Toxicity deep eutectic solvents

Related to ionic liquids are substances known as deep eutectic solvents or mixtures. A series of these materials based on choline chloride (HOCH2CH2NMe3Cl) and either zinc chloride or urea have been reported (Abbott et al., 2002 2003). The urea/choline chloride material has many of the advantages of more well-known ionic liquids (e.g. low volatility), but can be sourced from renewable feedstocks, is non-toxic and is readily biodegradable. However, it is not an inert solvent and this has been exploited in the functionalisation of the surface of cellulose fibres in cotton wool (Abbott et al, 2006). Undoubtedly, this could be extended to other cellulose-based materials, biopolymers, synthetic polymers and possibly even small molecules. 

This chapter clearly exemplifies the maturity gained by Deep Eutectic Solvents as new green and biorenewable solvents in different applications of modem synthesis. As the reader have noticed, a huge number of synthetic reactions and chemical processes can be presently performed in eutectic mixtures as effectively as in classical organic media. More importantly, enhanced or completely new reactivities have been in some cases observed using DESs as a solvent. Despite all these promising applications, much effort is still needed in order to widen the utilization of DESs as green, low toxic and biocompatible reaction medium. 

Hayyan M, Hashim MA, Hayyan A, Al-Stiadi MA, AlNashef IM, Miightuii MES, Saheed OK (2013) Are deep eutectic solvents benign or toxic Chemosphere 90(7) 2193-2195. doi 10.1016/j.chemosphere.2012.11.004... 

Although many ionic liquids and deep eutectic mixtures based on choline have the advantages to be cheap and no-toxic, they are all hydrophilic and miscible with aqueous solvents. This may be a problem for applications such as the extraction of metal ions from an aqueous phase or the electrodeposition of reactive metals (aluminium, magnesium, tantalum..). 

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