A green approach for aerobic oxidation of benzylic alcohols catalysed by Cu<sup>I</sup>–Y zeolite/TEMPO in ethanol without additional additives

Senthilkumar, Samuthirarajan; Zhong, Wei; Natarajan, Mookan; Lü, Chunxin; Xu, Binyu; Liu, Xiaoming

doi:10.1039/d0nj03776a

Cited by 31 publications

(14 citation statements)

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“…To drive forward efficiently and selectively the oxidation, developing either homogenous or heterogenous catalytic systems has been one of the intensively studied areas. [ 4–14 ] Being inspired by the enzymatic chemistry of galactose oxidase, which is a copper‐containing protein catalysing aerobic oxidation of primary alcohols into aldehydes, [ 15,16 ] copper‐based catalytic systems, particularly cuprous systems, have been investigated in tremendous enthusiasm in the past decades. [ 5,17–31 ] In such systems, the basic combination is Cu(I) salt and a radical compound like TEMPO (2,2,6,6‐tetramethylpiperidine‐1‐oxyl).…”

Section: Introductionmentioning

confidence: 99%

The superiority of cuprous chloride to iodide in the selective aerobic oxidation of benzylic alcohols at ambient temperature

Xiao

Zhong

et al. 2021

Applied Organom Chemis

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Cuprous halides, best described as (CuX)n (X = Cl−, Br−, and I−) in their solid state, catalyse selective aerobic oxidation of alcohols with the assistance of both NMI (N‐methylimidazole) and TEMPO (2,2,6,6‐tetramethylpiperidine‐1‐oxyl), and the iodide generally demonstrates the highest activity, for example, in the oxidation of 1‐octanol at ambient temperature under 24 h' reaction. However, in the aerobic oxidation of benzylic alcohols, the chloride showed superiority to the iodide in that the aerobic oxidation was quantitatively completed within 3 h at ambient temperature whereas the iodide showed only about half the activity of the chloride analogue. By probing the system using electrochemistry, electric conductivity, and 1H NMR titration, it was revealed that the surprising anomaly was due to the difference in the rate of forming active species, [Cu (NMI)2X(MeCN)], from the polymeric solid in a two‐stage process. Substrates expansion of 11 benzylic alcohols indicated that CuCl/NMI/TEMPO system demonstrated quantitative conversion of benzylic alcohols into corresponding aldehydes within 3 h and showed great tolerance to the substituents on the phenyl ring of the substrates. Furthermore, electron‐withdrawing substituent was beneficial to the oxidation and could offset the steric effect at orthro‐substituent. Such a behaviour suggested that in the catalysis, increasing the acidity of the hydroxyl group (OH) of the substrates could ease the oxidation, which implied that the deprotonation via an internal pathway might be one of the rate‐determining steps. Our results also showed that the anion halide participated actively in the catalysis by coordinating to Cu(I) in the active species.

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Section: Introductionmentioning

confidence: 99%

The superiority of cuprous chloride to iodide in the selective aerobic oxidation of benzylic alcohols at ambient temperature

Xiao

Zhong

et al. 2021

Applied Organom Chemis

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“…As oxidation of alcohol to aldehyde and carboxylic acid is a very important reaction in organic as well as biochemistry, many catalytic systems have been developed with different reaction conditions and yields. [ 31–61 ] Despite several reports, the existing methodologies are often plagued by disadvantages like harsh reaction conditions, use of toxic metals, and poor recyclability. Photocatalysis emerged as an important tool to carry out such reaction in a more environmentally friendly condition without application of external heat.…”

Section: Resultsmentioning

confidence: 99%

“…Alcohol oxidation by copper catalyst is a well-known process and extensively studied as reported in literature. [31][32][33][34][35][36][37][38][39] The oxidation process has been explored in various methodologies including traditional heating, [40][41][42][43][44] microwave irradiation, [39,[45][46][47] electrochemical method, [48][49][50][51][52] and ultrasonic irradiation. [53][54][55] Interestingly, though alcohol oxidation is reported by photocatalytic systems like Ag 2 S-CdS junction [56][57][58] and platinum nanocluster/graphitic carbon nitride, [59,60] however, use of copper complexes as photocatalyst remains rare and largely unexplored.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of Cu(II) complexes by N,O‐donor ligand transformation and their catalytic role in visible‐light‐driven alcohol oxidation

Ranjan

Kundu

Kyarikwal

et al. 2021

Applied Organom Chemis

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Visible-light-driven photoreactions using metal complexes as catalysts are currently a research hotspot in terms of the development of environmentally friendly sustainable processes. To develop potential copper-based photocatalysts, a Mannich base ligand, namely, 2,4-dichloro-6-((4-(2-hydroxyethyl) piperazin-1-yl)methyl)phenol (H 2 L), has been synthesized and characterized.Two copper complexes [Cu (HL 1 )] ( 1) and [Cu (HL 2 )] (2) have been obtained from H 2 L, where the ligand undergoes an unprecedented transformation plausibly via oxidation of piperazine ring to ketone, subsequent oxidation of enol and nucleophilic attack of methanol followed by hydrolysis of amide bond, resulting piperazine ring cleavage. Under the irradiation of visible light, these catalysts can oxidize primary alcohols into corresponding aldehydes with very good conversion and high selectivity in the presence of molecular oxygen. The photocatalysts could be recovered almost quantitatively after completion of the catalytic cycle and recycled at least four times without much depreciation of catalytic activity. A plausible mechanistic pathway for alcohol oxidation has been explored through electrospray ionization mass spectrometry (ESI-MS) spectrometric, cyclic voltammetry, UV-vis, and computational study.

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“…Thus, it would be highly desirable to develop heterogeneous catalysts containing both metal and TEMPO radical species that could be easily separated after the reaction by filtration for use in the next cycle. The existing approaches are mainly focused on the heterogenization of one part of the system using immobilized TEMPO − or metal-based heterogeneous catalysts such as Cu-Y zeolite to regenerate TEMPO . However, these approaches cannot provide similar catalytic performances and still require complex separation procedures.…”

Section: Introductionmentioning

confidence: 99%

TEMPO-Ru-BEA Composite Material for the Selective Oxidation of Alcohols to Aldehydes

et al. 2022

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The selective aerobic oxidation of alcohols to aldehydes is an important industrial challenge due to the easy further overoxidation of these products to acids and esters. The most common industrial methods require organic radicals such as 2,2,6,6,-tetramethylpiperidine-1-oxyl (TEMPO) for the selective conversion of alcohols to carbonyl compounds with the formation of TEMPOH, which can be regenerated back to TEMPO by oxygen over metal complexes. The high cost and difficulties related to the separation of complexes prompted us to develop heterogeneous catalysts by coordinating TEMPO over acid sites in zeolite BEA with encapsulated RuO2 nanoparticles. The catalyst demonstrates excellent activity, selectivity, and stability for the oxidation of alcohols to aldehydes. The analysis of the reaction mechanism confirms the activation of alcohols by TEMPO and the subsequent regeneration of TEMPOH by RuO2.

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A green approach for aerobic oxidation of benzylic alcohols catalysed by Cu^I–Y zeolite/TEMPO in ethanol without additional additives

Abstract: CuI–Y zeolite catalysts, which are robust and recyclable, assisted by TEMPO catalyses quantitatively the aerobic oxidation of a wide range of benzylic alcohols into aldehydes in ethanol under mild conditions without additional additives.

Cited by 31 publications

References 51 publications

The superiority of cuprous chloride to iodide in the selective aerobic oxidation of benzylic alcohols at ambient temperature

The superiority of cuprous chloride to iodide in the selective aerobic oxidation of benzylic alcohols at ambient temperature

Synthesis of Cu(II) complexes by N,O‐donor ligand transformation and their catalytic role in visible‐light‐driven alcohol oxidation

TEMPO-Ru-BEA Composite Material for the Selective Oxidation of Alcohols to Aldehydes

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A green approach for aerobic oxidation of benzylic alcohols catalysed by CuI–Y zeolite/TEMPO in ethanol without additional additives

Abstract: CuI–Y zeolite catalysts, which are robust and recyclable, assisted by TEMPO catalyses quantitatively the aerobic oxidation of a wide range of benzylic alcohols into aldehydes in ethanol under mild conditions without additional additives.

Cited by 31 publications

References 51 publications

The superiority of cuprous chloride to iodide in the selective aerobic oxidation of benzylic alcohols at ambient temperature

The superiority of cuprous chloride to iodide in the selective aerobic oxidation of benzylic alcohols at ambient temperature

Synthesis of Cu(II) complexes by N,O‐donor ligand transformation and their catalytic role in visible‐light‐driven alcohol oxidation

TEMPO-Ru-BEA Composite Material for the Selective Oxidation of Alcohols to Aldehydes

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A green approach for aerobic oxidation of benzylic alcohols catalysed by Cu^I–Y zeolite/TEMPO in ethanol without additional additives