Aqueous solutions of glycerol were hydrogenolysed at 180 °C under 80 bar H₂-pressure in the presence of supported metal catalysts in an attempt to selectively produce 1,2- and 1,3-propanediol. Catalysts (Cu, Pd, Rh), supports (ZnO, C, Al₂O₃), solvents (H₂O, sulfolane, dioxane) and additives (H₂WO₄) were tested to improve reaction rate and selectivity to the target molecules. The best selectivity (100%) to 1,2-propanediol was obtained by hydrogenolysis of water solution of glycerol in the presence of CuO/ZnO catalysts. To improve the selectivity to 1,3-propanediol the reaction was conducted with rhodium catalysts with tungstic acid added to the reaction medium. The best result in terms of conversion and selectivity to 1,3-propanediol (1,3-PDO/1,2-PDO = 2) was obtained by operating in sulfolane. The presence of iron dissolved in the reaction medium was also beneficial for the selectivity to 1,3-PDO. A mechanism was proposed to account for the effect of these different parameters.

A survey highlighting the most recent palladium catalytic systems produced and their performances for progress in direct synthesis of indole backbones by heterocarbocyclization of reactive substrates is provided. The discussion is developed in relation with the principles of sustainable chemistry concerning atom and mass economy. In this respect, the general convergent character of the syntheses is of particular interest (one-pot, domino, cascade or tandem reactions), and the substrates accessibility and reactivity, together with the final waste production, are also important. This critical review clearly indicates that the development of ligand chemistry, mainly phosphines and carbenes, in the last few decades gave a significant impetus to powerful functionalization of indoles at virtually all positions of this ubiquitous backbone (118 references).