Aerobic and Additive‐free Oxidative Dehydrogenation of N‐heterocycles over Commercial MnCO₃‐derived Manganese Oxides

Abstract

Herein, manganese oxides by simply pyrolyzing commercial MnCO3 are found to be active and stable for aerobic oxidative dehydrogenation of N‐heterocycles in the absence of any additives. The oxides are fully characterized by XRD, BET, XPS, and SEM. The analysis results suggest that high surface area, the involvement of Mn3+ and Mn4+ species, and labile lattice oxygen are key factors for the reactions. Moreover, kinetic analysis demonstrates that the apparent activation for oxidative dehydrogenation of 1,2,3,4‐tetrahydroquinoline is 37.7 kJ mol−1, and radical anions may involve in the reaction.

Manganese(III) Acetate Catalyzed Aerobic Dehydrogenation of Tertiary Indolines, Tetrahydroquinolines and an N‐Unsubstituted Indoline

“…As expected, no dehydrogenation product was detected when using 2,2,4,7‐tetramethyl‐1,2,3,4‐tetrahydroquinoline 3 e (Scheme 5c) or 1‐(pyrimidin‐2‐yl)‐1,2,3,4‐tetrahydroquinoline 3 f (Scheme 5d) as the substrate, highlighting the importance of the α C−H proton and the N−H motif in 1,2,3,4‐tetrahydroquinoline‐type substrate for the successful dehydrogenation. These results are consistent with other research studies, [18c,19b–e] which suggest that a similar reaction mechanism via a SET initiated dehydrogenation to form an imine intermediate, tautomeric cyclic imine, and second dehydrogenation process might be involved for the aerobic dehydrogenation of 1,2,3,4‐tetrahydroquinolines under current Mn(OAc) 3 ⋅ 2H 2 O/O 2 catalytic system.…”

Clean Stepwise Extraction of Valuable Components from Electrolytic Manganese Residue via Reducing Leaching–Roasting

“…The peaks at 642.06 and 654.07 eV were assigned to the characteristic peak of MnCO 3. 27 The MnO satellite feature at 646.2 eV further confirmed the presence of Mn 2+ . The position of Mn 2p was determined after acid leaching.…”

Efficiently Aerobic Dehydrogenation of N‐Heterocycles and Hydrocarbons over MnAl Oxides

“…Finally, 1,2,3,4-tetrahydroquinoline could transformed to quinoline quantitatively through catalytic aerobic dehydrogenation over MnAlO under the optimized conditions, obviously superior to the reported results based on manganese. [23][24][25][26] In order to demonstrate the scope of substrates, the MnAlO catalyst was then tested in the dehydrogenation of a variety of 1,2,3,4-tetrahydroquinolines under the optimized conditions. As shown in Scheme 1, 1,2,3,4-tetrahydroquinoline and its derivatives with methyl or methoxyl substituent locating at the 6position could be converted to the corresponding quinolines with excellent 91-98 % yields (2 a-2 c).…”

“…Actually, some progress has been made in the last decade based on Co, [2,[15][16][17] Ni, [18,19] Cu, [20][21][22] Mn, [23][24][25][26] et al Among these non-noble metals, manganese-based catalysts exhibited greater application potential. Mesoporous manganese oxides reported by Suib et al can accomplish the reactions at 130 °C with an air balloon, [23] but the yields of the product are not satisfied, and the preparation procedure of catalyst is complicated.…”

“…Mesoporous manganese oxides reported by Suib et al can accomplish the reactions at 130 °C with an air balloon, [23] but the yields of the product are not satisfied, and the preparation procedure of catalyst is complicated. The manganese oxides by simply pyrolyzing commercial MnCO 3 reported by Chen et al can also accelerate the reactions at 120 °C with an O 2 balloon, [24] but the catalytic activity for the substrates with electron-withdrawing substituent is quite low. Tang et al have developed an environmentally friendly catalytic system by the use of Na-doped manganese oxide as heterogeneous catalyst and O 2 as the terminal oxidant for oxidative dehydrogenation of various N-heterocycles, [25] but catechol was required as co-catalyst.…”