Remarkable differences between benzaldehyde and isobutyraldehyde as coreductant in the performance toward the iron(III) porphyrins-catalyzed aerobic Baeyer–Villiger oxidation of cyclohexanone, kinetic and mechanistic features

We ever reported that benzaldehyde was more effective than isobutyraldehyde toward the Baeyer–Villiger oxidation of cyclohexanone by using meso-tetraphenylporphyrin chloride (FeTPPCl) as catalyst in the presence of molecular oxygen (96% yield of ɛ-caprolactone in the presence of benzaldehyde vs 11% in the presence of isobutyraldehyde. J. Porphyrins Phthalocyanines 2008, 12, 94–100.). In this paper, the root causes for the remarkable differences in performance have been illuminated from the investigation of kinetic and mechanism. Based on the results of in situ FTIR, UV–vis spectra, and starch/KI experiments, the differences could be attributed to the varied mechanism for the two reaction systems. In the isobutyraldehyde-mediated aerobic Baeyer–Villiger oxidation of cyclohexanone system, peroxy isobutyric acid was the oxidative species to produce ɛ-caprolactone. However, the process was via the generation of high-valent iron porphyrin, which was the active species in the benzaldehyde-mediated Baeyer–Villiger oxidation of cyclohexanone.