2021 Volume 79 Issue 3 Pages 188-196
Hydrogen (H2) is regarded as a clean energy source due to the production of only H2O as a by-product by its combustion, and widely utilized as a reductant in organic chemistry. However, the handing of flammable H2 should be strictly regulated by law and H2 is industrially produced by the steam forming of CH4 accompanied with emission of CO2. Therefore, the development of methodology to generate H2 in situ without generating CO2 and the direct use of H2 is eagerly desired from the viewpoints of green sustainable chemistry. We continuously investigate two types of H2 generation methods using mechanochemical activation of water, alkanes, etc. and heterogeneous platinum group metal-catalyzed dehydrogenation of alcohols, unsaturated alicyclic hydrocarbon derivatives, etc. Mechanochemical collision and friction energy of stainless steel (alloy of Fe, Cr, and Ni) balls in a planetary ball mill realized the quantitative generation of H2 from H2O and in situ-generated H2 could be directly used as a reductant towards organic compounds bearing reducible functionalities, such as alkenes, alkynes, nitro group, aromatic halides, etc. Meanwhile, the commercially available carbon-supported platinum group metal catalysts (e.g., Pd/C, Rh/C, Ru/C, and Pt/C) were found to catalyze the dehydrogenative oxidation of alcohols in H2O as a green solvent to generate H2, which was effectively utilized in the reduction of comparatively stable aromatic fluorides and arene nuclei. Furthermore, in situ-generated H2 was also adapted as an activator of platinum metal to facilitate the H-D exchange reaction (deuterium-labelling) of various organic compounds. Furthermore, the Pd/C-catalyzed dehydrogenation of unsaturated alicyclic hydrocarbon derivatives has the potential to provide a wide variety of aromatic compounds.
