Metal-Free Synthesis of Adipic Acid via Organocatalytic Direct Oxidation of Cyclohexane under Ambient Temperature and Pressure

A direct metal-free approach for the production of adipic acid from cyclohexane is reported. The use of N-hydroxyphthalimide (NHPI) as a catalyst in the presence of HNO3/TFA enables the direct oxidation of cyclohexane to yield adipic acid under ambient temperature and pressure via a simple procedure. This reaction proceeds through an initial oxidation of cyclohexane to cyclohexanone oxime and cyclohexanone followed by a second oxidation of these intermediates to adipic acid. NHPI plays a crucial role in both oxidation steps to achieve a high yield and selectivity for adipic acid.