Olefinic Bond Research Articles

Hydrogenation and C[sbnd]S bond activation pathways in thiophene and tetrahydrothiophene reactions on sulfur-passivated surfaces of Ru, Pt, and Re nanoparticles

Thiophene-H2 reactions proceed via sulfur removal and hydrogenation routes on dispersed metal nanoparticles that become decorated by refractory S adlayers during catalysis. The identity and kinetic relevance of the required elementary steps are described here based on rates measured at S-chemical potentials set by H2S/H2 ratios similar to those prevalent during practical catalysis on Re, ReSx, Ru, and Pt catalysts. The free energies of formation of S adatoms from H2S/H2 reactants are large and negative at low coverages (< −50 kJ mol−1 on Pt(111) and < −150 kJ mol−1 on Re(0001) and Ru(0001)), but strong repulsion among adatoms prevents full saturation, leading to sub-monolayer coverages and to passivated surfaces that expose uncovered interstices. The residual interstitial spaces (*) within adlayers of unreactive S-atoms (S′) bind intermediates and transition states reversibly, thus allowing these passivated surfaces to carry out catalytic turnovers. These interstices are larger on Pt than on Ru or Re surfaces, leading to concomitantly higher turnover rates for thiophene hydrogenation and desulfurization routes. The identity and kinetic relevance of elementary steps for desulfurization (to form C4 hydrocarbons) and hydrogenation (to form tetrahydrothiophene; THT) are similar among these catalysts; they involve kinetically-relevant H-addition steps of thiophene-derived intermediates that cleave their CS bonds or “over-hydrogenate” to THT in one surface sojourn. THT undergoes CS bond cleavage in secondary reactions that correct this over-hydrogenation to form the more unsaturated species that cleave CS bonds. THT/C4 product ratios are insensitive to H2S/H2 ratios and thiophene pressure, even though active interstitial spaces are covered by kinetically-detectable S* and bound thiophene; therefore, primary and secondary reactions must occur on the same active ensembles. The observed increase in THT/C4 ratios with H2 pressure shows that THT formation transition states involve a larger number of H-atoms than for CS cleavage. CS bonds cleave in species with partial unsaturation (H-contents between those in THT and thiophene), in processes that are reminiscent of the requirement to add or remove H-atoms from C and O atoms in cleaving CC and CO bonds in alkanes and alkanols, as well as CO bonds in CO hydrogenation reactions. The rate and selectivity data and the mechanistic conclusions described here show that thiophene hydrogenation and desulfurization routes require similar binding interstices within refractory S adlayers and that metal-sulfur bond energies act as indirect descriptors of reactivity because they determine the number, size, and binding properties of the exposed weakly-binding ensembles that stabilize the relevant transition states and enable catalytic turnovers.

Computational exploration of the 1,3‐dipolar cycloaddition reaction of 7‐isopropylidenebenzonorbornadiene with nitrile oxide and cyclic nitrone derivatives

AbstractThe synthesis of isoxazolidine and isoxazole derivatives, versatile building blocks for the construction of a wide range of complex heterocyclic architectures in synthetic organic and medicinal chemistry, is efficiently achieved via the 1,3‐dipolar cycloaddition reaction (1,3‐DC). Herein, we report an extensive theoretical study on the peri‐, regio‐, stereo, and enantio‐selectivities of 1,3‐DC of 7‐isopropylidenebenzonorbornadiene with nitrile oxide and cyclic nitrone derivatives using density functional theory calculations. Acetophenone‐substituted nitrile oxide periselectively adds across the endocyclic olefinic bond of the dipolarophile to furnish the exo‐cycloadduct as the major product, a reaction that has a rate constant of 1.88 × 109 s−1. The endo approach of this periselective path is the closest competing pathway with a rate constant of 4.59 × 107 s−1. Different substituents on the nitrile oxide do not affect the peri‐ and stereo‐selectivity of the reaction. Diethyl ether solvation has no substantial effect on the energetic patterns observed in the gas phase computation. Also, we report a novel 1,3‐DC between cyclic nitrone derivatives and 7‐isopropylidenebenzonorbornadiene as an efficient way to generate isoxazolidine derivatives. Even though the reactions of the cyclic nitrone derivatives have slightly higher activation barriers than the acyclic nitrile oxide derivatives, the former is more enantioselective than the latter. Whereas electron‐donating groups (EDGs) on the cyclic nitrone favor the formation of the exo‐cycloadduct, electron‐withdrawing groups (EWGs) favor the formation of the endo‐cycloadduct. Both 1,3‐dipoles add across the dipolarophile via a concerted asynchronous mechanism.

Elucidating the differences in oxidation of high-performance \u03b1- and \u03b2- diisobutylene biofuels via Synchrotron photoionization mass spectrometry

Biofuels are a promising ecologically viable and renewable alternative to petroleum fuels, with the potential to reduce net greenhouse gas emissions. However, biomass sourced fuels are often produced as blends of hydrocarbons and their oxygenates. Such blending complicates the implementation of these fuels in combustion applications. Variations in a biofuel’s composition will dictate combustion properties such as auto ignition temperature, reaction delay time, and reaction pathways. A handful of novel drop-in replacement biofuels for conventional transportation fuels have recently been down selected from a list of over 10,000 potential candidates as part of the U.S. Department of Energy’s (DOE) Co-Optimization of Fuels and Engines (Co-Optima) initiative. Diisobutylene (DIB) is one such high-performing hydrocarbon which can readily be produced from the dehydration and dimerization of isobutanol, produced from the fermentation of biomass-derived sugars. The two most common isomers realized, from this process, are 2,4,4-trimethyl-1-pentene (α-DIB) and 2,4,4-trimethyl-2-pentene (β-DIB). Due to a difference in olefinic bond location, the α- and β- isomer exhibit dramatically different ignition temperatures at constant pressure and equivalence ratio. This may be attributed to different fragmentation pathways enabled by allylic versus vinylic carbons. For optimal implementation of these biofuel candidates, explicit identification of the intermediates formed during the combustion of each of the isomers is needed. To investigate the combustion pathways of these molecules, tunable vacuum ultraviolet (VUV) light (in the range 8.1–11.0 eV) available at the Lawrence Berkeley National Laboratory’s Advanced Light Source (ALS) has been used in conjunction with a jet stirred reactor (JSR) and time-of-flight mass spectrometry to probe intermediates formed. Relative intensity curves for intermediate mass fragments produced during this process were obtained. Several important unique intermediates were identified at the lowest observable combustion temperature with static pressure of 93,325 Pa and for 1.5 s residence time. As this relatively short residence time is just after ignition, this study is targeted at the fuels’ ignition events. Ignition characteristics for both isomers were found to be strongly dependent on the kinetics of C4 and C7 fragment production and decomposition, with the tert-butyl radical as a key intermediate species. However, the ignition of α-DIB exhibited larger concentrations of C4 compounds over C7, while the reverse was true for β-DIB. These identified species will allow for enhanced engineering modeling of fuel blending and engine design.

Polymeric 19F MRI Contrast Agents Prepared by Ring-Opening Metathesis Polymerization/Dihydroxylation

The capability of ring-opening metathesis polymerization (ROMP) to efficiently incorporate bulky monomers and conserve olefin bonds during polymerization was exploited to design water-soluble fluor...

Measuring the Olefin‐to‐Pd(0) Bond Strength: A Kinetic Study Involving Olefin Exchange Reactions on Palladium(0) Complexes Bearing Isocyanide Ligands

AbstractIn this article, the synthesis and characterization of new palladium(η2‐olefin) complexes bearing isocyanides as spectator ligands are described. These derivatives have been tested on olefin exchange reactions, allowing to define a scale of strength of the palladium(0)‐olefin bond. In this way we have proved that dimethyl fumarate can be released by the metal center much more easily than the other olefins and that (Z)‐1,2‐ditosylethene is by far the most firmly anchored to palladium.When the sterically encumbered tetramethylethene‐1,1,2,2‐tetracarboxylate (tmetc) is involved in the olefin exchange, the reaction kinetics can be monitored by UV‐Vis spectrophotometry, showing that the process follows a second‐order rate law. This response indicates that the reaction mechanism is associative, as is also confirmed by a DFT study.

DFT исследование гомолитического разрыва C–H связей алканов и реакции дегидрирования пропиленгликоля на кластерах Fe4O7, NiFe3O7 и их протонированных и гидроксилированных формах

The results of a DFT study of elementary acts, both catalytic transformations of alkanes on hydride-hydroxyl forms of Fe4O7 and NiFe3O7 clusters, and processes of hydrocarbons transformation on iron and nickel-oxide clusters without initially hydride-hydroxyl filling are presented. Homolytic scission of the C–H bonds of alkanes on the hydride-hydroxyl form of the Fe4O7 cluster is accompanied by the formation of alkyl radicals capable of biradicals recombination according to the singlet type. There is also an additional reaction direction, which is represented by a singlet intra-associative rearrangement generating alcohols chemisorbed with the iron atom of the Fe4O6 cluster. This reaction is irreversible, proceeds with a large exothermic effect of 45.90 kcal∙mol-1, sufficient to overcome the chemisorption bond and diffuse into the volume of the supercritical fluid. The calculated characteristics of the interaction of alkanes with an iron-positioned hydroxyl group indicate that the activation energies of the forward direction of elementary acts in the homologous series: primary and secondary C–H bonds, lie in the range of 30.91-32.74 kcal∙mol-1, that is, these reactions are not very selective and strongly endothermic, since the activation energies of the reverse directions of the corresponding elementary acts are in the range of 1.40-3.27 kcal∙mol-1. The transition in the homologous series from the primary and secondary C–H bonds of propane to the tertiary C–H bonds of isobutane significantly changes the activation specificity of the homolytic scission of C–H bonds. The relative activation energy of the forward direction of the reaction decreases by about 8.00 kcal∙mol-1. A reaction system with the participation of the nickel-iron-oxide cluster NiFe3O7 and propane has been studied quantum-chemically. The result of the interaction of these reagents is the formation of isopropyl alcohol (propan-2-ol), which is chemisorbed with the nickel atom of the NiFe3O6 cluster. This reaction is irreversible and proceeds with a large exothermic effect of 50.95 kcal∙mol-1. The energetics of this process qualitatively coincides with the activation characteristics of the second stage of methane transformation on the Fe4O6 cluster; however, in this case, the reaction is a one-stage. It is noted that when carrying out various SCF extraction processes, for example, during the purification and regeneration of nickel and iron oxide catalysts, it should be borne in mind that the use of a propane-butane mixture as a supercritical fluid can be accompanied by its saturation with heavier hydrocarbons of linear and branched structure and alcohols. However, in real technological SCF processes, it is realistic to select the optimal temperature and flow regime that minimizes this effect. In the presence of a pre-reaction complex involving the hydrogen bond of the hydroxyl group of the initial propylene glycol and the interstitial oxygen atom (Fe–O–Fe) of the Fe4O7 cluster, a one-stage reaction with the oxidation product 1-hydroxypropan-2-ol becomes possible. The Fe4O6 iron oxide cluster with four coordinated iron centers having a hydroxyl group bound to each of them interacts with propylene glycol to form 1-hydroxypropan-2-ol, and the Fe–OH and Fe–O–Fe cluster substructures are the oxidative centers. In this case, the product of the reaction is a water molecule chemisorbed on the iron center and a hydrogen atom chemisorbed on the Fe–O–Fe substructure. This reaction is extremely exothermic (Q = 62.55 kcal∙mol-1) and has a very low activation energy for the forward direction of the reaction. By the example of the described heterogeneous hydrate-dissociative effects involving metal oxide surfaces and simple or functionalized alkanes, it can be seen that it is the protonated and hydroxylated forms of metal oxide surfaces that are responsible for elementary acts related to supercritical water oxidation.

Efficient catalytic transfer hydrogenation reactions of carbonyl compounds by Ni(II)-diphosphine complexes

The catalytic transfer hydrogenation reactions of a series of aromatic and aliphatic carbonyl compounds were investigated using divalent Ni(II)-diphosphine complexes, [L2NiCl2] (where L2 = 1,1-bis(diphenylphosphino)methane (dppm), 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp), 1,1-bis(diphenylphosphino)ferrocene (dppf), and N-butyl-N-(diphenylphosphino)-1,1-diphenylphosphinamine (dppba)). This is a single-step reaction in the presence of potassium hydroxide and isopropyl alcohol to afford the corresponding alcohols. This protocol tolerates other sensitive functional groups like olefinic double bonds and also achieves high chemoselectivity. All the reactions were monitored by GC and GC–MS. The plausible mechanism is also discussed. The method reported in the present article is simple, cost-effective, and provides excellent conversions. Nickel-diphosphine complexes appear as a potential alternative to expensive transition metal complexes.

Computational study on the mechanism of the reaction of benzenesulfonyl azides with oxabicyclic alkenes.

The reaction of benzenesulfonyl azides with oxabicyclic alkenes to form aziridines could either proceed via initial [3 + 2] cycloaddition to form triazoline intermediates which then leads to aziridines, or via initial dinitrogen cleavage of the benzenesulfonyl azide to afford a nitrene intermediate followed by addition of this nitrene species across the olefinic C-C bond of the oxabicyclic alkene. Calculations at the DFT M06-2X/6-311G(d,p) level indicate that the initial [3 + 2] cycloaddition reaction of benzenesulfonyl azide and oxabicyclic alkene has barriers of 15.0kcal/mol (endo) and 10.3kcal/mol (exo) and rate constants of 5.23 × 103s-1 (endo) and 3.86 × 106s-1 (exo) whereas the pathway involving initial formation of nitrene species has a high activation barrier of 39.2kcal/mol and rate constant of 8.92 × 10-12s-1, indicating that the reaction will go through the former route to form an exo triazoline intermediate. The exo triazoline can either undergo a concerted C-C, N-N bond cleavage to form a ring-opened intermediate, a reaction that has a barrier of 23.4kcal/mol, followed by dinitrogen extrusion and C-C, C-N bond regeneration with barriers of 29.1 and 23.5kcal/mol respectively to form endo aziridines, or it can undergo direct nitrogen extrusion to form the exo product, a reaction with a barrier of 38.3kcal/mol. Since the rate-determining step of the former route is 9.2kcal/mol more favored than the latter, the former route rate is favored. The rate constants of the rate-determining steps are 1.30 × 10-5s-1 (endo) and 3.16 × 10-11s-1 (exo), indicating that endo aziridine would be formed as the major product and this is in conformity with the experimental observations of Chen et al. (J. Org. Chem. 18:11863-11872, 2019). The position of substituents on the benzene group of the benzenesulfonyl azide affects the endo/exo diastereoselectivity.Graphical abstract.

The oxidative degradation of Caffeine in UV/Fe(II)/persulfate system-Reaction kinetics and decay pathways.

In this study, the degradation of caffeine was investigated by UV/Fe2+ /persulfate (PS) process. Caffeine (CAF) degradation in sole-UV, UV/Fe2+ , UV/PS, and Fe2+ /PS systems was also conducted to examine the contribution of isolated processes to CAF degradation. The effects of pH levels, the concentration of Fe2+ and PS, inorganic anions, and initial concentration of CAF on the performance of UV/Fe2+ /PS process were evaluated. Radical competitive reactions indicated both hydroxyl radicals and sulfate radicals played important roles in CAF degradation in UV/Fe2+ /PS system. Nine intermediates, among which three were detected for the first time, were identified by ultra-performance liquid chromatography/electrospray-time-of-flight mass spectrometry (UPLC/ESI-TOF-MS) and SPME (solid-phase microextraction)/GC/MS. The possible degradation pathways of CAF were proposed, among which demethylation, hydroxylation, the oxidation of olefinic double bond, and the cleavage of pyrimidine ring and imidazole ring were involved in the degradation of CAF in UV/Fe2+ /PS system. PRACTITIONER POINTS: Caffeine degradation by UV/Fe2+ /PS process was investigated. Caffeine degradation did not follow a simple pseudo-first order kinetics Chloride ions promoted CAF degradation. The anions NO3 - , SO4 2- , and H2 PO4 - exerted a negative influence on caffeine degradation. Nine intermediates were detected, and decay pathways were proposed.

Synthesis of novel fluorinated building blocks via halofluorination and related reactions.

A study exploring halofluorination and fluoroselenation of some cyclic olefins, such as diesters, imides, and lactams with varied functionalization patterns and different structural architectures is described. The synthetic methodologies were based on electrophilic activation through halonium ions of the ring olefin bonds, followed by nucleophilic fluorination with Deoxo-Fluor®. The fluorine-containing products thus obtained were subjected to elimination reactions, yielding various fluorine-containing small-molecular entities.

A Track-Based Molecular Synthesizer that Builds a Single-Sequence Oligomer through Iterative Carbon-Carbon Bond Formation

Summary We report an artificial molecular machine that moves along a track, iteratively joining building blocks to form an oligomer of single sequence with a continuous backbone of carbon-carbon bonds. The rotaxane features a macrocycle bearing an aldehyde-terminated chain and an axle containing different phosphonium ylides separated by rigid spacers. Each ylide is large enough to block the passage of the macrocycle, trapping the ring between the stopper at the terminus of original threading and the next ylide along the track. Once a building block is reachable, it is removed from the track through a Wittig reaction that adds it to the terminus of the growing chain. Operation on a four-barrier tetra(phosphonium salt) track produces a tetra(diphenylpropane) of single sequence linked through alkene bonds. The prototype extends the principle for molecular machines that build polymers by moving along tracks to the synthesis of sequence-encoded chains with continuous carbon backbones.

Metathesis of Classical and Functionalized Olefins Catalyzed by Silica‐Supported Single‐Site Well‐Defined W and Mo Pre‐catalysts

AbstractOlefin metathesis of α‐olefins (C6, C8, C10), α, β‐unsaturated ester, α, β‐ unsaturated acetate and cross‐metathesis of 1‐octene and ethyl 6‐heptenoate were carried out using well‐defined [(≡Si−O−)W(CH3)5] and [(≡Si−O−)Mo(≡CtBu)(CH2tBu)2] pre‐catalysts. During the reaction, it was observed that irrespective of the chain length, linear α‐olefins are almost showing similar TON. We observed that Mo pre‐catalyst performs better with TONs between 700 and 1478 as compared to W with TONs between 213 and 962 at room temperature. Both pre‐catalysts performed equally at 70 °C, with almost similar activity as well as TON (≈1700). We also carried out self‐metathesis of functionalized olefins using both silica‐supported W and Mo pre‐catalysts. It was observed that W pre‐catalyst performs much better than Mo pre‐catalyst for functionalized olefin metathesis reaction in our conditions. Additionally, we noticed that W pre‐catalyst provides selective metathesis product, whereas Mo pre‐catalyst gives a range of products due to the isomerization of the olefinic bond.

Cardanol and Eugenol Sourced Sustainable Non-halogen Flame Retardants for Enhanced Stability of Renewable Polybenzoxazines.

Olefin bonds participate in co-reaction with the benzoxazine functionality of the monomer and are one of the strategies used to affect the crosslink density of a polybenzoxazine network. In general, the double bond incorporation in starting material is usually catalyzed by expensive, rare earth metals affecting the sustainability of the reaction. The natural abundance of feedstocks with inherent double bonds may be a powerful platform for the development of novel greener structures, with potential applications in polymers. Here, we report the design, synthesis, and characterization of a biobased non-halogen flame retardant, consisting of naturally occurring phenols, eugenol (E), and cardanol (C). The presence of a covalently linked phosphazene (P) core allowed the synthesis of hexa-functional flame retardant molecules, abbreviated as EP and CP. The chemical structures of the synthesized EP and CP were confirmed by Fourier transform infrared (FTIR), nuclear magnetic resonance (1H, 13C, 31P NMR), and single crystal XRD (only in the case of EP). Their polymerization with cardanol sourced tri-oxazine benzoxazine monomer, C-trisapm, was followed by FTIR, NMR, and DSC studies. The thermal stability and flame retardant properties of the hybrid phosphazene-benzoxazine copolymers was determined by thermogravimetry analysis (TGA), limiting oxygen index (LOI), vertical burning, and smoke density analyses. SEM images of the char residues of the polymers with or without the addition of reactive phosphazene molecules confirmed the intumescent flame retarding mechanism. Current work highlights the utility of sustainable origin non-halogen flame retardant (FR) molecules and their utility in polybenzoxazine chemistry.

Nickel-Catalyzed Four-Component Carbocarbonylation of Alkenes under 1 atm of CO

Transition-metal-catalyzed carbonylation is one of the most straightforward strategies to prepare carbonyl compounds. However, compared to well-established noble-metal-catalyzed carbonylation reactions, analogue coupling via base-metal, nickel catalysis has received less attention because of the easy formation of highly toxic and unreactive Ni(CO)4 species between Ni(0) and CO. To date, the use of inexpensive and widely available carbon monoxide (CO) gas for nickel-catalyzed carbonylation reaction remains challenging, and nickel-catalyzed four-component carbonylative reaction has not been reported yet. Here, we report a highly selective nickel-catalyzed four-component carbocarbonylation of alkenes under 1 atm (1 atm) of CO gas to efficiently achieve an array of complex carbonyl compounds, including fluorinated amino acids and oligopeptides of great interest in medicinal chemistry and chemical biology. This reaction relies on a nickel-catalyzed one-pot cascade process to assemble CO, arylboronic acids, and difluoroalkyl electrophiles across the carbon-carbon double bond of alkenes, paving a new way for base-metal-catalyzed carbonylative cascade reaction.

Influence of Physicochemical Properties on Gas Transport Properties of Silver-Containing Ionic Liquid Mixtures for Olefin/Paraffin Membrane Separation

Olefin/paraffin separation by cryogenic distillation is one of the most energy-consuming processes not only among the entire chemical processes but also among all the energy-consuming activities by human beings. The purification of propylene and ethylene accounts for 0.3% of global energy use (1). Membrane separation is an attractive alternative, owing to its high energy-efficiency compared to conventional distillation processes. Liquid membranes that utilize gas transport through the liquid phase confined in the pore structures have shown promising performance due to the faster transport compared to solid membrane materials (2).Since the liquid phase is where the transport of olefin/paraffin molecules occurs, the liquid membrane performance in terms of permeability, selectivity, and stability mainly relies on the properties of the liquid component. Ionic liquids are a suitable material since the liquid component in the membranes provide stable separation performance owing to their extremely low vapor pressure and good thermal/chemical stability. Moreover, the limitless turnability of ionic liquids can be manipulated to enhance the molecular interaction with certain gas molecules to result in better gas solubility. For olefin/paraffin separation, in addition to physical solubility of the olefin in the ionic liquid, silver ions are commonly added to further improve olefin solubility. The silver ions can complex with olefin molecules via interaction between the double bonds of olefins and the orbitals of silver ions.Here we have investigated the effect of the anion, concentrations of the silver salt, and temperatures on the physicochemical properties of the silver-containing ionic liquid mixtures. The macroscopic physicochemical properties, such as viscosity and density, affect the filling of the membrane pores and stability to transmembrane pressure. However, we show that they are also indicators of ion aggregation in the mixtures, which can be correlated with relevant membrane properties, including solubility, diffusivity and silver ion reactivity with contaminant gases. The physiochemical viewpoint on the silver-containing ionic liquid mixture will provide appropriate insight for understanding the olefin/paraffin gas transport in the ionic liquid mixture, which leads to a design idea for better separation performance.(1) D. S. Sholl, R. P. Lively, Seven chemical separations: to change the world: purifying mixtures without using heat would lower global energy use, emissions and pollution--and open up new routes to resources. Nature 532, 435 (2016).(2) C. M. Sanchez, T. Song, J. F. Brennecke, B. D. Freeman, Hydrogen Stable Supported Ionic Liquid Membranes with Silver Carriers: Propylene and Propane Permeability and Solubility. Industrial & Engineering Chemistry Research 59, 5362-5370 (2020).

Crystal structure determination, hirshfeld surface analysis and quantum computational studies of (3E,5E)-1-ethyl-3,5-bis (naphthalen-1-yl-methylidene) piperidin-4-one: A novel RORc inhibitor

The title compound (3E,5E)-1-ethyl-3,5-bis (naphthalen-1-yl-methylidene) piperidin-4-one (C29H25NO), belongs to a class of polysubstituted piperidones with the olefinic double bonds being in an E configuration. It crystallizes in the monoclinic space group with one molecule in the asymmetric unit. The crystal packing in the α, β-unsaturated ketone is a consequence of dominant intra and intermolecular C—H···O interactions. The crystal structure is further stabilized by four C—H···π interactions. Hirshfeld surface analysis was carried out to quantify the interactions and an interaction energy analysis was done to study the interactions between pairs of molecules. The optimized structure calculated was calculated using density functional theory at the B3LYP/ 6–31G(d,p) level and was compared with the experimentally determined solid state structure. Molecular docking studies was carried out in silico to investigate the biological activity of the title compound with the human RORc protein (PDB ID: 4WLB).

Asymmetric Cyanation of Activated Olefins with Ethyl Cyanoformate Catalyzed by Ti(IV)-Catalyst: A Theoretical Study

The reaction mechanism and origin of asymmetric induction for conjugate addition of cyanide to the C=C bond of olefin were investigated at the B3LYP-D3(BJ)/6-31+G**//B3LYP-D3(BJ)/6-31G**(SMD, toluene) theoretical level. The release of HCN from the reaction of ethyl cyanoformate (CNCOOEt) and isopropanol (HOiPr) was catalyzed by cinchona alkaloid catalyst. The cyanation reaction of olefin proceeded through a two-step mechanism, in which the C-C bond construction was followed by H-transfer to generate a cyanide adduct. For non-catalytic reaction, the activation barrier for the rate-determining C-H bond construction step was 34.2 kcal mol−1, via a four-membered transition state. The self-assembly Ti(IV)-catalyst from tetraisopropyl titanate, (R)-3,3′-disubstituted biphenol, and cinchonidine accelerated the addition of cyanide to the C=C double bond by a dual activation process, in which titanium cation acted as a Lewis acid to activate the olefin and HNC was orientated by hydrogen bonding. The steric repulsion between the 9-phenanthryl at the 3,3′-position in the biphenol ligand and the Ph group in olefin raised the Pauli energy (ΔE≠Pauli) of reacting fragments at the re-face attack transition state, leading to the predominant R-product.

Chemoselective Catalytic Oxidation of Olefin Derivatives with Co–Salen Immobilized SBA-15

Chemoselective catalytic oxidation of olefin derivatives containing alcoholic and olefinic groups is important in organic synthesis. In the present study, Co–Salen immobilized on SBA-15 was synthesized and characterized to study its chemoselective catalytic activity towards the oxidation of cinnamyl alcohol and cinnamaldehyde, with tert-butyl hydroperoxide as the oxidant at 60, 70 and 80 oC. Cinnamyl alcohol selectively yielded cinnamaldehyde at the reactant ratio of cinnamyl alcohol tert-butyl hydroperoxide equal to 1:0.5. Cinnamaldehyde selectively yielded 2,3-epoxy-cinnamaldehyde at the ratio of cinnamaldehyde tert-butyl hydroperoxide equal to 1:0.5. The catalyst yielded epoxide with many styrene derivatives and benzaldehyde with benzyl alcohol, but only cinnamaldehyde with cinnamyl alcohol, thus proving its applicability for chemoselective catalytic oxidation of olefin derivatives. The cinnamaldehyde conversion and selectivity to 2,3-epoxy-cinnamaldehyde increased with the increase in the content of tert-butyl hydroperoxide. So, this study establishes that the catalyst can be applied to selective oxidation of primary alcoholic function without affecting olefinic double bonds. The conversion was maximum at 70 oC. The conversion and product selectivity remained the same for 5 cycles thus endorsing stability of the catalysts. Based on the activity and selectivity of the catalysts, it is inferred that the same catalyst can be exploited for selective oxidation of multifunctional olefin derivatives.

A chemical kinetic model for the decomposition of perfluorinated sulfonic acids

Perfluorinated sulfonic acids (such as perfluorooctanesulfonic, PFOS, and short-chain analogues) are notorious halogenated pollutants that exhibit severe toxicity, even at minute levels. Limited number of experimental studies addressed their thermal decomposition at elevated temperatures. Such scenarios are particularly relevant to open fires and incineration of materials laden with perfluoroalkyl compounds (PFCs). Herein, we construct a detail kinetic model that illustrates major chemical reactions underpinning initial degradation of 1-butanesulfonic acid (CF3(CF2)3SO2OH), as a model compound of PFOS, and perfluorinated sulfonic acids in general. Reaction rate parameters were estimated based on an accurate density functional theory (DFT) formalism. The kinetic model incorporates four sets of reactions, namely, unimolecular decomposition channels, hydrofluorination, hydrolysis, and fragmentation of the alkyl chain. Results are discussed considering recent experimental measurements. Temperature-dependent profiles for a large array of perfluoroalkyl acyl fluorides, short perfluorinated cuts, and perfluorinated cyclic compounds, are presented. SO2 emerges as the main sulfur carrier, with a minor contribution from SO3. HF addition to double carbon bonds in alkenes, and to carbonyl bonds in aldehydic structures signifies a major sink pathway for hydrogen fluoride. Addition of moisture was shown to expedite the destruction of relatively large perfluoroalkyl acyl fluorides into C1 species. Construction of this model could aid in a better understanding of the fate and chemical transformation of PFCs under a pyrolytic environment pertinent to waste incineration and fluorine mineralization.

Oxidative dehydrogenation of ethane with carbon dioxide over silica molecular sieves supported chromium oxides: Pore size effect

SBA-15 with varied pore size from 4 to 8 nm were synthesized by tuning the temperature of hydrothermal treatment, the supports were then used to load the active phase CrO x through a conventional impregnation method. The resulting catalysts were characterized by small/wide angle XRD, N 2 adsorption/desorption, FT-IR, TEM-EDX, XPS, TPR and CO 2 -TPD to study the feature of structure, surface chemical state, redox and basicity. It was found from these results that the metal species could be well dispersed on catalysts with larger pore size. Cr 6+ species could enter into the framework by substituting the Si atoms of SBA-15, and Cr 3+ mainly exist on extra framework. Pore size had profound effects on reducibility, surface composition and basicity. Cr 6+ species were necessary to activate the C-H bonds of alkanes, while the basicity played an important role in activating C-O bonds of CO 2 . The best performances were achieved over the sample Cr supported on SBA-15 with a pore diameter of 7 nm in oxidative dehydrogenation of ethane in the presence of CO 2 . • Pore size of SBA-15 was tuned by changing hydrothermal temperature. • Cr 6+ could enter the framework of SBA-15 by partially replacing Si atoms. • Cr 6+ and Cr 3+ species co-existed on extra framework of SBA-15. • Cr 6+ species were important for activating alkane. • Activation of CO 2 was related to basicity of catalysts.