Mechanism of hydantoin ring opening in iprodione in aqueous media

Abstract

Abstract The hydrolysis kinetics of iprodione in alkaline solutions of pH 8.3 to 12 at 25°C have been determined by ultraviolet spectrophotometry. Under these conditions, iprodione leads quantitatively and irreversibly to N ‐(3,5‐dichloroanilinocarbonyl)‐ N ‐(isopropylaminocarbonyl)glycine. The reaction is not subject to a general basic catalysis and the rate law takes the form K obs = K OH ‐ [OH −1 ]. The activation entropy of ‐77 J mol −1 deg −1 , the value of the kinetic solvent isotope effect k OH− /k OD− of 0.79 and the value of 0.60 for the Hammett parameter σ, obtained for the hydrolysis of a series of 3‐aryl‐ N ‐isopropyl‐2,4‐dioxoimidazolidine‐1‐carboxamides are all in agreement with the rate‐determining attack by the hydroxyl ion on the carbonyl in the 4‐position of the hydantoin ring of the fungicide.