Chemoselective and efficient carbomethoxylation of the alcoholic chain of phenols by dimethyl carbonate (DMC)

The efficiency of dimethyl carbonate (DMC) as chemoselective carbomethoxylating agent of the alcoholic chain of phenols has been investigated. In the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) or sulfuric acid as catalysts, new carbomethoxylated phenolic compounds were obtained in quantitative yields. A new efficient derivatization of the aliphatic alcoholic chain of the precious natural hydroxytyrosol is described, which increases the lipophilicity of the hydroxytyrosol. The antioxidant activity of this new carboxymethylated hydroxytyrosol 8 has been investigated using DPPH radical scavenging test. The results showed that this new compound has an antioxidant activity similar to hydroxytyrosol.     

Cyclocondensation of amidines with dimethyl acetylenedicarboxylate: A convenient entry into tetramic acids

Amidines undergo cyclocondensations with dimethyl acetylenedicarboxylate (DMAD) to give highly functionalized 5‐dialkylamino‐4‐pyrrolin‐3‐ones. The products are crystalline, highly colored compounds that are uniquely functionalized and represent advanced intermediates in the construction of several other heterocyles, in particular the biologically active tetramic acids. The synthetic transformations of these compounds to tetramic acids are also described.     

Lanthanum(III) isopropoxide catalyzed chemoselective transesterification of dimethyl carbonate and methyl carbamates

A practical transesterification of less reactive dimethyl carbonate and much less reactive methyl carbamates with primary (1°), secondary (2°), and tertiary (3°) alcohols was established with the use of a lanthanum(III) complex, which was prepared in situ from lanthanum(III) isopropoxide (3 mol %) and 2-(2-methoxyethoxy)ethanol (6 mol %). In particular, corresponding carbonates and carbamates obtained were of synthetic utility from the viewpoint of the selective protection and/or deprotection of 1°-, 2°-, and 3°-alcohols.     

Reactions of diols with dimethyl carbonate in the presence of W(CO)6 and Co2(CO)8

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.     

TiO(acac)2催化碳酸二甲酯和苯基乙酸酯合成碳酸二苯酯

碳酸二苯酯(DPC)是非光气法生产聚碳酸酯(PCs)的重要原料,具有多种酯交换法合成路线,如碳酸二甲酯(DMC)与苯酚酯交换法、DMC与苯基乙酸酯(PA)酯交换法、草酸二甲酯(DMO)与苯酚酯交换法等.本文对比测定了几种金属乙酰丙酮配合物和有机钛化合物对碳酸二甲酯(DMC)与苯基乙酸酯(PA)酯交换合成DPC反应的催化性能,结果表明,乙酰丙酮氧钛[TiO(acac)2]是一种良好的酯交换催化剂,具有优良的催化性能.在反应条件θ=180℃,n(PA)=0.8 mol,n(DMC)/n(PA)=1/2,n(TiO(acac)2)/n(PA)=0.006,t=4 h下,DMC转化率可达74.9%,甲基苯基碳酸酯(MPC)和DPC的选择性分别可达56.9%和38.9%.探索并提出了TiO(acac)2催化DMC与PA酯交换合成DPC反应的机理.     

Deoligomerization of siloxanes with dimethyl carbonate over solid-base catalysts

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%.     

Mg-Al水滑石催化甘油与碳酸二甲酯的酯交换反应简

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.     

A convenient phosphoryloxylactonization of pentenoic acids with(diacetoxyiodo)benzene

<正>The convenient one-pot method for phosphoryloxylactonization of alkenoic acids was reported:when(diacetoxyiodo)benzene, various 4-pentenoic acids and phosphates were mixed in CH_3CN at room temperature,phosphoryloxylactones were obtained in good to excellent yields in short times,some had two diastereoisomers.     

Protic ionic liquid-promoted synthesis of dimethyl carbonate from ethylene carbonate and methanol

In this work,the protic ionic liquid[DBUH][Im](1,8-diazabicyclo[5.4.0]-7-undeceniumimidazolide)was developed as an efficient catalyst for the transesterification of ethylene carbonate with methanol to produce dimethyl carbonate.At 70℃,up to 97%conversion of ethylene carbonate and 91%yield of dimethyl ca rbonate were obtained with 1 mol%[DBUH][Im](relative to ethylene carbonate)as catalyst in 2 h.Even at room temperature,the conversion of ethylene carbonate can reach 94%and the yield of dimethyl carbonate can approach 81%for 6 h.Catalytic mechanism investigation showed the high catalytic efficiency of this ionic liquid results from the synergistic activation effect,wherein the cation can activate ethylene carbonate and the anion can activate methanol through hydrogen bond formatio n.Although the reusability of the ionic liquid need to be further improved,high efficiency and comme rcial availability of[DBUH][Im]render it a promising catalyst for the preparation of dimethyl carbonate.     

Physical and electrolytic properties of difluorinated dimethyl carbonate

The physical and electrolytic properties of difluorinated dimethyl carbonate (DFDMC) synthesized using F₂ gas (direct fluorination) were examined. The dielectric constant and viscosity of DFDMC are higher than those of monofluorinated dimethyl carbonate (MFDMC) and dimethyl carbonate (DMC). The oxidative decomposition voltage of DFDMC is higher than those of DMC and MFDMC. The specific conductivity in DFDMC solution is considerably lower than those in MFDMC and DMC solutions. The ethylene carbonate (EC)-DFDMC equimolar binary solution containing 1 mol dm⁻³ LiPF₆ shows a moderate conductivity of 6.91 mS cm⁻¹ at 25 °C. The lithium electrode cycling efficiency (charge-discharge coulombic cycling efficiency of lithium electrode) in EC-DFDMC equimolar binary solution containing 1 mol dm⁻³ LiPF₆ is higher than 80%. The EC-DFDMC solution is a good electrolyte for rechargeable lithium batteries.     

Kinetic study of the reaction of dimethyl carbonate with trialkylamines

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 E_a (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 E_a 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     

Ca-Al催化剂上甘油与碳酸二甲酯酯交换合成碳酸甘油酯

生物柴油是一种环保、可再生、使用安全、可替代石化柴油的新型液体燃料,其产量和使用范围正逐年扩大。然而生物柴油生产过程中的主要副产物甘油严重过剩,因此甘油资源化转化和利用已经成为近年研究热点。甘油可以作为一种平台化合物实现向多种高附加值化学品的转化,例如通过催化氢解合成1,2-丙二醇,通过发酵和催化氧化制备二羟基丙酮,通过脱水制备丙烯醛和羟基丙酮,通过酯交换反应生成甘油酯等。其中,以甘油为原料合成的碳酸甘油酯(GC)具有很好的工业应用前景。以碳酸二甲酯(DMC)为原料与甘油进行酯交换合成GC是近年内比较有工业发展潜力的合成路线。前期研究发现,固体碱对该反应具有很好的催化活性,而且随着催化剂碱性增强,甘油转化率明显增加,然而当催化剂(如NaOH, KOH和K2CO3等)碱性过强时,产物选择性明显降低。水滑石类化合物是一种常见的碱性温和的固体催化剂,而且其碱性与结构可以调节,因此我们选择了一种常见水滑石——水铝钙石作为本研究的重点。 本文通过共沉淀法制备了一系列不同Ca/Al比(1–6)的Ca-Al水滑石,并以此作为前驱体制备了新型的固体碱催化剂。 XRD结果表明,当Ca/Al比为1–6时,所有样品都出现了明显的水滑石特征衍射峰,但当铝含量过高时会出现氢氧化铝杂相。 SEM结果发现,当Ca/Al =2–4时,样品中水滑石的结晶度高,有较完整的水滑石晶片, Ca/Al =6的样品中水滑石晶片较小, Ca/Al =1的样品中有明显的无定形氧化铝杂相。 TG-DSC结果表明, Ca/Al =2的样品除了几个与水滑石相关的特征失重峰以外,在786oC还检测到明显的热吸收峰,说明此时钙铝石已经发生分解,生成了单独的Ca12Al14O33晶相和氧化钙,这与SEM结果一致。这些水滑石经焙烧后用于温和条件下催化甘油与DMC酯交换生成GC的反应,发现上述催化剂对该反应具有很高的催化活性和目的产物选择性。当DMC与甘油的摩尔比为3时,70oC反应3 h后,甘油转化率达到93%, GC选择性高于97%。表征结果显示,甘油转化率主要取决于焙烧后Ca-Al催化剂中强碱性中心数量。其中经800oC焙烧后Ca/Al =2的样品中强碱性中心数量最多,因而表现出最高的催化活性。焙烧后催化剂中形成的Ca12Al14O33晶相在多次重复使用后仍可以稳定存在,但是表面CaO易流失,可能会降低催化剂的重复使用活性。     

Synthesis of dimethyl adipate from cyclopentanone and dimethyl carbonate over solid base catalysts

A facile route for the synthesis of dimethyl adipate (DAP) from cyclopentanone and dimethyl carbonate (DMC) in the presence of solid base catalysts has been developed.It was found that the intermediate carbomethoxycyclopentanone (CMCP) was produced from cyclopentanone with DMC in the first step,and then CMCP was further converted to DAP by reacting with a methoxide group.The role of the basic catalysts can be mainly ascribed to the activation of cyclopentanone via the abstraction of a proton in the α-position by base sites,and solid bases with moderate strength,such as MgO,favor the formation of DAP.     

2-Chloroethyl dimethyl sulfonium iodide. A convenient reagent for spiroannelation of ketones

Ketones are readily spiroannelated by 2-chloroethyldimethyl sulfonium iodide 1 in the presence of t-butoxide anion in t-butanol. The procedure affords a simple one step -spirocyclopropanation of ketones in good yields.     

A convenient enantioselective synthesis of (S)-alpha-trifluoromethylisoserine

[reaction: see text] This report describes two straightforward synthetic methodologies to obtain alpha-CF3-isoserine, a new alpha,alpha-disubstituted beta-amino acid, from alpha-(trifluoromethyl)acrylic acid. The routes involve the synthesis of five-membered cyclic sulfates (using sulfuryl chloride) or sulfamidates (using the Burgess reagent) from the corresponding chiral diols, which are obtained by a catalytic asymmetric dihydroxylation (AD) reaction.     

Polymerization of vinylene carbonate in dimethyl sulfoxide

Pure vinylene carbonate polymerizes readily in dimethyl sulfoxide solutions upon initiation by azobisisobutyronitrile (AIBN). The monomer conversion is characterized by a limiting value which appears to be a function of the temperature and the initial concentrations of both the initiator and the monomer. Increasing both initiator concentration and temperature results in higher final conversions, whereas a maximum conversion is indicated for initial monomer concentrations in the range of 80% to 90%. Principal kinetic quantities were found to be adequately represented by the equations k_d = 24.3 × 10⁵ exp {?11300/RT} and k_p(f/k_t)^1/2 = 46.3 × 10⁵ exp {?8900/RT} for the temperature range of 50–80°C. The average degree of polymerization was found to be affected by chain transfer to the solvent. A value of 5.8 × 10^?4 was determined for the corresponding chain transfer constant.