Selective Oxidation of Aliphatic Alcohols using Molecular Oxygen at Ambient Temperature: Mixed-Valence Vanadium Oxide Photocatalysts

Abstract

Here we report a class of photocatalysts: mixed-valence vanadium oxide particles grafted onto a variety of oxide supports. In these catalysts V6O13 species with mixed oxidation states (V4+ or V5+) are believed to be catalytically active sites. These catalysts successfully enable alcohol oxidation to selectively produce aldehydes and ketones using O2 as the oxidant. The catalytic process is driven by visible light irradiation at room temperature and, most importantly, progresses with negligible overoxidation. The catalysts can even selectively oxidize aliphatic alcohols, which are much more challenging to control in comparison to aromatic analogues. They can also be applied to the activation and oxidation of the otherwise stable C–H bonds of saturated aromatic hydrocarbons, such as toluene and xylene, under irradiation. Both experimental results and density functional theory (DFT) simulations suggest the formation of V6O13-alkoxide species as the initial step in the catalytic cycle. The V6O13-alkoxide then acts as the light harvester, being excited by light of wavelength shorter than 550 nm. Facile room-temperature C–H bond cleavage in the excited state V6O13-alkoxide in the presence of O2 leads to the carbonyl-containing products. These findings demonstrate an example of light-driven selective oxidation of diverse alcohols via in situ formation of photoresponsive V6O13-alkoxide species. This catalytic process is especially valuable for the synthesis of temperature-sensitive products and represents an alternative pathway to many conventional thermal oxidation reactions.

Photoelectrochemical Catalysis toward Selective Anaerobic Oxidation of Alcohols

“…The oxidation of BA to benzaldehyde by variousp hotocatalystsh as been reported, but with al ow reactionr ate (normally below 10 mmolg À1 h À1 )a nd rigorous conditions (e.g.,e xternal O 2 import, organic solvent, high temperature and pressure). [19][20][21][22][23][24][25][26]48] The PEC catalysis in this work yields an order of magnitude enhancement in reaction rate ( % 76 mmol g À1 h À1 )u nder mild reaction conditions (room temperature, aqueous media), in comparisonwith photocatalysis process ( Figure 3D).…”

“…For instance, photocatalytic reactions based on semiconductorsa re widely investigated in water splitting, [8][9][10][11] environmental remediation, [12][13][14][15] and CO 2 transformation to fuel. [16][17][18] Remarkably,a lthough af ew exam-ples have been successively developed (e.g.,selective photocatalytico xidation of toluene or aromatic alcohols), [19][20][21][22][23][24][25][26] photocatalysis-based organic synthesis demonstrates al arge potential for green synthesis. However,a ll these photocatalytic transformations require certain rigorous conditions (e.g.,e xternal O 2 import, organic solvent,a sw ell as relativelyh igh temperature and pressure) due to the sluggish reaction kinetics and limited efficiency.T herefore,t he development of facile synthesis routesf or the transformationo fo rganic substrates remains ab ig challenge in organic synthesis and green chemistry.Photoelectrochemical (PEC) waters plitting has been envisioneda sapromising route for harvesting the energy of sunlight and storing it in the form of chemical bonds( H 2 and O 2 ).…”

Cyclohexene Promoted Efficient Biomimetic Oxidation of Alcohols to Carbonyl Compounds Catalyzed by Manganese Porphyrin under Mild Conditions

“…The aerobic oxidation of alcohols catalyzed by TEMPO (2,2,6,6‐tetra‐ methylpiperidyl‐l‐oxy) or its derivatives in absence of transition metal is gathering much attention . A variety of methods were reported on the aerobic oxidation of alcohols catalyzed by metal catalysts like ruthenium, manganese, cobalt, and Au‐Pd alloy nanoparticles or vanadium oxide presenting excellent activity.…”

A Photo-Enzymatic Cascade to Transform Racemic Alcohols into Enantiomerically Pure Amines

“…To further utilize visible light, numerous other heterogeneous catalysts have been tested [18]. By using graphitic carbon nitride (g-C 3 N 4 ) [19,20] and vanadium-oxide grafted to numerous carriers [21,22], efficient alcohol oxidation mediated by visible light has been reported. Besides heterogeneous systems, water-soluble sodium anthraquinone-2-sulfonate (SAS) is also known as an effective and inexpensive homogeneous photocatalyst [23][24][25][26][27].…”