A facile oxidation conversion of cyclohexanone to e-caprolactone using molecular oxygen in a new type reactor-the airlift loop sonochemical reactor was studied. The influences of ultrasound intensity, reaction temperature, molar ratio of benzaldehyde to cyclohexanone and oxygen gas flow rate on the conversion and selectivity of cyclohexanone, were investigated and discussed. An optimized set of operating conditions was found and e-caprolactone production yield of 87.7% was achieved. The reactor plays a synergistic effect of sonochemsity and higher mass transfer. Possible reaction mechanism steps were outlined and the reasons of ultrasound promoting the reaction were analyzed. (c) 2006 Published by Elsevier B.V.