Silver-Catalyzed Dehydrogenative Synthesis of Carboxylic Acids from Primary Alcohols

Reduced Tiara-like Palladium Complex for Suzuki Cross-Coupling Reactions

The design of highly active and structurally well-defined catalysts has become a crucial issue for heterogeneous catalysed reactions while reducing the amount of catalyst employed. Beside conventional synthetic routes, the employment of polynuclear transition metal complexes as catalysts or catalyst precursors has progressively intercepted a growing interest. These well-defined species promise to deliver catalytic systems where a strict control on the nuclearity allows to improve the catalytic performance while reducing the active phase loading. This study describes the development of a highly active and reusable palladium-based catalyst on alumina (Pd8 /Al2 O3 ) for Suzuki cross-coupling reactions. An octanuclear tiara-like palladium complex was selected as active phase precursor to give isolated Pd-clusters of ca. 1 nm in size on Al2 O3 . The catalyst was thoroughly characterised by several complementary techniques to assess its structural and chemical nature. The high specific activity of the catalyst has allowed to carry out the cross-coupling reaction in 30 min using only 0.12 mol % of Pd loading under very mild and green reaction conditions. Screening of various substrates and selectivity tests, combined with recycling and benchmarking experiments, have been used to highlight the great potentialities of this new Pd8 /Al2 O3 catalyst.

Benzobicyclic ketones, cycloheptenone oxide derivatives, guaiane-type sesquiterpenes, and alkaloids isolated from Taraxacum mongolicum Hand.-Mazz

Ten previously undescribed compounds, including two benzobicyclic ketones, one cycloheptenone oxide derivative, three guaiane-type sesquiterpenes, and four alkaloids, along with one known cycloheptenone oxide derivative, were isolated from the whole plants of Taraxacum mongolicum Hand.-Mazz. Their structures were elucidated by UV, IR, HR-ESI-MS, 1D and 2D NMR spectroscopy, ECD spectroscopy, or X-ray diffraction analysis. Notably, benzobicyclic ketones have never been isolated from nature before. The 70% EtOH-H₂O extract of T. mongolicum displayed a significant inhibitory activity (33%) against croton oil-induced mouse ear edema. The two cycloheptenone oxide derivatives exhibited anti-inflammatory activities at 10 μM and significantly reduced the nitric oxide (NO) and interleukin-6 (IL-6) levels in RAW 264.7 macrophages induced by lipopolysaccharide (LPS), with inhibitory rates of 26.4-64.4%.

Acceptorless dehydrogenation of alcohols to carboxylic acids by palladium nanoparticles supported on NiO: delving into metal-support cooperation in catalysis

In this work, we have developed a simple NiO-supported Pd nanocatalyst (Pd@NiO) for oxidant-free dehydrogenative oxidation of primary alcohols to carboxylic acids along with hydrogen gas as a byproduct. The catalyst has been characterized by techniques like XRD, HRTEM, SEM-EDX, XPS and ICP-AES. The nanostructured Pd@NiO material showed excellent dehydrogenative oxidation activity and outperformed the activity of free NiO or Pd nanoparticles supported on silica/carbon as a catalyst, which could be attributed to synergistic effect of Pd and NiO. A diverse range of aromatic and aliphatic primary alcohols could be efficiently converted to their corresponding carboxylates in high yields with a catalyst loading as low as 0.08 mol%. Notably, highly challenging biomass derived heterocyclic alcohols such as furfuryl alcohol and piperonyl alcohol can also be efficiently converted to their corresponding acids. Moreover, our catalyst can convert benzyl alcohol to benzoic acid on a gram scale with 89% yield. Interestingly, the H₂ gas liberated in the reaction can also be used as a substrate for the hydrogenation of 3a to 4a in 65% yield. The nanostructured catalyst is highly reusable and no significant decrease in activity was observed after six reaction cycles. A kinetic study revealed that the reaction followed first-order kinetics with a rate constant of k = 1.47 × 10^-4 s^-1, under optimized conditions. The extent of reactivity of different functionalities towards dehydrogenation was also investigated using a Hammett plot showing good linearity.

Pyridine dicarbanion-bonded Ag13 organometallic nanoclusters: synthesis and on-surface oxidative coupling reaction

Unprecedented pyridine dicarbanion-bonded Ag13 nanoclusters were constructed according to a macrocycle-involved two-step synthetic protocol.

Atomically Dispersed Co Clusters Anchored on N-doped Carbon Nanotubes for Efficient Dehydrogenation of Alcohols and Subsequent Conversion to Carboxylic Acids

The catalytic dehydrogenation of readily available alcohols to high value-added carbonyl compounds is a research hotspot with scientific significance. Most of the current research about this reaction is performed with noble metal-based homogeneous catalysts of high price and poor reusability. Herein, highly dispersed Co-cluster-decorated N-doped carbon nanotubes (Co/N-CNTs) were fabricated via a facile strategy and used for the dehydrogenation of alcohols with high efficiency. Various characterization techniques confirmed the presence of metallic Co clusters with almost atomic dispersion, and the N-doped carbon supports also enhanced the catalytic activity of Co clusters in the dehydrogenation reaction. Aldehydes as dehydrogenation products were further transformed in situ to carboxylic acids through a Cannizzaro-type pathway under alkaline conditions. The reaction pathway of the dehydrogenation of alcohols was clearly confirmed by theoretical calculations. This work should provide an effective and simple approach for the accurate design and synthesis of small Co-clusters catalysts for the efficient dehydrogenation-based transformation of alcohols to carboxylic acids under mild reaction conditions.

Oxidation of Primary Alcohols and Aldehydes to Carboxylic Acids via Hydrogen Atom Transfer

The oxidation of primary alcohols and aldehydes to the corresponding carboxylic acids is a fundamental reaction in organic synthesis. In this paper, we report a new chemoselective process for the oxidation of primary alcohols and aldehydes. This metal-free reaction features a new oxidant, an easy to handle procedure, high isolated yields, and good to excellent functional group tolerance even in the presence of vulnerable secondary alcohols and tert-butanesulfinamides.

Direct Oxidation of Primary Alcohols to Carboxylic Acids

Oxidation of primary alcohols to carboxylic acids is a fundamental transformation in organic chemistry, yet despite its simplicity, extensive use, and relationship to pH, it remains a subject of active research for synthetic organic chemists. Since 2013, a great number of new methods have emerged that utilize transition-metal compounds as catalysts for acceptorless dehydrogenation of alcohols to carboxylates. The interest in this reaction is explained by its atom economy, which is in accord with the principles of sustainability and green chemistry. Therefore, the methods for the direct synthesis of carboxylic acids from alcohols is ripe for a modern survey, which we provide in this review.

1 Introduction

2 Thermodynamics of Primary Alcohol Oxidation

3 Oxometalate Oxidation

4 Transfer Dehydrogenation

5 Acceptorless Dehydrogenation

6 Electrochemical Methods

7 Outlook

Highly Efficient N-Heterocyclic Carbene/Ruthenium Catalytic Systems for the Acceptorless Dehydrogenation of Alcohols to Carboxylic Acids: Effects of Ancillary and Additional Ligands

The transition-metal-catalyzed alcohol dehydrogenation to carboxylic acids has been identified as an atom-economical and attractive process. Among various catalytic systems, Ru-based systems have been the most accessed and investigated ones. With our growing interest in the discovery of new Ru catalysts comprising N-heterocyclic carbene (NHC) ligands for the dehydrogenative reactions of alcohols, we designed and prepared five NHC/Ru complexes ([Ru]-1–[Ru]-5) bearing different ancillary NHC ligands. Moreover, the effects of ancillary and additional ligands on the alcohol dehydrogenation with KOH were thoroughly explored, followed by the screening of other parameters. Accordingly, a highly active catalytic system, which is composed of [Ru]-5 combined with an additional NHC precursor L5, was discovered, affording a variety of acid products in a highly efficient manner. Gratifyingly, an extremely low Ru loading (125 ppm) and the maximum TOF value until now (4800) were obtained.

Bidentate Ru(ii)-NC complexes as catalysts for the dehydrogenative reaction from primary alcohols to carboxylic acids

Complex 1 is active for alcohol dehydrogenative reactions, and two critical intermediates were isolated and characterized.

Highly active bidentate N-heterocyclic carbene/ruthenium complexes performing dehydrogenative coupling of alcohols and hydroxides in open air

A highly active and robust bidentate NHC/Ru complex for the acceptorless dehydrogenative coupling of alcohols and hydroxides in open air.

Zinc Oxide-Catalyzed Dehydrogenation of Primary Alcohols into Carboxylic Acids

Zinc oxide has been developed as a catalyst for the dehydrogenation of primary alcohols into carboxylic acids and hydrogen gas. The reaction is performed in mesitylene solution in the presence of potassium hydroxide, followed by workup with hydrochloric acid. The transformation can be applied to both benzylic and aliphatic primary alcohols and the catalytically active species was shown to be a homogeneous compound by a hot filtration test. Dialkylzinc and strongly basic zinc salts also catalyze the dehydrogenation with similar results. The mechanism is believed to involve the formation of a zinc alkoxide which degrades into the aldehyde and a zinc hydride. The latter reacts with the alcohol to form hydrogen gas and regenerate the zinc alkoxide. The degradation of a zinc alkoxide into the aldehyde upon heating was confirmed experimentally. The aldehyde can then undergo a Cannizzaro reaction or a Tishchenko reaction, which in the presence of hydroxide leads to the carboxylic acid.

A general and efficient Mn-catalyzed acceptorless dehydrogenative coupling of alcohols with hydroxides into carboxylates

A general and efficient Mn-catalyzed acceptorless dehydrogenative coupling of alcohols with hydroxides into carboxylates has been developed.