Psi H2 Research Articles

Hydrogen-induced O–H peak growth in Ge-doped optical fibers: Verification of empirical and theoretical models

Migration of hydrogen in optical fibers and its chemical reactions with the glass fiber core create added optical loss, that may deteriorate the light transmission through the fiber. Although this subject has been extensively studied and a few theoretical and empirical models linking the attenuation to hydrogen pressure, temperature and time were proposed, none of the models was verified in a broad range of experimental conditions. In this work we investigate a single mode germanium doped fiber that was exposed to 25–––100 psi H2 pressures at temperatures in the range 150 – 250 °C and the exposure times up to 28 days. Different aging protocols were applied to the fiber, and the focus was given to O–H peak development. An empirical approach and a theoretical model, that assumes Gaussian distribution of the activation energies were applied to fit the experimental results. From the theoretical model, it was found that the concentration of precursor available for reaction with hydrogen is orders of magnitude higher than that of non-bridging oxygen hole centers, and that at the applied temperatures the reacted sites belong to the lower-energy wing of the Gaussian distribution. It was also found that parameters of the theoretical model cannot be accurately determined via fitting even a large array of experimental data. In contrast, parameters of the empirical model are easily obtainable from the experiment which makes this approach more practical in hydrogen-related lifetime predictions.

Designer Biosynthetic Jet Fuels Derived from Isoprene and α-Olefins

Isoprene was hydrovinylated with a series of α-olefins (1-pentene, 1-hexene, 1-heptene, 1-octene) to produce acyclic branched C10–C13 alkenes. The process utilized CoBr2(DPPE) as the precatalyst in loadings as low as 0.1 mol % and zinc as the reducing agent. Use of the cobalt catalyst resulted in primarily 1,4-addition, with carbon coupling at the 4-position of isoprene. A significant amount (∼20%) of the coupling products at the 1-position of isoprene was also observed. Each of the discrete C10, C11, C12, and C13 products were then hydrogenated with 10% Pd/C (200 °C; 650 psi H2) to yield jet fuel blendstocks. In addition to the reactions with pure α-olefins, an equimolar mixture of the C5–C8 α-olefins was used to mimic a stream of olefins produced from ethanol dehydration/oligomerization or Fischer–Tropsch catalysis. The different fuel blends exhibited densities ranging from 0.73 to 0.76 g mL–1, gravimetric net heats of combustion (NHOC) from 43.91 to 44.13 MJ kg–1, and −20 °C kinematic viscosities from 2.4 to 6.3 mm2 s–1. The NHOC values were ∼2.9% higher than the lower limit for Jet-A, while the low-temperature viscosities were up to 70% lower than the upper limit for Jet-A. In addition to studying the suitability of the lightly branched hydrocarbons generated in this process as jet fuel blendstocks, it was of interest to explore their potential as diesel fuels. The equimolar C10–C13 fuel mixture exhibited a derived cetane number (DCN) of 56, which is 16 units higher than that required for Diesel #2 (40). The outstanding fuel properties of the isoprene-derived fuels suggest that they have applications as replacements for both petroleum-derived Jet-A and Diesel #2.

Exploitation of Liquid CO2 Based Greener Process for Valorization of Citronellal-Rich Essential Oils Into Flavor Grade (−)-Menthol Using Novel Sn/Al-B-NaYZE Composites

A two-step greener catalytic process has been developed for the semi-synthesis of (−)-menthol from citronellal-rich essential oils such as Cymbopogon winterianus and Corymbia citriodora by using novel bi-acidic composites. These novel composites (Al-B-NaYZE or Sn-B-NaYZE) were prepared by impregnation of Sn-B and Al-B over NaYZE framework to increase the Lewis and Bronsted acidic sites. These composites were thoroughly characterized using TDP, FT-IR, UV, XRD, SEM, HRTEM, SA, and TGA. The composite Sn-B-NaYZE cyclized 99% of citronellal to isopulegol isomers with 99% selectivity in 45 min under a liquid CO2 medium, while composite Al-B-NaYZE is showing 95% selectivity towards isopulegol isomers. Sn-B-NaYZE displayed enhanced selectivity due to its higher Lewis and Bronsted acidic characteristics. The chiral study indicated that the Sn-B-NaYZE composite is giving the highest selectivity (94%) towards (−)-isopulegol. (+)-Citronellal or citronella essential oil was found as an ideal substrate for (−)-menthol production. It observed that the Sn-B molar ratio over base material NaY-Zeolite played a major role in catalytic activity and selectivity towards (−)-isopulegol. Further, isopulegol isomers were reduced to 98% of menthol using 1%Pd/AC at 40 psi H2 pressure in 1 h. The reaction mixture was slowly frozen to -40 °C for trouble-free isolation of the crude menthol. Further, pharmaceutical and flavor grade (−)-menthol was purified from the crude menthol through an esterification process. This (−)-menthol was found to be 100% biobased on 14C-radiocarbon-dating to authenticate as nature-identical.

Effect of vulcanization and reaction temperature of the carbide supported on activated carbon on glycerol trioleate deoxygenation

Cobalt molybdenum carbide supported on activated carbon was synthesized and the effect of sulfiding on the catalytic activity of the glycerol trioleate deoxygenation process (DOX) was evaluated. Prior to the glycerol trioleate deoxygenation reactions, the catalyst was reduced and sulfided with CS2/H2. The CoMo/CA carbide was characterized by specific area (B.E.T), X-ray diffraction (XRD), elemental analysis (CHON-S), potentiometric titration with n-butylamine and X-ray photoelectron spectroscopy (XPS). The specific area of the CoMo/CA carbide and the support were 246 m2/g and 881 m2/g, respectively. XRD analysis proved the presence of Co6Mo6C2 and metallic cobalt. XPS showed the presence on the surface of signals assignable to Moδ+, Mo4+, Mo6+, Co2+, S2– and SO42–. Sulfided CoMo/CA carbide showed higher activad to glycerol trioleate esoxygenation than unsulfided CoMo/CA carbide. The highest yield was obtained at 310 °C, 900 psi H2 and 2 h of reaction (100% conversion) and a higher selectivity towards heptadecane (55%) and octadecane (45%) favoring decarboxylation (HDCX) and decarbonylation (HDCn) than hydrodeoxygenation (HDO).

Scalable Synthesis of Pt/SrTiO3 Hydrogenolysis Catalysts in Pursuit of Manufacturing-Relevant Waste Plastic Solutions.

An improved hydrothermal synthesis of shape-controlled, size-controlled 60 nm SrTiO3 nanocuboid (STO NC) supports, which facilitates the scalable creation of platinum nanoparticle catalysts supported on STO (Pt/STO) for the chemical conversion of waste polyolefins, is reported herein. This synthetic method (1) establishes that STO nucleation prior to the hydrothermal treatment favors nanocuboid formation, (2) produces STO NC supports with average sizes ranging from 25 to 80 nm with narrow size distributions, and (3) demonstrates how SrCO3 formation and variation in solution pH prevent the formation of STO NCs. The STO synthesis was scaled-up and conducted in a 4 L batch reactor, resulting in STO NCs of comparable size and morphology (m = 22.5 g, davg = 58.6 ± 16.2 nm) to those synthesized under standard hydrothermal conditions in a lab-scale 125 mL autoclave reactor. Size-controlled STO NCs, ranging in roughly 10 nm increments from 25 to 80 nm, were used to support Pt deposited through strong electrostatic adsorption (SEA), a practical and scalable solution-based method. Using SEA techniques and an STO support with an average size of 39.3 ± 6.3 nm, a Pt/STO catalyst with 3.6 wt % Pt was produced and used for high-density polyethylene hydrogenolysis under previously reported conditions (170 psi H2, 300 °C, 96 h; final product: Mw = 2400, Đ = 1.03). As a well-established model system for studying the behavior of heterogeneous catalysts and their supports, the Pt/STO system detailed in this work presents a unique opportunity to simultaneously convert waste plastic into commercially viable products while gaining insight into how scalable inorganic synthesis can support transformative manufacturing.

Catalytic hydrogenolysis of As-enriched Pteris vittata L. into high quality biofuel and study on the migration of heavy metals

As-enriched Pteris vittata L. (PVL, a kind of hyper-accumulator biomass) was converted into high-quality biofuel by the catalytic hydrogenolysis, aiming to achieve effective treatment and high-value utilization of hyper-accumulators. After pretreatment of PVL to remove lipids and lignin, more than 64% of heavy metals were transferred into water, and the As content in the solid biomass was reduced from 1328 mg/kg to 483 mg/kg. The multifunctional catalysts RhCl3/NaI/HCl/H2 were used in a biphasic reaction system to convert PVL into biofuel with high selectivity. The main products are C5 and C6 furans and low oxygen content ketones, which have a high heating value (HHV) and can be directly used as biofuel. The highest yields of C5 and C6 products were obtained with 60.2% and 61.1% (based on the corresponding hemicellulose and cellulose) under the optimal reaction conditions (160 °C, 4 h, 300 psi H2, 4 mmol NaI, H2O/toluene = 1:1). The total biofuel yield based on dry PVL was 18.8 wt.%. After the reaction, more than 50% heavy metals (Cu, Pb, Zn, Cd, As) remained in the bio-char, while the heavy metals in the biofuel were less than 20% (As content was less than 55 mg/kg). Therefore, catalytic hydrogenolysis was perceived as a promising technique for PVL treatment to obtain high-quality biofuel and arsenic recovery.

Synergistic interaction between Cu and ZrO2 promotes ethyl formate hydrogenation to produce methanol

Converting formate to methanol is an economic strategy to expand the production of formate from CO2 electro-reduction while satisfying the increasing market demand for methanol. For selective hydrogenation of formate esters to methanol, it is crucial to understand how the interaction between metal catalyst and support affects catalytic performance. In this paper, ZrO2 was employed as the support to promote the Cu catalysts’ activity and selectivity in liquid-phase hydrogenation of ethyl formate. To maximize the production yield of methanol, various catalyst properties and reaction condition were investigated. Under the optimized conditions, i.e., 160 °C and 400 psi H2, ∼ 53 % of methanol were yielded from the hydrogenation of ethyl formate in anhydrous ethanol solvent over the 20 wt% Cu/ZrO2 catalyst. The calcination temperature in the catalyst synthesis had profound effects on the Cu valence states, the structure of the ZrO2 support, and the interactions between Cu and ZrO2. A variety of characterization tools, including XRD, XPS, and HRTEM, were used to elucidate the structure-activity relationship of the Cu/ZrO2 catalysts. These findings will facilitate the next-generation catalyst design and elucidate the synergistic interaction between Cu and ZrO2 that promotes ester hydrogenation reactions.

Upcycling Single-Use Polyethylene into High-Quality Liquid Products.

Our civilization relies on synthetic polymers for all aspects of modern life; yet, inefficient recycling and extremely slow environmental degradation of plastics are causing increasing concern about their widespread use. After a single use, many of these materials are currently treated as waste, underutilizing their inherent chemical and energy value. In this study, energy-rich polyethylene (PE) macromolecules are catalytically transformed into value-added products by hydrogenolysis using well-dispersed Pt nanoparticles (NPs) supported on SrTiO3 perovskite nanocuboids by atomic layer deposition. Pt/SrTiO3 completely converts PE (Mn = 8000–158,000 Da) or a single-use plastic bag (Mn = 31,000 Da) into high-quality liquid products, such as lubricants and waxes, characterized by a narrow distribution of oligomeric chains, at 170 psi H2 and 300 °C under solvent-free conditions for reaction durations up to 96 h. The binding of PE onto the catalyst surface contributes to the number averaged molecular weight (Mn) and the narrow polydispersity (Đ) of the final liquid product. Solid-state nuclear magnetic resonance of 13C-enriched PE adsorption studies and density functional theory computations suggest that PE adsorption is more favorable on Pt sites than that on the SrTiO3 support. Smaller Pt NPs with higher concentrations of undercoordinated Pt sites over-hydrogenolyzed PE to undesired light hydrocarbons.

One-pot catalytic hydrogenolysis of rice straw into biogasoline

The waste rice straw is a sustainable bioresource with large reserves and low-cost, thus can be used to produce fuels and chemicals to enhance its value. In this paper, we have developed a new method to convert rice straw into biogasoline with high yield in one step by using multifunctional catalyst of RhCl3/NaI/HCl/H2 in a biphasic reaction system. Lipid and lignin in the rice straw hindered its conversion and need to be removed by pretreatment. The major products are C5 and C6 furan, furfural, and cyclic ketones, which are low in oxygen content and can be used as biogasoline. Under the optimal reaction conditions (140 °C, 4 h, 300 psi H2, toluene to water volume ration 1:1), C5 from hemicellulose with 77.2% yield and C6 from cellulose with 71.7% yield can be obtained. The total biogasoline yield based on dry rice straw is 23.5 wt%, which is quite significant. The mechanism of the conversion process was also well studied.

Meet the Associate Editors: Adam Trevitt

My group studies photoactivation and photochemistry of ions – this includes ion/radical reactions and photodissociation spectroscopy. We combine ion trap mass spectrometry with tunable UV–Vis lasers to better understand photostability and photodissociation of protonated chromophores (including the effect of protonation isomers). We also studying ion/radical reactions with neutral molecules to better understand and predict radical chemistry relevant to atmospheric, combustion and extra-terrestrial gas-phase chemistry. I don't recall any epiphany – but I was attracted to instrumentation and lasers. I was also drawn to fundamental chemistry, and mass spectrometry is often deployed in conjunction with lasers for the study of gas-phase spectroscopy and kinetics. I was working on a liquid-beams project for my Honours year at the University of Adelaide (with Mark Buntine and Greg Metha) – the idea was that we would fire an IR laser at the liquid beam in the vacuum chamber to drive molecules out of the water beam to the gas-phase where they were to be ionised by a UV laser. Ions were then detected using TOF-MS. We got it to work! It was a great introduction to research. The IR laser pulse was generated by a Nd:YAG pulse directed through a Raman shifter – in this case a gas cell containing about 100 psi H2 gas – and it generated a huge range of Raman “shifted” wavelengths into the visible, UV and IR. I remember directing the output of the shifter through a dispersion prism and across the room onto the wall. I could see scores of vibrational Stokes and Anti-Stokes lines that separated into discrete rotationally resolved bands when given enough distance to spread out. I was nerding-out big time. Gosh – I don't think I can answer this question. I think you need to extract pathological excitement and satisfaction from your research – it's the fuel. My PhD supervisor, Evan Bieske (University Melbourne), deserves some blame for the way I turned out. And I've been lucky to have other great people around me, including when I was at UC Berkeley/LBNL (Steve Leone, David Osborn, Craig Taatjes, Kevin Wilson). When I started at Wollongong I was ensconced in a supportive, collegial School of Chemistry. Steve Blanksby (now at QUT) and I hit off a great collaboration and friendship that was essential to my survival. Develop skills – real, technical skills – and become experts. I think this is key to a satisfying career (regardless of what path you ultimately take). I would say laser photodissociation, naturally. Over the next decade or so, I'm predicting the laser photoactivation will become as ubiquitous as CID for the fragmentation and general torture of ions. It's going to be exciting times. One tricky thing will be how the fundamental areas remain well-funded. As an academic, I see clearly how modern mass spectrometry is built on the fundamental advances of past researchers. I hope we don't forget how this translation happens and we continue to patiently support fundamental, discovery-driven, science so that in years to come new tools will come online. There are no short-cuts in this innovation pipeline. I am keen on mountain biking. Wollongong has some pretty good trails and I find it cleansing for my head to get out into the hills and ride (avoiding trees). I get the road bike out a couple of times a week too. Take a long, restorative holiday with my family. I'd also get myself back in the lab more and do some solid tinkering. My partner – my wife. She is so kind and unjudgmental.

Highly selective solvent-free hydrogenation of pinenes to added-value cis-pinane

Heterogeneous catalysts based on different active metals (Pd, Pt, Ru, and Rh) and supports (carbon and alumina) were systematically tested for hydrogenation of pinenes under various reaction conditions including heating and/or sonication. Among all, Ru provided some of the best results. After sonication, Ru/C was found highly active and selective for the reduction of α-pinene alone into cis -pinane (99% selectivity at 100% conversion). However, in the absence of sonication the same catalyst was completely inactive. Alumina appeared to be a support with a beneficial chemical effect on the activity of the Ru. Indeed, Ru/Al 2 O 3 was found very active and selective for hydrogenation of both α- and β-pinene into cis -pinane (99–100% selectivity at 100% conversion) under mild reaction conditions (room temperature, 400 Psi H 2 ). The selectivity toward cis -pinane decreased in the following order: Ru > Rh > Pt > Pd. An extremely low leaching rate of Ru and other metals determined by inductively coupled plasma mass spectrometry confirmed the heterogeneous nature of this catalytic solvent-free hydrogenation. Ru/C was successfully recycled seven times with no decline in activity and selectivity, whereas Ru/Al 2 O 3 could be used only once to convert pinenes to cis -pinane. Solubilization prediction tests of some natural products have revealed that pinane compares very well with n -hexane and may be an alternative to this fossil-based solvent. When compared experimentally with n -hexane, cis -pinane solubilized 42, two, and three times more of β-carotene, vanillin, and rosmarinic acid, respectively. Des catalyseurs hétérogènes avec différents métaux actifs (Pd, Pt, Ru et Rh) et sur des supports variés (carbone et alumine) ont été systématiquement testés pour l'hydrogénation des pinènes sous différentes conditions réactionnelles comprenant une activation par chauffage et/ou sonication. Parmi tous, le Ru a donné quelques-uns des meilleurs résultats. Après sonication, le Ru/C s'est avéré hautement actif et sélectif pour la réduction de l’α-pinène en cis -pinane (99% de sélectivité et 100% de conversion). En absence de sonication, ce même catalyseur était cependant complètement inactif. L'alumine semble être un support ayant un effet chimique bénéfique sur l'activité du Ru. En effet, le Ru/Al 2 O 3 s'est avéré très actif et sélectif pour l'hydrogénation de l’α-et du β-pinène en cis -pinane (99–100% de sélectivité et 100% de conversion) dans des conditions réactionnelles douces (température ambiante, 400 Psi H 2 ). En général, la sélectivité vis-à-vis du cis -pinane a diminué dans l'ordre suivant: Ru > Rh > Pt > Pd. Un taux de lixiviation extrêmement faible du Ru, ainsi que de tous les autres métaux, déterminé par ICP/MS, a confirmé le caractère hétérogène de cette hydrogénation catalytique sans solvant. Le Ru/C a été recyclé avec succès sept fois sans réduction, ni de l'activité, ni de la sélectivité, tandis que le Ru/Al 2 O 3 n'a pu être utilisé qu'une seule fois pour convertir les pinènes en cis -pinane. Les tests de prédiction de la solubilisation de certains produits naturels ont révélé que le pinane ainsi produit se compare très bien avec le n -hexane et peut être une alternative à ce solvant d'origine fossile. Comparé expérimentalement avec le n -hexane, le cis -pinane résultant de nos essais a solubilisé respectivement 42, 2 et 3 fois plus de β-carotène, de vanilline et d'acide rosmarinique.

Ecofriendly Palladium on Wool Nanocatalysts for Cyclohexene Hydrogenation.

Use of natural wool fiber supports in the fabrication of novel composite materials incorporating metal nanoparticles, which offer the possibility of “environmentally friendly” catalytic materials, has been investigated. The catalytic hydrogenation of cyclohexene to cyclohexane by palladium nanoparticles immobilized on wool (Pd/wool) was studied using moderate pressure of pure hydrogen gas. The performance of wool-supported catalysts was explored over a palladium nanoparticle loading ranging from 1.6 to 2.6 wt %. The effect of the catalytic testing conditions, including stirring rate, amount of reactants, gas pressure, and target temperature were explored. A systematic series of catalytic-activity tests carried out at 400 psi H2 for 5 and 24 h reaction times at 40 °C using a stirring rate 750 rpm allowed us to identify differences in performance within the series of Pd/wool nanocatalysts studied. The most catalytically active samples contained Pd nanoparticles with average sizes of ca. 5 nm located predominantly on the surface and within the topmost layer of wool fibers, making them more accessible to the reactants.

Simultaneous Upgrading of Furanics and Phenolics through Hydroxyalkylation/Aldol Condensation Reactions.

The simultaneous conversion of cyclopentanone and m-cresol has been investigated on a series of solid-acid catalysts. Both compounds are representative of biomass-derived streams. Cyclopentanone can be readily obtained from sugar-derived furfurals through Piancatelli rearrangement under reducing conditions. Cresol represents a family of phenolic compounds, typically obtained from the depolymerization of lignin. In the first biomass conversion strategy proposed here, furfural is converted in high yields and selectivity to cyclopentanone (CPO) over metal catalysts such as Pd-Fe/SiO2 at 600 psi (∼4.14 MPa) H2 and 150 °C. Subsequently, CPO and cresol are further converted through acid-catalyzed hydroxyalkylation. This C-C coupling reaction may be used to generate products in the molecular weight range that is appropriate for transportation fuels. As molecules beyond this range may be undesirable for fuel production, a catalyst with a suitable porous structure may be advantageous for controlling the product distribution in the desirable range. If Amberlyst resins were used as a catalyst, C12 -C24 products were obtained whereas when zeolites with smaller pore sizes were used, they selectively produced C10 products. Alternatively, CPO can undergo the acid-catalyzed self-aldol condensation to form C10 bicyclic adducts. As an illustration of the potential for practical implementation of this strategy for biofuel production, the long-chain oxygenates obtained from hydroxyalkylation/aldol condensation were successfully upgraded through hydrodeoxygenation to a mixture of linear alkanes and saturated cyclic hydrocarbons, which in practice would be direct drop-in components for transportation fuels. Aqueous acidic environments, which are typically encountered during the liquid-phase upgrading of bio-oils, would inhibit the efficiency of base-catalyzed processes. Therefore, the proposed acid-catalyzed upgrading strategy is advantageous for biomass conversion in terms of process simplicity.

The microwave-assisted ionic liquid nanocomposite synthesis: platinum nanoparticles on graphene and the application on hydrogenation of styrene.

The microwave-assisted nanocomposite synthesis of metal nanoparticles on graphene or graphite oxide was introduced in this research. With microwave assistance, the Pt nanoparticles on graphene/graphite oxide were successfully produced in the ionic liquid of 2-hydroxyethanaminium formate [HOCH2CH2NH3][HCO2]. On graphene/graphite oxide, the sizes of Pt nanoparticles were about 5 to 30 nm from transmitted electron microscopy (TEM) results. The crystalline Pt structures were examined by X-ray diffraction (XRD). Since hydrogenation of styrene is one of the important well-known chemical reactions, herein, we demonstrated then the catalytic hydrogenation capability of the Pt nanoparticles on graphene/graphite oxide for the nanocomposite to compare with that of the commercial catalysts (Pt/C and Pd/C, 10 wt.% metal catalysts on activated carbon from Strem chemicals, Inc.). The conversions with the Pt nanoparticles on graphene are >99% from styrene to ethyl benzene at 100°C and under 140 psi H2 atmosphere. However, ethyl cyclohexane could be found as a side product at 100°C and under 1,520 psi H2 atmosphere utilizing the same nanocomposite catalyst.

An efficient and stable Ru–Ni/C nano-bimetallic catalyst with a comparatively low Ru loading for benzenehydrogenation under mild reaction conditions

A prepared 0.024%Ru–1.00%Ni/C nano-bimetallic catalyst reported in this work is a highly efficient and stable catalyst for the hydrogenation of benzene to cyclohexane, with an unprecedented TOF up to 7905 h−1 under mild reaction conditions (20 °C, 40 psi H2) without adding any solvent. The method for the preparation of catalyst is very simple and low-cost. Therefore, this cyclohexane synthetic approach is potentially more environmentally friendly and economical than existing technology.

Partial Deoxygenation of 1,2-Propanediol Catalyzed by Iridium Pincer Complexes

Iridium pincer complex (POCOP)IrH2 (1; POCOP = κ3-C6H3-1,3-[OP(tBu)2]2) catalyzes hydrogenolysis of 1,2-propanediol to n-propanol in good yield under mild conditions (acidic aqueous dioxane, 50–125 °C, 100–600 psi H2). Studies of catalyst speciation revealed that the catalyst reservoir species is (POCOP)Ir(CO) (2), formed by decarbonylation of the substrate. Complex 2 is a superior catalyst precursor, since it is air-stable and readily prepared by treating complex 1 with CO.

Synthesis, characterization, and biphasic ionic liquid media 1-hexene hydrogenation reaction of RuCl2(DMSO)2(NC5H4CO2Na-3)2

RuCl2(DMSO)2(NC5H4CO2Na-3)2 is very soluble in the ionic liquid (IL) 1-n-butyl-3-methylimidazolium tetrafluoroborate, [(BMIM)BF4]. The complex was prepared by reacting RuCl2(DMSO)4 with NC5H4CO2Na-3, sodium nicotinate, in toluene, and was characterized by spectroscopic methods. The complex catalyzes the hydrogenation of 1-hexene (600 psi H2, 100 °C) in a two-phase system consisting of cyclohexane/[(BMIM)BF4] with 75% conversion in 24 h and modest substrate isomerization. The complex shows good stability and can be reused several times with little loss in activity.

Hydrogenolysis versus Methanolysis of First- and Second-Generation Grubbs Catalysts: Rates, Speciation, and Implications for Tandem Catalysis

An unexpected “generation gap” is uncovered between the Grubbs catalysts RuCl2(L)(PCy3)(═CHPh) (1a, L = PCy3; 1b, L = IMes, N,N′-bis(mesityl)imidazol-2-ylidene) in their reactions with hydrogen versus methanol, in the presence of base. Treatment of the first-generation catalyst 1a with H2 and NEt3 (CH2Cl2, 60 °C, 1000 psi H2) affords RuHCl(H2)(PCy3)2 (2a) in 75% yield within 30 min, as determined by in situ NMR analysis. Complex 2a is in turn efficiently converted (96%; 2 h) into the important hydrogenation catalyst RuHCl(CO)(PCy3)2 (3a) by mild thermolysis with methanol and NEt3 (4:1 CH2Cl2−MeOH, 60 °C), 72% net yield for the 1a−3a transformation. In comparison, subjecting the second-generation catalyst 1b to this two-step process effects <40% net conversion to RuHCl(CO)(IMes)(PCy3) (3b) (hydrogenolysis of 1b: ca. 60% RuHCl(H2)(IMes)(PCy3) (2b) (1 h); carbonylation of isolated 2b: 65% 3b (2.5 h)), owing to the susceptibility of the dihydrogen derivative 2b to disproportionation and decomposition. The opposite trend in efficiency for 1a versus 1b is found for methanolysis under argon in the presence of base: 1b undergoes 83% conversion to 3b, versus <60% for the 1a−3a transformation (4:1 CH2Cl2−MeOH, 60 °C). This difference reflects the longer duration of the methanolysis reaction (8 h for 1a vs 4 h for 1b; cf. 30 min and 1 h, respectively, for hydrogenolysis) and the lower thermal robustness of 1a. These findings highlight the importance of tailored, catalyst-specific approaches in devising efficient tandem catalysis methodologies based on the first- and second-generation Grubbs complexes. They are directly relevant to the improved synthesis of advanced polymer materials via tandem ROMP−hydrogenation and potentially relevant to RCM- and CM-functionalization processes.

Synthesis of Isoeuparin and Isotubaic Acid.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Synthesis of Isoeuparin and Isotubaic Acid

The compounds containing the benzofuran moiety are widely distributed in nature. They are used as versatile intermediates in organic and natural product synthesis. They have also shown a range of biologically activities. Among these, isoeuparin (1) was isolated from the roots of Tagetes patula and isotubaic acid (2) (rotenic acid) was obtained from the natural insecticide rotenone as a degradation product (Figure 1). The synthetic approaches to isoeuparin and isotubaic acid had been reported. We have used these known reactions in the synthesis of isoeuparin derivatives, but these reactions produce the expected products in low yield. The necessity for overcoming this problem has prompted a search for new routes for the synthesis of isoeuparin (1) and isotubaic acid (2). We have interest in the rhodium(II)-catalyzed reaction of iodonium ylides with several substrates. Recently, we have tried rhodium(II)-catalyzed reactions of iodonium ylides with electron-deficient and conjugated alkynes. These reactions provided tetrahydrobenzofuran derivatives 3-6 in moderate yields (Scheme 1). As an application of these methodologies, we describe herein an efficient total synthesis of isoeuparin (1) and isotubaic acid (2) starting from 6. Our synthetic strategy of isoeuparin (1) and isotubaic acid (2) is depicted in Scheme 2. The crucial starting material 6 was readily prepared in 53% yield from the iodonium ylide and 2-methyl-1-buten-3-yne in the presence of 1 mol % of Rh2(Opiv)4. 8 The reaction of 6 with methyl carbonate using excess NaH in the presence of a catalytic amount of KH in THF gave 7 in 96% yield. Oxidation of 7 with DDQ in refluxing 1,4-dioxane afforded aromatic compound 8 in 46% yield. Support for the structural assignment of 8 comes from spectroscopic analysis. The H NMR spectrum of 8 shows the expected two aromatic protons at δ 7.73 (d, J = 8.8 Hz) and δ 6.96 (d, J = 8.8 Hz). Conversion of 8 to isoeuparin (1) was accomplished by hydrolysis and the subsequent addition of MeLi. Reaction of 8 with 2.5 M NaOH in refluxing methanol gave acid 9 in 97% yield, which was treated with excess MeLi (4 eq) in toluene at 50 C for 4 h to afford 1 in 65% yield. The spectroscopic properties of our synthetic material 1 agreed well with those reported in the literature. Conversion of 9 to isotubaic acid (2) was carried out by catalytic hydrogenation. Hydrogenation of 9 at 20 psi H2 for 10 min in ethyl acetate afforded 2 in 88% yield. The spectral data of our synthetic material 2 agreed well with those reported in the literature. In conclusion, we have described here the synthesis of isoeuparin (1) and isotubaic acid (2) starting from tetrahydrobenzofuran 6. These synthetic approaches are expected to be widely used in the total synthesis of other natural products containing the benzofuran moiety.