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1.
A series of M/MgO (M?=?CaO, KNO3, KOH, K2CO3) catalysts were prepared by a dry impregnation method and used for synthesis of glycerol carbonate from glycerol and dimethyl carbonate. It was found that K2CO3/MgO was the most efficient catalyst, with a glycerol carbonate yield of approximately 99% under the conditions: DMC/glycerol molar ratio 2.5:1, catalyst/raw material weight ratio 1%, reaction time 2?h, and reaction temperature 80?°C. FTIR, BET, TEM, and XRD were used for characterization of the catalyst and showed that the active sites seemed to be K2O formed on the K2CO3/MgO catalyst. Finally, a recycling experiment showed that the catalyst was relatively stable and could be reused up to four times, at least, by regeneration.  相似文献   

2.
Dimethoxyalkanes and dimethyl alkanediyl biscarbonates were synthesized by reactions of diols with dimethyl carbonate in the presence of tungsten and cobalt carbonyls. Optimal reactant and catalyst ratios and reaction conditions were found to ensure selective formation of dimethoxyalkanes or dimethyl alkanediyl biscarbonates.  相似文献   

3.
An intermolecular Pd/PPh(3)-catalyzed transesterification of diallyl carbonate with glycerol to generate glycerol carbonate has been developed. Analysis of the reaction kinetics in THF indicates a first-order dependence on Pd and diallyl carbonate, that the Pd bears two phosphines during the turnover limiting event, and that increasing the glycerol concentration inhibits reaction, possibly via change in the polarity of the medium. (13)C isotopic labeling studies demonstrate that the Pd-catalyzed transesterification requires at least one allyl carbonate moiety and that there is rapid equilibrium of the allyl carbonate with CO(2) in solution, even when present only at low concentrations. A mechanism that is consistent with these results involves oxidative addition of the allyl carbonate to Pd followed by reversible decarboxylation, with the intermediate η(1)- and η(3)-allyl Pd alkoxides mediating direct and indirect transesterification reactions with the glycerol. Using this model, successful simulations of the kinetics of reactions conducted under atmospheres of N(2) or CO(2) could be achieved, including switching in selectivity between etherification and transesterification in the early stages of reaction. Reactions with the higher polyols threitol and erythritol are also efficient, generating the terminal (1,2) monocarbonates with high selectivity.  相似文献   

4.
The kinetic patterns of the reaction between dimethyl carbonate and anilines in the presence of a potassium methylate as a catalyst were studied. The mechanism of aminolysis was clarified, which includes the detachment of the proton from the amino group of aniline and the subsequent attack of the resulting anion on the carbonyl group of dimethyl carbonate. It is shown that when the reaction occurs in the dimethyl carbonate-methanol 3:1 system, the process can be described as an irreversible first-order reaction in the aniline though the target reaction is complicated by side interaction between potassium methylate and dimethyl carbonate. The rate constants of the target reaction with substituted anilines and of the side reaction in the temperature range of 70-90°C were determined. It is shown that the influence of the substituent on the reaction rate is described by the Hammett equation, with the constant of the reaction series being positive and the best correlation being achieved for σ-scale. The results obtained are consistent with the proposed mechanism of the reaction and are explained by the facilitation of the aniline deprotonation with increasing acceptor properties of the substituent. Effective activation energies for the reaction of various anilines with dimethyl carbonate are found.  相似文献   

5.
Quantum chemical calculations on large supermolecular carbonate-water and carbonate mineral clusters are used to predict equilibrium constants for 13,12C-isotope-exchange reactions between CO2(g), aqueous carbonate species, and the common carbonate minerals. For the aqueous species, we evaluate the influence of the size and conformational variability of the solvation shell, the exchange-correlation functional, and the basis set. The choice of exchange-correlation functional (PBE vs B3LYP), the basis set (6-31G* vs aug-cc-pVDZ), and solvation shell size (first shell only vs first shell and a partial second shell) each produce changes of approximately 5-10 per mil in the reduced partition function ratio. Conformational variability gives rise to a standard error of approximately 0.5 per mil using approximately 10 solute-solvent conformations. The best results are obtained with the B3LYP/aug-cc-pVDZ combination, but because the improvements in the basis set and exchange correlation functional drive the reduced partition function ratios in opposite directions, reasonably good results are also obtained with the PBE/6-31G* combination. To construct molecular clusters representative of mineral environments, a new method is introduced on the basis of conservation of Pauling bond strength. Using these clusters as models for minerals, calculations of mineral-gas and mineral-aqueous carbon-isotope fractionation factors, are in good agreement with experimental measurements. Carbon-isotope fractionation factors for gas, aqueous, and mineral phases are thus integrated into a single theoretical/computational framework.  相似文献   

6.
2-amino-4,6-dimethoxypyrimidine (ADM) was prepared from 2-amino-4,6-dihydroxypyrimidine (ADH) in the presence of potassium carbonate and phase transfer catalyst (PTC), with dimethyl carbonate (DMC) instead of conventional toxic reagents (such as haloalkane and dimethyl sulfate, etc.). The best conversion (87.7 %) of ADH and selectivity (40.5 %) toward ADM were achieved under optimized conditions: tetrabutyl ammonium bromide (TBAB) as PTC, n(ADH):n(DMC):n(TBAB):n(K2CO3) = 1:5:0.1:3, reaction time = 10 h and reaction temperature = 150 °C.  相似文献   

7.
Quaternary ammonium compounds are produced worldwide in hundreds of millions of pound volume annually for a plethora of end‐uses from fabric‐care formulations to asphalt emulsifiers, typically from nongreen alkylating reagents. The kinetics of a reaction employing dimethyl carbonate (DMC) as a green alkylating agent was investigated using three trialkylamines (tributylamine, trihexylamine, and trioctylamine) at several temperatures. Arrhenius and Eyring analysis of the data showed that values of Ea (79 kJ/mol), ΔH? (75 kJ/mol), and ΔS? (220 J/(mol K)) were the same for all three amine reactants, consistent with a report that Ea is independent of alkyl chain length when the chain length is greater than three carbons. Although rates are significantly slower with DMC than with other alkylating reagents, the resulting methyl carbonate anion has advantages for clean anion metathesis, which is important for some applications, especially those involving ionic liquids. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 221–225, 2010  相似文献   

8.
以反相微乳液法和沉淀法相结合制备了核壳结构TiO2@SiO2,首次用于碳酸二甲酯与苯酚酯交换合成碳酸二苯酯反应,显示较好的催化活性. 采用200 ℃焙烧的TiO2@SiO2,用量0.20 g,反应9 h,苯酚转化率达41.8%,酯交换选择性为100%. 透射电镜显示TiO2@SiO2核厚壳薄,TiO2核直径220-300 nm,SiO2壳厚度40-60 nm,具有介孔结构. TiO2@SiO2对碳酸二甲酯与苯酚酯交换反应有好的重复使用性,使用4次苯酚转化率仍保持在40%以上. TiO2与SiO2发生相互作用,Ti进入骨架形成Ti-O-Si键,骨架Ti的形成提高了TiO2@SiO2的催化性能.  相似文献   

9.
The synthesis of dimethyl carbonate by oxidative carbonylation of methanol over CuCl/SiO2-TiO2 catalysts has been investigated in a slurry reaction system. The γ-Cu2(OH)3Cl crystals were detected by X-ray diffraction on the catalysts after reaction. It was revealed that γ-Cu2(OH)3Cl was formed by CuCl reacting with O2 and by-product water. The catalytic tests showed that γ-Cu2(OH)3Cl was largely inactive for this reaction, may be attributed to its high stability that resisted the Cu+/Cu2+ redox cycle.  相似文献   

10.
Hexamethyldisiloxane and hexamethylcyclotrisiloxane were almost completely deoligomerized with dimethyl carbonate over alumina-supported potassium fluoride catalyst to form methoxytrimethylsilane (85% yield) and dimethoxydimethylsilane (94% yield), respectively, and moreover the addition of a small amount of methanol to the hexamethyldisiloxane deoligomerization reaction enhanced the methoxytrimethylsilane yield to 98%.  相似文献   

11.
12.
Mg-Al水滑石催化甘油与碳酸二甲酯的酯交换反应   总被引:1,自引:0,他引:1  
报道了温和条件下甘油和碳酸二甲酯在一系列不同Mg/Al比(0.5-6)的Mg-Al水滑石催化下合成碳酸甘油酯(GC)的反应. 发现,Mg-Al水滑石对该反应具有很高的GC选择性,其中Mg/Al=2经400℃处理所得水滑石催化效率最高:70 ℃反应3 h甘油转化率达66.9%时,GC选择性维持在97%以上. 表征结果表明,水滑石样品的比表面积、孔径、结晶度和表面碱性对其催化活性影响很大.  相似文献   

13.
A simple, clean, safe, and reproducible catalyst system, polymer-supported nanogold, was successfully developed for the fixation of CO2 to cyclic carbonate and for the carbonylation of amines to disubstituted ureas with unprecedented catalytic activity (TOF > 50 000 mol/mol/h and TOFP approximately 3000 mol/mol/h, respectively). To the best of our knowledge, it was the first to report that nanogold catalysts have exclusive catalytic activity for activation of carbon dioxide, and that the catalytic activity of the polymer-immobilized nanogold catalysts could be controlled by the particle size of the nanogold.  相似文献   

14.
[reaction: see text] At 130 degrees C, in the presence of CO2 (5-200 bar), primary aliphatic amines react with dimethyl carbonate (MeOCO2Me, DMC) to yield methyl carbamates (RNHCO2Me) and N-methylation side-products (RNHMe and RNMe2). The pressure of CO2 largely influences both the reaction conversion and the selectivity toward urethanes: in general, conversion goes through a maximum (70-80%) in the midrange (40 bar) and drops at lower and higher pressures, whereas selectivity is continuously improved (from 50% up to 90%) by an increase of the pressure. This is explained by the multiple role of CO2 in (i) the acid/base equilibrium with aliphatic amines, (ii) the reactivity/solubility of RNHCO2- nucleophiles with/in DMC, and (iii) the inhibition of competitive N-methylation reaction of the substrates. Cosolvents also affect the reaction: in particular, a drop in selectivity is observed with polar protic media (i.e., MeOH), plausibly because of solvation effects (through H-bonds) of RNHCO2- moieties. The reaction shows also a good chemoselectivity: bifunctional aliphatic amines bearing either aromatic NH2 or OH substituents [XC6H4(CH2)n NH2, X = NH2, OH; n = 1, 2], undergo methoxycarbonylation reactions exclusively at aliphatic amino groups and give the corresponding methyl carbamates [XC6H4(CH2)n NHCO2Me] in 39-65% isolated yields.  相似文献   

15.
This study is focused on modelling the phase equilibrium behaviour of the reaction mixture (CO2 + methanol + DMC + H2O) at high pressure–temperature conditions using the Patel–Teja (PT) and Peng–Robinson–Stryjek–Vera (PRSV) equations of state along with the van der Waals One-Fluid (1PVDW) mixing rule. The optimum values of the binary interaction parameters (kij) were calculated from VLE data found in the literature, and then adjusted to a lineal temperature equation. As a result, the temperature-dependent model was applied to predict the fluid phase equilibria of the corresponding binary a ternary sub-systems and, later, successfully contrasted with experimental data. In addition, phase equilibrium data were experimentally measured at high pressure (8 MPa to 15 MPa) for the ternary system (CO2 + methanol + DMC), in order to confirm the ability of the model to predict the phase behaviour of the ternary system at high pressure–temperature. The agreement between the experimental data and the proposed model enables to predict the phase equilibrium behaviour of the mixture (CO2 + methanol + DMC + H2O), and thus, optimise the operation conditions in several reaction and separation processes.  相似文献   

16.
A series of metal-organic frameworks MOF-808-X (6-connected) were synthesized by regulating the ZrOCl2·8H2O/1,3,5-benzenetricarboxylic acid (BTC) molar ratio (X) and tested for the direct synthesis of dimethyl carbonate (DMC) from CO2 and CH3OH with 1,1,1-trimethoxymethane (TMM) as a dehydrating agent. The effect of the ZrOCl2·8H2O/BTC molar ratio on the physicochemical properties and catalytic performance of MOF-808-X was investigated. Results showed that a proper ZrOCl2·8H2O/BTC molar ratio during MOF-808-X synthesis was fairly important to reduce the redundant BTC or zirconium clusters trapped in the micropores of MOF-808-X. MOF-808-4, with almost no redundant BTC or zirconium clusters trapped in the micropores, exhibited the largest surface area, micropore size, and the number of acidic-basic sites, and consequently showed the best activity among all MOF-808-X, with the highest DMC yield of 21.5% under the optimal reaction conditions. Moreover, benefiting from the larger micropore size, MOF-808-4 outperformed our previously reported UiO-66-24 (12-connected), which had even more acidic-basic sites and larger surface area than MOF-808-4, mainly because the larger micropore size of MOF-808-4 provided higher accessibility for the reactant to the active sites located in the micropores. Furthermore, a possible reaction mechanism over MOF-808-4 was proposed based on the in situ FT-IR results. The effects of different reaction parameters on DMC formation and the reusability of MOF-808-X were also studied.  相似文献   

17.
Over exploitation of natural resources and human activities are relentlessly fueling the emission of CO2 in the atmosphere. Accordingly, continuous efforts are required to find solutions to address the issue of excessive CO2 emission and its potential effects on climate change. It is imperative that the world looks towards a portfolio of carbon mitigation solutions, rather than a single strategy. In this regard, the use of CO2 as a C1 source is an attractive strategy as CO2 has the potential to be a great asset for the industrial sector and consumers across the globe. In particular, the reduction of CO2 offers an alternative to fossil fuels for various organic industrial feedstocks and fuels. Consequently, efficient and scalable approaches for the reduction of CO2 to products such as methane and methanol can generate value from its emissions. Accordingly, in recent years, metal-free catalysis has emerged as a sustainable approach because of the mild reaction conditions by which CO2 can be reduced to various value-added products. The metal-free catalytic reduction of CO2 offers the development of chemical processes with low cost, earth-abundant, non-toxic reagents, and low carbon-footprint. Thus, this perspective aims to present the developments in both the reduction and reductive functionalization chemistry of CO2 during the last decade using various metal-free catalysts.

This review article documents the key developments in the metal-free catalytic reduction of CO2 into various energy intensive chemicals and fuels, and reductive functionalization of CO2 for the formation of new C–N bonds.  相似文献   

18.
采用溶胶-凝胶法制备了SiO2-ZrO2复合氧化物载体,通过和CuCl2进行离子交换制备了Cu+/SiO2-ZrO2催化剂,并研究其催化甲醇液相氧化羰基化合成碳酸二甲酯性能。结果表明,Zr以离子形式进入无定型SiO2骨架结构中形成Si-O-Zr键,同时产生较强的B酸中心。CuCl2通过热处理自还原为CuCl分散在SiO2-ZrO2载体表面,并与载体表面B酸发生离子交换形成Cu+物种,从而保留了活性金属组分Cu,脱除大部分的Cl元素,改善催化剂失活和设备腐蚀等问题。当焙烧温度为450℃时,催化剂表现出良好的催化活性,CH3OH转化率、DMC选择性和时空收率分别达到10.0%、79.4%和1.45g/(g·h)。
  相似文献   

19.
To explore the ambident electrophilic reactivity of dimethyl carbonate (DMC), reactions with the ambident nucleophile phenylhydrazine were investigated. When a Br?nsted base was used, selective carboxymethylation occurred at N-1, after that several other compounds were produced selectively utilizing various conditions. Formation of these compounds was explained by using the Hard-Soft Acid-Base (HSAB) theory. Catalysis by some metal salts altered the reactivity of phenylhydrazine, which effected selective carboxymethylation at N-2 of phenylhydrazine instead.  相似文献   

20.
Abundant in nature, CO2 poses few health hazards and consequently is a promising alternative to phosgene feedstock according with the principles of Green Chemistry and Engineering. The synthesis organic carbonates from CO2 instead of phosgene is highly challenging as CO2 is much less reactive. As part of our ongoing research on the investigation of catalysts for dimethyl carbonate (DMC) synthesis from methanol and CO2, we herein report results aimed at comparing the catalytic behavior of new SnO2-based catalysts with that of ZrO2. Silica-supported SnO2 and ZrO2 exhibit turnover numbers which are an order of magnitude higher than those of the unsupported oxides. Tin-based catalysts also promote methanol dehydration which makes them less selective than the zirconium analogues. Last but not least, comparison with soluble Bu2Sn(OCH3)2 highlights the superiority of the organometallic precursor for achieving 100% selectivity to DMC but it deactivates by intermolecular rearrangement into polynuclear tin species.  相似文献   

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