Study On Dimethyl Carbonate Synthesis from Methyl Nitrite And CO1

Recently, dimethyl carbonate (DMC) has attracted much attention as a less toxic reagent in relation to environmental problem. DMC is a novel reagent for methylation and carbonylation in place of toxic dimethyl sulfate and phosgene, respectively. DMC is also a promising fuel additive because it can improve octane number.     

KBr催化剂上DMC与苯酚甲基化合成苯甲醚的反应机理研究

结合原位FT-IR,热力学分析及反应规律研究了KBr催化剂上碳酸二甲酯（DMC）氧位甲基化苯酚合成苯甲醚的反应机理。FT-IR显示KBr催化剂高于100℃活化苯酚生成酚盐,但至200℃也不活化DMC。共吸附的FT-IR及反应数据均显示苯甲醚高于150℃时生成。反应中检测到少量羰基甲氧基化产物苯基甲基碳酸酯（MPC）先于苯甲醚而生成,结合热力学计算及MPC分解转化的实验结果分析,生成MPC的反应是与生成苯甲醚的甲基化反应并行的可逆副反应。甲基化反应的机理为苯酚先被去质子化而形成酚盐,高于150℃时,酚盐的酚氧负离子亲核进攻DMC的甲基碳而生成苯甲醚。     

Strained silacycles in organic synthesis: a new reagent for the enantioselective allylation of aldehydes

A new reagent for the enantioselective allylation of aliphatic aldehydes has been developed. The reagent is easily prepared in a single step from commercially available materials and may be stored without significant decomposition. The reactivity of the reagent is attributed to strain-release Lewis acidity.     

Palladium‐catalysed cyclocarbonylation reactions in dimethyl carbonate,an eco‐friendly solvent and ring‐opening reagent

Dimethyl carbonate (DMC) is used as an alternative and eco‐friendly solvent for selective cyclocarbonylation reactions of allyl phenol derivatives for the synthesis of lactones; in some cases, depending on the reaction condition, DMC behaves as a ring‐opening reagent producing methoxycarbonyl compounds. Copyright © 2003 John Wiley & Sons, Ltd.     

Visible-light photocatalytic activation of N-chlorosuccinimide by organic dyes for the chlorination of arenes and heteroarenes

A variety of arenes and heteroarenes are chlorinated in moderate to excellent yields using N-chlorosuccinimide (NCS) under visible-light activated conditions. A screening of known organic dye photocatalysts resulted in the identification of methylene green as the most efficient catalyst to use with NCS. According to mechanistic studies described within, the reaction is speculated to proceed via a single electron oxidation of NCS utilizing methylene green under visible-light photoredox pathway. The photo-oxidation of NCS amplifies the electrophilicity of the chlorine atom of the NCS, thus leading to enhanced reactivity as a chlorinating reagent with aromatic substrates.     

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.     

Determination of N,N-dimethylaminoethyl chloride and the dimethylaziridinium ion at sub-ppm levels in diltiazem hydrochloride by LC-MS with electrospray ionisation

An LC-MS method is described for the determination of the synthetic reagent N,N-dimethylaminoethyl chloride (DMC) in the drug substance diltiazem hydrochloride, for which the permissible limit is not more than 1 ppm (microgram g-1). The N,N-dimethylaziridinium ion (DMA), the reactive intermediate formed by cyclisation of DMC, is also detected. A column switching arrangement is used: diltiazem hydrochloride is trapped on a reversed-phase HPLC column, and the polar analytes are separated by ion exchange chromatography. Ionisation is effected by positive-ion electrospray, and the quadrupole filter mass spectrometer is operated in the selected ion recording mode. The detection limit (peak height-to-baseline noise ratio = 3) for DMC varies from day to day in the range < 0.05 to 0.1 ppm. The response for DMC is linear (r > 0.999) over the concentration range 0.2-10 ppm, and the repeatability is better than 7% (relative standard deviation) at 1.0 ppm. Concentrations of DMC in diltiazem hydrochloride from the manufacturing facility under study ranged from undetectable to about 0.07 ppm. An indirect TLC method has been published for the determination of DMC in mepyramine maleate, but it lacks the necessary sensitivity and specificity. The LC-MS method presented is direct, straightforward and suitable for routine use.     

Stereoselectivity in DNA-templated organic synthesis and its origins

DNA-templated synthesis is a surprisingly general strategy for controlling chemical reactivity that enables synthetic products to be manipulated in ways previously available only to biological macromolecules. The chiral nature of the DNA template raises the possibility that DNA-templated synthesis can proceed stereoselectively. Here, we show that DNA-templated substitution reactions can exhibit stereoselectivity without the assistance of chiral groups other than those present in DNA. By characterizing changes in stereoselectivity as a result of systematic changes in the structure of the template-reagent complexes, we begin to reveal the origins of the observed stereoselectivity. We propose that the conformations of nucleotides adjacent to the reactants are largely responsible for stereoselectivity. Indeed, template and reagent sequences that can adopt either a left-handed Z-form DNA helix or a normal right-handed B-form DNA helix generate opposite stereoselectivities in the Z-form and B-form even though they share the same covalent structure and the same absolute stereochemistry. Our findings establish ways in which the chirality of an information carrier can be transmitted to the stereochemistry of encoded products through templated synthesis.     

Reaction of the ambident electrophile dimethyl carbonate with the ambident nucleophile phenylhydrazine

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.     

Facile and effective approach for oxidation of boronic acids

This present work illustrates facile and effective approach for oxidation of boronic acids using environmentally benign dimethyl carbonate (DMC) as a solvent with H₂O₂ as an oxidant at room temperature. In contrast to previous reaction reports, which make use of metal catalyst, hazardous reagent and oxidants that creates environmental concern. This method provides good to excellent yield of products and showed better tolerance towards various functional groups present on boronic acids. Moreover, this developed process is an alternative in terms of inexpensive, non toxic and easy reaction conditions.     

单原子催化甲烷直接转化的研究进展

将甲烷直接转化(DMC)为高附加值化学品(如甲醇等化合物),是实现天然气高效利用的有效途径.因甲烷结构非常稳定,使其在温和条件下(反应温度≤150℃的非强酸介质体系)的高效活化极具挑战性.近年来,单原子催化剂(SACs)因其活性物种的高利用率和高选择性,已引起国内外研究者的广泛关注,并被尝试应用于多种反应.研究表明,S...     

Polymeric oxidizing reagents based on polyacrylamides: Effect of the nature and extent of crosslinking on reactivity

Acrylamide was copolymerized with N,N′-methylene-bis-acrylamide (NNMBA), tetraethyl-eneglycol diacrylate (TEGDA), and divinyl benzene (DVB) in different proportions to afford crosslinked polyacrylamides with varying nature and extent of crosslinking. These insoluble polymers were functionalized with the N-bromoamide function and the reactivity of the resulting polymeric N-bromoamide was investigated under different conditions. The capacities of the reagents varied from 6.7 mequiv / g for the linear polymeric reagent to 1.1 mequiv / g for the 15% DVB-crosslinked reagent. Oxidation of benzoin to benzil was used as the model reaction. Investigation of the reaction under different conditions of solvent and varying molar excess revealed a significant influence of the nature and extent of crosslinking in deciding the extent of reaction. In the case of NNMBA-crosslinked reagents, the reactivity increased up to 10% crosslinking and then decreased. The reactivity of the reagents increased up to 15% crosslinking in the case of TEGDA-crosslinked ones and for DVB-crosslinked reagents the reactivity decreased with crosslinking. The polarity of the crosslinking agent and its molar percentage on the polymeric reagent (crosslink density) are factors affecting the solvent compatibility, which in turn, is decisive in the facilitation of the reactions.     

Solid-phase reagent containing the 3,5-dinitrophenyl tag for the improved derivatization of chiral and achiral amines, amino alcohols and amino acids in high-performance liquid chromatography with ultraviolet detection

A solid-phase reaction technique is described for improved derivatization of aliphatic amines, amino alcohols and amino acids. A polymeric activated ester is used for the immobilization of the 3,5-dinitrobenzoyl group, which can then be used for derivatizations of strong or weak nucleophiles, while avoiding solution-phase derivatization conditions. The reagent is easily prepared and can be regenerated after use to attain its original reactivity. The resulting chromatograms are free of system peaks due to excess derivatizing reagent, and sample handling is kept to a minimum. The reagent can be used in conjunction with both reversed- and normal-phase chromatography and can be used for off-line gas chromatographic or high-performance liquid chromatographic (HPLC) derivatizations. In addition, the reagent can be used on-line for derivatization in HPLC. Since the labelling reagent is a strong pi-acid, chiral substrates can be derivatized and separated on a Pirkle-type pi-donor column. The confirmation and quantitation of amphetamine in urine was accomplished using a polymer containing two labelling moieties, p-nitrobenzoyl and 3,5-dinitrobenzoyl. The derivatization and separation of chiral and achiral amines, amino alcohols and amino acids is described.     

A unique and highly efficient method for catalytic olefin aziridination

A facile, high yielding, and stereospecific method for olefin aziridination is described. This process capitalizes on the unique reactivity of sulfamate esters in combination with 1-2 mol % Rh2(tfacam)4 and PhI(OAc)2 as the terminal oxidant to promote N-atom transfer reactions. A range of structurally and electronically disparate alkenes are found to react under conditions that employ substrate as the limiting reagent and only a slight excess of H2NSO3CH2CCl3 as the nitrogen source. The product alkoxysulfonyl aziridines are useful intermediates that react smoothly with nucleophiles to generate 1,2-amine derivatives. Following aziridine ring-opening, the N-trichloroethoxysulfonyl group can be removed under mild reductive conditions (Zn(Cu)/AcOH-MeOH) to give the corresponding 1 degrees amine. The efficient and convenient performance of this chemistry should establish it as a useful tool for synthesis.     

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.     

Regioselective and high-yielding bromination of aromatic compounds using hexamethylenetetramine-bromine

A regioselective and highly efficient method for bromination of aromatic compounds in the presence of a stoichiometric amount of hexamethylenetetramine-bromine (HMTAB) as an efficient reagent in dichloromethane is reported. The selectivity depends on the temperature and nature of the substituent on the substrate. The reactivity of this reagent was increased by supporting it to silica gel for bromination of less activated compounds.     

新型的承载双金属氰化物络合催化剂

用双金属氰化物(DMC)络合催化剂可制得相对分子质量高、相对分子质量分布窄和不饱和度低的聚醚多元醇。为提高DMC催化剂的利用率,降低催化剂和聚醚的生产成本,国外开发了承载的DMC催化剂。它不仅可简化聚醚的后处理工艺,而且使聚醚的连续化大规模生产得以实现,因此代表了DMC催化剂的一个重要发展方向。     

Rhodium-catalyzed methylenation of aldehydes

The rhodium-catalyzed methylenation of aldehydes using trimethylsilyldiazomethane and triphenylphosphine produces a variety of terminal alkenes in excellent yields. These mild and nonbasic reaction conditions allow the conversion of enolizable substrates (keto aldehydes and nonracemic alpha-substituted aldehydes) to terminal alkenes without epimerization. Optimization of the reaction conditions led to the conclusion that a variety of rhodium(I) sources can be used as catalysts. The effect of the solvent on the reaction has also been studied, and it indicates that although the THF is the best solvent, other solvents may be used. The reactivity of the system is very much dependent on the nature of the phosphine reagent. The use of an easily removable phosphine is also described. Spectroscopic studies indicate that the reaction proceeds via an unusual mechanism which leads to the in situ formation of the salt-free phosphorus ylide, methylenetriphenylphosphorane.     

Metal-assisted reactions—Part 11: Rapid reduction of N-nitrosoamines to N,N-disubstituted hydrazines; the utility of some low-valent titanium reagents

The rapid reduction of N-nitrosoamines to N,N-disbustituted hydrazines by a low-vanet titanium reagent is described. The reagent is selective in that many other functional groups are unaffected by it. The nature of the low-valent titanium reagent is discussed in terms of experimental results of comparisons of its reactivity and that of other low-valent titanium reducing agents.