Catalytic Oxidation Processes Using N-Hydroxyphthalimide

N-Hydroxyphthalimide (NHPI) has emerged as a versatile organocatalyst for aerobic and stoichiometric oxidation of a wide range of organic substrates. Central to its activity is the generation of the phthalimide-N-oxyl (PINO) radical, a highly electrophilic species capable of abstracting hydrogen atoms from unactivated C–H bonds. Under mild conditions and in the presence of molecular oxygen or suitable oxidants, PINO mediates selective oxidation of benzylic, aliphatic and heteroatom-adjacent positions, often in synergy with transition-metal co-catalysts such as cobalt or manganese salts. The broad substrate scope ranges from simple hydrocarbons and alcohols to complex natural products and polymer precursors. NHPI-based systems have demonstrated industrial relevance, for example in the efficient conversion of cyclohexane to cyclohexanol and cyclohexanone, and in the synthesis of fine chemicals under “green” conditions. Recent advances include tailored NHPI derivatives bearing lipophilic or electron-withdrawing substituents, which enhance solubility and tune radical reactivity, and mechanistic studies that illuminate the role of secondary oxidants in catalyst turnover. Collectively, these developments underscore NHPI’s potential to replace metal-centric processes, reduce waste and improve energy efficiency in large-scale oxidations.

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Catalytic Oxidation Processes Using N-Hydroxyphthalimide publication trend

The graph below shows the total number of articles in catalytic oxidation processes using n-hydroxyphthalimide across all publications each year (not limited to Nature Index journals).

Technical terms

N-hydroxyphthalimide (NHPI): An organic compound that generates phthalimide-N-oxyl radicals under oxidative conditions.

Phthalimide-N-oxyl (PINO) radical: The catalytically active N-oxyl species responsible for hydrogen atom abstraction.

Hydrogen atom transfer (HAT): A radical mechanism in which a hydrogen atom is transferred from a substrate to a radical species.

Bond dissociation enthalpy (BDE): The energy required to homolytically cleave a chemical bond, often used to predict radical reactivity.

References

1. A Mechanistic Investigation of the N‑Hydroxyphthalimide Catalyzed Benzylic Oxidation Mediated by Sodium Chlorite. The Journal of Organic Chemistry (2024).
2. 5,8-Di-tert-butyl-2-hydroxy-1H-benzo[de]isoquinoline-1,3(2H)-dione—A New Lipophilic N-oxyl Radical Precursor. Molbank (2023).