Pathways For Formation Of Products Research Articles

Intermolecular Photoredox Coupling: Alternative to Norrish Type II Reaction and Yang Cyclization in Ketones with γ‐C−H Bonds

AbstractA new reaction pathway for the photoconversion of butyrophenone in acetonitrile was investigated. In addition to the classic intramolecular photoreactivity of ketones with γ‐C−H bonds (Norrish type II fragmentation and Yang cyclization), intermolecular generated species were isolated and characterized: 1,2‐Dibenzoylethane, 2‐phenacylacetonitrile (oxidized species) and pinacols (reduced species). They account for approx. 20 % of the converted starting material, similar to the Yang product. The acetophenone enol intermediate, formed in situ via the Norrish type II reaction, has been identified as an H‐atom donor for the main intermolecular reaction steps, and has been distinguished from other conceivable mechanistic possibilities. Experimental results with analogue compounds suggest that the intermolecular product formation pathway may be of general relevance.

Experimental and kinetic modeling studies of di-n-propyl ether pyrolysis at low and atmospheric pressures

The pyrolysis of di-n-propyl ether (DPE), a potential biofuel candidate, was studied under a temperature range of 850–1350 K in a flow reactor at low and atmospheric pressures. Synchrotron vacuum ultraviolet photoionization mass spectrometry was used for isomeric identification and mole fraction measurements of the pyrolysis products, especially the free radicals. Specific products were observed and measured for the unimolecular decomposition reactions of DPE. A detailed kinetic model of DPE pyrolysis was developed based on the n-propanol combustion model. Modeling analyses including the rate of production (ROP) and sensitivity analyses were performed to reveal the consumption pathways of DPE, as well as the formation and consumption pathways of intermediates and products. ROP and sensitivity analyses indicated that the consumption reaction of DPE was mainly controlled by the unimolecular decomposition reactions and H-abstractions at both low and atmospheric pressures. The pericyclic reaction, leading to n-propanol + propylene, was the most important unimolecular decomposition reactions, especially at low pressure. The H-abstraction reactions of DPE played crucial roles in its consumption. Further β-C–C and β-C–O scission reactions of the three primary radicals can produce some oxygenated and hydrocarbon products. Relatively high mole fractions of C1–C3 aldehydes and C1–C3 alkane, alkene, and alkyl radicals were observed, which demonstrated the structural feature of DPE. Comparison of the product distribution between DPE and n-propanol were also analyzed.

How Small Molecules Affect the Thermo-Oxidative Aging Mechanism of Polypropylene: A Reactive Molecular Dynamics Study.

Understanding the aging mechanism of polypropylene (PP) is fundamental for the fabrication and application of PP-based materials. In this paper, we present our study in which we first used reactive molecular dynamics (RMD) simulations to explore the thermo-oxidative aging of PP in the presence of acetic acid or acetone. We studied the effects of temperature and oxygen on the aging process and discussed the formation pathways of typical small molecule products (H2, CO, CO2, CH4, C2H4, and C2H6). The effect of two infection agents, acetic acid and acetone, on the aging reaction was analyzed emphatically. The simulation results showed that acetone has a weak impact on accelerating the aging process, while acetic acid has a significant effect, consistent with previous experimental studies. By tracking the simulation trajectories, both acetic acid and acetone produced small active free radicals to further react with other fragment products, thus accelerating the aging process. The first reaction step of acetic acid is often the shedding of the H atom on the hydroxyl group, while the reaction of acetone is often the shedding of the H atom or the methyl. The latter requires higher energy at lower temperatures. This is why the acceleration effect of acetone for the thermo-oxidative aging of PP was not so significant compared to acetic acid in the experimental temperature (383.15 K).

Effect of unsaturated fatty acids on glycation product formation pathways

Glycation and lipid oxidation in high-nutrient foods are closely related and exhibit complex interactions. To evaluate the effect of unsaturated fatty acids (UFAs) on glycation pathways, glycation products in glucose-lysine-UFA models were detected by ultra performance liquid chromatography-tandem mass spectrometry and electron spin resonance spectroscopy, together with multivariate data analysis. Results indicated that UFAs inhibited glucose oxidation by decreasing the contents of carbonyl compounds about 73.85–86.19%. UFAs promoted the formation of glycation products mainly via production of active radical. In three models, linoleic acid (LA) exhibits stronger glycation activity than oleic acid and eicosapentaenoic acid. LA significantly promoted radical formation, as well as the formation and degradation of fructosyllysine (FL), the signal intensity of active radical increased 647.45% and FL increased 78.73%. The comparison of E(k3), E(k7) and variable importance in projection values of orthogonal projections to latent structures discriminant analysis in three models also proved these conclusions. By studying the characteristics of LA on glycation in three UFA, we hypothesized that unsaturation is not the key factor in evaluating their effects on glycation, the radical activity, UFA solubility, spatial structure and interaction should be considered as potentially important factors.

Atmospheric and high pressures pyrolysis study of n-decane in a flow reactor with online GC-MS/FID analysis: Experiments and modeling

The atmospheric and high-pressure pyrolysis of n-decane was studied in a flow tube reactor combined with online GC–MS/FID at 723−1123 K, 0.1–3.0 MPa (highly diluted in helium). Compared with 0.1 MPa, the conversion of n-decane and mole fraction of alkenes clearly increased at 3.0 MPa at the fixed temperature, and more aromatics were observed including toluene, styrene, ethylbenzene, indene and naphthalene, suggesting that the secondary reactions are more intense under high pressure. To account for these differences, a detailed kinetic model with 191 species and 1117 reactions was constructed by incorporating the aromatics subset to a n-decane model developed in previous low-pressure work, and further validated against literature data covering a wide pressure range (0.004–7.2 MPa) with reasonable reproducibility. The current model was compared against three literature kinetic models (LLNL, JetSurf 2.0 and Rev1stGen) and showed a better accordant with the conversion of n-decane and the selectivity of major products. Based on the rate of production and sensitivity analysis using the current model, the results show that although the total consumption of n-decane is weakly pressure-dependent at fixed temperature and residence time under the investigated conditions, the formation and consumption pathways of primary products change significantly attributed to the enhanced bimolecular abstraction and combination reactions at higher pressures. For the formation of benzene, the combination of 1,3-butadien-2-yl with ethylene is the main pathway at both 0.1 and 3.0 MPa, while the additional combination reactions: propargyl with allyl and cyclopentadienyl (c-C5H5) with CH3 become dominant at 0.1 MPa and 3.0 MPa, respectively. For the formation of larger aromatic naphthalene, the self-recombination of c-C5H5 is the most important channel at all investigated pressures.

Experimental and Density Functional Theory Studies on 1,1,1,4,4,4-Hexafluoro-2-Butene Pyrolysis.

A series of thermal decomposition experiments were conducted over a temperature range of 873–1073 K to evaluate the thermal stability of 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz(Z)) and the production of hydrogen fluoride (HF). According to the detected products and experimental phenomena, the thermal decomposition of HFO-1336mzz(Z) could be divided into three stages. Our experimental results showed that HF concentration gradually increased with the elevation of thermal decomposition temperature. In this present study, a total of seven chemical reaction pathways of HFO-1336mzz(Z) pyrolysis were proposed to explore the generated mechanism on products through density functional theory (DFT) with M06-2X/6-311++(d,p) level theory. The thermal decomposition mechanism of pure HFO-1336mzz(Z) was discussed and the possible formation pathways of HF and other main products were proposed.

Effect of unsaturated fatty acids on glycation product formation pathways (Ⅰ) the role of oleic acid

Research on advanced glycation end-products (AGEs) and their formation pathways in food processing has gradually increased because AGEs are associated with human health, especially with involvement of lipids. In this study, radicals and glycation products were detected via electron spin resonance (ESR) and ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) respectively. The correlation of important intermediates was used to explain the effect of oleic acid (OA) on the glycation products and pathways. The results indicated OA participation decreased the content of stable radicals and glycosyl compounds in Maillard Reaction (MR). The oxidation of OA produced active radicals, and electron transfer caused lysine to transform radical form. These radicals participated in the formation of fructosyllysine (FL) with glucose (Glc) via the MR. The participation of OA is acted as inhibiting the way of Glc autoxidation and promoting the glycation pathway from FL to 3-deoxyglucosone (3-DG) to fluorescent-AGEs. Orthogonal projection to latent structures discriminant analysis results indicated that 3-DG, D-glucosone and methylglyoxal are key products in discriminating the glycation reaction.

Coupling biology to synthetic nanomaterials for semi-artificial photosynthesis.

Biohybrid artificial photosynthesis aims to combine the advantages of biological specificity with a range of syntheticnanomaterials to create innovative semi-synthetic systems for solar-to-chemical conversion. Biological systems utilize highly efficient molecular catalysts for reduction-oxidation reactions. They can operate with minimal overpotentials while selectively channeling reductant energy into specific transformation chemistries and product forming pathways. Nanomaterials can be synthesized to have efficient light-absorption capacity and tuneability of charge separation by manipulation of surface chemistries and bulk compositions. These complementary aspects have been combined in a variety of ways, for example, where biological light-harvesting complexes function as antenna for nanoparticle catalysts or where nanoparticles function as light capture, charge separation components for coupling to chemical conversion by redox enzymes and whole cells. The synthetic diversity that is possible with biohybrids is still being explored. The progress arising from creative approaches is generating new model systems to inspire scale-up technologies and generate understanding of the fundamental mechanisms that control energy conversion at the molecular scale. These efforts are leading to discoveries of essential design principles that can enable the development of scalable artificial photosynthesis systems.

Insight into the Formation and Transfer Process of the First Intermediate of CO2 Reduction over Ag-Decorated Dendritic Cu.

It is still poorly understood how the first intermediates of CO2 reduction are formed and converted to multi-carbon products over Cu-based electrodes. Herein, Ag is used to decorate dendritic Cu and a high Faradaic efficiency (FE) for C2 H4 (25 %) is obtained on a CuAg electrode, which is about five times higher than dendritic Cu. The intermediates including *CO2 - , OH groups, Cu-CO, C-O rotation, and CHx species are investigated by in situ Raman spectroscopy. This work provides spectroscopic evidence that the first intermediate of CO2 reduction on Ag-decorated Cu is carboxylate anion *CO2 - bonded with the catalyst surface through the C and O atom. The formation and evolution process of the *CO2 - intermediate over the applied potential are investigated in depth as well. This research contributes to a better understanding of the mechanism of CO2 reduction and multi-carbon product formation pathways over Ag-decorated Cu.

Hyperglycemia induces spermatogenic disruption via major pathways of diabetes pathogenesis

Diabetes-induced hyperglycemia has previously been shown to impact on male sub-/infertility, however, still little is known about the underlying mechanisms. In the present study we have addressed three major biochemical pathways implicated in the pathogenesis of hyperglycemia induced organ damage (the advanced glycation end product (AGE) formation pathway, the diacylglycerol-protein kinase C pathway (PKC), and the polyol pathway) in both testis and epididymis of the Ins2Akita mouse model of Type 1 diabetes (T1DM). Hyperglycemia activated both the PKC and the polyol pathway in a significant and progressive manner within the testis, but not within the epididymis. While the AGE receptor was ubiquitiously expressed in the testis, concentrations of precursor methylglyoxal and AGE carboxymethyllysine were increased in both epididymis and testis in diabetic mice. However, AGEs did not activate intracellular pathways of ERK1, ERK2, Rela, Nrf-2, IkBkB, NFkB except CDC42, Akt1. In conclusion, two of the major pathways of hyperglycemia-induced organ damage were clearly activated within the testis of T1DM mice. This provides therapeutical opportunities in the treatment of diabetic male reproductive dysfunction.

Exploration of the pyrolysis chemistry of 1,1-diethoxybutane: A flow reactor and kinetic modeling study

1,1-Diethoxybutane is a promising next-generation biofuel and this work reports the first study for its pyrolysis chemistry. Pyrolysis of 1,1-diethoxybutane was investigated in a flow reactor at 0.04 and 1 atm using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). A series of oxygenated and hydrocarbon products, including several radicals, were detected and their mole fractions were evaluated. A detailed kinetic model of 1,1-diethoxybutane, including 253 species and 1577 reactions, was developed and validated against the present experimental data. Modeling analyses including the rate of production analysis and sensitivity analysis were performed to reveal the crucial consumption pathways of 1,1-diethoxybutane, as well as the formation and consumption pathways of intermediates and products. The H-abstraction reactions of 1,1-diethoxybutane play a key role in fuel consumption. The intra-molecular elimination reactions and unimolecular CC or CO dissociation reactions of 1,1-diethoxybutane make minor contributions to fuel consumption. The sensitivity analysis also shows that the fuel consumption reactions have large sensitivities to 1,1-diethoxybutane. Further β-CC and β-CO scission reactions closely connect the consumption of six fuel radicals and the formation of most oxygenated products. The observation of high mole fractions of C1–C4 acids and aldehydes demonstrates the structural features of 1,1-diethoxybutane. Besides, several hydrocarbon products, such as C2–C4 alkenes, benzene and its precursors, were detected, some of which, such as propene, are also produced from the consumption reactions of fuel radicals. Besides, hydrocarbon products can also be produced from the combination reactions of small species, such as the combination reactions of C3 species to produce benzene and the combination reaction of allyl and methyl to produce 1-butene. The low benzene production ability of 1,1-diethoxybutane implies its low sooting tendency compared with fossil-derived transportation fuels.

Hydrogen production via propane dry reforming: Carbon deposition and reaction-deactivation study

Carbon deposition during carbon dioxide reforming reaction of C3H8 has been studied over alumina-supported bimetallic Mo/CoNi catalysts. To better understand the carbon-induced deactivation during the reforming reaction, changes in catalyst morphology and carbon deposition kinetics were examined. Different characterization techniques were used for both fresh and rejuvenated catalysts including liquid nitrogen adsorption/desorption, chemisorption via hydrogen, ammonia and CO2 desorption, and thermogravimetric measurement of the coked catalysts. The time dependant reaction rate profiles indicated that MoNi catalyst has higher syngas (H2/CO) formation rates with lower CO2 rate of consumption compared to CoNi catalyst. However, the H2:CO ratio values were almost the same for both catalysts suggesting similarity in the product formation pathway. Conversion-time analysis showed that MoNi catalyst was more stable and active during a 72-h run while CoNi suffered noticeable deactivation after 30 h on-stream. Reaction-deactivation models implicated a higher deactivation coefficient (kd) with activation energy of Ed = 78.1 kJ mol−1 for the cobalt-containing Ni catalyst, while the Ni catalyst with molybdenum had a lower deactivation coefficient with smaller activation energy of just under 70 kJ mol−1. Post-mortem analysis (TPR-TPO dual cycle and TOC) of spent catalysts confirmed that the surface of CoNi catalyst has more carbon residue than the MoNi sample which was consistent with the higher deactivation of CoNi.

Synthesis, Structures, and Reactivity of Single and Double Cyclometalated Complexes Formed by Reactions of [Cp*MCl2]2 (M = Ir and Rh) with Dinaphthyl Phosphines.

Reactions of two dinaphthyl phosphines with [Cp*IrCl2]2 have been carried out. In the case of di(α-naphthyl)phenylphosphine (1a), a simple P-coordinated neutral adduct 2a is obtained. However, tert-butyldi(α-naphthyl)phenylphosphine (1b) is cyclometalated to form [Cp*IrCl(P^C)] (3b). Complexes 2a and 3a undergo further cyclometalation to give the corresponding double cyclometalated complexes [Cp*Ir(C^P^C)] (4a,b) upon heating. In the presence of sodium acetate, reactions of 1a,b with [Cp*IrCl2]2 directly afford the final double cyclometalated complexes (4a,b). In the absence of acetate, [Cp*RhCl2]2 shows no reaction with 1a,b, whereas with acetate the reactions form the corresponding single cyclometalated complexes [Cp*RhCl(P^C)] (5a,b), which react with tBuOK to form the corresponding rhodium hydride complexes (6a,b). Treatment of 4a with CuCl2 or I2 leads to opening of two Ir–C σ bonds to yield the corresponding P-coordinated iridium dihalide (7 or 8) by means of an intramolecular C–C coupling reaction. A new chiral phosphine (11) is formed by the ligand-exchange reaction of 8 with PMe3. Reactions of the single cycloiridated complex 3b with terminal aromatic alkynes result in the corresponding five- and six-membered doubly cycloiridated complex 12 and/or η2-alkene coordinated complexes 13–15; the latter discloses that the electronic effect of terminal alkynes affects the regioselectivity. While the single cyclorhodated complex 5b reacts with terminal aromatic alkynes to form the corresponding six-membered cyclometalated complexes 16a–c by vinylidene rearrangement/1,1-insertion. Plausible pathways for formation of insertion products 13–16 were proposed. Molecular structures of twelve new complexes were determined by X-ray diffraction.

Mechanism for Three-Component Ni-Catalyzed Carbonyl–Ene Reaction for CO2 Transformation: What Practical Lessons Do We Learn from DFT Modelling?

In the present study, we use computational quantum chemistry to examine the nickel-catalyzed three-component coupling for transforming CO2 into a homoallylic alcohol. We find that the reaction is limited by several Ni-assisted atom transfer reactions in the catalytic cycle, in which a new product formation pathway is found from our calculations. Our results also point towards several key factors for an efficient reaction. Thus, substrates that would lead to a stabilized alkene facilitate a key step in the catalytic cycle. The optimal phosphine ligand should provide a good balance between directing stereochemistry with its steric bulk and enabling the reaction without being excessively bulky. Our calculations also highlight the importance of carefully chosen substrates and ligands in order to avoid potential side reactions, and that knowing the conformational preference in the substrate alone may not be sufficient for predicting the stereochemistry.

Competing Pathways in O-Arylations with Diaryliodonium Salts: Mechanistic Insights.

A mechanistic study of arylations of aliphatic alcohols and hydroxide with diaryliodonium salts, to give alkyl aryl ethers and diaryl ethers, has been performed using experimental techniques and DFT calculations. Aryne intermediates have been trapped, and additives to avoid by‐product formation originating from arynes have been found. An alcohol oxidation pathway was observed in parallel to arylation; this is suggested to proceed by an intramolecular mechanism. Product formation pathways via ligand coupling and arynes have been compared, and 4‐coordinated transition states were found to be favored in reactions with alcohols. Furthermore, a novel, direct nucleophilic substitution pathway has been identified in reactions with electron‐deficient diaryliodonium salts.

Thermal decomposition of HFO-1234yf through ReaxFF molecular dynamics simulation

The thermal decomposition of HFO-1234yf with O2 was studied by ReaxFF molecular dynamics simulation at the wide temperature ranges of 1900–3500K. The results show that the initial reactions of HFO-1234yf pyrolysis including CC cleavage, CH cleavage and CF cleavage starts at 2100K and then release free radicals (CF3, F and H). The oxidation reaction starts at 2500K and numerous intermediates (H2O, CF3OH and FCOOH) are produced. The main products observed from simulation are HF, COF2 and CO2 and these products agree with the result of related experiments. Ten formation pathways of primary products are observed from ReaxFF. The concentrations of free radicals (FCOO, F, H, HOO and OH) have a great impact on the reaction activity of HFO-1234yf oxidation. The chain transfer process is primarily carried by the conversion from HOO to OH radical. Our work presents the decomposition mechanisms of HFO-1234yf with O2 from the molecule level and provides a reference for the study of the thermal stability of organic working fluids.

A simple method to control glycolytic flux for the design of an optimal cell factory

BackgroundA microbial cell factory with high yield and productivity are prerequisites for an economically feasible bio-based chemical industry. However, cell factories that show a kinetic imbalance between glycolysis and product formation pathways are not optimal. Glycolysis activity is highly robust for survival in nature, but is not optimized for chemical production.ResultsHere, we propose a novel approach to balance glycolytic activity with the product formation capacity by precisely controlling expression level of ptsG (encoded glucose transporter) through UTR engineering. For various heterologous pathways with different maximum production rates, e.g., n-butanol, butyrate, and 2,3-butanediol, glycolytic fluxes could be successfully modulated to maximize yield and productivity, while minimizing by-product formation in Escherichia coli.ConclusionsThese results support the application of this simple method to explore the maximum yield and productivity when designing optimal cell factories for value-added products in the fields of metabolic engineering and synthetic biology.

Navigating Past a Fork in the Road: Carbocation-π Interactions Can Manipulate Dynamic Behavior of Reactions Facing Post-Transition-State Bifurcations.

Dynamics calculations are described for carbocation rearrangements involving product-forming pathways with post-transition-state bifurcations. We show that noncovalent interactions with associated benzene rings (a simple model of aromatic amino acid side chains) can switch inherent dynamical tendencies for competing modes of disrotation, establishing that meaningful changes in dynamically controlled product selectivity can be achieved with few weak noncovalent interactions.

Non-oxidative dehydrogenation of propane, n-butane, and isobutane over bulk ZrO2-based catalysts: effect of dopant on the active site and pathways of product formation

Non-oxidative dehydrogenation (DH) of propane, n-butane, and isobutane was investigated over bare ZrO2 and binary MZrOx (M = Li, Ca, Mg, Y, Sm or La) materials.

A DFT Mechanistic Study on Ethylene Tri- and Tetramerization with Cr/PNP Catalysts: Single versus Double Insertion Pathways.

The mechanism of ethylene trimerization and tetramerization with a chromium-diphosphinoamine (Cr-PNP) catalyst system has been studied by theoretical (DFT) methods. Two representative ligands have been explored, namely Ph2 PN(Me)PPh2 and (o-MeC6 H4 )2 PN(Me)P(o-MeC6 H4 )2 . Calculations on the former ligand reveal how a combination of single and double ethylene insertion mechanisms may lead to 1-hexene, 1-octene and the major side products (cyclopentanes and n-alkanes). For the latter ligand, introduction of o-alkyl substitution leads to a more sterically congested active species, which suppresses the available pathways for tetramerization and side product formation. Hence, the high selectivity of o-aryl substituted PNP ligands for trimerization can be rationalized.