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.