Evidence of desulfurization in the oxidative cyclization of thiosemicarbazones.: Conversion to 1,3,4-oxadiazole derivatives

The addition of pyridine-2-carbaldehyde 4N-methylthiosemicarbazone (C8H10N4S) to an aqueous solution of copper(II) nitrate yields [{Cu(C8H9N4S)(NO3)}(2)] (1). This complex consists of centrosymmetric dinuclear entities containing square-pyramidal copper(II) ions bridged through the sulfur thioamide atoms, The oxidation of I with KBrO3 or KlO(3) gives rise to a compound with formula [{Cu-(C8H8N4O)(H2O)(2)(SO4)}(2)].2H(2)O (2) (C8H8N4O = 2-methylamino5-pyridin-2-yl-1,3,4-oxadiazole). The structure of 2 is made up of centrosymmetric dimers, where the copper(II) ions exhibit a distorted octahedral coordination and are connected by the oxadiazole moiety. The metal Ions in 2 can be removed by addition of K-4[Fe(CN)(6)], and then the oxadiazole ligand can be isolated and recrystallized as (C8H8N4O).3H(2)O (3).