PALLADIUM-CATALYZED SYNTHESIS OF N,N'-DIPHENYLUREA FROM NITROBENZENE, ANILINE, AND CARBON-MONOXIDE

N,N'-Diphenylurea has been synthesized from nitrobenzene, aniline, and carbon monoxide in a batch reactor at 80-160-degrees-C and 15-75 bar. Homogeneous catalyst systems consisting of a palladium(II) salt, an onium salt, and triphenylphosphine dissolved in xylene or toluene were found to be highly efficient, giving isolated urea yields up to 98% at 100% nitrobenzene conversion. The effects of catalyst composition and other reaction variables were studied. The reaction consumed more aniline than nitrobenzene on a molar basis, suggesting the existence of a new reaction path in addition to the well-known path of the reaction consuming equimolar nitrobenzene and aniline. The presence of excess aniline was essential in order to reuse the catalyst system for new batches without appreciable loss of activity.