Dehydrogenation Of Alcohols Research Articles

Radical‐driven imine hydrogenation promoted by the cooperativity of nickel and a redox‐active ligand

In the case of N‐alkylation reaction via borrowing hydrogen (BH) methods, imine hydrogenation is one of the critical steps. Mechanistically, the majority of imine hydrogenation, either by dihydrogen gas or by alcohol in case of BH methods, follow two‐electron chemistry, where a metal‐hydride intermediate plays a pivotal role. Herein we demonstrate a completely complementary protocol, where the hydrogenation is governed by a radical pathway. Such a pathway is adopted from the redox active nature of the azophenolate ligand backbone. The facile and reversible 2e‐/2H+, azo/hydrazo redox couple in a nickel catalyst helps in storing the hydrogen from alcohol dehydrogenation. An imine substrate is reduced by one‐electron from the azo motif with the assistance of the nickel center. The reduced imine drives a critical hydrogen atom transfer step from the hydrazo motif to conduct the hydrogenation. A set of kinetics experiments including Eyring analysis, radical inhibition experiment along with computational probation attest for the radical‐promoted hydrogenation mechanism.

Terpyridine Ni(II) Complex Grafted CdS Nanorods for Cooperative Selective Benzyl Alcohol Oxidation and Hydrogen Production.

Efficient utilization of photogenerated charge carriers to realize photocatalytic solar fuel production and oxidative chemical synthesis is a challenging task. Herein, a conventional amidation reaction route is adopted to successfully construct a novel composite photocatalyst composed of a Ni(II)-terpyridine complex with carboxyl groups grafted on CdS nanorods (labeled as CdS@Ni(terpyC)2). Experimental results have unequivocally revealed that the as-fabricated composite catalyst exhibited a remarkable enhancement in photocatalytic activity for the dehydrogenation of benzyl alcohol under visible light, demonstrating superior hydrogen evolution efficiency and benzaldehyde selectivity, surpassing both pristine CdS and the blend of CdS and Ni(terpyC)2. The carrier dynamics study demonstrated that the Ni(terpyC)2 on the surface of CdS could quickly extract the photogenerated electrons of CdS, which reduced the carrier recombination efficiency, further improving the photocatalytic activity of the catalyst. This work illustrates the effect of surface active site engineering on photocatalysis and is expected to shed substantial inspiration on future surface modulation and design of semiconductor photocatalysts.

Can ZnO/Cu catalyst provide promising activity for glycerol direct dehydrogenation? A combined density functional theory and coverage-dependent microkinetics study

Non-oxidative dehydrogenation (NODH) reaction of glycerol is a perfect atom economical technical route to produce higher-value 1,3-dihydroxyacetone (DHA). Cu-based catalyst (especially ZnO/Cu system), is known as active species for alcohol dehydrogenation, which may be also promising one for glycerol NODH. In this study, we combine coverage-dependent free energy profile using first-principle calculation, and microkinetic model, to investigate the NODH of glycerol on the ZnO/Cu(111) surface, and a detailed comparison is made with Cu (111) surface. The coverage-dependent microkinetic model takes into account the lateral adsorbate–adsorbate self-interactions and cross-interactions, and their effect on binding energy of both intermediate and transition state. Besides, it guarantees the reaction kinetics is based on the coverage self-consistent between surface model and microkinetic result under practically reaction conditions. Compared with coverage-dependent kinetics simulation (20 %–30 %), coverage-independent model overestimates the DHA selectivity on Cu (111) (over 90 %). Our coverage-dependent kinetics simulation illustrates that both glycerol conversion and DHA selectivity are most determined by the first dehydrogenation step (OH bond scission) of glycerol on Cu (111). However, when ZnO cluster adsorbed on the Cu (111) surface, ZnO cluster promotes the electron transferring between glycerol and Cu sites, which accelerates OH bond scission process of glycerol. Under coverage-dependent microkinetic model, the turnover frequency and selectivity of DHA on ZnO/Cu(111) get much improvement compared with Cu (111). Finally, the superior of ZnO/Cu(111) is further proved by continuous stirred tank reactor simulation, where NODH of glycerol need shorter residence times or lower temperature to reach 100 % conversion, as well as keep higher DHA selectivity.

Well Defined Phosphine Free Ni-Catalyzed Dehydrogenation of Secondary Alcohols for the Synthesis of Ketones and Ketazines.

In this work, we unveil a novel synthesis of bench stable Ni (II) complexes supported by tetradentate Schiff-base ligands and the complexes were devoid of any phosphine or phosphine-based ligand. These Ni-complexes were successfully applied for the dehydrogenation of secondary alcohols for ketone and ketazine syntheses. Secondary alcohols with different functional groups were well tolerated during catalytic cycle. Moreover, we successfully extended this protocol for the synthesis of biologically significant ketones and ketazines. On the basis of various control experiments, probable reaction pathway was proposed and an acceptorless alcohol dehydrogenation mechanism was suggested.

Acceptorless Dehydrogenation of Alcohols and Polyols Over Cu‐Based Catalysts Prepared by NaBH4 Reduction

AbstractFor the first time, oxide (TiO2, CeO2, ZnO, Al2O3) supported Cu catalysts, prepared by the aqueous reduction method using sodium borohydride, were employed for the acceptorless dehydrogenation of 2‐octanol and various C4–C8 polyols. The method used to prepare the catalysts enabled the formation of small Cu particles in the range of 14–36 nm, depending on the point of the zero charge of the support. We showed that the conversion increased with Cu surface area, where Cu/TiO2 led to the highest conversion of 2‐octanol (>99.9%). The selectivity depends on the support and conversion. Up to 80% conversion, the selectivity to 2‐octanone was between 83% and 90% when using Cu/TiO2. In this study, we also report for the first time the acceptorless dehydrogenation of 1,3‐butanediol, 2,3‐butanediol, 1,2‐pentanediol, and 1,5‐pentanediol in liquid phase. While metal active sites promoted the dehydrogenation reaction, the presence of acidic and basic sites favored the formation of by‐products, mainly resulting from dehydration reactions, pinacol rearrangements, and aldol and retro‐aldol condensations. In addition to value‐added chemicals, all the reactions also released molecular hydrogen.

Visible Light Mediated Iron‐Catalyzed One‐Pot Synthesis of Chromenopyrroles from Benzyl Alcohols, 2‐Hydroxyacetophenones and Methyl/Ethyl Isocyanoacetate at Room Temperature

AbstractAn effective, facile, trivial, and one‐pot procedure for the synthesis of chromenopyrroles from benzyl alcohols, 2‐hydroxyacetophenones, and methyl/ethyl isocyanoacetate at room temperature in the presence of visible light has been developed. The Ag salt plays an important role in the activation of isocyanoacetate and the cyclization step. Air‐stable and low‐cost Knölker iron complex has been utilized for the dehydrogenation of primary alcohols that would typically require a higher temperature. The established protocol is scalable and has an extensive functional group tolerance, generating good to excellent yields of the chromenopyrroles at room temperature.

Recent Advances in Heterogeneously Catalyzed Acceptorless Dehydrogenation of Alcohols to Carbonyl Derivatives and N-heterocyclic Compounds

: Oxidation of alcohols in an oxidant-free condition, commonly known as the acceptorless dehydrogenation (AD) reaction, has recently emerged as one of the widely used processes in synthetic organic chemistry. Alcohol acts as an excellent chemical precursor that produces a variety of dehydrogenated value-added products such as carbonyls, acids, acetals, and several coupling products, followed by the concomitant evolution of molecular hydrogen gas. AD reaction of alcohol, therefore, can be considered as a vital reaction for the hydrogen economy using alcohols as a liquid hydrogen carrier. Over the past decade, the growing importance of AD reactions has set the way for the continuous development of various homogeneous and heterogeneous catalytic systems. With the advantage of reusability and recyclability, heterogeneous catalysts have now become more promising and significant in the catalytic domain. This review aims to make an overview of the transition metal-based heterogeneous catalytic system of acceptorless alcohol dehydrogenation reaction reported till December, 2023.

Acceptorless Dehydrogenation under Neat Reaction Conditions: Synthesis of 2-Aryl/Alkyl Quinazolinones Using Supported Ni NPs as Catalyst

AbstractWe report here a Ni-NPs-catalyzed one-pot synthesis of 2-alkyl/aryl quinazolinone motifs via acceptorless dehydrogenation of alcohol, condensation of an aldehyde intermediate with 2-aminobenzamide, followed by a second dehydrogenation of the cyclized intermediate. The protocol is atom-economical and require earth-abundant Ni as the catalyst. The present report involves the annulation of 2-aminobenzamide with various types of primary alcohols, including aryl/heteroaryl methanol, and aliphatic alcohols, and produces high yields of the desired products under neat conditions. The catalyst was synthesized via a high-temperature pyrolysis strategy, using ZIF-8 as the sacrificial template. The Ni NPs@N-C catalyst was characterized by XPS, HR-TEM, HAADF-STEM, XRD, and ICP-MS. The catalyst is stable even in air at room temperature and displayed excellent activity in the acceptorless dehydrogenative coupling synthesis of quinazolinones and could be recycled five times without appreciable loss of its activity.

Harnessing Oxoammonium Salts for Oxidations in Organic Synthesis and Catalysis: Origins and Applications

The oxoammonium cation has been identified as the true oxidant intermediate in many aerobic oxidations promoted by long‐lived nitroxide radicals. Various oxoammonium salts have been synthesized and utilized to perform these oxidation reactions. In addition to alcohol dehydrogenation and oxidative coupling reactions, new types of reactions involving oxoammonium salts have recently been reported. This concept aims to discuss these oxidations from the perspective of reaction mechanisms, with a focus on progress made since 2019. Beyond the electron transfer route for synthesizing oxoammonium salts, four types of reaction mechanisms are included.

Escherichia coli alcohol dehydrogenase YahK is a protein that binds both iron and zinc.

Previous studies have highlighted the catalytic activity of Escherichia coli alcohol dehydrogenase YahK in the presence of coenzyme nicotinamide adenine dinucleotide (NAD) and metal zinc. Notably, competitive interaction between iron and zinc ligands has been shown to influence the catalytic efficiency of several key proteases. This study aims to unravel the intricate mechanisms underlying YahK's catalytic action, with a particular focus on the pivotal roles played by metal ions zinc and iron. The purified YahK protein from E. coli cells cultivated in LB medium was utilized to investigate its metal-binding properties through UV-visible absorption measurements and determination of metal content. Subsequently, the effects of excess zinc and iron on the metal-binding ability and alcohol dehydrogenase activity of the YahK protein were explored using M9 minimal medium. Furthermore, site-directed mutagenesis technology was employed to determine the iron-binding site location within the YahK protein. Polyacrylamide gel electrophoresis was conducted to examine the relationship between iron and zinc with respect to the YahK protein. The study confirmed the presence of iron and zinc in the YahK protein, with the zinc-bound form exhibiting enhanced catalytic activity in alcohol dehydrogenation reactions. Conversely, the presence of iron appears to play a pivotal role in maintaining overall stability of the YahK protein. Furthermore, experimental findings indicate that excessive zinc within M9 minimal medium can competitively bind to iron-binding sites on YahK, thereby augmenting its alcohol dehydrogenase activity. The dynamic binding of YahK to iron and zinc unveils its intricate regulatory mechanism as an alcohol dehydrogenase, thereby highlighting the possible physiological role of YahK in E. coli and its significance in governing cellular metabolic processes. This discovery provides a novel perspective for further investigating the specific impact of metal ion binding on YahK and E. coli cell metabolism.

Mechanism regulation over dual-atom catalyst enables high-performance oxidative alcohol esterification

The development of heterogeneous catalysts with well-defined uniform isolated or multiple active sites is of great importance for understanding catalytic performances and studying reaction mechanisms. Herein, we present a CoCu dual-atom catalyst (CoCu-DAC) where bonded Co–Cu dual-atom sites are embedded in N-doped carbon matrix with a well-defined Co(OH)CuN6 structure. The CoCu-DAC exhibits higher catalytic activity and selectivity than the Co single-atom catalyst (Co-SAC) and Cu single-atom catalyst (Cu-SAC) counterparts in the catalytic oxidative esterification of alcohols and a variety of methyl and alkyl esters have been successfully synthesized. Kinetic studies reveal that the activation energy (29.7 kJ mol−1) over CoCu-DAC is much lower than that over Co-SAC (38.4 kJ mol−1) and density functional theory (DFT) studies disclose that two different mechanisms are regulated over CoCu-DAC and Co-SAC/Cu-SAC in three-step esterification of alcohols. The bonded Co–Cu and adjacent N species efficiently catalyze the elementary reactions of alcohol dehydrogenation, O2 activation and ester formation, respectively. The stepwise alkoxy pathway (O–H and C–H scissions) is preferred for both alcohol dehydrogenation and ester formation over CoCu-DAC, while the progressive hydroxylalkyl pathway (C–H and O–H scissions) for alcohol dehydrogenation and simultaneous hemiacetal dehydrogenation are favored over Co-SAC and Cu-SAC. Characteristic peaks in the Fourier transform infrared spectroscopy analysis may confirm the formation of the metal-C intermediate and the hydroxylalkyl pathway over Co-SAC.

Highly enhanced photocatalytic hydrogen production via GO-modified Cu-TiO2 system for dehydrogenation of alcohols under UV & sunlight irradiation

The high efficiency of the production of hydrogen from alcohols is vital to the advancement of energy technology. This study thoroughly investigates the process of alcohol dehydrogenation utilising GO-modified Cu-TiO2 photocatalyst under UV light and sunlight exposure. GO-modified Cu-TiO2 photocatalyst was synthesised using the hydrothermal method. Various experimental techniques, including FESEM, HRTEM, XPS, and DRS, confirmed the formation of the ternary composite. The influence of different alcohols (methanol, ethanol, propanol) and their concentrations (same vol% and molarity) on the amount of hydrogen (H2) production was examined in this study. The study thoroughly investigated the impact of various parameters, such as the influence of GO and Cu loading on TiO2 and their combined effect, time course, nature of alcohol and the reaction conditions on the photocatalytic hydrogen production. The GO(0.5 wt%)/Cu(3 wt%)-TiO2 (G0.5C3T) composite demonstrated the highest quantity of hydrogen production during methanol dehydrogenation when subjected to both UV and sunlight irradiation. The composite exhibited remarkably about three-fold higher hydrogen evolution in sunlight(881 mmol) than in UV light(294 mmol). The exceptional performance of this composite can be attributed to the efficient transfer of charge carriers and the delayed recombination of electron-holes, which is a result of the cooperative effect of GO and Cu deposited over the TiO2 system. This approach offers a proactive strategy, signifying the synergetic effect of loading GO and Cu over TiO2 to enhance the photocatalytic hydrogen production, which is regarded as a green fuel solution, and turns these materials into useful energy sources by using inexpensively synthesised photocatalysts.

Enable biomass-derived alcohols mediated alkylation and transfer hydrogenation

A single-atom catalyst with generally regarded inert Zn–N4 motifs derived from ZIF-8 is unexpectedly efficient for the activation of alcohols, enabling alcohol-mediated alkylation and transfer hydrogenation. C-alkylation of nitriles, ketones, alcohols, N-heterocycles, amides, keto acids, and esters, and N-alkylation of amines and amides all go smoothly with the developed method. Taking the α-alkylation of nitriles with alcohols as an example, the α-alkylation starts from the (1) nitrogen-doped carbon support catalyzed dehydrogenation of alcohols into aldehydes, which further condensed with nitriles to give vinyl nitriles, followed by (2) transfer hydrogenation of C=C bonds in vinyl nitriles on Zn–N4 sites. The experimental results and DFT calculations reveal that the Lewis acidic Zn-N4 sites promote step (2) by activating the alcohols. This is the first example of highly efficient single-atom catalysts for various organic transformations with biomass-derived alcohols as the alkylating reagents and hydrogen donors.

Direct ketone synthesis from primary alcohols and alkenes enabled by a dual photo/cobalt catalysis

Catalytic methods to couple alcohol and alkene feedstocks are highly valuable in synthetic chemistry. The direct oxidative coupling of primary alcohols and alkenes offers a streamlined approach to ketone synthesis. Currently, available methods are based on transition metal-catalyzed alkene hydroacylation, which involves the generation of an electrophilic aldehyde intermediate from primary alcohol dehydrogenation. These methods generally require high reaction temperatures and a high loading of precious metal catalysts and are predominantly effective for branch-selective reactions with electron-rich alkenes. Herein, we designed a dual photo/cobalt-catalytic method to manipulate the reactivity of nucleophilic ketyl radicals for the synthesis of ketones from primary alcohols and alkenes in complementary reactivity and selectivity. This protocol exhibits exceptional scope across both primary alcohols and alkenes with high chemo- and regio-selectivity under mild reaction conditions. Mechanism investigations reveal the essential role of cobalt catalysis in enabling efficient catalysis and broad substrate scope.

Ether Functional Groups Enable Oxidative Dehydrogenation of Aliphatic Secondary Alcohols in Water

Ether Functional Groups Enable Oxidative Dehydrogenation of Aliphatic Secondary Alcohols in Water

Controlled incorporation of Zn into nitrogen-doped porous carbon boosts the alcohol dehydrogenation to carboxylic acids

The dehydrogenation of primary alcohols to carboxylic acids is a crucial process in chemical industries such as fibers and plastics. Carboxylic acids, the resulting products, are not only important chemical raw materials but also fundamental pharmaceutical intermediates. Zn-based catalysts have gained attention as a promising option for this transformation owing to their economic cost and abundant reserves. However, stability issues, including structure collapse and morphological changes, have plagued the reported Zn-based catalysts during this transformation. In response to these challenges, this study focused on the design and development of Zn-based catalysts via controlled incorporation of Zn into nitrogen-doped porous carbon to modulate the numbers of defects and Lewis acid-base site pairs. Through extensive screening of various parameters, the best-performing catalyst, namely Zn@NC-800, exhibited high activity and remarkable stability, surpassing all the reported Zn-based catalysts. Moreover, this catalyst demonstrated great recyclability since it could maintain approximately 90 % yields after 9 cycles. Notably, the product formation rate of this catalyst could reach 3833 μmol·gcat.−1·h−1, exceeding that of most reported non-noble metal heterogeneous catalysts. Consequently, this study offers a promising approach for efficiently and stably catalyzing alcohol dehydrogenation reactions using non-noble metals.

Half‐sandwich iridium complexes: Synthesis and catalytic activity in dehydrogenation of alcohols to carboxylic acids

A series of N,N‐chelate half‐sandwich iridium complexes were synthesized by a simple method with good yields. The dehydrogenation of a series of aromatic and aliphatic primary alcohols to corresponding carboxylic acids has been successfully achieved by the prepared air stable iridium complexes under mild reaction conditions. Carboxylic acids were obtained in high yields under open flask condition with broad substrates and good tolerance to sensitive functional groups. Such a half‐sandwich iridium catalyst system showed desirable stability and catalytic activity, and the achievement of a high TOF of 372.0 h−1 could be observed with an extremely low catalyst loading of only 0.05 mol%. Furthermore, the sustainable catalyst could be reused for a minimum of five cycles without obviously losing its activity, highlighting its potential application in industry. Structure of N,N‐chelate iridium complexes 1 and 3 were determined by single‐crystal X‐ray analysis.

Copper‐cobalt bimetallic nanoparticles for the acceptorless dehydrogenation of alcohols: a combined experimental and theoretical study.

Bimetallic Cu and Co nanoparticles were prepared using the polyol process. The nature of the polyol was found to be decisive to control the distribution of the two metals within the particles, resulting in either core‐shell or quasi‐alloyed structures, as shown by chemical analysis at the single particle level. The particles can be prepared over the entire composition range with a very good control of the Cu/Co molar ratio. The introduction of Cu in the synthetic system allows decreasing significantly the mean size of the resulting particles. The two sets of particles were used as unsupported catalysts for the solvent‐free acceptorless dehydrogenation of octan‐2‐ol. Very good ketone yields were measured when using the quasi‐alloyed particles while lower activities were obtained with core‐shell structures. The Cu25Co75 quasi‐alloyed catalyst could be recycled at least ten times without a significant loss in catalytic activity and particle‐scale chemical analyses confirmed that the recovered particles are still alloyed with no observed demixing. The catalytic results are discussed in the light of different exposed metal surface areas and possible synergetic effects using theoretical predictions.

Iron- and Organo-Catalyzed Borrowing Hydrogen for the Stereoselective Construction of Tetrahydropyrans.

Stereocontrolled oxa-Michael additions are challenging, given the high reversibility of the process, which ultimately leads to racemization of the newly formed stereocenters. When iron-catalyzed borrowing hydrogen from allylic alcohols was combined with a stereocontrolled organocatalytic oxa-Michael addition, a wide array of chiral tetrahydropyrans were efficiently prepared. The reaction could be performed in a diastereoselective manner from pre-existing stereocenters or enantioselectively from achiral substrates. The key to success was the reactivity of the iron complex, which was selective for allylic alcohol dehydrogenation and irreversibly led the reaction to the final product.

Half-Sandwich Iridium Complexes: A Recyclable and Stable Catalyst for Dehydrogenation of Alcohols to Carboxylic Acids.

A series of acylhydrazone-based N,N-chelate half-sandwich iridium complexes have been synthesized through a facile route in good yields. The dehydrogenation of a series of aromatic and aliphatic primary alcohols to corresponding carboxylic acids has been accomplished catalyzed by the prepared air stable iridium complexes under mild reaction conditions. Carboxylic acids were obtained in high yields under open flask condition with broad substrates and good tolerance to sensitive functional groups. Such a half-sandwich iridium catalyst system exhibited high catalytic activity and stability, and a high TOF of 316.7 h-1 could be achieved with a catalyst loading as low as 0.05 mol %. Furthermore, the sustainable catalyst could be reused at least five times without obviously losing its activity, highlighting its potential application in industry. Molecular structure of iridium complex 1 was confirmed by single-crystal X-ray analysis.