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Do group 1 metal salts form deep eutectic solvents?

Accepted version
Peer-reviewed

Type

Article

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Authors

Abbott, AP 
D'Agostino, C 
Davis, SJ 
Gladden, LF 
Mantle, MD 

Abstract

Mixtures of metal salts such as ZnCl2, AlCl3 and CrCl3·6H2O form eutectic mixtures with complexing agents, such as urea. The aim of this research was to see if alkali metal salts also formed eutectics in the same way. It is shown that only a limited number of sodium salts form homogeneous liquids at ambient temperatures and then only with glycerol. None of these mixtures showed eutectic behaviour but the liquids showed the physical properties similar to the group of mixtures classified as deep eutectic solvents. This study focussed on four sodium salts: NaBr, NaOAc, NaOAc·3H2O and Na2B4O7·10H2O. The ionic conductivity and viscosity of these salts with glycerol were studied, and it was found that unlike previous studies of quaternary ammonium salts with glycerol, where the salt decreased the viscosity, most of the sodium salts increased the viscosity. This suggests that sodium salts have a structure making effect on glycerol. This phenomenon is probably due to the high charge density of Na+, which coordinates to the glycerol. 1H and 23Na NMR diffusion and relaxation methods have been used to understand the molecular dynamics in the glycerol-salt mixtures, and probe the effect of water on some of these systems. The results reveal a complex dynamic behaviour of the different species within these liquids. Generally, the translational dynamics of the 1H species, probed by means of PFG NMR diffusion coefficients, is in line with the viscosity of these liquids. However, 1H and 23Na T1 relaxation measurements suggest that the Na-containing species also play a crucial role in the structure of the liquids.

Description

Keywords

Deep Eutectic Solvents, PFG NMR, NMR relaxation, conductivity, viscosity

Journal Title

Phys Chem Chem Phys

Conference Name

Journal ISSN

1463-9076
1463-9084

Volume Title

18

Publisher

Royal Society of Chemistry (RSC)
Sponsorship
A. P. Abbott would like to thank the Royal Society for funding the work through the Brian Mercer Award. C. D’Agostino would like to acknowledge Wolfson College, Cambridge, for supporting his research activities. S. Davis thanks EPSRC for funding a PhD studentship.