Alkyne Concentration Research Articles

Characteristics of volatile organic compounds in 11 cities along Taihang Mountain, an industrial region in Northern China

The cities along Taihang Mountain, one of the most important industrial regions in China, have faced challenges in atmospheric pollution control due to the development of industries. However, few studies have focused on the pollution characteristics of volatile organic compounds (VOCs) in this region. The concentrations, composition, sources, and chemical reactivity of VOCs were analyzed in 11 cities along Taihang Mountain. The average VOC concentration in the 11 cities (31.4 ± 11.3 ppbv) was higher than that for most cities in China, which was attributed to emissions from coal combustion and industrial processes. Four cities in Hebei province had the highest VOC concentration (32.9 ± 10.9 ppbv). Alkene (7.4 ± 3.9 ppbv) and alkyne (2.6 ± 1.9 ppbv) concentrations in the 11 cities were higher than those in other Chinese cities (2.4–5.9 and 1.0–3.8 ppbv, respectively). Shanxi Province had the largest contributions of alkenes (23.6%) and alkynes (9.7%). Based on the benzene/toluene (B/T) ratio, the 11 cities were divided into three categories: four had B/T ratios of 0.5–0.6, and were classified the “traffic” cities, and four with B/T ratios of 1.5–2.2 were classified as “coal combustion” cities. The chemical reactivity results showed that alkenes were the most important VOCs in terms of ozone formation. Coal combustion and industrial processes were the main emission sources affecting VOCs and O3 pollution in the 11 cities along Taihang Mountain. VOC researchers should pay more attention to this region, and more refined research should be conducted.

Scope of tetrazolo[1,5-a]quinoxalines in CuAAC reactions for the synthesis of triazoloquinoxalines, imidazoloquinoxalines, and rhenium complexes thereof.

The conversion of tetrazolo[1,5-a]quinoxalines to 1,2,3-triazoloquinoxalines and triazoloimidazoquinoxalines under typical conditions of a CuAAC reaction has been investigated. Derivatives of the novel compound class of triazoloimidazoquinoxalines (TIQ) and rhenium(I) triazoloquinoxaline complexes as well as a new TIQ rhenium complex were synthesized. As a result, a small 1,2,3-triazoloquinoxaline library was obtained and the method could be expanded towards 4-substituted tetrazoloquinoxalines. The compatibility of various aliphatic and aromatic alkynes towards the reaction was investigated and the denitrogenative annulation towards imidazoloquinoxalines could be observed as a competing reaction depending on the alkyne concentration and the substitutions at the quinoxaline.

In Situ Formation of an Efficient Catalyst for the Semihydrogenation of Alkynes from Imidazolone and BH3

We herein report the finding that a sterically encumbered imidazolone turns the simplest borane, i.e., BH3, into a potent catalyst for the semihydrogenation of alkynes. The efficiency of this catalyst system was demonstrated by the successful semihydrogenation of 15 different alkynes with excellent Z-selectivity. Kinetic studies show that the reaction rate depends on the alkyne concentration but is independent of the hydrogen pressure. Thus, the catalytic reaction can be operated at low hydrogen pressures (2 bar). Further mechanistic investigations and dispersion-corrected double-hybrid density functional theory (DFT) computations revealed that the imidazolone undergoes an initial protodeborylation with a tri-alkenylborane, formed in situ by hydroboration of the alkyne with BH3. The protodeborylation yields an imidazolonate borane that resembles a frustrated Lewis pair and is capable of activating dihydrogen.

Liquid-Phase Hydrogenation of 1-Phenyl-1-propyne on the Pd1Ag3/Al2O3 Single-Atom Alloy Catalyst: Kinetic Modeling and the Reaction Mechanism.

This research was focused on studying the performance of the Pd1Ag3/Al2O3 single-atom alloy (SAA) in the liquid-phase hydrogenation of di-substituted alkyne (1-phenyl-1-propyne), and development of a kinetic model adequately describing the reaction kinetic being also consistent with the reaction mechanism suggested for alkyne hydrogenation on SAA catalysts. Formation of the SAA structure on the surface of PdAg3 nanoparticles was confirmed by DRIFTS-CO, revealing the presence of single-atom Pd1 sites surrounded by Ag atoms (characteristic symmetrical band at 2046 cm−1) and almost complete absence of multiatomic Pdn surface sites (<0.2%). The catalyst demonstrated excellent selectivity in alkyne formation (95–97%), which is essentially independent of P(H2) and alkyne concentration. It is remarkable that selectivity remains almost constant upon variation of 1-phenyl-1-propyne (1-Ph-1-Pr) conversion from 5 to 95–98%, which indicates that a direct alkyne to alkane hydrogenation is negligible over Pd1Ag3 catalyst. The kinetics of 1-phenyl-1-propyne hydrogenation on Pd1Ag3/Al2O3 was adequately described by the Langmuir-Hinshelwood type of model developed on the basis of the reaction mechanism, which suggests competitive H2 and alkyne/alkene adsorption on single atom Pd1 centers surrounded by inactive Ag atoms. The model is capable to describe kinetic characteristics of 1-phenyl-1-propyne hydrogenation on SAA Pd1Ag3/Al2O3 catalyst with the excellent explanation degree (98.9%).

Adsorption separation of liquid-phase C5-C6 alkynes and olefins using FAU zeolite adsorbents

Isoprene is of great importance as a valuable monomer for most chemical industries owing to the increasing demand for synthetic rubber. To obtain polymer-grade olefins, the removal of alkyne compounds from isoprene is mandatory and challenging. Adsorption separation using zeolites is one of the most promising alternatives for alkyne/olefin separation. Herein, a combination of batch, fixed bed column experiments and configurational-bias grand canonical Monte Carlo (CB-GCMC) simulations was applied to study alkyne’s selective adsorption from binary liquid-phase isoprene/1-pentyne mixtures in faujasite (FAU) zeolites. The adsorption separation performance, including the adsorption capacity and selectivity, was obtained based on the liquid-phase measurement method developed in this study. FAU zeolites exhibited 218 mg/g alkyne adsorption capacity and relatively high adsorption selectivity at low alkyne concentrations. Liquid adsorption separation of linear alkyne/olefin mixtures, covering 1-pentyne/1-pentene (C5) and 1-hexyne/1-hexene (C6), in FAU zeolites, was performed further to investigate the separation performance for alkynes and olefins. The binary isotherms for the 1-pentyne/isoprene system and extended studied olefin/alkyne systems were reproduced well by CB-GCMC simulations. The visualized average occupation profiles of adsorbate molecules in FAU zeolites showed that alkyne and olefin molecules were mainly distributed near the 4-rings and 6-rings. The concentrated areas were arranged perpendicular to each other.

The Gold‐Catalyzed Hydroarylation of Alkynes with Electron‐Rich Heteroarenes – A Kinetic Investigation and New Synthetic Possibilities

AbstractThe gold‐catalyzed mono‐hydroarylation and two‐fold hydroarylation of alkynes with electron‐rich heteroarenes was analyzed by a 1H NMR kinetic study. The obtained rate constants for the decreasing alkyne concentration provide information on the reactivity of this addition reaction. The examinations show the orthogonal reactivity of gold and a proton for the two reaction steps. The first hydroarylation is exclusively promoted by gold(I), whereas the second step is premised on a proton which will be reversibly derived from the formation of σ,π‐acetylide complexes from the terminal alkynes or by interaction with solvents. Based on kinetic data, it was possible to synthesize a large range of mono‐adducts in moderate to good yields, furthermore the synthesis of hetero‐di‐adducts, bearing two different substituents, was explored.magnified image

Formation Kinetics and Scaling of “Defect-Free” Hyperbranched Polystyrene Chains with Uniform Subchains Prepared from Seesaw-Type Macromonomers

Using a facile approach, we successfully made large “defect-free” hyperbranched polystyrene (PSt) chains with uniform subchains between two branching points from the interchain “clicking” of a seesaw-type linear macromonomer [azide∼∼∼alkyne∼∼∼azide] prepared by ATRP with a following conversion of two bromine-ends into two azide-ends, where ∼∼∼ denotes a PSt chain (1.65–31.0 kg/mol). The “click” reaction kinetics monitored by a combination of size exclusion chromatography (SEC) and laser light scattering (LLS) reveals that the degree of self-polycondensation (DP) is related to the reaction time (t) as ln(DP+ 1)/2 = ([A]0kAB,0)/β arctan(βt), where [A]0 and kAB,0 are the initial alkyne concentration and the initial reaction rate between the azide and alkyne groups, respectively; β is a constant and its reciprocal (1/β) represents the time at which kAB = kAB,0/2. The results reveal that 1/β is scaled to the macromonomer’s molar concentration ([C]) and molar mass (M) as 1/β ∼ [C]−0.35M0.55, indicating that 1/β...

Lanthanide- and Actinide-Mediated Terminal Alkyne Hydrothiolation for the Catalytic Synthesis of Markovnikov Vinyl Sulfides

The Markovnikov-selective lanthanide- and actinide-mediated, intermolecular hydrothiolation of terminal alkynes by aliphatic, benzylic and aromatic thiols using Cp*2LnCH(TMS)2 (Cp* = C5Me5; Ln = La, Sm, Lu), Ln[N(TMS)2]3 (Ln = La, Nd, Y), Cp*2An(CH2TMS)2, and Me2SiCp′′2An(CH2R)2 (Cp′′ = C5Me4; An = Th, R = TMS; An = U, R = Ph) as precatalysts is studied in detail. These transformations are shown to be Markovnikov-selective, with selectivities as high as >99%. Kinetic investigations of the Cp*2SmCH(TMS)2-mediated reaction between 1-pentanethiol and 1-hexyne are found to be first-order in catalyst concentration, first-order in alkyne concentration, and zero-order in thiol concentration. Deuterium labeling of the alkyne −C≡C−H position reveals kH/kD = 1.40(0.1) and 1.35(0.1) for the organo-Sm- and organo-Th-catalyzed processes, respectively, along with evidence of thiol-mediated protonolytic detachment of the vinylic hydrothiolation product from the Sm center. Mechanistic findings indicate turnover-limiting ...

Organozirconium Complexes as Catalysts for Markovnikov-Selective Intermolecular Hydrothiolation of Terminal Alkynes: Scope and Mechanism

The efficient and selective organozirconium(IV)-mediated, intermolecular hydrothiolation of terminal alkynes by aliphatic, benzylic, and aromatic thiols using CGCZrMe(2) (CGC = Me(2)SiCp'' NCMe(3), Cp'' = C(5)Me(4)), Cp*ZrBn(3) (Cp* = C(5)Me(5), Bn = benzyl), Cp*ZrCl(2)NMe(2), Cp*(2)ZrMe(2), and Zr(NMe(2))(4) precatalysts is reported. These transformations are shown to be highly Markovnikov-selective, with selectivities up to 99%, and typically in greater than 90% yields. The reaction has been demonstrated on the preparative scale with 72% isolated yield and 99% Markovnikov selectivity. A mixture of anti-Markovnikov products is occasionally observed as a result of a known, non-organometallic, radical mechanism, which can be suppressed by addition of a radical inhibitor. Kinetic investigations show that the CGCZrMe(2)-mediated reaction between 1-pentanethiol and 1-hexyne is first-order in catalyst concentration, first-order in alkyne concentration, and also first-order in thiol at lower concentrations but transitions to zero-order at concentrations > 0.3 M. Deuterium labeling of the alkyne yields k(H)/k(D) = 1.3(0.1), along with evidence of thiol-mediated protonolytic detachment of product from the Zr center. Activation parameters for CGCZrMe(2)-mediated 1-pentanethiol hydrothiolation of 1-hexyne measured over the temperature range of 50-80 degrees C are DeltaH(double dagger) = +18.1(1.2) kcal/mol and DeltaS(double dagger) = -20.9(2.5) e.u. for [alkyne] and [thiol] at 0.2 M. These and other findings are consistent with turnover-limiting alkyne insertion into the Zr-SR bond, followed by a thiol-induced Zr-C protonolysis. Observed zirconium-thiolate dimers in the reaction medium suggest instances of dimeric catalyst resting states and possible aggregated, hydrothiolation-active species.

Base and concentration effects on the product distribution in copper-promoted alkyne–azide cycloaddition: additive-free route to 5-iodo-triazoles

Formation of 5-iodo-triazoles in CuI-promoted cycloadditions between alkynes and azides is controlled by DMAP and low alkyne concentrations.

Organoactinide-Mediated Hydrothiolation of Terminal Alkynes with Aliphatic, Aromatic, and Benzylic Thiols

Atom-efficient organoactinide-catalyzed intermolecular hydrothiolation of terminal alkynes is achieved by Th(IV) and U(IV) complexes to yield vinyl sulfides. The conversion is highly Markovnikov selective and is capable of utilizing aromatic, benzylic, and aliphatic thiols. Kinetic measurements of the transformation mediated by Me(2)SiCp(2)''Th[CH(2)(TMS)](2) (1a; Cp'' = eta(5)-Me(4)C(5)) shows the reaction is zero-order in [thiol], first-order in [1a], first-order in [alkyne] at lower alkyne concentrations, and zero-order at higher [alkyne]. The proposed catalytic cycle invokes turnover-limiting insertion of the alkyne into the Th-S bond followed by a rapid Th-C bond protonolysis. All reactions except entries 7 and 8 are quantitative by (1)H NMR.

Stereoselective hydrogenation of phenyl alkyl acetylenes on pillared clays supported palladium catalysts

The stereospecific hydrogenation of phenyl alkyl acetylenes at 298 K and atmospheric pressure of hydrogen over Pd supported catalysts has been studied. The catalysts were prepared by impregnation Al-PILC and Ca-Mont with Pd(acac) 2 precursor, with metal content close to 1 wt.%. All the solids were characterised by nitrogen adsorption–desorption isotherms at 77 K, TPR, H 2 and CO chemisorption, XRD and TEM measurements. The reactions were found to be zero order concerning the alkyne concentration. At conversion levels up to 80% (reaction time lower than 90 min), only a limited overhydrogenation occurred. It was found that at higher reactant molecule:Pd atom ratios (R:P = 7000), the activity is approximately half of that obtained at lower R:P (R:P = 3500). The results suggested that the hydrogenation of phenyl alkyl acetylenes to cis-alkene is “structure insensitive”. All catalysts displayed high selectivity to cis-alkene isomer being the 1% Pd/Al-PILC the most active catalyst.

π-Ligand Exchange on Phosphenium Ions: Reversible Exchange between Free and Coordinated Alkynes in Phosphirenium Salts

The rate of reversible alkyne exchange between 1-methyl-1,2,3-triphenylphosphirenium triflate and ethylphenylacetylene, and that of the reverse reaction between 2-ethyl-1-methyl-1,3-diphenylphosphirenium triflate and diphenylacetylene, are independent of alkyne concentration, which suggests a mechanism that involves rate-determining elimination of alkyne from the phosphirenium triflate to give a transient phosphenium triflate. The mechanism is supported by the observation of crossover products upon mixing phosphirenium triflates containing different substituents.

Role of the irradiation temperature on the modifications of swift-heavy-ion irradiated polyethylene

The damage processes triggered by swift heavy ions, SHI, can be very different to those induced by classical low ionising particles. This is due to the very high electronic stopping power, (d E/d x) e, of SHI. This paper concerns the effects of SHI on polyethylene, PE. In PE, low (d E/d x) e irradiations induce crosslinking and in-chain double bond formation. At high (d E/d x) e, the creation yield of vinyl groups becomes significant. Above a (d E/d x) e threshold, alkyne and allene groups appear. We present results on low temperature irradiations that bring new enlightenment on the damage process by preventing the migration of radiation-induced radicals and molecules. Two SHI specific modifications are studied: vinyl groups and alkyne end groups. We have irradiated PE films with oxygen and sulphur beams at 13.6 and 11.2 MeV/amu, respectively. The modifications were followed by in situ infrared spectroscopy (FTIR). We have performed irradiations at 8 and 290 K. The samples irradiated at 8 K have been annealed up to 290 K for investigating the effect of radical migration. Lowering the irradiation temperature to 8 K increases the creation yield of vinyl groups and alkyne end groups. The enhancement factor between 290 and 8 K is around three. Consequently the formation of defects specific to SHI irradiations is sensitive to radical migration and hence requires some time. During annealing, the alkyne concentration remains stable indicating that the creation of this group cannot be induced by radical recombination. The annealing spectra of vinyl groups are more complex.

Diverse catalytic activity of the cationic actinide complex [(Et 2N) 3U][BPh 4] in the dimerization and hydrosilylation of terminal alkynes. Characterization of the first f-element alkyne π-complex [(Et 2N) 2U(CC tBu)(η 2-HCC tBu)][BPh 4

The cationic actinide complex [(Et 2N) 3U][BPh 4] is an active catalytic precursor for the selective dimerization of terminal alkynes. The regioselectivity is mainly towards the geminal dimer but for bulky alkyne substituents, the unexpected cis-dimer is also obtained. Mechanistic studies show that the first step in the catalytic cycle is the formation of the acetylide complex [(Et 2N) 2UC CR][BPh 4] with the concomitant reversible elimination of Et 2NH, followed by the formation of the alkyne π-complex [(Et 2N) 2UC CR(RC CH)][BPh 4]. This latter complex (R= t Bu) has been characterized spectroscopically. The kinetic rate law is first order in organoactinide and exhibits a two domain behavior as a function of alkyne concentration. At low alkyne concentrations, the reaction follows an inverse order whereas at high alkyne concentrations, a zero order is observed. The turnover-limiting step is the C C bond insertion of the terminal alkyne into the actinideacetylide bond to give the corresponding alkenyl complex with Δ H ‡=15.6(3) kcal mol −1 and Δ S ‡=−11.4(6) eu. The following step, protonolysis of the uraniumcarbon bond of the alkenyl intermediate by the terminal alkyne, is much faster but can be retarded by using CH 3C CD, allowing the formation of trimers. The unexpected cis-isomer is presumably obtained by the isomerization of the trans-alkenyl intermediate via an envelope mechanism. A plausible mechanistic scenario is proposed for the oligomerization of terminal alkynes. The cationic complex [(Et 2N) 3U][BPh 4] has been found to be also an efficient catalyst for the hydrosilylation of terminal alkynes. The chemoselectivity and regiospecificity of the reaction depend strongly on the nature of the alkyne, the solvent and the reaction temperature. The hydrosilylation reaction of the terminal alkynes with PhSiH 3 at room temperature produced a myriad of products among which the cis- and trans-vinylsilanes, the alkene and the silylalkyne are the major components. At higher temperatures, besides the products obtained at room temperature, the double hydrosilylated alkene, in which the two silicon moieties are connected at the same carbon atom, is obtained. The catalytic hydrosilylation of (TMS)C CH and PhSiH 3 with [(Et 2N) 3U][BPh 4] was found to proceed only at higher temperatures. Mechanistically, the key intermediate seems to be the uranium–hydride complex [(Et 2N) 2UH][BPh 4], as evidenced by the lack of the dehydrogenative coupling of silanes. A plausible mechanistic scenario is proposed for the hydrosilylation of terminal alkynes taking into account the formation of all products.

Rhodium-Promoted Linear Tetramerization and Cyclization of 3,3-Dimethylbut-l-yne.

With tetrahydrofuran as the solvent [Rh(thf)(2)(cod)](+) promotes the selective coupling of tBuC(2)H to form triene-yne 1; at high alkyne concentrations, however, an unusual C-H activation process intervenes, leading to the formation of complex 2, which contains two linked five-membered rings. cod=1,5-cyclooctadiene.

Control of selectivity in the cobalt(I)-catalysed cocyclisation of alkynes with nitriles

The selectivity of photochemical synthesis of pyridines based on alkynes (e.g., ethyne, propyne, butyne, dimethylbutyne) and nitriles (e.g., benzo-, aceto-, trimethoxybenzonitrile, n-butylcyanoacetate, tert-butylcyanide) with cobalt(I) complexes ([YCo(cod)]; Y= η 5-cyclopentadienyl, η 5-indenyl, η 5-tetraphenylcyclopentadienyl, η 5-acetylcyclopentadienyl, η 3- cyclooctenyl, η 6-1-phenylborinato; cod=cycloocta-1,5-diene) can be controlled. Thus, very high chemoselectivities are obtained at low alkyne concentrations. For gaseous reactants the appropriate concentrations can be adjusted by choosing the correct partial pressures. One also can take advantage of the temperature dependent solubility of gases in different solvents. In water, for example, the product distribution can be shifted in favour of the formation of pyridines. The regioselectivity can be advantageously influenced by the properties of the ligands in the precatalyst and by the application of bulky nitriles and alkynes. Instead of artificial light sunlight can also be employed as a radiation source without loss of selectivity.

Catalytic Hydrosilylation of Diarylalkynes by Layer-Segregated Platinum−Ruthenium Cluster Complexes Pt3Ru6(CO)20(μ3-RC2R)(μ3-H)(μ-H)

It has been found that the layer-segregated platinum−ruthenium cluster complex Pt3Ru6(CO)20(μ3-PhC2Ph)(μ3-H)(μ-H), 2a, is an effective catalyst for the hydrosilylation of diphenylacetylene by triethylsilane to yield (E)-[(1,2-diphenyl)ethenyl]triethylsilane at a turnover frequency, TOF (TON/h), of 29 h-1. The activation parameters, ΔH ⧧ = 17(2) kcal/mol and ΔS ⧧ = −18(5) eu, were established. Small amounts of cis-stilbene were also formed. A kinetic analysis showed the reaction is first order in cluster and silane concentrations but zero order in alkyne concentration. The reaction is strongly inhibited by CO but is unaffected by mercury. A mechanism involving CO dissociation, silane oxidative addition, alkyne addition, a Si−C bond-forming step, and silylolefin dissociation is proposed with all transformations occurring at a ruthenium triangle. Pt3Ru6(CO)20(μ3-TolC2Tol)(μ3-H)(μ-H), 2b, was also found to be an effective catalyst for the hydrosilylation of TolC2Tol to (E)-Tol(H)C2(SiEt3)Tol, TOF of 32 h-1. Ru3(CO)9(μ3-PhC2Ph)(μ-H)2 and PtRu2(CO)8(μ3-PhC2Ph)(dppe) are relatively poor catalysts, TOF = 3.9 and 2.3 h-1, respectively. [NBu4][Pt3Ru6(CO)20(μ3-PhC2Ph)(μ-H)], 3, formed by deprotonation of 2a, also exhibits good catalytic activity, but its catalysis is inhibited by mercury, which may be indicative of heterogeneous catalysis.

A Modified Procedure for Sonogashira Couplings: Synthesis and Characterization of a Bisporphyrin, 1,1-Bis[zinc(II) 5‘-ethynyl-10‘,15‘,20‘-trimesitylporphyrinyl]methylenecyclohexane

The preparation of a bisporphyrin, 1,1-bis[zinc(II) 5‘-ethynyl-10‘,15‘,20‘-trimesitylporphyrinyl]methylenecyclohexane (1), is described. The new molecule was prepared by two routes employing modified palladium-mediated coupling methodology. Our modification consists of in situ liberation of alkyne from the corresponding TMS-protected compound. This variation decreases yields of undesired products presumably by keeping the unprotected alkyne concentration low during the reaction. In addition, our method obviates TMS-alkyne deprotection and subsequent purification steps. The electronic absorption spectrum of 1 is compared to two model compounds.

Mechanistic Investigation of Stoichiometric Alkyne Insertion into Pt−B Bonds and Related Chemistry Bearing on the Catalytic Diborylation of Alkynes Mediated by Platinum(II) Diboryl Complexes

The insertion reactivity of alkynes with the diboryl complex (Ph3P)2Pt(BCat)2 (1, Cat ≡ {C6H4O2}2-) has been investigated. Under stoichiometric conditions 1 mediates cis-diborylation of alkynes and the (PPh3)2Pt fragment is trapped by alkyne to give the corresponding Pt−alkyne complexes. Kinetic studies under pseudo first-order conditions of alkyne indicate that the reaction is first order in 1. In the absence of added phosphine, no alkyne dependence is observed. The stoichiometric reaction is inhibited by phosphine addition, and under these conditions, a first-order dependence on alkyne concentration is observed for the disappearance of 1. The stoichiometric results exclude simple, bimolecular insertion of an alkyne into Pt−B bonds of 1, and the observed dependence on phosphine and alkyne strongly favors a mechanism where phosphine dissociation generates a three-coordinate intermediate that mediates alkyne insertion. Activation parameters for the stoichiometric alkyne insertion were derived from the temp...