Protective Effects of 2-Thioquinazolin-4-One Derivatives on Steel 20 in Various Corrosive Media

Abstract

This study was intended to continue investigations [1] of the inhibitive effect-structure correlations for a series of 2-thioquinazolin-4-one derivatives. These compounds were chosen because they contain alkyl radicals and several reactive sites (N atoms, carbonyl and thio groups, and benzene and thiophene rings). It is known that aromatic rings fused with N-, O-, and Scontaining heterocycles make the electrons of the common π -system more mobile, thus enhancing its reactivity [2][3][4][5][6][7][8][9]. In recent years, they have attracted the attention of researchers as probable inhibitors of metal corrosion.In [1], it was demonstrated that 2-thioquinazolin-4-one derivatives effectively inhibit the acid corrosion of steel 20 and there is a correlation between their inhibitive properties and the resonance constants of parasubstituents in the benzene ring. However, the possibility of using derivatives of this series as inhibitive additives to alkaline media and natural waters and soils has not been studied or documented.This study was devoted to the inhibitive effects of new 2-thioquinazolin-4-one derivatives differing in the positions of reactive sites (Table 1) in various corrosive media. EXPERIMENTALThe inhibitive effects of the compounds were estimated electrochemically with an annealed steel 20 in 0.1 M HCl, 0.1 M NaOH, and 0.3 to 3% NaCl (P-5828 potentiostat) and by gravivolumetry as described in [10][11][12]. Investigations were carried out in media simulating real operating conditions for steel structures (without buffering additives). The pH values of the working solutions varied during the corrosion tests: from 1.1 to 1.72 in 0.1 M HCl, from 6.0 to 6.6 in 0.3 to 3% NaCl, and from 11.0 to 12.4 in 0.1 M NaOH. The tests were carried out at 293 K; the concentration of the inhibitor was 1 mmol/l.The Tafel constants a c , b c , a a , and b a , the cathodic and anodic currents ( I c , I a ) and potentials ( E c , E a ), and the rate and potential of electrochemical corrosion ( I cor , E cor ) were determined from voltammograms for acidic electrolytes. The inhibition factors of the electrochemical corrosion γ cor and the cathodic and anodic reactions ( γ c , γ a ) were calculated. The partial contributions to the resultant coefficient γ = γ 1 + γ 2 + γ 3 + γ 4 were estimated (where γ 1 and γ 2 are the kinetic inhibition factors, γ 3 is the blocking (shielding) inhibition factor, and γ 4 is the energetic (adsorption) inhibition factor) [11]. The corrosion rates K M and K H , the protective value Z , and the inhibition factors γ M (from weight losses) and γ H (from the hydrogen volume evolved) were calculated from the gravivolumetric data.The standard measurement error for a sample of n = 6 and Student's quantile t = 2.75 did not exceed 5 to 10% at a confidence level of 95% [13]. RESULTS AND DISCUSSIONThe experimental data obtained for inhibitors (In) in our corrosion tests are summarized in Tables 2-4. In an acidic electrolyte (Fig. 1), the free corrosion potential is more positive by 10 to 50 mV for all the test ...

A study of the influence of 3,4-dichloro-(2H)-pyridazin-3-one derivatives on corrosion resistance of steel

“…On the basis of quantum chemical calculations based on up to date software (MOPAC, Gaussian 03), [1][2][3][4][5][6][7][8][9][10][11][12][13] demonstrated that anticorrosive properties of HCs in acid mediums are related with the value of charge on reactive centers of their molecules. The charge value on reactive centers have an effect on the ability of HCs to adsorb on a metal surface and the formation of protective films in the form of complex metal compounds.…”

“…In complex metal compounds, the strength of the "metal-inhibitor" coordination bond corresponds to the electron density on reactive portions of inhibitor molecule [10][11][12]; in neutral and alkaline media, the dependence of anticorrosive activity on dipole moment of molecule (µ) can be detected, which char acterizes its capacity for physical adsorption [13].…”