Highly effective derivatives of 4-alkylthio-1,3,5-triazine-2-amine as inhibitors of acid corrosion of steel: synthesis and study of anticorrosive properties

• N.V. Stolpovskaya, A.A. Kruzhilin, D.S. Shevtsov, Yu.V. Aseeva and Kh.S. Shikhaliev

Voronezh State University, 1 Universitetskaya Sq., 394018 Voronezh, Russia

Abstract: A highly efficient synthetic route and comprehensive investigation of a series of 4-(alkylthio)-1,3,5-triazin-2-amines with varying alkyl chain lengths (CH₃, C₃H₇, C₄H₉, C₅H₁₁, i-C₅H₁₁, C₇H₁₅, C₁₀H₂₁) as corrosion inhibitors for low-carbon steel in 24% HCl solution are proposed. The two-step synthesis of the target alkylmercaptotriazines involves the initial cyclization of amidinothiourea with triethyl orthoformate to form 4-mercapto-1,3,5-triazine-2-amine, followed by alkylation with the corresponding alkyl halides in a DMF medium. To evaluate the inhibitory activity of the synthesized compounds toward steel corrosion in 24% HCl, gravimetric and electrochemical techniques (potentiodynamic polarization and polarization resistance measurements) were employed. It was established that the degree of protection (Z) of steel against hydrochloric acid corrosion exceeds 95% at an inhibitor concentration of 0.5–2.0 g∙L^–1, with the highest efficiency (up to 99.5%) exhibited by compounds bearing C₅–C₇ alkyl radicals. The best performance was observed for 4-(heptylthio)-1,3,5-triazine-2-amine, providing Z=98.0% at C_inh=0.5 g∙L^–1 and Z=99.5% at C_inh=2.0 g∙L^–1. Compounds with shorter alkyl substituents (C₁–C₄) showed lower inhibition efficiency, whereas the derivative with an excessively long alkyl chain (C₁₀) exhibited limited solubility in the test medium, which adversely affected its anticorrosion properties. Electrochemical data indicate a mixed inhibition mechanism – the addition of all studied inhibitors leads to a decrease in the corrosion current density for both cathodic and anodic processes. Thus, it has been demonstrated that 4-(alkylthio)-1,3,5-triazin-2-amines possess high inhibition efficiency toward the corrosion of low-carbon steel in 24% HCl solution and are promising candidates for application as corrosion inhibitors in acid pickling and drilling fluids used in the petroleum industry.

Keywords: corrosion, steel, corrosion inhibitors, heterocyclic compounds, aminotriazines, 1,3,5-triazines, hydrochloric acid, potentiodynamic polarization, acid pickling, oil production

Int. J. Corros. Scale Inhib., 2025, 14, no. 4, 2298-2311
doi: 10.17675/2305-6894-2025-14-4-31

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