Catalysis of Organic..

Gelder, Jackson and Lok 169hydrogenation reaction profile also displays very different behavior to thenitrobenzene hydrogenation reaction profile (Figure 1).10080Mol % in solution6040NSBAZOXYA20AZO00 20 40 60 80 100 120Time (min)Figure 1. Reaction profile of nitrosobenzene hydrogenation.In the reaction profile shown in Figure 1 (similar to that shown by Smith etal. (10)) the initial product was azoxybenzene. However this figure is deceptive;firstly azoxybenzene may be produced by a non-catalyzed reaction betweennitrosobenzene and phenyl hydroxylamine (10), secondly the figure does notshow the mass balance. Indeed at 10 min when all nitrosobenzene has beenremoved from the solution the amount of azoxybenzene formed was 18.6 mmol,equivalent to 37.2 mmol of reacted nitrosobenzene. Therefore, 42.8 mmol of theoriginal 80 mmol of nitrosobenzene (53.5 %) were unaccounted for. It ispossible that the missing mass is in the form of phenyl hydroxylamine insolution, which continues to disproportionate to produce aniline andnitrosobenzene and subsequently azoxybenzene and azobenzene. However aswe shall subsequently discover this interpretation is unsustainable.Azobenzene was also present during the hydrogenation of nitrosobenzeneand a stepwise hydrogenation process of nitrosobenzene to azoxybenzene toazobenzene to aniline is a credible route. No azoxybenzene was observedduring the hydrogenation of nitrobenzene.The hydrogenation of nitrobenzene and nitrosobenzene were also studiedusing deuterium. The hydrogen/deuterium up-take graphs are shown in Figures2 and 3.