Chlorination of Toluene to o-Chlorotoluene Catalyzed by Ionic Liquids

Ionic liquids with [BMIM], [Et3NH], and [BPy] cations and AlnCl−3n+1, ZnnCl−2n+1, and CunCl−n+1 anions were used as the catalysts for the chlorination of toluene with Cl2. The ZnnCl−2n+1 containing ionic liquids with high Lewis acid strength had high catalytic activity for the selective chlorination of toluene to o-chlorotoluene via the electrophilic substitution reaction. Dichlorotoluenes were favorably formed when the AlnCl−3n+1 containing ionic liquids with both Lewis and Brönsted acid sites were used as the catalysts. When the CunCl−n+1 containing ionic liquids with weak Lewis acid strength were used as the catalysts, more benzyl chloride was formed via the radical chlorination of methyl group. When the [BMIM]Cl-2ZnCl2 ionic liquid was used as the catalyst, after reacting at 80 °C for 8 h, the conversion of toluene was 99.7% and the selectivities of o-chlorotoluene, p-chlorotoluene, m-chlorotoluene, benzyl chloride, and dichlorotoluenes were 65.4%, 26.0%, 4.0%, 0.4%, and 4.2%, respectively. The [BMIM]Cl-2ZnCl2 ionic liquid catalyst had good recycling performance.