Mamtani, Kapil, Farid, Mohammed Mehdi, and Shahbaz, Kaveh (2026) From Structure to Stability: A Comparative Evaluation of Ammonium- and Phosphonium-Based Deep Eutectic Solvent Catalysts in Glycerolysis. Chemcatchem, 18 (11). e70844.

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Abstract

Deep eutectic solvents (DESs) are efficient catalysts; however, their foundational hydrogen-bonding framework is susceptible to water-induced disruptions. In this study, a structure-stability-performance relationship is examined for two acidic DESs: tetrabutylammonium hydrogensulfate (N-DES) and tetraphenylphosphonium bromide (P-DES) with p-toluenesulfonic acid monohydrate (PTSAM), in a glycerolysis reaction. Glycerolysis of free fatty acids (FFAs) generates water as by-product, creating dynamic water-rich reaction environment, providing a controlled basis for comparing two DESs against water-ingression. N-DES being more acidic achieved equilibrium conversion faster than P-DES, under identical conditions, validated by lower apparent activation energy for N-DES. Both DESs remained in the glycerol phase post-reaction, and under recycle routine there was water build-up in glycerol phase. The water ingress affected the catalytic stability of both DESs, while removing water via oven evaporation, resulted in improved catalytic conversion- N-DES (40% to 62%) in comparison to P-DES (46% to 81%), at the end of fifth cycle. TGA data confirms thermal stability of both DESs within operational ranges, eliminating DES degradation behind decreased catalytic ability. Insights from viscosity and molecular self-diffusion data highlights the differences in component mobility and hydrogen-bond network organization, as most probable cause of divergent resistance to water-induced disruption during recycling.

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