Abstract
The Pd, Ni, Ni-Sn, Cu and Ag@Pd nanocatalyst having different shape and size were used for direct dehydrogenation of cyclic ketones to the corresponding phenols in the presence of O2 as the oxidant. Among all catalyst tested, metallic Pd-1 nanoparticles exhibited excellent catalytic performance both in presence and absence of p-toluenesulfonic acid. The dehydrogenation of cyclohexanone catalyzed by Pd-1 nanocatalyst led to a 93% yield of the desired cyclohexenone and phenol. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed that there was no change in morphology, crystal phases and particles size of Pd-1 nanocatalyst after the reaction.
4. Conclusions
In summary, we have identified a Pd nanocatalyst heterogeneous system that enables direct dehydrogenation of cyclic ketones to the corresponding phenols in the presence of O2 as the oxidant. The tested catalysts include Pd-1, Pd-2, Pd-3, Ni, Ni-Sn, Cu, and Ag@Pd. The metallic Pd-1 nanoparticles exhibited excellent catalytic performance as compared with Pd-2, Pd-3, Ni, Ni-Sn, Cu and Ag@Pd nanoparticles. When O2 pressure increased from 1 to 5 atm the phenol yield from 15 to 49% was increased and further increase in the O2 pressure up to 10 atm also enhanced product yield and phenol yield. The best results were obtained by using (15 mol%) p-toluenesulfonic acid with Pd-1 nanocatalyst in dimethylsulfoxide (DMSO), under 1 atm of O2 at 80 °C. The ability to replace stoichiometric reagents with O2 as an oxidant has important implications for large scale applications of these methods in pharmaceutical and fine chemical synthesis.
