Degradation D'un Herbicide, La Flurochloridone, Par Hydrolyse et Photolyse Hydrolysis and Photodegradation of the Herbicide Flurochloridone

Abstract

The degradation during hydrolysis and photolysis of flurochloridone, a weed-killer, which belongs to the chemical class of pyrrolidones was studied in diluted solutions. Hydrolysis reactions, carried out on a large pH scale (from 5.5 to 9.5) and for temperatures ranging from 20°C to 40°C, demonstrated that there was no significant elimination of flurochloridone. The decrease of this compound was at the very most 2% or 3% for more than 100 days of hydrolysis. The presence of aquatic humic substances had no effect on chemical stability of this molecule. In neutral or basic medium, hydrolysis led to the epimerisation of the molecule of flurochloridone. Thus, a thermodynamic equilibrium (70 / 30) was obtained between the trans and cis epimerics. No additionnal modification of the structure of this molecule could be observed for long-lasting reactions. UV photolysis (253.7 nm) or polychromatic irradiation (metallic iodide lamp) allowed a total removal of flurochloridone for short reaction times. Some reaction by-products could be eliminated by further UV irradiation, however they remained quite stable with the polychromatic light source. These by-products identified by GC/MS had a chemical structure very close to that of flurochloridone; they were the result of a substitution of a Cl atom and/or of hydroxylation on the five-member cycle.