Acid-Catalyzed Decomposition of the Benzyl Nitrite Intermediate in HNO3-Mediated Aerobic Oxidation of Benzyl Alcohol

Benzyl nitrite (PhCH2ONO) was previously identified as the pivotal intermediate in the HNO3-mediated oxidation of benzyl alcohol. Its acid-catalyzed decomposition yields benzaldehyde and HNO, the precursor of undesirable N2O. Most likely, an analogous mechanism is responsible for the formation of N2O during the oxidation of cyclohexanol and cyclohexanone to adipic acid, the largest industrial source of this important greenhouse gas. In this paper, the decomposition of benzyl nitrite is studied in more detail, allowing the kinetic isotope effect and the influence of substituents to be determined. A linear EvansPolanyi correlation between the measured Arrhenius activation energies and the computed reaction energies was established. Furthermore, the differences in the reactivities of the substituted benzyl nitrites are reflected in the oxidation of the corresponding alcohols, and also affect the rate-determining step in the overall mechanism. The results of this study corroborate the importance of the nitrite intermediate in HNO3-based oxidation technology.