Perfluoroalkyl- vs alkyl substituted malonamides: Supramolecular effects and consequences for extraction of metals

Substitution of extracting molecules with a long perfluoroalkyl chain was performed in order to modulate the weak intermolecular interactions and the supramolecular ordering of an organic system employed to recover metals of interest during liquid-liquid extraction processes. The fluorous compounds were compared to their hydrocarbon counterparts: both molecules present a hydrophilic moiety, responsible for metal chelation, and a hydrophobic chain, which enables solubility into organic media. But this chain is also oleophobic in the case of the fluorous compound. We observed that the oleophobic character the fluorous chain prevails over the tendency of hydrophilic moieties to self-assemble: in the organic phase, fluorous compounds lead to direct aggregates with a fluorous core, whereas hydrocarbon compounds lead to reverse aggregates with a hydrophilic core. This difference of supramolecular ordering of the extracting molecules has a great impact on the extraction process, and its selectivity: Pd was selectively extracted over Nd although the complexing head of the extracting molecules remains identical. This study reveals that perfluoroalkyl chains can also be successfully employed to tune the extraction properties of organic phases, even when based on classical organic oils.