Important Class Of Reactions Research Articles

Alkene Dihydroxylation with Malonoyl Peroxides: Catalysis Using Fluorinated Alcohols

The effect of fluorinated alcohols on the dihydroxylation of alkenes using cyclopropyl malonoyl peroxide is described. Addition of perfluoro-tert-butyl alcohol to a toluene solution of alkene and peroxide increases the rate of product formation and the stereoselectivity observed, providing a simple and effective method for acceleration of this important class of reaction. Basic hydrolysis of the crude reaction mixture provides access to syn-diols in high yield and stereoselectivity.

The out-of-focus bias in drug surveillance

Existing drug safety systems with phase II and III studies and post-marketing surveillance by principle do not allow for the recognition of an important class of adverse drug reactions (ADRs). ADRs that are resistant to being detected reliably may a) appear as if they are age-related chronic diseases, which also manifest themselves in a high degree without drug treatment, b) arise in "old" drugs, c) arise during long-term application, and d) arise with the administration to frail and aged populations. "Silent" and multi-factorial health problems evolving from long-term drug treatment must therefore be addressed with a systematic search strategy, as a third track along with the phase II and III studies and spontaneous reporting systems which still exist.

Active Sites for Outer-Sphere, Inner-Sphere, and Complex Multistage Electrochemical Reactions at Polycrystalline Boron-Doped Diamond Electrodes (pBDD) Revealed with Scanning Electrochemical Cell Microscopy (SECCM)

The local rate of heterogeneous electron transfer (HET) at polycrystalline boron-doped diamond (pBDD) electrodes has been visualized at high spatial resolution for various aqueous electrochemical reactions, using scanning electrochemical cell microscopy (SECCM), which is a technique that uses a mobile pipet-based electrochemical cell as an imaging probe. As exemplar systems, three important classes of electrode reactions have been investigated: outer-sphere (one-electron oxidation of ferrocenylmethyltrimethylammonium (FcTMA(+))), inner-sphere (one-electron oxidation of Fe(2+)), and complex processes with coupled electron transfer and chemical reactions (oxidation of serotonin). In all cases, the pattern of reactivity is similar: the entire pBDD surface is electroactive, but there are variations in activity between different crystal facets which correlate directly with differences in the local dopant level, as visualized qualitatively by field-emission scanning electron microscopy (FE-SEM). No evidence was found for enhanced activity at grain boundaries for any of the reactions. The case of serotonin oxidation is particularly interesting, as this process is known to lead to deterioration of the electrodes, because of blocking by reaction products, and therefore cannot be studied with conventional scanning electrochemical probe microscopy (SEPM) techniques. Yet, we have found this system nonproblematic to study, because the meniscus of the scanning pipet is only in contact with the surface investigated for a brief time and any blocking product is left behind as the pipet moves to a new location. Thus, SECCM opens up the possibility of investigating and visualizing much more complex heterogeneous electrode reactions than possible presently with other SEPM techniques.

ChemInform Abstract: Proton‐Coupled Electron Transfer Originating from Excited States of Luminescent Transition‐Metal Complexes.

AbstractReview: 44 refs.

Detailed chemical kinetic modeling of JP‐10 (exo‐tetrahydrodicyclopentadiene) high‐temperature oxidation: Exploring the role of biradical species in initial decomposition steps

AbstractThe initial pathways of JP‐10 (exo‐tetrahydrodicyclopentadiene) decomposition are expected to have a significant effect on combustion and pyrolysis behavior of the fuel, affecting, for example, product distribution and ignition delay. Modeling of JP‐10 decomposition should capture these initial decomposition processes as accurately as possible. Two classes of computational approaches have been applied to study intramolecular disproportionation—an important class of reactions in the initial stages of JP‐10 decomposition: (1) the second‐order, multiconfigurational, quasidegenerate perturbation theory employing the complete active space self‐consistent field (CASSCF) reference; and (2) the size‐extensive, left‐eigenstate, completely renormalized (CR) coupled‐cluster (CC) method with singles, doubles, and noniterative triples, termed CR‐CC(2,3), capable of describing reaction pathways involving biradicals. Applying higher levels of theory to points along the CASSCF reaction paths, the barriers to intramolecular disproportionation are much smaller and some barriers appear to vanish. The conventional ring‐opening + disproportionation pathway is compared with an alternative concerted reaction pathway. Overall, this investigation has yielded insights into alkyl disproportionation and ring‐opening reactions that may be of more general use in chemical kinetic modeling. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 179–193, 2012

Highly efficient base catalysis and sulfide oxidation reactions over new functionalized mesoporous polymers

Base catalyzed aldol condensation reactions and selective partial oxidation of sulfides are very important classes of reactions in synthetic organic chemistry. We have prepared a new alkali exchanged form of mesoporous polytriallylamine, OH-MPTA-1 and a Cr-grafted material Cr-MPTA-1 via the simple and facile in situ radical polymerization of a triallylamine template by organic–organic self-assembly of anionic surfactant systems. The materials have been characterized by elemental analysis, powder X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), UV-vis diffuse reflectance spectroscopy (DRS), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). Powder XRD and TEM image analyses suggests the presence of mesophase and disordered wormhole-like mesopores in these samples. Our experimental results reveal that the alkali exchanged material OH-MPTA-1 acts as a very efficient base catalyst for the direct aldol reaction of different aromatic aldehydes with acetone. On the other hand, the Cr-grafted material Cr-MPTA-1, obtained through the reaction of potassium chromate with MPTA-1, acts as a very efficient catalyst for the liquid phase partial oxidation of sulfides to sulfoxides. Both OH-MPTA-1 and Cr-MPTA-1 can be recycled more than five times without an appreciable loss in activity for their respective catalytic reactions.

Iron reduction in nontronite-type clay minerals: Modelling a complex system

Reduction–oxidation or redox processes constitute a class of important reactions in a wide range of mineral environments. The specific focus in this investigation is on iron-bearing (ferruginous) clay minerals, where the redox reaction has important consequences for their structural and chemical integrity. Although this process has been studied experimentally, it is not yet fully understood where and how this occurs within clay mineral layers. The investigation presented here addresses this question from first principles using density functional theory (DFT), planewaves, pseudopotentials and periodic cells. The first issue addressed is that of simulating a dynamic reduction process using static models. Careful consideration is paid to the introduction of artificial electrostatic interactions, their subsequent identification and the effect these may have on the results. As a consequence of these considerations, three sets of models based on nontronite (Fe2(Si,Al)4O10(OH)2) are presented. The electronic structures of these clay mineral models are allowed to relax, to attain their own state of redox. By extensively analysing the Mulliken charges, magnetic states and orbital occupancy of iron, aluminium, silicon and oxygen, we have been able to draw firm conclusions about the relative reduction of iron within the tetrahedral and octahedral sheets of three varieties of nontronite. Reduction occurs to the greatest extent in the octahedral sheet iron and oxidation in the tetrahedral sheet iron. As these results reflect general, local environments within a clay mineral, they are therefore applicable to similar local environments and thus provide the foundations for further studies into more complex, geochemical systems.

Selectivity patterns in heterogeneously catalyzed hydrogenation of conjugated ene-yne and diene compounds

Selectivity control in heterogeneously catalyzed hydrogenation of conjugated hydrocarbons (ene-yne and diene compounds) is a challenging task. Available studies on the topic mainly encircle 1,3-butadiene as the substrate and palladium as the catalyst, while more elaborated playground molecules and other metals remain largely unexplored. This study investigates the gas-phase hydrogenation of valylene (2-methyl-1-butene-3-yne) and isoprene (2-methyl-1,3-butadiene) over Pd, Pb-poisoned Pd, CO-modified Pd, Cu, Ni, and bimetallic Cu Ni catalysts. Chemoselectivity, regioselectivity, full hydrogenation, and C C bond formation/scission footprints of the catalytic systems at different inlet hydrogen-to-hydrocarbon ratios and conversion degrees have been rationalized. Complementary studies of 3-methylbutyne and 1-penten-4-yne hydrogenation were carried out in order to analyze (i) the impact of isomerization on the observed mono-olefin distribution in valylene/isoprene hydrogenation and (ii) the conjugation issue in partial ene-yne hydrogenation. Our results lead to an improved understanding of hydrogenation of polyunsaturated hydrocarbons and open doors to design more selective heterogeneous catalysts and related processes for this practically important class of reactions.

Proton‐Coupled Electron Transfer Originating from Excited States of Luminescent Transition‐Metal Complexes

Proton-coupled electron transfer (PCET) is of fundamental importance for small-molecule activation processes, such as water splitting, CO(2)-reduction, or nitrogen fixation. Ideally, energy-rich molecules such as H(2), CH(3)OH, or NH(3) could be generated artificially using (solar) light as an energy input. In this context, PCETs originating directly from electronically excited states play a crucial role. A variety of transition-metal complexes have been used recently for fundamental investigations of this important class of reactions, and the key findings of these studies are reviewed in this article. The present minireview differs from other reviews on the subject of PCET in that it focuses specifically on reactions occurring directly from electronically excited states.

Cardanol-based materials as natural precursors for olefin metathesis.

Cardanol is a renewable, low cost natural material, widely available as a by-product of the cashew industry. It is a mixture of 3-n-pentadecylphenol, 3-(pentadeca-8-enyl)phenol, 3-(pentadeca-8,11-dienyl)phenol and 3-(pentadeca-8,11,14-trienyl)phenol. Olefin metathesis (OM) reaction on cardanol is an important class of reactions that allows for the synthesis of new olefins that are sometime impossible to prepare via other methods. The application of this natural and renewable material to both academic and industrial research will be discussed.

Mapping the reaction dynamics in Liouville space onto a reaction coordinate space: A first-principle- based theory

We have derived here an exact kinetic equation for the time evolution of the probability distribution for a general reaction coordinate space, starting from a multidimensional Liouville equation based on first-principles theory. To make the equation tractable we use two standard approximations, which reduce the exact equation into a Fokker-Planck-type equation with a sink term. As illustrative examples, we consider its application to two important classes of reactions, viz., the electron transfer and diffusion-controlled reactions. The kinetic equations for the reaction coordinates corresponding to these reactions become one dimensional. We also provide a scheme to find the critical value of the reaction coordinate at which the reaction takes place, and also to obtain the initial distribution function in the same space for different experimental situations. In the case of photoinduced electron transfer, we introduce the effect of excitation frequency through the use of suitable initial distribution functions.

Highly efficient mesoporous base catalyzed Knoevenagel condensation of different aromatic aldehydes with malononitrile and subsequent noncatalytic Diels–Alder reactions

Knoevenagel condensation and [4 + 2] cycloaddition reactions are very important class of reactions in synthetic organic chemistry. We have prepared amino-functionalized mesoporous silica through co-condensation of 3-aminopropyltriethoxy-silane (APTES) along with tetraethylorthosilicate (TEOS) in presence of a cationic surfactant CTAB hydrothermally. Small angle powder XRD, HR TEM, FE SEM, N 2 sorption and FT IR spectroscopic tools are used to characterize the 2D-hexagonal mesostructure and to identify the presence of surface –NH 2 groups in amino-functionalized mesoporous silica material. Our experimental results reveal that amino-functionalized mesoporous silica is an efficient base catalyst for the Knoevenagel condensation of different aromatic aldehydes with malononitrile to α,β-unsaturated dicyanides under very mild reaction condition and in the presence of ethanol solvent. The isolated α,β-unsaturated dicyanides obtained through the condensation reaction further react very efficiently with cyclopentadiene to form a series of Diels–Alder cycloaddition products in excellent yields in the absence of any catalyst.

Highly Efficient Hydroformylation of 1‐Hexene over an ortho‐Metallated Rhodium(I) Complex Anchored on a 2D‐Hexagonal Mesoporous Material

AbstractThe hydroformylation reaction is an important class of reaction as it enhances the carbon chain length of an olefin molecule. RhI complexes are conventionally used as the catalyst for this reaction although they possess severe drawbacks with respect to separation and recycling. A phenyl‐functionalised 2D‐hexagonal mesoporous silica material has been synthesised by a surfactant templating pathway. The phenyl group of this mesoporous material was functionalised through nitration, followed by its reduction to the amine derivative. The amine group was further subjected to Schiff‐base condensation, and the RhI complex was then heterogenised over its surface to yield the ortho‐metallated complex anchored on the mesoporous silica matrix. The materials have been characterised by using powder X‐ray diffraction, transmission electron microscopy and nitrogen adsorption/desorption studies. The RhI‐loaded mesoporous material acts as a very efficient catalyst for the hydroformylation reaction of 1‐hexene and exhibits high selectivity towards the formation of n‐heptanal at 343 K in the presence of H2/CO at 50 bar pressure.

Industrial Applications of C-C Coupling Reactions

Aromatic substitutions are a very important class of reaction for both the fine chemical and pharmaceutical industries. The use of palladium as a catalyst for these types of reactions is common during the research stages of product development. Its desirable criteria include high selectivity, being compatible with many types of functional groups, typical use without protection groups and strong bases, and introduction at relatively late stages of the total synthesis. However, its use is less common in large-scale manufacture due to their cost and availability of aromatic halides at scale. In addition, palladium contamination of pharmaceutical products has to be 10 ppm or less that is difficult to achieve without strenuous and typically wastefully remediation strategies in place. In this contribution, we aim to give an overview of the use of a range of greener methodologies and catalysts trends in C-C couplings at industrial scale, with selected examples of current compounds industrially produced via such reactions.

Anion Exchange Kinetics of Nanodimensional Layered Metal Hydroxides: Use of Isoconversional Analysis

Anion exchange reactions of nanodimensional layered metal hydroxide compounds are utilized to create materials with targeted physical and chemical properties and also as a means for controlled release of intercalated anions. The kinetics of this important class of reaction are generally characterized by model-based approaches. In this work, a different approach based on isothermal, isoconversional analysis was utilized to determine effective activation energies with respect to extent of reaction. Two different layered metal hydroxide materials were chosen for reaction with chloride anions, using a temperature range of 30-60 °C. The concentrations of anions released into solution and the changes in polycrystalline solid phases were evaluated using model-based (Avrami-Erofe'ev nucleation-growth model) and model-free (integral isoconversional) methods. The results demonstrate the utility of the isoconversional approach for identifying when fitting to a single model is not appropriate, particularly for characterizing the temperature dependence of the reaction kinetics.

Reduction of a Chelating Bis(NHC) Palladium(II) Complex to [{μ‐bis(NHC)}2Pd2H]+: A Terminal Hydride in a Binuclear Palladium(I) Species Formed under Catalytically Relevant Conditions

Catalytic processes featuring N-heterocyclic carbene (NHC) ligands have been extensively studied following the isolation of free imidazol-2-ylidenes An important reaction class is the base-assisted palladium-mediated C–C/N coupling, such as the Sonogashira, Buchwald–Hartwig, and Mizoroki–Heck reactions

‘Ossification’– A Novel Approach for Immobilisation of Platinum Group Metal Complex Catalysts

The technique known as ‘ossification’ has emerged as one of the most promising approaches for immobilisation of metal complexes, generating highly selective, stable and recyclable heterogeneous counterparts of homogeneous catalysts.‘Ossification’ involves modifying the ligand(s) in a metal complex catalyst to achieve inherently insoluble forms of the metal complexes, without destroying the configuration responsible for their catalytic properties. The ossified catalysts have been demonstrated to show high catalytic activity and selectivity for a number of industrially important reaction classes such as palladium-catalysed carbonylation and Suzuki coupling and rhodium-catalysed hydroformylation. The characterisation of these catalysts has also shown that the key features of their homogeneous metal complex analogues are retained on immobilisation. The approach is very useful for the design and development of immobilised catalysts with specific features and functionality for various applications. It is also advantageous for catalyst–product separation. This article reviews the recent work on ossification involving platinum group metal complex catalysts in our research group.

Recent Advances in Noble Metal Nanocatalysts for Suzuki and Heck Cross-Coupling Reactions

Since metal nanoparticles have a high surface-to-volume ratio and very active surface atoms, they are very attractive catalysts for a wide variety of organic and inorganic reactions, compared to bulk catalysts. Metal nanoparticles suspended in colloidal solutions and those adsorbed onto bulk supports have been used as catalysts for a wide variety of carbon-carbon bond formation reactions such as the Suzuki and Heck cross-coupling reactions. This review article highlights some of the latest advances in the application of noble metal nanoparticles as catalysts for these two industrially important classes of cross-coupling reactions. We will discuss several important advances in using metal nanocatalysts in Suzuki and Heck cross-coupling reactions such as investigations on the nanoparticle shape dependence on the catalytic activity, novel types of supported metal nanoparticles as nanocatalysts, and the use of bi-metallic, tri-metallic and multi-metallic nanoparticles as catalysts for the Suzuki and Heck cross-coupling reactions.

Stereoselective transition metal-catalysed higher-order carbocyclisation reactions

Transition metal-catalysed higher-order carbocyclisation reactions represent an important class of reactions due to their ability to construct complex polycyclic systems in a highly selective and atom-economical fashion. A key and striking feature with these transformations is the dichotomy in reactivity that a substrate displays with different transition metal complexes, which is akin to the manner enzymes direct terpene biosynthesis. This tutorial review details the historical development of higher-order carbocyclisation reactions, specifically the variants of [m+2+2] that involve carbon-based pi-systems, where m = 2, 3 and 4, in the context of critical developments with various transition metal complexes.

Modeling of partial oxidation in gas–solids downer reactors

AbstractSelective partial oxidations represent an important class of reactions in the process industry. Of particular interest is the partial oxidation of n‐butane to maleic anhydride (MAN), which is arguably the largest commercialized alkane partial oxidation process. Partial oxidation of n‐butane, which uses vanadium phosphorous oxide (VPO) as a heterogeneous catalyst, is believed to operate through a unique mechanism in which lattice oxygen oxidizes n‐butane selectively to MAN. Past work has shown that performing partial oxidation reactions in gas–solids riser configuration is realizable and commercially viable, which has lead to commercialization of this technology in the last decade. Though the riser configuration allows optimal and independent control of the oxidation and reduction steps, the riser unit suffers from solid backmixing at walls, which in turn result into lower conversion, nonoptimal selectivity and diminished overall yield of desired product. In recent years, there has been growing interest in downers involving cocurrent downflow of both solids and gas phases, hence offering relatively uniform flow characteristics. In this contribution, we explore through modeling the implications of effecting partial oxidation reactions in a downer (gas–solids cocurrent downflow) compared to that in a conventional riser reactor (gas–solids cocurrent up flow) operated under equivalent operating conditions. Further, we explore the operational space of downers for these reactions, suggesting ways for improving the productivity of downer for partial oxidation applications. © 2009 American Institute of Chemical Engineers AIChE J, 2010