Theoretical study on the catalytic reactivity of N-hydroxyphthalimide tuned by different heterocyclic substitutions on its phenyl ring for aerobic oxidation

Hydrogen Atom Transfer from Benzyl Alcohols to N-Oxyl Radicals. Reactivity Parameters

A model for predicting the rate constants of hydrogen atom transfer (HAT) from the α-C-H bond of p-substituted benzyl alcohols to N-oxyl radicals was proposed. To quantify the factors governing the reactivity of both N-oxyl radicals and benzyl alcohols, multivariate regression analysis was performed using various combinations of reactivity parameters. The analysis was based on a 2D array of 35 HAT reactions, the rate constants of which span 4 orders of magnitude. The proposed polyparameter equation approximates the experimental rate constants of reactions with high accuracy using three independent parameters: Brown and Okamoto's substituent constants σ⁺ in alcohol molecules and the spin population on O and N atoms in the N-O^• fragment of N-oxyl radicals [calculated by DFT/B3LYP/6-31G(d,p)]. The rate constants of HAT reactions from p-substituted benzyl alcohols to a series of aryl-substituted phthalimide-N-oxyl radicals containing either electron-withdrawing or electron-donating substituents (4-Cl, 4-HOOC, 4-CH₃O), quinolinimide-N-oxyl, benzotriazole-N-oxyl, and violuric acid radicals were experimentally determined at 30 °C in acetonitrile.

Catalytic Synthesis of 2,5-Furandicarboxylic Acid from Concentrated 2,5-Diformylfuran Mediated by N-hydroxyimides under Mild Conditions

Producing polyester monomer 2,5-furandicarboxylic acid (FDCA) from biomass as an alternative to fossil-derived terephthalic acid has drawn much attention from both academy and industry. In this work, an efficient FDCA synthesis was proposed from 10.6 wt % 2,5-diformylfuran (DFF) in acetic acid using a combined catalytic system of Co/Mn acetate and N-hydroxyimides. The intermediate product of 5-formyl-2-furandicarboxylic acid (FFCA) possesses the least reactive formyl group. N-hydroxysuccinimide was found to be superior to N-hydroxyphthalimide in catalyzing the oxidation of the formyl group in FFCA intermediate, affording a near 95 % yield of FDCA under mild conditions of 100 °C. Trace maleic anhydride was detected as by-product, which mainly came from the oxidative cleavage of DFF via furfural, furoic acid and 5-acetoxyl-2(5H)-furanone as intermediates.