Phenoxyalkane carboxylic acids

Over 40 years of extensive use testifies to their safety and efficiency, and in the United States consumption of 2,4-D alone is in excess of 32 000 tonnes per annum. It is produced by some six companies and marketed in over 15000 different formulations. 2,4-D and MCPA possess several advantages  

Selectivity of action (they kill broad-leaved weeds but do not affect cereal and grass crops, and so great is their selectivity that relatively little skill is needed in their applications). 

Effectiveness at low concentrations, e.g. lOOgha (approx. 100 ppm) (interestingly, at much lower concentrations they can be used as plant growth stimulants—25 g spread over 100000 pineapple plants causes them to start flowering, and this is reportedly done in Hawaii to have plants flowering throughout the year for the benefit of tourists). 

Their synthesis is easy and cheap, e.g. the Dow process for synthesis of 2,4-D. 

The Dow process is a batch process, and in the second step the solution must be kept alkaline and a 50% molar excess of 2,4-dichlorophenol is used in order to minimize formation of HOCH2CO2H. The synthesis of MCPA is similar to that of 2,4-D but the starting phenol is o-cresol. 

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System for the determination of phenoxyalkane carboxylic acids in water General remarks... 

Phenoxyalkane carboxylic acids, approx. 10 pg/ml in nanograde methanol (see empirical list,. 2.6)... 

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