CORROSION INHIBITION STUDY OF A HETEROCYCLIC SCHIFF BASE DERIVED FROM ISATIN

Aliyin Abdul Ghani 1,a, Hadariah Bahron 2,b, Mohamad Kamal Harun 3,c, Karimah Kassim 4,d

1,2,3,Faculty of Applied Sciences, Universiti Teknologi MARA (UiTM) 40450, Shah Alam, Selangor, Malaysia

4Institute of Science, Universiti Teknologi MARA (UiTM), Shah Alam, 40450 Selangor, Malaysia

aaliyinabdulghani@gmail.com , bhadariah@salam.uitm.edu.my, cmohamadkamal@salam.uitm.edu.my , dkarimah@salam.uitm.edu.my

Keywords: Schiff base, Isatin, Corrosion inhibitor, Mild steel, Hydrochloric acid

Abstract: A Schiff base, 3-(phenylimino)indolin-2-one, was successfully obtained from the

condensation reaction of isatin and aniline in absolute ethanol with a yield of 72%. The ligand was

successfully characterized via physical and spectroscopic techniques namely melting point,

Elemental Analysis (C, H, N), 1H Nuclear Magnetic Resonance (NMR) and Fourier Transform

Infrared (FTIR) Spectroscopy. The corrosion inhibiting property of the Schiff base and that of a

mixture of its starting materials on mild steel in 1 M HCl solution was studied through

Electrochemical Impedance Spectroscopy (EIS) and Linear Polarization Resistance (LPR). The

concentration of the Schiff base and the precursor molecules were varied from 1 x 10-3

M to 1 x 10-5

M. The results showed that the percentage of inhibition efficiencies increased with the increase of

compound’s concentrations. Comparing the two sets of results for the Schiff base and the mixture of

its starting materials, it was shown that the Schiff base was a much better inhibitor than the mixture

of the starting materials, clearly indicating the importance of the presence of imine group (C=N)

bearing lone pairs of electrons and π electrons in corrosion inhibition.

Introduction

Mild steel are the most commonly used metal in many engineering applications that are susceptible

to corrosion especially in acidic media [1]. In order to reduce or prevent corrosive reactions on

metals, corrosion inhibitors are used as a barrier between metal surface and the environment

containing oxygen and moisture [2]. Heterocyclic organic compounds containing electronegative

nitrogen, oxygen and sulphur are generally preferred as effective inhibitors [3]. These types of

inhibitors form an adsorption between the lone pair of electron or π electron cloud of the inhibitor

and the vacant d-orbital of the metal atoms. Therefore, it can effectively adsorb on metal surfaces

and block the active sites, thus reduce corrosion rate [4].

Schiff bases are condensation product of amines and carbonyls with functional group called imine,

RC=NR’ [5]. A wide range of studies have investigated the corrosion inhibition of Schiff base

compounds where the inhibition efficiency of these compounds is relatively high due to the

presence of the imine group. However, in some previous studies, imine group can be unstable in

acidic medium where it undergoes hydrolysis forming its precursor molecules [6].

The aim of the present work was to synthesize and characterize 3-(phenylimino)indolin-2-one, and

to determine and compare the corrosion inhibition efficiencies of 3-(phenylimino)indolin-2-one and

its starting materials which are aniline and isatin.

Experimental:

Synthesis and characterization of 3-(phenylimino)indolin-2-one, 3-PII

A mixture of 10 mmol of isatin and 10 mmol of aniline in absolute ethanol was refluxed for 6 hours.

The precipitate formed will be filtered off and washed thoroughly with cold ethanol. The end

product as in Fig. 1 was dried in vacuum pump and weighed to obtain the yield (0.799g, 72%), m.p

Advanced Materials Research Vols. 554-556 (2012) pp 425-429Online available since 2012/Jul/26 at www.scientific.net© (2012) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.554-556.425

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 131.151.244.7, Missouri University of Science and Technology, Columbia, United States of America-04/10/13,20:59:23)

223.7 °C, (Found: C, 74.97; H, 4.54; N, 12.59. C14H10N2O requires C, 75.66; H, 4.54; N, 12.60 %);

νmax (KBr): C=N, 1651.8; C=C, 1614.57cm-1

; 1H NMR (CDCl3) δ/ppm: 6.65-7.44 (9 H, m, Ph),

9.70 (1 H, s, NH).

NO

N

H

Fig. 1. Molecular structure of 3-(phenylimino)indolin-2-one

Electrochemical analysis

The corrosion inhibiting property of the Schiff base and that of a mixture of its starting materials on mild steel in 1 M HCl solution was studied through Electrochemical Impedance Spectroscopy (EIS) and Linear Polarization Resistance (LPR) using a conventional three-electrode cell consisting of a mild steel working electrode, a saturated calomel electrode (SCE) as reference and platinum as counter electrode. The working electrode was prepared by embedding the mild steel in epoxy resin and exposing a flat surface of approximately 0.049 cm

2 to the electrolyte. Prior to each

measurement, the electrode surface was mechanically abraded with a series of grit emery paper (200, 320, 500, 800, 1200), rinsed with distilled water and dried. The concentration of the Schiff base and the precursor molecules in 1 M HCl were varied from 1 x 10

-3 M to 1 x 10

-5 M. In order to

obtain a steady state open circuit potential, the working electrode was immersed into the test solution for 15 minutes before the measurements. All experiments were performed at least three times to ensure reproducibility.

Results and Discussion

Synthesis and characterization of 3-PII

The 1H NMR and elemental analysis indicated that the desired Schiff base has been obtained,

confirmed by the appearance of the ν(C=N) and disappearance of ν(C=O) and ν(N-H) infrared peaks.

Impedance measurements

The Nyquist plots of mild steel in 1 M HCl in the presence and absence of Schiff base ligand and its precursor molecules are given in Fig. 2 and Fig. 3. The impedance parameters and the equivalent circuit diagram are given in Table 1 and Fig. 4 respectively.

Fig. 2. Nyquist plot for mild steel in 1 M HCl

in the presence and absence of different

concentrations of 3-PII

Fig. 3. Nyquist plot for mild steel in 1 M HCl in

the presence and absence of different

concentrations of 3-PII’s starting materials

mixture

0

100

200

300

400

500

600

700

800

0 500 1000 1500 2000

1 x 10-3 M

1 x 10-4 M

1 x 10-5 M

Blank 1 M

HCl

0

50

100

150

200

250

300

350

0 200 400 600 800 1000

1 x 10-3 M

1 x 10-4 M

1 x 10-5 M

Blank 1 M

HCl

426 Advances in Chemistry Research II

Table 1. Impedance parameters for mild steel electrode in 1 M HCl in the presence of different

concentrations of 3-PII and mixture of the starting materials.

Compound Concentration,C

(M)

Solution resistance,

Rs

(Ω cm2)

Polarization

resistance, Rp

(Ω cm2)

Inhibition

efficiency (%)

3-PII Blank 1 M HCl 0.19 14.80 -

1 x 10-5

M 0.29 28.03 47.20

1 x 10-4

M 0.33 39.15 62.20

1 x 10-3

M 0.19 82.32 81.91

Mixture of starting Blank 1 M HCl 0.19 14.80 -

materials (Aniline 1 x 10-5

M 0.32 17.49 15.38

and Isatin) 1 x 10-4

M 0.18 20.43 27.56

1 x 10-3

M 0.24 40.52 63.47

Based on the results, polarization resistance (Rp) values increases with the increase of sample’s

concentrations, thus increasing the inhibitor’s efficiencies in inhibiting metal substrate. In this

study, the synthesized inhibitor, namely 3-PII exhibit more corrosion inhibition of mild steel as

compared to the mixture of its starting materials.

Fig. 4. The equivalent circuit of the impedance spectra obtained for both samples

The equivalent circuit diagram composed of a constant phase element (Q), solution resistance (Rs) and polarization resistance (Rp) is a classical circuit design [7] which corresponds to a single capacitive loop for both of the samples.

Polarization measurements

The Tafel plots of mild steel in 1 M HCl at various concentrations are shown in Fig. 5 and Fig. 6, whereas the electrochemical parameters are summarized in Table 2. From the figures, it can be interpreted that the addition of 3-PII and mixture of the starting materials into the acidic media changes the anodic and cathodic slopes. However, the changes are more prominent in the anodic domain for both of the samples.

Fig. 5. Tafel plot for mild steel in 1 M HCl in the presence and absence of different concentrations of 3-PII

Fig. 6. Tafel plot for mild steel in 1 M HCl in the presence and absence of different concentrations of 3-PII’s starting materials mixture

Rs

Rp

Q

Advanced Materials Research Vols. 554-556 427

Table 2. Polarization parameters for mild steel electrode in 1 M HCl in the presence of different

concentrations of 3-PII and mixture of the starting materials.

The corrosion inhibition efficiency from the impedance and polarization data of the Schiff base

compared to its starting materials revealed major implications which are the 3-PII was proven to be

more efficient even at lower concentrations compared to its precursor molecules which shows that

the lone pair and π electron on C=N of the Schiff base play an important role in inhibiting

corrosion. Therefore, it shows that the Schiff base has not hydrolyzed to its starting materials in the

presence of acid which is corrosion medium.

Conclusions

A Schiff base, 3-(phenylimino)indolin-2-one was successfully synthesized and characterized.

Corrosion inhibition investigations shows that the presence of C=N bearing lone pairs of electrons

and π electrons are important in corrosion inhibition and the Schiff base did not hydrolyze into its

starting materials at acidic conditions.

Acknowledgements

This work is funded by Ministry of Higher Education Malaysia for Fundamental Research Grand

Scheme for financing this research (FRGS/1/10/SG/UiTM/03/05) and also Fellowship scholarship

UiTM, Faculty of Applied Sciences, Institute of Science and Universiti Teknologi MARA for

providing research facilities.

References

[1] Mallaiya, K., Subramaniam, R., Srikandan, S. S., Gowri, S., Rajasekaran, N., Selvaraj, A.,

(2011). Electrochemical characterization of the protective film formed by the unsymmetrical

Schiff’s base on the mild steel surface in acid media. Electrochimica Acta, 56, 3857-3863

[2] Sethi, T., Chaturvedi, A., Upadhyaya, R.K. and Mathur, S.P., (2007). Synergistic inhibition

between Schiff’s bases and sulfate ion on corrosion of aluminium in sulfuric acid.

Protection of Metals and Physical Chemistry of Surfaces, 45, 466-471

[3] Yurt, A., Aykin, O., (2011). Diphenolic Schiff bases as corrosion inhibition for aluminium in

0.1 M HCl: Potentiodynamic polarization and EQCM investigations. Corrosion Science, 53,

3725-3732

[4] Qu, Q., Hao, Z., Li, L., Bai, W., Liu, Y. and Ding, Z., (2009). Synthesis and evaluation of Tris-

hydroxymethyl-(2-hydroxybenzylidenamino)-methane as a corrosion inhibitor for cold

rolled steel in hydrochloric acid. Corrosion Science, 51, 569-574.

428 Advances in Chemistry Research II

[5] da Silva, A. B., D’Elia, E., da Cunha Ponciano Gomes, J. A., (2010). Carbon steel corrosion

inhibition in hydrochloric acid solution using a reduced Schiff base of ethylenediamine.

Corrosion science, 52, 788-793

[6] Hosseini, M.G., Ehteshamzadeh, M. and Shahrabi, T., (2007). Protection of mild steel corrosion

with Schiff bases in 0.5 M H2SO4 solution. Electrochimica Acta, 52, 3680-3685.

[7] Emregul, K. C., Atakol, O., (2004). Corrosion inhibition of iron in 1 M HCl solution with Schiff

base compounds and derivatives. Materials chemistry and physics, 83, 373-379.

Advanced Materials Research Vols. 554-556 429

Advances in Chemistry Research II 10.4028/www.scientific.net/AMR.554-556 Corrosion Inhibition Study of a Heterocyclic Schiff Base Derived from Isatin 10.4028/www.scientific.net/AMR.554-556.425