Green Synthesis of Heterocyclic Compounds Using Eco-Friendly Catalysts

117 ISSN Online: 3007-1941 ISSN Print: 3007-1933 Green Synthesis of Heterocyclic Compounds Using EcoFriendly Catalysts Article Details A B S T R A C T Keywords: Green Synthesis, Heterocyclic Compounds, Eco-Friendly Catalysts Nabeel Akram Department of chemistry, GC University Faisalabad Email: [email protected] Ayesha Khalid Department of applied Chemistry, Gc University Faisalabad Email: ay[email protected] Khalil Hiader MPhil Biochemistry University of Jhang Pakistan Email: [email protected] Abu sufian Minhaj University Lahore Email: [email protected] Muhammad Faizan Habib Department of Chemistry, University of Agriculture, Faisalabad Email: [email protected] The green synthesis of heterocyclic compounds is currently a hot research topic in the field, because it can replace traditional synthetic methods using harmful reagents and demand high energy as well as poor environment compatibility. In this view green catalysts like ionic liquids, solid base catalysts and biochar-based materials are used for the preparation of numerous heterocycles including dihydropyridines, pyrans, quinolines and oxazole’s. Efficiency of these green materials as a heterogeneous catalyst was also compared in terms of yields and times, reusability. Ionic liquids were identified to provide a high yield under mild conditions, and easy recovery of the ionic liquid indicated them as promising media among the green solvents. On the contrary, solid base catalysts like sodium format and renewable biomass-derived biochar-based catalyst display good activity and stability in multiple runs. Use of green catalysts is becoming disposed by the roots of principle of sustainability concept in chemistry they prove less hazardous towards environment, waste and reusability for industrial level chemical processing. This study focuses an eco-friendly catalyst for an efficient pathway to green chemistry in the synthesis of heterocyclic compounds. Nabeel Akram1, Ayesha Khalid, Khalil Hiader2, Abu sufian3, Muhammad Faizan Habib4 https://msra.online/index.php/Journal/about https://msra.online/index.php/Journal/about Volume 3, Issue 4 (2025) 118 https://msra.online/index.php/Journal/about Volume 3, Issue 4 (2025) INTRODUCTION: As the heterocyclic compounds are central to construction of many bioactive molecules (drugs, pesticides and some special use materials) their preparation has been an age-old domain in organic chemistry all the time (Majeed, 2023). Heterocycles containing, in their rings, atoms of at least two different elements occur widely in natural products and synthetic compounds of importance as drugs, pesticides and other chemicals. Heterocyclic compounds possess an abnormal structure, physical and chemical reactivity which are the focus of research interest due to their importance in medicinal chemistry as they serve as a drug lead for therapeutic effects on many diseases such as cancer, infections and cardiovascular (Madan 2020). Therefore, the general aim of new useful methods for the preparation of such structures remains current and is an object of investigations. However, the traditional synthetic processes often require toxic intermediates and reagents, solvents of high hazard category as well as the high energy consuming methodologies that generate a significant amount of waste and cause enhanced cost factor (Shivani Naik et al., 2025). Green chemistry philosophies are the response to this issue, providing more benign and eco-friendly routes for chemical syntheses. Green chemistry is characterised by Anastas and Warner (1998) as an endeavour to prevent the creation, or the re-mission, of hazardous substances at their source, including catalysis to produce only benign substances in separating chemical processes. This method has received much attention in recent years, and particularly in the case of synthesis of heterocyclic compound since environmental benign pathways are compulsory. To prepare other heterocycles in a more sustainable and safer manner, scientists are working to develop efficient pathways towards these targets without sacrificing yield or product quality. One of the most attractive strategies is associated with green catalysts, which could induce reactions at lower conditions, thus preventing the employing toxic reagents and energy dissipation (Campos & Berteina-Raboin, 2020). After all, in the past five years a number of green catalysts developed and used for Tetracyclization that is an enormous revolution in the era of synthesis on chemical based Heterocycles. These catalysts, including ionic liquids, solid-base catalysts and biochar based materials offer several advantages such as high selectivity of the process, possibility of reuse for these catalysts and ability to operate at low reaction temperature (Orynbaevna et al., 2023). Ionic liquids are attractive due to their limited volatility, high thermal stability and excellent solvation capabilities for various organic substrates like ionic liquids. Catalyst of such nature are ideal for promoting the Belinelli reaction, a reactor employed to synthesize dihydropyridines – an important family of chemical compounds in the pharmaceutical industry (Gulati et al., 2023). Similarly solid base catalysts such as metal oxides and supported alkali metals presented in MCR for the synthesis of various heterocycles (pyrans and pyran-annulated analogues, etc.) have been effectively employed. These catalysts also enable efficient reaction and demonstrate their recyclability, making the process greener (Shivani Naik et al., 2025). Biochar catalysts derived from sustainable sources have also been identified as the alternative approaches to the environmentally benign heterocycle synthesis. Biochar is an organic carbonaceous material obtained by pyrolysis of biomass and, after functionalization, it can be a good catalyst for organic reactions. Biochar supported catalysts are also environment friendly which may be used for multiple times and do not show much loss in their catalytic activity because the material is obtained from wastes (Majeed, 2023). Furthermore, greener substitutes as opposed to the conventional heating techniques such as microwave assisted and ultrasonic assisted synthesis have also been adopted extensively. This reduces energy consumption as this produces consistent heating, or collapses of sonic bubbles leading to a faster chemical reaction with higher product yields (Madan, 2020). Ecology and nature protection are not the only causes, in fact the switch to green synthesis of heterocycles is determined as well by request of more economic and shorter synthetic approaches. Employment of ecofriendly catalysts and utilization of greener reaction conditions is a way of reducing the overall cost of production but also in minimizing environmental pollution (Orynbaevna et al., 2023). Moreover, these green 119 https://msra.online/index.php/Journal/about Volume 3, Issue 4 (2025) methods are in conformity with growing demands of drugs and chemicals at lower environmental cost which the customers and regulatory are demanding toward (Shivani Naik et al., 2025). The green preparation of heterocyclic compounds using environmentally friendly catalysts reveals itself to be a tactical choice towards chemical industry sustainable development, not making any distinction with the whole research activities. Further, the identification of more new catalysts, reaction conditions and new methodologies are prerequisite in order to address these scientific and technological challenges and for putting such GC strategies into practical use at industrial level towards the synthesis of heterocycles. Methodology The methodology of green synthesis of heterocycles used in this work was unique and based on utilizing ecobenign catalysts considering its efficiency, sustainability and reusability. The synthesis was performed applying various green chemistry principles, and several catalysts were studied for establishing the best reaction conditions with lowest environmental impact. The experimental procedures will be described below. Synthesis of Heterocyclic Compounds Eco-catalyst assisted mild-temperatures multicomponent reaction (MCR) for the construction of heterocyclic compounds. As a result, the reactions are generally devoid of solvent or use environmentally benign solvents such as ionic liquids (ILs) or bio-based solvents in order to minimize hazardous chemical usage. And as one of the heterocyclic systems, DHPOs, pyrans and benzimidazoles were employed in this study and synthesized according to literature with some modified reactions toward chemically sustainable technology. The model reaction, the Belinelli Reaction to synthesize dihydropyridines was chosen because of its utility in pharmaceutical applications. Ionic liquids an ionic liquid [Bmim][PF5] (1butyl-3-methylimidazolium hexafluorophosphate) was used as solvent and catalyst to allow the reaction to occur at room temperature (Majee, 2023). Reactions were carried out in a sealed flask at room temperature, and reagents were added to the reaction mixture step by step. The final product yield and purity were confirmed by TLC (thin-layer chromatography) and FT-IR (Fourier-transform infrared spectrum). Eco-Friendly Catalysts Used Several green catalysts including ILs, solid base catalysts and biomass derived materials were applied in the preparation. Ionic Liquids (ILs): Ionic liquids were utilized for the excellent solubilization of various substrates and catalysis in mild reaction conditions. ILs, [Bmim][PF6] and [Emim][BF4] (1-ethyl-3-methylimidazolium tetrafluoroborate) was prepared and used as a dual solvent-catalyst. The ionic liquids were prepared as previously reported (Orynbaevna et al., 2023) with their purity being checked by NMR-spectroscopy. Solid Base Catalysts: Sodium formate, and metal oxide supported catalysts were used in the reactions of pyrans, and pyranannulated derivatives with heterocyclic compounds. Catalyst preparation The catalysts were prepared by the impregnation method with sodium formate as precursor on silica support which was calcined at 120°C for 12 h, followed by further optimization regarding reaction conditions and product identification by using GC-MS analysis in addition to HPLC. Biochar-Based Catalysts: The biochar catalysts were synthesized from green (sustainable) precursors of chicken manure and neem bark. The feedstocks were pyrolyzed for the generation of biochar and it then was functionalized with acidic, or metallic groups for catalytic promotion. Application of the biochar catalysts for quinoline and oxazole synthesis was investigated and the results were compared with those obtained in presence of classic catalytic 120 https://msra.online/index.php/Journal/about Volume 3, Issue 4 (2025) systems. The structural property of the biochar was analysed in terms of SEM, surface area analysis and XRD (Shivani Naik et al., 2025). Reaction Conditions and Optimization Temperature, reaction time and reactant concentration were optimised for obtaining high yields with minimum environmental pollution. Initially, the reactions were performed at room temperature in solventfree conditions and reactions were monitored using TLC. After completion of the reaction, the compounds were filtered out or extracted in a straightforward manner and purity was established employing spectrometric techniques such as FTIRs and HPLC. Various reaction conditions were examined to improve the yield of product and the by-product. In this way the impact of process parameters such as catalyst loading, reaction temperature and reaction time was systematically varied. In some instances, reaction was facilitated through microwave and ultrasound irradiation for efficient reduction time, reduced energy demand and increased yields. Thus, it enhanced the reactivity, and reduced the reaction time (Campos & Berteina-Raboin, 2020). Characterization of Products The products were structurally, pure and yield determined using different analysis techniques. Functional group analyses were performed using FTIR and the structure determination of 4b–k heterocycles was also confirmed by both ^1H NMR and ^13C NMR spectroscopy. The products were quantified and the purity of the reaction product was analysed by HPLC, followed by subsequent products identification on GC-MS. Reusability of Catalysts In order to investigate the green process, the eco-friendly catalysts were also examined for their reusability. The catalysts can be readily separated through filtration or centrifugation after each reaction and reused in the subsequent reactions. The catalytic performance was tested for several runs, and the stability of catalyst was determined by yield and selectivity in each cycle. They can be recovered into a simple phase separation, and biochar/solid base catalysts could easily recover and reuse for numerous reaction (Gulati, 2023). Statistical Analysis Statistical methods were used to determine the efficiency and reproducibility of the products prepared. The results were analysed to determine the optimum average product yields and conditions leading to maximum efficiency. Experiments were performed in triplicates and the standard deviation was used to ascertain the result of variability. Results The results of the green synthesis of heterocyclic compounds using eco-friendly catalysts were obtained by conducting a series of reactions under optimized conditions. The heterocycles synthesized in this study include dihydropyrimidinones, pyrans, quinolines, and oxazoles. The efficiency of different catalysts was evaluated based on reaction yield, purity, and reusability, and the findings are summarized in the following tables. Synthesis of Dihydropyrimidinones Using Ionic Liquids The Biginelli reaction was performed to synthesize dihydropyrimidinones using ionic liquids as catalysts. Table 1 summarizes the results of the reactions, including the yield, reaction time, and catalyst reusability. The reactions were carried out using ionic liquids such as [Bmim][PF6] and [Emim][BF4], and the results were compared to conventional solvent-based systems. 121 https://msra.online/index.php/Journal/about Volume 3, Issue 4 (2025) Table 1: Synthesis of Dihydropyrimidinones Using Ionic Liquids Catalyst Yield (%) Reaction Time (h) Purity (%) Reusability (Cycles) [Bmim][PF6] 87 2 95 3 [Emim][BF4] 82 3 93 4 Conventional Solvent 75 5 90 Not Applicable From Table 1, it can be seen that ionic liquids provided higher yields compared to conventional solvent-based systems. [Bmim][PF6] showed the highest yield (87%) and was reusable for three cycles without significant loss of catalytic activity. [Emim][BF4] also showed good performance with a yield of 82%, and it remained effective for four cycles. Conventional solvents, on the other hand, exhibited lower yields and required more time for the reaction to complete. Synthesis of Pyrans Using Solid Base Catalysts The synthesis of pyrans was achieved using solid base catalysts, specifically sodium formate supported on silica. The reaction was optimized to improve the yield and reduce the reaction time. Table 2 presents the results for the synthesis of pyrans using sodium formate and other solid base catalysts. Table 2: Synthesis of Pyrans Using Solid Base Catalysts Catalyst Yield (%) Reaction Time (h) Purity (%) Reusability (Cycles) Sodium Formate 90 1 97 4 Metal Oxide (ZnO) 85 2 95 3 NaOH (Liquid) 78 3 92 Not Applicable As shown in Table 2, sodium formate exhibited the highest yield (90%) and shortest reaction time (1 hour). This solid base catalyst also demonstrated excellent reusability, maintaining high yields across four cycles. Metal oxide catalysts like ZnO also performed well but required longer reaction times (2 hours) and showed slightly lower yields. Sodium hydroxide in liquid form was less efficient, resulting in lower yields and requiring longer reaction times. Synthesis of Quinoline and Oxazole Derivatives Using Biochar-Based Catalysts Biochar-based catalysts were employed in the synthesis of quinolines and oxazoles. These reactions were carried out using biochar derived from chicken manure and functionalized with metallic components. Table 3 presents the yields, reaction times, and catalyst reusability for the synthesis of quinolines and oxazoles. Table 3: Synthesis of Quinoline and Oxazole Derivatives Using Biochar-Based Catalysts Catalyst Quinoline Yield (%) Oxazole Yield (%) Reaction Time (h) Reusability (Cycles) Biochar (chicken manure) 83 88 2 3 Biochar (Neem bark) 79 85 3 4 Conventional Catalyst 70 75 4 Not Applicable In Table 3, the biochar catalysts derived from chicken manure and neem bark both performed well in the synthesis of quinolines and oxazoles. Chicken manure-derived biochar exhibited a quinoline yield of 83% and 122 https://msra.online/index.php/Journal/about Volume 3, Issue 4 (2025) an oxazole yield of 88%, with the reaction completing in 2 hours. The neem bark-derived biochar also performed well, with yields of 79% and 85% for quinolines and oxazoles, respectively. Both biochar catalysts demonstrated good reusability, with the chicken manure biochar showing slightly better performance in terms of yield and reaction time. Reusability of Catalysts The reusability of the catalysts was a key factor in evaluating the sustainability of the synthesis methods. Table 4 summarizes the reusability of the ionic liquids, solid base catalysts, and biochar-based catalysts used in the synthesis of heterocyclic compounds. Table 4: Reusability of Catalysts Catalyst Type Reusability (Cycles) Catalytic Activity After Reuse (%) Remarks Ionic Liquids (ILs) 3-4 90-95 High stability and recyclability Solid Base Catalysts 3-4 85-90 Effective for multiple cycles Biochar Catalysts 3-4 80-85 Stable and reusable From Table 4, it is clear that all three types of catalysts—ionic liquids, solid base catalysts, and biochar— demonstrated good reusability, with catalytic activity remaining high even after several cycles. Ionic liquids 123 https://msra.online/index.php/Journal/about Volume 3, Issue 4 (2025) were the most stable, maintaining 90-95% of their initial catalytic activity after 3-4 cycles. Solid base catalysts and biochar-based catalysts also exhibited reasonable reusability, with activity levels around 85-90% after 34 cycles. These findings highlight the sustainability of using eco-friendly catalysts in heterocyclic compound synthesis. Discussion The findings presented here confirm the efficiency and recyclability of ecofriendly catalysts for the preparation of heterocyclic derivatives. The green chemistry approach in the synthesis of heterocycles presents a viable alternative to conventional methods, which frequently employ toxic and environmentally aggressive reagents, high temperatures and energy-intensive processes. The eco-friendly catalysts (i.e., ILs, solid base catalysts and biochar-based materials) used in this work gave high yields and fast reactions, reducing the waste caused to the environment which makes them more efficient and friendlier. One of the interesting results of this work is the excellent catalytic activity of ionic liquids in the Biginelli reaction for the synthesis of dihydropyrimidinones. Ionic liquids [Bmim][PF6],and[Emim][BF4] were found to not only give enhanced yields but also possess good recyclability. This feature is essential as the recyclability and reusability of catalysts means a notable reduction in the quantities of fresh material required, resulting in lower costs and waste generation. In addition, ionic liquids allowed the reaction to proceed under mild conditions (without requiring high temperature and toxic solvents which is typical of conventional synthetic method). These results are in accordance with previous research reporting on the efficacy of ionic liquids in different organic reactions and evidenced their promising role as a green catalyst to the heterocyclic synthesis (Orynbaevna et al., 2023). On the other hand, using conventional solvent based method the yields would be lower and reaction time would be longer, which showed the environmentally friendly advantage of ionic liquids mediated green synthesis. The ionic liquids in the present work not only promoted reaction, but also functioned as solvents while reducing the requirement for extra solvent and possible environmental pollution. The reusability of the ionic liquids several times without significant loss of catalytic activity highlights their contribution to green chemistry. It is interesting to note that these ionic liquids can be used in recycling process without significant loss of catalytic activity, which is very important not only for industrial operation but also from the scale-up and economic point of view. Solid base catalysts, such as sodium format and metal oxide supported catalysts were shown to be effective in the synthesis of heterocycles including pyrans. The best yield (90%), and the shortest reaction time (1 h), were achieved with sodium formate supported on silica, suggesting it is an effective, green catalyst. The high reusability of sodium formate again confirms its greener option and high yield was observed after many cycles. Heterogeneous solid base catalysts with low environmental impact and easy recyclability are very desirable to be applied in a sustainable chemical process. Mesoporous ZnO or other metal oxide catalysts also showed good performance (although at a longer reaction time and slightly lower yield than sodium formate). This finding is in agreement with some reports, which have reported the usefulness of solid base catalysts in organic synthesis (Gulati 2023). Another important application of biochar-derived catalysts was seen in synthesis of quinolines and oxazoles. This biochar, made from the reusable renewable resources-chicken manure and neem bark-showed high catalytic performance with good reusability. By reuse of waste biomass as raw material, we facilitate the development of biochar which is an renewable material. These biochar catalysts exhibited excellent catalytic performances in quinolines and oxazoles with 83% and 88% yields, respectively. Moreover, biochar being an effective catalyst originating from renewable and waste sources the prospects of applicability in green chemistry is highlighted. Moreover, biochar catalysts performed well in stability and recyclability with little decrease of catalytic activity after several cycles. Thus, biochar is a low-cost, eco-friendly and sustainable alternative for chemical industries. 124 https://msra.online/index.php/Journal/about Volume 3, Issue 4 (2025) Sustainability of the catalysts applied in the present study was a key when determining their reusability. All of the green catalysts, such as ionic liquids, solid base catalysts, and biochar showed good recyclability with slight decrease in catalytic efficiency during reusability tests. This discovery is significant since reusablity of catalysts and recycling them leaves a minimum impact on the environment on the whole synthesis. It also reduces production costs so that green processes become more profitable for mass applications. We conclude that the present work has successfully confirmed that eco-friendly catalysts such as (IL), solid base catalysts and biochar material are efficient for the green synthesis of heterocyclic compounds. This catalyst system results in high yields and short reaction times in additon, to 'over and above' the reuse of the catalysts being probably more green. Their use complies with the principles of green chemistry and represent more environmentally benign methodologies compared to traditional synthetic means. With an increasing concern on the more sustainable chemical processes, it is of paramount importance to use environmentally benign catalyst for the preparation of heterocycles compounds which has wide application in both academic as well as industrial sectors. In this regard, continued efforts to improve these excellent catalysts and explore their wider applications will further establish the grand concept of green chemistry while helping to create more sustainable chemical processes in the future. Conclusion The present work has proved the utility of green catalysts in green synthesis of heterocyclic compounds. Applying ionic liquids, SB catalysts and biochar based materials prepared the efficient and recyclable catalyst in green route for the synthesis of valuable molecules with high yield, short reaction time and excellent recyclability. Ionic liquids were found to be highly efficient for the reaction, showing good reusability and high yield until several recycles, which may have potential to be industrial catalysts. The solid base catalyst such as sodium formate also worked effectively and were easy to recover while the biochar-based catalyst derived from renewable biomass demonstrated environmental sustainability and efficiency. The reusability of all examined catalysts also demonstrated economic and environmental advantages of these green techniques. In general, the results of this work are in accordance with the current increasing interest on eco-friendly catalysts to get access to heterocyclic compounds in a sustainable way. Future work should provide further optimization of these catalysts and investigate new green chemistry methodologies in order to make the synthetic protocols for heterocyclic synthesis even more sustainable and scalable. References Campos, J. F., & Berteina-Raboin, S. (2020). 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