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Several cyclic hydroxylamines containing hydrophobic substituents were prepared. All these hydroxylamines were tested for corrosion inhibition of carbon steel in 1M HCl at 60°C by gravimetric and electrochemical methods. All compounds showed excellent corrosion inhibition efficiency (IE per cent) in acidic solutions containing 400 ppm of the inhibitors; Inhibitor Efficiencies in the range 66‐98 per cent were measured by the gravimetric method. Comparable results were obtained by the electrochemical method using Tafel plots for the IE of some of the selected synthesised compounds.

A variety of bisquaternary ammonium salts was prepared for the first time by reacting N,N,N′,N′‐tetraallyl‐1,6‐hexanediamine with allyl chloride, propargyl chloride, benzyl chloride, and 1‐bromododecane in excellent yields (>90 per cent). Inhibition efficiency for different concentrations of the synthesised compounds for the inhibition of corrosion of carbon steel in 1 M HCl exposed for 6 h at 60°C was determined gravimetrically. The bisquaternary salts exhibited excellent inhibition efficiencies (97‐99 per cent) in the acidic solution containing 400 ppm of the inhibitor. Comparable results were obtained by the electrochemical method using Tafel plots for the inhibition efficiency of the synthesised compounds. The adsorption of these compounds on carbon steel surface was found to obey Temkin's adsorption isotherm. The work marked the beginning of constituting an important class of new inhibitors containing multiple adsorption centres of positive nitrogens as well as π‐donor moieties.

To investigate the capability of a series of nitrogen‐based heterocyclic organic compounds in inhibiting corrosion of iron in HCl and elucidate the dominant active form of the applied compounds during the adsorption process to explore the mechanism of their action.

The tested compounds were pyrimidine containing compounds, which were selected, based on molecular structure considerations. Gravimetric method has been applied with various electrochemical techniques (polarisation resistance, polarisation curves and electrochemical impedance spectroscopy) to investigate inhibition efficiency and mechanism.

The inhibiting action of the investigated pyrimidine containing compounds depends primarily on their concentration and molecular structure. These compounds act as mixed type inhibitors and function via adsorption on the surface, which follows Frumkin adsorption isotherm. The inhibition by the tested pyrimidine derivatives could be attributed to their chemisorption on the metal surface forming donor/acceptor type of bond between the inhibitor molecules and the vacant d orbitals of the surface iron atoms. Contribution from electrostatic adsorption, via interaction between the protonated form of the inhibitor and the charged metal surface, is also possible.

The applied inhibitors were tested in the presence of chloride ions as a corrosive medium. Whether these inhibitors will function well in the presence of other ions that are typically present in natural corrosive environment is unknown.

This paper provides useful information regarding inhibition effect of pyrimidine and series of its derivatives. The outcome of this work contributes to better understanding of the mechanism of inhibition by this class of N‐based heterocyclic organic compounds.