Structural Mimics of Acetylene Hydratase: Tungsten Complexes Capable of Intramolecular Nucleophilic Attack on Acetylene

Bioinspired complexes employing the ligands 6-tert-butylpyridazine-3-thione (SPn) and pyridine-2-thione (SPy) were synthesized and fully characterized to mimic the tungstoenzyme acetylene hydratase (AH). The complexes [W(CO)(C₂H₂)(CHCH-SPy)(SPy)] ( 4 ) and [W(CO)(C₂H₂)(CHCH-SPn)(SPn)] ( 5 ) were formed by intramolecular nucleophilic attack of the nitrogen donors of the ligand on the coordinated C₂H₂ molecule. Labelling experiments using C₂D₂ with the SPy system revealed the insertion reaction proceeding via a bis-acetylene intermediate. The starting complex [W(CO)(C₂H₂)(SPy)₂] ( 6 ) for these studies was accessed by the new acetylene precursor mixture [W(CO)(C₂H₂)_n(MeCN)_3−nBr₂] (n=1 and 2; 7 ). All complexes represent rare examples in the field of W−C₂H₂ chemistry with 4 and 5 being the first of their kind. In the ongoing debate on the enzymatic mechanism, the findings support activation of acetylene by the tungsten center.     

Reaction of Tribenzylaluminium with Acetylene

Acetylene reacts smoothly with tribenzylaluminium both by ‘normal’ addition to the Al? C bond and by aromatic substitution in ortho position; further addition reactions can take place.     

Theoretical Study of the Products of Acetylene Addition to HgCl2

The ab initio MP2 method is used with the LANL2DZ basis to calculate the mercury chloride ,-complex with two acetylene molecules (1) and various isomeric forms of mercury di()-vinyl chloride -complexes (2): cis-cis (2A), cis-trans (2B), and trans-trans (2C). The ,-complex is the most stable form of all those considered; the difference between 1 and 2A is 24.9 kcal/mole. A relation between the total energies (kcal/mole) for isomeric forms 2 is established to be 2A (0) < 2B (0.98) < 2C (1.58). Complex 1 is shown to be transformed into 2A via the intermediate formation of 3, which is a hybrid form of the complex (,-complex of mercury chloride with two acetylene molecules). The structures of the transition states for the transformations of 1 into 3 (structure 4) and of 3 into 2A (structure 5) and the corresponding transition activation energies are determined. The interaction of 2A, 2B, and 2C with the Cl^- anion as a model nucleophile is considered. It is shown that the resulting anions (6A, 6B, 6C) have a planar structure with the relative stability increasing in the series 6A<6B<6C.     

溶剂对钯催化的叔丁基乙炔低聚反应化学选择性的调控作用

报道了溶剂对钯催化的叔丁基乙炔低聚反应化学选择性的调控作用. 反应可在苯-正丁醇双组分溶剂体系中顺利进行, 当双组分溶剂体系中苯占优势比例时, 反应发生递次的三分子炔烃顺式插入, 经由顺式s-烯钯中间体生成环三聚产物1,3,5-三叔丁基苯; 而当双组分溶剂中正丁醇组分上升至一定比例, 反应选择性生成(3Z,5Z)-2,2,7,7-四甲基- 3,6-二氯-3,5-辛二烯或(3Z,5Z)-2,2,7,7-四甲基-3,6-二溴-3,5-辛二烯, 这是由于正丁醇可显著加快C—Pd σ键的断裂, 并与叔丁基乙炔、σ-烯钯中间体形成弱氢键作用力, 同时也与Pd(II)和Cu(II)等离子存在配位效应. 在强极性质子溶剂H₂O中, 反应生成偶联双炔: 2,2,7,7-四甲基-3,5-辛二炔. 文中就反应溶剂体系、钯铜催化剂及反应可能机理等分别进行了探讨.     

Acetylene Pyrolysis in Tubular Reactor

Pyrolysis of acetylene was investigated in a tubular reactor of graphite with an internal lining of alumina. The temperature range was 850–1650 °C, and the pressure was about 0.133 bar (100 Torr). Pure acetylene and acetylene diluted with argon or hydrogen were used as feed. Carbon and hydrogen are the main products from acetylene pyrolysis particularly at higher conversion. At lower conversion of acetylene, other gas products were formed; the amount of these depended on temperature, dilution, and conversion. Benzene and vinyl acetylene are the main gas products from pyrolysis of pure acetylene below 1000 °C and at low conversion. Diacetylene increases with increasing temperature. Dilution with hydrogen changes the composition of the gas product, decreases the selectivity of vinyl acetylene and benzene, and increases the formation of methane and ethylene. Gas‐phase equilibrium may be approached between some components. The conversion of acetylene with argon dilution and low conversion was found to be of second order. Pyrolysis of pure acetylene at lower temperature and low conversion gave the rate constant k = 3.1 × 10⁹ · exp(?34.8/RT) L mol^?1 s^?1 with an activation energy of 34.8 kcal mol^?1. The initial reaction at 864 °C is a molecular formation of vinyl acetylene. The initial activation of acetylene in gas phase seems to be rate determining and of second order in acetylene. Decomposition of acetylene can take place both homogeneously and heterogeneously. Above a critical partial pressure of acetylene, the decomposition is apparently explosive with instant plugging of the reactor with carbon.     

Acetylene; a new reducing agent used in scr of NO on zeolite catalysts in an oxygen-rich atmosphere

Summary Nanosized MnO_x-MO_y(M=Cu, V)-promoted sulfated yttria-stabilized zirconia-titania catalysts were synthesized and studied for propane activation and conversion. The derived catalysts are amorphous in general and the primary particle size of all the samples is ca. 10-30 nm. Elemental distributions are rather uniform throughout the catalysts. In a mixture of C₃H₈/He (v/v = 9.4/90.6) or C₃H₈/O₂/He (v/v/v = 12.5/6.3/81.2) and within the temperature range of 350-550°C, two major types of reactions occurred on the catalysts. One is oxidation yielding propenal, propanone, propanal as well as propenoic and propanoic acids; the other is carbon-carbon bond formation generating products such as butadiene and cyclopentadiene.</o:p>     

Anti‐Inflammatory Activity of a Novel Acetylene Isolated from the Roots of Angelica tenuissima Nakai

Three polyacetylenes, one novel and two known, were isolated from the root of Angelica tenuissima. Using ¹H‐ and ¹³C‐NMR, COSY, HMBC, and HMQC, their structures were found to be (3R,8S)‐heptadeca‐1‐en‐4,6‐diyne‐3,8‐diol ( 1 ), falcarindiol ( 2 ), and oplopandiol ( 3 ). Absolute configurations of compound 1 were established using Mosher's esterification. In addition, the polyacetylenes ( 1 – 3 ) were evaluated for their anti‐inflammatory activity. Compounds 1 and 3 showed potent inhibitory activity against lipopolysaccharide‐induced nitric oxide (NO) production in RAW267.7 macrophage cells with IC₅₀ values of 4.31 and 5.06 μm, respectively. Compound 1 strongly inhibited inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)‐2 in a concentration‐dependent manner.     

Acetylene diethers: Dineopentyloxyethyne

Dineopentyloxyethyne has been synthesized fromtrans-2,3-dichloro-1,4-dioxane according to a general procedure already described. In contrast with alkyl neopentyloxyacetylenes, RC=COCH₂Bu^t, which only polymerize when are strongly heated (150°), dineopentyloxyethyne is a kinetically unstable acetylene diether that polymerizes readily at room temperature. However, the compound has been trapped with Co₂(CO)₈ to give either the corresponding hexacarbonyl complex, m.p. 74–75°, or the cyclic trimer, m.p. 205–206°, depending upon the experimental conditions.     

Acetylene mit Elektronendonator und Elektronenakzeptorgruppen

Acetylenes having both electrondonating and electronaccepting groups ( 1 ) may be obtained in good yield from the correspondingly substituted olefines via bromination and elimination of HBr. The reaction of the acetylene aldehyde 1a with proton acids yields, after rearrangement of the primary adducts, the β-substituted acrylamides. Addition of nucleophiles leads to the β-disubstituted α.β-unsaturated carbonyl compounds. With hydrazines one obtains pyrazoles and pyrazolones. The acetylenes 1 undergo [2+2]-, [2+3]- and [2+4]-cycloaddition reactions.     

Absolute rate constant for the reaction of Phenyl radical with Acetylene

The absolute rate constant for the reaction of phenyl radical with acetylene has been measured at 20 torr total pressure in the temperature range of 297 to 523 K using the cavity-ring-down technique. These new kinetic data could be quantitatively correlated with the data obtained earlier with a relative rate method under low-pressure (10^?3–10^?2 torr) and high-temperature (1000–1330 K) conditions. These kinetic data were analyzed in terms of the RRKM theory employing the thermochemical and molecular structure data computed with the BAC-MP4 technique. The calculated results reveal that the total rate constant for the C₆H₅ + C₂H₂ reaction (k_t) is pressure-independent, whereas those for the formation of C₆H₅C₂H (k_b) and the C₆H₅C₂H₂ adduct (k_c) are strongly pressure-dependent. A least-squares analysis of the calculated values for 300–2000 K at the atmospheric pressure of N₂ or Ar can be given by and all in units of cm³/s. The latter equation effectively represents the two sets of experimental data. © 1994 John Wiley & Sons, Inc.     

Acetylene chemistry. Part 23 . N-vinylation on acridinones

The vinylation of 9(10H)-acridinones 1a-1d with propiolic acid ethylester resulting in acridinonyl-N-acrylic esters is reported.     

A New Thiophen Acetylene from Artemisia Absinthium

The investigation of the dried roots of A. absinthium afforded two known lignans of tetrahydrofuran skeleton, sesamin and yangambin, one known coumarin, 6‐methoxy‐7,8‐methylenedioxy coumarin and a new thiophen acetylene. The structures were elucidated by spectroscopic methods.     

Structural and Infrared Spectroscopic Study on Solvation of Acetylene by Protonated Water Molecules

The effect of solvation on the conformation of acetylene has been studied by adding one water molecule at a time. Quantum chemical calculations of the H⁺(C₂H₂)(H₂O)_n (n=1-5) clusters indicate that the H₂O molecules prefer to form the OH…π interaction rather than the CH…O interaction. This solvation motif is different from that of neutral (C₂H₂)(H₂O)_n (n=1-4) clusters, in which the H₂O molecules prefer to form the CH…O and OH…C H-bonds. For the H⁺(C₂H₂)(H₂O)_n cationic clusters, the first solvation shell consists of one ring structure with two OH…π H-bonds and three water molecules, which is completed at n=4. Simulated infrared spectra reveal that vibrational frequencies of OH…π H-bonded O-H stretching afford a sensitive probe for exploring the solvation of acetylene by protonated water molecules. Infrared spectra of the H⁺(C₂H₂)(H₂O)_n(n=1-5) clusters could be readily measured by the infrared photodissociation technique and thus provide useful information for the understanding of solvation processes.     

Intermetallic GaPd2 Thin Films for Selective Hydrogenation of Acetylene

The preparation of single-phase and catalytically active GaPd₂ coatings was accomplished via DC magnetron sputtering using an intermetallic sputter target. Thin and uniform layers were deposited on borosilicate glass, Si(111) and planar as well as micro-structured stainless steel foils. The specimens were examined regarding their phase composition, film morphology and microstructure. Thin films of different layer thickness were catalytically characterized in the semi-hydrogenation of acetylene, which was conducted at 473 K and a feed gas composition of 0.5 vol.% C₂H₂, 5 vol.% H₂ as well as 50 vol.% C₂H₄ in helium. Pre-reduction of the catalyst was found to be essential to enhance the catalytic selectivity. Sputtered GaPd₂ showed a high selectivity of 73 % for the hydrogenation to ethylene at conversion levels above 80 %. The surface-specific activity was strongly increased to 8.97 mol_acetylene · (A₀ · h)^–1 compared to bulk- or nanoscale GaPd₂ (1.93 and 0.30 mol_acetylene · (A₀ · h)^–1, respectively) caused by the high specific surface area of the thin films.     

Acetylene aggregates via cluster-building algorithm and molecular tailoring approach

Acetylene clusters are prototypical of simple non-aromatic systems bonded through C–H…π interactions. The present work explores structures and properties of acetylene clusters (C₂H₂) _n , n = 8 and 10, employing cluster-building algorithm and molecular tailoring approach (MTA). The former uses electrostatics guidelines for building (C₂H₂)₈ and (C₂H₂)₁₀ structures. These clusters are treated at MP2 level of theory with correlation-consistent basis sets using MTA. The Hessian matrix and vibrational spectra for the best five structures of (C₂H₂)₈ and (C₂H₂)₁₀ are computed employing MTA. Actual calculations on these clusters using conventional methods employing large basis sets are prohibitively difficult to perform. All the frequencies for these structures extracted using MTA-based Hessian matrix are found to be real, confirming their local minimum nature. This study points to the possibility of using the present approach for exploring structures, energetics and vibrational spectra of even larger clusters at higher levels of theory.     

Simulation‐Assisted Evaluation of Acetylene Effect on Macromolecular Crosslinking Rate under Polyethylene Irradiation

Gel content data on acetylene accelerated radiation crosslinking (R.A. Jones, J. Polym. Sci., Part B: Polym. Phys. 1994 , 32, 2049) have been used to illustrate a new method to determine macromolecular crosslinking and scission yields. The sol‐gel analysis data have been plotted as log(sol) versus log(dose) resulting in quite linear plots having different slopes. The linear approximations with the least squares method resulted in gel‐points with a high accuracy. Computer simulations have shown the plot slope to be dependent on relative rate of competitive macromolecular scission. The scission/crosslink ratios have been found from the plot slopes using simulation software GelSim6. As a result acetylene gas has been found to be accelerating both crosslinking and scission rates: 60 times and 130 times, respectively. Obviously, the radiation yield of radicals is increased due to acetylene inhibiting the recombination of primarily induced radicals in a cage.

Gel content vs. irradiation dose data plotted as log(sol) versus log(dose). Numbers near the curves indicate concentrations of acetylene gas (mmol · kg⁻¹).     

Chemistry of Anthracene–Acetylene Oligomers XXV: On‐Surface Chirality of a Self‐Assembled Molecular Network of a Fan‐Blade‐Shaped Anthracene–Acetylene Macrocycle with a Long Alkyl Chain

An anthracene cyclic dimer with two different linkers and a dodecyl group was synthesized by means of coupling reactions. The calculated structure had a planar macrocyclic π core and a linear alkyl chain. Scanning tunneling microscopy observations at the 1‐phenyloctane/graphite interface revealed that the molecules formed a self‐assembled monolayer that consisted of linear striped bright and dark bands. In each domain, the molecular network consisted of either Re or Si molecules that differed in the two‐dimensional chirality about the macrocyclic faces, which led to a unique conglomerate‐type self‐assembly. The molecular packing mode and the conformation of the alkyl chains are discussed in terms of the intermolecular interactions and the interactions between the molecules and the graphite surface with the aid of MM3 simulations of a model system.     

Acetylene chemistry,part 32: Alkinylation and cyclic rearrangement of theophylline with unsaturated alcohols by Mitsunobu reaction

Summary The reaction of theophylline (1) with 2-methyl-3-butyn-2-ol and 1-butyn-3-ol under Mitsunobu conditions gave the respective 9-substituted derivatives 9-[2-(2-methyl-3-butynyl)]-theophylline (2) and 9-[2-(3-butynyl)]-theophylline (3). On reaction with 2-methyl-3-buten-2-ol, theophylline yielded in addition to the 9-[2-(2-methyl-3-butenyl)]-theophylline (4), two more cyclic products, identified as 1,5,5a,8-tetrahydro-1,3,8,8-tetramethyl-2H-pyrrolo[1,2-e]purine-2,4(3H)-dione (5) and 8a,9-dihydro-1,3,6,6-tetramethyl-1H-pyrrolo[2,1-f]purine-2,4(3H,6H)-dione (7).

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Acetylenchemie, 32. Mitt.: Alkinylierung und cyclische Umlagerung von Theophyllin mit ungesättigten Alkoholen mittels Mitsunobu-Reaktion

Zusammenfassung Die Reaktion von Theophyllin (1) mit 2-Methyl-3-butin-2-ol und 1-Butin-2-ol unter Mitsunobu-Bedingungen führte zu den 9-substituierten Derivaten 9-[2-(2-Methyl-3-butinyl)]-theophyllin (2) bzw. 9-[2-(3-Butinyl)]-theophyllin (3). Bei der Reaktion mit 2-Methyl-3-buten-2-ol ergab Theophyllin außer 9-[2-(2-Methyl-3-butenyl)]-theophyllin (4) noch zwei weitere cyclisierte Produkte, die als 1,3,8,8-Tetramethyl-1,5,5a,8-tetrahydro-pyrrolo[1,2-e]purin-2,4(3H)-dion (5) und 1,3,6,6-Tetramethyl-8a,9-dihydro-1H,6H-pyrrolo[2,1-f]purin-2,4-dion (7) identifiziert wurden.

     

Acetylene adsorption on a clean iridium surface

The interaction of C₂H₂ with a polycrystalline iridium surface at 140 KT500 K has been studied by AES, XPS and UPS. A model of the bonding between C₂H₂ and Ir by the 1 orbitals of the hydrocarbon is proposed. The more pronounced energy splitting between the orbitals of acetylene during adsorption compared to that in the gas phase is ascribed to deformation of the acetylene molecule.

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C₂H₂ . 140 KT500 K AES, XPS UPS. C₂H₂ Ir 1- . - , , .