The acidity of carboxylic acid is stronger than that of phenol

Carboxylic Acid Acidity Than Phenol Strong Cause Analysis

In chemistry, acidity is a measure of a substance's ability to release hydrogen ions, and differences in acidity of different compounds are often discussed. A common problem is that "carboxylic acids are more acidic than phenols". The answer to this question is yes, carboxylic acid is indeed more acidic than phenol. We will analyze the causes of this phenomenon in detail, and discuss the molecular structure, reaction mechanism and other aspects in depth.

THE MOLECULAR STRUCTURE AND ACIDITY RELATIONSHIP OF CARBOXYLIC ACIDS

One of the core factors of acidity is molecular structure. The molecular structure of carboxylic acid contains a carboxyl group (-COOH), which makes it easier for carboxylic acid to release hydrogen ions (H) in water. In aqueous solution, the carboxyl group of a carboxylic acid can ionize with a water molecule to form a hydrogen ion and a carboxylate ion (R-COO-). Because the carboxylate ion is stable, the molecule tends to lose hydrogen ions, which makes the carboxylic acid more acidic.

In contrast, phenol has a molecular structure in which the hydroxide group (-OH) is directly attached to the benzene ring. In aqueous solution, the oxygen atoms of phenol combine with hydrogen atoms to form hydrogen ions, but phenol has less tendency to release hydrogen ions. Therefore, phenol is less acidic than carboxylic acid.

Conjugate base stability of carboxylic acids and phenols

In addition to the molecular structure, the strength of the acid is also related to the stability of the conjugate base of the acid. Conjugate base refers to the negative ion formed after the acid loses its hydrogen ion. For carboxylic acids, the carboxylate ion (R-COO-) formed after the loss of the hydrogen ion is relatively stable, because this negative charge can be dispersed by the resonance effect between the two oxygen atoms. This dispersion of electrons increases the stability of the conjugate base, which drives the release of hydrogen ions.

The phenoxide ion (C6H5O-) formed after the loss of hydrogen ions in phenol, although it can also disperse negative charges through the resonance effect of the benzene ring, is far less stable than the carboxylate ion. The negative charge of the phenoxide ion is mainly concentrated on the oxygen atom, and the stability is poor, so the ability of phenol to release hydrogen ions is weak, and the acidity is relatively weak.

acidic than phenol experimental data support

Through the experimental data, we can further verify the conclusion that the acidity of carboxylic acid is stronger than that of phenol. For example, on the acidity value (pKa value), carboxylic acids generally have a lower pKa value, meaning that they release hydrogen ions more readily in water. The pKa value of phenol is generally higher, indicating that it does not readily release hydrogen ions in water. It is clear from these experimental data that carboxylic acids are much more acidic than phenol.

Summary

The phenomenon of "the acidity of carboxylic acid is stronger than that of phenol" can be explained from the aspects of molecular structure, stability of conjugate base and experimental data. The carboxyl structure of carboxylic acid and the stability of its conjugate base make the carboxylic acid have strong acidity, while the acidity of phenol is weak, mainly due to its molecular structure and the stability of the conjugate base is low. Understanding these factors is important for the prediction and practical application of chemical reactions.