Critical Assessment of Copper-Alginate Hydrogel Beads as Recyclable and Heterogeneous Catalysts for Aqueous Azide-Alkyne Cycloaddition

Yanina Moglie^1*Eduardo Buxaderas¹Agoney González Cabrera²David Díaz Díaz^2*

• ¹Instituto de Quimica del Sur, Bahía Blanca, Argentina
• ²Universidad de La Laguna Instituto Universitario de Bio-Organica Antonio Gonzalez, San Cristóbal de La Laguna, Spain

In this work, we report the development of a reproducible and sustainable catalytic system based on copper ion-crosslinked alginate hydrogels for the synthesis of 1,2,3-triazoles via aqueous 1,3-dipolar cycloaddition at room temperature. The catalyst, derived from a biodegradable biopolymer matrix, is prepared through a simple, energy-efficient process and operates under mild conditions. Critical optimization identified sodium ascorbate as a key reducing agent, enabling the generation of catalytically active Cu(I) species. Among the evaluated morphologies, copper(II)-alginate hydrogels (Cu(II)-AHG) exhibited the highest performance, delivering near-quantitative yields (>95%) within 3 hours using only 2 mol% catalyst. Critical optimization revealed that sodium ascorbate, as a reducing agent, plays a pivotal role in enhancing catalytic efficiency. The Cu(II)-alginate hydrogel [Cu(II)-AHG] emerged as the optimal catalyst, achieving nearly quantitative yields (>95%) within 3 hours and a catalyst loading of 2 mol%, outperforming both its aerogel and xerogel counterparts. The protocol tolerates a broad range of terminal alkynes, offering excellent substrate scope and operational simplicity. The system operates under predominantly heterogeneous conditions and can be recycled up to four times with minimal loss of activity. Detailed structural and morphological characterization (FT-IR, SEM, EDX, TGA, and AAS) confirmed the integrity and mesoporous nature of the catalyst, correlating these features with its catalytic efficiency. This work highlights the potential of alginatebased materials as tunable, eco-friendly supports for transition metal catalysis and contributes to the advancement of green chemistry and circular economy strategies in synthetic methodologies.