Thermal behaviour of esters and nitriles of 2-(3-acylselenoureido)benzoic and 2-(3-acylselenoureido)thiophene-3-carboxylic acids

The thermally initiated transformation of esters and nitriles of 2-(3-acyls elenoureido)benzoic and 2-(3-acylselenoureido)thiophene-3-carboxylic acids under heating without solvent to the temperature ca. 300 degrees C was stud ied. The thermal behaviour was studied by methods of the thermal analysis. It was found that selenoureas in ester series afford isoselenoureas at the temperature lower than their melting points. This change occurs in the soli d state as an exothermic process. The next exothermic change starts by the following increase in temperature. Two molecules of isoselenoureas eliminat e one hydrogen molecule by air oxygen action. The oxidation is connected wi th Se-Se bond formation and diselenides are formed. Nitriles undergo a tran sformation to di(2-pyrimidyl)diselenides in the course of several steps in melt in the presence of air oxygen.