EPR studies of nitrogen-centred free radicals. Part 50. Unusual decomposition behaviour of isolable stable thioaminyl free radicals at high temperature

Thermal stabilities of N-(4-nitrophenylthio)-N-(4-tert-butyl-2,6-diphenylphenyl)aminyl 1a, N-(4-nitrophenylthio)-N-(2,4,6-triphenylphenyl)aminyl 2a, N-(2,4-dichlorophenylthio)-N-(2,4,6-triphenylphenyl)aminyl 2b and N-(4-nitrophenylthio)-N-(2-tert-butyl-4,6-diphenylphenyl)aminyl 3a have been studied. When la, 2a and 2b are heated in degassed benzene at 80 degrees C for 24-30 h, they almost completely decompose, giving two non-radical compounds. On the other hand, 3a is thermally much more stable and the complete decomposition requires heating for 8 days. On the basis of the product analysis study the thermal decomposition mechanism-is proposed and the reason why 3a is so stable at high temperature is discussed.