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2,4-dichlorophenoxyacetic acid[¦tü ¦fȯr dī¦klȯr·ō·fə¦näk·sē·ə′sēd·ik ′as·əd]
(also called 2,4-D), C12C6H3OCH2COOH, a herbicide for combating dicotyledonous weeds in sowings of grain crops and in meadows. In pure form it exists as white odorless crystals; melting point, 140.5° C. Its solubility in water is 560 mg per liter at 20° C. The industrial preparation has an unpleasant phenolic odor caused by an admixture of 2,4-dichlorophenol. In industry, 2,4-D is made by the reaction of salts of monochloroacetic acid with sodium 2,4-dichlorophenate and by chlorination of phenoxyacetic acid. It is the most extensively produced and utilized herbicide. It is used in the form of water-soluble salts with acyclic amines (dimethylamine, diethylamine, ethanolamines, and so on) and in the form of a sodium salt, esters with various alcohols (isopropanol, butanol, octanol, and others), and amides (for example, the o-chloroanilide).
At the consumption levels of 0.5-2.0 kg per hectare (kg/ha), almost all dicotyledonous weeds can be killed (creeping thistle, hogweed, and centaurea). Grain crops are treated in the tillering stage.
Plants that are sensitive to the action of 2,4-D include cotton and sunflower plants, fruit trees (apple, pear, plum, cherry, apricot, and peach), and berries (currant, strawberry, gooseberry, and raspberry), as well as deciduous trees and shrubs. The action of the herbicide is weaker on poor soils and in periods of drought; plants raised on rich and moist soils die more quickly. 2,4-D is moderately toxic to animals and humans.
The mechanism of action of 2,4-D has not been conclusively studied. It is known to be rapidly absorbed by plant leaves and to cause expansion of meristematic cells, which leads to the destruction of tissues and to curling and death of the plant. It is comparatively rapidly destroyed by microorganisms in the soil and does not accumulate.
REFERENCESMel’nikov, N. N., and lu. A. Baskakov. Khimiia gerbitsidov i reguliatorov rosta rastenii. Moscow, 1962.
Crafts, A., and W. Robbins. Khimicheskaia bor’ba s sorniakami Moscow, 1964. (Translated from English.)
Mel’nikov, N. N. Khimiia pestitsidov. Moscow, 1968.
N. N. MEL’NIKOV