Classification Of Hydroxy Acids

According to their structure, they can be divided into two categories: aliphatic hydroxy acids and aromatic hydroxy acids.
1. Aliphatic hydroxy acid
Aliphatic hydroxy acids, also known as alkyds, can be divided into: based on the position of the hydroxyl group attached to the carbon atom of the carboxylic acid:
(1) α-hydroxy acid, such as α-hydroxypropionic acid (lactic acid), when heated, two molecules of acid can remove two molecules of water and form lactide.
(2) Beta-hydroxy acid. When heated, one molecule of acid can remove a molecule of water to form an unsaturated acid. For example, beta-hydroxybutyric acid can be dehydrated to form crotonic acid.
(3) γ-hydroxy acid and δ-hydroxy acid, such as γ-hydroxybutyric acid OH-CH2CH2CH2·COOH. When heated, one molecule of acid removes one molecule of water to form lactone. Aliphatic hydroxy acids are generally crystals that are easily soluble in water, and their melting points and solubility in water are higher than those of the corresponding fatty acids. There are both alcohol reactions and acid reactions.
2. Phenolic acid
Phenolic acids contain hydroxyl groups on the aromatic nucleus (benzene ring or condensed benzene ring) in aromatic hydroxy acids. For example, phenolic acids can participate in various reactions unique to acids and phenols, and can also perform halogenation, nitration, sulfonation, etc. reaction.