Reaction Of Thiophene Research Articles

Endo Selective Diels—Alder Reactions of Furan in Ionic Liquids.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Magnesia-supported Mo, CoMo and NiMo sulfide catalysts prepared by nonaqueous impregnation: parallel HDS/HDN of thiophene and pyridine and TEM microstructure

MgO-supported Mo, CoMo and NiMo sulfide catalysts were prepared by impregnation using slurry MoO3/methanol and solutions of Ni and Co nitrates in methanol. The catalysts exhibited very high hydrodesulfurization activity and low hydrodenitrogenation activity in competitive reactions of thiophene and pyridine. The promotion effect for HDS of Ni and Co was higher for our MgO-supported MoS2 catalysts than for conventional Al2O3-supported catalysts. The specific features in the TEM images of MgO-supported catalysts as compared to conventional Al2O3-supported catalysts were fairly broad MoS2 slab length distribution and the presence of unusually long MoS2 slabs.

A kinetic study of gas-phase reaction of thiophene with NO 3 by using absolute and relative methods

The gas-phase rate coefficient for the reaction of thiophene with nitrate radical, NO 3, has been determined, using relative (gas chromatography as analytical tool) and absolute methods at 298 K. The absolute experiments were carried out using a fast-flow-discharge technique, with detection of the NO 3 radical by Laser Induced Fluorescence (LIF). The proposed rate coefficient at 298 K is, k=(3.16±0.27)×10 −14 cm 3 molecule −1 s −1 . The temperature dependence was studied by the absolute technique in the range 260–433 K, observing that in the interval of 260–277 K the rate coefficient decreases as the temperature increases and from 298 K onwards the rate coefficient increases with temperature.

Adsorption and reaction of thiophene on α-Mo2C([formula omitted

Thiophene adsorbs reversibly and irreversibly on α-Mo2C(0001). Irreversible thiophene adsorption results in decomposition to surface C, surface S, and gaseous dihydrogen. The chemical states of the carbon and sulfur as identified by X-ray photoelectron spectroscopy are carbidic and sulfidic, respectively, implying that the surface decomposition products are bound to metal sites. The H2 is evolved in two features during thermal desorption spectroscopy experiments, a low temperature desorption-limited peak and a high temperature reaction-limited peak. The reaction-limited peak is likely due to the decomposition of a surface hydrocarbon species that results from thiophene decomposition. Photoemission results indicate that C–S bond scission occurs by 170 K and possibly as low as 105 K.

Kinetic, infrared, and X-ray absorption studies of adsorption, desorption, and reactions of thiophene on H-ZSM5 and Co/H-ZSM5

Temperature programmed desorption and infrared and X-ray absorption near-edge spectroscopies were used during adsorption and reactions of thiophene in order to probe adsorbed intermediates and catalytic structures responsible for thiophene reactions with propane or H2 on H-ZSM5 and Co/H-ZSM5. Infrared spectra showed that thiophene interacts with acidic OH groups in H-ZSM5 via hydrogen bonding at ambient temperature. No additional bands were detected on Co/H-ZSM5, suggesting the absence of specific interactions with Co cations. During adsorption at ambient temperatures, infrared bands assigned to CH2 groups near CC bonds or S-atoms and to S–H species were detected and H-ZSM5 and Co/H-ZSM5 acquired colors typical of thiophene oligomers. Slightly above ambient temperatures, benzene and H2S formed from pre-adsorbed thiophene. These results indicate that hydrogen-bonded thiophene undergoes ring opening or oligomerization near ambient temperature on acidic OH groups in H-ZSM5. Some of the adsorbed thiophene (20–50%) interacts weakly with channel walls or with residual Na cations and desorbs unreacted. The remaining adsorbed thiophene desorbs as H2S, aromatic hydrocarbons, and organosulfur compounds, such as methylthiophene and benzothiophene, or forms irreversibly adsorbed unsaturated organic deposits. In situ infrared studies during thiophene and thiophene–propane reactions at 773 K on H-ZSM5 and Co/H-ZSM5 showed that surface coverages of thiophene-derived intermediates were low on acidic OH groups and Co cations. Co K-edge X-ray absorption near-edge spectra measured during these reactions confirmed that Co2+ cations do not reduce or sulfide; their local environment, however, changes slightly, apparently because of interactions of strongly adsorbed species with Co cations. Sulfur K-edge X-ray absorption spectra detected small amounts of organosulfur species, but no inorganic sulfides, after thiophene, thiophene–H2, and thiophene–propane reactions, consistent with the observed stability of exchanged cations against reduction and sulfidation. S∶Al ratios were less than 0.04 at. on all samples; these amounts represent less than 1% of the S-atoms removed from thiophene as H2S during catalytic propane–thiophene reactions.

Ab initio study of the photochemical isomerization of thiophene derivatives

The photochemical isomerization reactions of thiophene, thiophene-2-carbonitrile, and 2-phenylthiophene were studied using ab initio methods. The results are in agreement with the previously reported data obtained through semiempirical methods. Triplet excited thiophene is a π,σ ∗ triplet with LSOMO at −9.94 eV and HSOMO at −9.51 eV and the biradical intermediate is a π,π ∗ species with LSOMO at −10.12 eV and HSOMO at −4.82 eV. In this case, the singlet excited state can evolve giving the Dewar thiophene, while the corresponding excited triplet state cannot be obtained. Furthermore, the triplet state cannot be converted into the biradical intermediate because this intermediate shows a higher energy than the triplet state, thus preventing the formation of the cyclopropenyl derivatives. Triplet excited thiophene-2-carbonitrile is a π,π ∗ species. It shows the LSOMO at −11.38 eV and the HSOMO at −7.36 eV. In this case, the direct irradiation involves the population of the excited singlet state, and then the formation of the Dewar isomer is possible. The intersystem crossing to the triplet state can occur; however, its interconversion into the corresponding biradicals cannot be efficient considering that the biradicals show a higher energy, even if for a little amount, than that of the triplet state. Triplet excited 2-phenylthiophene is a π,π ∗ species. It shows the LSOMO at −9.32 eV and the HSOMO at −6.24 eV. In this case, the direct irradiation involves the population of the excited singlet state, and then the formation of the Dewar isomer is possible. The energy of the excited singlet state was obtained from the UV absorption of the substrate. The intersystem crossing to the triplet state cannot occur; because it shows higher energy than the corresponding singlet state. Furthermore, its interconversion into the corresponding biradicals cannot be efficient considering that the biradicals show the same energy of the triplet state. The high efficiency of this reaction can be explained on the basis of low energy of the Dewar isomer.

Kinetic Study of Catalytic Hydrogenation of Thiophene on a Palladium Sulfide Catalyst

The kinetics of thiophene hydrogenation on a palladium sulfide catalyst is studied at high hydrogen pressures. The reaction mainly occurs via the consecutive scheme: the reaction of thiophene with hydrogen results in the formation of tetrahydrothiophene, which partially decomposes under the action of hydrogen to yield butane and hydrogen sulfide. A kinetic model describing the reaction rates and the selectivity to tetrahydrothiophene at 0.2–3.0 MPa and 493–533 K is proposed. The rate constants and activation energies are determined. The effect of temperature and pressure on the maximal yield of tetrahydrothiophene is examined.

Endo Selective Diels-Alder Reactions of Furan in Ionic Liquids

Diels-Alder reactions of the heteroaromatic diene furan proceed with enhanced isolated yields and reversal of endo/exo selectivity (2:1 endo vs exo) in the ionic liquids [bmim]BF 4 and [bmim]PF 6 compared to conventional methods. The potential utility of ionic liquids as solvents in Diels-Alder reactions of thiophene and pyrrole derivatives has also been demonstrated.

Isotopic Tracer Studies of Thiophene Desulfurization Reactions Using Hydrogen from Alkanes on H-ZSM5 and Co/H-ZSM5

Reaction pathways for the desulfurization of thiophene using alkanes as hydrogen sources were probed by measuring the chemical and isotopic composition of products formed from 13C-labeled C3H8 and unlabeled C4H4S mixtures on H-ZSM5 and Co/H-ZSM5. Aliphatic hydrocarbons formed only from propane carbon atoms while aromatic molecules contained carbon atoms from both propane and thiophene. Hydrogen-deficient thiophene and thiophene-derived species react with surface hydrogen and alkenes formed from propane and desorb as unreactive aromatics, in steps that lead to the irreversible exit of alkenes from oligomerization-cracking cycles. These steps remove kinetic bottlenecks in thiophene desulfurization resulting from the irreversible formation of strongly adsorbed unsaturated species, which cannot desorb without reactions with hydrogen or hydrogen-rich surface species. This kinetic coupling between alkane and thiophene reactions leads to the observed concurrent increase in the rates of both propane aromatization and thiophene desulfurization compared with those achieved with each pure reactant. The scavenging of unsaturated intermediates formed via thiophene decomposition using hydrogen or hydrogen-rich intermediates formed from propane decreases the rate of bimolecular Diels–Alder reactions, which lead to larger organosulfur compounds and to low H2S selectivity. As a result, H2S selectivities are higher and deactivation rates are lower when propane is present as a co-reactant during reactions of thiophene.

A DFT Study of the Cracking Reaction of Thiophene Activated by Small Zeolitic Clusters

A theoretical study of the cracking reaction of thiophene by small zeolitic cluster catalysts is reported. Cluster density functional theory calculations have been performed. It is shown that cracking of thiophene is catalyzed by Lewis basic oxygen atoms. Several active sites are proposed and tested. Moreover, it appears that the use of a partner molecule, strongly adsorbed to the acidic proton, allows for an important decrease of the cracking activation energy barrier. The effect of hydrogenation of thiophene prior to the cracking reaction has been checked. Interestingly, hydrogenation does not affect dramatically the activation energy barrier (−10 kJ/mol). However a large stabilization of the product of the reaction has been found (−40 kJ/mol).

Thiophenes in Organotransition Metal Chemistry: Patterns of Reactivity

Thiophenes, including benzothiophenes and dibenzothiophenes, undergo a variety of reactions with transition metal complexes that lead to products in which the thiophene is partially reduced or cleaved at a C−S bond. The specific types of reactivity depend on the modes of thiophene coordination to the metal, which in turn depend on the particular metal and its associated ligands. It is the intent of this review to organize these numerous reactions of thiophenes into categories that illustrate distinct patterns of reactivity. It is hoped that an understanding of such patterns will stimulate the use of thiophene−organotransition metal chemistry in synthetic organic chemistry.

Effect of synthesis conditions on the molybdenum nitride catalytic activity

Properties of the molybdenum nitrides supported on alumina as well as on active carbon has been investigated in the reactions of thiophene and vacuum gas oil (VGO) hydrodesulfurization (HDS) as well as in the reaction of cyclohexene with hydrogen. Supported molybdenum nitride was more active in thiophene hydrogenolysis than sulfided Mo/Al 2O 3. Also in the reaction of VGO HDS alumina supported molybdenum nitride was more active than sulfided counterpart, however Mo 2N supported on active carbon exhibit low activity. In the products of the cyclohexene reaction over supported Mo 2N methyl-cyclopentanes and benzene has been found.

Selective metallation of thiophene and thiazole rings with magnesium amide base

Selective hydrogen–metal exchange reaction of thiophene and thiazole proceeded smoothly with magnesium amide base (iPr2NMgCl) under mild conditions.

Electronic and Vibrational Properties of Thiophene on Si(100)

The surface reactions of thiophene on Si(100)-2×1 have been investigated as part of a larger study on the interaction between five-membered heterocyclic aromatic molecules and silicon substrates. Using XPS, UPS, and HREELS, two adsorption states are identified at 120 K, corresponding to physisorbed and chemisorbed thiophene. The former desorbs below 200 K, whereas the latter strongly binds to the surface, showing lower C(1s) and S(2s) binding energies. HREELS reveals that chemisorbed thiophene is a 2,5-dihydrothiophene-like species which exhibits coverage-dependent reorientation from nearly parallel to tilted relative to the surface plane. Based on the frontier molecular orbital theory and work function measurements, an inverse Diels−Alder cycloaddition mechanism for thiophene with Si(100)-2×1 is proposed. Above 400 K, chemisorbed species either desorbs as molecular thiophene or decomposes possibly via α-thiophenyl and Si−H, and metallocycle-like intermediate and atomic S through a sulfur abstraction mech...

Nucleophilic Addition of Amines to Silyl- and Germyl-Substituted Thiophene 1,1-Dioxides

Nucleophilic addition of secondary amines to tert-butyl-, trimethylsilyl- and trimethylgermyl-2,5-disubstituted thiophene 1,1-dioxides has been studied. It has been shown that the reactivity and reaction pathway depend strongly on the thiophene 1,1-dioxide structure, the basicity of the amine and the nature of the solvent. Addition of amines to 2,5bis(tert-butyl)thiophene 1,1-dioxide does not occur either in organic or in aqueous media. In organic solvents, 2,5-bis(trimethylsilyl)-, 2-trimethylsilyl-5-trimethylgermyl- and 2,5-bis(trimethylgermyl)thiophene 1,1-dioxides add one piperidine molecule, the vinylsilane fragment being more active than the vinylgermane one. The corresponding reactions of thiophene 1,1-dioxides with morpholine and diethylamine failed to occur. In water, the addition of morpholine and diethylamine (one molecule in each case) or dimethylamine and piperidine (two molecules in each case) was accompanied by concomitant demetallation. The molecular structure of 3-piperidino-5-trimethylgermyl-2,3-dihydrothiophene 1,1-dioxide was confirmed by X-ray analysis.

Electrophilic 2-Thienylselenenylation of Thiophene. Preparation of Oligo(seleno-2,5-thienylenes)

The substitution reactions of thiophene and 2-methylthiophene with the electrophilic selenenylating agent produced from the 2,2′-dithienyl diselenide by oxidation with iodobenzene diacetate involve only the α-positions and give rise to the formation of oligo(seleno-2,5-thienylenes). Products deriving from the attack at the α-positions of thiophene and 2-methylthiophene were also observed starting from the 5,5′-dimethyl-2,2′-dithienyl diselenide. The same electrophilic reagents reacted with furan and 2-methylfuran to afford a mixture of the mono- and di-substituted compounds.

Periodic Trends in Hydrotreating Catalysis: Thiophene Hydrodesulfurization over Carbon-Supported 4d Transition Metal Sulfides

The kinetics of atmospheric gas-phase thiophene hydrodesulfurization (HDS) over five carbon-supported 4d transition metal sulfide catalysts (Mo, Ru, Rh, Pd, and CoMo) were studied. Reaction orders (thiophene, H2S, and H2), apparent activation energies, and pre-exponential factors were determined. The activity trends for these catalysts follow the well-known volcano-shape curve. The most active catalyst shows the lowest thiophene reaction order, which is taken to imply that a strong interaction between transition metal sulfide (TMS) and thiophene results in a high HDS activity. The kinetic results are interpreted in terms of trends in metal–sulfur bond energy. These trends are counter to commonly held correlations between metal–sulfur bond energy and periodic position of the transition metal. Both Sabatier's principle and the “bond energy model” appear to be inadequate in explaining the observed trends in kinetic parameters. Instead, an alternative proposal is made: the metal–sulfur bond strength at the TMS surface relevant to HDS catalysis depends on the sulfur coordination number of the surface metal atoms. Transition metals (TM) at the left-hand side of the periodic table, i.e., Mo, form stable sulfides, leading to a low sulfur addition energy under reaction conditions. The sulfur addition energy is the energy gained upon addition of a sulfur atom (e.g., in the form of thiophene) to the TMS. Over to the right-hand side of the periodic table, the stability of the TMS decreases due to lower bulk metal–sulfur bond energies. This can result in more coordinative unsaturation of the TM surface atoms and possibly the formation of incompletely sulfided phases with higher sulfur addition energies. At the right-hand side of the periodic table the activity decreases due to weak metal–sulfur interactions, leading to poisoning of the metallic state.

Investigation of the Adsorption and Reactions of Thiophene on Sulfided Cu, Mo, and Rh Catalysts

The surface chemistry of thiophene (C4H4S) on sulfided Cu/Al2O3, Mo/Al2O3, and Rh/Al2O3 catalysts has been investigated under well-defined conditions using infrared (IR) spectroscopy and temperature programmed desorption (TPD). The results of these experiments have been found to correlate nicely with CO chemisorption measurements of site densities and thiophene hydrodesulfurization (HDS) activities measured in a flow reactor system. In agreement with the literature, the catalysts were found to have dramatically different thiophene HDS activities increasing in the following order: sulfided Cu < sulfided Mo < sulfided Rh. The trend of HDS activities is mirrored in similar trends for the site densities and turnover frequencies for the sulfide catalysts. IR spectra of adsorbed thiophene on the sulfided Cu, Mo, and Rh catalysts at low temperatures show that the amount of thiophene adsorbed on cus metal sites of the sulfide catalysts correlates with the CO chemisorption estimates of site densities. Thiophene reactivity on the catalysts differs significantly, with reaction in thiophene/H2 mixtures observed on the sulfided Mo and Rh catalysts annealed at 300 and 500 K, respectively, and not at all on a sulfided Cu catalyst annealed up to 700 K. Strongly adsorbed species produced on the sulfided Cu, Mo, and Rh catalysts during the annealing sequence were subjected to TPD experiments that yielded C4 hydrocarbons and H2S, with the predominant C4 product being butenes. IR and TPD measurements of 1,3-butadiene and 1-butene on sulfided Rh/Al2O3 catalysts, both in the pure gas and in gas/H2 mixtures, provide evidence for the tentative assignment of strongly adsorbed species produced by cleavage of C−S bonds in thiophene to be a σ-bonded allyl species with C4H7 stoichiometry.

Kinetics of sulfur model molecules competing with H 2S as a tool for evaluating the HDS activities of commercial CoMo/Al 2O 3 catalysts

The relative-volume activities (RVAs) for real feedstocks HDS of four commercial CoMo/Al 2O 3 catalysts have been compared to the rates for thiophene and dibenzothiophene conversion. The reaction of thiophene competing with H 2S was studied in flow microreactors under a wide range of conditions: 300–400°C, overall pressure 0.1 or 3 MPa, thiophene pressure 8–125 kPa, H 2S content 0–15 mol%. The reaction of dibenzothiophene (DBT, 2 wt% in decaline) was carried out in a batch reactor at 335°C and 4 MPa. The conversion of the two model molecules proceeds through the same mechanism with a preliminary dearomatization step followed by parallel hydrogenolysis and hydrogenation. From kinetic modeling, the global rates and the contribution of the hydrogenation and hydrogenolysis routes to HDS were determined. Under pressure, hydrogenolysis was predominant. In that case, thiophene and DBT behaved similarly and their initial relative rates did not correlate the RVA. Industrial HDS is controlled by hydrogenation as evidenced by the good correlation between RVA and the rates of dearomatization of thiophene at atmospheric pressure and hydrogenation of the product biphenyl from DBT under pressure. It is concluded that the reaction of model molecules under selected conditions can appraise rapidly industrial HDS.

Identification of the Adsorption Mode of Thiophene on Sulfided Mo Catalysts

The adsorption and reactions of thiophene (C4H4S) on sulfided Mo/Al2O3 catalysts have been investigated over wide ranges of pressure (10-9−5 × 102 Torr) and temperature (140−693 K) using infrared (IR) spectroscopy and temperature-programmed desorption (TPD). When dosed at 190 K, thiophene adsorbs molecularly onto sites located on MoS2-like structures and on uncovered alumina regions of sulfided Mo/Al2O3 catalysts as determined by IR spectroscopy. Thiophene is weakly chemisorbed to the catalyst surface and desorbs in a single peak with a maximum rate of desorption at 243 K. Based upon interpretation of IR spectra, the adsorption mode of thiophene on the sulfided Mo portion of the catalyst surface has been determined to be η1(S), with thiophene bonded to coordinately unsaturated (cus) Moδ+ sites located on the edge planes of MoS2-like structures. The saturation coverage of thiophene on MoS2-like structures of a sulfided 17.6 wt % Mo/Al2O3 catalyst is estimated to be C4H4S/Mo = 0.074. Thiophene is observed to become reactive on sulfided Mo/Al2O3 catalysts only in the presence of gas-phase hydrogen and at high temperatures (i.e., 693 K). Temperature-programmed desorption in ultrahigh vacuum following heating of a sulfided 9.4 wt % Mo/Al2O3 catalyst to 693 K in a thiophene/H2 mixture results in desorption of C4 hydrocarbons, H2S, and H2 from the catalyst surface.