Bond Of Epoxides Research Articles

Design of composite based on UiO-66 and ionic liquid for the CO2 conversion into cyclocarbonate

Exploiting an effective catalyst for CO2 conversion into value-added chemicals under mild circumstances still remains a challenge. Herein, UiO-66 decorated with ionic liquids (ILs) (denoted as UiO-66-ILs) were facilely synthesized by the mixed ligands of 1,4-benzene dicarboxylic acid and pyridyl-containing mono-carboxylic acid isomer (including nicotinic acid (NA), isonicotinic acid (INA), and 2-pyridine carboxylic acid (PCA)), followed by the further modification with different bromoalkanes. Among various UiO-66-ILs, UiO-66 derivative containing the ILs composed of PCA and bromoethane (named as UiO-66-ILs(PCA-EtBr)) displayed superior catalytic performance on CO2-epichlorohydrin cycloaddition into chloropropene carbonate, with a high yield of 90 % under 0.1 MPa CO2 at 110 °C without the addition of any solvent and cocatalyst. Whereas, UiO-66-ILs(NA-EtBr) and UiO-66-ILs(INA-EtBr) as analogues of UiO-66-ILs(PCA-EtBr) presented a low yield of 77 % and 67 %, respectively, unveiling that the orientation of carboxyl at monocarboxyl pyridine ligand played a great influence on the catalytic activity. The excellent activity of UiO-66-ILs(PCA-EtBr) was attributed to the synergetic effect of Lewis acidity from MOF nodes for activating C–O bond of epoxide, CO2 absorption by pyridyl moiety, and nucleophilicity of ILs decoration. In addition, UiO-66-ILs(PCA-EtBr) exhibited a broad scope of epoxide substrate, as well as a great recyclability. Moreover, a possible catalytic mechanism was proposed for CO2 conversion into cyclocarbonate.

Synergistic Catalysis of Ionic Liquid-Decorated Covalent Organic Frameworks with Polyoxometalates for CO2 Cycloaddition Reaction under Mild Conditions

The cycloaddition of carbon dioxide (CO2) with epoxides to yield highly value-added cyclic carbonates is an effective way to chemically utilize and convert CO2. Here, a heterogeneous catalyst of imidazole ionic liquid-decorated covalent organic framework with polyoxometalates (POM@ImTD-COF) was constructed by the covalent modification of ionic liquids to COFs and the electrostatic interaction between POMs and ionic liquids. The obtained POM@ImTD-COF shows high catalytic activity for CO2 cycloaddition reaction under mild conditions (1 atm and 80 °C) in the presence of a co-catalyst, and the catalytic activity of POM@ImTD-COF has no obvious decrease during reusing five times. The excellent catalytic performance is mainly attributed to the synergistic effect of ionic liquids, POMs, and COFs. In the cycloaddition process, ionic liquids and the co-catalyst weaken the C-O bond of epoxides and promote the ring opening of epoxides. POMs as the Lewis acids facilitate the insertion of CO2 to form reaction intermediates. The multiple activation effect of ionic liquids and POMs together with the CO2 adsorption effect and well-dispersed active sites in COFs contribute to the remarkable catalytic performance.

Efficient synthesis of amine-functionalized graphene oxide by ultrasound-assisted reactions and density functional theory mechanistic insight

Herein described is a facile preparation protocol by which amino-alcohol derivatives of graphene oxide (GO) can be conveniently synthesized in high yield and short time by an ultrasound treatment of ethanol-graphite-oxide suspensions and amines. Linear primary amines of different chain length rapidly react with graphite oxides prepared from powder and flakes, leading to the formation of GO amino-alcohol derivatives. Characterization of the amine-modified materials by XRD, TGA, FTIR, and Raman spectroscopy demonstrates the proposed derivatization; the findings are corroborated by SEM and TEM observations. Additionally, quantum-chemical investigations shed additional light on the reaction, suggesting an alcohol-accelerated SN2 mechanism where the initial step, the simultaneous formation of a C–N bond (GO-amine) and rupture of an epoxide bond in GO, is rate-determining. Energy barriers lower than 8 kcal/mol are estimated, which can be overcome with the energy supplied by the sonotrode tip (ca. 2 kcal) and the use of ethanol to facilitate it.

Regio-selective metalloradical catalyzed carbon[sbnd]oxygen bond cleavage of epoxides with rhodium porphyrin hydride

The carbon-oxygen bond activation (COA) of epoxides with rhodium(II) and rhodium (III) porphyrins have been examined. RhIII(ttp)H (1) (ttp = 5,10,15,20-tetratolylporphyrinato dianion) was found to cleave the less sterically hindered carbon-oxygen bond of epoxides selectively at room temperature under neutral conditions to generate the stoichiometric COA product rhodium porphyrin β-hydroxyl alkyls in moderate to good yields.

Commercial Polymer Microsphere Grafted TBD-Based Ionic Liquids as Efficient and Low-Cost Catalyst for the Cycloaddition of CO2 with Epoxides

Development of efficient, cheap and recyclable catalysts for the synthesis of cyclic carbonates from CO2 and epoxides is still a very attractive topic. Herein, the polymer grafted TBD-based ionic liquids (ILs) were fabricated from commercially available polystyrene (PS) and ingredients of the ILs, and used as heterogeneous catalysts for the conversion of CO2 into cyclic carbonates in the absence of solvent and co-catalyst. To improve the catalytic performance, various substitutes (such as –COOH, –OH and –NH2) were functionalized on the TBD cation. Among the as-obtained catalysts, carboxyl-containing catalyst (PS–[CETBD]Br) showed superior activity than others, which may be attributed to the stronger polarization capability of –COOH on the C–O bond of epoxide through the formed hydrogen bonding. Additionally, the combined synergistic effect of the nucleophilic attack by the halide anions also account for the facile ring-opening of epoxide. It is noted that CO2 can be activated by the formation of carbamate between CO2 and alkaline nitrogen of the TBD cations, thus facilitating the formation of cyclic carbonates. Moreover, the catalyst shows good chemical stability and catalytic reusability, which is very important for the practical conversion of CO2 in chemical industry.

Reaction of Benzyne with Styrene Oxide: Insertion of Arynes into a C-O Bond of Epoxides

Benzyne inserts into one of the C-O bonds of styrene oxide to form a dihydrobenzofuran as the major product together with five other reaction products. A detailed study of the reaction mixture clarified an intriguing forty-year-old personal communication from Stiles and Haag. © Georg Thieme Verlag Stuttgart.

Epoxide Formation on the Aromatic B Ring of Flavanone by Biphenyl Dioxygenase of Pseudomonas pseudoalcaligenes KF707

Prokaryotic dioxygenase is known to catalyze aromatic compounds into their corresponding cis-dihydrodiols without the formation of an epoxide intermediate. Biphenyl dioxygenase from Pseudomonas pseudoalcaligenes KF707 showed novel monooxygenase activity by converting 2(R)- and 2(S)-flavanone to their corresponding epoxides (2-(7-oxabicyclo[4.1.0]hepta-2,4-dien-2-yl)-2, 3-dihydro-4H-chromen-4-one), whereby the epoxide bond was formed between C2' and C3' on the B ring of the flavanone. The enzyme also converted 6-hydroxyflavanone and 7-hydroxyflavanone, which do not contain a hydroxyl group on the B-ring, to their corresponding epoxides. In a previous report (S.-Y. Kim, J. Jung, Y. Lim, J.-H. Ahn, S.-I. Kim, and H.-G. Hur, Antonie Leeuwenhoek 84:261-268, 2003), however, we found that the same enzyme showed dioxygenase activity toward flavone, resulting in the production of flavone cis-2',3'-dihydrodiol. Extensive structural identification of the metabolites of flavanone by using high-pressure liquid chromatography, liquid chromatography/mass spectrometry, and nuclear magnetic resonance confirmed the presence of an epoxide functional group on the metabolites. Epoxide formation as the initial activation step of aromatic compounds by oxygenases has been reported to occur only by eukaryotic monooxygenases. To the best of our knowledge, biphenyl dioxygenase from P. pseudoalcaligenes KF707 is the first prokaryotic enzyme detected that can produce an epoxide derivative on the aromatic ring structure of flavanone.

Soybean Epoxide Hydrolase: IDENTIFICATION OF THE CATALYTIC RESIDUES AND PROBING OF THE REACTION MECHANISM WITH SECONDARY KINETIC ISOTOPE EFFECTS

Soybean epoxide hydrolase catalyzes the oxirane ring opening of 9,10-epoxystearate via a two-step mechanism involving the formation of an alkylenzyme intermediate, which, in contrast to most epoxide hydrolases studied so far, was found to be the rate-limiting step. We have probed residues potentially involved in catalysis by site-directed mutagenesis. Mutation of His(320), a residue predicted from sequence analysis to belong to the catalytic triad of the enzyme, considerably slowed down the second half-reaction. This kinetic manipulation provoked an accumulation of the reaction intermediate, which could be trapped and characterized by electrospray ionization mass spectrometry. As expected, mutation of Asp(126) totally abolished the activity of the enzyme from its crucial function as nucleophile involved in the formation of the alkylenzyme. In line with its role as the partner of His(320) in the "charge relay system," mutation of Asp(285) dramatically reduced the rate of catalysis. However, the mutant D285L still exhibited a very low residual activity, which, by structural analysis and mutagenesis, has been tentatively attributed to Glu(195), another acidic residue of the active site. Our studies have also confirmed the fundamental role of the conserved Tyr(175) and Tyr(255) residues, which are believed to activate the oxirane ring. Finally, we have determined the secondary tritium kinetic isotope effects on the epoxide opening step of 9,10-epoxystearate. The large observed values, i.e. (T)(V/K(m)) approximately 1.30, can be interpreted by the occurrence of a very late transition state in which the epoxide bond is broken before the nucleophilic attack by Asp(126) takes place.

Unusual triplet state relaxation in C60 oxide

Abstract The photophysics of C 60 O has been investigated. The calibrated UV–visible absorption spectrum, fluorescence quantum yield, and triplet–triplet absorption spectrum are compared to those of C 60 . Intrinsic triplet decay is anomalous, with typically weak temperature dependence below 180 K but unusual strong activation ( E A =20 kJ mol −1 ) above. At 295 K, the triplet lifetime is only 4.2 μs, or 34 times shorter than that of C 60 . It is proposed that the activated decay channel involves reversible cleavage of the C–C epoxide bond. C 60 O efficiently quenches triplet C 60 with a rate constant of 3.6×10 9 M −1 s −1 .

Surface modification of polymers. III. Grafting of stabilizers onto polymer films

AbstractPolypropylene, polystyrene, and polyethylene have been grafted with glycidyl acrylate and glycidyl methacrylate. After 5 min of grafting with UV irradiation, polystyrene was extensively grafted to 91% coverage of glycidyl acrylate according to ESCA, while polypropylene was grafted to only 50% coverage. With glycidyl acrylate the grafting depth is estimated to be 0.1 μm for PP and 0.23 μm for PS. Glycidyl methacrylate is grafted in a thinner layer than glycidyl acrylate. The stabilizers 2,4‐dihydroxybenzophenone, phenyl 4‐aminosalicylate, and 4‐amino‐2,2,6,6‐tetramethylpiperidine were attached to LDPE surfaces containing grafted glycidyl acrylate by opening of the epoxide bond. The reaction between epoxide and stabilizer is diffusion controlled at high concentrations of stabilizer. UV spectroscopy on an LDPE film grafted and reacted with 2,4‐dihydroxybenzophenone showed that 227 nmol stabilizer/cm2 was bound to the surface.

Reaction of lithium aluminium hydride with 4,4-dimethyl-4a,5-epoxy-A-homocholestane derivatives and mass spectral fragmentation of some degradation products

Reductive opening of the epoxide ring of stereoisomeric 4,4-dimethyl-4a,5-epoxy-A-homocholestane derivatives with oxygen containing substituent (OH, OCOCH3, OCH3) in the position 3 was investigated. In the absence of other directing effects, than the stereoelectronic ones, the epoxide ring of 4aα,5α-epoxides is opened at the side of the less substituted carbon C(4a), under formation of 5α-hydroxy derivatives, while in the case of 4aβ,5β-epoxides both the cleavage of the C(4a)-O bond, leading to the formation of 5β-hydroxy derivatives, and the cleavage of the C(5)-O bond, leading to the formation of 4aβ-hydroxy-5,6-unsaturated derivatives take place. The participation of the substituent in the position 3 leads to an abnormal cleavage both in 4aα,5α-and 4aβ,5β-epoxides, i.e. to the cleavage of the C(5)-O bond under formation of 3,5-epoxides. The effect of the character of the substituent in the position 3 on the direction of the reductive cleavage of the epoxide ring is also discussed from the point of view of conformational and electronic effects. In mass spectrometry the main product of the fragmentation of the molecular ions of the 4a-hydroxy-3,5-epoxides XIII and XXV and the 4a-ketones XVII and XXVIII is the ion [C23H40O]+. which is formed after the breaking of the C(3)-O bond by the splitting off of the ring A. The fragmentation of the molecular ion of the semi-ketal XVIII is determined by the cleavage of the epoxide bond O-C(5).

Photochemistry of 5.6-epoxy-1,3-dienes : Influence of a 7-hydroxy substituent

Triplet sensitization of the 7-hydroxy-5,6-epoxy-1,3-diene 10 causes cleavage of the C(5),0 epoxide bond followed by the formation of the three isomers 11– 13 or induces scission of the C(6), C(7) bond followed by the formation of the aldehyde 14 and the bicyclo[3.2.0]heptanols 15 and 16. However, irradiation of the corresponding acetate 18 gives only C(5),0 epoxide bond scission ( 18 → f) followed by the cyclization process f → 19, the 1,2-Me shifts f → 20, 21 and the γ-H abstraction f → g leading to the cyclopropane formation g → 22.