Lattice Sulfur in Transition‐Metal Sulfides Enables Heteroatom‐Exchange Conversion of Biomass‐Derived Furans to Thiophene Derivatives: A Proof‐of‐Concept Study

Direct incorporation of sulfur into biomass‐derived oxygenates remains a largely unexplored challenge for the sustainable synthesis of sulfur‐containing heterocycles. Herein, we demonstrate that lattice sulfur in transition‐metal sulfides can serve as a reactive sulfur source for heteroatom‐exchange sulfurization, enabling the conversion of biomass‐derived furans into thiophene derivatives. A series of Fe _{(1− x )} Ni _x S ₂ bimetallic sulfides were synthesized via a one‐step hydrothermal method and evaluated as stoichiometric sulfurization reagents for converting 5‐hydroxymethylfurfural (HMF) and cellulose to methyl 5‐(methoxymethyl)thiophene‐2‐carboxylate (MMTC). Fe _0.5 Ni _0.5 S ₂ exhibited the highest sulfurization performance, affording an MMTC yield of 10.8 wt% from HMF and outperforming all other compositions. Raw cellulose was also converted to MMTC with a yield of 3.9 wt% through direct heteroatom‐exchange sulfurization. Characterization results suggest that the enhanced sulfurization performance of Fe _0.5 Ni _0.5 S ₂ correlates with balanced surface acidity and an increased proportion of lattice‐derived S ₂ ²⁻ species, which participate in sulfur transfer during heteroatom exchange. A plausible reaction pathway is proposed to rationalize MMTC formation. This work establishes a proof‐of‐concept strategy that lattice sulfur in transition‐metal sulfides can directly participate in biomass‐derived heteroatom‐exchange sulfurization, providing a conceptual foundation for sulfur‐mediated biomass valorization.