The hydrogenation of aromatic nitriles to produce primary amines is of high importance within the agrichemical and pharmaceutical industries. Typically skeletal metal catalysts are used, however, in fine chemical applications the selectivity to the desired amine is often compromised by reduction of other functional groups. The use of a Pd/C catalyst in the liquid phase hydrogenation of various aromatic nitriles has been studied in order to assess the effectiveness of this type of catalyst for this class of reaction.On modifying the nitrile substituent and upon introducing conjugation, varying degrees of conversion were observed. Incomplete mass balance profiles were linked to spill-over to the carbon support and in the case of benzonitrile hydrogenation, a hydrogenolytic step led to the loss of selectivity to the primary amine to yield toluene with ultimately 100% selectivity as shown in figure 1. Co-hydrogenation measurements on mixtures of benzonitrile and benzylamine indicate the presence of site-selective chemistry. Co-hydrogenation studies on mixtures of benzonitrile and benzyl cyanide highlight the competitive nature of the reaction system and, indirectly, establish a contribution from adsorbed imine species. Figure 1 . Reaction profile and mass balance for the hydrogenation of benzonitrile over 0.5 g 5% Pd/C, at 333 K, 4.0 bar, ca. 0.0175 moles of benzonitrile.  The dashed line represents the incident concentration of benzonitrile.

Application of carbon supported catalysts to selectively hydrogenate aromatic nitrile compounds

247th National Meeting (2014)

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