KINETICS AND MECHANISMS OF PHOTOINDUCED REDUCTION OF IODINE BY MONOAMINE-N-POLYCARBOXYLATE IONS IN AN AQUEOUS-SOLUTION

The photo-induced reduction kinetics of iodine by monoamine-N-polycarboxylate ions, such as nitrilotriacetic acid (H3nta), iminodiacetic acid (H2ida), 2-hydroxyethyliminodiacetic acid (H2hida), as well as o-, m-, and p-isomers of N-(carboxyphenyl)iminodiacetic acid (H3cpida), were made in an aqueous solution containing iodide ions in excess over the pH range 1.6-7.6; the photo-induced reductions of iodine by triethylamine (TEA) and tris(2-hydroxyethyl)amine (TEOA) were also studied. There active species are a I2 radical-anion radical anion, produced in the primary photoreaction, and a fully deprotonated species of monoamine-N-polycarboxylate, TEOA, or TEA. Both hydrogen ion and complex-forming metal ions, such as copper(II) and zinc(II), were strong inhibitors for all of the reactions investigated. The role of the lone electron pair on the amine nitrogen is discussed.