Are Aqueous Biphasic Systems Composed of Deep Eutectic Solvents Ternary or Quaternary Systems?

resumo

Deep eutectic solvents (DES) have emerged in the past few years as a new class of solvents with promising applications in several fields. In the present work, the application of DES (formed by binary mixtures of cholinium chloride and carboxylic acids or urea) as phase-forming components of aqueous biphasic systems (ABS) is investigated. The mechanisms associated with the phases demixing of ABS composed of DES, as well as the DES stability in aqueous solutions, are investigated to address the critical question whether DES-based ABS are in fact ternary or quaternary mixtures. It is shown that the DES integrity is destroyed in ABS by the disruption of the hydrogen-bonding interactions of the complex (a result of the isolated components preferential solvation by water), and as confirmed by a nonstoichiometric partition of the DES components between the coexisting phases. As a result, there are no "real" DES-based ABS; instead, there is the formation of ABS composed of four components, where the carboxylic acid used as the hydrogen-bond donor species seems to act as an additive. Finally, it is shown that these ABS have an outstanding potential to be used in extraction processes, as it is here demonstrated with the complete separation of two dyes. However, the volatile nature of short chain carboxylic acids and the nonstoichiometric partition of the DES components in ABS make the development of recovery and recycling steps more difficult to accomplish.

palavras-chave

TEMPERATURE MIXTURES LTTMS; IONIC LIQUIDS; PHYSICAL-PROPERTIES; CARBOXYLIC-ACIDS; 2-PHASE SYSTEMS; EXTRACTION; MEDIA; WATER; CATALYSIS; CHLORIDE

categoria

Chemistry; Science & Technology - Other Topics; Engineering

autores

Passos, H; Tavares, DJP; Ferreira, AM; Freire, MG; Coutinho, JAP

nossos autores

agradecimentos

This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT ref. UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when appropriate cofinanced by FEDER under the PT2020 Partnership Agreement. The authors also acknowledge FCT for the doctoral grants SFRH/BD/85248/2012 and SFRH/BD/92200/2013 of H.P. and A.M.F., respectively.

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