Andrea MEZZETTA1,2, Christian POMELLI2, Lorenzo GUAZZELLI2
1Consorzio INSTM, Firenze, Italy
2Dipartimento di Farmacia, UniversitÓ di Pisa, Pisa, Italy
Transition toward sustainable chemistry is boosting the search for solvents endowed with safe, renewable and environmentally friendly profiles which can be suitable alternative to traditional volatile organic solvents. In this context, Deep eutectic solvents (DESs) emerged as one of the most encouraging media for several research areas. DESs are binary mixtures of two distinct species which display freezing temperatures at the eutectic point well below the ideal expected ones. Usually, this deviation from ideality is rationalized considering the strong hydrogen bonding interactions between a hydrogen bond donor (HBD) and a hydrogen bond acceptor (HBA) that cause in some cases impressive freezing temperature decrement. A very attractive feature of the DESs is the possibility to fine-tune their physico-chemical properties by choosing the appropriate partners, molar ratio and amount of water. This peculiar aspect holds true for a subset of DESs, the so-called Natural DESs (NaDESs), which are mixtures composed solely by natural partners (such as organic acids, plant metabolites, sugars or aminoacids). NaDESs are regarded as the most promising solvent option for the development of sustainable chemistry on account of the ease of preparation and low cost, the modulability of their physicochemical properties, their benign (eco)toxicological profiles.
In the last years, the use of DESs as green innocent solvents in organic synthesis has been reported for a wide range of reactions. Particular emphasis has been direct towards the possible dual solvent-catalyst role played by DESs. However, their use as reactive media has been almost completely overlooked. In the present work, the potential of reactive DESs (ReDESs) as innovative media for the synthesis of bio-derived compounds has been investigated. Sustainability aspects have been evaluated by using green metric parameters, while the effect of these innovative systems on the reaction mechanism has been assessed by means of DFT calculations.
 M. A. R. Martins, S.P. Pinho and J. A. P. Coutinho, J Solution Chem, 2019, 48, 962.
 A. P.R. Santana, J. A. Mora-Vargas, T. G.S. Guimarães, C. D.B. Amaral, A. Oliveira, M. H. Gonzalez, J Mol Liq, 2019, 293,111452.
 D. A. Alonso, A. Baeza, R. Chinchilla, G. Guillena, I.M. Pastor, Diego J. Ramón, Eur J Org Chem, 2016, 612.