Amino acids as eco-friendly bio-organocatalysts in ROCOP for the preparation of biobased oligomers from fatty acid epoxides and waste sunflower oil

Abstract

Epoxy fatty acids and waste vegetable oils can be strategically utilized as renewable feedstock for the synthesis of novel bio-based oligomers. Herein, we present an efficient synthetic methodology for producing a wide range of bio-oligomers from the ring-opening copolymerization (ROCOP) reaction of linoleic acid-derived epoxides (MLO, methyl linoleate oxide; ELO, ethyl linoleate oxide; ILO, isopropyl linoleate oxide) or epoxidized sunflower oil (ESO) with cyclic anhydrides (such as phthalic anhydride PA, and maleic anhydride MA). The reaction is catalyzed by a wide variety of commercially available amino acids (AAs) along with tetrabutylammonium iodide (TBAI) serving as a cocatalyst. Among the studied AAs as bio-organocatalysts, L-glutamic acid (L-Glu) exhibited the best performance for the preparation of poly(MLO-co-PA), poly(ELO-co-PA), poly(ILO-co-PA), poly(MLO-co-MA), poly(ELO-co-MA), and poly(ILO-co-MA) achieving a 100 % conversion at 80 °C in only 30 min. In contrast, the synthesis of poly(ESO-co-PA) and poly(ESO-co-MA) required 1 h to reach full conversion under the same conditions. The resulting oligomers were extensively characterized by using NMR, FT-IR, GPC, and TGA. Additionally, a set of computational simulations based on density functional theory (DFT) method was also carried out to support our experimental findings. Climbing-image nudged elastic band (CI-NEB) method was employed to find the minimum energy path (MEP) that describes the reaction mechanism associated with the first step of this chemical transformation. The calculated reaction path provides an energetic and atomistic picture of the studied reaction which aims to understand the role of both catalysts.