Stability of Cholinium Chloride-Based Deep Eutectic Solvents with Carboxylic Acids: A Study on Ester Formation

abstract

Deep eutectic solvents (DES), especially those derived from cholinium chloride ([Ch]Cl), have been studied as alternative solvents for various chemical processes. Despite their widespread use, the understanding of the possible formation of impurities in these solvents, such as esters, is still incomplete. In this study, the thermal and long-term stability of [Ch]Cl-based DES were investigated. Specifically, three [Ch]Cl-based DES with carboxylic acids (acetic acid, formic acid, and lactic acid - and their mixtures with water were investigated. The results show that the DES formed with [Ch]Cl: formic acid has lower thermal and long-term stability, but the addition of water to DES significantly reduces the rate of ester formation. The DES [Ch]Cl: lactic acid, and [Ch]Cl: acetic acid were found to exhibit good long-term stability. However, [Ch]Cl: lactic acid has the disadvantage of containing a significant amount of lactide ester originally. It is noteworthy that the esterification in the preparation of the DES [Ch]Cl: acetic acid only took place at temperatures up to 40 degrees C and no further impurities were formed, making it the most suitable DES for processes at this temperature. In summary, the choice of acid appears to influence ester formation, with temperature accelerating the reaction and the addition of water playing a crucial role in slowing the rate of ester formation. In the long term, however, ester formation appears to be unavoidable, as esterification continues even after its production. Therefore, investigating [Ch]Cl: carboxylic acid combinations, with a focus on the ester content and its influence on the process, is essential.

keywords

ECOTOXICITY

subject category

Chemistry; Science & Technology - Other Topics; Engineering

authors

Ferreira, RSB; Ferreira, AM; Coutinho, JAP; Batista, EAC

Groups

G4 - Renewable Materials and Circular Economy

Projects

Collaboratory for Emerging Technologies, CoLab (EMERGING TECHNOLOGIES)

CICECO - Aveiro Institute of Materials (UIDB/50011/2020)

CICECO - Aveiro Institute of Materials (UIDP/50011/2020)

Associated Laboratory CICECO-Aveiro Institute of Materials (LA/P/0006/2020)

acknowledgements

The authors would like to thank the Brazilian Funding Agencies: Sao Paulo Research Foundation (FAPESP - grant number: 2014/21252-0) and National Council for Scientific and Technological Development (CNPq-grant numbers: 311994/2021-0, 401955/2022-2, 200136/2022-4). This study was financed in part by the Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior-Brasil (CAPES)-Finance Code 001. This work was partly developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 (DOI 10.54499/UIDB/50011/2020), UIDP/50011/2020 (DOI 10.54499/UIDP/50011/2020) & LA/P/0006/2020 (DOI 10.54499/LA/P/0006/2020), financed by national funds through the FCT/MCTES (PIDDAC). AMF also acknowledges FCT for the research contract CEECIND/00361/2022 (DOI 10.54499/2022.00361.CEECIND/CP1720/CT0020) under the Scientific Stimulus-Individual Call.