**5. Conclusion**

ILs are good solvents or co-solvent for metallic induced hydrogenation reactions. At first, their physical-chemical properties can be tunable depending on the anion-cation association. Consequently, the appropriate IL has to be simply chosen/found for the studied reaction. In addition, ILs are highly thermically stable, which is an advantage in the case of high-temperature hydrogenation reactions. The more important points are that they present good solubility of hydrogen and they are able to solubilise and stabilise metallic catalysts. As a consequence, they can promote hydrogenation reactions in mild conditions, sometimes the selectivity of the reaction, and/or they can allow the recyclability of the catalyst.

Hydrogenation in "usual" ILs has been performed on various unsaturated and aromatic substrates with various metallic catalysts or nanoparticles. In general, satisfying conversions and/or yields were observed. These reactions mainly used imidazoliums derivatives. They are the more common ILs, but also present (eco)toxicity and are not biodegradable.

To contour this problem, biobased and green ILs can be used. These compounds can be easily obtained from different biomass, such as amino acid, acids from bioprocess, carbohydrates or fatty oils. Despite their low biodegradability at the moment, they present in general lower (eco)toxicity than the commercials ILs. Similar to the "usual" ILs, biobased ILs are ideal solvent for hydrogenation reaction and can even bring improvements. When used as co-solvent, ammonium biobased ILs showed better selectivity and recyclability for 1,5-cyclooctadiene hydrogenation into cyclooctene in mild conditions than commercial ILs. Also biobased ILs can be chiral, brought by the chirality of their biobased building blocks, and be used for enantioselective hydrogenation reactions. With prolinate ILs, isophorone and carvone were hydrogenated in mild conditions with a good enantiomeric and diastereoisomeric excess, respectively. Transfer hydrogenation reactions were also recently investigated with biobased ILs. High conversion of acetophenone was achieved in the presence of γ-valerolactone-derived ILs, and the systems were reused four times without loss of reactivity.

Even if improvement needs to be made, especially for biodegradability of the compounds and simplification of their synthesis, biobased ILs seem to be good solvents, not only for hydrogenation reaction, but also for a wide range of chemical transformations (coupling reactions, oxidation, etc.). Moreover, with the increasing interest of valorisation of the biomass and the need to replace compounds derived from oil, new structures and applications of biobased ILs are expected for a near future.
