SYNTHESIS AND BLEACHING ACTIVITY OF 3-PROPARGYLTHIO-4-(SUBSTITUTED PHENYL)-4H-1,2,4-TRIAZOLES

A number of 3-allylthio-4-aryl-4H-1,2,4-triazoles were synthesized and evaluated for their bleaching activity by using a lettuce seedling te st. In a series of 4-phenyl-4H-1,2,4-triazoles, 3-propylthio and 3-pro pargylthio analogs caused complete bleaching symptoms at 50 ppm, while the activity fell off with increasing or decreasing size of the alkyl thio group at the 3-position of the triazole ring. The introduction of a chloro, trifluoromethyl, methyl or ethoxy substituent at the meta- or para-position on the benzene ring increased the activity in compari son with that of the phenyl analog. 4-(3-Chlorophenyl and 4-chlorophen yl)-3-propargylthio-4H-1,2,4-triazole (16 and 17) markedly reduced bet a-carotene content as well as chlorophyll in plants. Inhibition of p-c arotene formation was accompanied by an accumulation of large amounts of phytoene, suggesting that these 1,2,4-triazoles inhibit the desatur ation of phytoene.