addition, it is worth

Table 2. Rusting Rates of HSE-C12-Tz-R′, DSE-C12-Tz-R′, and DSE-C12-C8 conc. of ester derivatives (ppm)

HSE-C12-Tz-C8

HSE-C12-Tz-C12

HSE-C12-Tz-C18

DSE-C12-Tz-C8

DSE-C12-Tz-C12

DSE-C12-Tz-C18

DSE-C12−C8a

20 40 80 150 300

severe pass pass pass pass

severe severe light pass pass

severe severe light pass pass

severe light pass pass pass

severe severe moderate pass pass

severe severe moderate light pass

severe severe severe severe

a

Data were obtained from ref 28. 9674



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Table 3. Weight Loss of Mild Steel and the η % and CR of Ester Derivatives η %a

weight loss (mg)a

a

CR (mm/year)a

ester derivatives

20

40

80

150

300

20

40

80

150

300

20

40

80

150

300

HSE-C12-Tz-C8 HSE-C12-Tz-C12 HSE-C12-Tz-C18

1.7 4.7 6.6

1.4 4.5 5.4

0.2 0.7 1.2

0.08 0.1 0.2

0.02 0.04 0.06

75.7 56.3 38.4

80.0 58.6 49.9

97.8 93.1 88.9

98.8 99.1 98.3

99.7 99.6 99.4

1.6 4.4 6.3

1.3 4.2 5.1

0.1 0.7 1.1

0.08 0.09 0.15

0.02 0.04 0.06

DSE-C12-Tz-C8 DSE-C12-Tz-C12 DSE-C12-Tz-C18

1.4 6.9 8.3

1.2 5.0 5.6

0.2 0.7 4.5

0.05 0.05 0.3

0.03 0.05 0.07

79.4 35.8 22.9

82.8 53.4 47.8

97.0 93.6 58.3

99.3 99.5 96.9

99.5 99.6 99.4

1.3 6.5 7.8

1.1 4.7 5.3

0.2 0.7 4.2

0.04 0.05 0.3

0.03 0.04 0.07

DSE-C12-C8b

13.6

13.4

13.2

13.3

11.5

11.3

11.2

11.2

11.3

13.4 b

At concentration of ester derivatives (ppm) as below. Data were obtained from reference 28.

Figure 4. SEM images of the surface of carbon steel after corrosion test in a mixed solution of seawater and paraffin oil containing (a) no HSE or DSE, and HSE-C12-Tz-C8 of (b) 20 ppm, (c) 80 ppm, and (d) 300 ppm, and (e) DSE-C12-C8 of 300 ppm, and DSE-C12-Tz-C8 of (f) 20 ppm, (g) 80 ppm, and (h) 300 ppm. The scale bar indicates micrometer.

similar to each other at 99.1 ± 0.8 and 0.081 ± 0.077, respectively. Finally, the weight loss data of DSE-C12-C8 indicate poor corrosion inhibition behavior of the compound.28 The SEM images of the corroded steel in a mixture of seawater and paraffin oil containing various amounts of ester derivatives are shown in Figure 4. Figure 4a reveals that when the steel is immersed in the mixed solution without corrosion inhibitor, the corrosion occurs on the surface extensively. On the other hand, in the presence of HSE-C12-Tz-C8 of 20 ppm in the paraffin oil (Figure 4b), the steel surface is corroded, only to some extent. As the amount of HSE increases to 80 ppm, the steel surface is less corroded and less rough (Figure 4c). In the case of HSE-C12-Tz-C8 of 300 ppm, the steel surface is no longer corroded, suggesting high corrosion inhibition efficiency of HSE-C12-Tz-C8 under the experimental condition (Figure 4d). Figure 4e shows the SEM image of DSE-C12-C8 of 300 ppm. It is seen that the steel surface is severely corroded, indicating that the DSE-C12-C8 is not an effective corrosion inhibitor. This means that the presence of triazole group is very important for corrosion inhibition. In the case of the steels in a

mixed solution of seawater and paraffin oil containing DSEC12-Tz-C8, a similar trend is also observed (Figure 4f−4 h). To find the chemical elements on the corroded steel surface, the steel surfaces were analyzed using the EDX method. In Figure 5, there is no EDX peak for nitrogen atoms, suggesting that the nitrogen atoms of triazole of derivatives do not bind tightly to the steel surface. On the other hand, a small EDX peak for chlorine atoms is seen at about 2.6 keV in the spectra for the carbon steel in a mixed solution without HSE and DSE (Figure 5a) and with the HSE-C12-Tz-C8 (Figure 5b) and DSE-C12-Tz-C8 (Figure 5f) of 20 ppm. This peak is due to the presence of a chlorine element of seawater (NaCl) on the corroded surface, indicating that the seawater contacts with the steel surface, to some extent. At 80 ppm, however, this peak is no longer present (Figures 5c and 5g), implying that the seawater does not make contact with the steel surface effectively any more during the first 24 h of immersion. As expected, at 300 ppm, the EDX spectra show no peak for NaCl (Figures 5d and 5h). Above findings tell us that the ester derivatives with triazole and carboxylic acid groups can participate to constitute close 9675



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Figure 5. EDX spectra for the surface of carbon steel after corrosion test in a mixed solution of seawater/paraffin oil containing (a) no HSE or DSE, and HSE-C12-Tz-C8 of (b) 20 ppm, (c) 80 ppm, and (d) 300 ppm, and (e) DSE-C12-C8 of 300 ppm, and DSE-C12-Tz-C8 of (f) 20 ppm, (g) 80 ppm, and (h) 300 ppm.

cover the steel surface completely, and, thus, the seawater can contact with the steel surface, to some extent, resulting in corrosion.

packed protective layer on the metal surface. That is, the polar triazole and carboxylic acid groups of HSE-C12-Tz-R′ and DSE-C12-Tz-R′ bind with metal, but not tightly, and two or three hydrophobic alkyl chains, that is, C12 of a succinate unit and one or two alkyl (R′) chains of triazole units, are oriented outward. At high concentrations of ester derivatives, the density of hydrophobic alkyl chains on the steel surface is high enough to hold paraffin oil in the vicinity of the steel surface; the doped paraffin layer on the steel surface is effective for the corrosion inhibition. Needless to say, at low concentrations of ester derivatives, the density of alkyl chains on the steel surface is relatively low so that the alkyl chains and paraffin oil cannot

4. CONCLUSIONS In the present work, as possible green corrosion inhibitors, dodecyl succinate derivatives having one alkyl triazole (HSE) or two alkyl triazoles (DSE) were synthesized. As a synthesis protocol, we used, first, the nucleophilic substitution reaction of sodium azide to alkyl halide, second, the click coupling reaction between alkyl azide and propargyl alcohol, and third, the esterification reaction between dodecyl succinic anhydride and 9676



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(8) Amitha Rani, B. E.; Basu, B. B. J. Green inhibitors for corrosion protection of metals and alloys: An overview. Int. J. Corros. 2012, 2012, Article ID 380217. (9) Negm, N. A.; Zaki, M. F.; Salem, M. A. I. Synthesis and evaluation of 4-diethyl amino benzaldehyde schiff base cationic amphiphiles as corrosion Inhibitors for carbon steel in different acidic media. J. Surfactants Deterg. 2009, 12, 321. (10) Khaled, K. F. Understanding corrosion inhibition of mild steel in acid medium by some furan derivatives: A comprehensive overview. J. Electrochem. Soc. 2010, 157, C116. (11) Machnikova, E.; Kenton, H.; Whitmire, K. H.; Hackerman, N. Corrosion inhibition of carbon steel in hydrochloric acid by furan derivatives. Electrochim. Acta 2008, 53, 6024. (12) Yıldırım, A.; Ç etin, M. Synthesis and evaluation of new long alkyl side chain acetamide, isoxazolidine and isoxazoline derivatives as corrosion inhibitors. Corros. Sci. 2008, 50, 155. (13) Khaled, K. F. Molecular simulation, quantum chemical calculations and electrochemical studies for inhibition of mild steel by triazoles. Electrochim. Acta 2008, 53, 3484. (14) Lagrenée, M.; Mernari, B.; Bouanis, M.; Traisnel, M.; Bentiss, F. Study of the mechanism and inhibiting efficiency of 3,5-bis(4methylthiophenyl)-4H-1,2,4-triazole on mild steel corrosion in acidic media. Corros. Sci. 2002, 44, 573. (15) Quraishi, M. A.; Jamal, D. Fatty acid triazoles: Novel corrosion inhibitors for oil well steel (N-80) and mild steel. J. Am. Oil Chem. Soc. 2000, 77, 1107. (16) Bentiss, F.; Traisnel, M.; Gengembre, L.; Lagrenée, M. A new triazole derivative as inhibitor of the acid corrosion of mild steel: electrochemical studies, weight loss determination, SEM and XPS. Appl. Surf. Sci. 1999, 152, 237. (17) Bentiss, F.; Lagrenee, M.; Traisnel, M.; Hornez, J. C. The corrosion inhibition of mild steel in acidic media by a new triazole derivative. Corros. Sci. 1999, 41, 789. (18) Ashassi-Sorkhabi, H.; Shaabani, B.; Seifzadeh, D. Effect of some pyrimidinic schiff bases on the corrosion of mild steel in hydrochloric acid solution. Electrochim. Acta 2005, 50, 3446. (19) Bentiss, F.; Lebrini, M.; Vezin, H.; Lagrenée, M. Experimental and theoretical study of 3-pyridyl-substituted 1,2,4-thiadiazole and 1,3,4-thiadiazole as corrosion inhibitors of mild steel in acidic media. Mater. Chem. Phys. 2004, 87, 18. (20) Zhang, S.; Tao, Z.; Liao, S.; Wu, F. Substitutional adsorption isotherms and corrosion inhibitive properties of some oxadiazoltriazole derivative in acidic solution. Corros. Sci. 2010, 52, 3126. (21) Wang, D.; Li, S.; Ying, Y.; Wang, M.; Xiao, H.; Chen, Z. Theoretical and experimental studies of structure and inhibition efficiency of imidazoline derivatives. Corros. Sci. 1999, 41, 1911. (22) Ramachandran, S.; Tsai, B.-L.; Blanco, M.; Chen, H.; Tang, Y.; Goddard, W. A., III Self-assembled monolayer mechanism for corrosion inhibition of iron by imidazolines. Langmuir 1996, 12, 6419. (23) Duda, Y.; Govea-Rueda, R.; Galicia, M.; Beltrán, H. I.; ZamudioRivera, L. S. Corrosion inhibitors: Design, performance, and computer simulations. J. Phys. Chem. B 2005, 109, 22674. (24) Cao, P.; Gu, R.; Tian, Z. Electrochemical and surface-enhanced Raman spectroscopy studies on inhibition of iron corrosion by benzotriazole. Langmuir 2002, 18, 7609. (25) Kim, S.; Kwon, M. S.; Park, J. Silylation of primary alcohols with recyclable ruthenium catalyst and hydrosilanes. Tetrahedron Lett. 2010, 51, 4573. (26) Suzuki, T.; Watahiki, T.; Oriyama, T. A novel and efficient method for the silylation of alcohols with methallylsilanes catalyzed by Sc(OTf)3. Tetrahedron Lett. 2000, 41, 8903. (27) Tillu, V. H.; Jadhav, V. H.; Borate, H. B.; Wakharkar, R. D. Solvent free selective silylation of alcohols, phenols and naphthols with HMDS catalyzed by H-β zeolite. Arch. Org. Chem. 2004, xiv, 83. (28) Baek, S. Y.; Kim, Y. W.; Chung, K. W.; Yoo, S. H.; Park, S. J. Synthesis and lubricating properties of succinic acid alkyl ester derivatives. Appl. Chem. Eng. 2011, 22, 196. (29) American Society for Testing and Materials, ASTM designation, D665-98, Philadelphia, PA, 2000.

triazole alcohol. The chemical structures of the HSE and DSE derivatives were confirmed by NMR, FT-IR, and elemental analysis techniques. The rust preventing properties of the HSE and DSE derivatives in paraffin oil were also studied. To do so, the steel specimens were immersed in the mixed solution of seawater/paraffin oil containing various amounts of ester derivatives for 24 h. It was found that at low concentrations, the HSE showed slightly better corrosion inhibition efficiency than the DSE, indicating that the carboxylic acid groups might enhance the formation of lubricant layer on the steel surface, to some extent. On the other hand, with increasing amount of HSE and DSE derivatives, the corrosion inhibition efficiency increased drastically. Especially, above 150 ppm, the HSE and DSE derivatives acted as corrosion inhibitors very effectively during the first 24 h of immersion. At high concentrations, the HSE and DSE derivatives showed similar corrosion inhibition efficiencies. It was also found that, with increasing alkyl chain length of triazole, the corrosion inhibition efficiency decreased. This was, in part, due to the increasing molecular weight of ester derivatives, which resulted in the decrease in the amount of ester derivative to keep the same solution concentration. In the light of the molecular weights and the numbers of alkyl chains of ester derivatives, we concluded that the most important factor to determine corrosion inhibition efficiency was the total number of alkyl chains of ester derivatives in a system. The above results suggest that the HSE and DSE derivatives can be used as green corrosion inhibitors.

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AUTHOR INFORMATION

Corresponding Author

*Phone: +82-42-860-7605 (Y.-W.K.), +82-62-230-7211 (J.S.K.). Fax: +82-42-860-7669 (Y.-W.K.), +82-62-232-2474 (J.S.K.). E-mail: [email protected] (Y.-W.K.), [email protected] (J.-S.K.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This study was supported by the R & D Center for Valuable Recycling (Global-Top Environmental Technology Development Program) funded by the Ministry of Environment, Korea (Project No.:11-D27-OD).

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REFERENCES

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(30) Shyamala, M.; Arulanantham, A. Eclipta Alba as corrosion pickling inhibitor on mild steel in hydrochloric acid. J. Mater. Sci. Technol. 2009, 25, 633. (31) Suzuki, T.; Nishihara, H.; Aramaki, K. The synergistic inhibition effect of octylmercaptopropionate and 8-quinolinol on the corrosion of iron in an aerated 0.5 M Na2SO4 solution. Corros. Sci. 1996, 38, 1223. (32) Tsuji, N.; Nozawa, K.; Aramaki, K. Ultrathin protective films prepared by modification of an N,N-dimethylalkylamine monolayer with chlorosilanes for preventing corrosion of iron. Corros. Sci. 2000, 42, 1523.

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Synthesis and Rust Preventing Properties of Dodecyl Succinate

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