Hydroxy acid is also called hydroxy carboxylic acid, that is, the molecule contains both hydroxyl (- OH) andcarboxyl(- COOH)chemical compound, is a class of organic compounds,
According to its structure, it can be divided intoAliphatic groupHydroxy acids and aromatic hydroxy acids.
Hydroxy acid is a kind of acid with hydroxyl - OH andcarboxyl- Compounds of COOH.With acidity, the carboxyl group in the molecule can ionize hydrogen ions
Esterification of hydroxy acids
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Hydroxy acid molecule contains hydroxyl and carboxyl, two functional groups that can interact with each other, so hydroxy acid can undergo both intramolecular esterification and intermolecular esterification[1]
Molecular lactonization - lactone formation
Molecular lactonization - lactone formation
γ - hydroxy acid and δ - hydroxy acid form lactones under neutral or acidic conditions;Under alkaline conditions, lactones can be opened to form carboxylates, and then become lactones after acidification[2]
Intermolecular esterification - lactide formation
Intermolecular esterification - lactide formation
When heated, α - hydroxy acids are prone to intermolecular esterification to form lactides[3]
polymerization
polymerization
Hydroxyl acids with a strong tendency to form five membered and six membered cyclolactones[4], other hydroxyl acids under the action of appropriate esterification catalyst[4]And continuously removing water during the reaction process to obtain polyester with high relative molecular weight[4]。Proton acid or Lewis acid commonly used as catalyst[4]；If high temperature is required, Sb ₂ O is commonly used to avoid hydroxyl dehydrationthreeZn(OAc)twoIsobasic catalyst[4]
classification
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According to its structure, it can be divided intoAliphatic groupHydroxy acids and aromatic hydroxy acids.
Aliphatic hydroxy acid
Aliphatic hydroxyl acid, also called alkyd, is based on thecarbon atomThe position on the can also be divided into: (1) α - hydroxy acid, such as α - hydroxypropionic acid（lactic acid）When heated, the two molecules of acid can remove the two molecules of water and form ester.（2）β - hydroxy acidDuring heating, a molecule of acid can be removed from a molecule of water to form an unsaturated acid, for example, β - hydroxybutyric acid can be dehydrated to formButenoic acid。（3）Gamma hydroxy acidAnd δ - hydroxy acids, such as γ - hydroxybutyric acid OH - CH2CH2CH2 · COOH, which is formed by removing a molecule of water from a molecule of acid during heatinglactone。Aliphatic hydroxy acids are generally soluble in watercrystal, melting point and in watersolubilityAre higher than the corresponding fatty acids.There are reactions of both alcohol and acid.
Phenolic acid
Aromatic Nuclei in Aromatic Hydroxy Acids（benzene ringOr fused benzene ring)Phenolic acidFor example, phenolic acid can participate in various reactions unique to acids and phenols, and can also carry out halogenation, nitration, sulfonation and other reactions.
Properties of hydroxy acid
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QIANG JI SUAN
That is, the hydroxyl group is located at the α position (andcarboxylThe carbon atoms directly connected to each other), and the COOH interaction of this kind of hydroxyl acids is relatively active,
The classification is the same as above. The two groups of this type are not active enough, but for them, the H on the carbon site between the two carbon sites is α - H, and the two H of the molecule are active H, so they are also active, but this substance does not occurSilver mirror reaction。It is easy to generate unsaturated acid by intramolecular dehydration after heating.
γ - hydroxy acid and δ - hydroxy acid
When heated, it is easy to dehydrate into rings within the molecule and generatelactone。
