Photooxidation of Cyclohexane by Visible and Near-UV Light Catalyzed by Tetraethylammonium Tetrachloroferrate

Abstract

Tetraethylammonium tetrachloroferrate catalyzes the photooxidation of cyclohexane heterogeneously, exhibiting significant photocatalysis even in the visible portion of the spectrum. The photoproducts, cyclohexanol and cyclohexanone, initially develop at constant rates, implying that the ketone and the alcohol are both primary products. The yield is improved by the inclusion of 1% acetic acid in the cyclohexane. With small amounts of catalyst, the reaction rate increases with the amount of catalyst employed, but then passes through a maximum and decreases, due to increased reflection of the incident light. The reaction rate also passes through a maximum as the percentage of dioxygen above the sample is increased. This behavior is due to quenching by oxygen, which at the same time is a reactant. Under one set of reaction conditions, the photonic efficiency at 365 nm was 0.018 mol/Einstein. Compared to TiO2 as a catalyst, Et4N[FeCl4] generates lower yields at wavelengths below about 380 nm, but higher yields at longer wavelengths. Selectivity for cyclohexanol is considerably greater with Et4N[FeCl4], and oxidation does not proceed past cyclohexanone.

Direct Synthesis of Acetone by Aerobic Propane Oxidation Promoted by Photoactive Iron(III) Chloride under Mild Conditions

“…Although some authors proposed FeCl 4 – as photoactive species, , we claim that other iron complexes should be considered. To test this hypothesis, results from catalytic tests performed in excess sulfuric acid and hydrochloric acid were compared.…”

“…For [FeCl 4 ] − [FeCl 2 (CH 3 CN) 2 ] + , an additional weak band at 450 nm appears, reproducing the shallow sloping of the 360 nm band in the experiment. Although some authors proposed FeCl 4 − as photoactive species, 28,29 we claim that other iron complexes should be considered. To test this hypothesis, results from catalytic tests performed in excess sulfuric acid and hydrochloric acid were compared.…”

Organic–inorganic interactions revealed by Raman spectroscopy during reversible phase transitions in semiconducting [(C2H5)4N]FeCl4

“…A number of complexes with a tetrahedral tetrachloroferrate(III) anion [FeCl 4 ] À mixed with organic cation have been reported for their interesting catalytic properties. [15][16][17][18] For instance, the tetraethylammonium tetrachloroferrate ([(C 2 H 5 ) 4 N]FeCl 4 ) compound has already been used as photocatalyst for the oxidation of the cyclohexane 19 and the toluene 20 under visible light. This is a notable advantage over TiO 2 compound which requires ultraviolet (UV) irradiation to induce a photocatalytic oxidation of toluene.…”