Photolysis of Fungicide Guazatine on Glass Surfaces

Abstract

The photolysis of ¹⁴C-labeled guazatine-triacetate (TA), 1, 1′-iminodi(octamethylene)-diguanidine triacetate, was investigated in the solid state as a thin film on glass surfaces. When guazatine-TA was irradiated by artificial sunlight lamps (12hr/day), the compound initially underwent a rapid degradation (T_1/2=39.8hr) and was then photolysed slowly (T_1/2=912hr). A major photoproduct (Pm) and other minor ones were concomitantly produced, and the amounts of the products increased with the decrease in the amount of intact guazatine. After a 336hr irradiation, the amounts of Pm and the sum of the minor photoproducts accounted for 31.2% and 37.7% of the applied radiocarbon, respectively. The photolysis of ¹⁴C-guazatine-TA by natural sunlight was quantitatively and qualitatively comparable to that by the artificial sunlight. After isolation of Pm by thin-layer chromatography, the guanidine moieties of Pm were chemically converted to pyrimidine rings, and infrared, nuclear magnetic resonance, and mass spectral data were compared with those of the pyrimidine derivative of guazatine. The data indicated that Pm was formed by (1) photo-oxidation of the methylene group (probably 4 position) to the carbonyl group and (2) methylation of one of the methylene group (probably 3 or 5 position). In addition, one of the minor photo-products was identified as the photo-oxidation product of guazatine, which was considered to be an intermediate in the formation of Pm.