Question

What happens when — (write chemical equation only):
i) Phenol reacts with Br$_2$ water?
ii) Acetylation of phenol happens in the presence of pyridine?
iii) Phenol is heated with PCl$_5$?
iv) Phenol reacts with NaOH?
v) Vapour of the mixture of phenol and methyl alcohol is passed through hot thoria (ThO$_2$)?

Hint:

Phenol is strongly activated: Br$_2$(aq) gives 2,4,6-tribromophenol instantly.
Aryl–OH is not converted to aryl chloride by PCl$_5$; use diazonium route for Ar–Cl.
Hot thoria catalyzes vapour-phase O-alkylation to anisole.

Answer 1

i) Phenol + Br$_2$(aq):
\[ \mathrm{C_6H_5OH + 3\,Br_2 \;\rightarrow\; 2,4,6\!-\!C_6H_2Br_3OH \downarrow + 3\,HBr} \] (Product: 2,4,6-tribromophenol, white ppt.)
ii) Acetylation (pyridine as base):
\[ \mathrm{C_6H_5OH + CH_3COCl \xrightarrow{pyridine} C_6H_5OCOCH_3 + HCl} \] (Product: phenyl acetate)
iii) Phenol + PCl$_5$ (on heating):
\[ \text{No reaction (aryl–OH is not replaced by Cl by PCl}_5\text{).} \] iv) Phenol + NaOH:
\[ \mathrm{C_6H_5OH + NaOH \;\rightarrow\; C_6H_5ONa + H_2O} \] (Product: sodium phenoxide)
v) Vapours over hot ThO$_2$ (vapour‐phase alkylation):
\[ \mathrm{C_6H_5OH + CH_3OH \xrightarrow{ThO_2,\;\Delta} C_6H_5OCH_3 + H_2O} \] (Product: anisole)