Showing papers on "Epoxide published in 2012"

Kinetic Studies of the Alternating Copolymerization of Cyclic Acid Anhydrides and Epoxides, and the Terpolymerization of Cyclic Acid Anhydrides, Epoxides, and CO2 Catalyzed by (salen)CrIIICl

Abstract: Copolymerization of a series of cyclic acid anhydrides with several epoxides using (salen)CrCl/onium salt catalysts has afforded polyesters with high molecular weights and narrow molecular weight distributions. The (salen)CrCl catalyst in the presence of the onium salts with formula PPNX (X = Cl–, N3–) for the copolymerization of the anhydrides, maleic (MA), succinic (SA), phthalic (PA), cyclohexene (CHE), and cyclohexane (CHA) with the epoxides, cyclohexene oxide (CHO), propylene oxide (PO), and styrene oxide (SO) resulted in completely alternating enchainment of monomers to provide pure polyesters. Temperature dependent studies of the ring-opening copolymerization of phthalic anhydride and cyclohexene oxide monomers in toluene solution have yielded activation parameters of ΔH‡ = 67.5 kJ mol–1 and ΔS‡ = −95.3 J mol–1, where the rate limiting step was ring-opening of the epoxide by the enchained anhydride. For the cyclic acid anhydride (CHA), the relative order of reactivity with epoxides decreased PO > C...

Formation of Cyclic Carbonates from Carbon Dioxide and Epoxides Coupling Reactions Efficiently Catalyzed by Robust, Recyclable One-Component Aluminum-Salen Complexes

Abstract: Aluminum salen complexes bearing appended quaternary ammonium salt substituents have been synthesized and shown to be effective catalysts for the coupling of epoxides and carbon dioxide to generate cyclic carbonates. 27Al NMR spectra have demonstrated that these exist as both five- and six-coordinate Al(III) species in dimethylsulfoxide (DMSO) solution, whereas only a five-coordinate Al(III) species was detected in the (salen)AlCl analogue in the presence of an external onium salt. The onium salt group tethered on the salen ligand was found to play an important role in enhancing the catalytic activity. The effects of reaction variables such as temperature, time, pressure, molar ratio of epoxide to catalyst on the catalytic performance were systematically investigated. These bifunctional catalysts were found to be highly stable to moisture and oxygen, resistant to impurities, and recyclable with only minor losses in catalytic activity.

Cobaltoporphyrin-Catalyzed CO2/Epoxide Copolymerization: Selectivity Control by Molecular Design

Abstract: A series of cobalt(III) chloride porphyrin complexes of the general formula 5,10,15,20-tetra(p-alkoxy)phenylporphyrin cobalt chloride (4b–e) and the related 5,10,15,20-tetra(p-nitro)phenylporphyrin cobalt chloride (4f) are presented and their reactivity toward propylene oxide (PO)/CO2 coupling/copolymerization is explored. While the nitro-substituted complex (4f), in conjunction with an onium salt, shows moderate activity toward cyclization, the 4b–e/onium systems show superior copolymerization activity in comparison to tetraphenylporphyrin Co(III) chloride (4a) with high selectivity and conversion to poly(propylene carbonate) (PPC). A comprehensive copolymerization behavior study of the alkoxy-substituted porphyrin complexes 4b–e in terms of reaction temperature and CO2 pressure is presented. Complexes bearing longer alkoxy-substituents demonstrate the highest polymerization activity and molecular weights, however all substituted catalyst systems display a reduced tolerance to increased temperature with ...

The Origin of the Activity of Amine‐Functionalized Metal–Organic Frameworks in the Catalytic Synthesis of Cyclic Carbonates from Epoxide and CO2

Abstract: The conversion of carbon dioxide into bulk chemicals at lower energy cost is a scientific and technological challenge. 2] Acid–base-pair catalysts are interesting for such applications because they can promote concerted reactions. The adsorption of CO2 occurs on the basic sites to form activated species; then, the epoxide coordinates onto the neighboring acidic site and ring-opening occurs by nucleophilic attack of the activated species. One example of rationally designed acid–base catalysts is amine-functionalized mesoporous Ti(Al)-SBA-15. Ratnasamy and co-workers reported a “volcanic plot” of the reaction rate as a function of amine basicity, in which secondary amines showed the optimum reactivity. They suggested that CO2 is too-weakly activated on primary amines, whereas it is too-strongly adsorbed onto tertiary amines. Hence, moderate CO2-adsorption onto amine-functionalized solid acids appears to provide good candidates as catalyst for this reaction. It is generally acknowledged that metal–organic frameworks (MOFs) are appropriate materials for designing single-site acid– base catalysts. In a spectroscopic study on MOFs, Gascon et al. showed the functionalization of MOF-5 by an amino substituent (2-amino-1,4-benzenedicarboxylate), also known as IRMOF-3. The amine group acted as an electron donor (Lewis base) on CO2. [7] This “amino effect” on CO2-adsorption has been experimentally observed on various MOFs and was later confirmed by ab initio calculations. The concept of concerted reactions on acid–base MOFs has been reported by Baiker and co-workers in the synthesis of propylene carbonate with amine-containing mixed-linker MIL-53 (co-catalyzed by tetraalkylammonium halides). A turnover frequency (TOF) of 400 h 1 was measured under solvent-free conditions. Another significant example is the activity of amine-functionalized UiO66 in the cross-aldol reaction reported by De Vos and co-workers. Hence, we anticipated that the use of MOFs that contain acid–base pairs, such as a Brønsted acid MOF that is functionalized with NH2, could lead to potential catalyst candidates for the synthesis of carbonate from CO2. Herein, we elucidate the role of the NH2-functionalization of MIL-68(In)-NH2 [14] as a catalyst for the synthesis of styrene carbonate from styrene oxide and CO2. Surprisingly, we show by using ab initio calculations and spectroscopic investigations that the modification of the electronic structure of the inorganic component by ligand-substitution has a much-larger impact on the activation of CO2 than the amine substituents. MIL-68(In) and MIL-68(In)-NH2 were prepared by precipitation reactions of indium nitrate and terephthalic acid or aminoterephthalic acid in DMF. X-ray diffraction, surface areas, DRIFT analysis, and the H NMR spectra were in agreement with previous reports (see the Supporting Information). These results confirmed that the MOFs were empty of any organic solvent or occluded reactants. MIL-68(In) and MIL-68(In)-NH2 were tested in the synthesis of carbonate (Scheme 1). This evaluation was performed in a glass vial at 150 8C under CO2 pressure (8 bar).

Tension trapping of carbonyl ylides facilitated by a change in polymer backbone.

Abstract: Epoxidized polybutadiene and epoxidized polynorbornene were subjected to pulsed ultrasound in the presence of small molecules capable of being trapped by carbonyl ylides. When epoxidized polybutadiene was sonicated, there was no observable small molecule addition to the polymer. Concurrently, no appreciable isomerization (cis to trans epoxide) was observed, indicating that the epoxide rings along the backbone are not mechanically active under the experimental conditions employed. In contrast, when epoxidized polynorbornene was subjected to the same conditions, both addition of ylide trapping reagents and net isomerization of cis to trans epoxide were observed. The results demonstrate the mechanical activity of epoxides, show that mechanophore activity is determined not only by the functional group but also the polymer backbone in which it is embedded, and facilitate a characterization of the reactivity of the ring-opened dialkyl epoxide.

N-halamine copolymers for biocidal coatings

Abstract: A vinyl N-halamine acrylamide monomer was copolymerized with silane-, epoxide-, and hydroxyl group-containing monomers. The resultant copolymers were coated onto cotton fabric through hydrolysis of alkoxy groups with formation of silyl ether bonding, opening of the epoxide ring and subsequent reaction with hydroxyl groups on cellulose, and by crosslinking between the hydroxyl groups on the copolymer and on cellulose, respectively. The coatings were rendered biocidal upon exposure to dilute household bleach solution. All of the coatings provided complete inactivation of about six log of Staphylococcus aureus and Escherichia coli O157:H7 within minutes of contact time. The effects of the aforementioned tethering groups on wash fastness and ultraviolet light exposure were also studied.

Vanadium Catalyzed Synthesis of Cyclic Organic Carbonates

Abstract: Vanadium complexes bearing easily synthesized, differently functionalized salen and salphen ligands were prepared and tested for their ability to catalyze the cycloaddition of carbon dioxide to epoxides resulting in cyclic organic carbonates. The reactivity of the prepared catalysts dramatically increases when a coordinating hydroxyl group is present as a substituent in the organic epoxide. The commercially available [VO(acac)2] complex was used as reference compound, and, in this case, we found that V10O26⋅(NBu4)4 was formed during the catalytic reactions. This compound, characterized by X-ray diffraction analysis, is likely the active catalyst, and it results in significantly better yields of cyclic carbonates compared to those obtained with Schiff base containing vanadyl complexes. The high activity of the mixed polyoxo vanadyl-vanadate complex marks it as a powerful catalyst within the context of CO2 fixation chemistry.

Mechanism of the Cycloaddition of Carbon Dioxide and Epoxides Catalyzed by Cobalt-Substituted 12-Tungstenphosphate

Abstract: Co II -substituted a-Keggin- type 12-tungstenphosphate ((n- C4H9)4N)4HA11CoA2O)O39)- A11Co) is synthesized and used as a single-component, solvent-free cata- lyst in the cycloaddition reaction of CO2 and epoxides to form cyclic carbo- nates. The mechanism of the cycloaddi- tion reaction is investigated using DFT calculations, which provides the first computational study of the catalytic cycle of polyoxometalate-catalyzed CO2 coupling reactions. The reaction occurs through a single-electron trans- fer from the doublet Co II catalyst to the epoxide and forms a doublet Co III - carbon radical intermediate. Subse- quent CO2 addition forms the cyclic carbonate product. The existence of radical intermediates is supported by free-radical termination experiments. Finally, it is exhilarating to observe that the calculated overall reaction bar- rier (30.5 kcal mol 1 ) is in good agree- ment with the real reaction rate (83 h 1 ) determined in the present ex- periments (at 1508C).

Nanosponge Formation from Organocatalytically Synthesized Poly(carbonate) Copolymers

Abstract: Advanced organocatalytic synthesis methods were employed to prepare linear poly(carbonate)s with control over functional group incorporation and molecular weight. Pendant allyl or epoxide groups served as reaction partners in thiol–ene click or epoxide–amine reactions with ethylene oxide-containing cross-linking groups to form a panel of six novel poly(carbonate) nanosponges with cross-linking densities ranging from 5, 10, and 20% via an intermolecular chain cross-linking approach.

Mechanistic Basis for High Reactivity of (salen)Co–OTs in the Hydrolytic Kinetic Resolution of Terminal Epoxides

Abstract: The (salen)Co(III)-catalyzed hydrolytic kinetic resolution (HKR) of terminal epoxides is a bimetallic process with a rate controlled by partitioning between a nucleophilic (salen)Co–OH catalyst and a Lewis acidic (salen)Co–X catalyst. The commonly used (salen)Co–OAc and (salen)Co–Cl precatalysts undergo complete and irreversible counterion addition to epoxide during the course of the epoxide hydrolysis reaction, resulting in quantitative formation of weakly Lewis acidic (salen)Co–OH and severely diminished reaction rates in the late stages of HKR reactions. In contrast, (salen)Co–OTs maintains high reactivity over the entire course of HKR reactions. We describe here an investigation of catalyst partitioning with different (salen)Co–X precatalysts and demonstrate that counterion addition to epoxide is reversible in the case of the (salen)Co–OTs. This reversible counterion addition results in stable partitioning between nucleophilic and Lewis acidic catalyst species, allowing highly efficient catalysis thro...

Effect of Surface and Oxygen Coverage on Ethylene Epoxidation

Abstract: Ethylene epoxidation was studied as a function of oxygen coverage; for three different surfaces (111), (100) and (110) of three different IB metals using periodical DFT calculations. Oxygen coverage dependence was tested for 11, 25 and 33 % surface oxygen on Ag(111) surface. Calculations showed that increasing oxygen amount increased the exothermicity of the reaction while lowering the activation barriers. At studied oxygen ratios ethylene oxide and acetaldehyde formations proceed through OMC intermediate. In agreement with earlier studies, predicted selectivity is independent of surface structure. Generally the activation barriers for aldehyde formation are lower than those for epoxide formation on the studied surfaces. On copper surfaces the high stability of the precursor intermediates caused high activation barriers for the product formations. Also, epoxide formation is endothermic with respect to pre-oxygenated copper surfaces. On the other hand gold surfaces showed the smallest activation barriers for the product formations. Ag surfaces did not show conclusive differences for the activation barriers for epoxide versus aldehyde formation, which is in agreement with the ~50 % EO selectivity of the un-promoted metallic silver.

Branched Acid-Degradable, Biocompatible Polyether Copolymers via Anionic Ring-Opening Polymerization Using an Epoxide Inimer

Abstract: The introduction of acid-degradable acetal moieties into a hyperbranched polyether backbone has been achieved by the design of a novel epoxide-based degradable inimer. This new monomer, namely, 1-(glycidyloxy)ethyl ethylene glycol ether (GEGE), has been copolymerized in the anionic ring-opening polymerization (AROP) with ethylene oxide (EO) or glycidol (G), respectively, yielding branched polyethers, that is, P(EO-co-GEGE) and P(G-co-GEGE), that possess an adjustable amount of acid-cleavable acetal units. In addition, a novel class of multiarm star copolymers P(G-co-GEGE-g-EO) with acid-labile polyether core and PEG side chains was synthesized by using the P(G-co-GEGE) copolymers as multifunctional macroinitiators for AROP of EO. The new materials have been characterized in a detailed manner, revealing narrow to moderate molecular weight distributions. The degradation of these polymers under acidic conditions was characterized via SEC and 1H NMR spectroscopy.

Dioxomolybdenum(VI) complexes with pyrazole based aryloxide ligands: synthesis, characterization and application in epoxidation of olefins.

Abstract: Synthesis, characterization, and epoxidation chemistry of four new dioxomolybdenum(VI) complexes [MoO2(L)2] (1–4) with aryloxide-pyrazole ligands L = L1–L4 is described. Catalysts 1–4 are air and moisture stable and easy to synthesize in only three steps in good yields. All four complexes are coordinated by the two bidentate ligands in an asymmetric fashion with one phenoxide and one pyrazole being trans to oxo atoms, respectively. This is in contrast to the structure found for the related aryloxide-oxazoline coordinated Mo(VI) dioxo complex 5. This was confirmed by the determination of the molecular structures of complexes 1–3 by X-ray diffraction analyses. Compounds 1–4 show high catalytic activities in the epoxidation of various olefins. Cyclooctene (S1) is converted to its epoxide with high activity, whereas the epoxidation of styrene (S2) is unselective. Internal olefins (S3 and S4) are also acceptable substrates, as well as the very challenging olefin 1-octene (S5). Catalyst loading can be reduced t...

Sequential enzymatic epoxidation involved in polyether lasalocid biosynthesis.

Abstract: Enantioselective epoxidation followed by regioselective epoxide opening reaction are the key processes in construction of the polyether skeleton. Recent genetic analysis of ionophore polyether biosynthetic gene clusters suggested that flavin-containing monooxygenases (FMOs) could be involved in the oxidation steps. In vivo and in vitro analyses of Lsd18, an FMO involved in the biosynthesis of polyether lasalocid, using simple olefin or truncated diene of a putative substrate as substrate mimics demonstrated that enantioselective epoxidation affords natural type mono- or bis-epoxide in a stepwise manner. These findings allow us to figure out enzymatic polyether construction in lasalocid biosynthesis.

Molybdenum(VI) catalysts obtained from η3-allyl dicarbonyl precursors: Synthesis, characterization and catalytic performance in cyclooctene epoxidation

Abstract: The oxidative decarbonylation of the η3-allyl dicarbonyl complexes [Mo(η3-C3H5)Cl(CO)2(L)] (L = 2,2′-bipyridine (bipy) (1), 4,4′-di-tert-butyl-2,2′-bipyridine (di-tBu-bipy) (2)) by reaction with aqueous tert-butylhydroperoxide (TBHP) or H2O2 gave the following compounds in good to excellent yields: the oxo-bridged dimers [MoO2Cl(L)]2O (L = bipy (3), di-tBu-bipy (6)) using TBHP(10 equiv.)/CH3CN/r.t.; the molybdenum oxide/bipyridine hybrid material {[MoO3(bipy)][MoO3(H2O)]}n (4) and the octanuclear complex [Mo8O24(di-tBu-bipy)4] (7) using TBHP(50 equiv.)/H2O/70 °C; the oxodiperoxo complexes MoO(O2)2(L) (L = bipy (5), di-tBu-bipy (8)) using H2O2(10 equiv.)/CH3CN/r.t. The structure of 7·x(solvent) (where solvent = CH2Cl2 and/or diethyl ether) was determined by single crystal X-ray diffraction. Despite possessing the same windmill-type complex as that described previously for 7·10CH2Cl2, the crystal structure of 7·x(solvent) is unique due to differences in the crystal packing. Compounds 1–8 were examined as catalysts or catalyst precursors for the epoxidation of cyclooctene using aqueous TBHP or H2O2 as oxidant at 55 or 70 °C. Reactions were performed without co-solvent or with the addition of water, ethanol or acetonitrile. Cyclooctene oxide was always the only reaction product. Solids recovered after 24 h reaction at 70 °C were identified by FT-IR spectroscopy as the hybrid 4 from (1,3–5)/TBHP, complex 5 from (1,3–5)/H2O2, and complex 8 from (2,6–8)/H2O2. With TBHP as oxidant, the highest epoxide yields (for 24 h reaction at 70 °C) were obtained using excess H2O as solvent (28–38% for 1,3–5; 87–98% for 2,6–8), while with H2O2 as oxidant, the highest epoxide yields were obtained using CH3CN as solvent (54–81% for 3–8).

Synthesis of cyclic carbonates:catalysis by an iron-based composite and the role of hydrogen bonding at the solid/liquid interface

Abstract: Say it with flowers: Flower-like Fe(3)O(4)@Fe(OH)(3) composite catalysts show good activity and stability in the synthesis of cyclic carbonates from epoxides and CO(2). The role of hydrogen bonding between the surface hydroxyl groups of the solid and the epoxides at the solid/liquid interface is proposed as a key factor in activating the epoxide and stabilizing the ring-opened carbonate intermediates.

New insights into the mechanism of oxodiperoxomolybdenum catalysed olefin epoxidation and the crystal structures of several oxo-peroxo molybdenum complexes.

Abstract: [Mo(O)(O2)2(L)2] compounds (L = pz, pyrazole; dmpz, 3,5-dimethylpyrazole) were reacted stoichiometrically, in the absence of an oxidant, with cis-cyclooctene in an ionic liquid medium where selective formation of the corresponding epoxide was observed. However, this oxo-transfer reaction was not observed for some other olefins, suggesting that alternative reaction pathways exist for these epoxidation processes. Subsequently, DFT studies investigating the oxodiperoxomolybdenum catalysed epoxidation model reaction for ethylene with hydrogen peroxide oxidant were performed. The well known Sharpless mechanism was first analysed for the [Mo(O)(O2)2(dmpz)2] model catalyst and a low energy reaction pathway was found, which fits well with the observed experimental results for cis-cyclooctene. The structural parameters of the computed dioxoperoxo intermediate [Mo(O)2(O2)(dmpz)2] in the Sharpless mechanism compare well with those found for the same moiety within the [Mo4O16(dmpz)6] complex, for which the full X-ray report is presented here. A second mechanism for the model epoxidation reaction was theoretically investigated in order to clarify why some olefins, which do not react stoichiometrically in the absence of an oxidant, showed low level conversions in catalytic conditions. A Thiel-type mechanism, in which the oxidant activation occurs prior to the oxo-transfer step, was considered. The olefin attack of the hydroperoxide ligand formed upon activation of hydrogen peroxide with the [Mo(O)(O2)2(dmpz)2] model catalyst was not possible to model. The presence of two dmpz ligands coordinated to the molybdenum centre prevented the olefin attack for steric reasons. However, a low energy reaction pathway was identified for the [Mo(O)(O2)2(dmpz)] catalyst, which can be formed from [Mo(O)2(O2)(dmpz)2] by ligand dissociation. Both mechanisms, Sharpless- and Thiel-type, were found to display comparable energy barriers and both are accessible alternative pathways in the oxodiperoxomolybdenum catalysed olefin epoxidation. Additionally, the molecular structures of [Mo(O)(O2)2(H2O)(pz)] and [Hdmpz]4[Mo8O22(O2)4(dmpz)2]·2H2O and the full X-ray report of [Mo(O)(O2)2(pz)2] are also presented.