The inhibition effect of some pyrimidine derivatives on austenitic stainless steel in acidic media

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Abstract

5-Benzoyl-4-(substitutedphenyl)-6-phenyl-3,4-dihydropyrimidine-2(1H)-(thio)ones (DHPMs) (I and II) were synthesized using the Biginelli three component cyclocondensation reaction of an appropriate β-diketone, arylaldehyde, and (thio) urea. The effect of these corrosion inhibitors on the corrosion of austenitic stainless steel in 0.5 M H2SO4 has been studied by electrochemical methods using Tafel plot, linear polarization and electrochemical impedance spectroscopy at 298 K. The inhibition efficiencies obtained from all the methods employed are in good agreement. The adsorption of the DHPMs onto the stainless steel surface was found to follow Langmuir and Dubinin–Radushkevich adsorption isotherm models. Negative values of ΔGads in the acidic media ensured the spontaneity of the adsorption process. Results show DHPM I to be the best inhibitor with a mean efficiency of 91% at 2 × 10−3 M additive concentration.

Research highlights

▶ In this study we examine the inhibition efficiencies of pyrimidine compounds in 0.5 M H2SO4. ▶ The efficiency increases with the inhibitor concentration and the presence of the sulphur atom. ▶ Adsorption of the inhibitors on stainless steel surface is spontaneous. ▶ Also Dubinin–Radushkevich model suggests that DHPMs are adsorbed by physical mechanism.

Introduction

Stainless steel has a wide scope of applications in different industries. This type of stainless steel is covered with a protective film rich in chromium (oxides/hydroxides) that imparts corrosion resistance to its surface. Amount of chromium prevents the formation of rust in “unpolluted” atmospheric environments. However, acidic solutions are aggressive to this film layer and results in severe pitting formation [1], [2]. Acid solutions are widely used in industries for pickling, acid cleaning of boilers, descaling and oil well acidizing [3], [4]. Sulfuric acid is generally the choice in the steel surface treatment basically due to its lower cost, minimal fumes and non-corrosive nature of the SO42− ion [5]. Corrosion inhibitors are needed to reduce the corrosion rates of metallic materials in this area. Most of the well-known acid inhibitors are heterocyclic compounds containing π bonds, heteroatom phosphorus, sulfur, oxygen and nitrogen [6] as well as aromatic rings in their structure which are the major adsorption centers [7]. The compounds containing both nitrogen and sulfur can provide excellent inhibition, compared with compounds containing only nitrogen or sulfur [4], [8]. Generally, a strong interaction causes higher inhibition efficiency, the inhibition increases in the sequence O < N < S [9], [10].

Recently, some studies have been presented on heterocyclic compounds, such as pyrimidine [9], [11], pyridazine [10], bicycloisoxazolidine [12], Schiff base [13], [14], and pyrazole derivatives [15] as effective corrosion inhibitors for metals in acidic media.

The aim of this study is to investigate the corrosion of stainless steel in 0.5 M H2SO4 solution in the presence of two pyrimidine compounds namely 5-benzoyl-4,6-diphenyl-1,2,3,4-tetrahydro-2-thiopyrimidine (DHPM I) and 5-benzoyl-6-phenyl-4-p-tolyl-3,4-dihydropyrimidine-2(1H)-one (DHPM II) that these compounds contain –NH–CO–NH– and –NH–CS–NH– groups as active centers (Scheme 1). Moreover, these molecules can be easily synthesized from relatively cheap materials. Pyrimidines, however, have hardly been studied in spite of their corrosion inhibition properties. They find diverse applications in pharmaceutical applications such as analgesic, antipyretic, antihypertensive, anti-inflammatory drugs, pesticides, herbicides, plant growth regulators, and organic calcium channel modulators [16], [17], [18], [19], [20], [21], [22], [23], [24].

DHPMs were prepared via the general method of Biginelli cyclocondensation reaction in acetic acid. The investigation is performed using potentiodynamic polarization and electrochemical impedance spectroscopy techniques in order to explain the mechanism of the inhibition action. Adsorption isotherms were tested for their relevance to describe the adsorption behavior of the studied compounds.

Section snippets

Preparation of electrode

The working electrode was mounted in polyester with following chemical composition (wt.%) C: 0.0425; Si: 0.421; Mn: 2.13; P: 0.0133; S: 0.113; Cr: 18.51; Mo: 0.563; Ni: 8.34; Al: 0.0334; Co: 0.0901; Cu: 0.358; Fe: balance. The steel electrode was coated with polyester except its bottom surface with surface area of 0.19625 cm2.

Materials

A mixture of 1,3-diphenyl-1,3-propanedione (1.6 mmol), aryl aldehyde (1.1 mmol), (thio)urea (1.1 mmol) and 20 ml of glacial acetic acid containing a few drops concentrated

Polarization measurements

Potentiodynamic polarization curves of steel in 0.5 M H2SO4 in the absence and presence of various concentrations of DHPMs at 298 K are shown in Fig. 1, Fig. 2. Anodic and cathodic currents were inhibited more effectively with an increase in the concentration of the inhibitors, but the reduction in the anodic current was greater than that of the cathodic current.

These results showed that the addition of DHPMs reduces anodic dissolution and also retards the hydrogen evolution reaction.

The

Conclusions

The inhibition and adsorption effect of DHPMs on the corrosion behavior of the stainless steel in 0.5 M H2SO4 was studied using different techniques. The following points can be emphasized:

  • 1.

    The pyrimidine compounds studied are good inhibitors for stainless steel in 0.5 M H2SO4.

  • 2.

    The inhibition efficiency increases with inhibitor concentration.

  • 3.

    The addition of DHPM I and DHPM II induces a decrease in both anodic and cathodic currents. The corrosion potential (Ecorr) of DHPM I was observed to shift

Acknowledgement

This study was supported by the Research Fund of Yüzüncü Yıl University, Van, Turkey.

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