H-ZSM-5催化甲苯与碳酸二甲酯和甲醇甲基化的反应机理

对二甲苯是重要的石油化工产品之一, 可以通过甲苯甲基化生产. 本文采用“our own-N-layeredintegrated molecular orbital+molecular mechanics”(ONIOM)和密度泛函理论(DFT)结合的方法, 计算了H-ZSM-5催化甲苯与碳酸二甲酯(DMC)和甲醇甲基化反应机理. 考察了反应物吸附和产物脱附. 描述了主要的中间物种和过渡态的结构. 用计算的速率常数来估计甲苯甲基化反应的动力学活性. H-ZSM-5 催化的甲苯与DMC和甲醇甲基化的机理不同. 甲苯和DMC甲基化包括DMC完全解离, 接着甲基化生成二甲苯异构体. 相比而言, 在甲苯甲基化反应中, 甲醇作为甲基化试剂的活性比DMC更好. 甲苯和甲醇甲基化的分步反应路径和联合反应路径的本征活化能相似. 在773 K, 分步反应路径的速率常数比联合反应路径更高. 在甲苯和这两种试剂甲基化的反应中, 生成对二甲苯为动力学优先, 而间二甲苯为能量最低产物. 我们的计算结果和实验观察到的现象一致.     

Methylation of Cyanidin-3-O-Glucoside with Dimethyl Carbonate

The approach presented in this study is the first for the hemisynthesis of methylated anthocyanins. It was possible to obtain cyanidin-3-O-glucoside derivatives with different degrees of methylation. Cautious identification of 4′-, 5-, and 7-OH monomethylated derivatives was also accomplished. The methylation agent used was the “green chemical” dimethyl carbonate (DMC), which is characterized by low human and ecological toxicity. The influence of the temperature, reaction time, and amount of the required diazabicyclo[5.4.0]undec-7-en (DBU) catalyst on the formation of the products was examined. Compared to conventional synthesis methods for methylated flavonoids using DMC and DBU, the conditions identified in this study result in a reduction of reaction time, and an important side reaction, so-called carboxymethylation, was minimized by using higher amounts of catalyst.     

Dimethyl carbonate as a novel methylating reagent for fatty acids in analytical pyrolysis

Dimethyl carbonate (DMC) was investigated as a mild, harmless and odorless reagent for pyrolytic methylation of fatty acids. Soybean oil was selected as test material for its high content of (poly)unsaturated fatty acids. Pyrolyses were performed at 500, 700 and 900 degrees C by means of a heated platinum filament pyrolyser on-line and off-line to the GC-MS apparatus. Methyl esters of palmitic, linoleic, oleic and stearic acid were formed as prominent products from off-line pyrolysis of soybean oil in the presence of DMC and zeolite 13X. Fatty acid methyl esters (FAMEs) were not observed at important levels in the absence of zeolite, while on-line Py-GC-MS experiments resulted principally in the formation of free fatty acids and hydrocarbons. The FAME profiles obtained from the DMC/zeolite off-line pyrolysis were compared to those resulting from tetramethylammonium hydroxide (TMAH) thermochemolysis and BF3-methanol procedure. The observed differences between pyrolysis and methanolysis methods were principally attributed to the thermal degradation of unsaturated fatty acids. The effectiveness of the DMC/zeolite pyrolytic methylation was further demonstrated by the analysis of tripalmitine and soybean seeds.     

碘甲烷在碳酸二甲酯直接合成中的作用

Dimethyl carbonate (DMC) is an environmentally friendly compound and a substitutive intermediate for highly toxic phosgene or dimethyl sulfate in carbonylation and methylation reactions as well as a promising octane booster. The common methods for its preparation are the oxidative carbonylation of methanol catalyzed by a variety of transition metal ions and the transesterification of ethylene carbonate or propene carbonate with methanol[1]. The direct synthesis of DMC from carbon dioxide and methanol is a challenging route in which the most abundant carbon resources and a main greenhouse gas is used as feedstock. A new method for the direct synthesis of DMC catalyzed by the methoxide of main group metal has attracted more and more attention since it was reported[2～6] . However the lower conversion of the reaction has become the main obstacle for its application. In this letter, an efficient promoter for the direct synthesis of DMC is reported.     

Direct formation of Ge-C bonds from GeO(2)

Germanium dioxide in the presence of 5% KOH reacted with dimethyl carbonate (DMC) at 250 degrees C to give (MeO)(4)Ge. The reaction of GeO(2) and DMC is similar to that reported for SiO(2); however, the rate of reaction for germanium is much higher than that of the corresponding silicon reaction. In a side-by-side experiment using SiO(2) and GeO(2) where the surface area of the silicon dioxide was 2 orders of magnitude higher than that of the GeO(2), the base-catalyzed reaction with DMC was about an order of magnitude higher for the germanium dioxide. When GeO(2) and 5% KOH were reacted with DMC at 350 degrees C, two products formed: (MeO)(4)Ge (70%) and MeGe(OMe)(3) (30%). Confirmation of the identity of MeGe(OMe)(3) was by GCMS, (1)H and (13)C NMR, and comparison to an authentic sample made by reaction of MeGeCl(3) with NaOMe. Experiments to determine the mechanism of the direct formation of Ge-C from GeO(2) ruled out participation from CO, H(2), or carbon. The KOH-catalyzed reaction of other metal oxides was explored including B(2)O(3), Ga(2)O(3), TiO(2), Sb(2)O(3), SnO(2), and SnO. Boron reacted to give unknown volatile products. Antimony reacted to give a solid which analyzed as Sb(OMe)(3). SnO reacted with DMC to give a mixture that included (MeO)(4)Sn and possibly Me(3)Sn(OMe).     

Reaction of functionalized anilines with dimethyl carbonate over NaY faujasite. 3. chemoselectivity toward mono-N-methylation

In the presence of NaY faujasite, dimethyl carbonate (MeOCO(2)Me, DMC) is a highly chemoselective methylating agent of functionalized anilines such as aminophenols (1), aminobenzyl alcohols (2), aminobenzoic acids (3), and aminobenzamides (4). The reaction proceeds with the exclusive formation of N-methylanilines without any concurrent O-methylation or N-/O-methoxy carbonylation side processes. Particularly, only mono-N-methyl derivatives [XC(6)H(4)NHMe, X = o-, m-, and p-OH; o- and p-CH(2)OH; o- and p-CO(2)H; o- and p-CONH(2)] are obtained with selectivity up to 99% and isolated yields of 74-99%. DMC, which usually promotes methylations only at T > 120 degrees C, is activated by the zeolite catalyst and it reacts with compounds 1, 2, and 4, at 90 degrees C. Aminobenzoic acids (3) require a higher reaction temperature (> or =130 degrees C).     

Metal-organic frameworks MOF-808-X as highly efficient catalysts for direct synthesis of dimethyl carbonate from CO2 and methanol

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.     

A density functional theory investigation on the mechanism and kinetics of dimethyl carbonate formation on Cu2O catalyst

A theoretical analysis about the mechanism and kinetics of dimethyl carbonate (DMC) formation via oxidative carbonylation of methanol on Cu₂O catalyst is explored using periodic density functional calculations, both in gas phase and in solvent. The effect of solvent is taken into account using the conductor‐like screening model. The calculated results show that CO insertion to methoxide species to produce monomethyl carbonate species is the rate‐determining step, the corresponding activation barrier is 161.9 kJ mol^?1. Then, monomethyl carbonate species reacts with additional methoxide to form DMC with an activation barrier of 98.8 kJ mol^?1, above reaction pathway mainly contributes to the formation of DMC. CO insertion to dimethoxide species to form DMC is also considered and analyzed, the corresponding activation barrier is 308.5 kJ mol^?1, suggesting that CO insertion to dimethoxide species is not competitive in dynamics in comparison with CO insertion to methoxide species. The solvent effects on CO insertion to methoxide species involving the activation barriers suggest that the rate‐determining step can be significantly affected by the solvent, 70.2 kJ mol^?1 in methanol and 63.9 kJ mol^?1 in water, which means that solvent effect can reduce the activation barrier of CO insertion to methoxide species and make the reaction of CO insertion to methoxide in solvents much easier than that in gas phase. Above calculated results can provide good theoretical guidance for the mechanism and kinetics of DMC formation and suggest that solvent effect can well improve the performance of DMC formation on Cu₂O catalyst in a liquid‐phase slurry. © 2012 Wiley Periodicals, Inc.     

The effects of substituting groups in cyclic carbonates for stable SEI formation on graphite anode of lithium batteries

Monofluoropropylene carbonate (MFPC) and trifluoropropylene carbonate (TFPC) with a monofluoromethyl (or trifluoromethyl) replacing the methyl group in propylene carbonate (PC) as well as EC-CH₂CH₂Si(CH₃)₂OSi(CH₃)₃ (Si-A) and EC-CH₂CH₂Si(CH₃)₃ (Si-B) have been synthesized. The charge–discharge studies in a Li/MCMB (mesocarbon microbeads) cell using electrolyte containing these compounds show that the solid electrolyte interphase (SEI) formation capability of MFPC/DMC (dimethyl carbonate) and TFPC/DMC are about the same as ethylene carbonate (EC)/DMC, and TFPC/PC/DMC is better than that of EC/PC/DMC, while MFPC/PC/DMC is poorer than the EC/PC/DMC. The superior SEI formation capability of TFPC could be attributed to the strong electron withdrawing group of CF₃, which promote the “ring-opening” reaction. In contrast, the electron donating group CH₃ in the PC structure may demote the “ring opening” and cause the poor SEI formation. The results of MFPC with weaker electron withdrawing group give further support of this hypothesis. The bi-solvent electrolytes of Si-A/DMC and Si-B/DMC have comparable SEI formation capability as EC/DMC and TFPC/DMC, regardless of their bulky chains. This indicates that if proper chain structures are used, good SEI formation capability could be obtained for cyclic carbonate with bulky chains. These new solvents provide valuable information in studying the SEI formation mechanism and designing new electrolytes.     

Green organic syntheses: organic carbonates as methylating agents

Dimethylcarbonate (DMC) is a valuable methylating reagent that can replace methyl halides and dimethylsulfate in the methylation of a variety of nucleophiles. It couples tunable reactivity and unprecedented selectivity towards mono-C- and mono-N-methylation. In addition, it is a prototype example of a green reagent, because it is nontoxic, is made by a clean process, is biodegradable, and reacts in the presence of a catalytic amount of base, thereby avoiding the formation of undesirable inorganic salts as by-products. Depending on the reaction conditions, DMC can be reacted under plug-flow, CSTR, or batch conditions. Other remarkable reactions are those where DMC behaves as an oxidant. The reactivity of other carbonates is reported as well.     

Synthesis of dimethyl carbonate from methanol and supercritical carbon dioxide

The synthesis of dimethyl carbonate (DMC) from methanol and supercritical carbon dioxide over various base catalysts has been studied. Compounds of group-I elements (Li, Na and K) were used as base catalysts. The promoter and the dehydrating agent were also used to enhance the yield of DMC. The effects of the catalysts, promoter and dehydrating agent on the yield of DMC were investigated. By-products such as dimethyl ether (DME) and C₁–C₂ hydrocarbons were formed with the DMC as a main product. The yield of DMC with different alkali metal catalysts ranked in the following order: K > Na > Li. The catalysts of the metal-CO₃ compounds were more effective than the metal-OH compounds in DMC synthesis. The maximum DMC yield reached up to about 12 mol% in the presence of K₂CO₃ (catalyst), CH₃I (promoter) and 2,2-dimethoxypropane (dehydrating agent) at 130–140°C and 200 bar. The reaction mechanism of DMC synthesis from methanol and supercritical carbon dioxide was proposed.     

Quantum Monte Carlo study of the reaction: Cl+CH3OH-->CH2OH+HCl

A theoretical study is reported of the Cl+CH3OH-->CH2OH+HCl reaction based on the diffusion Monte Carlo (DMC) variant of the quantum Monte Carlo method. Using a DMC trial function constructed as a product of Hartree-Fock and correlation functions, we have computed the barrier height, heat of reaction, atomization energies, and heats of formation of reagents and products. The DMC heat of reaction, atomization energies, and heats of formation are found to agree with experiment to within the error bounds of computation and experiment. M?ller-Plesset second order perturbation theory (MP2) and density functional theory, the latter in the B3LYP generalized gradient approximation, are found to overestimate the experimental heat of reaction. Intrinsic reaction coordinate calculations at the MP2 level of theory demonstrate that the reaction is predominantly direct, i.e., proceeds without formation of intermediates, which is consistent with a recent molecular beam experiment. The reaction barrier as determined from MP2 calculations is found to be 2.24 kcal/mol and by DMC it is computed to be 2.39(49) kcal/mol.     

VAC与甲基丙烯酰氧乙基三甲基氯化铵无皂乳液共聚合动力学研究

研究了醋酸乙烯酯 (VAC)与甲基丙烯酰氧乙基三甲基氯化铵 (DMC)无皂乳液共聚合动力学 ,考察了引发剂偶氮二异丁基脒盐酸盐 (AIBI)浓度、单体浓度、温度等因素对聚合反应速率的影响 ,得到单体总浓度和引发剂浓度影响反应速率的动力学方程为 :Rp=k1 [M]0 6 3[AIBA]1 0 ;各单体浓度影响反应速率的动力学方程为 :Rp=k2 [VAC]0 1 6 [DMC]0 89.聚合表观活化能为 4 4 0 1kJ·mol- 1 ,初步探讨了聚合反应机理 .     

Dual nucleophilic catalysis with DABCO for the N-methylation of indoles

DABCO is an extremely active catalyst for the methylation of indoles in conjunction with dimethyl carbonate (DMC). This green chemistry is highly effective and produces N-methylindoles in nearly quantitative yields. The reaction sequence consists of competing alkylation and acylation pathways and involves 1,4-diazabicyclo[2.2.2]octane (DABCO) dually as a nucleophilic catalyst, ultimately resulting in a single product: the N-methylated indole.     

Alkylation of phenol with dimethyl carbonate over AlPO4, Al2O3 and AlPO4-Al2O3 catalysts

The vapor-phase catalytic alkylation of phenol with dimethyl carbonate over different AlPO₄ (Al/P=1), Al₂O₃ and AlPO₄-Al₂O₃ (5–25 wt.% Al₂O₃) catalysts produces anisole (O-alkylation) as the major reaction product althougho-cresol (C-alkylation) and methylanisoles were also found. The reaction is first order in phenol while O-and C-alkylation follow parallel processes. As compared with methanol, DMC is far more effective as a methylating agent, and the methylation proceeds at a lower temperature and with higher O-alkylation selectivity.     

Studies on the carboxymethylation and methylation of bisphenol A with dimethyl carbonate over TiO2/SBA-15

Carboxymethylated species were selectively synthesized from dimethyl carbonate (DMC) and bisphenol A (BPA) over TiO₂/SBA-15. On the basis of catalyst characterization by means of XRD, FT-IR, HPLC and GC–MS, the relations between catalytic performance and catalyst properties were discussed. Si–O–Ti was active sites for reaction, and the interaction mode between Ti–O–Si and DMC was main factor to determine carboxymethylation and methylation. When DMC was attacked by Ti–O–Si on two oxygen atoms of CH₃–O moiety, BPA attacked carbonyl carbon to form carboxymethylated products. If the interaction occurs through the oxygen of CO moiety, BPA attacked methyl carbon to form methylated products. Chemisorbed H₂O over TiO₂/SBA-15 made DMC to act as methylating agent. After chemisorbed H₂O was removed, carboxymethylated species of two-methylcarbonate-ended-BPA (DmC(1)) and one-methylcarbonate-ended-BPA (MmC(1)) were selectively synthesized.     

Vapor Phase Carbonylation Reactions Using Methyl Nitrite Over Pd Catalysts

Vapor phase carbonylation reactions using methyl nitrite (MN) as an oxidant have been developed by Ube Industries, Ltd. Dimethyl oxalate (DMO) and dimethyl carbonate (DMC) are synthesized efficiently over Pd(0) and Pd(II) catalysts under mild condition in gas phase, respectively. In these synthesis procedures, two kinds of separate reactions are involved. The first reaction is the catalytic synthesis of DMO or DMC from MN and CO; and the second reaction is non-catalytic MN synthesis from methanol, O₂ and NO, which is produced from the first reaction. The high DMO or DMC selectivity and suppression of catalyst deactivation originate from the facts that O₂ is not involved and H₂O is not produced in the first reaction.     

Structure and stability of solvation complexes of trimethyl phosphate and dimethyl methyl phosphonate

The presently used electrolytes in Lithium ion batteries, dimethyl carbonate (DMC), and ethylene carbonate are flammable. Trimethyl phosphate (TMP) and dimethyl methyl phosphonate (DMMP) have been shown to be potential nonflammable electrolytes. Density functional theory is used to calculate the structure and stability of the solvation complexes of TMP and DMMP. The calculations indicate that TMP and DMMP can form a solvation complex of the form Li⁺(X)₄ where X is the TMP or DMMP molecule. Calculations of the solvation energy and bond dissociation energies to remove one TMP and DMMP from the solvation complexes are compared with the same calculations on DMC. The results indicate that TMP and DMMP are considerably more stable than DMC.     

Photoinduced decarboxylative benzylation of phthalimide triplets with phenyl acetates: a mechanistic study

The photodecarboxylative benzylation of N-alkyl, N-arylalkyl, and N-aryl phthalimides with arylacetic acids in aqueous solution proceeds via electron transfer from the arylalkanoate to the excited triplet state of the phthalimide, either formed directly or upon sensitization with acetone. The rate constant for triplet quenching of N-methylphthalimide is k(q) < 10(7) M(-1) s(-1) for 2-phenylacetic acid and k(q) = (1-3) x 10(9) M(-1) s(-1) for its mono-, di- and trimethoxy-substituted derivatives, suggesting a change of the mechanism for the primary oxidation step from a Photo-Kolbe type reaction yielding an acyloxy radical to a pseudo-Photo-Kolbe process involving the formation of resonance-stabilized zwitterion radicals as intermediates.