Addition Of Alkynes Research Articles

NH2OH Disproportionation Mediated by Anaerobic Ammonium-oxidizing (Anammox) Bacteria.

Anammox bacteria produce N2 gas by oxidizing NH4+ with NO2–, and hydroxylamine (NH2OH) is a potential intermediate of the anammox process. N2 gas production occurs when anammox bacteria are incubated with NH2OH only, indicating their capacity for NH2OH disproportionation with NH2OH serving as both the electron donor and acceptor. Limited information is currently available on NH2OH disproportionation by anammox bacteria; therefore, the stoichiometry of anammox bacterial NH2OH disproportionation was examined in the present study using 15N-tracing techniques. The anammox bacteria, Brocadia sinica, Jettenia caeni, and Scalindua sp. were incubated with the addition of 15NH2OH, and the production of 15N-labeled nitrogenous compounds was assessed. The anammox bacteria tested performed NH2OH disproportionation and produced 15-15N2 gas and NH4+ as reaction products. The addition of acetylene, an inhibitor of the anammox process, reduced the activity of NH2OH disproportionation, but not completely. The growth of B. sinica by NH2OH disproportionation (–240.3‍ ‍kJ mol NH2OH–1 under standard conditions) was also tested in 3 up-flow column anammox reactors fed with 1) 0.7‍ ‍mM NH2OH only, 2) 0.7‍ ‍mM NH2OH and 0.5‍ ‍mM NH4+, and 3) 0.7‍ ‍mM NH2OH and 0.5‍ ‍mM NO2–. NH2OH consumption activities were markedly reduced after 7‍ ‍d of operation, indicating that B. sinica was unable to maintain its activity or biomass by NH2OH disproportionation.

Metal-Free Synthesis of N-Vinyl Sulfoximines Via Dabco-Participated Micheal Addition of Terminal Carbonyl Alkynes with N-Chlorosulfoximines

Metal-Free Synthesis of N-Vinyl Sulfoximines Via Dabco-Participated Micheal Addition of Terminal Carbonyl Alkynes with N-Chlorosulfoximines

Photocatalytic Markovnikov-type addition and cyclization of terminal alkynes leading to 4-sulfonyl quinoline-2(1H)-ones.

A new and expedient photocatalytic protocol for the construction of quinolin-2(1H)-ones via Markovnikov-type sulfonylation/6-endo-trig cyclization/selective C(O)-CF3 bond cleavage starting from N-alkyl-N-(2-ethynylphenyl)-2,2,2-trifluoroacetamides and sulfinic acids has been developed. It is as an unprecedented protocol for the preparation of 4-sulfonylquinoline-2(1H)-ones with high efficiency, mild reaction conditions, acceptable yields and a wide range of substrates.

On the formation chemistry of brominated polycyclic aromatic hydrocarbons (BrPAHs)

Brominated polycyclic aromatic hydrocarbons (BrPAHs) have been consistently detected in various environmental matrices, and measured at alarming rates in stack emissions. However, formation mechanisms and bromination patterns of BrPAHs remain unclear. This contribution constructs detailed mechanistic pathways for the synthesis of selected BrPAHs (namely bromine-bearing naphthalene, acenaphthylene, anthracene, and phenanthrene). Mapped-out pathways follow the Bittner-Howard's route in the hydrogen abstraction acetylene addition (HACA) mechanism, in which a second C2HBr molecule is added to the first one. Constructed kinetic model portrays temperature-dependent profiles of major and minor species. Direct loss of an H atom from the acetylenic fragment appears to be more important at elevated temperatures, when compared with further addition of C2HBr cuts or ring-cyclization reactions. The occurrence of closed-shell Diels-Alder pathway should be inhibited owing to sizable enthalpic barriers. Fukui Indices for electrophilic substitutions (f−1) establish bromination’ s pattern of selected BrPAHs. The diradical character of BrPAHs coupled with electron-deficient C(Br) sites, render BrPAHs as potent precursors for the formation of environmentally persistent free radicals (EPFRs). Findings reported herein shall be useful in comprehending the formation chemistry of BrPAHs, a less-investigated category of toxicants in thermal systems.

An experimental and kinetic modeling study of benzene pyrolysis with C2−C3 unsaturated hydrocarbons

A combined experimental and kinetic modeling study is carried out to explore the influences of added acetylene, ethylene, propylene, and propyne on the reaction schemes of benzene pyrolysis. Pyrolysis of benzene with and without the presence of the C2- or C3- unsaturated hydrocarbons (HCs) is conducted in a single pulse shock tube coupled to gas chromatography-mass spectrometry technique. A minimum of 30 species is detected in each reaction system, and their mole fraction profiles are obtained over the temperature range 1030–1800 K at a nominal pressure of 20 bar and a nominal reaction time of 4 ms. With updates based on recent theoretical studies, our ongoing detailed kinetic model with 552 species and 4958 reactions can successfully reproduce the decomposition reactivity of the fuels, formation of decomposition products, and the growth of aromatics in the pyrolysis of different fuel mixtures. Various considerations apply to all studied binary mixtures. The addition of C2- and C3- HCs to the reaction system leads to C2H2 formation, and consequently promotes the HACA mechanism starting from phenyl radical (C6H5) at relatively low temperatures. The resulted phenylacetylene, formed through C6H5+C2H2 reaction, promotes the addition-elimination reaction C6H5C2H + C6H5 leading to the enhanced and early formation of all C14H10 PAH isomers including ethynyl biphenyl, methylene-fluorene, diphenylacetylene, phenanthrene, and anthracene. It is also noteworthy that the existence of C2H2 as fuel or its production from C2H4, C3H6, and C3H4-P decomposition results in numerous compounds with ethynyl branches such as ethynyl biphenyl, diethynyl naphthalene, and ethynyl acenaphthylene. Considering the specific features of the different fuel mixtures, the addition of acetylene intensifies the HACA route leading to greater acenaphthylene formation, while naphthalene formation remains similar to the pure benzene case due to the limited H-atoms. Differently, in benzene-C2H4 co-pyrolysis, naphthalene and acenaphthylene are mainly formed through reactions between PAH radicals (phenylacetylene radical and naphthyl radical, respectively) and ethylene. Concerning benzene-C3 co-pyrolysis, indene is the major C9 species resulting from the reaction of benzene/phenyl with C3 fuels. This is an important theoretical pathway to indene which is experimentally probed here for the first time. The high concentration of indene leads to the enhanced formation of naphthalene and acenaphthylene through the reactions of indenyl radical with methyl and propargyl (C3H3) radicals, respectively. Afterwards, the naphthyl radicals participate in the formation of several larger C11–13 PAHs such as methylnaphthalene, ethynylnaphthalene and fluorene through their reactions with CH3, C2H2 and C3H4-P/C3H3, respectively.

Microwave-assisted synthesis of benzo[b]phosphole oxide derivatives by oxidative addition of acetylenes and secondary phosphine oxides or alkyl phenyl-H-phosphinates

A new and practical microwave (MW)-assisted method was developed for the fast and efficient oxidative addition of secondary phosphine oxides or alkyl phenyl-H-phosphinates and acetylenes. The reaction was optimized in respect of the oxidative agent, the reaction time, the temperature and the molar ratio of the starting materials. The protocol developed enabled the synthesis of novel benzo[b]phosphole oxide derivatives under mild conditions for a short reaction time. By the use of special reagents, such as alkyl phenyl-H-phosphinates or ethyl phenylpropiolate, reactive groups (phosphinic acid ester and carboxylic ester) could be integrated into the benzophosphole skeleton, which may be further functionalized towards various synthetic directions, therefore, fine-tuning the optical properties of the target molecules. The crystal structure of a benzo[b]phosphole oxide derivative was investigated by X-Ray diffraction, which gave structural information about the compound and its molecular interactions in the crystal.

Reactive molecular dynamics simulations of soot formation in acetylene combustion with hydrogen addition

Soot emission from combustion devices not only reduces energy efficiency but also poses a serious risk to global warming and human health. The reactive molecular dynamics simulation is used to study the soot formation process of acetylene as the initial fuel and oxygen as the oxidant, and the chemical effect of hydrogen addition on the soot formation of acetylene combustion is deeply analyzed in this paper. The study found that: in addition to the hydrogen abstraction acetylene addition mechanism, it is also an important path that the long carbon chain aliphatic hydrocarbon with branched chain form polycyclic aromatic hydrocarbons by condensation after continuous dehydrogenation; the chemical effect of hydrogen addition linearly reduces the number of carbon in soot particles, the bond angle energy and torsion angle energy of soot, resulting in a smaller soot particle size and a sparse soot morphology. The shape of the soot gradually changes from a dense spindle-shaped structure to a sparse planar structure; the main chemical effect of hydrogen doping inhibits the dehydrogenation reaction of aliphatic hydrocarbons and aromatic hydrocarbons mainly through H + CaHb↔CaHb−1 + H2, thereby inhibiting the formation of polycyclic aromatic hydrocarbons and soot nucleation, ultimately leading to a reduction in soot production.

Simulating yield and morphology of carbonaceous nanoparticles during fuel pyrolysis in laminar flow reactors enabled by reactive inception and aromatic adsorption

Carbon black and soot are synthesized by gas-phase pyrolysis of hydrocarbons. Inception, surface growth, and coagulation control process yield and agglomerate morphology. Here, we present a sectional population balance model (SPBM) coupled with chemistry to simulate carbon black formation by ethylene pyrolysis in laminar flow reactors. The SPBM tracks agglomerate size distribution and morphology. New particles are formed by the dimerization of polycyclic aromatic hydrocarbons (PAHs) and grow with hydrogen abstraction acetylene addition as well as the addition of PAHs on their surface. Three different dimerization models for inception and PAH adsorption are compared: irreversible, reversible, and reactive. With irreversible PAH dimerization and surface growth, more than 90% of PAH mole fraction converts to particles even at low-temperatures (T<1200 K) causing an overestimation of the primary particle number density due to non-stop new particle formation. With reversible dimerization, the mass yield is underestimated by more than a factor of 3. With reversible dimerization and surface growth followed by a chemical bond formation step (chemical dimerization/reactive model), particles form and grow mostly at high temperatures (T>1200 K); the particle size distribution, as well as the average primary particle and mobility diameters are predicted within 30% of measurements. The reactive model enhances the agglomerate morphology prediction in the low-temperature regions of the reactor and appears to be more consistent with the latest understanding of inception and surface growth.

Cyclotrimerization of Acetylene under Thermal Conditions: Gas-Phase Kinetics of V+ and Fe+ + C2H2.

The kinetics of successive reactions of acetylene (C2H2) initiated on either vanadium or iron atomic cations have been investigated under thermal conditions using the variable-ion source and temperature-adjustable selected-ion flow tube apparatus. Consistent with the literature results, the reaction of Fe+ + C2H2 primarily yields Fe+(m/z = (C2H2)3); however, analysis via quantum chemical calculations and statistical modeling shows that the mechanism does not form benzene upon the third acetylene addition. The kinetics are more consistent with successive addition of three acetylene molecules, yielding Fe+(C2H2)3, followed by an addition of a fourth acetylene molecule, initiating cyclotrimerization, yielding either Fe+(C2H2) + neutral benzene or Fe+(Bz) + acetylene, where Bz is a benzene ligand. In contrast, the reaction of V+ + C2H2 yields products via successive associations V+(m/z = (C2H2)n) either with or without a bimolecular step involving loss of one H2 and V+C2(m/z = (C2H2)m), where n and m extend at least up to 11 under conditions of 0.32 Torr at 300 K. Stabilized V+(Bz) is not a significant intermediate in the association mechanism. We propose a plausible mechanism for the generation of neutral benzene in this reaction and compare with the Fe+ results. The reaction steps that produce benzene result in turnover of the single-atom catalyst, and the large hydrocarbons produced that remain associated to the catalyst are proposed to be polycyclic aromatic hydrocarbons.

Tribological Properties and Corrosion Resistance Properties of NbN/TiN Multilayer, TiNb-N&lt;sub&gt;X&lt;/sub&gt; Single-Layer and Coatings that are Doped with Carbon

NbN/TiN, TiNb-NX and CH-TiNb-N12 coatings are deposited by RF magnetron sputtering to determine the tribological properties and corrosion resistance. ‘x’ is the flux rate for nitrogen and ‘CH’ signifies the addition of acetylene. In terms of the corrosion resistance, all the coatings have a similar corrosion potential and NbN/TiN multilayer coatings exhibit the lowest corrosion current. The NbN/TiN multilayer has a low pitting potential so severe pitting corrosion is observed on the surface. CH-TiNb-N12 coating is most resistant to corrosion and exhibits no pitting before the test ends. In contact with counter-bodies with a Si3N4 ball or an AISI 52100 ball, a CH-TiNb-N12 coating acts as a solid lubricant so the wear mechanism shows the least abrasion. The CH-TiNb-N12 coating has the lowest wear rate and coefficient of friction for sliding against Si3N4 and AISI 52100 balls. The wear rate is respectively 3.2 and 6.8 times less than that for SKH51 substrate when sliding against Si3N4 and AISI 52100 balls. The results for this study show that a TiNb-N12-CH coating has the best tribological properties and corrosion resistance.

Direct Evidence on the Mechanism of Methane Conversion under Non‐oxidative Conditions over Iron‐modified Silica: The Role of Propargyl Radicals Unveiled

AbstractRadical‐mediated gas‐phase reactions play an important role in the conversion of methane under non‐oxidative conditions into olefins and aromatics over iron‐modified silica catalysts. Herein, we use operando photoelectron photoion coincidence spectroscopy to disentangle the elusive C2+ radical intermediates participating in the complex gas‐phase reaction network. Our experiments pinpoint different C2‐C5 radical species that allow for a stepwise growth of the hydrocarbon chains. Propargyl radicals (H2C−C≡C−H) are identified as essential precursors for the formation of aromatics, which then contribute to the formation of heavier hydrocarbon products via hydrogen abstraction–acetylene addition routes (HACA mechanism). These results provide comprehensive mechanistic insights that are relevant for the development of methane valorization processes.

Direct Evidence on the Mechanism of Methane Conversion under Non-oxidative Conditions over Iron-modified Silica: The Role of Propargyl Radicals Unveiled.

Radical‐mediated gas‐phase reactions play an important role in the conversion of methane under non‐oxidative conditions into olefins and aromatics over iron‐modified silica catalysts. Herein, we use operando photoelectron photoion coincidence spectroscopy to disentangle the elusive C2+ radical intermediates participating in the complex gas‐phase reaction network. Our experiments pinpoint different C2‐C5 radical species that allow for a stepwise growth of the hydrocarbon chains. Propargyl radicals (H2C−C≡C−H) are identified as essential precursors for the formation of aromatics, which then contribute to the formation of heavier hydrocarbon products via hydrogen abstraction–acetylene addition routes (HACA mechanism). These results provide comprehensive mechanistic insights that are relevant for the development of methane valorization processes.

Enantioselective Synthesis of the Sex Pheromone of Lichen Moth, Miltochrista calamine, and Its Diastereomer

AbstractThe synthesis of a Miltochrista calamine sex pheromone and its diastereomer has been developed. The key steps of the synthetic approach involved Evans’ chiral auxiliaries and the addition of alkyne to aldehyde, which were firstly applied to prepare this sex pheromone and its diastereomer. The synthetic sex pheromone could be used to trap insects and study physiological and ecological questions of the lichen moth.

Hydrogen and syngas production from methane-acetylene rich combustion in inert porous media burner

This work shows the experimental results from methane-acetylene rich combustion inside an inert porous media burner with the specific goal of improving the performance of inert porous media burners for hydrogen and syngas production. A cylindrical burner was implemented where temperatures, velocities, and chemical species concentrations were acquired for methane-air mixtures with acetylene addition at different equivalence ratios. Recorded combustion wave temperature profiles retain their sinusoidal like behavior for fuel-rich mixtures. Acetylene addition increases the temperature of the reaction and syngas production for a range of equivalence ratios. It is shown that by adding a small amount of acetylene (2.5% of the total fuel-air mixture), increments in the H2 production of up to 3.04% and 0.36% were achieved for ∅ = 1.2 and ∅ = 2.4, respectively. While an 11% increment on the CO production was recorded for ∅ = 1.2, which presents an opportunity to determine the optimized conditions. Methane-acetylene rich combustion showed improvements on hydrogen and syngas production when compared to methane-air rich mixtures.

Growth of Polycyclic Aromatic Hydrocarbons by C2H2 Mediated by Five-membered Rings: Acenaphthylene Conversion to Phenanthrene

ABSTRACT To investigate the role of five-membered rings in the growth of PAHs, the conversion of acenaphthylene to phenanthrene is studied using density functional theory and composite method. Two pathways are considered that initiate with H-abstraction from different sites on acenaphthylene and are followed by acetylene addition on the radical sites. The reactions in both pathways progress with the formation of two fused five-membered rings and H-migration reactions that eventually get converted to a six-membered ring to form either phenanthrene or phenanthryl radical. The reaction kinetics are calculated using RRKM theory, and the new reactions are added to a detailed hydrocarbon mechanism to test their effect on the profiles of phenanthrene and acenaphthylene. The flame simulations indicate that the phenanthrene concentration increases by 58% with the addition of the proposed reactions to the mechanism and helps in matching the experimental phenanthrene profile with the computed one. Thus, the pathways studied in this work can be considered to be important for phenanthrene formation.

B(C6F5)3-Catalyzed Sequential Additions of Terminal Alkynes to para-Substituted Phenols: Selective Construction of Congested Phenol-Substituted Quaternary Carbons.

We have developed a borane-catalyzed sequential addition of terminal alkynes to para-substituted phenols, which affords a wide range of ortho-propargylic alkylated phenols bearing congested quaternary carbons. Control experiments combined with DFT calculations suggest that the reaction undergoes a sequential phenol alkenylation/hydroalkynylation process. Further extension of this strategy to the construction of triaryl-substituted quaternary carbons demonstrates the broad utility of this method.

Concise total synthesis of antiarrhythmic drug dronedarone via a conjugate addition followed intramolecular heck cyclization

AbstractA concise, scalable, and an efficient total synthesis for dronedarone (2) was described using conjugate addition followed by intramolecular Heck cyclization. The other key reaction includes selective reduction of nitro functionality and addition of lithiated terminal alkyne to the aldehyde. The overall yield of this approach is 44% in six steps.

Visible Light‐Mediated Construction of Sulfonated Dibenzazepines

Main observation and conclusionA new method to access sulfonated dibenz[b,e]azepines via visible‐light photoredox catalysis is described. Employing inexpensive and commercially available sulfonyl chlorides to form the sulfonyl radicals enables the alkyne addition reaction followed by a 7‐membered radical cyclization step to furnish sulfonated dibenzazepines. In addition, an Ugi‐type multicomponent reaction (MCR) for the synthesis of o‐aminophenylacetylene derivatives can also be used as a rapid substrate synthesis method for the cascade radical cyclization protocol to obtain a series of highly functionalized sulfonylated dibenzazepines, which undoubtedly greatly simplifies the synthetic steps of the dibenzazepine compounds that are important core structures in pharmaceuticals.

Modeling soot formation in laminar coflow ethylene inverse diffusion flames

A numerical study is conducted using the CoFlame code to investigate the sooting characteristics of ethylene-fueled laminar coflow inverse diffusion flames (IDFs), aiming to gain insights into the different flame structure and soot formation features between an IDF and a normal diffusion flame (NDF). The effects of oxygen mole fraction in the oxidizer stream, denoted as Oxygen Index (OI), on flame structure and soot production are studied over the OI range of 21% to 33%. The soot model parameters were chosen to produce overall reasonably good agreement between the predicted and measured in terms of soot volume fraction, mean primary particle size, and the mean number of primary particles per aggregate in both the normal and inverse configurations. A sensitivity study showed that soot nucleation and soot surface growth by PAH adsorption modeling should be considered simultaneously as a strongly coupled process through competing for polycyclic aromatic hydrocarbons (PAHs). The IDF configuration displays distinct characteristics from the NDF one in terms of flame structure as well as soot production. In IDFs soot is formed along the outer edge of reaction front, and does not cross the reaction front to the oxidizer, decoupling completely soot oxidation which leads to soot emission from the open flame tip. Modeling results indicate that in the IDF configuration the hydrogen abstraction acetylene addition (HACA) process is severely suppressed, while the adsorption of PAH molecules is dominant to soot surface growth at relatively low temperatures. Nucleation of new particles is significant all along the flame height, causing emission of young soot. IDF represents an ideal configuration to study soot surface growth by PAH adsorption. Increasing OI enhances all the soot processes, especially surface growth by PAH adsorption. Although soot oxidation rate by OH radicals is also strongly enhanced, it remains about two orders of magnitude lower than soot surface growth rate by PAH adsorption.

Nitrate removal by anammox biomass with intracellular carbon source as electron donors via DNRA pathway

In this work, a novel nitrate (NO3−) reduction pathway by anaerobic ammonium oxidation (anammox) biomass was firstly discovered with the intracellular carbon sources as the only electron donors. And the possible reaction mechanism was deduced to be intracellular dissimilatory nitrate reduction to ammonium (DNRA) pathway according to the experimental results. In batch experiments, without any external electron donors, NO3−-N (about 50 mg/L) was reduced to N2 within 48 h, and a small amount of NO2−-N was detected (the maximum of 2 mg/L) with the anammox biomass concentration of 4400 mg/L. Acetylene (4.46 mmol/L) addition resulted in obvious NH4+ accumulation during NO3− degradation by anammox biomass, since acetylene mainly interfered in hydrazine (N2H4) generation from NH4+ and NO. Without HCO3− addition, the NO3−-N degradation rate was slower than that with HCO3− addition. Simultaneously, glycogen contents inside anammox biomass decreased to 133.22 ± 1.21 mg/g VSS and 129.79 ± 1.21 mg/g VSS with and without HCO3−, respectively, from 142.20 ± 0.61 mg/g VSS. In the long-term experiment, anammox biomass stably degraded NO3−-N without external electron donors addition, and the maximum removal efficiency of NO3−-N reached 55.4%. The above results indicated the anammox bacteria utilized the DNRA pathway to reduce NO3− to NO2− and further NH4+, then normal anammox metabolism would continue to convert the produced NO2− and NH4+ to N2. The intracellular stored carbon sources (e.g., glycogen) were supposed to be electron donors for NO3− degradation. This capability would enhance the viability and living space of anammox bacteria in different natural ecosystems, and make it plausible that complete nitrogen removal could be implemented only by the anammox process.