toluene-4-sulfonic acid Ambient temperature;

1.1: phosphorus tribromide / dichloromethane / 1 h / 0 °C / |Inert atmosphere 1.2: 8 h / 20 °C / |Inert atmosphere 2.1: toluene-4-sulfonic acid / neat liquid / 8 h / 25 - 30 °C / |Inert atmosphere View Scheme