Phenoxyacetic acid explained

Phenoxyacetic acid, POA, is a white solid with the formula of C₈H₈O₃.^{[1] [2]} Although not itself usefully active as an herbicide, it forms the part-structure of many phenoxy herbicide derivatives including MCPA and 2,4-D.

Structure and synthesis

Phenoxyacetic acid is an O-phenyl derivative of glycolic acid. It is both a monocarboxylic acid and an aryl ether. Its preparation from sodium phenolate and sodium chloroacetate in hot water was first reported in 1880.^[3]

1) C₆H₅O⁻Na⁺ + ClCH₂COO⁻Na⁺ → C₆H₅OCH₂COO⁻Na⁺ + NaCl

2) C₆H₅OCH₂COO⁻Na⁺ + HCl → C₆H₅OCH₂COOH + NaCl

The phenolate anion reacts via nucleophilic attack on the methylene carbon of the chloroacetic acid, forming an ether bond.

Properties

Phenoxyacetic acid is a white or clear crystalline compound at room temperature.^[2] When impure, it can appear to be a light tan to brown. The compound has a solubility in water of 12 g/L and is highly soluble in organic solvents including ethanol, diethyl ether and benzene. Phenoxyacetic acid is a weak acid and weak base with a pKa of 3.7.^[4]

Uses

Phenoxyacetic acid has found minor uses as a food additive and perfume component and is categorised as "generally recognised as safe" in these applications.^{[5] [6]}

Notes and References

1. David S. Wishart. Showing metabocard for Phenoxyacetic acid (HMDB0031609).
2. Web site: 2021. Phenoxyacetic acid. 2021-02-17. Sigmaaldrich.
3. 10.1039/CA8803800307 . Phenoxyacetic Acid . Journal of the Chemical Society, Abstracts . 1880 . 38 . 318–319 .
4. 10.1289/ehp.793075 . Some physical factors in toxicological assessment tests . 1979 . Freed . V. H. . Chiou . C. T. . Schmedding . D. . Kohnert . R. . Environmental Health Perspectives . 30 . 75–80 . 446460 . 1637710 .
5. Web site: Phenoxyacetic acid . The Good Scents Company . 2021-02-17 .
6. 10.2903/j.efsa.2007.417 . free . Opinion of the Scientific Panel on food additives, flavourings, processing aids and materials in contact with food (AFC) related to Flavouring Group Evaluation 23 (FGE.23): Aliphatic, alicyclic and aromatic ethers including anisole derivatives from chemical groups 15, 16 and 26 (Commission Regulation (EC) No 1565/2000 of 18 July 2000 . EFSA Journal . 2007 . 5 . 5 .