Abstract
DES are mixtures of two or more compounds, able to form liquids upon mixing, with lower freezing points when compared to the individual constituents (eutectic mixtures). This attitude is due to the specific hydrogen-bond interactions network between the components of the mixture. A notable characteristic of DES is the possibility to develop tailor-made mixtures by changing the components ratios or a limited water dilution, for special applications, making them attractive for pharmaceutical purposes. In this review, we focused our attention on application of ChCl-based DES in the synthesis of pharmaceutical compounds. In this context, these eutectic mixtures can be used as solvents, solvents/catalysts, or as chemical donors and we explored some representative examples in recent literature of such applications.
Highlights
Within the framework of green chemistry, known as sustainable chemistry, solvents play a very strategic role, considering their importance as reaction media and in purification processes
A large number of studies have been conducted to replace classical organic solvents with new sustainable ones, with the aim to improve the protection of environmental and human health [2]. This approach comprises the use of different systems, such as the deep eutectic solvents (DES), first described by Abbott et al as potential alternative solvents to ionic liquids (ILs) [3]
When a DES is composed by natural origin components, it is further defined as a natural deep eutectic solvent (NADES) [4]
Summary
Within the framework of green chemistry, known as sustainable chemistry, solvents play a very strategic role, considering their importance as reaction media and in purification processes. Density functional theory (DFT) demonstrated that, in ChCl-based DES, the electronegative anion chloride is capable to provide more binding sites to form hydrogen bonds, and a competitive activity was observed between various HBD and choline cation [29] In this scenario, the formation of hydrogen bonds and the consequent delocalization of charges, in addition to designing the three-dimensional network, significantly decreases the melting points of the different eutectic mixtures. Biernacki et al reported an experimental and theoretical study of ChCl-based NADES with sorbitol and xylitol In these solvents, the oversaturation of the HBD groups results in more extensive self-interaction compared to NADESs with ethylene glycol and glycerol, with higher viscosities and densities [32]. Aonmgotnhge tnhuenmuemroeuros ursearcetaicotniosnpsrporpoopsoedse,dt,htehebebsetsyt iyeiledlds s(5(500–8–08%0%) )wweerereoobbttaaiinneeddiinn the ssyynntthheessiiss ooff hhyyddrraazzoonnoommeetthhyyll--BBIIMMiinnHH222OO//[[CChhCCll//gglylycecerorol l((22:1:1))]]((33::11)) ssttaarrttiinngg froomm aallkkyyllhhyyddrraazzoonneess ((SScchheemmee22))
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