Black yet green: Sulfonic acid functionalized carbon as an efficent catalyst for highly selective isomerization of α-pinene oxide to trans-carveol

[Display omitted] •In-situ single step synthesis of stable bifunctional acid-base Carbon derived hydrothermally from fishery Bio-waste (Chitosan).•The catalyst is active for isomerization of α-pinene oxide with 100 % conversion and highest selectivity of 85 % towards desired product, trans-carveol.•Highest selectivity of 85 % towards desired product, trans-carveol noted with the synthesized catalyst.•Double Bio-valorization. In this study, an inexpensive, high yielding, and environmentally benign bifunctional acid-base catalyst is prepared using a simple low-temperature hydrothermal carbonization method from a fishery bio-waste, chitosan as a carbon source and sulfuric acid, as _SO3H source. The successful formation of _SO3H group grafted carbon was confirmed by various physiochemical characterization methods such as powder XRD, FTIR, RAMAN, FESEM, EDAX, HRTEM, and XPS. Under the optimized reaction conditions, the bio-derived sulfonated hydrothermal carbon catalyst showed excellent performance for the isomerization of α-pinene oxide to trans-carveol (85% yield) at 160 °C in 1.5 h. The product selectivity was influenced mainly by the type of solvent used for the isomerization. No leaching of the sulfonated groups was observed even after five cycles without any significant loss in conversion and selectivity.