Abstract The promoting effect of ultrasound on the selective reduction of nitroarenes to N- arylhydroxylamines by use of Zn in an environmentally benign CO 2–H 2 O system has been demonstrated. The yield of N-phenylhydroxylamine reaches 95% when the reaction is carried out with a Zn-to-nitrobenzene molar ratio of 2.2 under ultrasound (40 kHz) at 25° C and normal pressure of CO 2 for 60 min. Application of ultrasound to the reaction has the ...