SYNTHESIS OF 3,3´-(1,4-PHENYLENE)BIS(1-(4-R-PHENYL)-5-PHENYL-5,6-DIHYDRO-1,2,4,5-TETRAZINIUM) PERCHLORATES

Abstract

A series of 3,3'-(1,4-phenylene)bis(1-4-R-phenyl)-5-phenyl-5,6-dihydro-1,2,4,5-tetrazinium) perchlorates containing hydrogen, methyl, bromio, methoxy, acetyl and nitro groups (R = H, Me, Br, OMe, COMe, NO2) as substituents were obtained as a result of a three-stage synthesis from terephthalic aldehyde. The synthesis of tetrazinium salts was carried out by reaction of the corresponding formazans with formalin in the presence of perchloric acid in dioxane. Formazans were obtained by reaction of terephthalic aldehyde phenylhydrazone with arenediazonium tosylates in a mixture of DMF and pyridine. The usage of arenediazonium tosylates made it possible to extremely simplify the segregation and purification of formazans. The phenylhydrazone was synthesized according to the standard procedure from terephthalic aldehyde and phenylhydrazine/hydrochloric acid in aqueous dioxane. The formazans and tetrazinium perchlorates were isolated in individual state and characterized by elemental analysis, IR, UV, 1H and 13C NMR spectroscopy data. The process of electrochemical reduction of tetrazinium perchlorates was studied using the method of cyclic voltammetry (CV). Thus, the CV curves of all salts in the cathode region contain two one-electron reduction peaks, which are related to the sequential formation of a radical cation and a biradical. It was found that electron-donating substituents (R = Me, OMe) in the aromatic ring at position 1 facilitate the reduction of tetrazinium cation, while electron-withdrawing substituents (R = COMe, NO2) hinder this process. On this basis, it was suggested that the corresponding bis-verdazyl radicals should be easily formed in the presence of electron-donating substituents in the aromatic ring at position 1. Thus, 3,3´-(1,4-phenylene)bis(1-(4-R-phenyl)-5-phenyl-5,6-dihydro-1,2,4,5-tetrazinium-1) perchlorates are perspective precursors of symmetric biradical systems based on verdazyl radicals.