Hydrogenation of ethyl p-nitrobenzoate on Pd/Sibunit catalysts

A series of Pd/C catalysts (2–4 wt % Pd) with different particle sizes of the supported metal was prepared under varied conditions of the formation and surface deposition of the polynuclear hydroxo complexes (PHCs) of palladium(II) on powdered Sibunit carbon supports with their subsequent reduction to the metal. It was found that the liquid-phase hydrogenation of ethyl p-nitrobenzoate to anesthesine (benzocaine) on these catalysts is a structurally sensitive process, and the dependence of the activity of catalysts on their dispersity is expressed as an extremal function; in this case, the most effective catalysts had the average Pd particle size of 3–5 nm. It was demonstrated that the degree of catalyst utilization increased with the pH of Pd(II) PHC formation; this fact indicates that egg-shell-type catalysts were formed at high values of pH. The Pd/Sibunit catalysts are promising for use in the pharmaceutical industry for the synthesis of local anesthetics with p-nitrobenzoic acid as an intermediate.