Synthesis

2,4-D and 2,4,5-T are manufactured by the sn2 displacement of the chloro group of chloroacetate with a phenoxide anion as in reactions (8-51) and (8-52) or by the chlorination of phenoxyacetic acid, as in reaction (8-53).

ONa+ + ClCH2CO2

ONa+ + ClCH2CO2

-OCH2CO2Na+

-OCH2CO2Na+

ONa+ + ClCH2CO2

ONa+ + ClCH2CO2

OCH2CO2Na+

OCH2CO2Na+

OCH2CO2Na+

A variety of closely related 2,4-D analogues also show herbicidal activity. The carboxyl group can be replaced by an amide, nitrile, or ester group. In addition, a longer side chain can be used in place of the acetic acid moiety. However, this side chain must contain an even number of carbon atoms to be active. This result is consistent with ^-oxidation of the side chain by the plant (Section 7.2.4) to form the biologically active 2,4,-D.

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