Bond-breaking Reactions Research Articles

Analysis of oxygen-containing species in coal tar by comprehensive two-dimensional GC×GC-TOF and ESI FT-ICR mass spectrometry through a new subfraction separation method

High oxygen content and ultracomplex composition are the biggest property characteristics of coal tar, which is also the biggest reason for the difficulty of coal tar separation and processing. The distribution of oxygen-containing compounds (OCs) and asphaltene island/archipelago structure play a key role in the solubility and hydrogenation thermal conversion of coal tar. In this study, the composition and structure of OCs in medium and low temperature coal tar (MLCT) and its subfractions were innovatively studied in the molecular level by GC × GC-TOF MS and negative ion ESI FT-ICR MS coupled with collision-induced dissociation (CID) through isolating a narrow mass-defined window based on the improved MLCT subfraction separation method. It revealed that the predominant OCs in MLCT are phenols with relatively few naphthols, furans, and ketones. The OCs are hugely dominated by Ox species in aromatics, resins, and asphaltenes. The polyoxygenated OCs primarily exist in heavier components like asphaltenes. The O atoms prefer to be linked to the outsides of aromatic ring in the form of hydroxyl or carboxyl for low oxygen-containing compounds, and embedded in aromatic rings as the furan rings or cyclic ethers for multiple oxygen-containing compounds. Some Ox species with a high H/C contain relatively smaller aromatic cores with more alkyl sidechains, which are the “atypical” molecules with multiple heteroatoms and low DBE in MLCT asphaltenes. Besides, the island-type structures are dominant for OCs in MLCT. The OxNn compounds have greater island attributes, especially for the molecules with multiple oxygen atoms. The MLCT asphaltenes contain more archipelago structure than that of aromatics and resins. The aromatic cores of OCs are not easy to be destroyed under the optimized voltage although the bridge bond breaking reaction occurs during CID. The heterolysis mode is absolutely the major bond cleavages path for OCs in MLCT. The heterolysis mechanism influences much on the generation of less-heteroatomic fragments, and the homolytic cleavage play a relatively important role during the generation of poly-heteroatomic fragments.

Degradation of organic compounds in hypersaline wastewater concentrate by a supercritical oxidation approach

ABSTRACT Hypersaline wastewater is a typical industrial wastewater produced by iron and steel metallurgy, food material processing and other industries. Aiming at a waste liquid produced by mechanical vapour recompression evaporation and concentration in Tianjin coastal industrial zone, an environment-friendly supercritical water oxidation technology was used to efficiently remove the high-content organic matter in the hypersaline wastewater concentrate (HWC). A comparison of the degradation effects of various oxidants in the supercritical state showed that hydrogen peroxide (H2O2) could be used as a suitable agent for processing the HWC. The reaction parameters were systematically optimised by single-factor experiment and response surface design. The degradation mechanism and reaction characteristics were analyzed using gas chromatography mass spectrometry. Solid residues were characterised by field emission scanning electron microscope. The results indicated that when the dosage of hydrogen peroxide was 6.39%, the reaction temperature was 380°C, the reaction time was about 90 min and the optimal total organic carbon removal rate was 96.22%. Furthermore, it was found that hydroxyl radicals produced by hydrogen peroxide initiated the bond breaking and ring-opening reactions in organic matter, which eventually degraded organic matter into water and carbon dioxide.

First-Principles Simulation Study on the Weakening of Silane Coupling to Silica under Alkaline Conditions

Silane coupling is commonly used to connect organic polymers to inorganic substrates for surface modification and composite material fabrication. It is known that the covalent bonds that form between the silane coupling agent (SCA) and hydroxylated SiO2 weaken under alkaline conditions. In the present work, we theoretically investigated the microscopic mechanisms of this phenomenon by combining first-principles calculations of the deprotonation free energy with density functional theory (DFT), bond-breaking transition-state barrier energy calculations, and DFT-based molecular dynamics (MD) simulations. We found that the following occurs under alkaline conditions: (i) the terminal −OH of SiO2(001) is significantly deprotonated, while the −OH group of the SCA is hardly deprotonated; (ii) the transition-state barrier energy to break the Si–O bond between the SCA and SiO2(001) becomes less than 1 eV with the assistance of H2O dissociation when 50% of the terminal −OH groups on SiO2(001) is deprotonated; and (iii) the predicted Si–O bond-breaking reactions occurred in DFT–MD simulations with realistic settings.

Effect of rare earth oxides on the formation of gaseous products from low rank coal pyrolysis

ABSTRACT Rare earth elements and their compounds can be used as catalysts or promoters for pyrolysis of organic matter including those in coal, but relevant investigations, especially regarding the role of rare earth materials in coal pyrolysis are very scarce. This study focuses on the effect of cerium oxide (CeO2) and lanthanum oxide (La2O3) on the formation of gaseous products from low-rank coal pyrolysis by means of gas chromatography (GC). The mechanisms of two kinds of rare earth oxides (REOs) involved in the coal pyrolysis are also discussed tentatively. Results show that CeO2 can promote the formation of CO2 (400°C–600°C), CO (550°C–650°C), CH4 (300°C–500°C), C2H6 and C3H8 (350°C–750°C), and it is believed to catalyze the bond breaking reactions of the aliphatic side chain, carboxyl group and phenolic hydroxyl group, or the bridge bonds between aromatic nuclei. The catalytic effect of CeO2 on the breaking of bridge bonds is likely to be completed by the movement of oxygen vacancies (i.e., oxygen storage and release ability of CeO2) in the water vapor environment. In addition, the results also reveal that it is La2O(CO3)2, not La2O3, playing a role in coal pyrolysis, which can promote the formation of CO2 (500°C–750°C), H2 and unsaturated hydrocarbons (350°C–500°C), and could be considered to be a catalyst for dehydrogenation at low-medium temperature. The mechanism of CO2 formation catalyzed by La2O(CO3)2 is probably related to the decomposition of oxygen-containing ligands formed by La(III) and carboxyl group at high temperature.

DFT Study on the Biosynthesis of Verrucosane Diterpenoids and Mangicol Sesterterpenoids: Involvement of Secondary-Carbocation-Free Reaction Cascades.

Some experimental observations indicate that a sequential formation of secondary (2°) carbocations might be involved in some biosynthetic pathways, including those of verrucosane-type diterpenoids and mangicol-type sesterterpenoids, but it remains controversial whether or not such 2° cations are viable intermediates. Here, we performed comprehensive density functional theory calculations of these biosynthetic pathways. The results do not support previously proposed pathways/mechanisms: in particular, we find that none of the putative 2° carbocation intermediates is involved in either of the biosynthetic pathways. In verrucosane biosynthesis, the proposed 2° carbocations (II and IV) in the early stage are bypassed by the formation of the adjacent 3° carbocations and by unusual skeletal rearrangement reactions, and in the later stage, the putative 2° carbocation intermediates (VI, VII, and VIII) are not present as the proposed forms but as nonclassical structures between homoallyl and cyclopropylcarbinyl cations. In the mangicol biosynthesis, one of the two proposed 2° carbocations (X) is bypassed by a C–C bond-breaking reaction to generate a 3° carbocation with a C=C bond, while the other (XI) is bypassed by a strong hyperconjugative interaction leading to a nonclassical carbocation. We propose new biosynthetic pathways/mechanisms for the verrucosane-type diterpenoids and mangicol-type sesterterpenoids. These pathways are in good agreement with the findings of previous biosynthetic studies, including isotope-labeling experiments and byproducts analysis, and moreover can account for the biosynthesis of related terpenes.

Optically facet-resolved reaction anisotropy in two-dimensional transition metal dichalcogenides

Quantifying anisotropy in the chemical reactions of mesoscopic crystals has mostly resorted on the combination of electron microscopy and diffraction. In this work, we established crystal-facet-resolved kinetic measurements of oxidation reactions in two-dimensional (2D) transition metal dichalcogenides (TMDs) using optical second-harmonic generation spectroscopy and scanning probe microscopy. We show the in-plane anisotropy of their bond-breaking reactions is governed by their structure and strongly material-dependent among four TMDs. The facet-resolved analysis directly revealed that the reactions proceed fastest (slowest) for chalcogen (metal)-terminated zigzag edges with armchair edges in the middle. The degree of the anisotropy inducing trigonal oxidation patterns was much higher in MoS2 and MoSe2 than WS2 and WSe2. Kinetic Wulff construction based on edge-specific reaction rates verified the material-dependent mesoscopic reaction patterns. We also show that the reactions are initiated at substrate-mediated defects located on the bottom and top surfaces of 2D TMDs.

Clip Chemistry: Diverse (Bio)(macro)molecular and Material Function through Breaking Covalent Bonds.

In the two decades since the introduction of the "click chemistry" concept, the toolbox of "click reactions" has continually expanded, enabling chemists, materials scientists, and biologists to rapidly and selectively build complexity for their applications of interest. Similarly, selective and efficient covalent bond breaking reactions have provided and will continue to provide transformative advances. Here, we review key examples and applications of efficient, selective covalent bond cleavage reactions, which we refer to herein as "clip reactions." The strategic application of clip reactions offers opportunities to tailor the compositions and structures of complex (bio)(macro)molecular systems with exquisite control. Working in concert, click chemistry and clip chemistry offer scientists and engineers powerful methods to address next-generation challenges across the chemical sciences.

Recent Developments in Rh Heterogeneous Catalysts

Rh-based catalysts successfully catalyze bond making and bond breaking reactions in most cases [...]

Mechanistic insight into the catalytic cracking mechanism of α-olefin on H-Y zeolite: A DFT study

In the bifunctional catalyst for Fischer-Tropsch synthesis, the distribution of products in the secondary catalytic reaction of intermediate products is affected by the Brønsted acid sites in zeolites. Linear α-olefins are the intermediates of Fischer-Tropsch synthesis. In this work, density functional theory (DFT) calculation was carried out to understand further Brønsted Acid Sites’ mechanism in the secondary reaction of Fischer-Tropsch synthesis. The adsorption energy of linear α-olefins on H-Y zeolite decreased with the increase of the carbon chain. Besides, four essential reactions were simulated by the DFT method. The four elementary reactions' energy barriers are: β bond-breaking reaction > skeleton isomerization reaction > intramolecular hydrogen transfer reaction > protonation reaction. Then, a complete reaction network of straight-chain α-Nonylene on H-Y zeolite was designed. The β bond-breaking reaction is a key step to determine the type and distribution of products.

Oxygen reduction limited by surface diffusion at a rotating ring-disk electrode

The oxygen reduction reaction (orr) limited by surface diffusion is studied with an analytical model. The model considers the electrosorption of dissolved oxygen followed by surface diffusion of the adsorbate towards a catalyst centre for reaction. It includes the possibility of partial reduction to hydrogen peroxide. The model is solved for a catalyst dispersion embedded in the disk of a rotating ring-disk electrode (rrde). Simplified Eqs. are provided for the disk and ring currents, as well as Tafel slopes and Koutecký-Levich relations, as a function of surface diffusivity, catalyst dispersion, and reaction parameters. The disk current may show a peak at moderate overpotentials due to a maximum in surface diffusivity. Disk and ring currents are calculated for various orr mechanisms differing in the surface diffusion intermediate. The mechanism limited by OH* surface diffusion appears most favourable, however it requires partial charge transfer and O-O bond breaking reactions on the supporting surface. The model shows that orr electrocatalysis assisted by the surface transport of intermediates improves the performance of air cathodes of low temperature fuel cells and metal-air batteries.

Sulfonated Tetraphenylethylene-Based Hypercrosslinked Polymer as a Heterogeneous Catalyst for the Synthesis of Symmetrical Triarylmethanes via a Dual C–C Bond-Cleaving Path

AbstractA sulfonic acid functionalized tetraphenylethylene-based hypercrosslinked polymer (THP-SO3H) with a well-developed porous network and accessible sulfonic acid sites was synthesized and characterized by different analytical techniques. The catalytic prowess of the synthesized material THP-SO3H was investigated in a challenging dual C–C bond-breaking reaction for the synthesis of symmetrical triarylmethanes (TRAMs) in high yield. The scope of the developed metal-free method was also explored with a wide variety of substrates. The organocatalyst can be easily recovered by filtration and reused up to five consecutive cycles without substantial loss in its catalytic efficacy.

Self-Immolative Difluorophenyl Ester Linker for Affinity-Based Fluorescence Turn-on Protein Detection.

Currently most fluorogenic probes are developed for the analysis of enzymes, where a bond breaking or rearrangement reaction is required to transform a nonfluorescent enzymatic substrate into a fluorescent product. However, this approach cannot be used for proteins that do not possess enzymatic activities. In this article, we show that fluorogenic probes with a self-immolative difluorophenyl ester linker can mimic the bond disassembly processes of fluorogenic enzyme substrates for the rapid analysis of nonenzymatic proteins. Although numerous self-immolative reagents have shown promising applications in sensors, drug delivery systems, and material chemistry, all of them are triggered by either enzymes or small reactive molecules. In our strategy, the probe binds to the protein via a specific protein-ligand interaction, inducing a chemical reaction between the self-immolative linker and an amino acid of the protein, thereby triggering a cascade reaction that leads to the activation and release of the fluorogenic reporter. In contrast, a phenyl ester linker without the difluoro substituent cannot be triggered to release the fluorogenic reporter. With this probe design, live-cell imaging of extracellular and intracellular endogenous tumor marker proteins can be achieved with high selectivity and sensitivity.

Dialling-In New Reactivity into the Shono-Type Anodic Oxidation Reaction.

This Personal Account describes the author's groups' research in the field of electrosynthetic anodic oxidation, beginning with initial trial and error attempts with the Shono oxidation. Early setbacks with complex rotameric amide mixtures, provided the ideal environment for the discovery of the Oxa-Shono reaction-Osp 2 -Csp 3 bond cleavage of esters-providing two useful products in one-step: aldehyde selective oxidation level products and a mild de-esterification method to afford carboxylic acids in the process. The development of the Oxa-Shono reaction provided the impetus for the discovery of other electrically propelled-Nsp 2 -Csp 2 and Nsp 2 -Csp 3 -bond breaking reactions in bioactive amide and sulfonamide systems. Understanding the voltammetric behaviour of the molecule under study, switching between controlled current- or controlled potential- electrolysis, and restricting electron flow (the reagent), affords exquisite control over the reaction outcomes in batch and flow. Importantly, this bio-inspired advance in electrosynthetic dealkylation chemistry mimics the metabolic outcomes observed in nature.

Caspase-Activated Oligonucleotide Probe.

Light-activated ("caged") oligonucleotides provide a strategy for modulating the activity of antisense oligos, siRNA, miRNA, aptamers, DNAzymes, and mRNA-capturing probes with high spatiotemporal resolution. However, the near-UV and visible wavelengths that promote these bond-breaking reactions poorly penetrate living tissue, which limits some biological applications. To address this issue, we describe the first example of a protease-activated oligonucleotide probe, capable of reporting on caspase-3 during cellular apoptosis. The 2'-F RNA-peptide substrate-peptide nucleic acid (PNA) hairpin structure was generated in 30% yield in a single bioconjugation step.

Transition Metal-Catalyzed Selective Carbon-Carbon Bond Cleavage of Vinylcyclopropanes in Cycloaddition Reactions.

In this review, transition metal-catalyzed methodologies and applications that exploit C-C bond cleavage of vinylcyclopropanes (VCPs) are summarized with a focus on cycloaddition and related addition reactions. Transition metals, including palladium, nickel, iron, ruthenium, rhodium, cobalt, and iridium, can catalyze the cleavage of C-C bonds in activated or nonactivated VCPs. Additionally, these bond-breaking reactions can occur as intra- or intermolecular processes. The properties of activated and nonactivated VCPs are discussed in the Introduction. Various transition metal-catalyzed cycloaddition and addition reactions involving the cleavage of C-C bonds in activated VCPs are then discussed in the next chapter. The transition metal-catalyzed cycloadditions involving the cleavage of C-C in nonactivated VCPs are summarized in the following chapter. Finally, challenges and potential opportunities are outlined in the last chapter.

Structural trends in the dehydrogenation selectivity of palladium alloys.

Alloying is well-known to improve the dehydrogenation selectivity of pure metals, but there remains considerable debate about the structural and electronic features of alloy surfaces that give rise to this behavior. To provide molecular-level insights into these effects, a series of Pd intermetallic alloy catalysts with Zn, Ga, In, Fe and Mn promoter elements was synthesized, and the structures were determined using in situ X-ray absorption spectroscopy (XAS) and synchrotron X-ray diffraction (XRD). The alloys all showed propane dehydrogenation turnover rates 5–8 times higher than monometallic Pd and selectivity to propylene of over 90%. Moreover, among the synthesized alloys, Pd3M alloy structures were less olefin selective than PdM alloys which were, in turn, almost 100% selective to propylene. This selectivity improvement was interpreted by changes in the DFT-calculated binding energies and activation energies for C–C and C–H bond activation, which are ultimately influenced by perturbation of the most stable adsorption site and changes to the d-band density of states. Furthermore, transition state analysis showed that the C–C bond breaking reactions require 4-fold ensemble sites, which are suggested to be required for non-selective, alkane hydrogenolysis reactions. These sites, which are not present on alloys with PdM structures, could be formed in the Pd3M alloy through substitution of one M atom with Pd, and this effect is suggested to be partially responsible for their slightly lower selectivity.

Programming nanoparticle valence bonds with single-stranded DNA encoders.

Nature has evolved strategies to encode information within a single biopolymer to program biomolecular interactions with characteristic stoichiometry, orthogonality and reconfigurability. Nevertheless, synthetic approaches for programming molecular reactions or assembly generally rely on the use of multiple polymer chains (for example, patchy particles). Here we demonstrate a method for patterning colloidal gold nanoparticles with valence bond analogues using single-stranded DNA encoders containing polyadenine (polyA). By programming the order, length and sequence of each encoder with alternating polyA/non-polyA domains, we synthesize programmable atom-like nanoparticles (PANs) with n-valence that can be used to assemble a spectrum of low-coordination colloidal molecules with different composition, size, chirality and linearity. Moreover, by exploiting the reconfigurability of PANs, we demonstrate dynamic colloidal bond-breaking and bond-formation reactions, structural rearrangement and even the implementation of Boolean logic operations. This approach may be useful for generating responsive functional materials for distinct technological applications.

Highly-efficient degradation of triclosan attributed to peroxymonosulfate activation by heterogeneous catalyst g-C3N4/MnFe2O4

• g-C 3 N 4 /MnFe 2 O 4 was prepared via sol-gel method. • TCS was degraded effectively by g-C 3 N 4 /MnFe 2 O 4 (1:1) activation PMS. • Heavy metal leaching decreased after MnFe 2 O 4 combined with g-C 3 N 4 . • SO 4 · − , ·OH, ·O 2 − and 1 O 2 were contributed to the TCS degradation. • The main degradation pathway of TCS was preliminarily proposed. The g-C 3 N 4 /MnFe 2 O 4 as recyclable catalyst was synthesized via auto-combustion sol-gel method. Peroxymonosulfate (PMS) activation by the catalyst for triclosan (TCS) degradation was investigated considering the activation performance, reaction parameters and activation mechanism. The catalyst prepared with 1:1 of g-C 3 N 4 and MnFe 2 O 4 molar ratio performed the best catalytic activity in the TCS degradation and with lest metal leaching. The concentration of Cl − showed a dual effect on the TCS degradation, while HCO 3 − and SO 4 2− performed inhibitory effect. Sulfate radicals, hydroxyl radicals, superoxide and non-radical single oxygen contributed to the degradation of TCS. Compared with MnFe 2 O 4 /PMS system, few heavy metals were leached from g-C 3 N 4 /MnFe 2 O 4 (1:1)-PMS after each reuse ( Fig. S6 b), suggesting that g-C 3 N 4 was conducive to the stability of g-C 3 N 4 /MnFe 2 O 4 (1:1) catalyst. Dichlorination, hydroxylation, cyclization and other bond breaking reaction were inferred as the TCS degradation pathways. These results demonstrated that g-C 3 N 4 /MnFe 2 O 4 (1:1) was a highly effective and stable catalyst for PMS activation to treat toxic organic pollutants in water.

Calculation of Transition State Energies in the HCN-HNC Isomerization with an Algebraic Model.

Recent works have shown that the spectroscopic access to highly excited states provides enough information to characterize transition states in isomerization reactions. Here, we show that information about the transition state of the bond-breaking HCN-HNC isomerization reaction can also be achieved with the two-dimensional limit of the algebraic vibron model. We describe the system's bending vibration with the algebraic Hamiltonian and use its classical limit to characterize the transition state. Using either the coherent state formalism or a recently proposed approach by Baraban [ Science 2015 , 350 , 1338 - 1342 ], we obtain an accurate description of the isomerization transition state. In addition, we show that the energy-level dynamics and the transition state wave function structure indicate that the spectrum in the vicinity of the isomerization saddle point can be understood in terms of the formalism for excited-state quantum phase transitions.

Role of bitumen and NSOs during the decomposition process of a lacustrine Type-II kerogen in semi-open pyrolysis system

The purpose of this work is to investigate the generation characteristics of bitumen, NSO compounds, oil, and HC compounds during the artificial maturation of a lacustrine Type-II kerogen (which has not been given enough attention before) in order to determine its decomposition process. The analysis is based on the data itself, on the premise of jumping out of the generally accepted sequential reaction model. By taking the kerogen of the Chang 7 shale as an example, seven parallel experiments, in the temperature range from 300 °C to 420 °C were conducted on newly designed temperature-based semi-open pyrolysis system. The overall products are classified into oil and bitumen according to their phase, the C15+ fractions are classified into C15+sat, C15+aro and NSOs based on chemical compositions, and the NSOs are further classified into n-pentane NSOs and DCM NSOs according to Behar et al., (2008) and (2010). Results show that large proportion of oil is not merely a result of thermal cracking of bitumen, but also directly from the decomposition of kerogen itself. Both C15+sat and C15+aro are generated as soon as kerogen starts to decompose. It is not until the initial productivity of kerogen is basically exhausted that NSOs become the main precursor of hydrocarbons. The comparison with Behar et al. [2008, organic geochemistry 39, 1–22] further reveals that, for Chang 7 kerogen, initial decomposition of kerogen generates much more HCs than DCM NSOs. These results contradict the sequential reaction model described as: kerogen → bitumen → oil or kerogen → NSOs → hydrocarbons. Instead, they confirm the “alternate pathway” mechanism proposed by Burnham et al. [ACS symposium, 1989] in which hydrocarbons can be formed immediately from kerogen in parallel with NSOs and the formation of the two species are controlled by bond-breaking reactions that are independent of each other. This study adds geochemical insights into the decomposition mechanism of lacustrine Type-II kerogen.