Herbicidal Activity of Arylcarbamate Derivatives Part III.

Abstract

Forty-nine di- and tri-substituted-phenyl N-(6-methoxy-2-pyridyl)-N-methylcarbamates and thiono-type thiocarbamates were synthesized. Their herbicidal and phytotoxic activities against barnyardgrass and rice plants were evaluated under paddy field conditions to determine the relationships between chemical structure and the activity.Points identified as important for the most suitable structure to obtain herbicidal activity against barnyardgrass were as follows:1. When two substituents were introduced into phenoxy residue in O-phenyl N-(6-methoxy-2-pyridyl)-N-methylthiocarbamates, herbicidal activity was strongly affected by their substituted position. When dichloro and dimethyl groups were used as substituents, 3, 4-di-substituted derivatives showed the highest activity. No activity was observed when one of the substituents was bonded to the 2-position on O-phenyl ring.2. Comparison between 3, 4-di- and 3, 4, 5-tri-substituted-phenyl derivatives showed the former to exhibit stronger activity than the latter.3. Among 3, 4-substituents on phenyl ring in the phenyl carbamates, 3-alkyl-4-halogeno and 3, 4-dialkyl derivatives showed high activity, while among 3, 4-dialkyl derivatives, the activity of O-4-tert-butyl-3-methylphenyl thiocarbamate was the highest.4. Many compounds in the 3-alkyl -4-halogeno group on the phenyl ring showed high activity. In the case of 3-methyl and 3-ethyl derivatives, thiono-type thiocarbamates exhibited stronger activity than carbamates; among 3-isopropyl and 3-tert-butyl derivatives, on the other hand, the activity of the two were similar.5. The results of structure-activity correlation analysis by adaptive least-squares method for O-3, 4-di-substituted-phenyl derivatives showed that adequate hydrophobic and steric groups on O-phenyl ring are preferable to obtain high activity.6. For highly active compounds, herbicidal activity against barnyardgrass at the 1.5 leaf stage was also examined, and some compounds showed similar activity to pyributicarb.