Sonochemical bromination of acetophenones using p-toluenesulfonic acid–N-bromosuccinimide

Substituted acetophenones react with N-bromosuccinimide (NBS) and p-toluenesulfonic acid (p-TsOH) in the presence of ultrasound in methanol at 35±2°C to give α-bromoacetophenones in high yield. In the absence of ultrasound the reaction takes place at the boiling point of methanol (65°C) and takes longer time. The reaction does not take place in the absence of p-TsOH thermally or sonically. However the reaction is possible under photochemical conditions in the absence of p-TsOH. The best solvent for the reaction was found to be methanol.