One of the major topics within the green and sustainable chemistry field is replacing hazardous and/or harmful solvents with more environmentally friendly alternatives. One group of solvents that have been investigated for this purpose over recent years are ionic liquids. However, it is now felt that not all ionic liquids can be classified as ‘green’ and that their environmental impact is strongly dependent on the cation and anion used to make them. Natural compounds can be used to produce deep eutectic solvents, sugar melts or ionic liquids, generating a reaction media which combines the advantages of non-toxic and biodegradable starting materiuals with the physicochemical properties of ionic liquids.
In this Critical Review, Burkhard König and Carolin Ruß from the University of Regensburg, Germany look at the impact these low melting mixtures have had on organic synthesis and their various applications. The authors show that experimental and theoretical determinaton of the molecular structure of these solvents is needed in order to understand how this shapes their physcial properties. Given the huge number of naturally occuring anions and cations, there remains an enormous range combinations to investigate with the potential to produce low-environmental impact solvents with tailor-made properties.
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Low melting mixtures in organic synthesis – an alternative to ionic liquids? Carolin Ruß and Burkhard König, Green Chem., 2012, DOI: 10.1039/C2GC36005E