2-Chloropropionic acid explained

2-Chloropropionic acid (2-chloropropanoic acid) is the chemical compound with the formula CH₃CHClCO₂H. This colorless liquid is the simplest chiral chlorocarboxylic acid, and it is noteworthy for being readily available as a single enantiomer. The conjugate base of 2-chloropropionic acid (CH₃CHClCO₂^-), as well as its salts and esters, are known as 2-chloropropionates or 2-chloropropanoates.

Preparation

Racemic 2-chloropropionic acid is produced by chlorination of propionyl chloride followed by hydrolysis of the 2-chloropropionyl chloride. Enantiomerically pure (S)-2-chloropropionic acid can be prepared from L-alanine via diazotization in hydrochloric acid.^[1] Other α-amino acids undergo this reaction.

Reactions

Reduction of (S)-2-chloropropionic acid with lithium aluminium hydride affords (S)-2-chloropropanol, the simplest chiral chloro-alcohol. This alcohol undergoes cyclization upon treatment with potassium hydroxide, which causes dehydrohalogenation to give the epoxide, (R)-propylene oxide (methyloxirane).^[2]

2-Chloropropionyl chloride reacts with isobutylbenzene to give, after hydrolysis, ibuprofen.

Safety

In general, α-halocarboxylic acids and their esters are good alkylating agents and should be handled with care. 2-Chloropropionic acid is a neurotoxin.^[3]

See also

• 2,2-Dichloropropionic acid

Notes and References

1. 10.15227/orgsyn.066.0151. (S)-2-Chloroalkanoic Acids of High Enantiomeric Purity from (S)-2-Amino Acids: (S)-2-Chloropropanoic Acid. Organic Syntheses. 1988. 66. Koppenhoefer. Bernhardt . Schurig. Volker . 151.
2. 10.15227/orgsyn.066.0160. (R)-Alkyloxiranes of High Enantiomeric Purity from (S)-2-Chloroalkanoic Acids Via (S)-2-Chloro-1-Alkanols: (R)-Methyloxirane. Organic Syntheses. 1988. 66. 160. Bernhard Koppenhoefer . Volker Schurig.
3. Neuropathological changes in rat brain following oral administration of 2-chloropropionic acid. Simpson MG, Wyatt I, Jones HB, Gyte AJ, Widdowson PS, Lock EA. Neurotoxicology. 1996. 17. 2. 471–480. 8856742.