Phenols are the chemical compounds that have a benzene ring linked to a hydroxyl group. They are sometimes referred to as carbolic acids due to their extreme acidic character. Phenoxide is formed when phenols react with active metals like sodium and potassium. This interaction of phenol with metals suggests that it is acidic in nature. Benzonal is the IUPAC term for phenol. Phenol can be substituted using either one of the Ortho meta para or the numbering system. The parental molecule should be referred to as phenol in any situation, Cresols are common names given to some phenols, for example, phenols.

Phenols, like the aqueous sodium hydroxide, react to form phenoxide ions. This suggests that phenols are greater acidic in nature than alcohol and water molecules.

The Acidity of Phenols: An Explanation

The propensity of phenols to lose hydrogen ions and produce phenoxide ions accounts for their acidic nature.

The sp2 hybridized carbon atom of the benzene ring that is connected directly to the hydroxyl group works as an electron-withdrawing group in a phenol molecule.

The electronegativity of this sp2 hybridized carbon atom of a benzene ring connected directly to the hydroxyl group is greater compared to that of the hydroxyl group.

The electron density on the oxygen atom lowers due to the increase in electronegativity of this carbon atom in contrast to the hydroxyl group connected.

The reduction in electron density raises the polarity of the O-H bond, which results in increased phenol ionization.

As a result, a phenoxide ion is generated. The formation of a phenoxide ion is stabilized by the delocalization of the negative charge caused due to the resonance in the benzene ring.

Phenoxide ion is more stable than phenols because the charge separation occurs mostly during the resonance in the case of phenols. The delocalization of negative charge in phenoxide ions is explained by the resonance structures of the ions. The acidic nature of phenols rises in the presence of an electron-withdrawing group in the substituted phenols. This is all due to the phenoxide ion’s stability. The acidity of phenols rises much more if these groups are linked at ortho and para locations in the benzene. This is because the negative charge in the phenoxide ion is primarily delocalized in the ortho and para locations. The acidic nature of phenols, on the other hand, diminishes in the presence of electron-donating groups because they prevent the production of phenoxide ions.

Reaction Showing Acidic Nature Of Phenol

The acidic character of phenols can be represented by the two reactions given below:

1. When phenol interacts with sodium hydroxide, sodium phenoxide and water are produced as byproducts.
2. Phenol interacts with sodium to form sodium phenoxide, which releases H2.

The acidity of phenol is more than ethanol. This is because after losing a proton, the phenoxide ion undergoes resonance and gets itself stabilized, on the other hand the ethoxide ion does not/can not.

Resonance of Phenol

The ion or the molecule is said to have resonance when more than one Lewis structure can be drawn with it.

Resonance is a notion in which electrons are delocalized across three or more atoms in a compound or molecule, and the Lewis structure of that molecule or compound cannot be represented as a single, uncomplicated structure.

Please take note that three of the four contributing structures have a positive charge on the oxygen atom in the molecule/compound. As a result, the real hybrid structure, in other words the final structure, must have some positive charge in it. Due to the fact that oxygen is an electronegative element, the electrons in the oxygen-hydrogen bond orbital gravitate to the oxygen atom i.e., move towards the oxygen atom resulting in partly positive hydrogen in the molecule.

When a hydrogen ion is lost to a base, it produces a phenoxide ion that is resonance stabilized. Also, notice how the phenoxide anion is formed when hydroxy hydrogen is removed by the base. As shown by the contributing structures, this anion is resonance stabilized by the delocalization of an electron pair across the molecule.

Properties of Phenol as an Acid

A number of the features of phenol, when combined with different kinds of solutions, are described below-

• Considering indicators

The pH value of a typical dilute phenol solution in water ranges between 5 and 6, depending on the concentration of phenol. It signifies that a very dilute solution is not acidic enough to eventually turn a litmus paper into crimson color. Litmus paper, on the other hand, will be blue at pH = 8 and red at pH = 5, if there is anything in between, it will be represented as a shade of “neutral” therefore the color won’t change. When phenol interacts with sodium hydroxide solution, it produces a colorless solution containing sodium phenoxide in it. The strongly basic hydroxide ion in the sodium hydroxide solution eliminated the hydrogen ion during the reaction.

• With Sodium Carbonate or Sodium Hydrogen Carbonate

Phenol is insufficiently acidic to react with any of these compounds. Carbonate and hydrogen carbonate ions, on the other hand, are not solid enough to extract a hydrogen ion from a phenol. Unlike most other acids, phenol does not emit carbon dioxide when combined with another compound. Furthermore, this lack of reactivity is highly beneficial, We can also identify phenol for the reasons shown below.

• It is water-soluble but not completely soluble.
• It must be acidic because it frequently interacts with the sodium hydroxide solution to form a colorless solution.

Conclusion-

As discussed above we are discussing the acidic nature of phenols. Phenols, like the aqueous sodium hydroxide, react to form phenoxide ions. This suggests that phenols are greater acidic in nature than alcohol and water molecules. We have even talked about the reactions which show the acidic nature of phenols. We have talked about the properties of phenol as an acid.