Synthesis and Bleaching Activity of 1-Ethyl- and 1 -Propy 1-5-Substituted Imidazoles

Twenty-eight 1-ethyland l-p ropyl-5-substitu ted imidazoles were synthesized and their bleaching activity was evaluated by using the lettuce seedling test. 5-Phenyl1-propylimidazole (1) caused distinct chlorosis, while none o f the com pounds with various alkenyl groups at the 5-position o f the im idazole ring showed this bleaching activity. In troduction o f a brom o, chloro, fluoro, methyl o r trifluorom ethyl g roup a t the 4-position on the benzene ring o f com ­ pound 1 increased the activity in com parison w ith tha t o f com pound 1. 5-[4-(3-Chlorobenzyloxy)phenyl]-l-ethylim idazole (15) and l-ethyl-5-[4-(3-m ethylbenzyloxy)phenyl]imidazole (21), analogs with a large substituent a t the 4-position on the benzene ring, also caused pronounced chlorosis in the lettuce seedlings. Both com pounds 1 and 15 a t 30 ppm decreased to tal ca ro t­ enoid content in the lettuce seedlings to less than 40% o f th a t in the control, and the reduction o f total carotenoid content correlated well w ith treatm ent dose.