Degradation of anilinopyrimidine fungicides photoinduced by iron(III)–polycarboxylate complexes

Abstract

The photoinduced degradation of three anilinopyrimidine fungicides (cyprodinil, pyrimethanil and mepanipyrim) by Fe(III)-polycarboxylate complexes in aqueous solution was investigated. A photochemical redox reaction of Fe(III) complexes of oxalate and citrate occurs during irradiation (simulating sunlight) and is an important source of Fe(II) and a series of oxidants such as H2O2 and O radicals. The mechanism involves the formation of polycarboxylate radicals and/or carbon-centred radicals derived from decarboxylation, whereas the contribution of Fe(OH)2+ to O radical formation is negligible. The attack of O radicals on the fungicide molecules produces numerous photodegradation products, which were identified by means of LC-ES-MS and turned out to be mono- or dihydroxylated derivatives of the active ingredients, except for 2-amino-4,6-dimethylpyrimidine, which is only formed by pyrimethanil. The half-lives of the active ingredients, when submitted to irradiation in the presence of iron(III)-polycarboxylate complexes, were estimated to vary between 28 and 79 min (photodegradation rates in the same conditions: mepanipyrim > cyprodinil > pyrimethanil), and photodegradation is slower in citrate than in oxalate solutions. Photoproducts and their kinetics of formation are very similar for the three fungicides. The OH substitution involves the aromatic and the heterocyclic ring and the nitrogen bridge between the two rings, except for mepanipyrim when the hydroxylation also involves the propynylic side chain.

In-package nonthermal plasma degradation of pesticides on fresh produce

“…Ozone can also undergo reaction with water to yield peroxide and hydroxyl radicals. The degradation of cyprodinil is probably an outcome of the attack at the nitrogen bridge between the two rings or the phenyl ring and/or the pyrimidyl ring by hydroxyl radicals formed from ozone [39] as typified in Figure 6 and further oxidation by Criegee mechanism.…”

Photodegradation of cyprodinil under UV–visible irradiation – chemical and toxicological approaches

“…The elemental composition of [TP1 + H] + is C 8 H 12 N 3 , and TP1 was characterized as 4‐cyclopropyl‐6‐methylpyrimidin‐2‐amine based on its CID mass spectrum. The corresponding TP has also been observed for pyrimethanil and mepanipyrim . TP1 loses either NH 3 from the form protonated on the amino function to give m/z 133, or NCNH 2 from the structure protonated on another nitrogen atom to give m /z 108.…”

“…UV photolysis processes are commonly used as an alternative to chlorine disinfection. Some efforts have been devoted to the direct and catalyzed photodegradation of pesticides, including identification of photoproducts, kinetic studies and reaction pathway establishment, in order to integrate these TPs into pesticide control procedures . These studies showed that photolysis, in combination with other techniques multiplying the number of degradation pathways, would target a large range of pollutants.…”

“…Some efforts have been devoted to the direct and catalyzed photodegradation of pesticides, including identification of photoproducts, kinetic studies and reaction pathway establishment, in order to integrate these TPs into pesticide control procedures. [16] These studies showed that photolysis, in combination with other techniques multiplying the number of degradation pathways, would target a large range of pollutants. Regardless of the treatment methods used, knowledge of the chemical structures of the TPs would permit analytical methods to be established that are able to target those specific compounds and to predict their impact on the environment.…”

The Production, Separation and Stability of Pyoluteorin: A Biological Pesticide

“…Many compounds are light sensitive, such as aldicarb, parathion, mecoprop, linuron, and chlorpyrifos (Burrows & Canle, 2002;Anfossi et al, 2006). Thus, it is necessary to study the effect of UV/Vis irradiation on the degradation rate of Plt.…”