Animated Solution for Chemistry - Organic Chemistry: The above reaction requires which of the following reaction conditions?

Imagine trying to break a stick that is reinforced with steel. That is exactly what it feels like to perform a nucleophilic substitution on an aryl halide like chlorobenzene.

In a typical alkyl halide, the carbon-halogen bond is a simple single bond, making it relatively easy for a nucleophile (like $O{H}^{-}$) to swoop in and kick out the halogen. However, chlorobenzene plays by a different set of rules. The chlorine atom possesses lone pairs of electrons. Because it is attached directly to an $s{p}^2$ hybridized carbon of the benzene ring, these lone pairs can delocalize into the $\pi$-electron system of the ring.

This resonance effect creates a partial double bond character between the carbon and the chlorine atom. A double bond is significantly shorter and stronger than a single bond, meaning the activation energy required to break it skyrockets. Consequently, aryl halides are notoriously unreactive towards normal nucleophilic substitution reactions.

Brute Force Chemistry

So, how do we force chlorobenzene to react and yield phenol (or its salt, sodium phenoxide)? The answer lies in brute force.

Since the bond won't break under mild conditions, chemists employ drastic measures. By subjecting the reaction mixture to an intensely high temperature of $623\text{ K}$ and a crushing pressure of $300\text{ atm}$, the molecules are given enough kinetic energy to overcome the massive activation barrier.

This industrial method of manufacturing phenol from chlorobenzene is famously known as the Dow Process. Under these extreme conditions, the $O{H}^{-}$ nucleophile successfully displaces the chloride ion, forming sodium phenoxide ($C_6{H}_5{O}^{-}N{a}^{+}$).

Matching our chemical knowledge with the given options, the exact conditions required for this transformation are $623\text{ K}$ and $300\text{ atm}$. Therefore, the correct choice is clearly option (d).