Accelerated. Thermal. -Decomposition of Diazonium Compounds Following Photolysis

Abstract

When some kinds of diazonium compounds were partly photolyzed by UV or visible light, the remaining diazonium compounds decomposed at an accelerated rate. This enhanced thermal decoMposition of diazonium compounds was remarkable especially after the dye-sensitized photolysis. The decomposition rate was affected by the chemical structure of the diazonium compound, the extent of exposure and other factors such as-the pH of the solution; the amount of dissolved oxygen and the temperature. Benzene diazonium compounds with p-amino substituents showed notable enhanced thermal decomposition at a pH from 6 to 7 under an aerobic condition, where the dissolved oxygen played a significant role. After UV exposure, 4-diazodiphenylamine hydrogensulfate (4-DS) acceleratedly decomposed with a pseudo first-orderrate (activation energy: 26 kcal/mol). The species responsible for the enhanced thermaldecom, posi- tion was proposed to be p-hydroxydiphenylamine which was the main product of the UV photolysis.