Rediscovering Sodium Ionophores as Selective Agents for Lithium Recognition and Extraction

Abstract

ABSTRACT Conventional brine evaporation leads to substantial lithium losses through the formation of lithium‐containing solid precipitates that accumulate as salt stockpiles. Increasing global demand for lithium calls for selective and scalable extraction strategies for such solid materials. Solid–liquid extraction (SLE) enables direct processing of lithium‐bearing solids without prior dissolution of the inorganic matrix; however, suitable molecular extractants are scarce and often synthetically complex. Here, we show that long‐known sodium‐selective ionophores display a clear preference for lithium in solution and function as lithium‐selective extractants under SLE conditions. Hosts 1a–h are based on a modular scaffold accessible from catechol and N,N‐disubstituted haloacetamides and are readily prepared on a multigram scale (up to 58 g per batch). Lithium recognition proceeds through a hydration‐assisted binding mode, in which Li + is coordinated by water, ether, and carbonyl oxygen donors. This enables effective transfer of hydrated lithium salts, as supported by 1 H and 7 Li NMR spectroscopy, ICP‐MS, colorimetric analysis, DFT calculations, and x‐ray crystallography. Under semi‐preparative SLE conditions, nearly all available LiCl is recovered from a ∼100 g multicomponent salt mixture, affording >95% LiCl purity with Li/Na, Li/K, and Li/Mg selectivities above 3000.