Pulcherrimin: a bio-derived iron chelate catalyst for base-free oxidation of 5-hydroxymethylfurfural to furandicarboxylic acid

<h4>This study explores the green and sustainable catalytic properties of pulcherrimin, a naturally occurring iron chelate, for the base-free oxidation of 5-hydroxymethylfurfural (5-HMF) to high-value products such as 2,5-furandicarboxylic acid (FDCA), a vital precursor for renewable bioplastics. Pulcherrimin, derived from <i>Metschnikowia pulcherrima</i>, selectively oxidised 5-HMF to 5,5-diformylfuran (DFF) at 100 °C, while at 120 °C, the oxidation proceeded efficiently to FDCA with a conversion of 73.3 ± 1.1%, and FDCA selectivity of 89.0 ± 1.9% under mild, base-free conditions. Adding a mild base enhanced overall conversion but diverted the reaction pathway towards 5-hydroxymethyl-2-furancarboxylic acid (HMFCA), reducing the FDCA yield. The reusability of the pulcherrimin catalyst was tested over five reaction cycles, retaining a conversion activity of 59.1% and FDCA selectivity of 39.8%. These findings establish pulcherrimin as a promising, water-tolerant biocatalyst with potential environmental advantages, such as base-free operation and simplified product recovery, contributing to greener catalytic processes. Eliminating a homogenous base co-catalyst makes the process greener by avoiding the need for subsequent neutralisation steps while reducing environmental and economic costs.</h4><h4><br><br><b>Green foundation</b></h4><p dir="ltr">1. This work presents pulcherrimin, a bio-derived iron chelate, as a sustainable catalyst for the oxidation of 5-hydroxymethylfurfural (5-HMF) to 2,5-furandicarboxylic acid (FDCA) under mild, base-free conditions. The study demonstrates an efficient, and environmentally friendly pathway for FDCA production, avoiding the need for noble metal catalysts and homogeneous base co-catalysts.</p><p dir="ltr">2. The production of FDCA is critical for bioplastic synthesis, particularly in replacing petrochemical-based terephthalic acid in polyester manufacturing.</p><p dir="ltr">3. This study paves the way for biocatalyst-driven green chemistry, encouraging further exploration of bio-mineralised materials in catalysis. Future research will focus on enhancing catalyst stability and integrating bio-based catalysts into closed-loop biorefinery processes for scalable, low-impact chemical production.</p>