Question

Identify the reagents A and B used in the following reactions:
$C_6{H}_{5}OH\stackrel{A}{\to }{C}_6{H}_6\stackrel{B}{\to }{C}_6{H}_{5}Cl$
A. $Sn/HCl,C{l}_2/hv$
B. $C{l}_2/hv,Zn$
C. $C{l}_2/Fe,FeC{l}_3$
D. $Zn,C{l}_2/FeC{l}_3$

Answer 1

Hint: $C_6{H}_{5}OH$ is the formula of phenol. In this reaction, the reduction of phenol occurs and it gets converted into benzene. The formula of benzene is $C_6{H}_6$ . Benzene further reacts and one hydrogen gets replaced by chlorine, a halogen to form chlorobenzene.

Complete step by step answer:
The reaction is completed in 2 steps: first is reduction reaction (removal of oxygen or addition of hydrogen to a carbon atom) and the second is electrophilic substitution reaction (electrophile displaces the functional group in a compound, mainly hydrogen atom). Phenol reacts with $Zn$ dust, gets reduced, and converted into benzene because $Zn$ dust acts as a reducing agent. Then benzene further reacts with $C{l}_2$ (Chlorine) and $FeC{l}_3$(Ferric chloride) to form (Chlorobenzene ) $C_6{H}_{5}Cl$ . It is an electrophilic substitution reaction.
$C_6{H}_{5}OH\stackrel{Zn}{\to }{C}_6{H}_6\underset{FeC{l}_3}{\overset{C{l}_2}{\to }}{C}_6{H}_{5}Cl$
A = $Zn$ dust
B = $C{l}_2/FeC{l}_3$

So, the correct answer is Option D .

Additional Information:
Mechanism of the reaction is $Zn$ shows an oxidation state of $+2$. It itself oxidized into $ZnO$ and phenol converted into phenoxide ion due to removal of hydrogen ion and proton thus releasing an electron from zinc to form $H$ radical. After that carbon and oxygen bond breaks to form phenyl radical which combines with hydrogen radical to benzene. Thereafter, benzene reacts with chlorine. The $C{l}_2$ breaks into $C{l}^{-}$ and $C{l}^{+}$ where $C{l}^{-}$ attacks ferric chloride to form $FeC{l}_4^{-}$ and $C{l}^{+}$ attacks benzene. The addition of chlorine to the ring of the benzene results in the formation of chlorobenzene and released hydrogen from ring attacks $FeC{l}_4^{-}$ to form $FeC{l}_3$ and $HCl$ .

Note:
We use zinc dust instead of zinc granules because it can produce hydrogen gas at a faster rate. It happens due to an increase in surface areas results in increases in the rate of reaction. It is a bluish-gray powder with odorless and insoluble water.