Photo-induced disproportionation of iodomalonic acid

✍ Scribed by Gyula RÁBai; Ichiro Hanazaki

• Publisher: John Wiley and Sons
• Year: 1995
• Tongue: English
• Weight: 666 KB
• Volume: 27
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550270503

✦ Synopsis

The stoichiometry, equilibrium, and kinetics of the photo-induced disproportionation of iodomalonic acid to I-, 12, and tartronic acid have been studied by means of spectrophotometry and iodide selective electrode at 20.0 2 0.2"C, pH 2.0-4.0. At pH > 2.9, only Iand HOCH(COOHI2 are detected as major products and the reaction reaches 100% conversion. At pH < 2.9, 12 and malonic acid are also formed and the reaction stops at a conversion rate less than 100%. Both UV (band with a peak at 360 nm) and visible light (480 nm) have been found to be effective. Two primary photochemical processes are identified:

While both reactions are sensitive to UV light, only (M2) can be affected by visible light. (Ml) and (M2) are considered to initiate a chain reaction sequence in which I' radicals oxidize iodomalonic acid, Dual effects of reaction products on the reaction rate have been observed: while iodine increases the efficiency of visible light and accelerates the reaction, malonic acid inhibits the photo-decomposition by mediating the recombination of I' radicals to 12.