Chloroethanoic acids
From Biocrawler, the free encyclopedia.
In organic chemistry, the chloroethanoic acids (trivial name chloroacetic acids) are three related chlorocarbon carboxylic acids:
- chloroethanoic acid (chloroacetic acid), CH2ClCOOH
- dichloroethanoic acid (dichloroacetic acid), CHCl2COOH
- trichloroethanoic acid (trichloroacetic acid), CCl3COOH
As the number of chlorine atoms increases, the electronegativity of that end of the molecule increases, and the molecule adopts a progressively more ionic character: it's density, boiling point and acidity all increase.
| Acid | Melting point | Boiling point | Density | pKa |
| Ethanoic acid | 16.5°C | 118.1°C | 1.05 | 4.76 |
| Chloroethanoic | 61-63°C | 189°C | 1.58 | 2.87 |
| Dichloroethanoic | 9.7°C | 194°C | 1.57 | 1.25 |
| Trichloroethanoic | 57°C | 196°C | 1.63 | 0.77 |
Production
- Chloroethanoic acid is mainly made by hydrolysing trichloroethene in the presence of sulphuric acid:
- CCl2=CHCl + 2H2O → CH2ClCOOH + 2HCl
- Dichloroethanoic acid is manufactured in small quantities by reducing trichloroethanoic acid.
- Trichloroethanoic acid is made by the direct action of chlorine on ethanoic acid in the presence of a suitable catalyst.
Uses
- Chloroethanoic acid is chemical intermediate for production of various pharmaceuticals and insecticides.
- Trichloroethanoic acid is used for various analytic tests in biochemistry. Its sodium salt is used as a weedkiller.
Safety
All of these acids are unusually strong for organic acids, and should generally be treated with similar care as for strong mineral acids like hydrochloric acid. Even neutral salts however, tend to be significantly toxic, because the ions interfere in biological processes (such as the citric acid cycle) that normally process plain acetate ions. Interestingly, the chloroethanoate ion is the most toxic, with a rat, oral LD50 of about 0.5 g/kg.
