Abstract
Herbicidal and phytotoxic activities of fifty-three 2-naphthyl carbamates against barnyardgrass (Echinochloa oryzicola Vasing.) and rice (Oryza sativa L.) were evaluated under paddy field conditions to clarify the relationships between chemical structure and the activity.
Points clarified for the most suitable structure on herbicidal activity against barnyardgrass were as follows:
1) N-Alkyl-N-phenyl was preferable for amino moiety in carbamate skeleton of 2-naphthyl carbamates.
2) Among four types of carbamates of 2-naphthyl N-methyl-N-phenyl derivatives, thionotype thiocarbamates (O-2-naphthyl derivatives) showed the highest activity, and the next active was carbamates. Thiol-type thiocarbamates (S-2-naphthyl derivatives) and dithiocarbamates exhibited no activity.
3) Of the N-alkyl group in O-2-naphthyl N-alkyl-N-phenylthiocarbamates, only methyl group showed the activity.
4) With regard to substituents on the N-phenyl ring in O-2-naphthyl N-methyl-N-phenylthiocarbamates, there was a tendency that the activities of N-(meta-substituted phenyl) derivatives were higher than those of ortho- or para-substituents. For substituents on N-phenyl ring, hydrogen atom (=unsubstituted), methoxy and fluorine atom showed high activity.
5) When N-(2-pyridyl) group was introduced into O-2-naphthyl thiocarbamates, the activities of most compounds were weak and lower than those of corresponding N-phenyl derivatives. But O-2-naphthyl N-(6-methoxy-2-pyridyl)-N-methylthiocarbamate exhibited much higher activity than corresponding N-(3-methoxy-phenyl) thiocarbamate.
6) The activities of four types of carbamates having N-(6-methoxy-2-pyridyl)-N-methyl group were also examined. Thiono-type thiocarbamate showed the highest activity in a similar manner as N-phenyl derivatives.
Among the tested carbamates, O-2-naphthyl N-(6-methoxy-2-pyridyl)-N-methylthiocarbamate showed the highest activity.
