A Rationale of the Baeyer–Villiger Oxidation of Cyclohexanone to ε‐Caprolactone with Hydrogen Peroxide: Unprecedented Evidence for a Radical Mechanism Controlling Reactivity

Abstract

We demonstrate, for the first time, in the Baeyer-Villiger oxidation of cyclohexanone with aqueous hydrogen peroxide under conditions aimed at obtaining ε-caprolactone, that a thermally activated radical reaction leads to the concurrent formation of adipic acid, even when a stoichiometric amount of the oxidant is used. In fact, ε-caprolactone is the primary reaction product, but it is more reactive than cyclohexanone, and quickly undergoes consecutive transformations. When titanium silicalite-1 (TS-1) is used as a catalyst, the high concentration of hydroxy radicals within its pores accelerates the reaction rates, and the consecutive formation of adipic acid (and of lighter diacids as well) becomes largely kinetically preferred. The proper choice of the solvent, which also may act as a radical scavenger, both without catalyst and with TS-1, is a powerful tool for controlling the rates of the various reactions involved.

Nano silica boron sulfuric acid as a dual Brønsted/Lewis acid and a heterogeneous catalyst in Baeyer–Villiger oxidation of ketones with hydrogen peroxide

“…Effect of the amount of NSBSA e-Caprolactone is an important chemical compound, which is widely used in the synthesis of polyester [1,5,16,24,25]. Therefore, the B-V oxidation of cyclohexanone catalyzed by H 2 O 2 /NSBSA was chosen as a sample reaction to (Table 1).…”

“…The Baeyer-Villiger (B-V) oxidation reaction as a long-known versatile chemical transformation of ketones to either an ester or a lactone, has attracted great interest as a tool for the preparation of pharmaceuticals such as antibiotics and also compounds of fine chemicals, agrochemical and intermediate industries [1][2][3][4]. Many traditional oxidation processes are associated with the use of the organic peracids and also stoichiometric high-oxidation state transition metals [4,5].…”

A new hybrid porphyrin-heteropolyacid material: Synthesis, characterization and investigation as catalyst in Baeyer–Villiger oxidation. Synergistic effect

“…Large exothermic effect visible at 591°C is connected with the complete decomposition of hybrid. Lower decomposition temperature of hybrid in comparison with tungstophosphoric acid indicates that stability of the former is lower than the stability of H 3 [41]. It is understandable since tungstophosphoric acid possesses much stronger acidic properties than its molybdenum analogue.…”

“…This hybrid, its molybdenum analogue, tungstophosphoric and molybdophosphoric acids as well as their Mn, Fe and Co salts were applied in Baeyer-Villiger oxidation of cyclohexanone to caprolactone with molecular oxygen. Due to the synergistic effect porphyrin-heteropolyacid hybrids exhibit similar catalytic activity as appropriate heteropoly salts and much higher activity than parent heteropolyacids.Baeyer-Villiger oxidation of cyclic ketones to the corresponding lactones (Scheme 1) has received considerable attention in organic synthesis because products are very important industrial intermediates in the production of polymers, pharmaceuticals and herbicides [1][2][3]. Polyoxometalates are inorganic metal-oxygen clusters well-known as efficient catalysts for the selective oxidation of hydrocarbons [4][5][6].…”

“…Baeyer-Villiger oxidation of cyclic ketones to the corresponding lactones (Scheme 1) has received considerable attention in organic synthesis because products are very important industrial intermediates in the production of polymers, pharmaceuticals and herbicides [1][2][3]. Polyoxometalates are inorganic metal-oxygen clusters well-known as efficient catalysts for the selective oxidation of hydrocarbons [4][5][6].…”