Reaction Of C2 Research Articles

Investigation of thermal and magnetic properties of [MSalen/Saloph] (M = Cr3+, Fe3+ or Co3+) capped dinuclear complexes of two novel tetraoxocalix[2]arene[2]triazine ligands

In this study, tetraoxocalix[2]arene[2]triazine compound as starting compound codded as C1 was synthesized by reacting of 2,4,6-trichloro-1,3,5-triazine with methyl-3,5-dihydroxybenzoate in two stages. s-Triazine bridged calixarene ligands as target ligands, which we coded as C2 and C3, were obtained from the reaction of C1 coded compound with 4-aminobenzoic acid or 4-hydroxybenzoic acid at 1:2 mole ratio, respectively. [MSalen/Saloph] capped benzoic acid substitute tetraoksocalix[2] aren[2]triazine complexes were obtained from the reaction of C2 or C3 codded ligand with [(MSalen/Saloph)2O] (M=Cr3+, Fe3+ and Co3+) starting complexes in 1,4-dioxane media. The ligands obtained were characterized by using 1HNMR , FT-IR spectroscopy and elemental analysis techniques. The complexes obtained were characterized by using FT-IR, UV–vis spectroscopies, elemental analysis, magnetic susceptibility, and TGA-DTA techniques. Metal contents of the complexes were determined by using ICP-OES spectroscopy.

Tandem Hydrodeoxygenation Catalyst System for Hydrocarbons Production from Simulated Bio-oil: Effect of C–C Coupling Catalysts

Research in the sustainable conversion of biomass to fuels and chemicals is a necessity for the reduction of the carbon footprint in transport energy. Herein, we demonstrate an efficient tandem catalyst to selectively convert (simulated) bio-oil to hydrocarbons with enhanced C4+ fuel yield in a fixed bed reactor of a small pilot plant. The tandem catalytic system is a multifunctional dual bed system; carbon coupling catalysts (0.2 wt % X-TiO2(X: Ru, Pd, Au) at the upper layer and hydro-deoxygenation (Ru-MoFeP/Al2O3) at the bottom layer in a single fixed bed reactor. The upper-bed catalysts facilitated the carbon coupling reaction of C2–C4 light oxygenates and significantly reduced the light gases yield (C1–C5) to ca. 40% and increased the organic (C4+) phase ca. 15%. The analysis of the organic phase suggests that among the screened upstream catalysts, 0.2 wt % Ru/TiO2||Ru-MoFeP/Al2O3 recorded the optimum activity. The coupled light oxygenates (acetone) alkylated with the phenolic compounds and sequentially hydro-deoxygenated to yield higher C4+ hydrocarbons. This versatile tandem catalytic approach has a potential application in the emerging biorefinery concept.

Synthesis of Vinylene‐Linked Two‐Dimensional Conjugated Polymers via the Horner–Wadsworth–Emmons Reaction

In this work, we demonstrate the first synthesis of vinylene‐linked 2D CPs, namely, 2D poly(phenylenequinoxalinevinylene)s 2D‐PPQV1 and 2D‐PPQV2, via the Horner–Wadsworth–Emmons (HWE) reaction of C 2‐symmetric 1,4‐bis(diethylphosphonomethyl)benzene or 4,4′‐bis(diethylphosphonomethyl)biphenyl with C 3‐symmetric 2,3,8,9,14,15‐hexa(4‐formylphenyl)diquinoxalino[2,3‐a:2′,3′‐c]phenazine as monomers. Density functional theory (DFT) simulations unveil the crucial role of the initial reversible C−C single bond formation for the synthesis of crystalline 2D CPs. Powder X‐ray diffraction (PXRD) studies and nitrogen adsorption‐desorption measurements demonstrate the formation of proclaimed crystalline, dual‐pore structures with surface areas of up to 440 m2 g−1. More importantly, the optoelectronic properties of the obtained 2D‐PPQV1 (Eg=2.2 eV) and 2D‐PPQV2 (Eg=2.2 eV) are compared with those of cyano‐vinylene‐linked 2D‐CN‐PPQV1 (Eg=2.4 eV) produced by the Knoevenagel reaction and imine‐linked 2D COF analog (2D‐C=N‐PPQV1, Eg=2.3 eV), unambiguously proving the superior conjugation of the vinylene‐linked 2D CPs using the HWE reaction.

Photochemical degradation characteristics of alga-sourced dissolved organic matter in Chaohu Lake, China

Abstract Abundant algae-sourced dissolved organic matter (A-DOM) is produced during algal blooms in eutrophic lakes. Natural-light-driven photodegradation plays an important role in A-DOM function and its migration in aqueous systems. The photodegradation performance of A-DOM extracted from Chaohu Lake was tested and characterized under UV-A, UV-C irradiation, and dark condition, and the photochemical degradation characteristics and molecular weight changes of A-DOM during degradation were analyzed. A-DOM mainly includes four EEM-PARAFAC components, namely, C1 (protein-like tryptophan), C2 (protein-like tyrosine), C3 (long-wave humus), and C4 (short-wave humus). After irradiation for 168 h under UV-C, the protein-like components C1 and C2 had the highest fluorescence intensity reduction of 95.4% and 100%, respectively. The fluorescence intensities of fulvic-like components, namely C3 and C4, increased. The absorption coefficients (A355) of A-DOM were decreased by 84.46%, 70.83%, and 52.98% with UV-A, UV-C irradiation, and dark condition, respectively. The degradation reaction of C1 and C2 fitted with the first-order kinetic equation with a half-life of 21.59–83.51 h. The SUVA254 value decreased under UV irradiation and increased under dark condition, which is in accordance with the change of molecular weight results. The A-DOM photochemical reaction was driven by UV light irradiation, and the humification rate and molecular weight decreased.

Insight into the Mechanism of Ethylene Decomposition Over Co(0001) Surface: Formation of Carbon Species

Ethylene decomposition over Co(0001) surface has been systematically studied by spin-polarized density functional theory calculations aiming to investigate the detail mechanism at the atomic level. All C–H bond and C–C bond scission reactions were computed and all the intermediates were considered. It is concluded that the C–H bond breaking reaction is always advantageous for a species possessing both C–H scission and C–C scission modes. C2 cluster is practicable formed during ethylene decomposition, which is coincide with experiment results. However, the high activated barrier blocks the C–C bond scission reaction of C2. After comparative analysis, two pathways of C2 cluster formation and two pathways of carbon monomer formation were proposed. These results provide novel information on ethylene decomposition over Co(0001), deepening our understanding of relevant catalytic reactions such as the carbon deposition and initial path to graphene formation.

Rate constants of the reaction of C2–C4 peroxy radicals with OH radicals

The rate constants for the reaction of three peroxy radicals with OH have been measured using different precursors. Peroxy radicals have been prepared by either the reaction of Cl-atoms with C2H6, C3H8 and n-C4H10 or through photolysis of the corresponding alkyliodide. Using Cl-atoms, the following rate constants have been measured:C2H5O2+OH→productsk1=(1.3±0.3)×1010cm3s-1C3H7O2+OH→productsk2=(1.4±0.3)×1010cm3s-1C4H9O2+OH→productsk3=(1.5±0.3)×1010cm3s-1Experiments using 248nm photolysis of the corresponding alkyliodides as precursor enhances the rate constants by a factor of two, bringing up the suspicion of a fast reaction between I-atoms and OH radicals.

A Single-Site Mutation at Ser146 Expands the Reactivity of the Oxygenase Component of p-Hydroxyphenylacetate 3-Hydroxylase

The oxygenase component (C2) of p-hydroxyphenylacetate (4-HPA) 3-hydroxylase (HPAH) from Acinetobacter baumannii catalyzes the hydroxylation of various phenolic acids. In this report, we found that substitution of a residue close to the phenolic group binding site to yield the S146A variant resulted in an enzyme that is more effective than the wild-type in catalyzing the hydroxylation of 4-aminophenylacetate (4-APA). Product yields for both wild-type and S146A enzymes are better at lower pH values. Multiple turnover reactions of the wild-type and S146A enzymes indicate that both enzymes first hydroxylate 3-APA to give 3-hydroxy-4-aminophenylacetate (3-OH-4-APA), which is further hydroxylated to give 3,5-dihydroxy-4-aminophenylacetate, similar to the reaction of C2 with 4-HPA. Stopped-flow experiments showed that 4-APA can only bind to the wild-type enzyme at pH 6.0 and not at pH 9.0, while it can bind to S146A under both pH conditions. Rapid-quench flow results indicate that the wild-type enzyme has low reactivity toward 4-APA hydroxylation, with a hydroxylation rate constant (kOH) for 4-APA of 0.028 s-1 compared to 17 s-1 for 4-HPA, the native substrate. In contrast, for S146A, the hydroxylation rate constants for both substrates are very similar (2.6 s-1 for 4-HPA versus 2.5 s-1 for 4-APA). These data indicate that Ser146 is a key catalytic residue involved in optimizing C2 reactivity toward a phenolic compound. Removing this hydroxyl group expands C2 activity toward a non-natural aniline substrate. This understanding should be helpful for future rational engineering of other two-component flavin-dependent monooxygenases that have this conserved Ser residue.

Cover Picture: Non‐Oxidative Dehydrogenation Pathways for the Conversion of C2–C4 Alcohols to Carbonyl Compounds (ChemSusChem 23/2015)

The cover picture shows the utility of gold nanoparticles deposited on hydrotalcite (Au/HT) for the continuous gas-phase non-oxidative dehydrogenation reaction of bioderived C2–C4 alcohols to the respective carbonyl compounds and hydrogen. This study provides experimental evidence that the catalytic activity and selectivity of Au/HT catalysts depends critically on the temperature at which the support is pre-treated and the size of Au nanoparticles. Oxidant-free dehydrogenation reaction of alcohols is an attractive, atom-efficient alternative to conventional stoichiometric oxidation using toxic and expensive oxidants. The carbonyl compounds produced can serve as building blocks for the production of drop-in biofuels and biochemicals through condensation pathways. More details can be found in the Communication by S. Shylesh et al. on page 3959 in Issue 23, 2015 (DOI: 10.1002/cssc.201500786).

Non‐Oxidative Dehydrogenation Pathways for the Conversion of C2–C4 Alcohols to Carbonyl Compounds

AbstractInvited for this month′s cover is the group of Alexis T. Bell at The University of California, Berkeley in Berkeley, California. The image shows the utility of gold nanoparticles deposited on hydrotalcite (Au/HT) for the continuous gas‐phase non‐ oxidative dehydrogenation reaction of bioderived C2–C4 alcohols to the respective carbonyl compounds and hydrogen. The Communication itself is available at 10.1002/cssc.201500786.

ChemInform Abstract: Platinum‐Catalyzed Domino Reaction with Benziodoxole Reagents for Accessing Benzene‐Alkynylated Indoles.

AbstractA novel domino cyclization process for the synthesis of C5‐ or C6‐alkynylated indoles is developed using the reaction of C2‐ or C3‐substituted pyrroles with a hypervalent iodine alkynylating agent.

Dynamics of the reaction of C2 with C6H2: an implication for the formation of interstellar C8H.

The reaction C2 + C6H2 → C8H + H was investigated for the first time. Reactant C2 (C6H2) was synthesized from 1% C3F6/He (5% C2H2/He) by pulsed high-voltage discharge. We measured the translational-energy distribution, the angular distribution, and the photoionization spectrum of product C8H in a crossed molecular-beam apparatus using synchrotron vacuum-ultraviolet ionization. This reaction released average translational energy of 8.5 kcal mol(-1) corresponding to a fraction of 0.37 in translation. C8H was identified as octatetranyl based on the maximal translational-energy release 23 ± 2 kcal mol(-1) and the ionization threshold 8.9 ± 0.2 eV. Kinematic constraints can qualitatively account for the nearly isotropic angular distribution. The quantum-chemical calculations indicate that the exothermic reactions C2 (X (1)Σg (+)/a (3)Πu) + HC6H → C8H + H can proceed without entrance and exit barriers, implying the importance in the cold interstellar medium. This work verifies that interstellar C8H can be formed through the C2 + C6H2 reaction.

Room temperature polymerization of norbornene with a hydride-bridged dinuclear ruthenium complex system

A two-component system, [Ru(p-cymene)Cl2]2 (C1)/BH3•NMe3, allows for the catalytic ring-opening metathesis polymerization (ROMP) of norbornene at 60°C. A hydride-bridged complex isolated from the two-component system, [RuCl(p-cymene)]2(μ-H)(μ-Cl) (C2), is also active in the ROMP reaction, albeit at a reduced rate. Abstraction of one chloride ligand from C2, by the reaction with 1equiv of either AgPF6 or AgSbF6, leads to the generation of either [{Ru(p-cymene)}2(μ-H)(μ-Cl)2]PF6 (C3) or [{Ru(p-cymene)}2(μ-H)(μ-Cl)2]SbF6 (C4) and further reduction of ROMP activity. Importantly, a reaction of C2 with 2equiv each of AgSbF6 and BH3•NMe3 provides the ability to achieve room temperature ROMP of norbornene. Various hydride-bridged dinuclear ruthenium complexes have been observed in the room temperature system based on 1H NMR analysis. An independent synthesis of a complex mixture containing [{Ru(p-cymene)}2(μ-H)3]PF6 (C5) and a single-component complex [{Ru(η6-C6Me6)}2(μ-H)3]PF6 (C6) rules out the catalytic capacity of this tri-μ-hydrido species. A di-μ-hydrido complex, [{Ru(p-cymene)}2(μ-H)2(μ-Cl)]PF6 (C7), is therefore postulated to act as the ROMP reaction center at room temperature.

Product-controlled steady-state kinetics between cytochrome aa3 from Rhodobacter sphaeroides and equine ferrocytochrome c analyzed by a novel spectrophotometric approach

Cytochrome c oxidase (CcO) catalyzes the reduction of molecular oxygen to water using ferrocytochrome c (cyt c2+) as the electron donor. In this study, the oxidation of horse cyt c2+ by CcO from Rhodobacter sphaeroides, was monitored using stopped-flow spectrophotometry. A novel analytic procedure was applied in which the spectra were deconvoluted into the reduced and oxidized forms of cyt c by a least-squares fitting method, yielding the reaction rates at various concentrations of cyt c2+ and cyt c3+. This allowed an analysis of the effects of cyt c3+ on the steady-state kinetics between CcO and cyt c2+. The results show that cyt c3+ exhibits product inhibition by two mechanisms: competition with cyt c2+ at the catalytic site and, in addition, an interaction at a second site which further modulates the reaction of cyt c2+ at the catalytic site. These results are generally consistent with previous reports, indicating the reliability of the new procedure. We also find that a 6×His-tag at the C-terminus of the subunit II of CcO affects the binding of cyt c at both sites. The approach presented here should be generally useful in spectrophotometric studies of complex enzyme kinetics. This article is part of a Special Issue entitled: 17th European Bioenergetics Conference (EBEC 2012).

Direct ab initio dynamics study of the reaction of C2(A3Πu) with CH4

AbstractThe reaction of C2(A3Πu) with CH4 has been investigated over a wide temperature range 200–3,000 K by direct ab initio dynamics method at the BMC‐CCSD//BB1K/6‐311+G(2d,2p) level of theory. The optimized geometries and frequencies of the stationary points are calculated at the BB1K/6‐311+G(2d,2p) level, and then the energy profiles of the reactions are refined using the BMC‐CCSD method. The activation barrier height for H‐abstraction reaction was calculated to be 4.44 kcal/mol in temperature range (337–605 K), and the electron transfer behavior was also analyzed by quasi‐restricted molecular orbital method in detail. The canonical variational transition‐state theory (CVT) with the small curvature tunneling (SCT) correction method is used to calculate the rate constants over a wide temperature range 200–3,000 K. The theoretical results shows that variational effect is to some extent large in lower temperature range, and small curvature and tunneling effect play important roles to the H‐atom abstraction only at lower temperatures. The CVT/SCT rate constants are in good agreement with the available experimental results. Our theoretical study is expected to provide a direct insight into the reaction mechanism and may be useful for estimating the kinetics of the title reaction over a wide temperature range where no experimental data are available so far. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012

Reaction of C2(a Π3u) with methanol: Temperature dependence and deuterium isotope effect

Bimolecular rate constants for the gas-phase reactions of C2(a Π3u) with a variety of methanol isotopomers including CH3OH (k1), CH3OD (k2), CD3OH (k3), and CD3OD (k4) have been measured over the temperature range of 293–673 K by means of pulsed laser photolysis/laser-induced fluorescence technique. The rate constants, in units of cm3 molecule−1 s−1, can be fitted by the normal Arrhenius expressions: k1(T)=(1.32±0.02)×10−11 exp[−(366.80±4.44)/T], k2(T)=(1.34±0.02)×10−11 exp[−(376.86±5.09)/T], k3(T)=(1.09±0.02)×10−11 exp[−(640.00±7.23)/T], and k4(T)=(1.12±0.01)×10−11 exp[−(666.37±4.63)/T], where all error estimates are ±2σ and represent the precision of the fit. The observed deuterium kinetic isotope effects, k1/k2 and k1/k3, along with the positive temperature dependences of k(T), allow us to reach a conclusion that the reaction of C2(a Π3u) with methanol in 293–673 K proceeds via a site-specific hydrogen abstraction mechanism, that is, H-atom abstraction from the methyl site rather than from the hydroxyl site dominating reactivity.

Rate Constants and Kinetic Isotope Effects on the Reaction of C2(X1Σg+) with CH4 and CD4

Rate constants and kinetic isotope effect (KIE) for the reaction of singlet dicarbon, C(2)(X(1)Sigma(g)(+)), with CH(4) and CD(4) have been measured over the temperature range 294-376 K by using the pulsed laser photolysis/laser-induced fluorescence technique. C(2)(X(1)Sigma(g)(+)) were generated by multiphoton laser decomposition of C(2)Cl(4) at 248 nm and its decay trace was monitored on the (0,0) band of the Mulliken system at 231.2 nm. Measured rate constants showed slightly positive temperature dependence, whereas the KIE [= k(CH(4))/k(CD(4))] was almost independent of temperature and the value of which was 2.1 +/- 0.2 as a simple average of the values of KIE at different temperatures. Quantum chemical calculation with CASPT2 method indicated that the reaction proceeds via a direct hydrogen abstraction mechanism to form C(2)H and CH(3) radicals. Variational transition-state theory calculations were performed employing a dual-level method. Anharmonic effects along transitional modes were included in the calculation, and a comparison of the rate constants with and without anharmonic corrections demonstrated the importance of anharmonicity. The calculated rate constants and KIE showed good agreement with the experiments except for the temperature dependence of the KIE. A possible cause of the discrepancy was discussed in terms of the long-range interaction between the reactants.

Synthesis of isoalkanes over Fe–Zn–Zr/HY composite catalyst through carbon dioxide hydrogenation

The reaction path of isoalkanes formation via CO2 hydrogenation was studied over the Fe–Zn–Zr/HY composite catalyst, which gives high selectivity to isoalkanes. The results indicate that the reverse water–gas shift reaction is not the indispensable step for the synthesis of hydrocarbons. And i-C4 (iso-butane) is formed from propylene and methanol through MTG (methanol to gasoline) reaction and i-C5 (iso-pentane) obtained from the reaction of C2 and C3 through the additive dimerization. A part of C1, C4 is formed on the sole Fe–Zn–Zr catalyst from methanol for the CO2 hydrogenation over Fe–Zn–Zr/HY composite catalyst.

Structural and Reactivity Properties of Finite Length Cap-Ended Single-Wall Carbon Nanotubes

The reaction of C2 with growing single-wall carbon nanotubes of different chiralities is investigated using density functional theory. It is found that the energy of the frontier orbitals for (5,5) and (6,6) armchair carbon nanotubes exhibits periodic behavior with an increasing number of carbon atoms in the nanotube. Such periodic behavior induces oscillations in the reaction energy released by adsorption of C2 to the nanotube open edge. In contrast, the energy of the frontier orbitals of the (6,5) chiral tube remains constant as the number of C atoms increases, and the same stability is observed in the adsorption energy. It is suggested that this may be one of the reasons for the low percent of armchair single-wall carbon nanotubes found in the experimental synthesis.

An Experimental Study of the Intersystem Crossing and Reactions of C2(XΣg+) and C2(a3Πu) with O2 and NO at Very Low Temperature (24−300 K)

A low-temperature gas-phase kinetics study of the reactions and collisional relaxation processes involving C2(X1Sigma(g)+) and C2(a3Pi(u)) in collision with O2 and NO partners at temperatures from 300 to 24 K is reported. The experiments employed a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) apparatus to attain low temperatures. The C2 species were created using pulsed laser photolysis at 193 nm of mixtures containing C2Cl4 diluted in N2, Ar, or He carrier gas. C2(X1Sigma(g)+) molecules were detected via pulsed laser-induced fluorescence in the (D1Sigma(u)+ <-- X1Sigma(g)+) system, and C2(a3Pi(u)) molecules were detected via pulsed laser-induced fluorescence in the (d 3Pi(g) <-- a 3Pi(u)) system. Relaxation of 3C2 by intersystem crossing induced by oxygen was measured at temperatures below 200 K, and it was found that this process remains very efficient in the temperature range 50-200 K. Reactivity of C2(X1Sigma(g)+) with oxygen became very inefficient below room temperature. Using these two observations, it was found to be possible to obtain the C2(X1Sigma(g)+) state alone at low temperatures by addition of a suitable concentration of O2 and then study its reactivity with NO without any interference coming from the possible relaxation of C2(a3Pi(u)) to C2(X1Sigma(g)+) induced by this reagent. The rate coefficient for reaction of C2(X1Sigma(g)+) with NO was found to be essentially constant over the temperature range 36-300 K with an average value of (1.6 +/- 0.1) x 10(-10) cm3 molecule(-1) s(-1). Reactivity of C2(a3Pi(u)) with NO was found to possess a slight negative temperature dependence over the temperature range 50-300 K, which is in very good agreement with data obtained at higher temperatures.

Optical Emission Study of RF Thermal Plasma During Fullerene Synthesis

Results on studies of molecular spectra emitted in the initial stages of fullerene synthesis during processing of graphite powder in RF thermal plasma conditions are presented in this work. CN—usually present in carbon plasmas—and C2 were found as dominant molecular species. The role of CN radicals on the fullerene formation was discussed in detail. Intensities of CN and C2 lines were studied against the composition of gas phase and the feed rate of graphite powder. The rotational‐vibrational temperatures of CN species were calculated by fitting the experimental spectra to the simulated ones. It was concluded that in the plasma region CN radicals could be formed by the reaction of C2 with atomic nitrogen at smaller loads. This reaction lowered the yield of fullerenes. At larger loads, C2 formation was decreased due to lower temperature of the particles compared to smaller load. The CN radicals were produced by the surface reaction of the hot carbon particles with nitrogen atoms. Results confirmed that for effective fullerene synthesis, the nitrogen content of the precursors and the plasma gases should be minimized.