Novel inhibitory compositions based on 4,5,6,7-tetrahydro-[1,2,4]triazolo[1,5-a]pyrimidin-7-ol derivatives for steel acid corrosion protection

The inhibitive effect of several synthesized derivatives of the 1,2,4-triazole class on St3 steel corrosion in 24% HCl solution is revealed. The derivatives consist of 3-alky1-5-amino-1H-1,2,4-triazoles obtained from a mixture of fatty acids - coconut oil processing waste, individual 2-methyl-5-phenyl-4,5,6,7-tetrahydro-[1,2,4]triazolo[1,5-a]pyrimidin-7-ol, as well as two compositions based on these triazoles, cinnamaldehyde and surfactant. The structure of the synthesized compounds was proved using NMR spectroscopy and HPLC/MS spectrometry. Different electrochemical and physical methods were used to determine the high protective effect of the studied derivatives at concentration (C-inh) from 0.10 to 2.00 g. dm(-3). The SEM microphotographs of the steel surface after exposure in HCl solutions without additives and in the presence of the studied substances and compositions allowed us to visually evaluate the inhibition effectiveness of the obtained compounds. Quantum-chemical calculations were carried out using the density functional theory (DFT), as a result, the correlation between the protective properties and the electronic structure of the molecules of the studied compounds was found and substantiated. It has been established that the developed compositions of inhibitors, as well as 2-methyl-5-phenyl-4,5,6,7-tetrahydro-[1,2,4]triazolo[1,5-a]pyrimidin-7-ol, have a significant anticorrosive effect. Optimum results were obtained when inhibitor compositions were used: the protection degree for them was more than 95% at an inhibitor concentration of at least 0.50 g.dm(-3), while the corrosion rate was 0.4-1.0 g/m(2) . hour. The high protective effect of the developed compositions is probably associated with the reaction of aminotriazoles with cinnamaldehyde during the preparation of the inhibitory compositions. This reaction results in the formation of the corresponding derivatives of the 2-alkyl-5-phenyl-4,5,6,7-tetrahydro-[1,2,4]triazolo[1,5-c]pyrimidin-7-ol class, similarly to the formation of 2-methyl-5-phenyl-4,5,6,7-tetrahydro-[1,2,4]triazolo[1,5-a]pyrimidin-7-ol that we synthesized intentionally.