The accumulation of radical anions from 3,4-disubstituted 1,2,5thiadiazole S,S-dioxides (1) in solution of organic solvents is achieved by electrochemical, chemical and photoinduced pathways. Electrolytic and chemical reduction of 1 produces the radical anions (1 *-) in high molar yields (> ca. 80%). The survival of 1 *is measured for ca. three months. The stability of the reduced state depends on its structure and the composition (solvent, reducing agent, and supporting electrolyte) of the medium in which it is generated by the chemical and electrochemical routes. In solution of polar aprotic solvents, 1 *persists even in the presence of water or oxygen. Irradiation with 254 nm light generates 1 *but only in DMF solution; the proposed reaction mechanism involves the participation of the solvent. Radical anions are characterized by cyclic voltammetry, UV-Vis spectrophotometry and electron spin resonance spectroscopy. The chemical stability and the properties of 1/1

We report a study of the solvent-free condensation reaction of 1,2-dicarbonyl compounds with sulfamide catalyzed by a Keggin-type acid (H3PMo12O40?nH2O, MPA) to obtain 3,4-disubstituted 1,2,5-thiadiazole 1,1-dioxide derivatives. Some reactions were also performed in solution or using nano-sized silica-supported MPA catalyst in order to compare the results under different experimental conditions. Effects of the temperature used for the thermal pretreatment of the catalyst, the reaction temperature, the molar ratios sulfamide/1,2-dicarbonyl compound and MPA/1,2-dicarbonyl compound, and alternative experimental procedures on the yield of the reaction product were investigated. Under suitable experimental conditions eight compounds were obtained in good yields. The catalyst was recycled and reused, but with some loss of its catalytic activity. The presented synthetic method is a simple, clean, and environmentally friendly alternative for synthesizing different 1,2,5-thiadiazole 1,1-dioxide derivatives.