Basic Benzoheterocyclic Ketones with Adjustable Physical Properties Regulated by Alkalinity/Acidity and Rapid Response to Alkalinity in Biodiesel

Abstract Several common benzoheterocyclic ketones—benzofuran‐3(2H)‐one ( BFO ), benzo[b]thiophen‐3(2H)‐one ( BTO) , benzo[d]isoxazol‐3(2H)‐one ( BOZO ), and benzo[d]isothiazol‐3(2H)‐one ( BTZO )—exhibit remarkable halochromism properties. Notably, BFO and BTO demonstrate pronounced optical changes under acid‐base interactions, undergoing reversible keto‐enol isomerization when exposed to inorganic/organic alkalis ( BTO ) or acids. This color‐switching behavior persists in both liquid and solid states, enabling applications as anti‐counterfeiting inks and Fe 3 ⁺ sensors. Critically for biodiesel applications, BTO was found to induce significant emulsification in alkaline biodiesel due to salt formation under basic conditions. This discovery establishes benzoheterocyclic ketones as promising indicators for alkaline content monitoring in biodiesel systems. Our research provides both theoretical and practical foundations for developing novel quality control methods in biodiesel production and storage through molecular halochromism.