Synergistic effect of PEG-coated ZnO nanoparticles and ultrasonic irradiation on the C–B bond cleavage of aryl boronic acids

Abstract

Phenol and its derivatives are significant constituents for bioactive molecules which are also used as herbicides, insecticides and fungicides. The conventional methods to synthesize phenols and their derivatives involve complex procedures, harsh conditions, toxic chemicals and mostly transition metal-based homogeneous catalysts. Herein we intend to use a mild, green and ecofriendly protocol to synthesize phenol and its derivatives under ultrasonic vibration. Accordingly, a simplistic method has been developed to synthesize ZnO nanostructures by precipitation technique using a biodegradable polymer, polyethylene glycol (PEG) at 60 °C. The synthesized ZnO nanostructures have been characterized by different instrumental techniques. XRD studies confirmed the formation of well crystalline ZnO possessing hexagonal phase wurtzite structure. Electron microscopy study revealed that the additive plays an important role in controlling the size and morphology of the formed nanostructures. The optical spectroscopy studies confirmed the presence of various absorption and emission peaks originating due to various defects in the materials. The synthesized ZnO nanostructures efficiently catalyze the ipso-hydroxylation of various substituted aryl boronic acids, aliphatic boronic acid and aryl boronic acids containing heterocycles as well as sterically hindrance group with excellent yield under green and cost-effective environment using as low as 0.06 mL H2O2 in 3 min under ultrasonic vibration. The synthesized ZnO nanostructures are highly stable possessing excellent recyclability up to 6th runs with minimal loss of activity.