Thiophene hydrodesulfurization over modified alumina-supported molybdenum sulfide catalysts

Methanethiol has been synthesized by one‐step catalytic reaction from H₂S‐content syngas on K₂MoS₄/SiO₂ catalyst with selectivity over 95% under the optimum reaction conditions of 563 K, 2.0–3.0 MPa and 5–6% H₂S content in the feed syngas. The results of XRD and XPS showed that Mo–S–K phase on the surface of the catalyst K₂MoS₄/SiO₂ was responsible for the high activity and selectivity to methanethiol, and which may be restrained by the existence of (S–S)^2- species. This revised version was published online in July 2006 with corrections to the Cover Date.     

Developing a fulvene route to C1-bridged “constrained geometry” Ziegler catalyst systems

6-dimethylamino-6-methylfulvene (7) was converted to the [(C₅H₄)–CMe₂–NMe₂]⁻ ligand system (8) by treatment with methyllithium. Its reaction with MCl₄ (M = Zr, Ti) followed by treatment with CH₃Li gave the respective [(C₅H₄)–CMe₂–NMe₂]₂M(CH₃)₂ complexes (12). Their reaction with B(C₆F₅)₃ led to reactive metallocene cation complexes that instantaneously underwent CH activation at a N–CH₃ group to yield the metallacyclic cation complexes 15. (tert-butylaminomethyl)fluorene was prepared by the addition of tert-butylisocyanate to fluorenyllithium followed by hydride reduction. Deprotonation by a variety of bases gave rise to a series of competing and consecutive reactions to yield several unusually structured products, among them a fluorenyl-anellated η⁵-1-azapentadienyl anion equivalent (25) and [(flu)-CH₂–NCMe₃]Li₂ (23). An improved way of generating synthetically useful C₁-linked [Cp–C₁(R) _n –NR¹]^2- dianion equivalents was developed starting from 6-amino-6-methylfulvene (26). N-silylation followed by double deprotonation with, e.g., lithium diisopropylamide cleanly furnished the respective [(C₅H₄)–C(=CH₂)–NSiMe₃]^2- dianion 33 (isolated as the dilithio derivative). Its reaction with Cl₂Zr(NEt₂)₂ in THF gave [η⁵:κ-N-(C₅H₄)–C(=CH₂)–NSiMe₃]Zr(NEt₂)₂ 36. Activation of 36 with methylalumoxane in toluene led to the formation of a C₁-linked “constrained geometry” Ziegler catalyst that polymerized ethylene similarly as the [(C₅Me₄)SiMe₂NCMe₃]ZrCl₂ derived literature system. This revised version was published online in June 2006 with corrections to the Cover Date.     

Synthesis, Characterization and Thermogravimetric Analysis of Two Dicyclohexyl-18-crown-6 Pd, Pt Isomaleonitriledithiolate Complexes

Two organic–inorganic hybrid dicyclohexyl-18-crown-6 complexes, [K(DC18C6-B)]₂[Pd(i-mnt)₂] (1) and [K(DC18C6-A)]₂[Pt(i-mnt)₂] (2) (DC18C6-A=cis-syn-cis-dicyclohexyl-18-crown-6, A isomer; DC18C6-B = cis-anti-cis-dicyclohexyl-18-crown-6, B isomer; i-mnt=1,1-dicyanoethene-2,2-dithiolate, isomaleonitriledithiolate), were synthesized by the reaction of dicyclohexyl-18-crown-6 with K₂(i-mnt) and PdCl₂ or K₂PtCl₄ respectively. These were characterized by elemental analysis, FT–IR, UV–Vis spectroscopy and single crystal X-ray diffraction. In complex 1, two [K(DC18C6-B)]⁺ complex cations and one [Pd(i-mnt)₂]²⁻ complex anion formed a neutral molecule through two K–N coordination bonds. The resulting molecule adopted a 1D chain arrangement via K N weak interactions. Complex 2 showed a 1D chain-like structure that was assembled by two [K(DC18C6-A)]⁺ complex cations and one [Pt(i-mnt)₂]²⁻ complex anion through N–K–N interactions. An erratum to this article can be found at     

Fatty acid metabolism in marine fish: Low activity of fatty acyl Δ5 desaturation in gilthead sea bream (Sparus aurata) cells

Marine fish have an absolute dietary requirement for C₂₀ and C₂₂ highly unsaturated fatty acids. Previous studies using cultured cell lines indicated that underlying this requirement in marine fish was either a deficiency in fatty acyl Δ5 desaturase or C_18–20 elongase activity. Recent research in turbot cells found low C_18–20 elongase but high Δ5 desaturase activity. In the present study, the fatty acid desaturase/elongase pathway was investigated in a cell line (SAF-1) from another carnivorous marine fish, sea bream. The metabolic conversions of a range of radiolabeled polyunsaturated fatty acids that comprised the direct substrates for Δ6 desaturase ([1-¹⁴C]18∶2n−6 and [1-¹⁴C]18∶3n−3), C_18–20 elongase ([U-¹⁴C]18∶4n−3), Δ5 desaturase ([1-¹⁴C]20∶3n−6 and [1-¹⁴C]20∶5n−3), and C_20–22 elongase ([1-¹⁴C]20∶4n−6 and [1-¹⁴C]20∶5n−3) were utilized. The results showed that fatty acyl Δ6 desaturase in SAF-1 cells was highly active and that C_18–20 elongase and C_20–22 elongase activities were substantial. A deficiency in the desaturation/elongation pathway was clearly identified at the level of the fatty acyl Δ5 desaturase, which was very low, particularly with 20∶4n−3 as substrate. In comparison, the apparent activities of Δ6 desaturase, C_18–20 elongase, and C_20–22 elongase were approximately 94-, 27-, and 16-fold greater than that for Δ5 desaturase toward their respective n−3 polyunsaturated fatty acid substrates. The evidence obtained in the SAF-1 cell line is consistent with the dietary requirement for C₂₀ and C₂₂ highly unsaturated fatty acids in the marine fish the sea bream, being primarily due to a deficiency in fatty acid Δ5 desaturase activity.     

On the role of C<Subscript>2</Subscript>O radicals in the prompt-NO mechanism

The measurements of NO concentrations in the post-flame zone of different hydrocarbon + O₂ + N₂ flames at standard temperature and atmospheric pressure available in the literature are compared with predictions of the original Konnov reaction mechanism and with the same mechanism extended by the reaction of C₂O with N₂. The goal was to investigate the possible role of this reaction proposed by Williams and Fleming [Proc. Combust. Inst., Vol. 31 (2007), pp. 1109–1117]. This new reaction of C₂O with N₂ seems to be a reasonable explanation of the deficiencies in the prompt-NO route. Direct comparisons of the experimental measurements performed in different flames with the modeling strongly suggests that the upper limit of this reaction rate constant is k = 7 · 10¹¹ exp(−17,000/RT) [cm³/(mole · sec)]. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 5, pp. 3–7, September–October, 2008.     

Chemical fixation of carbon dioxide to dimethyl carbonate from propylene carbonate and methanol using ionic liquid catalysts

The synthesis of dimethyl carbonate (DMC) through the transesterification of propylene carbonate (PC) with methanol was investigated by using imidazolium salt ionic liquid catalysts. 1-alkyl-3-methyl imidazolium salts of different alkyl group (C₂, C₄, C₆, C₈) and anions (Cl⁻, Br⁻, BF₄⁻, PF₆⁻) were used for catalysts. The reaction was carried out in an autoclave at 140–180°C under carbon dioxide pressure of 1.48–5.61 MPa. The imidazolium salts of shorter alkyl group, and more nucleophilic counter anion exhibited higher catalytic activity. The conversion of PC increased as CO₂ pressure and reaction temperature increased. Kinetic studies were also performed to better understand the reaction mechanism. This paper was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Chemical Vapor Deposition of Pd(C<Subscript>3</Subscript>H<Subscript>5</Subscript>)(C<Subscript>5</Subscript>H<Subscript>5</Subscript>) to Synthesize Pd@MOF-5 Catalysts for Suzuki Coupling Reaction

Abstract  

The highly porous metal organic framework MOF-5 was loaded with the metal–organic compound [Pd(C₃H₅)(C₅H₅)] by metal–organic chemical vapor deposition (MOCVD) method. The inclusion compound [Pd(C₃H₅)(C₅H₅)]@MOF-5 was characterized by powder X-ray diffraction (PXRD), Fourier-transform infrared (FT-IR) spectroscopy, and solid-state nuclear magnetic resonance spectroscopy. It was found that the host lattice of MOF-5 remained intact upon precursor insertion. The –C₃H₅ ligand in the precursor is easier to lose due to the interaction between palladium and the benzenedicarboxylate linker in MOF-5, providing a possible explanation for the irreversibility of the precursor adsorption. Pd nanoparticles of about 2–5 nm in size was formed inside the cavities of MOF-5 by hydrogenolysis of the inclusion compound [Pd(C₃H₅)(C₅H₅)]@MOF-5 at room temperature. N₂ sorption of the obtained material confirmed that high surface area was retained. In the Suzuki coupling reaction the Pd@MOF-5 materials showed a good activity in the first catalytic run. However, the crystal structure of MOF-5 was completely destroyed during the following reaction runs, as confirmed by PXRD, which caused a big loss of the activity.     

From Electron Density Flow Towards Activation: Benzene Interacting with Cu(I) and Ag(I) Sites in ZSM-5. DFT Modeling

The effects of support pretreatment with nC₁–C₅ alcohols on the performance of Rh–Mn–Li/SiO₂ catalyst in the synthesis of C₂-oxygenates from syngas have been investigated by CO hydrogenation reaction, transmission electron microscopy (TEM), pulse adsorption of CO and H₂, and Fourier Transform infrared (FT-IR) spectroscopy. The catalysts prepared from the pretreated silica supports exhibited higher space time yields of C₂-oxygenates (STY_C2-oxy) and selectivities towards C₂-oxygenates (S_C2-oxy) than that prepared from the untreated silica support. The enhancement in the hydrophobicity of the pretreated silica supports would be favorable for increasing Rh dispersion and ratio of Rh⁺/Rh⁰ sites, therefore increasing the number of active sites, especially the active sites for CO insertion. Such variations are responsible for the improvements in the catalytic performance of the Rh–Mn–Li/SiO₂ catalyst.     

Effect of Temperature on C3S and C3S + Nanosilica Hydration and C–S–H Structure

This study aimed to monitor the effect of temperature and the addition of nanosilica on the nanostructure of the C–S–H gel forming during tricalcium silicate (C₃S) hydration. Two types of paste were prepared from a synthesized T₁ C₃S. The first consisted of a blend of deionized water and C₃S at a water/solid ratio of 0.425. In the second, a 90 wt% C₃S + 10 wt% of nanosilica blend was mixed with water at a water/solid ratio of 0.7. The pastes were stored in closed containers at 100% RH and 25°C, 40°C, or 65°C. The hydration reaction was detained after 1, 14, 28, or 62 d with acetone, and then pastes were studied by ²⁹Si magic angle spinning nuclear magnetic resonance (²⁹Si MAS NMR).The main conclusion was that adding nSA expedites C₃S hydration at any age or temperature and modifies the structure of the C–S–H gel formed, two types of C–S–H gel appear. At 25°C and 40°C, more orderly, longer chain gels are initially (1 d) obtained as a result of the pozzolanic reaction between nSA and portlandite (CH) (C–S–H_II gel formation). Subsequently, ongoing C₃S hydration and the concomitant flow of dimers shorten the mean chain length in the gel.     

Chain elongation of polyunsaturated fatty acids by vascular endothelial cells: Studies with arachidonate analogues

This study has utilized radiolabeled analogues of arachidonic acid to study the substrate specificity of elongation of long-chain polyunsaturated fatty acids. Human umbilical vein endothelial cells were incubated for 2–72 hr in medium supplemented with 0.9–2.6 μM [¹⁴C]fatty acid, and cellular glycerolipids were analyzed by gas-liquid chromatography with radioactivity detection. Elongation of naturally occurring C₂₀ polyunsaturated fatty acids occurred with eicosapentaenoate (20∶5(n−3))>Mead acid (20∶3(n−9))>arachidonate (20∶4(n−6)). Chain length markedly influenced the extent of elongation of 5,8,11,14-tetraenoates (18∶4>19∶4>20∶4>21∶4); effects of initial double bond position were also observed (6,9,12,15–20∶4>4,7,10,13–20∶4. Neither 5,8,14- nor 5,11,14–20∶3 was elongated to the extent of 5,8,11–20∶3. Differences between polyunsaturated fatty acids were observed both in the initial rates and in the maximal percentages of elongation, suggesting that the content of cellular C₂₀ and C₂₂ fatty acids may represent a balance between chain elongation and retroconversion. Umbilical vein endothelial cells do not exhibit significant desaturation of either 22∶4(n−6) or 22∶5(n−3). By contrast, incubation with 5,8,11,14-[¹⁴C]18∶4(n−4) resulted in formation of both [¹⁴C]20∶5(n−4) and [¹⁴C]22∶5(n−4). The respective time courses for the appearances of [¹⁴C]22∶5(n−4) and [¹⁴C]20∶5(n−5) suggests Δ6 desaturation of [¹⁴C]22∶4(n−4) rather than Δ4 desaturation of [¹⁴C]20∶4(n−4).     

Volatile compounds produced by irradiation of butterfat

Anhydrous butterfat was irradiated at 6 megarads in a special glass reaction flask, and the headspace and total condensate samples were examined by wide-range (−180C to 125C) gas chromatography combined with mass spectrometry. The nature and amounts of volatile compounds were not greatly influenced by whether the butterfat was irradiated under oxygen or under vacuum, nor (apart fromn-alkanoic acids) by storage for 1 and 9 weeks. Carbon dioxide was produced in greatest amount. Of the remaining compounds, aliphatic hydrocarbons predominated both in number and amount. Aliphatic oxygenated compounds including carbonyl compounds were isolated in relatively small amounts. The following compounds were identified positively: C_1–13 n-alkanes; C_4–9 2-methylalkanes; C_2–14 alk-l-enes; C_2–9 alk-l-ynes; C_2–5 n-alkanoic acids; C_1–5 n-alkan-l-ols and propan-2-ol; C_2–8 n-alkanals and 2-methylbut-2-enal; C_3–5,7 alkan-2-ones; C_1–4 n-alkyl formates, vinyl and isoamyl formate, methyl acetate and methyln-hexanoate; and carbon dioxide. Visiting Scientist from Division of Dairy Research, C.S.I.R.O., Highett, Victoria, Australia.     

Biosynthesis of (Z,Z)-6,9-heptacosadiene in the American cockroach

The biosynthesis of (Z,Z)-6,9-heptacosadiene, the major cuticular hydrocarbon component of the American cockroach, was examined by radiotracer and¹³C-nuclear magnetic resonance (NMR) techniques. Sodium [1-¹⁴C] acetate was incorporated about equally into the saturated and diunsaturated hydrocarbons, whereas [1-¹⁴C] linoleate preferentially labeled the C₂₇ alkadiene and [9,10-³H] oleate labeled the C₂₇ alkadiene almost exclusively.¹³C-NMR demonstrated that [2-¹³C] acetate labeled carbons 25 and 27 but not carbon 3 of the C₂₇ alkadiene. In addition, ozonolysis of the diene labeled from [1-¹⁴C] acetate followed by radio-gas liquid chromatography showed that carbons 1–6 were not labeled, whereas the fragment containing carbons 10–27 was labeled. The data presented in this paper indicate that linoleate from the diet or synthesized de novo is elongated by the addition of acetate units and is then decarboxylated.     

Catalyst’s Sulfur Displacement by Thiophene, as Monitored by Exchange of 35S Radiotracer

The isotopic exchange has been studied between catalyst radiosulfur and H₂S, formed in thiophene hydrodesulfurization (HDS) (named S-displace) on alumina supported molybdena, on CoMoO_x, PdMoO_x, PtMoO_x and on silica–alumina supported NiWO_x. S-displace was compared with radiosulfur exchange data between catalyst radiosulfur and gas phase H₂S (S^exc) determined previously. The extent of S^exc was higher than that of the S-displace for Mo, CoMo in and NiW, whereas the extent of S-displace from PdMoO and PtMoO was significantly higher, than that of S^exc. Thiophene HDS product distribution data are discussed in terms of increased C=C hydrogenation and C–C hydrogenolysis activity, explained by increasing H₂S production with longer circulation time of the thiophene/H₂ mixture, The C₁/C₃<1 ratios among C₄-hydrogenolysis products indicate some coke formation. The decrease of thiophene HDS activity is presumably a consequence of increasing site-blocking with the formation of more H₂S and coke with longer duration of thiophene treatment.     

Oxidative dehydrogenation of ethane over Co–BaCO3 catalysts using CO2 as oxidant: effects of Co promoter

Co–BaCO₃ catalysts exhibited high catalytic performance for oxidative dehydrogenation of ethane (ODE) using CO₂ as oxidant. The maximal formation rate of C₂H₄ was 0.264 mmol · min⁻¹ · (g · cat.)⁻¹ (48.0% C₂H₆ conversion, 92.2% C₂H₄ selectivity, 44.3% C₂H₄ yield) on 7 wt% Co–BaCO₃ catalyst at 650 °C and 6000 ml. (g · cat.)⁻¹. h⁻¹. Co–BaCO₃ catalysts were comparatively characterized by XRF, N₂ isotherm adsorption-desorption, XRD, H₂-TPR and LRs. It was found that Co⁴⁺–O species were active sites on these catalysts in ODE with CO₂. The redox cycle of Co–O species played an important role on the catalytic performance of Co–BaCO₃ catalysts. On the other hand, the co-operation of BaCO₃ and BaCoO₃ was considered to be one of possible reasons for the high catalytic activity of these catalysts.     

Conjugated opto/electroactive ethynylene-carbazole polymers with TTF as pendant group

Three conjugated ethynylene-carbazole polymers with Tetrathiafulvalene (TTF) as pendant group (P1–P3) were synthesized by using sonogashira coupling reaction and characterized by ¹H NMR, GPC, CV, UV–Vis, FL, and TGA. CV and UV–Vis spectra showed that an intramoleular interaction existed between the electron-rich moiety TTF and electron-deficient moiety polyethynylcarbazole of the polymers. A strong fluorescence quench (ca. 99%) could be observed, compared to the polyethynylene-carbazole without TTF units, which could be ascribed to the photo-induced electron transfer (PET) interaction from TTF moiety to the polyethynylene-carbazole backbone. The observed onset decomposition temperatures (T _d) for P1–P3 varied from 256 to 298 °C. The polymers mentioned above exhibited good thermal properties and higher conductivity (neutral conductivity ~7–11 × 10⁻⁷ S cm⁻¹; doped conductivity ~6–11 × 10⁻⁴ S cm⁻¹).     

Formation of C m H n (m ≥ 3, n ≤ m) hydrocarbons from C1 and C2 molecules by high‐temperature (≥1000°C), short‐contact‐time (1–10 ms) nozzle beam reactions

A nozzle, fabricated from nickel, molybdenum, iron, palladium, and quartz was utilized to produce longer chain hydrocarbons, C _m H _n (m ≥ 3, n≤ m) from C₂ (ethane, acetylene) and C₁ (methane) reactants at nozzle temperature range 1000–1150°C. The conversion of ethane was close to 100% at T _noz = 1000°C, while that of methane reached 20% at T _noz = 1150°C. The contact time in the nozzle is in the 10^-3–10^-2 s range. The reactions are first and higher order in reactant pressure. The reaction mechanism involves the formation of free radicals at the nozzle surface followed by gas‐phase reactions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Syntheses and Crystal Structures of Di- and Trimethyltin Carboxylates: Ladders and 1D Zig–Zag Chains Polymers

A series of organotin(IV) carboxylates complexes; namely, [(Me₂Sn)₄O₂(RCOO)₄] (R = C₁₂H₁₅ 1, C₉H₁₁ 2, C₈H₈ClO 3, C₇H₉ 4) and [Me₃(RCOO)]_n (R = C₁₂H₁₅ 5, C₉H₁₁ 6, C₈H₈ClO 7, C₇H₉ 8) have been synthesized. All complexes were characterized by elemental analysis, FT-IR, and NMR (¹H, ¹³C and ¹¹⁹Sn) spectroscopy. Among them, the structures of complexes 1–3 and 5–8 were also determined by X-ray crystallography. The structural analysis showed that complexes 1–3 are the same tetranuclear monomer, and complexes 5–8 are the same 1D zigzag chain coordination polymer. Furthermore, each complex 1, 2 and 3, can form a supramolecular chain through weak intermolecular interactions.     

Synthesis, Characterization and Photoluminescence of Dimeric and Polymeric Metallaynes of Group 10–12 Metals Containing Conjugation-breaking Diphenylmethane Unit

A novel approach based on conjugation interruption was developed for a luminescent and thermally stable platinum(II) polyyne polymer trans-[–Pt(PBu₃)₂C≡C(C₆H₄)CH₂(C₆H₄)C≡C–] _n (1) containing the diphenylmethane chromophoric spacer. Particular attention was focused on the photophysical properties of this group 10 polymetallayne and comparison was made to its binuclear model complex trans-[Pt(Ph)(PEt₃)₂C≡C(C₆H₄)CH₂(C₆H₄)C≡CPt(Ph)(PEt₃)₂] (2) and their closest group 11 gold(I) and group 12 mercury(II) neighbors, [MC≡C(C₆H₄)CH₂(C₆H₄)C≡CM] (M = Au(PPh₃) (3), HgMe (4)). The regiochemical structures of these angular-shaped compounds were studied by various spectroscopic analyses. Upon photoexcitation, each of them emits an intense purple-blue fluorescence emission in the near UV region in dilute fluid solutions at room temperature. Harvesting of organic triplet emissions harnessed through the strong heavy-atom effects of group 10–12 transition metals was examined. These metal-containing phenyleneethynylenes spaced by the conjugation-breaking CH₂ unit were found to have high optical gaps and high-energy triplet states. The influence of metal and sp³-hybridized methylene conjugation-interrupters on the intersystem crossing rate and the spatial extent of the lowest singlet and triplet excitons was fully elucidated. Our investigations indicate that high-energy triplet states in these materials intrinsically give rise to very efficient phosphorescence with fast radiative decays. Dedicated to Professor Didier Astruc in recognition of his outstanding contribution to metallodendrimers and polymers.     

Cycloaddition of carbon dioxide to epichlorohydrin using ionic liquid as a catalyst

The cycloaddition of carbon dioxide to epichlorohydrin was performed without any solvent in the presence of ionic liquid as catalyst. 1-Alkyl-3-methyl imidazolium salts of different alkyl group (C₂, C₄, C₆, C₈) and anions (Cl⁻, BF₄⁻, Br⁻, PF₆⁻) were used for this reaction carried out in a batch autoclave reactor. The conversion of epichlorohydrin was affected by the structure of the imidazolium salt ionic liquid; the one with the cation of longer alkyl chain length and with more nucleophilic anion showed better reactivity. The conversion of epichlorohydrin increased as the temperature increased from 60°C to 140°C. It also increased with increasing carbon dioxide pressure probably due to the increase of the absorption of carbon dioxide into the mixture of epichlorohydrin and the ionic liquid. Zinc bromide was also tested for its use as a cocatalyst in this reaction. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Kinetics Study of the Hydrodechlorination of Chlorobenzene Catalyzed by Immobilized Copper Complexes

The hydrodechlorination of chlorobenzene to benzene and biphenyl was studied using poly(4-vinylpyridine)-immobilized Cu catalysts under CO in basic (NaOH, N(C₂H₅)₃ or Na(CH₃CO₂)) aqueous 2-ethoxyethanol medium. This Cu system also catalyzed the water gas shift reaction. The catalytic activities for hydrodechlorination of chlorobenzene to benzene were studied as functions of the reaction parameters (nature of the base, reaction time, [Cu], P(CO), T, and S/C). Among the different base studied activity is maximum for NaOH. The rate of benzene formation displays a first-order dependence on [Cu] over the range 1.25–12.50 wt%. This observation was interpreted in terms of the presence of active species having the same nuclearity. The catalytic activity towards benzene formation proved to be first order dependence on P(CO) over the range 5–35 atm. The kinetics behavior with respect to P(CO) leads to the proposal that CO addition to the catalytic species precedes the rate-limiting step. The catalytic activity proved to be non-linear in chlorobenzene/Cu content, over the range 50–400 molar ratio. The results suggest that the rate-limiting step is preceded by reversible oxidative addition of chlorobenzene to Cu immobilized species.