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 ...

Inhibitors are one of the most effective means of controlling corrosion of metals [1][2][3]. For instance, salts of fatty acids have found application as inhibitors of steel corrosion in neutral media [3]. However, their low solubilities and the formation of insoluble soaps in hard water make them difficult to use. To eliminate this disadvantage and improve their service properties, vegetable oils are modified, e.g., by sulfation. Sulfated Abstract -The inhibitive properties of sulfated mustard oil in neutral and alkaline media (3% NaCl and 0.25 M CH 3 COONa) in the presence of alkyl-and arylbenzoimidazole derivatives were studied. Mixtures of diethylammonium salts of sulfated mustard oil with benzoimidazole derivatives were found to be promising combined inhibitors of metal corrosion.

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New 3,4 dichloro (2H) pyridazin 3 one derivatives have been synthesized, and the influence of these substances on the corrosion properties of steel structures has been preliminarily determined by quan tum chemical calculations. Experimental data have demonstrated that the considered compounds exhibit anticorrosive efficiency in acid media, which depends on the electron density on reactive centers of mole cules, their solubility, and the nature of acids.