Lactonization–Dimerization Competition in the Perchloric Acid-Catalyzed Conversion of Oleic Acid to γ-Lactone: Process Optimization and DFT Calculations

Perchloric acid exhibits excellent catalytic performance in the synthesis of lactones from unsaturated fatty acids. However, its potential explosive hazards limit its industrial application. To evaluate the feasibility of this catalytic system for industrialization and to provide guidance for the Brønsted acid-catalyzed lactone synthesis pathway, this study comprehensively investigates the reaction mechanism of the most commonly available 70 wt % perchloric acid in catalyzing the conversion of oleic acid to γ-lactone under mild conditions, combining experimental work with DFT calculations. A competitive reaction model between γ-lactonization and dimerization is proposed. The double bond migration was identified as the rate-determining step. Optimal conditions of 100–200 mol % (36–71 wt %) acid loading and a temperature range of 70–85 °C were established to maximize lactone yield, while polar solvents were found to be suboptimal for the reaction.