Dow's Process (Aryl Halide Reactivity)

$$\text{C}_6\text{H}_5\text{Cl} + 2\text{NaOH} \xrightarrow{623\text{ K}, \, 300\text{ atm}} \text{C}_6\text{H}_5\text{ONa} \xrightarrow{\text{H}^+} \text{C}_6\text{H}_5\text{OH}$$

Concept: Chlorobenzene requires drastic conditions ($$623\text{ K}$$, $$300\text{ atm}$$) to undergo nucleophilic aromatic substitution because the $$\text{C--Cl}$$ bond exhibits partial double bond character due to resonance with the benzene ring.

• Electron-withdrawing groups ($$-\text{NO}_2$$) at ortho and para positions significantly increase reactivity towards nucleophilic aromatic substitution $$S_N\text{Ar}$$
• Meta-positioned $$-\text{NO}_2$$ groups have negligible effect on reactivity.