Differences between lactic acid and glycolic acid

Lactic acid and glycolic acid are both organic carboxylic acids, but they also have many differences.

First of all, its structure. The structure of lactic acid contains a methyl group connected to the α-carbon atom, and its chemical formula is\ (C_ {3} H_ {6} O_ {3}\). The structure of glycolic acid is relatively simple, containing only a hydrogen atom connected to the α-carbon atom, and the chemical formula is\ (C_ {2} H_ {4} O_ {3}\). The structure is different, so its physical properties are also different.

Looking at the physical properties, lactic acid is mostly a colorless clear or slightly yellow viscous liquid at room temperature, with a slightly sour taste. Because of the formation of hydrogen bonds between molecules, the boiling point is high. Glycolic acid is often a white crystal with a relatively high melting point and good solubility in water, because both carboxyl and hydroxyl groups can form hydrogen bonds with water.

Re-discussion of chemical properties. Lactic acid is chiral and has optically active isomers. Its chemical activity is different from that of glycolic acid due to the presence of methyl groups. In some reactions, the reaction rate is different from that of glycolic acid. Glycolic acid has a relatively simple structure and a small space barrier to the reaction check point. In some reactions such as nucleophilic substitution or esterification, the reaction activity may be different. And the acidity of the two is also different. Although both are weak acids, the acidity of glycolic acid is slightly stronger than that of lactic acid. Because the electron-giving effect of the carboxyl group in glycolic acid is weaker than that of the methyl group in lactic acid, the carboxyl hydrogen is easier to dissociate.

The application of the two is also different. Lactic acid is used in the food industry as a sour agent and preservative, because it can adjust the acidity of food and has a certain bacteriostatic effect. In the field of medicine, it can be used to prepare slow-release drug carriers because of its biodegradability. Glycolic acid is mostly used in cosmetics, as a common fruit acid component, which can exfoliate and improve skin texture. In the chemical industry, it can be used to prepare degradable polyester materials, which can be condensed with polyols due to their good reactivity.

In summary, although lactic acid and glycolic acid have similarities, there are obvious differences in structure, physicochemical properties and applications, and they each develop their strengths in different fields.