Double-bond Isomerization Reactions Research Articles

UiO-66 derived ZrO2@C catalysts for the double-bond isomerization reaction of 2-butene.

1-Butene, as one of the widely used chemical raw materials, can be produced by the double bond isomerization of 2-butene. However, the current yield of the isomerization reaction is only up to 20% or so. It is therefore an urgent issue to develop novel catalysts with higher performances. In this work, a high-activity ZrO2@C catalyst that is derived from UiO-66(Zr) is fabricated. The catalyst is prepared by calcining the precursor UiO-66(Zr) at high temperature in nitrogen, and characterized by XRD, TG, BET, SEM/TEM, XPS and NH3-TPD. The results demonstrate that the calcination temperature has significant influences on the catalyst structure and performance. Regarding the catalyst ZrO2@C-500, the selectivity and yield of 1-butene are 94.0% and 35.1%, respectively. The high performance is due to multiple aspects, including the inherited octahedral morphology from parent UiO-66(Zr), suitable medium-strong acidic active sites and high surface area. The present work will lead to a better understanding of the ZrO2@C catalyst and guide the rational design of high-activity catalysts for the double bond isomerization of 2-butene to 1-butene.

Photoinduced Bisphosphination of Alkynes with Phosphorus Interelement Compounds and Its Application to Double-Bond Isomerization.

The addition of interelement compounds with heteroatom-heteroatom single bonds to carbon-carbon unsaturated bonds under light irradiation is believed to be an atomically efficient method to procure materials with carbon-heteroatom bonds. In this study, we achieved the photoinduced bisphosphination of alkynes using the phosphorus interelement compound, tetraphenyldiphosphine monosulfide (1), to stereoselectively obtain the corresponding (E)-vic-1,2-bisphosphinoalkenes, which are important transition-metal ligands. The bisphosphination reaction was performed by mixing 1 and various alkynes and then exposing the mixture to light irradiation. Optimization of the conditions for the bisphosphination reaction resulted in a wide substrate range and excellent trans-selectivity. Moreover, the completely regioselective introduction of pentavalent and trivalent phosphorus groups to the terminal and internal positions of the alkynes, respectively, was achieved. We also found that the novel double-bond isomerization reaction of the synthesized bisphosphinated products occurred with a catalytic amount of a base under mild conditions. Our method for the photoinduced bisphosphination of carbon-carbon unsaturated compounds may have strong implications for both organic synthesis and organometallic and catalyst chemistry.

Semisynthesis of (-)-Bufospirostenin A Enabled by Photosantonin Rearrangement Reaction.

An enantioselective semisynthesis of (-)-bufospirostenin A is described. The key steps in the synthesis involve use of our proposed biomimetic and diastereoselective photosantonin rearrangement reaction for construction of the 5/7 bicyclic motif, and a Co-catalyzed reversible double-bond isomerization reaction for installing the double bond in the seven-membered ring.

Berberine bridge enzyme-like oxidase-catalysed double bond isomerization acts as the pathway switch in cytochalasin synthesis

Cytochalasans (CYTs), as well as their polycyclic (pcCYTs) and polymerized (meCYTs) derivatives, constitute one of the largest families of fungal polyketide-nonribosomal peptide (PK-NRP) hybrid natural products. However, the mechanism of chemical conversion from mono-CYTs (moCYTs) to both pcCYTs and meCYTs remains unknown. Here, we show the first successful example of the reconstitution of the CYT core backbone as well as the whole pathway in a heterologous host. Importantly, we also describe the berberine bridge enzyme (BBE)-like oxidase AspoA, which uses Glu538 as a general acid biocatalyst to catalyse an unusual protonation-driven double bond isomerization reaction and acts as a switch to alter the native (for moCYTs) and nonenzymatic (for pcCYTs and meCYTs) pathways to synthesize aspochalasin family compounds. Our results present an unprecedented function of BBE-like enzymes and highly suggest that the isolated pcCYTs and meCYTs are most likely artificially derived products.

Mechanisms of Double-Bond Isomerization Reactions of n-Butene on Different Lewis Acids

Mechanisms of Double-Bond Isomerization Reactions of <i>n</i>-Butene on Different Lewis Acids

Design and synthesis of Pt/ZSM-22 catalysts for selective formation of iso-Dodecane with branched chain at more central positions from n-Dodecane hydroisomerization

The formation of centrally branched iso-dodecane was controlled by absorption modes of alkene intermediates on ZSM-22, which included pore mouth type and key lock type. In this paper, we have designed and synthesized two kinds of ZSM-22 catalysts for selective formation of iso-dodecane with branched chain at more central positions from n-dodecane hydroisomerization. Aluminosilicate ZSM-22 was modified via carbonization of template to block the micropores and borosilicate ZSM-22 was synthesized. The characterization results and performance evaluation validated that micropore blockage could limit the pore mouth type at low reaction temperatures which favored the formation of iso-dodecane with side chain near the end of the carbon chain. Owing to the weak acid strength, higher temperatures, which favored the key lock mode, were needed to run the n-dodecane hydroisomerization over Pt/borosilicate ZSM-22. Both the two strategies for catalyst design achieved key lock adsorption mode and improvement of the selectivity for centrally branched iso-dodecane. Most importantly, weak acid sites on borosilicate ZSM-22 could catalyze double-bond isomerization reactions, which enhanced centrally branched iso-dodecane distribution up to more than 47%. Our research provides a prospective strategy for selective formation of centrally branched iso-alkanes and Pt/borosilicate ZSM-22 is expected to have potential applications in n-alkane hydroisomerization.

Low-temperature oligomerization of 1-butene with H-ferrierite

The effect of temperature, pressure, and solvent on 1-butene oligomerization was studied over H-ferrierite. Two-dimensional GC (GC×GC–MS) was used to analyze the olefin, paraffin, aromatic, and cycloalkane products of the C4 olefin conversion. The reaction product mixture revealed H-ferrierite promoted double bond isomerization, skeletal isomerization, oligomerization, hydrogen transfer, cyclization and cracking reactions. The double bond isomerization reaction reached equilibrium for both C4 and C8 olefins. Primary products from C4 olefin dimerization were 3,4-dimethyl-2-hexene and 3-methyl-2-heptene. The oligomerization products followed the Schulz–Flory chain growth distribution. The chain growth distribution is a function of the C4 olefin conversion. Most of the heavier olefins (>C12) were highly branched (>trimethyl- and methyl-ethyl-species). The selectivity towards oligomerization products was maximized at low temperatures (below 473K). At temperatures above 473K olefins underwent cracking and hydride transfer reactions to produce olefins, paraffins, and aromatics. Co-feeding hexane solvent increased C4 olefin conversion and led to a shift of product distribution from heavier to lighter species. The medium pores were relatively stable for production of longer chain olefins (C6–C20) from C4 olefins near supercritical conditions. The reaction rate was second order in the near-critical region. The deactivation rate decreased with increasing 1-butene partial pressure.

Gold(I)-catalyzed 1,2-acyloxy migration/[3+2] cycloaddition of 1,6-diynes with an ynamide propargyl ester moiety: highly efficient synthesis of functionalized cyclopenta[b]indoles.

A gold-catalyzed cycloisomerization of 1,6-diynes containing an ynamide propargyl ester or carbonate moiety has been developed that provides an attractive route to a diverse-substituted 3-acyloxy-1,4-dihydrocyclopenta[b]indoles. Mechanistic studies indicate that the reaction likely proceeds through a competitive 1,2-OAc migration followed by [3+2] cycloaddition of the vinyl gold-carbenoid intermediate with the pendant triple bond. The synthetic utility of the obtained cyclopenta[b]indole products was demonstrated by their efficient transformations by deprotection or double-bond isomerization reactions.

Superbasic sodium stannate as catalyst for dehydrogenation, Michael addition and transesterification reactions

It has been shown that sodium stannate with superbasic sites generated on its surface can be obtained through simple thermal treatment of sodium stannate hydrate in pure N 2. In this study, we analyzed the as-prepared materials using powder X-ray diffraction, X-ray photoelectron spectroscopy, and N 2 physisorption methods. The superbasic sites were characterized by techniques of Hammett indicators and temperature-programmed desorption using CO 2 as adsorbate. It was shown that after undergoing calcination at 623 K, there are ample superbasic sites on sodium stannate: up to 0.254 mmol/g. The superbasicity of the materials was further confirmed by employing the 1-hexene as well as cyclohexa-1,4-diene double bond isomerization reactions. The superbasicity is attributed to the higher electron-donating ability of surface O 2−. The sodium stannate samples showed excellent catalytic efficiency towards selected reactions, namely the dehydrogenation of propa-2-nol, Michael addition of electron-deficient olefins, and transesterification of cyclic carbonate with methanol. It was observed that with rise of heat-treatment temperature from 573 to 623 K, both superbasicity and catalytic activity increased, reaching a maximum at 623 K, and then declined. It is deduced that catalytic efficiency is closely related to superbasicity of the sodium stannate catalysts.

Theoretical Study of the Double-Bond Isomerization of 1-Hexene to &lt;em&gt;cis&lt;/em&gt;-2-Hexene over ZSM-5 Zeolite

We investigated the double-bond isomerization reaction of 1-hexene to cis-2-hexene on the surface of ZSM-5 zeolite using density functional theory with a 54T cluster model simulating the local structures of zeolite materials. We found that the double-bond isomerization proceeded by a mechanism that did not involve the bifunctional (acid-base) nature of the zeolite active sites but exclusively involved the acid sites. According to this mechanism, 1-hexene is the first physically adsorbed onto the zeolite acid site resulting in the formation of a π-complex, and then the acidic proton of the zeolite transfers to a carbon atom of the double bond of the physisorbed 1-hexene. The other carbon atom of the double bond of the physisorbed 1-hexene bonds with the host oxygen and yields a stable alkoxy intermediate. Thereafter, the host oxygen abstracts a hydrogen atom from the C6H13 fragment and the C―O bond of the alkoxy intermediate is broken, which restores the zeolite active site and yields physisorbed cis-2-hexene. The proposed reaction pathway competes with the bifunctional pathway. The ratedetermining step is the decomposition of the alkoxy intermediate with an activation energy of 134. 64 kJ· mol. The calculated apparent activation energy for the isomerization reaction is 59. 37 kJ·mol-1, which is in good agreement with the reported experimental value. These results well explain the energetic aspects during the double-bond isomerization and extend the understanding of the nature of zeolite active sites. 1081 Acta Phys. ⁃Chim. Sin. 2011 Vol.27

Study of the selectivity in FCC naphtha hydrotreating by modifying the acid–base balance of CoMo/γ-Al 2O 3 catalysts

CoMo catalysts supported on a commercial γ-Al 2O 3 modified with B, Na or K were prepared in order to analyze the effect of acid–base characteristics on the FCC naphtha hydrotreatment. Catalysts were characterized by NH 3 TPD, IR of pre-adsorbed pyridine and CO 2, XPS, Raman, and XRD. In general, with either boron or alkaline metal modification the HDS/HYDO selectivity did not significantly improve. However, it is remarkable that when the alumina was modified to be either more acidic (B) or more basic (K, Na), improvements in the ratio between the HDS and the conversion of the internal branched olefin as well as in the ratio double-bond isomerization to HYD of linear olefins were observed. For both modifications, this fact was related to the promotion of the double-bond isomerization reaction from external to internal positions. For alkaline-doped catalysts, it was found that the double-bond isomerization was related to the existence of basic sites. For the boron, there is a range of boria content (2–3 wt.%) where the double-bond isomerization was promoted selectively over the cracking and alkylation reactions because only weak Brönsted acid sites are present. Additionally, both modifications (Boron or alkaline metals) of alumina led to a decrease in the HDS activity, which was found to be related to changes in the distribution of Co and Mo species in the oxide state. Alkaline metal introduction led to the formation of alkaline metal molybdates, whereas boron introduction increased the proportion of octahedral polymeric Mo species, consequently, decreasing the dispersion of the Mo phase.

Ruthenium-Catalyzed Addition of Primary Amides to Alkynes: A Stereoselective Synthesis of Secondary Enamides

The anti-Markovnikov addition of primary amides to terminal alkynes under the formation of Z-configured secondary enamides is efficiently promoted by a catalyst system generated in situ from bis(2-methallyl)(cycloocta-1,5-diene)ruthenium(II), 1,4-bis(dicyclohexylphosphino)butane, and ytterbium triflate. The thermodynamically more stable E-isomers are accessible by combining the above hydro­amidation with an in situ double-bond isomerization reaction, using triethylamine and molecular sieves.

1-Hexene Double Bond Isomerization Reaction Over SO 4 = Promoted NiO, Al2O3 and ZrO2 Acid Catalysts

Sulfated mixed oxides, SO 4 = /Ni–Al–O and SO 4 = /Zr–Al–O were evaluated for double bond isomerization (DBI) of 1-hexene using helium and hydrogen as carrier gases. The increase of temperature from 100 to 200 °C seems to favor the deprotonation pathway and contribute to increase the 1-hexene conversion for both catalysts and without regard of the carrier gas. The results indicate that temperature it is the main factor that contributes to improve both conversion and selectivity towards (cis + trans)-2-hexene, while the reductive atmosphere beneficiate only the SO 4 = /Ni–Al–O catalyst performance, as hydrogen prevents this catalyst from a fast deactivation.

Linoleic acid isomerization on Ru/Al2O3 catalyst

The selective double bond isomerization reaction of linoleic acid to cis-9,trans-11-conjugated linoleic acid and trans-10,cis-12-conjugated linoleic acid on commercial H2-preactivated Ru/Al2O3 catalyst studied at 135–165 °C under kinetic control in a slurry reactor under atmospheric pressure in n-decane solution using the linoleic acid-to-surface ruthenium molar ratios 2.5, 5, and 10, was investigated by mathematical modeling. Over such catalyst and at the conditions used, the reaction scheme involves competitive isomerization of linoleic acid to conjugated linoleic acid isomers as well as hydrogenation of linoleic acid to oleic acid. These competing steps are through a complex relation strongly affected by chemisorbed hydrogen on the Ru surface. The concentrations of chemisorbed hydrogen and adsorbed key intermediates on the ruthenium surface influenced the catalytic activity and the selectivities toward isomerization and hydrogenation products through a complex relation. The isomerization rate was enhanced by catalyst preactivation under hydrogen, but increased hydrogen coverage on the Ru surface also restrained the isomerization selectivity. A reaction network and mechanism were advanced. Mechanistic models were developed from proposed elementary stage mechanism and corresponding kinetic equations were derived. Data fitting allowed discrimination between rival mechanistic models, more specifically the influence of hydrogen on the isomerization kinetics.

Ruthenium‐Catalyzed Olefin Metathesis Double‐Bond Isomerization Sequence.

AbstractFor Abstract see ChemInform Abstract in Full Text.

DFT Study on Double-bond Isomerization of &lt;i&gt;trans&lt;/i&gt;-2-butene Catalyzed by Zeolites

Using density functional theory(DFT), the double-bond isomerization of 1-butene to trans-2-butene over zeolites is investigated with a 3T cluster model simulating zeolite. At the B3LYP/6-31G(d, p) level, the complete geometry optimization and the activation energy calculation are performed with a E(subscript ZP) correction. It is found that the process include three steps, physical adsorption →chemical reaction →physical desorption. Firstly, the OH group of the acidic site of zeolite adsorbs the double-bond of 1-butene and forms a π-complex. Secondly, the double-bond isomerization reaction shows a concerted mechanism and yields the adsorbed trans-2-butene. Lastly, trans-2-butene is produced by desorption and the zeolite active site is restored. The calculated apparent activation energy is 57.1 kJ•mol^(-1), which is in agreement with the experimental data.

Ruthenium-Catalyzed Olefin Metathesis Double-Bond Isomerization Sequence

A novel ruthenium-catalyzed tandem ring-closing metathesis (RCM) double-bond isomerization reaction is described in this paper. The utility of this method for the efficient syntheses of five-, six-, and seven-membered cyclic enol ethers is demonstrated. It relies on the conversion of a metathesis-active ruthenium carbene species to an isomerization-active ruthenium-hydride species in situ. This conversion is achieved by using various additives. Scope and limitations of the different protocols are discussed, and some mechanistic considerations based on (31)P and (1)H NMR spectroscopic studies are presented.

Alumina-supported cobalt–molybdenum sulfide modified by tin via surface organometallic chemistry: application to the simultaneous hydrodesulfurization of thiophenic compounds and the hydrogenation of olefins

Surface organometallic chemistry has been used to deposit tin atoms on an alumina-supported cobalt–molybdenum sulfide. The EXAFS spectra at the Mo and Co K-edges were not changed significantly by tin doping, which means that the initial morphology of sulfide phases was preserved during the synthesis. 119Sn Mössbauer spectroscopy indicated that the main neighbors of the deposited tin atoms were sulfur and oxygen atoms with no significant formation of metallic tin particles. Tin seems thus to have been deposited either on the sulfide slabs through sulfur bridges or on the support via oxygen bonding. According to the infrared spectroscopy, tin doping led to the blocking of different surface sites with slight electronic structure modification. Those surface sites are sulfur vacancies on sulfide slabs, Al3+ or hydroxyl groups on the support, or “interfacial” sites: support hydroxyl groups H-bonded with sulfide phases.The impact of tin doping on the activity and selectivity of the sulfide phases was studied by catalytic tests carried out using a synthetic FCC gasoline feed. Three main reactions were found to be involved: hydrodesulfurization of sulfur-containing molecules, double-bond isomerization and hydrogenation of olefins. Olefin hydrogenation was preceded by double-bond isomerization reaction, which gave quickly thermodynamically equilibrated composition. No clear correlation could be made between tin doping and isomerization performance and catalyst support was proposed as the main actor for this reaction. Small amounts of tin had little effect on the hydrogenation activity, but higher loadings resulted in an important decrease in activity. Contrary to the case of olefin hydrogenation, thiophene hydrodesulfurization activity decreased drastically at a low tin loading, and continued to decrease but more slightly at higher loadings. By comparison of the activity variations and the characterization results, the sulfur vacancies were found to play a major role in the hydrodesulfurization process. Interfacial sites were assumed to be involved in one of the key steps in the olefin hydrogenation pathway.

Hydrogenation versus isomerization in α,β-unsaturated alcohols reactions over Pd/TiO2 catalysts

Abstract Liquid phase hydrogenation and isomerization of some α,β-unsaturated primary and secondary alcohols have been investigated in tetrahydrofuran over a 2.5% TiO 2 supported palladium catalyst at 303 K and 0.01 MPa partial hydrogen pressure. The double bond isomerization reaction of these substrates leads also to formation of the corresponding saturated aldehydes or ketones. Catalytic activity and selectivity were found to depend strongly on the steric and electronic effects of the substituents on the double bond of the alcohol. The less crowded is the olefinic bond of the unsaturated alcohol, the higher is the activity. Formation of two σ-alkyl palladium bonded intermediates was postulated to explain the different selectivity towards hydrogenated and isomerized products observed for α,β-unsaturated alcohols used. 2-Propen-1-ol exhibited the highest activity and selectivity for double bond migration leading to propanal up to 80% yield.

Cis-2-Butene-1,4-diol as probe for studying isomerization versus hydrogenation and hydrogenolysis reactions

The liquid phase hydrogenation of cis-2-butene-1,4-diol over a supported palladium catalyst has been investigated in ethanol at 0.01≤PH2≤0.5MPa and 273≤T≤303K. The effect of substrate concentration, catalyst amount, agitation speed and H2 pressure on the reaction rate has also been studied under isothermal conditions. Under reduced H2 pressure, double bond isomerization reaction occurs to a high extent leading to 2-hydroxytetrahydrofuran up to 60% yield. Formation of all reaction products was explained on the basis of a reaction model in which a surface σ-alkyl derivative was postulated and the results were clarified on applying the steady-state approximation to this intermediate. Kinetic rate equations were derived following the Langmuir–Hinshelwood model by assuming a non-competitive adsorption of organic species and hydrogen on the palladium active sites. Rate constants and the adsorption constant for each reaction were determined by a non-linear regression analysis. An excellent agreement between the predicted concentrations versus time profiles and the experimental data was observed. Furthermore, the model predictions of hydrogenated and isomerized compounds formation at different pressures agree well with the experimental results obtained.