Photo- and Solvent-Mediated Production of the Highly Reactive N-Oxyl Radical and Its Efficient Catalytic Oxidation of Hydrocarbons at Ambient Temperature

Abstract

Selective oxidation of hydrocarbons with molecular oxygen at ambient temperature is full of challenge, and efficient activation of the inert C−H bond under mild conditions is the breakthrough point. Due to the promotion effect of the organic solvent hexafluoroisopropanol (HFIP) and α-Fe 2 O 3 , highly reactive phthalimide-N-oxyl radical (PINO) species were produced under the photoirradiation of blue light (455 nm, 3 W) without additional heating, which were utilized to activate various aromatic hydrocarbons. Combining with the hyperoxide decomposition catalysis, the excellent conversion (98%) and the total selectivity (99%) to the ketone (aldehyde) and alcohol were successfully obtained at the ambient temperature of 30 °C. It was found that the reactivity and lifetime of PINO was closely related with the adsorption attitude of PINO on the surface of α-Fe 2 O 3 , which could be modulated to be most beneficial for the catalytic efficiency by relying on the homogeneous interaction between PINO and HFIP and the heterogeneous interaction between PINO and the surface of α-Fe 2 O 3 .

Organic Synthesis Using Nitroxides

“…As mentioned for the benzylic and allylic oxidation using oxygen as terminal oxidant (Scheme a), different conditions were reported (without initiator) , and also different metal-based , initiators or cocatalysts such as Co­(acac) 2 , Mn­(acac) 2 , Cu­(acac) 2 , − Co­(OAc) 2 , , CoCl 2 , cobalt zeolitic imidazolate framework ZIF-67, SiO 2 /Al 2 O 3 -supported cobalt or manganese, [WZn­{Co­(H 2 O)} 2 (ZnW 9 O 34 ) 2 ] 12– , CuCl, , CuCl 2 , NaCr 2 O 7 , Fe­(NO 3 ) 3 , Fe­(acac) 3 /phenanthroline, Fe­(BF 4 ) 2 /KHB­(Ar) 3 , hemin, nonheme iron­(IV)–oxo complexes, horseradish peroxidase/H 2 O 2 , Fe­(NO 3 ) 3 , α-Fe 2 O 3 / h ν, , Rh 2 (esp) 2 , cerium oxide-modified CuFe 2 O 4 , and vanadium­(IV) complexes were used. In addition, transition-metal-free processes have been developed applying electrochemistry, − using excitation of ketones, , naphthalene imides, a dicyanopyrazine-derived chromophore, and graphitic carbon nitride or other (radical) starters such as azobis­(isobutyronitrile) (AIBN), − 2,2′-azobis­(4-methoxy-2,4-dimethylvaleronitrile) (V-70), peroxides, acridine yellow/Br 2 , tert -butyl nitrite, , dimethylglyoxime, acetaldehyde, and sodium periodate .…”

Solvent-free aerobic photocatalytic oxidation of C(sp3)–H and C(sp3)–OH to CO bonds

“…4,5 Recently, many photocatalytic systems have been developed for the photocatalytic selective oxidation of C-H bonds in benzylic hydrocarbons and benzyl C-OH of alcohols. Satisfactory activity and selectivity have been achieved over various photocatalysts such as 4CD/Bi 2 MoO 6 , 6 VO@g-C 3 N 4 , 7 BiVO 4 /Ag/ C 3 N 4 , 8 FePW/g-C 3 N 4 , 9 BiOBr x I 1−x , 10 p-BiOBr, 11 C,N-TiO 2 , 12 α-Fe 2 O 3 , 13 and CdS. 14,15 Additionally, solvents are often employed in these traditional photocatalytic systems, such as acetonitrile, 7 methanol, 12 trifluorotoluene, 15 and acetonitrile/ water.…”

Hydroxyl radical-dominated selective oxidation of ethylbenzene over a photoactive polyoxometalate-based metal–organic framework

“…So, very few reagents can activate specific C-H bonds in alkanes with high selectivity under mild reaction conditions currently. 3 Acetophenone is an important intermediate for the production of medicines, plasticizers, cellulose ethers, and fragrances. 4 It is generally produced by selective oxidation of ethylbenzene by utilizing highly reactive OH generated from TBHP (tert-butyl hydroperoxide) or H 2 O 2 (hydrogen peroxide) with the help of a catalyst at high temperatures.…”

“…So, very few reagents can activate specific C–H bonds in alkanes with high selectivity under mild reaction conditions currently. 3…”