First evidence of metal transfer into hydrophobic deep eutectic and low-transition-temperature mixtures: indium extraction from hydrochloric and oxalic acids

Abstract

This is the first report on metallic species transfer from aqueous hydrochloric and oxalic acid media into hydrophobic deep eutectic and low-transition-temperature mixtures composed of quaternary ammonium salts or menthol and carboxylic acids.

Quest for Green‐Solvent Design: From Hydrophilic to Hydrophobic (Deep) Eutectic Solvents

“…The first hydrophobic (D)ES reported were based on quaternary ammonium salts with long alkyl chains and decanoic acid, where the hydrophobic characterw as confirmed by studying the leachingo f( D)ES components into the water phase and water uptake. [11a] Following the same idea, severals tudies on the use of quaternary ammonium salts with long alkyl chains were then performed, [11,[13][14][15][16] using HBDs with different chemical structures,s uch as carboxylic acids and alcohols with different alkyl chains (C 2 -C 18 )a nd with double bonds. Regarding the use of [N 4444 ]Cl and [N 4444 ]Br,h ydrophobic (D)ES could be prepared using these compounds and two phases were obtained when in contact with water.T heir chemical stability will be discussed below and conclusions drawn.…”

Sustainable hydrophobic terpene-based eutectic solvents for the extraction and separation of metals

“…This is unlike previous metal extraction studies using carboxylate HES in which metal extraction was mainly due to the other component of the HES, namely lidocaine and a quaternary ammonium ionic liquid. 5,6 UV-vis analysis ( of the organic phase after extraction confirms that Cu(II) is extracted in the form of a Cu-capric acid complex with the presence of a large peak at 680 nm similar to that observed for Cu(acetate) 2 hydrate complexes. 11 Although pure capric acid, in the absence of diluent, displays a marginally greater extraction efficiency than the HES, it was discarded due to the surfactant qualities of pure unbranched carboxylic acids.…”

“…3,4 For any solvent to be eligible for use in solvent extraction, it must possess low water solubility, low vapour pressure, simple synthesis, low cost, high selectivity towards the target solute, high solvent loading, low viscosity and low toxicity. In this context, hydrophobic eutectic solvents (HES) have emerged as promising designer solvents for the extraction of varied inorganic 5,6 and organic solutes. 7,8 These eutectic mixtures are usually composed of two constituents associated by hydrogen bonding and dispersion forces.…”

“…9 HES were used for the recovery of indium and transition metals from chloride media. 5,6 Although promising, these results were limited by low extraction yields, a lack of selectivity between various transition metals and incomplete recycling of the HES. Sustainable HES composed of cheap naturally sourced terpenes (such as menthol and thymol) as hydrogen bond acceptor and fatty acids (from caprylic to stearic acids) as hydrogen bond donor were shown to be highly hydrophobic.…”

“…The obtained loading for the thymol:capric acid HES is significantly lower than conventional carboxylic extractant loading but one order of magnitude higher than that obtained for indium extraction using a menthol:lauric acid HES. 6 The nature of the salt additive was found to have an important impact on the loading of the HES phase (Fig. S7 in To ensure the viability of the hydrophobic eutectic solvent, the water content of the HES phase and 1 H-NMR analysis of the aqueous phase after extraction were performed to quantify any losses of the HES constituents.…”