Ultrasound assisted synthesis of N-aryl indole under multi-site phase-transfer catalyst: A kinetic study

The ultrasound assisted preparation of 1-benzyl-1-indole (arylation) from the reaction of benzyl chloride (BC) and indole was carried out successfully using solid sodium hydroxide and catalyzed by multi-site phase-transfer catalyst (MPTC) viz., 1,4-benzyl-1,4-diazoniabicyclo[ 2.2.2]octanium dichloride in a solid–liquid reaction condition (SL-PTC). Water was introduced in a trace quantity to the reaction system to avoid a serious hydration of active intermediate. The potentiality of the multi–site phase-transfer catalyst was demonstrated by following the kinetics arylation of indole under pseudo–first order conditions by employing aqueous sodium hydroxide and indole in excess. The reaction was monitored by gas Chromatography. The synthesized MPTC and 1-benzyl-1-indole were characterized by 1H NMR and 13C NMR. The reaction is greatly enhanced in the solid–liquid system, catalyzed by multi-site quaternary ammonium salt (MPTC) and ultrasound irradiation (28 kHz, 300W) in a batch reactor.