Question #d301a
1 Answer
The possibilities are dehydration and condensation.
1) 2-Hydroxyethanoic Acid (Glycolic Acid)
The molecule cannot dehydrate, but it can undergo condensation (esterification), in which the COOH of one molecule reacts with the OH in another molecule.
HOCH₂COOH + HOCH₂COOH → HOCH₂CO-OCH₂COOH + H₂O
The process continues repeatedly to form a polymer called poly(glycolic acid) or PGA.
2) 3-Hydroxypropanoic Acid
This compound dehydrates readily because the C=C bond being formed is conjugated with the C=O group. The product is propenoic acid.
HOCH₂CH₂COOH → CH₂=CHCOOH + H₂O
3) 4-Hydroxybutanoic Acid
In this molecule, rotations about the C-C bonds frequently bring the O atom of the alcohol close to the C=O group. Thus, it is easy to form a cyclic ester (a lactone).
The formation of a 5-membered ring is especially favourable because it introduces no bond angle strain.
The reaction is so fast that it needs only gentle warming, at most.
The product is butano-4-lactone.
