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In this work, for the first time, an approach was suggested for determining the pKa of triazolo[5,1-c][1,2,4]triazine compounds in N,N-dimethylformamide using potentiometric titration. It was noted that change in system potential in the titration curves of triazolo[5,1-с][1,2,4]triazine are observed for compounds containing either H+ located at the nitrogen atom in position 1 or an –NH2 group. The calculated pKa values of the studied molecules correspond to the pKa values of moderately strong acids and are in the range of 2–8. The relationship was established between the acidity of the heterocyclic fragment and the presence of electron donor substituents. The obtained pKa values of the compounds correlate with the calculated possible deprotonation centers of the molecule. It was found that determining the acidity constants of substances is useful for clarifying the mechanisms of their transformations. The possibility of establishing a relationship between the structure of the compound, pKa, and probable biological activity was shown.

For the first time, a bismuth-modified electrode is used for the quantitative voltammetric determination of formaldehyde (FA) in urotropin. The well-established method of forming formaldehyde hydrazone (FAH) in the presence of hydrazine sulphate (HRZ) was employed to transform the hydrated form of FA into its electrochemically active derivative. The reduction current of FAH was recorded in a phosphate buffer solution (PBS, pH 5.2±0.1) in the presence of 0.09 M HRZ on a screen-printed carbon electrode that had been preliminarily modified with a bismuth film. A 20-second electrolysis at an applied potential of –0.28 V in a solution comprising 1 M HCl, 0.5 M NaBr, and 4 g/L Bi(III) resulted in the formation of a well-developed metal layer with an active surface. The determination of FA in technical urotropin yielded satisfactory results, indicating the potential for further applications of Bi/SPCE in pharmaceutical analysis.

The results of this study of the electrochemical transformation of 3-R-4-hydroxy-1,4-dihydro-7-X-1,2,4-triazolo[5,1-c][1,2,4] obtained by voltammetry are presented. It was found that 3-R-4-hydroxy-1,4-dihydro-7-X-1,2,4-triazolo[5,1-c][1,2,4] derivatives are capable of electrochemical reduction in the potential range of –0.28 to –0.33 V (relative to Ag/AgCl) in Britton–Robinson buffer at pH = 2. The electrochemical behavior of the sodium salt of 3-nitro-4-hydroxy-7-methylthio-4H-[1,2,4]triazolo[5,1-c][1,2,4]triazinide monohydrate (compound 1), which in silico modeling predicted possible biological activity against various tick-borne encephalitis and Coxsackie B3 viruses. At the potentials of the first stage of electroreduction at pH = 2, the main transformation process is the three-electron reduction scheme of the nitro group of compound 1. It was established that compound 1 in an aprotic medium is reduced in ionic form, most likely in the form of an ion pair with the Na+ cation, and in an aqueous medium in the form of a protonated particle. Based on this, a scheme was proposed for the probable electrochemical transformation of the studied compound.

A different type of MnO2-induced oxidative cyclization of dihydrotriazines has been developed. These dihydrotriazines are considered as a “formal” Schiff’s base. This method provided easy access to naphthofuro-fused triazine via the C-C/C-O oxidative coupling reaction. The reaction sequence comprised the nucleophilic addition of 2-naphthol or phenol to 1,2,4-triazine, followed by oxidative cyclization. The scope and limitations of this novel coupling reaction have been investigated. Further application of the synthesized compound has been demonstrated by synthesizing carbazole-substituted benzofuro-fused triazines. The scalability of the reaction was demonstrated at a 40 mmol load. The mechanistic study strongly suggests that this reaction proceeds through the formation of an O-coordinated manganese complex.