Halogenated-alkanoic acid derivatives

Unsubstituted aliphatic acids have no herbicidal activity. Several of the halogenated acetic acid and propionic acid derivatives, however, reveal important herbicidal properties. Today, two compounds, trichloroacetic acid and 2,2-di-chloropropionic acid are of commercial importance. 

Halogenated-alkanoic acid derivatives are efficient mainly for the control of grass weeds. In agriculture they are always used in the form of their sodium salts, which are readily soluble in water. 

Monochloroacetic acid (MCA, I) is a halogenated-alkanoic acid derivative, the herbicidal properties of which were first described by Zimmermann and Hitchcock (1950, 1951). 

The sodium salt of monochloroacetic acid, prepared by the hydratation of trichloroethylene or by the chlorination of acetic acid, is used for the selective control of grass weeds in maize, potato and onion crops. 

The disadvantages of monochloroacetic acid are its weak activity, requiring its application at rates of 50-100 kg/ha, and the brief duration — a few days — of its effectiveness. Monochloroacetic acid is hydrolysed in the soil to glycolic acid. 

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Angibaud, P, Chaumette, J L, Desmurs, J R, Duhamel, L, Pie, G, Valnot, J Y, Duhamel, P, Asymmetric synthesis of 2-chloro- and 2-bromo-alkanoic acids by halogenation of a-D-glucofuranose-derived silyl ketene acetals. Tetrahedron Asymmetry, 6, 1919-1932, 1995. 

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