Phenoxycarboxylic acid

Various chemical classes of auxin herbicides with different weed spectra and types of selectivity have been synthesized and commercially introduced over the years. They include phenoxycarboxylic acids, benzoic acids, pyridine carboxylic acids, aromatic carboxymethyl derivatives and a relatively new category, the quinolinecarboxylic acids (Figure 1). These compounds basically act as synthetic mimics of indole-3-acetic acid (lAA), which is the principal natural auxin in higher plants [2,3,5,7]. 

An interesting field of application for anion exchange chromatography is the analysis of herbicides based on phenoxycarboxylic acids and their derivatives. Generally, these compounds were separated at chemically modified silicas using a methanol/water mix-... 

Fig. 3-90. Separation of phenoxycarboxylic acid-based herbicides. - Separator column IonPac AS4A eluent 0.025 mol/L NaN03 + 0.005 mol/L NaOH flow rate 2 mL/min detection UV (280 nm) injection volume 50 pL.

In agriculture, phenolic compounds are used as pesticides (Figure 1) and can also form from the degradation of chlorinated phenoxycarboxylic acids and organophosphorous insecticides". The herbicide DNOC sorption in a sandy aquifer (Denmark) has been reported ". 

Phenoxycarboxylic acids (phenoxyacetic acids such as 2,4-D, Fig. 53) are the most important herbicides in terms of production. 

Optical isomerism of phenoxycarboxylic acids also plays a decisive role in their activity. Of the amino acid derivatives of 2,4-dichlorophenoxyacetic acid and 2,4-dichlorophenoxypropionic acid only the derivatives of the dl- and L-amino acids are active, while the respective D-amino acid derivatives are completely inactive. This can be attributed to the fact that plants are unable to hydrolyse the peptide bond of the D-derivatives (Wood and Fontaine, 1952 Krewson et al., 1956). 

Heberer T, Butz S, Stan HJ (1995) Analysis of phenoxycarboxylic acids and other acidic compounds in tap, ground, surface and sewage water at the low ng/1 level. Int J Environ Anal Chem 58 43-53... 

Four main classes of natural and synthetic plant growth substances are distinguished 1) The 3-indolylacetic acid derivatives (lAA) and other C-3 substituted indoles, previously known as auxins, induce a pronounced longitudinal growth, stimulate the formation of roots and flowers, the activity of the cambium, and influence fruit ripening and numerous other developmental processes in the plant. In the literature many compounds with different constitutions are also designated as auxins if they have activities similar to those of lAA. These include, e. g., 2-naphthyloxyacetic acid, benzoic acid, phenoxycarboxylic acid derivatives. 

Such a variety of compounds requires the application of the full panoply of analytical techniques including ELISA, LC, LC-MS, GC-MS (negative and positive ion), GC-MS-MS. Newer methods may include online SPE systems combined with MS or UV or electrochemical detection systems. One important consideration is that analysis of a particular EDC should also include its degradation and/or metabolic products because these too may remain active. So for alkyl phenols the concurrent measurement of the appropriate alkyl phenol ethoxylates and alkyl phenoxycarboxylic acids is environmentally important and a significant analytical challenge. 

The efficiency of the extraction can be influenced by the polarity of the solvents or solvent mixtures and by pH, among other factors. Some triazines, ureas, phenoxycarboxylic acids, and OP and OC insecticides can be extracted from waters at different pH values with quite different... 

Some chlorinated hydrocarbon (chlorobenzenes, HCH isomers) were extracted with CO2 and toluene- and cyclohexane-containing CO2 from soil samples with high recovery (41f) (Table 1). A review with 62 references summarizes the recently-published methods for the analysis of PCBs, OC insecticides, s-triazine herbicides, phenoxycarboxylic acid herbicides, and PAHs in environmental samples (41g) (Table 1). 

A semi-polar cyclic five-membered transition state has been proposed to account for the unimolecular pyrolysis kinetics of primary, secondary, and tertiary 2-phenoxycarboxylic acids in the gas phase reaction rates increase in the order 2-phenoxyacetic, 2-phenoxypropionic, 2-phenoxybutyric, and 2-phenoxyisobutyric acid. Phenol formation in the rate-determining step is followed by formation and subsequent decompositon of an intermediate lactone to give carbon monoxide and the corresponding carbonyl compound however, in the case of 2-phenoxyisobutyric acid, a parallel elimination reaction gives phenol and methacrylic acid." ... 

Phenobarbitone, 212, 213 Phenol, 92, 97-99, 122, 123, 140, 179, 181-189, 191-199, 377 m-Phenol, 122 p-Phenol, 122 Phenol-formaldehyde, 33 Phenolic group, 29 Phenoxycarboxylic herbicide, 292 Phenoxy group, 182, 414 Phenylarsonic acid, 32 Phenylazo group, 414 Phenylfluorone, 22 Phenylhydrazono group, 414 Phenylindole, 426 Phenylmercury, 80 Phenylpyrrole, 426 Phosgene, 225, 326 Phosphate, 22, 35, 36 Phosphate ester, 157 Phosphinic acid, 36... 

Inhibitors not primarily involving photosynthesis.—Of the herbicides which do not inhibit photosynthesis, the phenoxycarboxylic herbicides have received the most attention with respect to their influence on the soil algae. These herbicides act on higher plants through interfering with nucleic acid metabolism and disrupting translocation systems. 

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