Hybrid Systems for the Separation (LHYS)

Fluorinated vs hydrogenated molecules: organic phase model systems

Better understanding of how a metal ion usually not soluble in an organic phase can be maintained into it by using an extractant is one of the main challenges in the liquid-liquid separation field.

One part of this challenge is to elucidate the role of the interactions which can take place at the molecular level (Fig. 1), especially the relations between first order interactions (such as chemical bonding or electrostatic interactions) and low energy second order interaction (H bonding, polarisation, dipole…).
In this study we focused our interest on the importance of Van der Waals forces in the solubilisation of metal species in organic media using a comparative study between fluorinated and hydrogenated amphiphilic extractants. A key point is to keep the molecular volume and the polar part of the extractant as much as possible unchanged. This is of prime importance in order to minimize the impact of any other interactions, especially the volumic entropic term and the coordination interactions of the polar part with the metal center. To reach this aim, we have first developed the synthesis and purification of several fluorinated extractants (diamide, phosphate, phosphonate…).
The short term objective is to study the differences in organization of the organic phase when a flurorinated extractant is used in place of a hydrogenated analog and correlate these structural hints with the extraction behavior (amount of extracted metal and specificity of the behaviour).

Thus we are comparing the supramolecular behaviour of diamide-dichloromethane-lanthanide phases as model system, from the extraction, solubility and structural points of view. First results show that the extraction behavior is very different: the hydrogenated system extracts the lanthanides whereas the fluorinated system does not (Fig. 2). The related structural studies (NMR, DOSY, SAXS, SANS) are still in progress to better understand this difference of behavior that probably comes from a different organization of the organic phases (reverse vs direct aggregates).

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