Ultrasound assisted intensified synthesis of 1-benzyloxy-4-nitrobenzene in the presence of phase transfer catalyst

Abstract

In the present work, the intensification of phase transfer catalyzed reaction has been investigated based on the use of ultrasound. The synthesis of 1-benzyloy-4-nitrobenzene from 1-chloronitrobenzene and benzyl alcohol catalyzed using potassium hydroxide flakes and also tetrabutylammonium bromide (TBAB) as a phase transfer catalyst (PTC) has been studied in the presence of ultrasound (40 kHz, 200 W) and organic solvent. It was established that the use of ultrasound in a batch mode of operation intensified the reaction in terms of higher conversion. The effect of different operating parameters such as agitation speed, frequency, ultrasonic power, type of phase transfer catalyst and loading, temperature, concentration of 4-chloronitrobenzene, volume of solvent, type of solvents and duty cycle on the progress of the reaction for the ultrasound assisted approach have been studied. The obtained results in terms of conversion and product formation were analysed by Gas chromatography (GC) and Fourier Transform Infrared Spectrophotometer (FTIR) respectively. Reaction rate, in general, increased with an increase in the amount of quaternary ammonium salts i.e. the PTC, ultrasonic power, stirring speed and temperature but with a decrease in the volume of chlorobenzene, which was the solvent. The optimum conditions established were duty cycle of 50%, ultrasonic power of 200 W and temperature of 60 °C which resulted in maximum conversion of 98% in the presence of ultrasound. It was demonstrated that the ultrasound assisted phase transfer catalyst (US-PTC) based approach is more efficient than conventional approach giving higher conversion of 4-chloronitrobenzene.