Chlorobenzene
Definition and meaning of Chlorobenzene in chemistry.
Chlorobenzene is an aromatic organic compound in which one hydrogen atom of benzene is replaced by a chlorine atom, giving the formula C6H5Cl. It is a colorless, volatile liquid with a characteristic almond-like odor.
In more detail
Chlorobenzene is produced industrially by electrophilic aromatic substitution: benzene reacts with chlorine gas in the presence of a Lewis acid catalyst such as FeCl3, which polarizes the Cl-Cl bond so the ring can attack it, releasing HCl as a byproduct. Because chlorine's lone pair delocalizes into the aromatic ring through resonance, the C-Cl bond gains partial double-bond character, making it much less reactive toward nucleophilic substitution than the C-Cl bond in an alkyl chloride. Consequently, converting chlorobenzene to phenol requires forcing conditions, historically the Dow process (concentrated NaOH, ~350°C, high pressure). It remains an important industrial solvent and synthetic intermediate for phenol, aniline, and various pesticides.
Key facts
| Formula | C6H5Cl |
|---|---|
| Molar Mass | 112.56 g/mol |
| Boiling Point | 131.7 °C |
| Field | Organic Chemistry |
Treating benzene with Cl2 gas over an FeCl3 catalyst at room temperature substitutes one ring hydrogen with chlorine, producing chlorobenzene and HCl gas.
Frequently asked questions
Why doesn't chlorobenzene undergo nucleophilic substitution as readily as alkyl halides?
The chlorine lone pair conjugates with the aromatic pi system, giving the C-Cl bond partial double-bond character that shortens and strengthens it, so typical SN1/SN2 pathways are strongly disfavored without harsh conditions.
What is chlorobenzene used for?
It is used as an industrial solvent and as a key intermediate in manufacturing phenol, aniline, and various pesticides, most notably DDT historically.