Development of a New <i>N</i>-Benzylbutanamide Type Herbicide

Abstract

The N-benzylbutanamides like N-(1-methyl-l-phenylethyl)-2-bromo-3, 3-dimethylbutanamide (bromobutide, S-47) with bulky substituents in the acid and amine moieties are new herbicides that are extremely effective against annual and also perennial weeds. These herbicides were designed according to previous quantitative structure-activity studies. Systematic modification of the amide at both the acid and amine moieties gave herbicides with bulky substituents that might inhibit degradation mechanisms. The effect of the substituents was analyzed by using Hansch-Fujita method. The herbicidal activity of N-(1-methyl-l-phenylethyl) acylamides against bulrush was related parabolically with both the hydrophobicity and minimum width of the substituents at the acid moiety. The greater the maximum width, the higher the activity. When tested against purple nutsedge, the greater the steric bulk of the substituents, the higher the activity and the haloalkyl substituent was detrimental to the activity. The activity of N-(α-substituted benzyl)-2-bromo-3, 3-dimethylbutanamides against bulrush was related parabolically with the maximum distance from the nitrogen atom to the edge of the α-substituents. The length of the benzene ring substituents was responsible for the variation in activity of the substituted phenyl derivatives. The N-[1-methyl-l-(p-methyl-phenyl) ethyl] group was favorable to the activity against purple nutsedge. The crystal structure of bromobutide was examined by X-ray analysis and the R-configuration at the acid moiety was essential to high activity. Bromobutide showed a broad herbicidal spectrum by controlling various weeds such as barnyardgrass, monochoria, bulrush, slender spikerush, spikerush, sedges and arrowhead with safety to the rice plant under paddy conditions and purple nutsedge, yellow nutsedge and barnyardgrass under upland conditions. N-(1-Methyl-1-phenylethyl)-2-ethyl-3, 3-dimethylbutanamide exhibited strong herbicidal activity under upland conditions against purple nutsedge. These compounds showed extensive movement in soil and gave good residual activities.