Showing papers on "Epoxide published in 2020"

Quaternary phosphonium salt-functionalized Cr-MIL-101: A bifunctional and efficient catalyst for CO2 cycloaddition with epoxides

Abstract: Integration of synergic Lewis acid sites and nucleophilic anions that can facilitate ring-opening of epoxide is a good way to develop efficient catalyst for cycloaddition of CO2 with epoxides. Herein, we prepared a novel metal-organic framework (MOF) catalyst (Cr-MIL-101-[BuPh3P]Br) through grafting quaternary phosphonium salt ionic liquid (IL) on Cr-MIL-101 by a facile post-synthetic approach. The introduction of phosphonium salt IL highly improves the catalytic activity and stability compared with the parent Cr-MIL-101-NH2. In the absence of any solvent and co-catalyst, Cr-MIL-101-[BuPh3P]Br showed excellent catalytic activity for the cycloaddition reaction under moderate reaction conditions. Under optimized conditions, the yield and TOF of propylene carbonate can be achieved 97.8% and 1086.7 h−1, respectively. This is because the synergetic interaction of dual functional sites including Cr3+ as Lewis acid sites in MOF and Br- as nucleophile in IL could promote the ring-opening of epoxide through the coordination of Cr3+ sites with O atom and the nucleophilic attack of Br- on the less sterically hindered β-carbon atom of epoxide, respectively. Comparison with other reported ILs-functionalized Cr-MIL-101 or other kinds of MOFs catalysts reveals that Cr-MIL-101-[BuPh3P]Br has superior catalytic performance and potential. Moreover, Cr-MIL-101-[BuPh3P]Br as a heterogeneous catalyst also showed good chemical stability and reusability.

Critical Roles of Doping Cl on Cu2O Nanocrystals for Direct Epoxidation of Propylene by Molecular Oxygen.

Abstract: Direct epoxidation of propylene by molecular oxygen alone is one of the "dream reactions" in heterogeneous catalysis. Despite much effort, the yield of propylene epoxide is still too low to be commercially attractive due to the trade-off between conversion and selectivity. Here, we demonstrate that doping Cl into the lattice of Cu2O nanocrystals by the intergrowth method not only can enhance the catalytic selectivity and conversion of direct propylene epoxidation but also can solve the long-existing Cl loss problem. In particular, Cl-doped rhombic dodecahedral Cu2O with (110) exposing facets exhibited 63% PO selectivity with a 12.0 h-1 turnover frequency at 200 °C, outperforming any other coinage metal-based catalysts under mild conditions. Comprehensive characterization and theoretical calculations revealed that the Cl-decorated Cu(I) facilitated formation of electrophilic oxygen species, thus boosting the production of propylene oxide. This work provides a general strategy to develop catalysts and explore the promoter effect by creating uniform isolated anion doping to activate a nearby metal center by virtue of well-defined nanocrystals.

Dual hydrogen-bond donor group-containing Zn-MOF for the highly effective coupling of CO2 and epoxides under mild and solvent-free conditions

Abstract: A novel zinc(II)-based 3D metal organic framework (MOF) [Zn3(L)3(H2L)·2DMF·H2O] with dual hydrogen-bond donor (HBD) groups of a free carboxyl and amine, was synthesized solvothermally via 2-aminoterephthalic acid (H2L) and 3,5-pyridinedicarboxylic acid ligands. The carboxyl and amine in the prepared Zn3(L)3(H2L) acting as HBD groups can promote the CO2 cycloaddition reaction with epoxides. Besides this, the contained sufficient amino groups showing Lewis base properties also facilitated Zn3(L)3(H2L) to activate CO2 by forming a carbamate intermediate, while Zn(II) centers acted as Lewis-acid sites accomplishing the epoxide activation. Therefore, Zn3(L)3(H2L) with Lewis acid–base properties and dual HBD groups exhibited an efficient heterogeneous catalysis for the coupling of epoxides and CO2. The yield of the propylene carbonate (PC) achieved 99% under 80 °C, 1.0 MPa CO2 and solvent-free conditions. Corresponding carbonate yields of various epoxides could be over 95% even at room temperature by prolonging the reaction time. Moreover, Zn3(L)3(H2L) showed extraordinary versatility to various epoxides and excellent recycling without any obvious loss in activity. Furthermore, a plausible mechanism was proposed for the CO2 cycloaddition to epoxides based on the structural evidence and catalytic effects.

Regioselective Cross-Electrophile Coupling of Epoxides and (Hetero)aryl Iodides via Ni/Ti/Photoredox Catalysis.

Abstract: A cross-electrophile coupling reaction of epoxides and (hetero)aryl iodides that operates via the merger of three catalytic cycles involving a Ni-, Ti-, and organic photoredox catalyst has been developed. Three distinct classes of epoxides, styrene oxides, cyclic epoxides, and terminal aliphatic epoxides, all undergo coupling in moderate to good yield and high regioselectivity with the use of three different nitrogen-based ligands for Ni under otherwise identical reaction conditions. The mild reaction conditions accommodate a broad scope of abundant and complex coupling partners. Mechanistic studies suggest that when styrene oxides are employed radical intermediates are involved via Ti-radical ring-opening of the epoxide. Conversely, for terminal aliphatic epoxides, involvement of an iodohydrin intermediate enables the formation of the unexpected linear product.

CO2 fixation by cycloaddition of mono/disubstituted epoxides using acyl amide decorated Co(II) MOF as a synergistic heterogeneous catalyst

Abstract: Dual ligand 3D MOF {[Co(BDC)(L)]·2H2O.xG}n (CoMOF-2; G = guest) was synthesized via simple room temperature stirring method. Bulk Phase purity of CoMOF-2 was assessed by various physicochemical methods including X‐ray diffraction (XRD). CO2 adsorption isotherms indicate that activated CoMOF-2 is efficient in CO2 uptake, which has been utilized for the CO2-Epoxide cycloaddition. The catalytic ability of CoMOF-2 as a binary catalyst revealed excellent results for variety of monosubstituted epoxide under solvent‐free conditions (1 bar/40 °C/12 h). Interestingly CoMOF-2/KI also showed great potential as a heterogeneous catalyst for disubstituted epoxide (10 bar/120 °C/24 h) with high yields/selectivity. The catalytic efficiency of the present investigation for scantly explored disubstituted epoxide is better/on par with the earlier reports and the recyclability of the catalyst is an added advantage. Probable mechanism for the catalytic reaction is deduced and verified the representative energy profile for cycloaddition of CO2-Cyclohexane oxide (CHO) by DFT calculation.

High-Activity Organocatalysts for Polyether Synthesis via Intramolecular Ammonium Cation Assisted S N 2 Ring-Opening Polymerization.

Abstract: This manuscript describes a kind of bifunctional organocatalyst with unprecedented reactivity for the synthesis of polyethers via ring-opening polymerization (ROP) of epoxides under mild conditions The bifunctional catalyst incorporates two 9-borabicyclo[331]nonane centers on the two ends as Lewis acidic sites for epoxide activation and a quaternary ammonium halide in the middle as the initiating site The catalyst could be easily prepared in two steps from commercially available stocks on up to kilogram scale with ≈100 % yield The organoboron catalyst mediated ROP of epoxides displays living behavior with low catalyst loading (5 ppm) and enables the synthesis of polyethers with molecular weights of over a million grams per mole (>106  g mol-1 ) Based on the investigations on crystal structure of catalyst, MALDI-TOF, and 11 B NMR spectroscopy, an intramolecular ammonium cation assisted SN 2 mechanism is proposed and verified by DFT calculations

Epoxidation Catalyzed by the Nonheme Iron(II)- and 2-Oxoglutarate-Dependent Oxygenase, AsqJ: Mechanistic Elucidation of Oxygen Atom Transfer by a Ferryl Intermediate.

Abstract: Mechanisms of enzymatic epoxidation via oxygen atom transfer (OAT) to an olefin moiety is mainly derived from the studies on thiolate-heme containing epoxidases, such as cytochrome P450 epoxidases. The molecular basis of epoxidation catalyzed by nonheme-iron enzymes is much less explored. Herein, we present a detailed study on epoxidation catalyzed by the nonheme iron(II)- and 2-oxoglutarate-dependent (Fe/2OG) oxygenase, AsqJ. The native substrate and analogues with different para substituents ranging from electron-donating groups (e.g., methoxy) to electron-withdrawing groups (e.g., trifluoromethyl) were used to probe the mechanism. The results derived from transient-state enzyme kinetics, Mossbauer spectroscopy, reaction product analysis, X-ray crystallography, density functional theory calculations, and molecular dynamic simulations collectively revealed the following mechanistic insights: (1) The rapid O2 addition to the AsqJ Fe(II) center occurs with the iron-bound 2OG adopting an online-binding mode in which the C1 carboxylate group of 2OG is trans to the proximal histidine (His134) of the 2-His-1-carboxylate facial triad, instead of assuming the offline-binding mode with the C1 carboxylate group trans to the distal histidine (His211); (2) The decay rate constant of the ferryl intermediate is not strongly affected by the nature of the para substituents of the substrate during the OAT step, a reactivity behavior that is drastically different from nonheme Fe(IV)-oxo synthetic model complexes; (3) The OAT step most likely proceeds through a stepwise process with the initial formation of a C(benzylic)-O bond to generate an Fe-alkoxide species, which is observed in the AsqJ crystal structure. The subsequent C3-O bond formation completes the epoxide installation.

Selective Catalytic Synthesis of 1,2- and 8,9-Cyclic Limonene Carbonates as Versatile Building Blocks for Novel Hydroxyurethanes

Abstract: The selective catalytic synthesis of limonene-derived monofunctional cyclic carbonates and their subsequent functionalisation via thiol-ene addition and amine ring-opening is reported. A phosphotungstate polyoxometalate catalyst used for limonene epoxidation in the 1,2-position is shown to also be active in cyclic carbonate synthesis, allowing a two-step, one-pot synthesis without intermittent epoxide isolation. When used in conjunction with a classical halide catalyst, the polyoxometalate increased the rate of carbonation in a synergistic double-activation of both substrates. The cis isomer is shown to be responsible for incomplete conversion and by-product formation in commercial mixtures of 1,2-limomene oxide. Carbonation of 8,9-limonene epoxide furnished the 8,9-limonene carbonate for the first time. Both cyclic carbonates underwent thiol-ene addition reactions to yield linked di-monocarbonates, which can be used in linear non-isocyanate polyurethanes synthesis, as shown by their facile ring-opening with N-hexylamine. Thus, the selective catalytic route to monofunctional limonene carbonates gives straightforward access to monomers for novel bio-based polymers.

Triazole based cobalt catalyst for CO2 insertion into epoxide at ambient pressure

Abstract: Over the past decades, a lot of efforts have been made for the fixation of carbon dioxide (CO2) into epoxide for the synthesis of industrially important cyclic carbonates. Here, a cobalt(II) complex based on triazole, namely Co(II)-1,2,3-1H-triazole-4-carboxylate, was synthesized, fully characterized by FTIR, NMR, mass spectrometry, and single crystal X-ray diffraction, and used as a catalyst for the cycloaddition of CO2 to epoxides. The catalytic studies demonstrated that the catalyst is highly active for the CO2 fixation, with high turnover number (TON, 85 × 103) even without the use of solvent and at ambient pressure (1 bar) to produce a variety of different cyclic carbonates depending on the epoxide. Remarkably, the catalyst was used continuously further by the addition of a fresh amount of the substrate within the same reaction mixture for at least five successive reaction cycles without any loss in the catalytic activity.

Metal-Free Triazine-Incorporated Organosilica Framework Catalyst for the Cycloaddition of CO2 to Epoxide under Solvent-Free Conditions

Abstract: The silicon-based materials with enriched superficial Si–OH groups are candidates in the field of the cycloaddition of CO2 to epoxide to cyclic carbonate; meanwhile, the triazine ring with a nitrog...

Unraveling the role of the lacunar Na7PW11O39 catalyst in the oxidation of terpene alcohols with hydrogen peroxide at room temperature

Abstract: In this work, we have assessed the activity of various Keggin heteropolyacid (HPA) salts in a new one-pot synthesis route of valuable products, which were obtained from the oxidation of terpenic alcohols (i.e., aldehyde, epoxide, and diepoxide), using a green oxidant (i.e., hydrogen peroxide) at mild conditions (i.e., room temperature). Lacunar Keggin HPA sodium salts were the goal catalysts investigated in this reaction. Starting from the HPAs (H3PW12O40, H3PMo12O40, and H4SiW12O40), we synthesized lacunar sodium salts (Na7PW11O39, Na7PW11O39 and Na8SiW11O39) and a saturated salt (Na3PW12O40). All of them were investigated in oxidation reactions in a homogeneous phase with nerol as a model molecule. Na7PW11O39 was the most active and selective towards the oxidation products. All the catalysts were characterized by FT-IR, TG/DSC, BET, XRD, and SEM-EDS analyses and potentiometric titration. The main reaction parameters were assessed. Geraniol, α-terpineol, β-citronellol and borneol were also successfully oxidized. Special attention was dedicated to correlating the composition and properties of the catalysts with their activity.

Experimental-theoretical study of the epoxide structures effect on the CO2 conversion to cyclic carbonates catalyzed by hybrid titanate nanostructures

Abstract: Hybrid nanostructures were produced from several ionic liquids (ILs) anchored on titanate nanotubes (TNT). Ionic liquids ILs composed by the 1-methyl-3-(3-trimethoxysilylpropyl)imidazolium cation associated with the [Cl−], [BF4−], [PF6−] or [Tf2N−] anions were studied. The highest anchored amounts of IL were obtained with the [Cl−] and [Tf2N−] anions, respectively, of 31.5 and 43.5 % w/w. These hybrid nanostructures were used in the direct conversion of CO2 to cyclic carbonates through the coupling reaction with various epoxides (epichlorohydrin, styrene oxide, glycidyl isopropyl ether, and propylene oxide). With styrene oxide, the best results were obtained using the [Cl−] and [BF4−] IL, showing TON values of 35.6 and 18.4, and TOF values of 17.2 and 9.2 h−1, respectively. The TNT-[IL][Cl] was also used with different epoxides (i.e. epichlorohydrin, styrene oxide, glycidyl isopropyl ether and propylene oxide) being more reactive in the reactions with epichlorohydrin (TON = 86.3, TOF =21.6 h−1) and styrene oxide (TON = 47.0 TOF =11.7 h−1). Theoretical studies showed that the high reactivity of styrene oxide can be associated with their lower HOMO-LUMO energy gap, while epichlorohydrin presented high electron withdrawing effect by chlorine, generating the higher electronegativity. Besides that, by NBO analysis, both molecules presented lower donor – acceptor interact energy which may favor the opening of the ring.

MIL-101(Cr) for CO2 Conversion into Cyclic Carbonates, Under Solvent and Co-Catalyst Free Mild Reaction Conditions

Abstract: Mild reaction conditions (nearly room temperature and atmospheric CO2 pressure) for the cycloaddition of CO2 with epoxides to produce cyclic carbonates were investigated applying MIL-101(Cr) as a catalyst. The MIL-101 catalyst contains strong acid sites, which promote the ring-opening of the epoxide substrate. Moreover, the high surface area, enabling the adsorption of more CO2 (substrate), combined with a large pore size of the catalyst is essential for the catalytic performance. Additionally, epoxide substrates bearing electron-withdrawing substituents or having a low boiling point demonstrated an excellent conversion towards the cyclic carbonates. MIL-101(Cr) for the cycloaddition of carbon dioxide with epoxides is demonstrated to be a robust and stable catalyst able to be re-used at least five times without loss in activity.

Organocatalytic carbon dioxide fixation to epoxides by perfluorinated 1,3,5-triols catalysts

Abstract: In order to improve epoxides conversion to carbonates by fixation of CO2 a new type of perfluorinated triol catalysts was developed. These simple acyclic scaffolds of enhanced acidity are efficient for catalysis through selective H-bonding activation of the epoxide. In combination with TBAI as co-catalyst, this useful transformation is performed under only 1 atmosphere of CO2 and between 30 to 80 °C. Both the 1,3,5-triol motif and the perfluorinated side chains are crucial in order to observe this epoxide opening under such mild conditions. In addition, the stereochemistry of the starting epoxide can efficiently be conserved during the carbonate formation.

Soybean Oil Epoxidation: Kinetics of the Epoxide Ring Opening Reactions

Abstract: The epoxide ring opening reaction (ROR) can be considered as the most important side reaction occurring in the epoxidation of soybean oil reaction network. This reaction consistently reduces the selectivity to epoxidized soybean oil (ESBO). The reaction is also important for producing polyols and lubricants. In this work, the reaction was studied in different operative conditions to evaluate the effect on ROR rate respectively: (i) The Bronsted acidity of the mineral acid (H2SO4 or H3PO4), used as catalyst for promoting the oxidation with hydrogen peroxide of formic to performic acid, that is, the reactant in the epoxide formation; (ii) the concentration of the nucleophilic agents, normally present during the ESBO synthesis like HCOOH, HCOOOH, H2O, H2O2; (iii) the stirring rate that changes the oil–water interface area and affects the mass transfer rate; (iv) the adopted temperature. Many different kinetic runs were made in different operative conditions, starting from an already epoxidized soybean oil. On the basis of these runs two different reaction mechanisms were hypothesized, one promoted by the Bronsted acidity mainly occurring at the oil–water interface and one promoted by the nucleophilic agents, in particular by formic acid. As it will be seen, the kinetic laws corresponding to the two mentioned mechanisms are quite different and this explain the divergent data reported in the literature on this subject. All the kinetic runs were correctly interpreted with a new developed biphasic kinetic model.

Triazine‐based Organic Polymer‐catalysed Conversion of Epoxide to Cyclic Carbonate under Ambient CO2 Pressure

Abstract: In this work we have achieved epoxide to cyclic carbonate conversion using a metal-free polymeric catalyst under ambient CO2 pressure (1.02 atm) using a balloon setup. The triazine containing polymer (CYA-ANIS) was prepared from cyanuric chloride (CYA-Cl) and o-dianisidine (ANIS) in anhydrous DMF as solvent by refluxing under the N2 gas environment. The presence of triazine and amine functional groups in the polymer results in the adsorption of CO2 up to 7 cc/g at 273 K. This inspired us to utilize the polymer for the conversion of a series of functionalised epoxides into their corresponding cyclic carbonates in the presence of tetrabutyl ammonium iodide (TBAI) as co-catalyst. The product has wide range of applications like solvent in lithium ion battery, precursor for polycarbonate, etc. The catalyst was efficient for the conversion of different mono and di-epoxides into their corresponding cyclic carbonates under atmospheric pressure in the presence of TBAI as co-catalyst. The study indicates that epoxide attached with electron withdrawing groups (like, CH2 Cl, glycidyl ether, etc.) displayed better conversion compared to simple alkane chain attached epoxides. This is mainly due to the stabilization of electron rich intermediates produced during the reaction (e. g. epoxide ring opening or CO2 incorporation into the halo-alkoxide anion). This catalyst mixture was capable to maintain its reactivity up to five cycles without losing its activity. Post catalytic characterization clearly supports the heterogeneous and recyclable nature of the catalyst.

Chemoenzymatic Epoxidation of Limonene Using a Novel Surface-Functionalized Silica Catalyst Derived from Agricultural Waste.

Abstract: Limonene is one of the most important terpenes having wide applications in food and fragrance industries. The epoxide of limonene, limonene oxide, finds important applications as a versatile synthetic intermediate in the chemical industry. Therefore, attempts have been made to synthesize limonene oxide using eco-friendly processes because of stringent regulations on its production. In this regard, we have attempted to synthesize it using a cost-effective and eco-friendly process. Chemoenzymatic epoxidation of limonene to limonene oxide was carried out using in situ generation of peroxy octanoic acid from octanoic acid and H2O2. In this study, agricultural-waste rice husk ash (RHA)-derived silica was surface-functionalized using (3-aminopropyl) triethoxysilane (APTS), which was cross-linked using glutaraldehyde for immobilization of Candida antarctica lipase B. Furthermore, the immobilized enzyme was entrapped in calcium alginate beads to avoid enzyme leaching. Thus, limonene oxide was prepared using this catalyst under conventional and microwave heating. The microwave irradiation intensifies the process, reducing the reaction time under the same conditions. Maximum conversion of limonene to limonene oxide of 75.35 ± 0.98% was obtained in 2 h at 50 °C using a microwave power of 50 W. In the absence of microwave irradiation, the conventional heating gave 44.6 ± 1.14% conversion in 12 h. The reaction mechanism was studied using the Lineweaver-Burk plot, which follows a ternary complex mechanism with inhibition due to peroxyoctanoic acid (in other words H2O2). The prepared catalyst shows high reusability and operational stability up to four cycles.

Enantioselective Radical‐Polar Crossover Reactions of Indanonecarboxamides with Alkenes

Abstract: Highly efficient asymmetric intermolecular radical-polar crossover reactions were realized by combining a chiral N,N'-dioxide/NiII complex catalyst with Ag2 O under mild reaction conditions. Various terminal alkenes and indanonecarboxamides/esters underwent radical addition/cyclization reactions to afford spiro-iminolactones and spirolactones with good to excellent yields (up to 99 %) and enantioselectivities (up to 97 % ee). Furthermore, a range of different radical-mediated oxidation/elimination or epoxide ring-opening products were obtained under mild reaction conditions. The Lewis acid catalysts exhibited excellent performance and precluded the strong background reaction.