Herbicidal Activities of Phosphoramidothionates

A large number of phosphorothionoamidates, phosphorothionothiolamidates, phosphorothiolamidates and phosphoramidates were synthesized and their herbicidal activities were tested. This paper deals with structure activity relationship and biological activity of some phosphorothionoamidates. O-Alkyl-O-(subst'd phenyl) phosphorothionoamidates were high in herbicidal activity. The phosphorothionoamidates having orthonitrophenyl substituted with halogen, lower alkyl and alkoxy at paraposition showed excellent herbicidal activity. O-Ethyl-O-(2-nitro-p-tolyl)N-isopropyl phosphoramidothionate, common name: amiprophos (supposed) was of the most interest from the points of herbicidal activity and compatability to crops. Amiprophos did not affect seed germination. It suppressed the growth of germinating shoots and roots as to both crops and weeds. The shoots and roots of treated plants showed abnormal enlargement and “club-shaped” appearance. The cells of treated plant at the apical meristem were as small and denese as those of untreated plant. Immediately behind this region, however, the cells of treated plants were abnormally large and aberrant. Amiprophos was highly persistent to rainfall and leaching. And then, it showed high placement selectivity to a number of deep-seeded crops such as rice, maize, beans, radish and carrot, and trans-planted crops such as rice, tomatoes, cucumber, lettuce and onion.