Fine-tuning the Basicity of Deep Eutectic Solvents by Substituting Guanidine for Urea in Reline

Tatsuya Umecky; Akihiro Goto; Naoki Hayashi; Kazuki Eguchi

doi:10.1021/acsomega.3c00706

Fine-tuning the Basicity of Deep Eutectic Solvents by Substituting Guanidine for Urea in Reline

ACS Omega. 2023 Apr 12;8(16):14694-14698. doi: 10.1021/acsomega.3c00706. eCollection 2023 Apr 25.

Authors

Tatsuya Umecky¹, Akihiro Goto¹, Naoki Hayashi¹, Kazuki Eguchi¹

Affiliation

¹ Graduate School of Science and Engineering, Saga University, Honjo-machi, Saga, 840-8502, Japan.

Abstract

The physicochemical properties of deep eutectic solvents (DESs) depend on the combination of hydrogen bond acceptors and hydrogen bond donors used. The basicity of a DES significantly influences its performance in CO₂ chemical absorption, biomass and protein dissolution, and catalytic reactions. To the best of our knowledge, a strategy for fine-tuning the basicity of DESs has not yet been reported. Therefore, in this study, we substituted the base urea (Ur) in reline, which is a 1:2 mixture of choline chloride (ChCl) and Ur, with the superbase guanidine (Gu) to fine-tune its basicity. Binary (2Gu-ChCl) and ternary (Gu-Ur-ChCl) DESs were prepared, and their CO₂ absorption capacities were investigated at 313.2 K. The equimolar mixture Gu-Ur-ChCl absorbed CO₂ gas up to the molar ratio [CO₂]/[ChCl] ≈ 1.0. Therefore, the basicity of ChCl-based DES can be continuously varied by substituting more molecules of Ur with Gu. Our strategy of combining functional and non-functional molecules with similar structures to vary the basicity of DESs has potentially wide applications that utilize DESs in the future.