Fenarimol solar degradation pathways and photoproducts in aqueous solution

Abstract

The degradation photoproducts of the fungicide fenarimol obtained from irradiation of aqueous solutions with sunlight were characterised. The photoproducts resulting from samples with different exposure times were extracted and separated using chromatographic techniques. Seven main photoproducts were detected using high performance liquid chromatography with a photodiode array detector, gas chromatography with mass spectrometry detector and Fourier transform infrared spectroscopy. Structures are suggested for possible photoproducts based on the characterisation results, minimum energy geometry of the parent compound, and the mass spectral behaviour of fenarimol. These correspond to the compounds with m/z 328 (three structural isomers (a), (b) and (c)), m/z 294 (two structural isomers (a) and (b)), m/z 292, 278 and 190. Of the various major products detected, the isomer 328(a) is seen to be particularly unstable under the action of sunlight. The most stable photoproducts are found to be those with m/z 294(a), 278 and 190. However, upon prolonged solar irradiation all of these break down to produce polar, low molecular weight compounds. Comparison with our own and other results on fenarimol photolysis indicate significant solvent effects on the process. The combination of these structural characterisation results and previous data from spectroscopic and photodegradation kinetics studies allows us to suggest some possible mechanisms for the photodegradation of fenarimol under sunlight.

Reaction pathways and mechanisms of photodegradation of pesticides

“…More recently, the dinyl] phosphorothioatej by UV light of different wavesame authors studied the kinetics and mechanism of lengths in water and water / soil suspensions. Diazinon photodegradation of fenarimol in natural water and the degraded faster in river water than in distilled water, and effect of salt solutions, using both sunlight and light of 313 this rate enhancement was higher upon exposure to sunnm [70]. The rate of photodegradation was found to decrease with increasing salinity.…”

Direct photolysis mechanism of pesticides in water

“…Either the oxidative cyclization as observed for stilbene or a radical mechanism via energy or electron transfer 172) is possible, but the mechanism has not been confirmed in most cases. The favorable orientation of two rings may be necessary for cyclization, as represented by the formation of the five-membered ring from diclofop-methyl, 173) haloxyfop-P, 4) and fenarimol, 174) or the six-membered ring from propiconazole, 175) pyridaben 4) and quinoxyfen. 4) An eight-membered ring was formed in the main photoproduct of fluopyram.…”

“…4) The photo-induced homolytic cleavage of the bond between the carbinol carbon and the pyrimidyl ring was proposed as an initial step 47,174) ; however, a concrete mechanism is unclear. Similar photo-induced migration was reported for flurprimidol 4) and the anti-histamine drug fexofenadine.…”

Solution and surface photochemistry of fenarimol: A comparative study

“…The fungicide fenarimol (␣-(2-chlorophenyl)␣-(4-chlorophenyl)-5-pyrimidine-methanol) (see Scheme 1) is commonly used in the form of a spray for treating mildew. Its solution photophysics and photochemistry have been well documented in the literature [3][4][5][6].…”