Document Type : Original Article

Authors

Department of Chemistry, College of Sciences, University of Baghdad, Baghdad, Iraq

Abstract

In the current study, new derivatives were synthesized by reaction of N-hydroxyphthalimide with chloro acetyl chloride in the presence of Et3N as a base to form 1,3-dioxoisoindolin-2-yl 2-chloroacetate (B1), which in turn enters several reactions with different amines where it interacts with primary amines to give 1,3-dioxoisoindolin-2-yl acetate derivatives (B2-B4) in basic medium, in the same way it interacts with these amines but with adding KNCS to form thiourea derivatives (B5-B7). It also reacts with diamines to give bis(azanediyl) derivatives (compounds B8-B10). The prepared derivatives were diagnosed using infrared FTIR and 1HNMR,13CNMR for some derivatives. Compounds B4, B5 and B9 were measured as corrosion inhibitors the inhibition efficiency varied from 85% to 99% and thermodynamic functions, i.e. Gibbs free energy, activation energy, enthalpy, entropy, were calculated for the derivatives at a concentration of (50 ppm) when mixed with carbon steel as additives and exposing the plate to an acidic medium of hydrochloric acid at a concentration of (1M) in different temperatures. The results revealed that as the temperature increases, the inhibition efficiency decreases.

Graphical Abstract

Novel Synthesis of Some N-Hydroxy Phthalimide Derivatives with Investigation of Its Corrosion Inhibition for Carbon Steel in HCl Solution

Keywords

Main Subjects

Introduction

Sometimes a material deformation occurs as a result of its interaction with the surrounding environment, and this process is called corrosion. As iron and its alloys can be corroded upon exposure to humid, salty or acidic air conditions, and this causes damage to devices and tools made of these metals. Therefore, recent research has focused on studying anticorrosive agents such as the organic compounds to form a buffer layer for external stimuli on the surface of the metal. Most of these compounds contain nitrogen, oxygen and sulfur atoms [1-6]. Recently, studies have uncovered that NHPI could be utilized for C-O bond [7, 8] as it does for C-H bonds in the formation of organic compounds [9]. N-alkoxyphthalimides are prepared easily with a high yield using different O-substituted hydroxyl amines; considering that these compounds are important in industry, NHPI was used as a catalyst for the first time in 1977 by Grochowski and associates for the reaction between ethers and diethyl azo di carboxylate and the preparation of aceton from the oxidation of 2-propanol [10]. A couple of years later, a proposal was made by Masui to prepare ketones by electrolytic oxidation of alcohols using (NHPI) as catalyst [11]. Ames and Grey’s [12] study underpins N-hydroxyphthalimide as the structure of "phthaloxime," as opposed to the anhydrideoxime.

Although compound N-hydroxyphthalimide is of limited use in industry, since most of its aforementioned uses are in the medical fields, the new derivatives prepared from it by simple methods of organic synthesis have been very effective in inhibiting corrosion of up to 99% and this indicates that the new derivatives have entered new and wide areas of application.

Material and methods

All chemicals and solvents which are used in our work were locally purchased from Fluke and BDH and were used directly without any further purification. Melting points were recorded using Gallenkamp capillary melting point apparatus and where uncorrected, FTIR spectrum was recorded with Perkin Elmer spectrophotometer using KBr disk; the frequencies were estimated in (cm-1); NMR spectra were recorded on Bruker Avance 600 spectrometer using DMSO-d6 as a solvent. Chemical shifts of compounds are expressed by δ (ppm). The reaction time was recorded using TLC silica gel. The solvent used was ethyl acetate: petroleum ether (2:1) and spots were shown by placing the TLC paper in contact with iodine vapor.

Measurements of Polarization were conducted using advanced potentiostat winking MLab-200 (2007) [Bank Elektronik- Intelligent controls GmbH] with all accessories; three types of electrode cell were used. First, the working carbon steel electrode which is polished with exposed area 1 cm2 was placed in the test solution. The second one is a saturated calomel electrode (SCE) and a platinum electrode were used as the reference and the last one is the counter electrodes, respectively. All potentials were recorded versus SCE.

 

Synthesis of 1,3-dioxoisoindolin-2-yl 2-chloroacetate [13] (B1)

A mixture of (NHPI) (2 mmol) and chloro acetyl chloride (4 mmol) in the presence of triethyl amine (2 mmol) was dissolved in DMF (10 ml) and refluxed for 1 hr at 50-60 °C, the product was cooled, filtered, washed with water and re-crystallized with ethanol.

White precipitate; M.Wt (C10H6NO3Cl) = (223.6) g/mol; yield (70%); M.P = (182-184) °C; FTIR (KBr): ν(C-H) at 2997 cm-1, ν(C=O) for esters at 1739 cm-1, ν(C-H) aromatic at 3045 cm-1, ν(C=C) aromatic at 1465 cm-1.

 

Synthesis of 1,3-dioxoisoindolin-2-yl acetate derivatives [14] (B2-B4)

A mixture of (NHPI) (0.8 mmol) and different heterocyclic aryl amines (0.8 mmol) in the presence of triethylamine (0.8 mmol) was dissolved in DMF (10 ml) and refluxed for 7 hr, the products were cooled, filtered, washed with water and re-crystallized with ethanol.

1,3-dioxoisoindolin-2-yl 2-(benzo[d]thiazol-2-ylamino)acetate (B2)

Pale-yellow precipitate; M.Wt (C17H11N3O4S) = (353.3) g/mol; yield (60%); M.P = (140-142) °C; FTIR (KBr):ν(N-H)at 3218 cm-1, ν(C-H) aromatic at 3104 cm-1, ν(C-H) at 2904 cm-1, ν(C=O) at 1710 cm-1, ν(C=N) at 1616 cm-1, ν(C=C) aromatic at 1541 cm-1.

 

1,3-dioxoisoindolin-2-yl 2-(thiazol-2-ylamino)acetate (B3)

Pale-orange precipitate; M.Wt (C13H9N3O4S) = (303.2) g/mol; yield (40%); M.P = (188-190) °C; FTIR (KBr): ν(N-H) at 3245 cm-1, ν(C-H) aromatic at 3015 cm-1, ν(C-H) at 2920 cm-1, ν(C=O) at 1703 cm-1, ν(C=N) at 1612 cm-1, ν(C=C) aromatic at 1469 cm-11H-NMR (DMSO-d6): δ 3.35 ppm (2H, d, CH2), δ 4.19 ppm (1H, t, NH), δ 7.83-7.29-6.88 ppm (1H, m, H aromatic); 13C-NMR (DMSO-d6): δ 60.84 ppm  (CH2), δ 134.57-107.56 ppm (C aromatic), δ 164.16 ppm (C=O), δ 172.71 ppm (C=N), δ 179.01 ppm (O-C=O).

 

1,3-dioxoisoindolin-2-yl 2-(pyridin-2-ylamino)acetate (B4)

Pale-orange precipitate; M.Wt (C15H11N3O4S) = (297.2) g/mol; yield (70%); M.P = (194-196) °C; FTIR (KBr): ν(N-H) at 3190 cm-1, ν(C-H) aromatic at 3008 cm-1, ν(C-H) at 2920 cm-1, ν(C=O) at 1704 cm-1, ν(C=N) at 1652 cm-1, ν(C=C) aromatic at 1514 cm-1; 1H-NMR (DMSO-d6): δ 3.34 ppm (2H, d, CH2), δ 3.97 ppm (1H, t, NH), δ 8.07-6.42 ppm (1H, m, H aromatic); 13C-NMR (DMSO-d6): δ 56.81 ppm (CH2), δ 159.69-107.93 ppm (C aromatic), δ 164.16 ppm (C=O), δ 185.49 ppm (O-C=O).

 

Synthesis of thiouria derivatives [14](B5-B7)

A mixture of (NHPI) (0.8 mmol), KNCS (0.8 mmol) in the presence of triethylamine (0.8 mmol) was dissolved in DMF (10 ml) and refluxed for 1hr, after cooling the mixture, different heterocyclic aryl amines (0.8 mmol) were added and refluxed for 2hr, the products were cooled, filtered, washed with water and re-crystallized with ethanol.

1,3-dioxoisoindolin-2-yl 2-(3-(benzo[d]thiazol-2-yl)thioureido)acetate (B5)

Pale-brown precipitate; M.Wt (C18H12N4O4S) = (380.3) g/mol; yield (65%); M.P = (122-124) °C; FTIR (KBr): ν(N-H) at 3170 cm-1, ν(C-H) aromatic at 3016 cm-1, ν(C-H) at 2916 cm-1, ν(C=O) at 1737 cm-1, ν(C=C) aromatic at 1539 cm-1, ν(C=S) at 1255 cm-1; 1H-NMR (DMSO-d6): δ 3.36 ppm (2H, d, CH2), δ 4.64 ppm (1H, t, NH), δ 8.00-6.98 ppm (1H, m, H aromatic), δ 8.62 ppm (1H, S, NH).

 

1,3-dioxoisoindolin-2-yl 2-(3-(thiazol-2-yl)thioureido)acetate (B6)

Brown precipitate; M.Wt (C14H10N4O4S) = (330.3) g/mol; yield (40%); M.P = (125-130) °C; FTIR (KBr): ν(N-H) at 3195 cm-1, ν(C-H) aromatic at 3099 cm-1, ν(C-H) at 2920 cm-1, Ѵ(C=O) at 1730 cm-1, ν(C=C) aromatic at 1506 cm-1, ν(C=S) at 1226 cm-1; 1H-NMR (DMSO-d6): δ 4.26-4.25 ppm (2H,d,CH2), δ 5.42 ppm (1H,t,NH), δ 8.17-7.22 ppm (1H, m, H aromatic),δ 8.47 ppm (1H, S, NH); 13C-NMR (DMSO-d6): δ 59.17 ppm (CH2), δ 134.56-114.60 ppm (C aromatic), δ 164.15 ppm (C=O), δ 169.28 ppm (C=N), δ 170.59 ppm (O-C=O), δ 177.93 ppm (C=S).

 

1,3-dioxoisoindolin-2-yl 2-(3-(pyridin-2-yl)thioureido)acetate (B7)

Yellowish-orange precipitate; M.Wt (C16H13N4O4S) = (357.3) g/mol; yield (40%); M.P = (122-126) °C; FTIR (KBr): ν(N-H) at 3193 cm-1, ν(C-H) aromatic at 3070 cm-1, ν(C-H) at 2921 cm-1, ν(C=O) at 1716 cm-1, ν(C=C) aromatic at 1487 cm-1, ν(C=S) at 1253 cm-1; 1H-NMR (DMSO-d6): δ 3.94-3.84 ppm (2H,d,CH2), δ 5.28 ppm (1H,t,NH), δ 7.87-6.43 ppm (1H,m,H aromatic),δ 8.32 ppm (1H, S, NH); 13C-NMR (DMSO-d6): δ 50.58 ppm (CH2), δ 134.55-108.22 ppm (C aromatic), δ 137.26 ppm (C=O), δ 147.16 ppm (O-C=O), δ 164.14 ppm (C=S).

 

Synthesis of bis(azanediyl)  derivatives [14] (B8-B10)

A mixture of (NHPI) (0.8 mmol) and different aliphatic and aromatic diamines (0.4 mmol) in the presence of triethylamine (0.8 mmol) was dissolved in DMF (10 ml) and refluxed for 2-3 hr. The products were cooled, filtered, washed with water and re-crystallized with ethanol.

 

bis(1,3-dioxoisoindolin-2-yl) 2,2'-(1,4-phenylenebis(azanediyl))diacetate (B8)

Off-white precipitate; M.Wt (C26H18N4O8) = (514.4) g/mol; yield (80%); M.P = (242-244) °C; FTIR (KBr): ν(N-H) at 3369 cm-1, ν(C-H) aromatic at 3058 cm-1, ν(C-H) at 2923 cm-1, ν(C=O) at 1708 cm-1, ν(C=C) aromatic at 1517 cm-1.

 

bis(1,3-dioxoisoindolin-2-yl) 2,2'-(butane-1,4-diylbis(azanediyl))diacetate (B9)

Gray precipitate; M.Wt (C21H16N4O8) = (452.3) g/mol; yield (83%); M.P = (232-234) °C; FTIR (KBr): ν(N-H) at 3139 cm-1, ν(C-H) aromatic at 3020 cm-1, ν(C-H) at 2991 cm-1, Ѵ(C=O) at 1706 cm-1, ν(C=C) aromatic at 1465 cm-1; 1H-NMR (DMSO-d6):δ 2.50 ppm (2H, d, CH2-CO), δ 3.39-3.36 ppm (1H, t, NH), δ 7.83 ppm (1H, m, H aromatic); 13C-NMR (DMSO-d6): δ 29.64 ppm (CH2), δ 42.56 ppm (CH2-C=O), δ 44.17 ppm (CH2-NH), δ 134.56-123.00 ppm (C aromatic), δ 164.15 ppm (C=O), δ 175.42 ppm (O-C=O).

 

bis(1,3-dioxoisoindolin-2-yl) 2,2'-([1,1'-biphenyl]-4,4' diylbis(azanediyl))diacetate (B10)

Dark-brown precipitate; M.Wt (C32H22N4O8) = (590.5) g/mol; yield (60%); M.P = (312-315) °C; FTIR (KBr): ν(N-H) at 3259 cm-1, ν(C-H) aromatic at 3039 cm-1, ν(C-H) at 2918 cm-1, ν(C=O) at 1712 cm-1, ѵ(C=C) aromatic at 1504 cm-1.

 

Result and Dissection

Forming new hetero compounds for having anti-corrosion properties is required, especially those with N, O, P, S atoms that improve the mixing process of the compound on the metal surface and create a protective layer for corrosion[15].

This inquiry addressed synthesis of new heterocyclic ring derivatives by reaction of (NHPI) with chloro acetyl chloride then with different amines, as shown in Scheme 1.

The compound (B1) was prepared through a nucleuphilic substitution reaction between (NHPI) and chloroacetyl chloride in the presence of basic medium (Et3N), carbonyl carbon tends to form a carbcation, which makes it a suitable site to attack, especially in the presence of the adjacent chloride group. This substitution mechanism, FT-IR spectral data for this compound shows new absorption bands [16] as ν(C-H)aliphatic at 2997 cm-1,ν(C=O) for esters at 1739 cm-1 with the existence of other groups which appears in the starting compound such as ν(C-H) aromatic at 3045 cm-1, ν(C=C) aromatic at 1465 cm-1.

The prepared derivative (B1) undergoes an SN2 mechanism by reacting with different alkyl amines in the presence of triethylamine to form 1,3-dioxoisoindolin-2-yl acetate derivatives,  bis(azanediyl) derivatives and in the presence of potassium thiocyanate to form thiourea derivatives [17]. These compounds showed FT-IR absorption bands at ѵ(N-H) 3300-3180 cm-1 indicating the presence of a secondary amine group, namely, 1H-NMR showing signals at the following chemical shifts δ 5.42-3.36 ppm (1H, t, NH) for the same group and δ 4.26-2.5 ppm (2H, d, CH2-NH) for the adjacent methylene group, also shown in 13C-NMR δ 60.84-44.17 ppm (CH2-NH).

 

Specimen

The composition used of carbon steel specimens were (0.36-0.42)% C, (0.15-0.30)% Si, (1.00-1.40)% Mn, 0.05% P, 0.05% S, 0.50% Cu, 0.20% Ni, 0.20% Cr and (96.88-97.49)% Fe with size 1cm diameter. Specimen were used for method of polarization. The samples were polished with belt grinding polishing machine successively and also with different grit emery papers (80, 150, 220, 240, 320, 400, 1000, 1200 and 2000) in sequence; in the end the specimens were washed with distilled water and dried.

 

Potentiostatic polarization study

Before starting the measurements, the electrode potential was allowed to stabilize for 15 min, by changing the electrode potential Tafel polarization. The curves were obtained automatically from -200 mV versus open circuit potential (OCP) to +200 mV versus OCP with scan rate of 2.0 mV s-1. All experiments were conducted at (293, 303, 313) K, inhibitor concentration of (50) ppm were tested, Tafel lines of potential versus, Icorr in a logarithm scale were plotted and corrosion current density (Icorr) and corrosion potential (Ecorr) were determined in the absence and presence of inhibitor[18].

 

 

 

 

Scheme 1: synthesis of new heterocyclic ring derivatives by reaction of (NHPI) with chloro acetyl chloride then with different amines

               


Measurements of polarization

Potentiostatic polarization curves were plotted for the corrosion of carbon steel in 1M HCl solution in the absence and presence of (50) ppm of (B4, B5, B9) at (293, 303, 313) K as shown in Figure 1.

Tafel slop appears as a linear region. As shown above, the controlled cathodic reaction was decreased and the current densities were decreased by adding the tested samples for both anodic and cathodic domains of potential which indicate the same compound studied were considered as mixed type inhibitors, mainly corrosion potential did not change with this type of inhibitors because both anodic and cathodic reactions were inhibited [19], although a competition occurred between these reactions causing small changes in potentials; electrochemical parameters values are illustrated in Table 1.


Figure 1: Polarization curves of carbon steel in 1M HCl in the absence and presence of (50) ppm from (B4, B5, B9) derivatives at different temperatures

Table 1: Polarization parameters of carbon steel in 1M HCl in the absence and presence of (50) ppm from (B4, B5, B9) derivatives at different temperatures


Inhibition efficiency (% IE), for the corrosion of carbon steel were calculated as follows [20]. Icorr and Icorr (inh) are the currents densities of corrosion in the absence and in presence of the organic inhibitor, which were determined respectively by extrapolation of the cathodic and anodic Tafel lines to corrosion potential (Ecorr); IE% was calculated from equation 1 [21-23].

 

 

IE%=(Icorr(blank)-(icorr)/Icorr(blank))×100                                                                                                        (1)

 


Effect of temperature

The relation of corrosion rate with temperature was studied in 1M HCl solution with or without (B4, B5, B9) inhibitors at (50) ppm concentration. Studying the temperature that is dependent on potentiostatic polarization helps for evaluation of the apparent activation energy. In Table 2 several electro chemical parameters were calculated. Icorr increased upon heating and the efficiency (%IE) decreased with temperature increase due to the nature of inhibitor mixing to carbon steel surface where physical adsorption occurred at minimum temperatures, on the other hand, chemisorption is favored at maximum temperatures.

In addition to thermodynamic model corrosion inhibition mechanism is explained with kinetic model. Arrhenius equation describes the corrosion reaction [24]:

Log Icorr = log A - Ea*/2.303RT                                  (2)

 

where icorr is symbolized for the corrosion current density, Ea* is the energy of activation for the corrosion reaction, R for the gas constant, T is the absolute temperature and A is the Arrhenius pre exponential factor. Figure 2 presents the Arrhenius plots of the natural logarithm of the current density vs1/T, for 1M solution of HCl, in presence and absence of (50) ppm of compounds (B4, B5, B9).

In equation 2, corrosion rates are lower at high values of Ea*, in this work, Ea* is high at compound B5, hence decreases the corrosion of carbon steel surface [25].   

 

 

Figure 2: Arrhenius plots of log icorr versus 1/T in presence and absence of (B4, B5, B9) derivatives at different temperatures

 

 

Activation energy, enthalpy, entropy, Gibbs free energy were calculated in the absence and presence of inhibitors from the transition state equation 3:

 

 

Log (Icorr/T) = (log (R/NAh)+(∆S*/2.303R))-∆H/2.303R*1/T                                                                             (3)

 

 

where Planck’s constant symbolized as h, NA for Avogadro’s number, R for the universal gas constant, ∆H is the enthalpy of the activation and ∆S* is the entropy of activation. Plotting of log (icorr/T) versus 1/T, for carbon steel in 1M HCl in the absence and presence of synthesized inhibitor gives straight lines as shown in Figure 3.

 

Figure 3: Arrhenius plots of log (icorr/T) versus 1/T in presence and absence of (B4, B5, B9) derivatives at different temperatures

 

It is found that activation energy increase in the present of inhibitors and Gipps free energy increase upon heating as shown in Table 2.


Table 2: The thermodynamic parameters of activation of the synthesized inhibitors (B4, B5 and B9) for carbon steel in 1M HCl


Conclusion

New derivatives of compound N-hydroxyphthalimide were prepared and diagnosed with organic diagnostic methods. The efficacy of (B4,B5 and B9) derivatives was tested as corrosion inhibitors. The results of measurements showed a high inhibition efficiency of carbon steel when exposed to an acidic medium of 1M HCl solution, so it is considered an effective method providing a simple preparation procedure to prepare high efficient inhibitors. Compound (B5) showed the highest activity where the inhibition efficiency reached 99% at the temperature of 239K, while compound B4 showed the lowest efficiency 85% with all temperatures noting that the inhibition efficiency decreased at higher temperatures, in contrast to the free energy values that increased with increasing temperatures.

 

Acknowledgment

We appreciate the service laboratory in Department of Chemistry, University of Baghdad, for providing the necessary facilities to carry out the study.

 

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

 

Authors' contributions

All authors contributed toward data analysis, drafting and revising the paper and agreed to be responsible for all the aspects of this work.

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