Question

Explain the conversion of phenol to benzene.

Answer 1

Phenol

1. Phenol is an aromatic hydrocarbon with molecular formula$\left({\mathrm{C}}_6{\mathrm{H}}_5\mathrm{OH}\right)$.
2. It is more acidic than benzene due to the presence of hydroxyl group.
3. It losses proton easily to form phenoxide ion.
4. It undergoes electrophilic substitution reaction due to rich electron density.
5. It can be converted to benzene $\left({\mathrm{C}}_6{\mathrm{H}}_6\right)$ with help of Zn dust.

Benzene

1. Benzene is an aromatic hydrocarbon with molecular formula$\left({\mathrm{C}}_6{\mathrm{H}}_6\right)$
2. It has a planar structure.
3. It is less acidic than phenol, due to absence of electron withdrawing group.
4. It It undergoes electrophilic substitution reaction very easily, due to delocalization of electrons.

Conversion of phenol to benzene.

The following steps are involved in the conversion of phenol to benzene.

1. Formation of phenoxide ion: Phenol is converted into phenoxide ion by removing proton. These proton are converted into hydrogen free radical with the help of zinc dust. $$\begin{gathered} {\mathrm{C}}_6{\mathrm{H}}_5\mathrm{OH}\to {\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{O}}^{-}+{\mathrm{H}}^{+} \\ \mathrm{Phenol}\mathrm{Phenoxide}\mathrm{ion}\mathrm{Proton} \end{gathered}$$
2. Formation of phenyl radical: After formation of phenoxide ion, phenoxide ion gives away oxygen and it gets converted to phenyl radical, the removed oxygen is carried by Zn to form zinc oxide. .$$\begin{gathered} {\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{O}}^{-}\to {\mathrm{C}}_6{{\mathrm{H}}_5}^{.}+\mathrm{ZnO} \\ \mathrm{Phenoxide}\mathrm{ion}\mathrm{Pheyl}\mathrm{radical}\mathrm{Zinc}\mathrm{oxide} \end{gathered}$$
3. Formation of benzene: The phenyl radical combines with hydrogen radical to form benzene. $$\begin{gathered} {\mathrm{C}}_6{{\mathrm{H}}_5}^{.}+{\mathrm{H}}^{.}\to {\mathrm{C}}_6{\mathrm{H}}_5 \\ \mathrm{Pheyl}\mathrm{radical}\mathrm{Hydrogen}\mathrm{radical}\mathrm{Benzene} \end{gathered}$$

4. The overall reaction is:

Figure: Diagram of conversion of phenol to benzene.

Phenol is converted to benzene in the presence of zinc dust. The products formed in the reaction are benzene and zinc oxide.