Concept Of Catalysis Research Articles

Micelle confined mechanistic pathway for 4-nitrophenol reduction

The model 4-nitrophenol reduction has been carried out by different groups in presence of metallic or even non-metallic catalyst elaborating different mechanistic aspects. In the present investigation, we have thoroughly studied the hydrogenation of 4-nitrophenol in a completely metal free homogeneous condition. The introduction of a non-fluorescent probe unequivocally generates a fluorescent molecule that indirectly justifies the anion radical stabilization in the micelle. The reduction mechanism under metal-free condition was proposed and the concept of stabilization of anion radical transition state of 4-nitrophenol at the positively charged Stern layer of anionic micelle was established. The plausible reduction mechanism has also enlightened the graphene-like conducting property of Stern layer of the homogeneous micellar system. Furthermore, the confinement effect for catalysis has also been authenticated by supporting experimental evidences. The borrowed concept of catalysis in confinement drives the catalytic study to a new era of catalysis.

The New Concept of Antimicrobial Catalysis: Disinfection of Ships Ballast Water

The New Concept of Antimicrobial Catalysis: Disinfection of Ships Ballast Water

Surface-active ionic liquids in catalysis: Impact of structure and concentration on the aerobic oxidation of octanol in water

We present design and synthesis of surface-active ionic liquids for the application in micellar catalysis. A series of 1-methyl-3-dodecylimidazolium based ionic liquids with variable core structures including dicationic and zwitterionic ones was synthesized and characterized. These surface-active ionic liquids where applied in the aerobic oxidation of aliphatic alcohols to carbonyl compounds. A strong dependence on the ionic liquid concentration and structure was identified, which is in accordance with the concepts of micellar catalysis. Optimum conditions for the oxidation of 1-octanol could be identified, and the use of surface-active ionic liquids strongly improved the reaction performance compared to pure water. Under optimized conditions, it was possible to isolate up to 75% of octanoic acid using only small amounts of surface-active ionic liquid in a 0.05mM solution in water without further ligands.

DNA-Accelerated Copper Catalysis of Friedel–Crafts Conjugate Addition/Enantioselective Protonation Reactions in Water

DNA-induced rate acceleration has been identified as one of the key elements for the success of the DNA-based catalysis concept. Here we report on a novel DNA-based catalytic Friedel-Crafts conjugate addition/enantioselective protonation reaction in water, which represents the first example of a reaction that critically depends on the >700- to 990-fold rate acceleration caused by the presence of a DNA scaffold. The DNA-induced rate acceleration observed is the highest reported due to the environment presented by a biomolecular scaffold for any hybrid catalyst, to date. Based on a combination of kinetics and binding studies, it is proposed that the rate acceleration is in part due to the DNA acting as a pseudophase, analogous to micelles, in which all reaction components are concentrated, resulting in a high effective molarity. The involvement of additional second coordination sphere interactions is suggested by the enantioselectivity of the product. The results presented here show convincingly that the DNA-based catalysis concept, thanks to the DNA-accelerating effect, can be an effective approach to achieving a chemically challenging reaction in water.

ChemInform Abstract: The First Organocatalytic Cope Rearrangement

AbstractReview: 11 refs.

Development of Multiactive Site Catalysts for Surface Concerted Catalysis Aimed at One-Pot Synthesis

Abstract Multiactive site catalysts have been developed for conducting one-pot synthesis and highly efficient reactions based on the principle of concerted catalysis. Ru-grafted hydrotalcite containing both Ru and base sites on its outer surface exhibits high catalytic activity for the one-pot synthesis of dinitrile compounds. A reaction system consisting of a strong acid, base, and Pd species is capable of catalyzing a one-pot process consisting of five successive reactions, esterification, deacetalization, aldol reaction, hydrogenation, and Michael reaction, to produce a final product, 2,4-dicyanoester, from starting materials containing cycnoacetic acid and acetal, with excellent overall yield. Immobilization of an amine base onto a solid acid surface affords an acid–base bifunctional catalytic surface with controlled acid–base interactions. Various nucleophilic addition reactions including the one-pot synthesis of dinitroalkane derivatives proceeds effectively by acid–base concerted catalysis. The concept of concerted catalysis on solid surfaces can be extended to synergistic/double-activation catalysis between a metal complex and organic base immobilized on a surface. Further, the concept of multiactive site catalysis can also be applied to a homogeneous catalyst system. For example, a Cu-bisphosphine complex exhibits excellent catalytic performance for the transformation of CO2 to valuable chemicals, such as cyclic carbonate, silyl formate, and formamides.

The First Organocatalytic Cope Rearrangement.

Exploiting the concept of iminium ion catalysis led to the discovery of the first organocatalytic Cope rearrangement of 1,5-hexadiene-2-carboxaldehydes. A diazepane catalyst exhibited optimal catalytic efficiency and offers possibilities for chiral modification.

Spin Catalysis over Conductive Solids: Enhancing the Rate of Model C−C Bond Cracking over Carbon Nanoparticles

AbstractThe concept of catalysis over a spin‐conductive mediator is investigated with quantum‐chemical calculations. Specifically, homolytic C−C bond cleavage in ethane over small edge‐oxidized half‐metallic carbon clusters in the presence of a methyl radical was considered with the complete active space self‐consistent field method. The methyl radical (spin catalyst) and carbon cluster (mediator) are found to share a common electronic orbital containing the radical unpaired electron, allowing nascent radicals emerging from ethane dissociation to interact with the spin catalyst through the carbon electronic system. This could result in spin flip, affording formation of a triplet radical pair not prone to recombination and thus resulting in the acceleration of the reaction rate. This demonstrates that new pathways may open up in controlled catalytic processes by allowing normally spin‐forbidden reactions and not necessarily lowering activation barriers in the traditional sense of catalysis.

Insights into the Mechanism of Tandem Alkene Hydroformylation over a Nanostructured Catalyst with Multiple Interfaces.

The concept of tandem catalysis, where sequential reactions catalyzed by different interfaces in single nanostructure give desirable product selectively, has previously been applied effectively in the production of propanal from methanol (via carbon monoxide and hydrogen) and ethylene via tandem hydroformylation. However, the underlying mechanism leading to enhanced product selectivity has remained elusive due to the lack of stable, well-defined catalyst suitable for in-depth comprehensive study. Accordingly, we present the design and synthesis of a three-dimensional (3D) catalyst CeO2-Pt@mSiO2 with well-defined metal-oxide interfaces and stable architecture and investigate the selective conversion of ethylene to propanal via tandem hydroformylation. The effective production of aldehyde through the tandem hydroformylation was also observed on propylene and 1-butene. A thorough study of the CeO2-Pt@mSiO2 under different reaction and control conditions reveals that the ethylene present for the hydroformylation step slows down initial methanol decomposition, preventing the accumulation of hydrogen (H2) and favoring propanal formation to achieve up to 80% selectivity. The selectivity is also promoted by the fact that the reaction intermediates produced from methanol decomposition are poised to directly undergo hydroformylation upon migration from one catalytic interface to another. This synergistic effect between the two sequential reactions and the corresponding altered reaction pathway, compared to the single-step reaction, constitute the key advantages of this tandem catalysis. Ultimately, this in-depth study unravels the principles of tandem catalysis related to hydroformylation and represents a key step toward the rational design of new heterogeneous catalysts.

Jarl Ivar van der Vlugt

Jarl Ivar van der Vlugt

Merging Visible Light Photoredox Catalysis with Metal Catalyzed C-H Activations: On the Role of Oxygen and Superoxide Ions as Oxidants.

ConspectusThe development of efficient catalytic systems for direct aromatic C–H bond functionalization is a long-desired goal of chemists, because these protocols provide environmental friendly and waste-reducing alternatives to classical methodologies for C–C and C–heteroatom bond formation. A key challenge for these transformations is the reoxidation of the in situ generated metal hydride or low-valent metal complexes of the primary catalytic bond forming cycle. To complete the catalytic cycle and to regenerate the C–H activation catalyst, (super)stoichiometric amounts of Cu(II) or Ag(I) salts have often been applied. Recently, “greener” approaches have been developed by applying molecular oxygen in combination with Cu(II) salts, internal oxidants that are cleaved during the reaction, or solvents or additives enabling the metal hydride reoxidation. All these approaches improved the environmental friendliness but have not overcome the obstacles associated with the overall limited functional group and substrate tolerance. Hence, catalytic processes that do not feature the unfavorable aspects described above and provide products in a streamlined as well as economically and ecologically advantageous manner would be desirable.In this context, we decided to examine visible light photoredox catalysis as a new alternative to conventionally applied regeneration/oxidation procedures. This Account summarizes our recent advances in this expanding area and will highlight the new concept of merging distinct redox catalytic processes for C–H functionalizations through the application of visible light photoredox catalysis. Photoredox catalysis can be considered as catalytic electron-donating or -accepting processes, making use of visible-light absorbing homogeneous and heterogeneous metal-based catalysts, as well as organic dye sensitizers or polymers. As a consequence, photoredox catalysis is, in principle, an ideal tool for the recycling of any given metal catalyst via a coupled electron transfer (ET) process.Here we describe our first successful endeavors to address the above challenges by combining visible light photoredox catalysis with different ruthenium, rhodium, or palladium catalyzed C–H activations. Since only small amounts of the oxidant are generated and are immediately consumed in these transformations, side reactions of substrates or products can be avoided. Thus, usually oxidant-sensible substrates can be used, which makes these methods highly suitable for complex molecular structure syntheses. Moreover, mechanistic studies shed light on new reaction pathways, intermediates, and in situ generated species. The successful development of our dual catalysis concept, consisting of combined visible light photoredox catalysis and metal catalyzed C–H functionalization, provides many new opportunities for further explorations in the field of C–H functionalization.

ChemInform Abstract: Cooperative Photoredox Catalysis

AbstractReview: 52 refs.

ChemInform Abstract: Disruptive Catalysis by Zeolites

AbstractReview: 172 refs.

An Undergraduate Chemistry Laboratory: Synthesis of Well-Defined Polymers by Low-Catalyst-Concentration ATRP and Postpolymerization Modification to Fluorescent Materials

A two-session experiment is designed to introduce undergraduate students to concepts in catalysis, transition metal complexes, polymer synthesis, and postpolymerization modifications. In the first session, students synthesize poly(glycidyl methacrylate) via low-catalyst-concentration atom transfer radical polymerization (ATRP). The low-catalyst-concentration technique simplifies the experimental setup, reduces the cost of the synthesis, eliminates the need for catalyst removal from the product, and thus ultimately makes ATRP an environmentally benign process. In the second session, students modify the well-defined epoxide-containing polymers with nicotinamide in the presence of acetone, to afford fluorescent polymers.

Bifunctional solid acid photocatalyst TiO2/AC/SO3H with high acid density for pure green photosynthesis of 2-quinoline carboxamide

Quinoline ramifications possess a wide range of biological activities and potential pharmacological activities. Here, a concept of bifunctional solid acid photocatalyst TiO2/AC/SO3H with high acid density is firstly purposed for efficiently pure green synthesis of 2-quinoline carboxamide under ultraviolet-visible light irradiation. After sulfonation, the acid density of TiO2/AC is markedly larger than that of sole TiO2 or AC, and the maximum yield of 2-quinoline carboxamide of 39% is obtained when the acid density of catalyst reaches 1.55mmol/g. The new concept of bifunctional catalysis using solid acid and photocatalyst is potential for industrial application and instructive in green organic synthesis reactions which need radical and acid simultaneously.

Using a Hands-On Hydrogen Peroxide Decomposition Activity To Teach Catalysis Concepts to K–12 Students

A versatile and transportable laboratory apparatus was developed for middle and high school (6th–12th grade) students as part of a hands-on outreach activity to estimate catalytic rates of hydrogen peroxide decomposition from oxygen evolution rates measured by using a volumetric displacement method. The apparatus was constructed with inherent safety features and is compatible with different types of catalysts, catalyst and peroxide concentrations, and reaction temperatures to enable the design of various experiments. The hands-on outreach activity was created with the aim of building scientific proficiency and stimulating interest in STEM fields among students with limited chemistry background. This activity is designed to be completed in short times (45 min) by students in small groups (3–5 students), where each group measures reaction rates at various activity stations and then gathers as a larger group (∼20 total) to discuss their observations and results and to assess their scientific understanding. A...

Design, Synthesis, and Binding Affinity Evaluation of Hoechst 33258 Derivatives for the Development of Sequence-Specific DNA-Based Asymmetric Catalysts

To date, the concept of DNA-based asymmetric catalysis has been successfully applied to various synthetic transformations by way of hybrid catalysts involving either an intercalator or an integrated ligand anchored through supramolecular interactions. We report here a new anchoring strategy based on the well-known groove-binder Hoechst 33258. The interaction between calf thymus DNA (ct-DNA) and poly[d(A-T)2] with a series of Hoechst 33258-derived ligands was studied by UV–vis absorption spectroscopy, thermal melting analysis, fluorescence emission, CD spectroscopy, mass spectrometry, and molecular docking. The results clearly show that a groove-binding anchoring strategy can be envisioned for DNA-based asymmetric catalysis, offering additional mechanistic insight on how the intrinsic chirality of DNA can be transferred to a reaction product. Most importantly, this new anchoring strategy offers interesting compartmentalization possibilities and provides a new way to reverse the enantioselectivity outcome o...

Lewis Acid Catalysis Confined in Zeolite Cages as a Strategy for Sustainable Heterogeneous Hydration of Epoxides

We report a heterogeneous catalysis strategy to the sustainable hydration of epoxides by designing robust Lewis acid catalysts confined in zeolite cages as natural shape-selective nanoreactors. In the case of ethylene oxide hydration, Sn-H-SSZ-13 zeolite exhibits remarkable catalytic performance, with an ethylene oxide conversion above 99% and a monoethylene glycol selectivity above 99%, at approaching stoichiometric water/ethylene oxide ratios and near-ambient reaction temperatures. It is revealed by theoretical studies that partially hydroxylated Sn species are the preferred Lewis acid sites for the hydration of ethylene oxide. The concept of Lewis acid catalysis confined in zeolite cages may be applied in the future in the chemical industry to develop energy-saving and environmentally benign processes.

ChemInform Abstract: The Developing Concept of Bifunctional Catalysis with Transition Metal N‐Heterocyclic Carbene Complexes

AbstractReview: [93 refs.

Using Pop‐It Beads in the Classroom to Enhance Student Comprehension of Enzyme Catalysis and Reaction Rate

A classroom activity was devised to introduce associate‐level deaf and hard‐of‐hearing (DHH) students to the concepts of enzyme activity and catalysis of reaction rate. Students’ hands manipulated Pop‐It Beads as the catalytic event and their progress was directly compared to the reaction progress in the absence of student manipulation (no catalysis). This kinesthetic approach also allowed students to experience first‐hand the effect of substrate depletion on their catalyzed reaction rate. Exam results suggested that students understood the targeted learning outcomes and survey responses revealed self‐perceived gains in knowledge. The potential, and benefit, of adapting the activity to explore Michaelis‐Menten kinetics is discussed.