Chlorotoluenes are aryl chlorides based on toluene in which at least one aromatic hydrogen atom is replaced with a chlorine atom. They have the general formula C<sub>7</sub>H<sub>8âÂÂn</sub>Cl<sub>n</sub>, where n = 1âÂÂ5 is the number of chlorine atoms.
Monochlorotoluenes are chlorotoluenes containing one chlorine atom. There are three isomers, each with the formula C<sub>7</sub>H<sub>7</sub>Cl.
The isomers differ in the location of the chlorine, but have the same chemical formula. All have very similar boiling points, although p-chlorotoluene has a much higher melting point due to a more tightly packed crystal structure.
Benzyl chloride is an isomer, which has a chlorine substituted for one of the hydrogens of toluene's methyl group, and it is sometimes named ñ-chlorotoluene.
A laboratory route to 2- and 4-chlorotoluene proceeds from 2- and 4-toluidines (i.e. 2- and 4-aminotoluene). These compounds are diazotized followed by treatment with cuprous chloride. Industrially, the diazonium method is reserved for 3-chlorotoluene. The industrial route to 2- and 4-chlorotoluene entails direct reaction of toluene with chlorine. The more valuable 4-chlorotoluene is separated from 2-chlorotoluene by distillation. Distillation cannot be applied to separating 3-chlorotoluene from 4-chlorotoluene.
2- and 4-chlorotoluene are precursors to the corresponding benzyl chloride (ClC<sub>6</sub>H<sub>4</sub>CH<sub>2</sub>Cl), benzaldehyde (ClC<sub>6</sub>H<sub>4</sub>CHO), and benzoyl chloride (ClC<sub>6</sub>H<sub>4</sub>C(O)Cl). 2- and 4-chlorotoluenes are converted to 2-chlorobenzonitrile and 4-chlorobenzonitrile, respectively. Chlorotoluenes are precursors to dichlorotoluenes.