Hydrazine in the presence of Co3S4 was successful as an alternative hydrogen source for the conversion of nitrobenzene to aniline. The reaction observed does have a slower rate compared to that of sodium borohydride, but the slower rate provided the opportunity to analyze the kinetics of the reaction. GC and 1H-NMR spectra demonstrated the formation of PHA, a known intermediate for this reaction. The reaction showed a change in reaction order at ca. 150 minutes. At this time, the concentration of nitrobenzene was low while the concentration of PHA was relatively high. The conversions observed using GC suggest that the reaction follows a zero order mechanism (typical of catalyzed reactions) and then it changes to a second order mechanism in later stages of the reaction. The reaction kinetics was followed using 1H-NMR, which showed evidence of the formation of N-phenylhydroxyl amine (PHA) in relatively high concentrations. The presence of PHA in high concentration suggests that the initial step is a four-electron process. The reaction conditions can be manipulated to stop the reduction selectively at the PHA stage. It was demonstrated through 1H-NMR that the catalyst promotes of nitrobenzene to PHA and it also affects the reduction of PHA into aniline.

Kinetics of the reduction of nitrobenzene using hydrazine hydrate and cobalt (II) sulfide

249th National Meeting (2015)

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