Vanadium‐Substituted Tungstophosphoric Acids as Efficient Catalysts for Visible‐Light‐Driven Oxygenation of Cyclohexane by Dioxygen

Abstract

This paper discloses that the oxygenation of cyclohexane by dioxygen (O2) to cyclohexanol and cyclohexanone over three vanadium‐substituted tungstophosphoric acids (PW11V1, PW10V2, PW9V3) can occur in MeCN under visible‐light irradiation, but provides very low cyclohexane conversion (0.8–2.4 %) with modest cyclohexanone selectivity (51–58.3 %). Importantly, an HCl aqueous solution was found to drastically promote this photooxygenation catalyzed by PW10V2 and especially PW9V3 acids, respectively providing approximately 20.4 and 23.4 % cyclohexane conversion and approximately 82.5 and 87.1 % cyclohexanone selectivity, with a concomitant formation of a small amount of chlorocyclohexane. However, such promoting effect was negligible in the PW11V1‐ photocatalyzed oxygenation and the other acids and the chlorine‐containing salts did not show any promotion effect on the present photocatalysis reaction. Notably, the HCl‐promoted photocatalytic oxygenation was significantly influenced by the amount of water. The cyclohexanone selectivity continuously and significantly increased with water amount, but photooxygenation efficiency drastically decreased if a slight excess amount of water was added. Based on these findings and the UV/Vis spectral and cyclic voltammetric measurements, a free‐radical mechanism initiated by the Cl atoms generated in the present photocatalysis system was proposed.

Tungsten-substituted molybdophosphoric acid impregnated with kaolin: effective catalysts for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones via biginelli reaction

“…Heteropoly acids (HPA) are well known as environmentally benign and economically feasible alternatives to traditional acid catalysts due to their Brönsted acidity, high proton mobility and relatively better stability. [1][2][3][4] One of the important structural subclass of HPAs is the Keggin anion, which is typically represented by the general formula XM 12 O 40 , xÀ8 where X is the central atom (Si, P, B, Zr etc. ), x is its oxidation state, and M is the metal ion (Mo 6+ or W 6+ ).…”

Visible‐Light‐Triggered Quantitative Oxidation of 9,10‐Dihydroanthracene to Anthraquinone by O2 under Mild Conditions

“…In recent years, light-triggered chemicalr eactions have emergeda sp owerful synthesis techniques for the production of fine chemicals under mild reactionc onditions. [33][34][35] In particular,t he selectiveo xidation of organic compoundsb ydioxygen (O 2 )o ra ir under visible light is believed to be user-and environmentally friendly,and thus, of great academic and practical significance. [36,37] Herein, we report an atom-efficient and ecofriendly photo-oxidation protocol for the synthesis of AQ from DHA withouta ny extra catalysts or additives under ambient temperature and pressure, which can fully meet the requirements ofg reen chemistry principles.…”

“…In recent years, light‐triggered chemical reactions have emerged as powerful synthesis techniques for the production of fine chemicals under mild reaction conditions . In particular, the selective oxidation of organic compounds by dioxygen (O 2 ) or air under visible light is believed to be user‐ and environmentally friendly, and thus, of great academic and practical significance .…”

Ce1−xCrxO2−δ Nanocrystals as Efficient Catalysts for the Selective Oxidation of Cyclohexane to KA Oil at Low Temperature under Ambient Pressure

“…For example, there are several catalysts reported using molecular oxygen asa no xidant, such as Co/ZSM-5 at 120 8Cu nder 1.0 MPa O 2 , [4] Au/ZSM-5 at 150 8Cu nder 1MPa O 2 , [5] mesoporous Ce 0.5 Mn 0.5 O x solid solution at 100 8Cu nder 10 bar O 2 , [6] Mn-Com ixed oxide at 140 8Cu nder 0.5 MPa O 2 , [7] Ce-doped MCM-48 140 8Cu nder 1.0 MPa O 2 , [8] CrCoAPO-5(AFI) at 115 8C under 1MPa O 2 , [9] ZnO-supported tetrakis(pentafluorophenyl)porphyrin-ironc hloride at 150 8Cu nder 0.7 MPa air, [10] and vanadium-substituted tungstophosphoric acids under visiblelight irradiation. [11] Although the use of molecular O 2 as an oxidant provides ac heap and green environment, the usual need of high pressure and high temperature, and/or low conversion for most catalysts limit their successful implementation. [12] Some organic oxidants, such as tert-butyl hydroperoxide [13] and iodosylbenzene, [14] have been reported as oxidants for cyclohexane oxidation, but tert-butyla lcohol or iodobenzene as byproducts needs furtherp rocesses to separate cyclohexane and its products.…”