Liquid Phase Oxidation of Toluene to Benzaldehyde with Molecular Oxygen over Copper-Based Heterogeneous Catalysts
TL;DR: In this paper, the authors conducted liquid phase oxidation of toluene with molecular oxygen over heterogeneous catalysts of copper-based binary metal oxides and found that iron-copper bi-nary oxide (Fe/Cu ¼ 0.3 atomic ratio) was the best catalyst.
Abstract: We conducted the liquid phase oxidation of toluene with molecular oxygen over heterogeneous catalysts of copper-based binary metal oxides. Among the copper-based binary metaloxides, iron-copper bi- nary oxide (Fe/Cu ¼ 0.3 atomic ratio) was found to be the best catalyst. In the presence of pyridine, overox- idation of benzaldehyde to benzoic acid was partially prevented. As a result, highly selective formation of benzaldehyde (86% selectivity) was observed after 2 h of reaction (7% conversion of toluene) at 463 K and 1.0 MPa of oxygen atmosphere in the presence of pyridine. These catalytic performances were similar or better than those in the gas phase oxidation of tol- uene at reaction temperatures higher than 473 K and under 0.5 - 2.5 MPa. It was suggested from competi- tive adsorption measurements that pyridine could re- duce the adsorption of benzaldehyde. At a long reac- tion time of 4 h, the conversion increased to 25% and benzoic acid became the predominant reaction prod- uct (72% selectivity) in the absence of pyridine. The yield of benzoic acid was higher than that in the Snia-Viscosa process, which requires corrosive halo- gen ions and acidic solvents in the homogeneous reac- tion media. The catalyst was easily recycled by simple filtration and reusable after washing and drying.
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TL;DR: It is reported here that supported gold-palladium nanoparticles on carbon or TiO2 are active for the oxidation of the primary carbon-hydrogen bonds in toluene and related molecules, giving high selectivities to benzyl benzoate under mild solvent-free conditions.
Abstract: Selective oxidation of primary carbon-hydrogen bonds with oxygen is of crucial importance for the sustainable exploitation of available feedstocks. To date, heterogeneous catalysts have either shown low activity and/or selectivity or have required activated oxygen donors. We report here that supported gold-palladium (Au-Pd) nanoparticles on carbon or TiO2 are active for the oxidation of the primary carbon-hydrogen bonds in toluene and related molecules, giving high selectivities to benzyl benzoate under mild solvent-free conditions. Differences between the catalytic activity of the Au-Pd nanoparticles on carbon and TiO2 supports are rationalized in terms of the particle/support wetting behavior and the availability of exposed corner/edge sites.
678 citations
TL;DR: An up-to-date overview of both technological and chemical aspects of liquid phase oxidation chemistry in continuous-flow microreactors is given, including the use of oxygen, hydrogen peroxide, ozone and other oxidants in flow.
Abstract: Continuous-flow liquid phase oxidation chemistry in microreactors receives a lot of attention as the reactor provides enhanced heat and mass transfer characteristics, safe use of hazardous oxidants, high interfacial areas, and scale-up potential. In this review, an up-to-date overview of both technological and chemical aspects of liquid phase oxidation chemistry in continuous-flow microreactors is given. A description of mass and heat transfer phenomena is provided and fundamental principles are deduced which can be used to make a judicious choice for a suitable reactor. In addition, the safety aspects of continuous-flow technology are discussed. Next, oxidation chemistry in flow is discussed, including the use of oxygen, hydrogen peroxide, ozone and other oxidants in flow. Finally, the scale-up potential for continuous-flow reactors is described.
402 citations
TL;DR: In this article, the boron-doped polymeric carbon nitride shows promising catalytic activity and high selectivity (≥87%) in the oxidation of benzylic aromatics.
Abstract: Oxidation of hydrocarbons with clean oxidants is a crucial process for the development of products ranging from commodity chemicals to speciality pharmaceuticals. While selective oxidation is commonplace in nature and mainly occurs through a broad variety of cytochrome P450 enzymes, the synthetic catalysts that have been identified so far are relatively inactive with aliphatic C–H bonds. We present here a promising strategy for modifying polymeric graphitic carbon nitride by replacing the carbon atoms in the “melon” network using boron. 11B solid-state MAS NMR and XPS spectral studies confirmed the incorporation of the boron atoms in the polymeric g-C3N4 as well as the degree of doping, while X-ray diffraction and IR indicated that the characteristic structural properties of polymeric g-C3N4, such as the original graphitic structure, and the C–N heterocycle units were essentially retained. The boron-doped polymeric carbon nitride shows promising catalytic activity and high selectivity (≥87%) in the oxidation of benzylic aromatics. The use of this metal-free, organic, semiconducting polymer as an oxidation catalyst and H2O2 or O2 as oxidants makes the reactions interesting from both an economic and environmental point of view. It is also hoped that our findings will stimulate further investigation and will open new possibilities to form hybrid carbon nitride materials with new and probably exciting applications.
380 citations
TL;DR: This critical review aims to update the recent development in the selective oxidation of organic compounds by gold catalysis, highlighting the progress in the last three years.
Abstract: This critical review aims to update the recent development in the selective oxidation of organic compounds by gold catalysis, highlighting the progress in the last three years. Following the impressive developments in the last decades, several protocols for catalytic oxidation are today available, which are based on the extraordinary properties of gold in terms of catalytic activity, selectivity, reusability and resistance to poisons. Beside many other applications, gold can be recommended for green processes dedicated to fine chemicals, pharmaceuticals and the food industry owing to its recognized bio-compatibility. The collected literature is focused on experiments concerning the oxidation of different chemical groups and could be of interest, in the wide area of organic chemistry, for improving previous processes or for exploring new catalytic pathways (174 references).
309 citations
TL;DR: In this article, the authors summarize the recent significant advances achieved in the field of oxidation and hydrogenation realized by graphitic carbon nitride (g-C3N4) based catalytic systems.
253 citations
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TL;DR: Palladium oxidase catalysis combines the versatility of Pd(II)-mediated oxidation of organic substrates with dioxygen-coupled oxidation of the reduced palladium catalyst to enable a broad range of selective aerobic oxidation reactions.
Abstract: Selective aerobic oxidation of organic molecules is a fundamental and practical challenge in modern chemistry. Effective solutions to this problem must overcome the intrinsic reactivity and selectivity challenges posed by the chemistry of molecular oxygen, and they must find application in diverse classes of oxidation reactions. Palladium oxidase catalysis combines the versatility of Pd(II)-mediated oxidation of organic substrates with dioxygen-coupled oxidation of the reduced palladium catalyst to enable a broad range of selective aerobic oxidation reactions. Recent developments revealed that cocatalysts (e.g. Cu(II), polyoxometalates, and benzoquinone) are not essential for efficient oxidation of Pd(0) by molecular oxygen. Oxidatively stable ligands play an important role in these reactions by minimizing catalyst decomposition, promoting the direct reaction between palladium and dioxygen, modulating organic substrate reactivity and permitting asymmetric catalysis.
1,227 citations
967 citations
TL;DR: In this article, the NHPI-catalyzed oxidation of alkylbenzenes with dioxygen could be performed even under normal temperature and pressure of DIOxygen.
Abstract: An innovation of the aerobic oxidation of hydrocarbons through catalytic carbon radical generation under mild conditions was achieved by using N-hydroxyphthalimide (NHPI) as a key compound. Alkanes were successfully oxidized with O2 or air to valuable oxygen-containing compounds such as alcohols, ketones, and dicarboxylic acids by the combined catalytic system of NHPI and a transition metal such as Co or Mn. The NHPI-catalyzed oxidation of alkylbenzenes with dioxygen could be performed even under normal temperature and pressure of dioxygen. Xylenes and methylpyridines were also converted into phthalic acids and pyridinecarboxylic acids, respectively, in good yields. The present oxidation method was extended to the selective transformations of alcohols to carbonyl compounds and of alkynes to ynones. The epoxidation of alkenes using hydroperoxides or H2O2 generated in situ from hydrocarbons or alcohols and O 2 under the influence of the NHPI was demonstrated and seems to be a useful strategy for industrial applications. The NHPI method is applicable to a wide variety of organic syntheses via carbon radical intermediates. The catalytic carboxylation of alkanes was accomplished by the use of CO and O2 in the presence of NHPI. In addition, the reactions of alkanes with NO2 and SO2 catalyzed by NHPI provided efficient methods for the synthesis of nitroalkanes and sulfonic acids, respectively. A catalytic carbon-carbon bond forming reaction was achieved by allowing carbon radicals generated in situ from alkanes or alcohols to react with alkenes under mild conditions.
1 Introduction
2 Discovery of NHPI as Carbon Radical Producing Catalyst from Alkanes
2.1 Historical Background
2.2 Catalysis of NHPI in Aerobic Oxidation
3 NHPI-Catalyzed Aerobic Oxidation
3.1 Oxidation of Benzylic Compounds
3.2 Alkane Oxidations with Molecular Oxygen
3.3 Oxidation of Alkylbenzenes
3.4 Practical Oxidation of Methylpyridines
3.5 Preparation of Acetylenic Ketones via Alkyne Oxidation
3.6 Oxidation of Alcohols
3.7 Selective Oxidation of Sulfides to Sulfoxides
3.8 Production of Hydrogen Peroxide by Aerobic Oxidation of Alcohols
3.9 Epoxidation of Alkenes using Molecular Oxygen as Terminal Oxidant
4 Carboxylation of Alkanes with CO and O2
5 Utilization of NOx in Organic Synthesis
5.1 First Catalytic Nitration of Alkanes using NO2
5.2 Reaction of NO with Organic Compounds
6 Sulfoxidation of Alkanes Catalyzed by Vanadium
7 Carbon-Carbon Bond Forming Reaction via Catalytic Carbon Radicals Generated from Various Organic Compounds Assisted by NHPI
7.1 Oxyalkylation of Alkenes with Alkanes and Dioxygen
7.2 Synthesis of α-Hydroxy-γ-lactones by Addition of α-Hydroxy Carbon Radicals to Unsaturated Esters
7.3 Hydroxyacylation of Alkenes using 1,3-Dioxolanes and Dioxygen
8 Conclusions
570 citations
TL;DR: In this paper, a review describes examples of remarkable acceleration of metal-catalyzed oxidation reactions by certain additives, which can not only dramatically improve yields of oxygenates but also control the selectivity of the reaction.
Abstract: This review describes examples of remarkable acceleration of metal-catalyzed oxidation reactions by certain additives. In some cases, reactions proceed 2 or 10 times more rapidly in comparison with the process in the additive’s absence, in other cases, reactions become possible only in the presence of the additive. Varying ligands at the metal center or additives, one can not only dramatically improve yields of oxygenates but also control the selectivity of the reaction. Understanding mechanisms of the additive’s action is very important for search of new efficient catalysts and catalytic systems. Additives considered in the review can play roles of the ligands at metal ion or proton or electron transfer reagents and they mimic certain enzymes (the active center or its environment). Often the mechanism of the effect of additives on the reaction rate and the product yield is unknown, and the main aim of the review is to attract investigator’s attention in creating new efficient catalytic systems, which contain not only a metal ion but also a necessary “additive”.
443 citations