Review article on the synthesis of 1,2,3-triazole using green solvents
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Green Solvent Synthesis of 1,2,3-Triazole: A Review
Introduction to 1,2,3-Triazole Synthesis
1,2,3-Triazoles are a class of heterocyclic compounds that have garnered significant interest due to their diverse applications in pharmaceuticals, agrochemicals, and materials science. The synthesis of these compounds has evolved to incorporate green chemistry principles, emphasizing the use of environmentally benign solvents and catalysts.
Green Solvents in 1,2,3-Triazole Synthesis
Glycerol as a Green Solvent
Glycerol has been identified as an effective green solvent for the synthesis of 1,2,3-triazoles. A notable method involves a one-pot three-component reaction using organic halides, terminal acetylenes, and sodium azide, catalyzed by CuI and diethylamine. This approach yields a variety of 1,2,3-triazoles in good to excellent yields at room temperature, showcasing glycerol's potential as a sustainable solvent .
Water as a Green Solvent
Water is another green solvent that has been successfully employed in the synthesis of 1,2,3-triazoles. A visible-light-promoted copper-catalyzed azide-alkyne cycloaddition (CuAAC) method uses water as the solvent under mild conditions. This method not only achieves high yields but also allows for the recycling of copper and the solvent, enhancing the process's sustainability. Additionally, a DBU-water catalytic system has been reported for the synthesis of 1,4,5-trisubstituted-1,2,3-triazoles, offering high atom economy and low environmental impact.
Deep Eutectic Solvents (DES)
A novel Cu(II)-acidic deep eutectic solvent (Cu(II)-ADES) has been developed, combining copper salt, choline chloride, and gallic acid. This solvent system facilitates the synthesis of 1,4-disubstituted 1,2,3-triazoles under base-free conditions, achieving yields up to 98%. The Cu(II)-ADES is stable and can be reused multiple times without significant loss of activity, making it a promising green solvent for large-scale synthesis.
Catalysts in Green Solvent Systems
Copper Nanoparticles
Copper nanoparticles have been effectively used in green solvent systems for the synthesis of 1,2,3-triazoles. For instance, copper nanoparticles on charcoal (Cu/C) catalyze the three-component coupling reaction in water, yielding 1,2,3-triazole derivatives with high regioselectivity and excellent yields. This method also allows for the catalyst to be recycled up to ten times without significant loss of activity.
Nanoreactors
A novel nanoreactor, Cu@KCC-1-NH-CS2, has been employed for the synthesis of 1,4-disubstituted 1,2,3-triazoles in water. This system offers high catalytic performance, short reaction times, and excellent reusability, highlighting the advantages of using engineered nanocatalysts in green solvent systems.
Alternative Green Solvent Systems
Fehling Solution
An alternative green solvent system involves the use of Fehling solution combined with N,N-diisopropylethylamine and hydrazine. This method facilitates the regioselective synthesis of 1,4-disubstituted-1H-1,2,3-triazoles via azide-alkyne cycloaddition under mild conditions without the need for organic solvents.
Click Chemistry Approach
The click chemistry approach has also been utilized to synthesize 1,4-disubstituted 1,2,3-triazole acetamide derivatives using water and n-butanol as alternative solvents. This method achieves excellent yields and reduces the environmental impact of the chemical processes involved.
Conclusion
The synthesis of 1,2,3-triazoles using green solvents has made significant strides, with various methods demonstrating high efficiency, sustainability, and recyclability. Glycerol, water, and deep eutectic solvents have emerged as promising green solvents, supported by innovative catalytic systems such as copper nanoparticles and nanoreactors. These advancements underscore the potential of green chemistry in developing environmentally friendly synthetic routes for 1,2,3-triazoles.
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