Q.Write Dow process for preparation of Phenol. What is the action of bromine water on phenol? Give reason: Group 16th elements have lower ionisation enthalpy compared to group 15th elements. Write two uses of dioxygen.

Four short answers: industrial phenol synthesis, phenol's characteristic bromination, an ionisation-enthalpy trend explained by half-filled-shell stability, and everyday uses of $O_2$.

Dow process for phenol: chlorobenzene is heated with aqueous NaOH (about 10%) under high temperature and pressure (≈623 K, 300 atm) with a copper catalyst, giving sodium phenoxide, which is then acidified to liberate phenol:

$C_6H_5Cl + 2NaOH \xrightarrow[Cu]{623K,\ 300\ atm} C_6H_5ONa + NaCl + H_2O$

$C_6H_5ONa + HCl \rightarrow C_6H_5OH + NaCl$

Action of bromine water on phenol: the $-OH$ group strongly activates the benzene ring towards electrophilic substitution (o,p-directing), so phenol reacts readily with bromine water at room temperature (without needing a catalyst) to give a white precipitate of 2,4,6-tribromophenol:

$C_6H_5OH + 3Br_2(aq) \rightarrow 2,4,6\text{-}Br_3C_6H_2OH\downarrow + 3HBr$

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