Ultrasonic synthesis of benzaldehyde from benzyl alcohol using H2O2:: Role of ultrasound

Ultrasound was used in the presence of hydrogen peroxide as the oxidant to synthesize benzaldehyde from benzyl alcohol. A commercially available homogeneous catalyst (heteropolyacid) and a phase-transfer catalyst (PTC) were used for the reaction. The effects of various parameters, such as solvent, amount of PTC, bulk temperature, mechanical agitation, concentration of hydrogen peroxide, amount of aqueous phase, amount of homogeneous catalyst, and benzyl alcohol concentration, on the extent of reaction have been studied. The kinetics of the reaction has also been studied. Enhancements in rates and selectivity of the benzaldehyde were observed in the presence of ultrasound as compared to their silent counterpart. The increased rates of reaction and selectivity are explained on the basis of ultrasonically generated cavitational effects. The work presented here clearly highlights the methodology to be followed for investigating the optimum extent of intensification achieved as a result of the use of ultrasound as compared to the conventional methods and should be followed by the design engineers to investigate a particular application in question.