Aerobic Oxidation Of Amines Research Articles

Visible light-driven aerobic oxidation of amines coupling with H2O2 production catalyzed by CoPc/alkali metal-doped g-C3N4 Z-scheme heterojunction

Three environmentally friendly Z-scheme CoPc/alkali metal-doped g-C3N4 heterojunction composites were fabricated via in-situ immobilizing cobalt phthalocyanine (CoPc) on the surface of alkali metal-doped g-C3N4 nanosheet by simple hydrothermal method. These composites acted as efficient and recyclable heterogeneous photocatalysts realized that the highly selective aerobic oxidation of amines to the corresponding imines coupling of hydrogen peroxide generation at room temperature. Under irradiation by LED lamp, the imines and H2O2 were obtained with conversion ranges from 87.9 % to 92.0 %, selectivity more than 99 %, and production rate ranges from 3.27 to 3.40 mmol g−1 h−1, respectively. Based on the mechanistic analysis and characterization, the excellent catalytic activity derived from the Z-scheme mechanic and synergistic effect originated from O2 reduction and amine oxidation. On completion, after centrifugation, washing with solvent and drying under vacuum, the catalysts can be recovered and reused for five successive cycles of testing with a slight decrease in reactivity. For this work, a promising photo synthesis pathway with merits of mild, low-cost, pollution-free, and energy-saving was developed to produce imines coupling with H2O2 generation.

The merger of a metal-organic framework and an electron-proton transfer mediator for photocatalytic selective aerobic oxidation of amines

The merger of a metal-organic framework and an electron-proton transfer mediator for photocatalytic selective aerobic oxidation of amines

Blue light-driven selective aerobic oxidation of amines by benzothiadiazole metal–organic framework photocatalysis

A zirconium-based benzothiadiazole metal–organic framework, UiO-68-BT, performs blue light-driven selective oxidation of benzyl amines with O2 by photocatalysis.

A Comprehensive Review on Cu‐Catalysed Aerobic Oxidation of Amines to Imines

AbstractImines are frequently used as valuable intermediates in organic transformation and pharmaceutical synthesis. Conventional imine synthesis includes Lewis acid catalysts, dehydrating agents, and unstable aldehydes. Developing eco‐friendly molecular assembly techniques has become increasingly important in recent years. In particular, there is a significant need for methods that recycle resources and have high atomic efficiency with minimal environmental impact. Oxidative synthesis of imines from amines has been investigated in presence of molecular oxygen (or air) which is readily accessible on Earth. The closely linked catalysts have been classified into metals, bio‐inspired, and MOF catalysts. Highly active, affordable, and adaptable copper based catalysts are given special attention here, some critical elements that influence reaction processes and catalytic activity are also displayed in the present study. The modern methods along with mechanistic routes for converting primary amines to imines using copper catalytic systems and ambient oxygen have been discussed in detail.

A biomimetic approach to aerobic oxidation of amines in water via a redox-active cacotheline organocatalyst

The low catalyst loading of cacotheline organocatalyst combined with the ready separation of products in high purity without further purification steps demonstrates the greener and more sustainable approach to the aerobic amine oxidation chemistry.

Solvent-controlled synthesis of Ti-based porphyrinic metal-organic frameworks for the selective photocatalytic oxidation of amines.

The photocatalytic activity of metal-organic frameworks (MOFs) can be managed by the milieu of synthesis. Herein, N,N'-dimethylacetamide (DMA) and N,N'-diethylformamide (DEF) were employed as solvents for the synthesis of two Ti-based porphyrinic MOFs, namely Ti-PMOF-DMA and Ti-PMOF-DEF, from tetrabutyl orthotitanate and 4,4',4'',4'''-(porphine-5,10,15,20-tetrayl)tetrakis(benzoic acid). Notably, both DMA and DEF were adsorbed onto the Ti-oxo clusters of the two MOFs to shape their properties. Ti-PMOF-DMA was observed with better optoelectronic response and charge transfer than Ti-PMOF-DEF. Moreover, Ti-PMOF-DMA owned a larger pore volume than Ti-PMOF-DEF, imparting more accessible sites to benzyl amines. Ti-PMOF-DMA exhibited better activity in selective photocatalytic aerobic oxidation of benzylamine than Ti-PMOF-DEF. Irradiated by red light-emitting diodes, outstanding results for selective conversion of benzyl amines to imines over Ti-PMOF-DMA were attained. Superoxide radical anion, generated by the electron transfer from porphyrin via Ti-oxo clusters to dioxygen, turned out to be the primary reactive oxygen species. There was generality towards aerobic oxidation of amines to imines and considerable stability for Ti-PMOF-DMA. This work provides a new perspective on the altering MOFs to enhance photocatalytic organic transformations.

Tuning the Photocatalytic Activity through Linkages of Porous Conjugated Polymers Based on Triazines for a Selective Oxidation Reaction

Conjugated polymers like conjugated microporous polymers (CMPs) and covalent organic frameworks (COFs) are burgeoning metal‐free photocatalysts for selective oxidation reactions. They possess outstanding features and salient advantages that are inextricably linked to structures at the molecular level. More effort should be devoted to seeking appropriate linkages which can define their crystallinity as well as photocatalytic activity. Herein, with thiazolo[5,4‐d]thiazole (TzTz) and imine as linkages, TzTz‐TA and TTI‐COF are prepared with triazine as the core, respectively. Conclusively, TTI‐COF shows high crystallinity, whereas TzTz‐TA is amorphous, belonging to CMP. However, TzTz‐TA exhibits better photocatalytic activities than TTI‐COF for the blue light‐driven selective aerobic oxidation of amines. The superior photoelectric properties and a more suitable reduction potential are imposed by the TzTz linkages to override the shortcoming of lack of crystallinity for TzTz‐TA. High selectivities for imines by photocatalytic oxidation of benzyl amines are achieved over TzTz‐TA. In addition, TzTz‐TA emerges with remarkable recoverability and recyclable stability. This study implies that tuning the linkages is essential for boosting the photocatalytic activity of porous materials.

Linker length-dependent photocatalytic activity of β-ketoenamine covalent organic frameworks

Myriad endeavors have shifted towards covalent organic frameworks (COFs) for their aptitude in visible light photocatalysis. Herein, three β-ketoenamine COFs with different linker lengths, i.e., TpPa-COF, TpBD-COF, and TpDT-COF, were synthesized from 1,3,5-triformylphloroglucinol and 1,4-benzenediamine, 4,4'-biphenyldiamine, and 4,4''-p-terphenyldiamine, respectively. With the shortest linker, a noticeable conversion of benzylamine was observed by TpPa-COF photocatalysis. By prolonging the linker length, TpBD-COF performed a better conversion of benzylamine, which might be due to more suitable redox potentials than TpPa-COF. However, with the longest linker, TpDT-COF resulted in a lower conversion than TpBD-COF, which might be ascribed to the slightly inferior optoelectronic properties. With a moderate linker length, TpBD-COF convincingly delivered the best photocatalytic activity for the violet light-driven aerobic oxidation of amines. This work sheds light on the dimension of linker length in designing more active COF photocatalysts.

Aerobic Oxidation of Amines to Imines by Single Atomic Fe Catalysts with Coexisting Fe Nanoclusters

Key words iron catalysis - nanoclusters - single-atom catalysis - oxidation - amines - imines

Extending the 2D conjugated microporous polymers linked by thiazolo[5,4-d]thiazole for green light-driven selective aerobic oxidation of amines

With pyrene as the donor, a conjugated microporous polymer linked by thiazolo[5,4-d]thiazole (TzTz) is with notable green light-driven performance in the selective aerobic oxidation of benzyl amines.

Hydroxynaphthalene–Nb2O5complex photocatalysis for selective aerobic oxidation of amines induced by blue light

Aerobic oxidation of benzylamine to imine by cooperative photocatalysis of DHNS–Nb2O5and TEMPO is viable.

Surface ligands enhance the catalytic activity of supported Au nanoparticles for the aerobic α-oxidation of amines to amides

Surface ligands control the electronic properties of supported Au nanoparticles and thereby regulate their catalytic activity for the selective aerobic oxidation of amines to amides.

Hydrazone-linked 2D porphyrinic covalent organic framework photocatalysis for visible light-driven aerobic oxidation of amines to imines

Covalent organic frameworks (COFs) have recently gained rising consideration for visible light photocatalysis. Their property could be accurately established with specific reactions in which the most investigated one turns out to be the aerobic oxidation of amines. In this contribution, a hydrazone-linked 2D (two-dimensional) porphyrinic COF, Por-DETH-COF, was assembled from 5,10,15,20-tetrakis(4-benzaldehyde)porphyrin (p-Por-CHO) and 2,5-diethoxyterephthalohydrazide (DETH) and its photocatalytic activity was duly appraised with the aerobic oxidation of amines. Thereby, the red light-driven selective oxidation of benzyl amines to imines was obtained in very high conversions and selectivities with ambient air as the oxidant. Importantly, the photocatalytic system exhibited remarkable compatibility of functional groups and extensive scope of benzyl amines. Notably, the Por-DETH-COF photocatalyst displayed outstanding recyclability after five successive cycles. This work suggests that 2D COFs could contribute a unique juncture for selective organic transformations by photocatalysis.

Cooperative Photocatalysis with 4-Amino-TEMPO for Selective Aerobic Oxidation of Amines over TiO2 Nanotubes.

Attaching π-conjugated molecules onto TiO2 can form surface complexes that could capture visible light. However, to make these TiO2 surface complexes durable, integrating 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) or its analogues as a redox mediator with photocatalysis is the key to constructing selective chemical transformations. Herein, sodium 6,7-dihydroxynaphthalene-2-sulfonate (DHNS) was obtained by extending the π-conjugated system of catechol by adding a benzene ring and a substituent sodium sulfonate (-SO3 - Na+ ). The DHNS-TiO2 showed the best photocatalytic activity towards the blue light-induced selective aerobic oxidation of benzylamine. Compared to TEMPO, 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO) could rise above 70% in conversion of benzylamine over the DHNS-TiO2 photocatalyst. Eventually, a wide range of amines could be selectively oxidized into imines with atmospheric O2 by cooperative photocatalysis of DHNS-TiO2 with 4-amino-TEMPO. Notably, superoxide (O2 •- ) is crucial in coupling the photocatalytic cycle of DHNS-TiO2 and the redox cycle of 4-amino-TEMPO. This work underscores the design of surface ligands for semiconductors and the selection of a redox mediator in visible light photocatalysis for selective chemical transformations.

Anchoring dye onto 1D Nb2O5 in cooperation with TEMPO for the selective photocatalytic aerobic oxidation of amines

Visible light-driven photocatalysis over semiconductors has emerged as one of the most desired strategies for animating diverse selective chemical transformations. Herein, one-dimensional (1D) Nb2O5 nanorods with a specific surface area of 264 m2•g−1 were synthesized via a straightforward hydrothermal method. Thereafter, an efficient visible light photocatalyst was constructed by in-situ anchoring of alizarin red S (ARS) onto the Nb2O5 nanorods to afford ARS-Nb2O5. Resultantly, the ARS-Nb2O5 nanorods can facilitate the selective aerobic oxidation of amines into imines, affording about twice of the result over 3D hierarchical Nb2O5. Notably, 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) could synchronize the intricate electron and proton transfers between ARS-Nb2O5 nanorods, amines, and superoxide (O2•−). In most cases, the green light-driven primary and secondary amines into imines could be completed with about 95% selectivity within 2 h. This work highlights the dimension of designing semiconductor materials to anchor visible light-active molecules for selective oxidation reactions under benign conditions.

Blue light-powered hydroxynaphthoic acid-titanium dioxide photocatalysis for the selective aerobic oxidation of amines

Solar photocatalysis is the key to resolve many environmental challenges but is usually hard to achieve over a metal oxide semiconductor. Therefore, assembling π-conjugated molecules onto semiconductors becomes an efficient approach to solar conversion via ligand-to-metal charge transfer. Here, a rational design of ligands for titanium dioxide (TiO2) is presented to produce robust visible light photocatalysts. Three hydroxynaphthoic acids (HNAs) were selected as ligands by extending an extra benzene ring of salicylic acid (SA) at 3,4 or 4,5 or 5,6 positions. These ligands could regulate the performance of TiO2 in which 2-hydroxy-1-naphthoic acid (2H1NA) endows the best outcome. In detail, blue light-powered cooperative photocatalysis of 2H1NA-TiO2 with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO, 5 mol%) inaugurates the expeditious formation of imines by oxidation of amines with atmospheric oxygen (O2). Interestingly, the increase of the O2 pressure from 1 atm to 0.4 MPa promoted the selective oxidation of benzylamine but thereafter declined with a further boost to 0.6 MPa. Notably, an electron transfer between the oxidatively quenched 2H1NA-TiO2 and TEMPO is established, offering a new pathway for environmental applications. This work presents a strategy in designing cutting-edge visible light photocatalysts via altering semiconductors with surface ligands.

Cooperative photocatalysis of dye-TiO2 nanotubes with TEMPO+BF4− for selective aerobic oxidation of amines driven by green light

Visible light photocatalysis could offer an eco-friendly alternative for selective transformation of organic molecules. Herein, a cooperative system is created with alizarin red S (ARS), TiO2 nanotubes (TNTs), and an extra redox mediator. The electron transfer between oxidatively quenched ARS-TNTs and the redox mediator is the key to secure cooperative photocatalysis. The selective aerobic oxidation of primary and secondary amines was constructed by cooperative photocatalysis of ARS-TNTs with 2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate (TEMPO+BF4−) driven by green light. Specifically, the activity of anatase TNTs could reach about 2.2 times that of the P25 (Aeroxide P25) TiO2 precursor. Due to increased polarity, TEMPO+BF4− serves more efficiently for electron transfer than (2,2,6,6-tetramethylpiperidin-1-yl)oxy (TEMPO), conferring above 1.5 times of activity that of TEMPO for the selective aerobic conversion of amines. This work features the potential of designing redox mediators in amplifying cooperative photocatalysis driven by visible light.

Thiazolo[5,4‑d]thiazole linked conjugated microporous polymer photocatalysis for selective aerobic oxidation of amines

Recently, conjugated microporous polymers (CMPs) comprised of thiazolo[5,4-d]thiazole (TzTz) linkages have received much attention due to their excellent photoelectric properties. Herein, the polycondensation of dithiooxamide and benzyl aldehydes of C2, C3, and D2h symmetry afforded three TzTz-linked CMPs, namely TzTz-CMP-1, TzTz-CMP-2, and TzTz-CMP-3. Importantly, the porous and flexible characteristics of TzTz-linked CMPs enable the smooth selective aerobic oxidation of amines in ethanol (C2H5OH), a clean but redox-active solvent. All three TzTz-linked CMPs significantly surpass the benchmark mesoporous graphite carbonnitride (mpg-C3N4) photocatalyst. Intriguingly, TzTz-CMP-2 displays the best photocatalytic activity for the blue-light-mediated selective transformation of primary and secondary amines into imines. The conversions of amines were up to 90% with excellent selectivities for imines. This work highlights that CMPs with TzTz linkages may offer efficient photocatalytic selective transformations under genuinely ambient conditions.

Visible-light-responsive lanthanide coordination polymers for highly efficient photocatalytic aerobic oxidation of amines and thiols

Photoinduced activation of oxygen by visible-light-responsive CPs via electron/energy transfer and its roles on aerobic oxidation of amines and thiols.

Sulfur-stabilised copper nanoparticles for the aerobic oxidation of amines to imines under ambient conditions

Nanodroplets of sulfur-stabilised copper nanoparticles effectively catalyse the aerobic oxidation of amines to imines under ambient conditions.