The strength of salicylic acid and glycolic acid is related to many factors. Compared with glycolic acid, salicylic acid and glycolic acid have their own conditions.

Salicylic acid has phenolic hydroxyl groups and carboxyl groups. Its phenolic hydroxyl groups can cause the distribution of electron cloud density to change in the benzene ring, which has an impact on the acidity of carboxyl groups. However, although the benzene ring conjugated system can disperse the negative ion charge after the dissociation of the carboxyl group, the phenolic hydroxyl group can partially weaken the acidity of the carboxyl group.

Glycolic acid has only carboxyl groups, and its structure is relatively simple. It has no complex effects such as the phenyl ring of salicylic acid and the phenolic hydroxyl group. In the dissociation of hydrogen ions by carboxyl groups, the dissociation is easier

Looking at the acidity constants of the two, the acidity constant of glycolic acid is larger than that of salicylic acid. This shows that under the same conditions, glycolic acid is easier to dissociate hydrogen ions in water, and the acidity is stronger.

Furthermore, from the perspective of reactivity, the steric resistance around the carboxyl group of glycolic acid is small, the reagent is easier to approach the carboxyl group, and the participation activity is higher, which also shows that its acidity is relatively active. Salicylic acid has a large steric resistance due to the presence of benzene ring, and the carboxyl group reactivity is slightly limited.

In summary, the strength of glycolic acid is stronger than that of salicylic acid, which is due to the difference in structure and the different influence on carboxyl groups between the two.