Modulating the hydroxylamine accumulation in the hydrogenation of substituted nitroarenes using vanadium-promoted RNi catalysts

The effect of vanadium promotion of Raney nickel on aryl hydroxylamine accumulation in the catalytic hydrogenation of electron deficient aromatic nitro compounds was investigated. High accumulation of 70–80% was observed with unmodified Raney nickel. Vanadium promoters were able to modulate the accumulation and depending on the modifier used, an increase (up to 86%) or a decrease (down to 11%) was found. Higher rates were obtained in the former (up to a factor 1.3), lower ones in the latter case (down to a factor 0.1) compared to the unmodified system. Supported or unsupported NH₄VO₃ was usually the most efficient modifier for obtaining low accumulation and reasonable rates, but the optimum concentration and modification procedure had to be determined for every substrate separately. In cases of low accumulation, the vanadium promoters worked as disproportionation catalysts. Dehalogenation was not significantly influenced by the presence of promoters: in all cases dehalogenation took only place after both the nitro arene and aryl hydroxylamine compound had been consumed completely. This revised version was published online in June 2006 with corrections to the Cover Date.