Electrochemistry of 1,2,5-thiadiazole 1,1-dioxide derivatives with 3,4 substituents presenting separated, connected, and fused Pi-systems

Abstract

The voltammetric electroreduction properties of 1,2,5-thiadiazole 1,1-dioxide derivatives with different 3,4 substituents have been investigated in aprotic (mainly acetonitrile) solvent solution. The 3,4 substituents, selected according to the characteristics of their π-system, were phenanthro-9,10 (connected π-system) and acenaphtho-1,2 (fused π-system). New measurements are also presented for 3,4-diphenyl (separated π-systems). The basic properties of the substrates were investigated through voltammetry in acidic acetonitrile solutions. The substrates were more easily electroreduced (between -0.6 and -1.0 V vs. Ag/Ag+, acetonitrile solvent) than the parent (non-1,1-dioxide) heterocycles (which are electroreduced at ca. -2.5 V). They were also more easily electroreduced (by ca. 0.4 V) than the corresponding diketones (benzil, 9,10-phenanthrenequinone, and acenaphthenequinone). The influence on voltammetric behavior of the electron-withdrawing properties of the 1,2,5-thiadiazole 1,1-dioxide ring and that of the structure of the molecules was analyzed in light of previous structural studies by X-ray crystallography and theoretical chemistry calculations. Bulk electrolysis experiments in acidic acetonitrile solutions of the phenanthro[9,10-c] derivative produced its previously unreported dihydrogenated derivative (thiadiazoline), which oxidizes easily. Infrared spectroscopy data suggested that the structure of this compound differs from that of 3,4-diphenyl-1,2,5-thiadiazoline 1,1-dioxide.Key words: organic electrochemistry, 1,2,5- thiadiazoles, structure-reactivity relations.

On experimental versus theoretically calculated properties of thiadiazole derivatives

“…In the course of those works, many physical and chemical properties of compounds 1 and 2 (as well as those of many derivatives of the important group of the 3,4-disubstituted 1,2,5-thiadiazole 1,1-dioxides) have been experimentally measured, including single-crystal X-ray crystallography, electrophilic characteristics, which agreed with those calculated using DFT, as mentioned earlier [4], electrochemical properties [13], nucleophilic addition reactions [7,12], new synthesis reactions [9], practical applications as corrosion inhibitors [5], and potential applications of their radical anions as charge storage devices [6].…”

“…Among the many experimental studies on the physical chemistry of thiadiazole derivatives that our group has performed over the years, several have concerned compounds 1 and 2 [5][6][7][8][9][10][11][12][13].…”

Additions of water, hydroxide ions, alcohols and alkoxide ions to carbonyl and azomethine bonds

“…Thus 3-and 4-alkyl or aryl substituted 1,2,5-thiadiazole-1,1-dioxides have the ability to bind covalently water and alcohols. Spectroscopic 130,131 and electrochemical [131][132][133][134] studies proved additions of numerous alcohols to the thiaziazole ring either in a acetonitrile solution or using the same alcohol both as a reagent and as a solvent. The equilibria in acetonitrile solutions are rather slowly established.…”

“…The role of the establishment of an equilibrium depends on concentration of water in the organic solvent but little on the acidity 131 . The addition is observed not only for separated Β-electron systems, such as represented by the 3,4-diphenyl derivative, but also for connected, liked the phenanthro-9,10 derivative 105 and also for fused Β-electron systems, like the acenaphtho-1,2 derivative of 1,2,5-thiadiazole-1,1-dioxide 106 134 . Authors presume 131 …”

Partial electrooxidation of nitrogenated heterocycles: novel synthesis of 1,10-phenanthroline-5,6-quinone by electrooxidation of 1,10-phenanthroline

“…Additionally, our interest in electrosynthetic methods for PLQ is related to our previous work in the electrochemistry of nitrogenated heterocycles [14][15][16][17][18][19], and to the fact that the electrochemistry of azaphenanthrenes and quinones is still considered an open field [20]. We report here a novel and clean synthetic route to PLQ, by controlled potential electrooxidation of PL.…”