A method for producing aniline or toluenediamine is disclosed which comprises forming a dispersion comprising hydrogen gas bubbles dispersed in a liquid medium comprising either nitrobenzene or dinitrotoluene, wherein the hydrogen gas bubbles have a mean diameter less than 1 micron; and subjecting the dispersion to hydrogenation reaction promoting conditions comprising pressure less than about 600 kPa and temperature less than about 200.degree. C., whereby at least a portion of the nitrobenzene or dinitrotoluene is hydrogenated to form aniline or toluenediamine, respectively. A system for carrying out the method is also disclosed.