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Ionic Liquids and Deep Eutectic Solvents in Catalysis: Current Status...
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Ionic Liquids and Deep Eutectic Solvents in Catalysis: Current Status and Future Outlook

A Special Issue of Molecules (ISSN 1420-3049) belonging to the section "Green Chemistry".

Deadline for manuscript submissions: closed (31 December 2025) | Viewed by 10800

Editors

Prof. Dr. Ignacio López-Coca

E-Mail Website
Guest Editor
Department of Organic and Inorganic Chemistry, School of Technology, Universidad de Extremadura, 10003 Cáceres, Spain
Interests: green chemistry; organic synthesis; catalysis; ionic liquids; activated carbons; adsorption
Special Issues, Collections and Topics in MDPI journals
Dr. Peter A. Goodrich

E-Mail Website
Guest Editor
Theoretical and Applied Catalysis Cluster, School of Chemistry and Chemical Engineering, Queen's University Belfast, Belfast BT9 5AG, Northern Ireland, UK
Interests: ionic liquids; deep eutectic solvents catalysis; green chemistry; organic synthesis

Special Issue Information

Dear Colleagues,

Organic synthesis is fundamental to societal progress, providing access to a wide range of essential compounds across various fields. In line with the principles of Green Chemistry, contemporary chemical research seeks to minimise its environmental impact.

One of the most promising and eco-friendly approaches involves using ionic liquids and deep eutectic solvents in catalysis. With their unique properties, such as negligible vapour pressure, thermal stability, and the ability to dissolve a wide range of compounds, these solvents have become versatile and efficient mediums in organic synthesis. They promote high yields and selectivities, significantly enhancing the sustainability of chemical processes.

The catalytic applications of ionic liquids and deep eutectic solvents span homogeneous, heterogeneous, and enzymatic catalysis, addressing specific challenges in synthetic processes. These applications improve reaction efficiency and reduce the reliance on harmful solvents. Furthermore, these solvents have demonstrated considerable potential in non-conventional energy activation methods, such as microwave and ultrasonic waves, optimising synthesis reactions by minimising by-products and waste.

This Special Issue aims to provide an open-access platform to present recent research advancements in applying ionic liquids and deep eutectic solvents in catalysis. It underscores their role in enhancing the efficiency and sustainability of organic synthesis reactions, emphasising their current status and future outlook in the field.

In this Special Issue, original research articles and reviews are welcome.

Research areas may include (but are not limited to) the following:

  1. Development of New Ionic Liquids (ILs) and Deep Eutectic Solvents (DESs) tailored for specific catalytic applications.
  2. Homogeneous Catalysis: Investigating ILs and DESs as solvents or co-solvents in homogeneous catalytic reactions.
  3. Heterogeneous Catalysis: Exploring the immobilisation of catalysts in ILs and DESs for heterogeneous catalytic processes.
  4. Enzymatic Catalysis: Application of ILs and DESs in enzymatic reactions to improve enzyme stability and activity.
  5. Green Chemistry and Sustainability: Evaluating the environmental impact and sustainability benefits of using ILs and DESs in catalytic processes.
  6. Non-Conventional Energy Activation: Use of ILs and DESs in catalysis under microwave, ultrasonic, or other non-conventional energy inputs to enhance reaction rates and selectivities.
  7. Reaction Mechanisms and Kinetics: Studying the mechanisms and kinetics of catalytic reactions in ILs and DESs.
  8. Industrial Applications: Case studies and applications of ILs and DESs in large-scale industrial catalytic processes.
  9. Recycling and Reusability: Research on ILs and DESs' recovery, recycling, and reuse in catalytic cycles.
  10. Comparative Studies: Comparing the efficiency of ILs and DESs with traditional solvents in various catalytic applications.
  11. Catalyst Design and Optimisation: Designing and optimising catalysts for use in ILs and DESs.
  12. Electrocatalysis and Photocatalysis: Application of ILs and DESs in electrochemical and photochemical catalytic processes.

We look forward to receiving your contributions.

Prof. Dr. Ignacio López-Coca
Dr. Peter A. Goodrich
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-anonymized peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • ionic liquids
  • deep eutectic solvents
  • green chemistry
  • catalysis
  • sustainable synthesis
  • homogeneous catalysis
  • heterogeneous catalysis
  • enzymatic catalysis
  • microwave irradiation
  • ultrasonic activation

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Published Papers (5 papers)

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Research

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17 pages, 1632 KB  
Article
Adsorption of Imidazolium-Based ILs Combined on Activated Carbon Obtained from Grape Seeds
by Ismael F. Mena, Elena Diaz, Jose Palomar and Angel F. Mohedano
Molecules 2025, 30(23), 4595; https://doi.org/10.3390/molecules30234595 - 29 Nov 2025
Viewed by 737
Abstract
In this work, the adsorption of imidazolium-based ionic liquids containing the bis(trifluoromethanesulfonyl) imide anion (NTf2−) from aqueous phase was evaluated using different activated carbons (ACs). Three commercial Acs and two Acs prepared from grape seeds (one produced by pyrolysis and [...] Read more.
In this work, the adsorption of imidazolium-based ionic liquids containing the bis(trifluoromethanesulfonyl) imide anion (NTf2−) from aqueous phase was evaluated using different activated carbons (ACs). Three commercial Acs and two Acs prepared from grape seeds (one produced by pyrolysis and the other by hydrothermal carbonization (HTC), both activated with potassium hydroxide) were tested, assessing the adsorption of both the cation and the anion. For commercial ACs, similar adsorption performances were observed, with maximum adsorption capacities ranging from 0.85 to 1.08 mmol g−1. These values increased under acidic conditions (pH 4), reaching 1.74 mmol g−1 for the 1-butyl-3-methylimidazolium cation (Bmim+) and 1.87 mmol g−1 for NTf2−. Among the prepared ACs, the HTC-derived AC showed slightly higher capacities than the commercial samples, while the pyrolysis-derived AC exhibited the highest adsorption capacity for BmimNTf2 (3.36 mmol g−1 at pH 4). In terms of reusability, the pyrolysis-derived AC maintained 84% of its initial adsorption capacity between the third and fifth regeneration cycles. These results highlight the high adsorption performance and recyclability of grape-seed-derived activated carbons, demonstrating their potential for the removal of ionic liquids from aqueous environments. Full article
(This article belongs to the Special Issue Ionic Liquids and Deep Eutectic Solvents in Catalysis: Current Status and Future Outlook)
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18 pages, 4789 KB  
Article
On the Hydrolytic Depolymerization of Polyurethane Foam Wastes by Ionic Liquids
by Rebeca Salas, Rocio Villa, Francisco Velasco, Maria Macia, Virtudes Navarro, Jairton Dupont, Eduardo Garcia-Verdugo and Pedro Lozano
Molecules 2025, 30(17), 3523; https://doi.org/10.3390/molecules30173523 - 28 Aug 2025
Cited by 6 | Viewed by 3441
Abstract
Flexible polyurethane foams (PUFs) are widely used materials whose crosslinked chemical structure hinders conventional recycling, leading to significant environmental challenges. This study presents a selective and scalable depolymerization strategy for polyurethane foam waste (PUFW), utilizing a combination of 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) as water-miscible [...] Read more.
Flexible polyurethane foams (PUFs) are widely used materials whose crosslinked chemical structure hinders conventional recycling, leading to significant environmental challenges. This study presents a selective and scalable depolymerization strategy for polyurethane foam waste (PUFW), utilizing a combination of 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) as water-miscible ionic liquid (IL) and a strong organic base to enable hydrolytic cleavage of urethane bonds under mild reaction conditions (98 °C, atmospheric pressure). The approach was evaluated across different PUFW formulations and successfully scaled up to a 1 kg reaction mass, maintaining high efficiency in both the depolymerization and separation steps. The recovered polyols exhibited high purity and structural fidelity, comparable to those of virgin polyols. The recycled products were integrated into a new foam formulation, resulting in a PUF with mechanical and morphological properties, as revelated by scanning electron microscopy (SEM), which closely resemble those of virgin polyol-based references and surpass those of foams produced using commercially recycled polyols. These findings support the feasibility of closed-loop polyurethane recycling and represent the transition towards circular polymer economy strategies. Full article
(This article belongs to the Special Issue Ionic Liquids and Deep Eutectic Solvents in Catalysis: Current Status and Future Outlook)
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19 pages, 2924 KB  
Article
Sustainable Synthesis of New Antioxidants from Hydroxytyrosol by Direct Biocatalytic Esterification in Ionic Liquids
by Susana Nieto, Inmaculada Lozano, Francisco J. Ruiz, Jose F. Costa, Rocio Villa and Pedro Lozano
Molecules 2024, 29(21), 5057; https://doi.org/10.3390/molecules29215057 - 26 Oct 2024
Cited by 5 | Viewed by 2703
Abstract
Hydroxytyrosol (HT) is a nutraceutical compound, mainly found in the fruit, leaves and waste from the olive oil industry, known for exhibiting one of the highest antioxidant activities among molecules of natural origin. To harness this bioactivity in cosmetics, pharmaceuticals and the food [...] Read more.
Hydroxytyrosol (HT) is a nutraceutical compound, mainly found in the fruit, leaves and waste from the olive oil industry, known for exhibiting one of the highest antioxidant activities among molecules of natural origin. To harness this bioactivity in cosmetics, pharmaceuticals and the food industry, it is essential to modify the hydrophilicity of HT to enhance its compatibility with lipid-based mixtures. This chemical modification must be carried out with high selectivity to avoid compromising its radical scavenging activity. This work presents a highly efficient and selective approach to perform the biocatalytic esterification of free fatty acids (FFAs) of different alkyl chain lengths with HT in a reaction medium based on the SLIL [C12mim][NTf2]. By using a 1:2 (mol/mol) HT:FFA mixture of substrates, the HT-monoester derivative was obtained up to 77% yield after 2 h at 80 °C. The optimized molar ratio of substrates, combined with the ability to recover the SLIL for further reuse, significantly reduces waste accumulation compared to other reported strategies and results in a more sustainable approach as demonstrated by different green metrics. The antioxidant activity of HT-monoester products was fully maintained with respect to that presented by the natural HT, being stable for at least 3 months at 4 °C, as demonstrated by the DPPH and FRAP antioxidant analysis. Full article
(This article belongs to the Special Issue Ionic Liquids and Deep Eutectic Solvents in Catalysis: Current Status and Future Outlook)
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Review

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37 pages, 3857 KB  
Review
Ionic Liquids in the Aza-Michael Reaction: From Early Imidazolium Salts to Bio-Based Catalytic Media
by Ignacio M. López-Coca, Shima Ghafouriraz, Carlos J. Durán-Valle and Silvia Izquierdo
Molecules 2026, 31(4), 628; https://doi.org/10.3390/molecules31040628 - 12 Feb 2026
Cited by 1 | Viewed by 1104
Abstract
The aza-Michael reaction is a fundamental transformation for carbon–nitrogen bond formation, providing efficient access to β-amino carbonyl compounds, nitriles, and related nitrogen-containing building blocks of broad importance in medicinal chemistry and organic synthesis. Over the past two decades, ionic liquids (ILs) have attracted [...] Read more.
The aza-Michael reaction is a fundamental transformation for carbon–nitrogen bond formation, providing efficient access to β-amino carbonyl compounds, nitriles, and related nitrogen-containing building blocks of broad importance in medicinal chemistry and organic synthesis. Over the past two decades, ionic liquids (ILs) have attracted considerable attention as alternative reaction media, promoters, and catalysts for aza-Michael reactions, owing to their distinctive physicochemical properties and tunable structures. This review presents a comprehensive and critical overview of ionic-liquid-mediated aza-Michael reactions, emphasizing the evolution of IL design from early imidazolium-based systems to modern task-specific, supported, and bio-derived ionic liquids. Conventional room-temperature ionic liquids are discussed as non-innocent solvents capable of stabilizing charged intermediates and enhancing electrophilicity, thereby enabling catalyst-free or metal-assisted aza-Michael additions. Subsequent sections focus on task-specific ionic liquids incorporating Brønsted acidic, basic, hydrogen-bond-donating, or bifunctional motifs, highlighting how rational structural design translates into improved activity, selectivity, and substrate scope. Particular attention is devoted to guanidine-, DABCO-, and DBU-based ionic liquids, where mechanistic studies reveal cooperative activation modes rather than simple acid–base catalysis. Recent advances in supported and polymeric ionic liquids are also reviewed, demonstrating effective strategies to combine IL-like reactivity with enhanced recyclability and operational simplicity. Overall, this review clarifies the diverse roles of ionic liquids in aza-Michael chemistry and outlines current challenges and future perspectives toward more sustainable and efficient C–N bond-forming methodologies. Full article
(This article belongs to the Special Issue Ionic Liquids and Deep Eutectic Solvents in Catalysis: Current Status and Future Outlook)
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32 pages, 2740 KB  
Review
Deep Eutectic Solvents as Green Media for Catalyst Synthesis in Advanced Oxidation Processes
by Bárbara Lomba-Fernández, Marta Pazos, Emilio Rosales and Ángeles Sanromán
Molecules 2026, 31(3), 421; https://doi.org/10.3390/molecules31030421 - 26 Jan 2026
Cited by 1 | Viewed by 2081
Abstract
At present, the contamination of wastewater by persistent organic pollutants is a problem causing significant concern. Advanced oxidation processes have emerged as effective and innovative technologies for the degradation of these pollutants. In these processes, the synthesis and usage of an appropriate catalyst [...] Read more.
At present, the contamination of wastewater by persistent organic pollutants is a problem causing significant concern. Advanced oxidation processes have emerged as effective and innovative technologies for the degradation of these pollutants. In these processes, the synthesis and usage of an appropriate catalyst is essential to enhance the generation of reactive species and improve treatment efficiency. In this sense, the use of greener solvents in the synthesis procedure has attracted great interest in recent years, improving the catalyst performance and reducing the associated synthesis impact. Among them, deep eutectic solvents stand out for the synthesis of catalytic materials in advanced oxidation processes for water treatment, offering a sustainable alternative to traditional methods due to their unique properties and low environmental impact. This review summarizes recent advances in this field, highlighting primarily the methods for preparing new catalytic materials using deep eutectic solvents and their application in different types of advanced oxidation processes. Full article
(This article belongs to the Special Issue Ionic Liquids and Deep Eutectic Solvents in Catalysis: Current Status and Future Outlook)
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