Selective aerobic oxidation of alcohols catalyzed by iron chloride hexahydrate/TEMPO in the presence of silica gel

Abstract

*An environmentally friendly and efficient process whereby FeCl 3 •6H 2 O/2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO)-catalyzed oxidation of alcohols to the corresponding aldehydes and ketones is accomplished in the presence of silica gel using molecular oxygen or air as the terminal oxidant. The electron-deficient benzyl alcohol was smoothly oxidized to the corresponding aldehydes with up to 99% isolated yield. It was found that silica gel not only could enhance the catalytic reaction rate but also increase the selectivity for the product. The high performance of FeCl 3 •6H 2 O/TEMPO catalyst system in the presence of silica gel might be attributed to the surface silanol groups. UV-visible spectra analysis showed that the Fe (III)-TEMPO complex could serve as the active intermediate species in the present catalytic system. A plausible mechanism of the catalytic system is proposed.

Photodecomposition of dichloromethane catalyzed by tetrachloroferrate(iii) supported on a Dowex anion exchange resin

“…The rate of photodissociation, eqn (11), can be assumed to be constant, while the rates of eqn (12) and (13) can be expressed approximately in terms of the volume fractions, especially in view of the fact that the formula weights of C 6 H 12 and CH 2 Cl 2 are almost identical. Given a steady state from these three steps, the rate of COCl 2 formation has the functional form…”

“…FeCl 3 has been used as a homogeneous catalyst for photooxidation, [8][9][10][11][12] chlorination, 13 and aerobic dechlorination, 2 but there have been no reports of its use as in a heterogeneous photocatalyst. The photochemical properties of FeCl 4 − are similar to those of FeCl 3 , although FeCl 4 − does not share its Lewis acidity.…”

Photocatalysis of ethanol oxidation by tetrachloroferrate(III) supported on Dowex 2‐X8

“…Among the objectives of green chemistry is that of oxidizing alcohols to aldehydes or ketones using molecular oxygen in place of permanganate and other strong oxidizing agents . A variety of catalytic systems have been studied for this purpose, using thermal or photochemical reaction conditions . In either case the goals include finding cheap catalysts and using a minimum amount of energy.…”

“…Thermal catalysis of alcohol oxidation has been carried out with a variety of systems, generally involving a transition metal ion and additional components. Thermal catalysis has been shown to be effective for aromatic alcohols such as benzyl alcohol, but relatively ineffective for aliphatic, especially primary, alcohols . For example, the oxidation of 1‐heptanol was attempted with a catalyst consisting of a mixture of FeCl 3 ⋅6H 2 O, TEMPO (2,2,6,6‐tetramethylpyridine N‐oxide) and silica gel.…”

“…For example, the oxidation of 1‐heptanol was attempted with a catalyst consisting of a mixture of FeCl 3 ⋅6H 2 O, TEMPO (2,2,6,6‐tetramethylpyridine N‐oxide) and silica gel. After 24 h at 80 °C under 5 atm of O 2 , 11% conversion to the aldehyde was obtained, and no aldehyde at all was formed under air …”