Ultrasound assisted regioselective sulfonation of aromatic compounds with sulfuric acid.

A simple and convenient methodology for selective sulfonation of aromatic compounds using sulfuric acid under sonication is described. The present methodology shows a considerable enhancement in the reaction rate along with improved selectivity compared with the reactions performed under silent conditions. The effect of various parameters such as agitation speed, sulfuric acid concentration, and temperature on reaction system have been investigated and are explained on the basis of ultrasonically generated cavitational effects.

Ultrasound promoted regioselective nitration of phenols using dilute nitric acid in the presence of phase transfer catalyst.

Phenols are selectively nitrated to o-nitrophenol along with rate enhancement using dilute nitric acid (6 wt%)/tetra butyl ammonium bromide (TBAB) under sonication. The selectivity can also be reversed to p-nitrophenol using NaBr as a catalyst. Kinetic analysis of nitration of phenol both with and without sonication has been investigated by variation of reaction parameters such as catalyst, nitric acid and substrate concentration.