Green Solvent System in Organic Reactions Advanced Approach and Applications: A review

Green solvent systems are transforming the landscape of organic chemistry by promoting environmentally friendly practices in chemical synthesis...
Shibaprasad Maity

 Green Planet -A Journal of Green Chemistry & Pharmaceutical Science

Published by the ChemArticle & ChemClip

Volume 1, Issue 2, August 2024, Pages 1-5

Green Solvent Systems in Organic Reactions: Innovations and Applications

➧ 
August, 2024 ➧ Green Planet -A Journal of Green Chemistry & Pharmaceutical Science ➧ 1Department of Chemistry, RKDF University, Ranchi, Jharkhand-834004, India ➧ Volume 1

Green solvent systems are transforming the landscape of organic chemistry by promoting environmentally friendly practices in chemical synthesis. This article reviews recent advancements in green solvents, focusing on their application in various organic reactions. Particular attention is given to ionic liquids, deep eutectic solvents (DESs), and supercritical fluids as alternatives to conventional organic solvents. The mechanisms underlying key reactions performed in these solvents are discussed, highlighting the advantages and challenges of adopting green solvents in industrial and academic settings.

: Green Chemistry, Environmental Science, Ionic Liquids, Deep Eutectic Solvents (DESs), Supercritical Carbon dioxide (scCO2)

Introduction

The demand for sustainable and eco-friendly chemical processes has led to the development of green solvent systems [1]. Traditional organic solvents, such as benzene, dichloromethane, and toluene, are often toxic, volatile, and non-biodegradable, contributing to environmental pollution and health hazards [2]. In contrast, green solvents are designed to minimize environmental impact, reduce toxicity, and enhance the safety of chemical processes [3]. The search for sustainable and environmentally friendly alternatives in chemical processes has driven significant advancements in green chemistry [4]. Traditional organic solvents, widely used in chemical synthesis, often pose serious environmental and health risks due to their toxicity, volatility, and non-biodegradability [5]. In response, green solvent systems have emerged as a promising solution, offering safer, more sustainable alternatives for conducting organic reactions. These systems include ionic liquids, deep eutectic solvents (DESs), and supercritical fluids, each with unique properties that enable efficient and eco-friendly chemical processes [6] [7]. Green solvents not only reduce the environmental footprint of chemical synthesis but also often enhance reaction efficiency and selectivity. This article explores the latest innovations in green solvent systems, examining their applications in various organic reactions, and discussing the underlying mechanisms that make these solvents effective [8]. By embracing green solvents, the chemical industry can move closer to a more sustainable and responsible future.

Types of Green Solvent Systems

Type one, Ionic liquids (ILs) are salts that remain liquid at or near room temperature [9]. They possess unique properties, such as negligible vapor pressure, high thermal stability, and tunable polarity, making them suitable for a wide range of organic reactions [10]. Their ability to dissolve both polar and non-polar compounds offers versatility in reaction mechanisms. Consider the Diels-Alder reaction between cyclopentadiene and methyl acrylate, which is a key cycloaddition reaction in organic synthesis [11]. In traditional solvents, this reaction requires high temperatures. However, in ionic liquids like 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), the reaction proceeds efficiently at lower temperatures due to the high polarity of the solvent, which stabilizes the transition state. A study of the thermophysical and thermodynamical properties of two important ionic liquids ([BMIM][PF6]) and Butyl-3-methylimidazolium Tetrafluoroborate ([BMIM][BF4]) at high pressures and a temperature range from the speed of sound measure. The anion increases in size ([BF4]- < [PF6]-), corresponds to the density increases and the speed of sound shows the opposite trend. In this study ILs differing in the anion, if the mass density increases, correspond to the molar volume increases at 1 atm pressure and 298 K temperature (experiment value Volume of [bmim][PF6] - Volume of [bmim][BF4] =20.3 cm3‚mol-1). this value credits the increase in the effective anion size factor from 0.089 nm3/anion of BF4- to 0.122 nm3/anion of PF6-. In this study, the heat capacities vary at 1atm and room temperature, Cp of [bmim][PF6] - Cp of [bmim][BF4]  = 44.1 J‚mol-1‚K-1. this value is significant because the PF6 ions give a large degree of freedom compared to  [BF4]- ions [12].

Type two, Deep Eutectic Solvents (DESs) [13] are formed by mixing two or more components, typically a hydrogen bond donor and an acceptor, resulting in a mixture with a melting point lower than that of its individual components [14]. DESs are biodegradable, non-toxic, and often composed of inexpensive, readily available materials. Reaction Mechanism in DESs, The Knoevenagel condensation, a carbon-carbon bond-forming reaction between aldehydes and active methylene compounds, can be efficiently carried out in a DES composed of choline chloride and urea. The DES not only acts as a solvent but also facilitates the reaction by providing a polar environment that stabilizes the intermediate carbanion. Type three, Supercritical fluids, such as supercritical carbon dioxide (scCO2), exhibit unique properties that combine those of gases and liquids. ScCO2 is a non-toxic, non-flammable, and easily recyclable solvent, making it an attractive green solvent for organic reactions. Reaction Mechanism in Supercritical Fluids, The hydrogenation of alkenes, a fundamental reaction in organic chemistry, can be carried out using scCO2 as the solvent. In this process, scCO2 dissolves both the hydrogen gas and the substrate, allowing the reaction to occur under mild conditions. The supercritical state of CO2 enhances mass transfer and reduces the need for high pressures, making the process more energy-efficient [15].

Applications of Green Solvent Systems

Green solvent systems have found widespread applications across various fields of organic chemistry, significantly advancing the sustainability of chemical processes. In pharmaceutical synthesis, ionic liquids and deep eutectic solvents (DESs) are employed to enhance reaction efficiency and reduce the need for hazardous organic solvents, leading to greener drug production methods. Supercritical fluids, particularly supercritical carbon dioxide (scCO2), are used in the extraction of natural products and in catalytic hydrogenation reactions, offering an environmentally benign alternative to traditional solvents. In polymer chemistry, green solvents facilitate eco-friendly polymerization processes, reducing the environmental impact of producing plastics and other materials. Additionally, green solvents are increasingly used in agrochemicals, where they enable the synthesis of pesticides and fertilizers with lower environmental toxicity. The versatility and environmental benefits of green solvent systems make them essential tools for developing more sustainable and efficient organic reactions across diverse industrial and research applications.

Advantages and Challenges

Advantages, Green solvent systems offer numerous advantages in organic chemistry, making them a key component in the shift towards more sustainable chemical processes. One of the primary benefits is their reduced environmental impact. Unlike traditional organic solvents, green solvents such as ionic liquids, deep eutectic solvents (DESs), and supercritical fluids are often non-toxic, non-volatile, and biodegradable, minimizing pollution and health hazards. These solvents can enhance reaction efficiency and selectivity, often enabling reactions to proceed under milder conditions with higher yields. Additionally, many green solvents, like DESs, are inexpensive and made from readily available materials, improving the economic viability of sustainable practices. The ability to recycle and reuse green solvents further contributes to cost savings and waste reduction. And Challenges, Despite their advantages, the adoption of green solvent systems faces several challenges. One significant hurdle is solubility limitations, as green solvents may not dissolve all reactants or catalysts effectively, requiring careful selection and optimization of reaction conditions. The scalability of green solvent applications remains an issue, particularly in industrial settings where large-scale processes may require new technologies for solvent recovery and recycling. Additionally, the compatibility of green solvents with existing chemical processes can be problematic, as some reactions may not perform as well or may require re-engineering to work in these new media. Addressing these challenges is crucial for the broader implementation of green solvents in organic chemistry.

  • Environmental Benefits: Green solvents are designed to minimize toxic emissions, reduce waste, and lower the carbon footprint of chemical processes.
  • Enhanced Safety: Many green solvents, such as water and scCO2, are non-flammable and less hazardous than traditional organic solvents.
  • Economic Viability: Some green solvents, like DESs, are composed of inexpensive and readily available components, making them cost-effective alternatives.

and Challenges

  • Solubility Issues: While green solvents are versatile, their solubility profiles may not match those of conventional solvents, requiring modifications to reaction conditions.
  • Scalability: The industrial-scale application of green solvents is still in its early stages, and challenges such as solvent recovery and recycling need to be addressed.
  • Compatibility: Not all reactions can be efficiently carried out in green solvents, and in some cases, the reaction mechanism may be altered, requiring further optimization.

Conclusion

Green solvent systems represent a transformative shift towards more sustainable and eco-friendly practices in organic chemistry. By reducing environmental impact and enhancing reaction efficiency, solvents like ionic liquids, deep eutectic solvents (DESs), and supercritical fluids offer significant advantages over traditional solvents. However, challenges such as solubility issues, scalability, and compatibility with existing processes must be addressed to fully realize their potential. Continued research and innovation are essential for overcoming these obstacles, paving the way for broader adoption of green solvents, and contributing to a more sustainable future in chemical synthesis.

References

  1. Doble, M., Kruthiventi, A.K. Alternate Solvents. Green Chemistry and Engineering, 5, 93-104 (2007)
  2. Mangotra, A., Singh, S.K. Volatile organic compounds: A threat to the environment and health hazards to living organisms – A review. Journal of Biotechnology, 382, 51-69 (2024) Article
  3. Nanda, B., Sailu, M.S. et al. Green solvents: A suitable alternative for sustainable chemistry. Materials Today: Proceedings, 47, 1234-1240 (2021) Article
  4. Kreuder, A.D., House-Kinght, T., et al. A Method for Assessing Greener Alternatives between Chemical Products Following the 12 Principles of Green Chemistry. ACS Sustainable Chem. Eng. 5, 4, 2927–2935 (2017) Article
  5. Joshi, D.R., Nisha, A. An Overview on Common Organic Solvents and Their Toxicity. JPRI. 28, 1-18 (2019) Article
  6. Chen, Y., Mu, T. Revisiting greenness of ionic liquids and deep eutectic solvents. Green Chemical Engineering. 2, 2, 174-186 (2021) Article 
  7. Alvarez, M.S., Longo, M.A. et al. The role of deep eutectic solvents in catalysis. A vision of their contribution to homogeneous, heterogeneous, and electrocatalytic processes. Journal of Industrial and Engineering Chemistry, 132, 36-49 (2024) Article 
  8. Otitoju, T.A., Kim, C-H., Ryu, M. et al. Exploring green solvents for the sustainable fabrication of bio-based polylactic acid membranes using nonsolvent-induced phase separation. Journal of Cleaner Production, 467, 142905 (2024) Article 
  9. Marsh, K.N., Boxall, J.A., Lichtenthaler, R. Room temperature ionic liquids and their mixtures-a review. Fluid Phase Equilibria. 219, 1, 93-98 (2004) Article
  10. Liu, J-F., Jiang, G-b., Liu, J-f. Jan A. J. Application of ionic liquids in analytical chemistry. TrAC Trends in Analytical Chemistry. 24, 1, 20-27 (2005) Article
  11. Hondrogiannis, G., Pagni, R.M., Kabalka, G.W., Anosike, R., Kurt, R. The diels-alder reaction of cyclopentadiene and methyl acrylate on γ,-alumina. Tetrahedron Letters. 31, 38, 5433-5436 (1990) Article
  12. Azevedo, R.G.,  Esperanc¸ J.M.S.S. et al. Thermophysical and Thermodynamic Properties of 1-Butyl-3-methylimidazolium Tetrafluoroborate and 1-Butyl-3-methylimidazolium Hexafluorophosphate over an Extended Pressure Range. J. Chem. Eng. Data. 50, 997-1008 (2005) Article
  13. Smith, E.L., Abbott, A.P. and Ryder, K.S. Deep Eutectic Solvents (DESs) and Their Applications. Chem. Rev. 114, 21, 11060–11082 (2014) Article
  14. Yi, L., Wu, X., Guo, L., Chen, J. et al. Applications of ionic liquids and deep eutectic solvents for the extraction of phenolic compounds from coal-based crude oils. Separation and Purification Technology. 337, 13, 126383 (2024) Article
  15. Wu, T., Han, B. (2019). Supercritical Carbon Dioxide (CO2) as Green Solvent. In: Han, B., Wu, T. (eds) Green Chemistry and Chemical Engineering. Encyclopedia of Sustainability Science and Technology Series. Springer, New York, NY.  Article