The development of renewable intermediates for bio-based polymeric materials requires environmentally friendly routes for the chemical functionalization of vegetable oils. In this study, sesame oil was epoxidized using Amberlite® IRC 120H and Dowex® 50WX2 acidic ion exchange resins as heterogeneous catalysts, with hydrogen peroxide and acetic acid as the in situ peracetic acid system and toluene as solvent. The novelty of this work lies in the comparative evaluation of these ion exchange resins for sesame oil epoxidation under different temperatures and reaction times, providing insight into the balance between double-bond conversion and oxirane stability. Reaction temperatures of 40, 60, and 80 \(^\circ\)C and reaction times of 2, 4, and 6 h were evaluated. Reaction progress was assessed by iodine value determination, while oxirane ring formation was confirmed by Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance spectroscopy (\(^1\)H NMR). The iodine value decreased markedly after reaction, confirming the consumption of carbon–carbon double bonds. Within the evaluated temperature range, 80 \(^\circ\)C was the most favorable temperature for both catalysts. The highest double-bond conversions were obtained after 4 h of reaction, reaching 95.2% with Dowex® 50WX2 and 87.8% with Amberlite® IRC 120H. For both catalysts, extending the reaction time to 6 h did not improve conversion, suggesting that prolonged reaction times may favor secondary reactions or epoxide degradation. FTIR spectra showed the appearance of characteristic oxirane bands in the 800–950 cm\(^{-1}\) region, together with a decrease in the olefinic =C–H band near 3005 cm\(^{-1}\). Similarly, \(^1\)H NMR showed a reduction in olefinic proton signals at 5.3–5.5 ppm and the formation of epoxide signals between 2.9 and 3.2 ppm. The results indicate that Dowex® 50WX2 provides higher double-bond conversion, while Amberlite® IRC 120H may favor greater oxirane stability.
