Herbicidal Activity of Derivatives Part II.

Abstract

Eighty-nine O-aryl N-alkyl-N-arylcarbamates, mainly thiono-type thiocarbamates, were synthesized and their herbicidal and phytotoxic activities against barnyardgrass and rice plants, respectively, were evaluated under paddy field conditions to determine the relationship between chemical structure and the activity.The following points were clarified regarding herbicidal activity against barnyardgrass:1. In the phenoxy residue in aryl N-(6-methoxy-2-pyridyl)-N-methylcarbamates, condensed aryl groups such as 2-naphthyl, 5, 6, 7, 8-tetrahydro-2-naphthyl and 1, 4-methano-1, 2, 3, 4-tetrahydro-6-naphthyl showed excellent herbicidal activity.2. With regard to substituents on O-phenyl ring in O-phenyl N-(6-methoxy-2-pyridyl)-N-methyl-thiocarbamates, 3- or 4-substituted derivatives (meta or pare) showed higher activity than one other (ortho). Excellent herbicidal activity was shown by the alkyl groups, 3-isopropyl, 3-tert-butyl and 4-tert-butyl. As substituents other than the alkyl group, halogen and trifluoromethyl exhibited strong activity. From the results of structure-activity correlation analysis by adaptive least-squares method for substituents on O-phenyl ring, it was apparent that adequate hydrophobic and steric groups such as 3-iso-propyl, 3-tert-butyl and 4-tert-butyl are prefer-able for high activity.3. Among four types of carbamate of 4-tert-butylphenyl N-(6-methoxy-2-pyridyl)-N-methyl-carbamates, thiono-type thiocarbamate showed the highest activity, while carbamate was less active. Thiol-type thiocarbamate and dithiocarbamate exhibited no activity.4. In the N-alkyl group in O-3-tert-butylphenyl N-alkyl-N-(6-methoxy-2-pyridyl)-thiocarbamates, methyl group showed the highest activity.5. With regard to substituents on N-(2-pyridyl) ring in O-3-tert-butylphenyl N-methyl-N-(2-pyridyl) thiocarbamates, the highest activity was exhibited by 6-methoxy group.6. When N-phenyl group was introduced into O-3-tert-butylphenyl thiocarbamates, N-3-methoxyphenyl derivative showed almost the same high activity as 6-methoxy-2-pyridyl derivative.7. For highly active compounds, herbicidal activity against barnyardgrass at the 1.5 leaf stage was also examined, and O-3-tert-butylphenyl N-(6-methoxy-2-pyridyl)-N-methyl-thiocarbamate, pyributicarb, was found to be the most effective.