Relation geometry-reactivity of perhydrophenanthridine, product of catalytic hydrotreatment of phenanthridine

In catalytic hydrotreating of nitrogen compounds, the limiting step is ofte n hydrogenation which is always followed by a fast hydrodenitrogenation (HD N) reaction. In this work, it was found that for phenanthridine under opera ting conditions (T = 340 degreesC, pH(2) = 70 bar), the reaction stops comp letely after molecule saturation (no HDN was observed). This is due to the weak reactivity of perhydrophenanthridine which would be a consequence of i ts trans-trans geometry as was determined by NMR. Such configuration would limit the perhydrophenanthridine adsorption and hence its reactivity in HDN .