ABSTRACT
Herbicides constitute a wide variety of chemicals, whose main classes include: chlorphenoxy acids and their esters, triazines, substituted ureas, dipyridyl derivatives, and mono- or dinitro aromatics. In the agricultural industry, the control of weeds and noxious vegetation is accomplished by the application of various contact herbicides that produce the rapid elimination of plant tissues for prolonged periods. Most of the chlorphenoxy compounds are odorless, colorless, crystalline compounds with low vapor pressures. The herbicides are effective against broad-leafed weeds and plants and some annual grasses. They are conveniently divided into selective and nonselective classes. Structurally, the chlorophenoxy herbicides consist of a simple aliphatic carboxylic acid moiety attached to a chlorine- or methyl-substituted aromatic ring through an ether bond. Paraquat (PQ) and diquat are nonselective bipyridyl herbicides used widely in agricultural and commercial residential applications to eradicate broad-leaf plants and shrubs. PQ is extremely toxic to humans and laboratory animals.
