*2.2.2. Reactions of phenols*

Phenolic compounds behave as nucleophiles in most of their reactions and also the reagents that interact on them behave as electrophiles. In phenolic compounds, the site of nucleophilic reactivity may occur at the hydroxyl group or the aromatic ring. The reactions are carried out on the aromatic ring results in electrophilic aromatic substitution [7].

*Halogenation*: Bromination and chlorination of phenols occur easily even in the absence of a catalyst. Substitution occurs primarily at the para position to the hydroxyl group. When the para position is blocked, ortho‐substitution is carried out.

*Nitration*: Phenol reacts with dilute nitric acid in either water or acetic acid. It is not necessary to use mixtures of nitric and sulfuric acids, due to the high reactivity of phenolic compounds. The o‐nitrophenol is a phenolic compound ortho‐substituted and therefore, this compound has considerably lower boiling point than the meta and para isomers. This is due to the hydrogen bond that is produced between the hydroxyl group and the substituent partially compensates for the energy required to go from the liquid to the vapor phase.

*Nitrosation*: The nitrosonium ion [N ≡ O<sup>+</sup> ] is obtained during the acidification of sodium nitrite, which is a weak electrophile and reacts with the strongly activated ring of a phenol. The resulting product is a nitrosophenol.

*Sulfonation*: The sulfonation of the ring can be carried out by reacting phenol with concen‐ trated sulfuric acid.

*Friedel‐Crafts alkylation*: Alcohols in combination with acids serve as sources of carbocations. Attack of a carbocation on the electron ring of a phenol results in the alkylation.

*Oxidation of phenols: quinones*: Phenols do not undergo oxidation in the same way that alco‐ hols do because they do not have a hydrogen atom on the hydroxyl‐bearing carbon. Instead, oxidation of a phenol yields a cyclohexa‐2,5‐diene‐1,4‐dione, or quinone [8].
