Selective Oxidation of Cyclohexane to Cyclohexanol/Cyclohexanone by Surface Peroxo Species on Cu-Mesoporous TiO₂

Abstract

Selective oxidation of cyclohexane to cyclohexanol/ cyclohexanone (KA−oil) is an important chemical process, which is still constrained by low conversion and selectivity and high energy consumption. In this study, Cu-doped mesoporous TiO 2 (Cu-MT) has been successfully synthesized via calcinating MIL-125(Ti) doped with copper acetylacetonate, which shows high reactivity in selective oxidation of cyclohexane to KA−oil by persulfate (PS) with the desirable cyclohexane conversion of 16.8% and a selectivity of 98.0% under mild conditions and the low ratio of PS/cyclohexane of 1:1. A series of characterizations and density functional theory calculations reveal that the doped Cu(I,II) on Cu-MT is the reactive site for non-radical activation of PS with the moderate elongation of the O−O bond in PS, which then abstracts 1H (1H + + 1e − ) from cyclohexane to form Cy • and eventually KA−oil. This study gives new insight on the importance of moderately activated PS in selective oxidation of C−H.

Copper‐Promoted Oxidative Amidation of Imines: A Facile Route to Amides

“…Meanwhile, considering that MeOH is an effective scavenger for both ⋅ OH and SO 4 ⋅ − , it can also be ruled out given it was the solvent used in this study [20] . Our recent works revealed that PS could be effectively activated via the non‐radical pathway on CuO or Cu‐doped mesoporous TiO 2 under alkaline conditions [12,13a] . To further investigate where the hydrogen of the N−H bond in the reaction, CH 3 OD was used to replace MeOH.…”

“…Oxone was proved to be the best choice, and there was no 3 a generation without the addition of oxidants (entry 11), indicating direct oxidation by air is negligible. In addition, different additives exhibited various yields (0-57 %, entries [12][13][14][15][16][17], and the yield was only 3 % (entry 18) in the absence of additives.…”

“…Persulfate (PS) and peroxymonosulfate (PMS, Oxone) are environmentally benign, safe, and easy‐to‐handle inorganic oxidants, which have been extensively used for selective activation of the alkenyl C(sp 2 )−H bonds via the H‐abstraction pathway [10a,11] . Our recent work also suggested the selective oxidation of C−H in cyclohexane to cyclohexanol and cyclohexanone by PS via the H‐abstraction pathway [12] . We therefore believe that the imine bonds can also be oxidized to amide bonds by PS and appropriate catalysts.…”

“…[10a,11] Our recent work also suggested the selective oxidation of CÀ H in cyclohexane to cyclohexanol and cyclohexanone by PS via the H-abstraction pathway. [12] We therefore believe that the imine bonds can also be oxidized to amide bonds by PS and appropriate catalysts. Given that our previous studies have revealed the moderate activation of the peroxo bond in PS on metal oxides (eg.…”

Highly Selective Photooxidation of Benzyl Alcohol to Benzaldehyde by Bi–Mo/g-C3N4 in Aqueous Solution

“…The oxidizing species on the surface of catalysts (e.g., superoxo and peroxo species) can effectively mediate the oxidation selectivity of H-rich substrates via the H-abstraction pathway. , For instance, our recent works suggested that the surface Bi–OO• superoxo and Bi–OOH peroxo during the photocatalytic activation of O 2 on Bi 2.15 WO 6 not only selectively oxidized benzyl alcohol to benzaldehyde via the H-abstraction pathway, but also contributed to the oxidation of various H-donors such as As­(III), glucose and phenolics with the production of H 2 O 2 , indicating the high reactivity of surface superoxo and peroxo species in H-abstraction . Likewise, Lyu et al suggested that the surface Ti–OOH peroxo on Pd@HTS-1 achieved 46.4% conversion of benzyl alcohol with high selectivity of 100% toward benzaldehyde.…”