Properties Of Hydroxy Acids

1. α-hydroxy acid (QIANG JI SUAN)
That is, the hydroxyl group is located at the α position (the carbon atom directly connected to the carboxyl carbon atom). The -COOH interaction of this type of hydroxyl acid is more active, has strong reducing properties, and can even undergo a silver mirror reaction. (General textbooks only introduce that the aldehyde group can undergo this reaction, which is actually incorrect.) After being heated, dehydration and ring formation between two molecules can easily occur, forming lactide.
2. β-Hydroxy acid
The classification is the same as above. The two groups in this category are not active enough, but because for them, the H on the carbon position between the two carbon positions is α-H, the two H's of the molecule are both active H , so it is also very active, but this substance does not undergo silver mirror reaction. After being heated, intramolecular dehydration easily occurs to generate unsaturated acid.
3. γ-hydroxy acid and δ-hydroxy acid
After being heated, intramolecular dehydration can easily occur to form a ring and produce lactone.
4. ε and above hydroxy acids
After being heated, it is easy for many molecules to lose water and grow into chains (linear polycondensation).