Action of Heat on Hydroxy Acids

Action of Heat on α, β, γ, δ, ε-Hydroxy Acids

Action of Heat on α-Hydroxy Acids

Alpha-hydroxy acids on heating give cyclic ester called Lactide. Six membered cyclic ester forms between two alpha-hydroxy acids.

Action of Heat on β-Hydroxy Acids

Beta-hydroxy acids on heating with strong mineral acid give α, β-unsaturated acid. This reaction is similar to dehydration of alcohol to an alkene.

Action of Heat on γ-Hydroxy Acids

Gamma-hydroxy acids when heated undergo an intramolecular esterification to form a five membered cyclic ester or internal ester known as Lactone. The lactone produced from γ-hydroxy acid is known as γ-Lactone.

Action of Heat on δ-Hydroxy Acids

Delta-hydroxy acids also undergo intramolecular esterification to form a six membered cyclic ester or internal ester known as δ-Lactone

Action of Heat on ε-Hydroxy Acids

Epsilon-hydroxy acids in which -COOH & -OH groups are separated by five carbon atoms have little tendency to form lactones as seven membered ring is less stable. So, they undergo intermolecular esterification to form linear polyesters.
Higher hydroxy acids also form linear polyesters.