The direct amination of benzene to aniline with hydroxylamine catalyzed by sodium metavanadate in acetic acid water under mild conditions took place more efficiently in open air than in a closed system. The presence of oxygen significantly enhanced the yield of aniline. Satisfactory aniline yield (64%) and turnover number (48 mol of aniline per mol of vanadium) were obtained under optimized reaction conditions. The decomposition of hydroxylamine was studied to understand its function during the amination process. A computational study on the UV-vis spectra of some typical vanadium complexes was carried out by the time-dependent DFT method. A free-radical mechanism is proposed based on the results of EPR, V-51 NMR, and UV-vis characterizations. (c) 2006 Elsevier Inc. All rights reserved.