Isomerization Process Research Articles

Electron-enriched Lewis acid-base sites on red carbon nitride for simultaneous hydrogen production and glucose isomerization

Glucose isomerization into fructose is a key process in industry for biomass valorization to produce value-added biofuels and biochemicals. Herein, considering the essential role of Lewis acid-base sites in proton transfer during glucose isomerization and hydrogen evolution process, a bifunctional polymeric red carbon nitride (PRCN) is rationally designed and fabricated by the salt-template-induced carbon incorporation strategy. The incorporation of carbon and potassium in the PRCN leads to the transient redistribution of photogenerated charges, acting as the electron-enriched Lewis base site and acid site for the deprotonation of O2-H and activation of aldehyde group of glucose, respectively. Besides, the interfacial Schottky junction boosts H2 production under visible light irradiation. This work demonstrates the feasibility of biomass photorefinery with H2 and value-added chemicals co-production under mild condition.

N‐Ligand‐Enabled Aromatic Nucleophilic Amination of 1,2‐Diaryl‐o‐Carboranes with (R2N)2Mg for Selective Synthesis of 4‐R2N‐o‐Carboranes and 2‐R2N‐m‐Carboranes

AbstractThe nucleophilic aromatic BH substitution reaction of carboranes is uncommon, compared to the electrophilic one. This work reported a pyridine‐enabled transition‐metal‐free regioselective nucleophilic aromatic cage B(4)‐H amination of 1,2‐diaryl‐o‐carboranes with magnesium bisamides, giving a series of B(4)‐aminated o‐carboranes. DFT calculations showcased a stepwise B−N formation/B−H cleavage process, in which Mg−H formation/cage closure is the rate‐determining step. Unprecedentedly, in the presence of 4,4′‐di‐tert‐butyl‐2,2′‐dipyridyl (dtbpy), a tandem B(4)‐amination/cage isomerization reaction of o‐carboranes was discovered for the facile preparation of B(2)‐aminated m‐carboranes. Control experiments indicated that magnesium complex, bidentate ligand (dtbpy) and reaction temperature were crucial in the cage isomerization process. This direct nucleophilic aromatic cage B−H amination reaction offers an alternative strategy for selective amination of o‐ and m‐carboranes.

N-Ligand-Enabled Aromatic Nucleophilic Amination of 1,2-Diaryl-o-Carboranes with (R2 N)2 Mg for Selective Synthesis of 4-R2 N-o-Carboranes and 2-R2 N-m-Carboranes.

The nucleophilic aromatic BH substitution reaction of carboranes is uncommon, compared to the electrophilic one. This work reported a pyridine-enabled transition-metal-free regioselective nucleophilic aromatic cage B(4)-H amination of 1,2-diaryl-o-carboranes with magnesium bisamides, giving a series of B(4)-aminated o-carboranes. DFT calculations showcased a stepwise B-N formation/B-H cleavage process, in which Mg-H formation/cage closure is the rate-determining step. Unprecedentedly, in the presence of 4,4'-di-tert-butyl-2,2'-dipyridyl (dtbpy), a tandem B(4)-amination/cage isomerization reaction of o-carboranes was discovered for the facile preparation of B(2)-aminated m-carboranes. Control experiments indicated that magnesium complex, bidentate ligand (dtbpy) and reaction temperature were crucial in the cage isomerization process. This direct nucleophilic aromatic cage B-H amination reaction offers an alternative strategy for selective amination of o- and m-carboranes.

Separation of Branched Alkanes Feeds by a Synergistic Action of Zeolite and Metal‐Organic Framework

Zeolites and metal‐organic frameworks (MOFs) are considered as “competitors” for new separation processes. The production of high‐quality gasoline is currently achieved through the total isomerization process that separates pentane and hexane isomers while not reaching the ultimate goal of a research octane number (RON) higher than 92. This work demonstrates how a synergistic action of the zeolite 5A and the MIL‐160(Al) MOF leads to a novel adsorptive process for octane upgrading of gasoline through an efficient separation of isomers. This innovative mixed‐bed adsorbent strategy encompasses a thermodynamically driven separation of hexane isomers according to the degree of branching by MIL‐160(Al) coupled to a steric rejection of linear isomers by the molecular sieve zeolite 5A. Their adsorptive separation ability is further evaluated under real conditions by sorption breakthrough and continuous cyclic experiments with a mixed bed of shaped adsorbents. Remarkably, at the industrially relevant temperature of 423 K, an ideal sorption hierarchy of low RON over high RON alkanes is achieved, i.e., n‐hexane ≫ n‐pentane ≫ 2‐methylpentane > 3‐methylpentane ⋙ 2,3‐dimethylbutane > isopentane ≈ 2,2‐dimethylbutane, together with a productivity of 1.14 mol dm−3 and a high RON of 92, which is a leap‐forward compared with existing processes.

Azobenzene modified metal-organic framework: For solar energy storage

A novel photochromic azo-grafted metal-organic framework (MOF), ZIF-90-AAT, was synthesized and characterized. ZIF-90-AAT not only retains the three-dimensional porous structure of ZIF-90 and high thermal stability, but also has sufficient free space for the isomerization reaction of azobenzene and photo-energy storage ability. ZIF-90-AAT displayed excellent reversible photochromic performance and can release photo-energy absorbed during the isomerization process. The result of differential scanning calorimetry (DSC) indicated that the energy storage density of ZIF-90-AAT is 5.796 J/g. In addition, ZIF-90-AAT also has the ability to melt broken ice during the isomerization-back process. This work demonstrated that MOFs can be used in the energy storage and expanded the application range of MOF materials.

Electronic Circular Dichroism Unravels Atropisomers of a Broadly Absorbing Fulgide Derivative

AbstractWe prepared and studied six atropisomers with different chiroptical properties emerging from a single, robust, broadly‐absorbing fulgide photoswitch. After separation of the different atropisomers via HPLC on a chiral column, their isomerization processes at room temperature and the energy barriers of the different species were investigated in detail using spectroscopic and theoretical methods.

Substrate Photoswitching for Rate Enhancement of a Organocatalytic Cyclization Reaction

AbstractIn this article, we report that applying in situ LED‐NMR irradiation with appropriate wavelength resulted in the photoswitching of an α,β‐unsaturated hydrazone C=N double bond configuration. This reaction was previously reported to be the first step in a chiral Brønsted acid‐catalyzed cyclization reaction, where the minor but stable Z‐isomer is the reactive intermediate. By enhancing the rate of the isomerization, we could show that the overall rate of the cyclization could be increased and followed directly by NMR kinetics. Exclusively light with a specific wavelength matching the isomerization process affected the cyclization. The light‐ and acid‐mediated isomerization provide complementary pathways that can be exploited in synthetic applications to increase reaction rates of asymmetric transformations, especially in reactions requiring high loadings of elaborate chiral catalysts.

Open-Form Configurational Isomers of a Tricyanofuran-Type Metastable-State Photoacid.

We determine the presence of four open-form configurational isomers for an unsubstituted metastable-state photoacid (mPAH) of the tricyanofuran (TCF) type in solution, at room temperature, via 2D NMR experiments. Electronic structure calculations are carried out to predict the relative stability of the isomers found experimentally and their isomerization barriers. According to the calculated rate constants for isomerization, the molecule can freely interconvert between the open-form isomers, thereby providing a thermal pathway between the isomers that might be better suited to access the cyclized closed-form configuration and those that are not. In establishing the open form isomeric makeup of the TCF mPAH under study, this work establishes the need to consider the four isomers in further studies on the thermal and excited-state isomerization processes and substituent effect thereon.

The Photocycle of Bacteriophytochrome Is Initiated by Counterclockwise Chromophore Isomerization.

Photoactivation of bacteriophytochrome involves a cis–trans photoisomerization of a biliverdin chromophore, but neither the precise sequence of events nor the direction of the isomerization is known. Here, we used nonadiabatic molecular dynamics simulations on the photosensory protein dimer to resolve the isomerization mechanism in atomic detail. In our simulations the photoisomerization of the D ring occurs in the counterclockwise direction. On a subpicosecond time scale, the photoexcited chromophore adopts a short-lived intermediate with a highly twisted configuration stabilized by an extended hydrogen-bonding network. Within tens of picoseconds, these hydrogen bonds break, allowing the chromophore to adopt a more planar configuration, which we assign to the early Lumi-R state. The isomerization process is completed via helix inversion of the biliverdin chromophore to form the late Lumi-R state. The mechanistic insights into the photoisomerization process are essential to understand how bacteriophytochrome has evolved to mediate photoactivation and to engineer this protein for new applications.

Mechanisms, reaction micro-kinetics and modelling of hydrocracking of aromatic biomass tar model compounds into benzene, toluene and xylenes (BTX) over H-ZSM-5 catalyst

Biomass tar chemical model compounds (tetralin, naphthalene and 1-methylnaphthalene) have been previously extensively investigated over alumina, various zeolite materials and metal(s)-modified rate catalysts. In this mechanistic work, the relationship between cascade molecular structures, intermediates and reactivity was examined as a first time quantification through detailed micro-kinetic modelling. Herein, systematic measurement-based kinetics, consisting of the 17 gas phase species, 23 bonded adsorbed molecules and sites with the 41 reactions between them, are reported. System was tested based on the obtained experimental data for 1,2,3,4-tetrahydronaphthalene, aromatics and isomer hydrocracking, hydrogenation, and isomerization processes. Proposed derived representation exhibited a good consistent agreement with statistical numerical variation only, including hydrogen-activated hydrocarbon conversion, BTX (benzene, toluene and xylenes) selectivity and coking. Experiments have been before carried out in a packed bed reactor over the H-beta, H-mordenite, H-USY, H-Y and H-ZSM-5, or (Ga, Nb, Ni, NiMo, Sn, W, Zr or H3[P(W3O10)4])/ZSM-5 without the sulphide standard procedures in the functional temperature range of 370–500 °C under applied atmospheric pressure. The most promising yield was achieved over H-ZSM-5. Plug flow reactor (PFR), ideal continuous stirred tank (CSTR) vessel, and coupling the PFR with diffusion was considered, where the 1st one is found as the most fitting to results. The influence of the feedstock on catalytic activity performance was also studied. Deactivation was detected due to stable coke formation, stability was decreased, but predictability was shown. A technique sensitivity analysis was also performed BTX products. Simulations indicated that heat or mass transfer resistances, either intra- or inter-particle, were negligible.

Spectroscopic Detection of Cyano-Cyclopentadiene Ions as Dissociation Products upon Ionization of Aniline.

The H-loss products (C6H6N+) from the dissociative ionization of aniline (C6H7N) have been studied by infrared predissociation spectroscopy in a cryogenic ion trap instrument at the free electron laser for infrared experiments (FELIX) laboratory. Broadband and narrow line width vibrational spectra in the spectral fingerprint region of 550–1800 cm–1 have been recorded. The comparison to calculated spectra of the potential isomeric structures of the fragment ions reveals that the dominant fragments are five-membered cyano-cyclopentadiene ions. Computed C6H7N•+ potential energy surfaces suggest that the dissociation path leading to H loss starts with an isomerization process, following a similar trajectory as the one leading to HNC loss. The possible presence of cyano-cyclopentadiene ions and related five-membered ring species in Titan’s atmosphere and the interstellar medium are discussed.

Merging Hydrogen Atom Transfer and Halogen Atom Transfer for Iodide-Catalyzed Radical Reductive Cyclization of 1,6-Enynes.

Described herein is the development of a metal-free iodide-catalyzed radical reductive cyclization of 1,6-enynes. A strategy involving in situ iodination/radical cyclization/silyl radical-mediated halogen atom transfer/hydrogen atom transfer for the synthesis of functionalized pyrrolidines has been proposed. Using this halogen-atom abstraction protocol, 1,6-enynes with various vinyl halides including inert fluorides, chlorides, and reactive bromides could be transformed into substituted pyrroles via a multistep radical isomerization process.

Synthesis and Characterization of Sulfated Zirconia Catalyst for Light Naphtha Isomerization Process

The platinum-loaded zirconium oxide (Pt/SO4-2/ZrO2) catalyst was developed for the light naphtha atoms over the reaction temperature range of 160 to 220 °C, 1 and 3 h-1 LSHV and 10 bar. Platinum improved the stability of the catalyst by preventing the formation of a coke precursor at the strong acid site of sulfur zirconium. The acidity of the catalyst was characterized by of NH3-TPD and the effect of sulfur and calcination temperature on the surface area of ​​the final prepared zirconia was studied. The prepared catalyst shows high structural similar activity at temperature between 200 and 210°C for two types of light naphtha feed.

Modeling and active constrained optimization of C5/C6 isomerization via Artificial Neural Networks

Optimizing oil refinery processes for fuel efficiency and product quality is becoming more important under increasingly tighter environmental regulations. In this paper, we consider the problems of offline and active optimization of the C5/C6 isomerization process using only process inputs and output key performance indicators (KPIs). For offline optimization, we simulate thousands of process configurations and study the impact of optimizing for one KPI (e.g., yield) on other KPIs (e.g., octane number). Surprisingly, for our choices of optimization variables, minimizing energy consumption is the least detrimental on other KPIs. Moreover, an artificial neural network (ANN) model significantly outperforms baseline models in predicting simulated data. For active optimization, we show that our easy-to-use and extensible method can find optimal feasible parameter configuration in as few as 30 experiments, enabling operators to optimize their processes without the need for a model of the refinery process.

Simple Double Hetero[5]helicenes Realize Highly Efficient and Narrowband Circularly Polarized Organic Light-Emitting Diodes

Simple Double Hetero[5]helicenes Realize Highly Efficient and Narrowband Circularly Polarized Organic Light-Emitting Diodes

Structural Capture of η1-OSO to η2-(OS)O Coordination Isomerism in a New Ruthenium-Based SO2-Linkage Photoisomer That Exhibits Single-Crystal Optical Actuation.

Recent discoveries of a range of single-crystal optical actuators are feeding a new form of materials chemistry, given their broad range of potential applications, from light-induced molecular motors to light sensors and optical-memory media. A series of ruthenium-based coordination complexes that exhibit sulfur dioxide linkage photoisomerization is of particular interest because they exhibit single-crystal optical actuation via either optical switching or nano-optomechanical transduction processes. We report the discovery of a new complex in this series of chemicals, [Ru(SO2)(NH3)4(3-fluoropyridine)]tosylate2 (1), which forms an η1-OSO photoisomer with 70% photoconversion upon the application of 505 nm light. The uncoordinated oxygen atom in this η1-OSO photoisomer impinges on one of the arene rings in a neighboring tosylate counter ion of 1 just enough that incipient nano-optomechanical transduction is observed. The structure and optical properties of this actuator are characterized via in situ light-induced single-crystal X-ray diffraction (photocrystallography), single-crystal optical absorption spectroscopy and microscopy, as well as single-crystal Raman spectroscopy. These materials-characterization methods were also used to track thermally induced reverse isomerization processes in 1. One of these processes involves an η1-OSO to η2-(OS)O transition, which was found to proceed sufficiently slowly at 110 K that its structural mechanism could be determined via a time sequence of photocrystallography experiments. The resulting data allowed us to structurally capture the transition, which was shown to occur via a form of coordination isomerism. Our newfound knowledge about this structural mechanism will aid the molecular design of new [RuSO2] complexes with functional applications.

Conversion of Geraniol into Useful Value-Added Products in the Presence of Catalysts of Natural Origin: Diatomite and Alum.

This article presents research related to the transformation of geraniol (GA), leading to the formation of products with very valuable properties. In the planned method, heterogeneous catalysts of natural origin in the form of alum and diatomite were used as catalysts. Initially, the process which we investigated was the process of isomerization of GA, but it turned out during the studies that GA is also transformed in other reactions. Before catalytic tests, these two minerals were subjected to detailed instrumental analyses using the following methods: XRD, SEM/EDX, XRF and FTIR, which allowed to obtain their full morphological characteristics. During the catalytic tests, the influence of such relevant parameters on the GA transformations was determined: temperature from 80 to 150 °C, catalyst content from 5 to 15% by weight and the reaction time from 15 min to 24 h. The tests presented in the article were carried out under atmospheric pressure (in air) as well as without the use of a solvent. The optimal conditions for the transformations of GA were determined on the basis of its conversion and selectivities of transformation to the main products in the form of: beta-pinene (BP), 6,11-dimethyl-2,6,10-dodecatriene-1-ol (DC) and thumbergol (TH). The above products were formed with the highest selectivity, respectively: 100 mol%, 50 mol% and 52 mol%. The results of the syntheses showed that for GA the best transformation results were obtained at the temperature of 80 °C (for both tested catalysts), with the catalyst content of 1 wt % (for both tested catalysts) and for the reaction time of 1 h (for diatomite)) and 3 h (for alum).

Tetratopic Terpyridine Building Unit as a Precursor to Wheel-Like Metallo-Supramolecules.

In an effort to construct molecules with distinct shapes and functions, the design and synthesis of multitopic ligands are often able to play an important role. Here, we report the synthesis of a novel tetratopic organic ligand LA, which can be viewed as a bis-tenon with successive angular orientations in space. The particular ligand has been treated with different tailored metal-organic ligands to afford new members of the molecular wheel family (multi-rhomboidal-shaped wheel and bis-trapezium-shaped wheel) that show enhanced stability. Two-dimensional (2D) diffusion nuclear magnetic resonance (NMR) spectroscopy (DOSY), electrospray ionization (ESI) mass spectrometry, traveling wave ion mobility (TWIM), and gradient tandem mass spectrometry (gMS2) experiments, as well as molecular modeling, have been employed to provide structural information and differentiate the isomeric separation process. In addition, considering that LA has rotational properties, it is expected to open the door to functional supramolecules and stimuli-responsive materials.

Synthesis of Tetrahydro‐4H‐pyrido[1,2‐b]isoquinolin‐4‐ones from Ugi 4‐CR‐Derived Dihydroisoquinoline‐Xanthates**

AbstractAn efficient protocol for the synthesis of poly‐functionalized 1,2,3,6‐tetrahydro‐4H‐pyrido[1,2‐b]isoquinolin‐4‐ones is described. First, propargyl‐containing Ugi adducts were transformed to polysubstituted dihydroisoquinolines by an intramolecular Au‐catalyzed alkyne hydro‐arylation, followed by the alkene isomerization process. Then, these pivotal intermediates were engaged in a xanthate‐based oxidative radical cascade addition/cyclization process with a suitable alkene.

DFT-based Raman spectral study of astaxanthin geometrical isomers

Astaxanthin is a carotenoid widely used in food additives, nutritional product and medicines, which shows many physiological functions such as antioxidant, anti-inflammatory, anti-hypertensive and anti-diabetic activities. It has been recognized that astaxanthin has all-trans and nine cis isomers, and these geometrical isomers have very different biological activities. The process of selective enrichment, metabolism and isomerization of astaxanthin in animals remains to be studied. Therefore, identifying isomers and obtaining their structural parameters are important for understanding the active mechanism of different molecular isomers. Although the traditional methods such as high-performance liquid chromatography (HPLC) and nuclear magnetic resonance (NMR) spectroscopy can be used to distinguish these isomers, these methods generally require considerable testing time, cost, sample volume, and hardly be applied in vivo. In this work, Raman spectroscopy combined with density functional theory (DFT) calculation was introduced to study different geometrical isomers of astaxanthin. The theoretical and experimental Raman spectra are in agreement, and we have demonstrated that all the known ten geometrical isomers of astaxanthin can be readily distinguished using this spectroscopic approach. The astaxanthin molecular vibrational modes, geometric structures, energies of ten geometric isomers are systematically scrutinized. Moreover, a lot of structural and Raman problems unsolved previously have been solved by the DFT-based spectral analysis. Therefore, this work provides an effective way for identification of different astaxanthin geometrical isomers, and may have important significance for promoting the research of astaxanthin isomers on biological property mechanisms and related applications in food molecular science.