溶剂对Diels-Alder反应的影响

Diels-Alder反应是有机合成中一类很重要的环加成反应,在精细化工,生物制药中有很广泛的应用.溶剂对Diels-Alder反应的反应速率和选择性有很重要的影响.本文综述了传统有机溶剂、水、超临界CO2和离子液体对Diels-Alder反应的影响.     

Studies on chitin

Summary Chitin was aminoalkylated with N,N-diethylaminoethyl chloride in organic solvents or aqueous solutions in the presence of sodium hydroxide. The substitution reactions in organic solvents occurred under heterogeneous conditions on dispersions of powdery chitin while those using alkali chitin solutions proceeded in solution. The latter reactions were more efficient and reproducible than the former ones due to the homogeneous reaction conditions. The resulting diethyl-aminoethyl-chitins showed much improved solubility in contrast to the insolubility of chitin. The derivatives prepared in aqueous solutions showed especially remarkable solubility; those with substitution degrees over 0.5 were readily soluble in water and highly swelled even in various common organic solvents.     

Allylic polymers from resin acids. Monomer synthesis at high temperature

New chemical compounds, i. e. ketones of the abietic acid-diallyl maleate Diels-Alder adduct, have been synthesized when the reaction of abietic acid and diallyl maleate was carried out at high temperatures (up to 250°C). Having unsaturated groups in their structure, they are polymerizable substances. The monomers and the polymers have been investigated by commonly used chemical and physical methods. The polymers are soluble in polar organic solvents only at low molecular weights. The behavior of these compounds as crosslinking monomers in copolymer systems has been examined.     

离子液体在有机反应中的应用

室温离子液体,由含氮的有机阳离子和无机阴离子组成,由于离子液体是很多化合物的溶剂,也能够溶解作为催化剂的过渡金属络合物,其阴离子还是潜在的配位体,故它们能起催化剂的功能,本文着重讨论这方面的发展状况。     

离子液体汽化焓的测量方法

离子液体具有蒸气压低、不易挥发、导电能力强、化学性质稳定、可循环利用等特点,具有以下作用：能够替代有机溶剂作为绿色环保的新型溶剂;可以作为催化剂催化化学反应;可以作为电解质溶液参与电化学反应,制作新型电池;可以作为吸附气体的吸附剂等。过去人们认为离子液体不挥发,也不能测量它们的汽化焓,回顾了近年来离子液体的相关研究成果,发现陆续有研究者提出测量离子液体汽化焓的方法,鉴于目前缺少相关总结工作,将系统性地介绍这些方法并阐述其原理,为今后的离子液体研究提供指导。     

离子液体在有机合成中的应用新进展

室温下的离子液体作为一种绿色、环保、可替代传统有机溶剂的新型溶剂受到了极大关注.总结了近年来离子液体在有机合成反应中的研究新进展,包括氧化反应、还原反应、Friedel-Crafts反应、Diels-Alder反应、Heck反应、硝化反应及其它合成反应.     

Lipase made active in hydrophobic media

Enzymes are distinguished from other catalysts by their high substrate specificity. This is a great asset when one wants to apply them for syntheses of various compounds. Their usage, however, generally is limited to hydrophilic reaction media, because they usually are not soluble and active in hydrophobic media. Recently, we have been able to make various enzymes soluble and active in highly hydrophobic organic solvents. The key to this success is the chemical modification of enzymes with an amphipathic synthetic polymer, polyethylene glycol. The activated polymers can be attached to enzymes in aqueous buffer solutions, and once enzymes are modified they become soluble and active in various organic solvents such as benzene, toluene and cholorinated hydrocarbons and exhibit high enzymic activities in these organic solvents. Modified hydrolytic enzymes catalyzed the reverse reaction of hydrolysis in organic solvents. The modified lipase catalyzed various ester synthesis reactions. Because the reactions were conducted in the pure solvent system, it also was possible to study the kinetics and the substrate specificity for ester synthesis reaction. It also catalyzed the polymerization of a hydroxy group containing carboxylic acid due to the bifunctional nature. The modified lipase catalyzed ester exchange between an ester and an alcohol, between an ester and a carboxylic acid and between two esters in organic solvents. When the two substrates for ester exchange were liquid, the reaction could take place without organic solvents. The modified lipase catalyzed an ester exchange reaction between trilaurin and triolein when dissolved in these substrates. Dilauroyl-monooleoylglycerol and monolauroyl-dioleoyl-glycerol were formed from these two substrates in the presence of the modified lipase. The modified enzyme was extremely thermostable in its substrates. In the ester synthesis and ester exchange reactions, a trace amount of water was necessary for expression of the enzymic activity. It is suggested that the amphipathic polymer molecules retained water in close proximity to the enzyme. Presented at the symposium “The Biology, Biochemistry and Technology of Lipase” at the 78th annual meeting of the American Oil Chemists’ Society held May 17–21, 1987, in New Orleans, Louisiana.     

SPECTROPHOTOMETRIC INVESTIGATION OF THE ACIDITY CONSTANTS OF FLUORESCEIN IN VARIOUS WATER-ORGANIC SOLVENT MEDIA

We use a new procedure for estimating acid ionization constants of fluorescein using the spectrophotometric method at 25°C and at the constant ionic strength I = 0.1 M (KNO₃) in pure water as well as in aqueous media containing variable percentages (10–50% w/v) of organic solvents. The used organic solvents were methanol, ethanol, N,N-dimethyl formamide, dimethyl sulfoxide, acetonitrile, and dioxane. The obtained results indicated that acidity constants decrease as the content of an organic solvent in the medium increases. The acidity constants of all related equilibria are estimated using the whole spectral fitting of the collected data. The DATAN program was applied for determination of acidity constants. The effects of various solvents on absorption properties and acidity constants of each component are also discussed.     

Development of novel Lewis acid catalysts for selective organic reactions in aqueous media

New types of Lewis acids as water-compatible catalysts have been developed. Various metal salts were found to work as Lewis acid catalysts in aqueous media, and catalytic asymmetric aldol reactions in such media have been attained. Furthermore, Lewis acid-surfactant combined catalysts, which can be used for reactions in water without using any organic cosolvents, have been also developed. These investigations will contribute to reducing the use of harmful organic solvents and to develop efficient catalytic systems which cannot be realized in conventional organic solvents.     

离子液体及其在有机合成中的应用

简要介绍了离子液体的组成和制备方法，归纳了离子液体的优越性质，综述了离子液体作为催化剂和绿色溶剂在催化加氢、Diels-Alder反应等有机合成反应中的应用，提出离子液体解决了催化剂的回收问题，避免了挥发性溶剂对环境的污染，实现了有机合成的绿色化。展望了离子液体在日化及其相关行业合成中的应用前景。     

CO2 absorption in aqueous solutions of hindered amines

Sterically hindered amines constitute a new class of chemicals which have recently come into industrial use in a variety of gas-treating processes: chemical solvents in both aqueous and non-aqueous solutions, rate promotion additives for the hot carbonate process, and chemical solvents for the selective removal of hydrogen sulfide. The scant published data on the behavior of hindered amines do not allow one to estimate the actual values of the apparent kinetic constants or equilibrium constants, and even less to establish the chemical steps involved.In this paper, the results of an investigation of the behavior of one particular amine, 2-amino-2-methyl-1-propanol (AMP), as a chemical solvent for CO₂ in aqueous solutions are reported. The equilibrium behavior of a hindered monoamine like AMP in aqueous solutions is dominated by the values of two equilibrium constants: the protonation constant K_p and the carbamate stability constant K_c. The value of K_p at infinite dilution has been determined experimentally, and is large enough to neglect formation of the carbonate ion. The value of K_c has been found experimentally to be significantly less than 10⁻¹ 1/gmol, as is expected for a hindered amine.A thermodynamic model has been developed and tested against experimental equilibrium data. Preliminary kinetic data seem to indicate that the reaction with CO₂ is first order with respect to both CO₂ and AMP. A first step in the elucidation of the chemical steps involved is presented.     

Correlations for prediction of molecular diffusivities in liquids at infinite dilution

Diffusivities measured at 278.2 K to 323.2 K are reported for propene in acetic acid, acetone, n-butanol, chloroben-zene, N, N dimethyl formamide, ethyl acetate and n-octane. Measurements were made utilizing the steady-state capil-lary cell method. It was found that the diffusivities were reduced in the associating solvents when compared with those obtained in non-polar solvents at the same temperature. Three new empirical correlations have been developed for the prediction of diffusivities in liquids at infinite dilution and these are: for n-alkane solutions, for dissolved gases in organic solvents, and for dissolved gases in water.     

Effect of water‐miscible solvents on the organic solvent‐resistant tyrosinase from Streptomyces sp. REN‐21

The effect of various water‐miscible organic solvents (ethanol, methanol, acetone, acetonitrile, N,N‐dimethylformamide (DMF) and dimethylsulfoxide (DMSO)) on the kinetics of 4‐tert‐butylcatechol (tBC) oxidation in the presence of different samples of organic solvent‐resistant tyrosinase (OSRT) has been studied. In contrast to mushroom tyrosinase the enzyme shows a high relative stability in solutions of organic solvents and increased activity toward the bulky and hydrophobic substrate, tBC, in respect to catechol. Rates of the studied OSRT‐catalyzed reactions are however reduced by the presence of organic solvents and for all studied samples of OSRT decrease exponentially with the content of an organic solvent. The effect has been satisfactorily described by the effect of organic solvents on the thermodynamic activity of tBC. The correlation of the inhibition parameters with the hydrophobicity of a particular solvent (log P), its intrinsic molar volume, V_i, and the Dimroth–Reichardt parameter, E_T(30), are shown. The results allow also the prediction of OSRT activity in aqueous solutions of water‐miscible organic solvents. Copyright © 2003 Society of Chemical Industry     

诺卜二烯的合成及应用研究进展

综述了诺卜二烯的合成方法及其在精细化工和有机合成中的应用。利用诺卜醇直接脱水反应、诺蒎酮的格氏反应、诺卜基醚或诺卜基磺酸酯的消去反应、硫代苯甲酸诺卜酯的光催化消去反应及桃金娘烯醛的Wittig反应等几种方法能够合成得到诺卜二烯。含共轭双键的诺卜二烯可直接用作精细化工配方成分,更多的是经过Diels-Alder反应用于合成香料、手性配体等物质,或者与含亲电基团的化合物反应合成一系列衍生物,或者作为单体合成聚合物产品。     

Design and Synthesis of Chiral Zn2+ Complexes Mimicking Natural Aldolases for Catalytic C–C Bond Forming Reactions in Aqueous Solution

Extending carbon frameworks via a series of C–C bond forming reactions is essential for the synthesis of natural products, pharmaceutically active compounds, active agrochemical ingredients, and a variety of functional materials. The application of stereoselective C–C bond forming reactions to the one-pot synthesis of biorelevant compounds is now emerging as a challenging and powerful strategy for improving the efficiency of a chemical reaction, in which some of the reactants are subjected to successive chemical reactions in just one reactor. However, organic reactions are generally conducted in organic solvents, as many organic molecules, reagents, and intermediates are not stable or soluble in water. In contrast, enzymatic reactions in living systems proceed in aqueous solvents, as most of enzymes generally function only within a narrow range of temperature and pH and are not so stable in less polar organic environments, which makes it difficult to conduct chemoenzymatic reactions in organic solvents. In this review, we describe the design and synthesis of chiral metal complexes with Zn²⁺ ions as a catalytic factor that mimic aldolases in stereoselective C–C bond forming reactions, especially for enantioselective aldol reactions. Their application to chemoenzymatic reactions in aqueous solution is also presented.     

Quantitative protection of chitin by one-step tritylation and benzylation to synthesize precursors for chemical modifications

Protections of hydroxyl groups of chitin by triphenylmethylation and benzylation were studied in detail to synthesize precursors for efficient regioselective chemical modifications in organic solvents. The reactions of squid ??-chitin with triphenylmethyl chloride and benzyl chloride proceeded much more facilely than those of shrimp ??-chitin, and quantitative 6-O-triphenylmethylation and 3,6-O-dibenzylation of ??-chitin were accomplished in the presence of dimethylaminopyridine and sodium hydride, respectively, in simple one-step reactions. The resulting protected derivatives exhibited high affinity for organic solvents and would allow modification reactions under homogeneous or almost homogeneous conditions in suitable solvents.     

Conductance behavior of some tris(ethylenediamine)cobalt(III) complexes and their ion association in some dipolar aprotic solvents

The conductance behavior of dilute solutions of tris(ethylenediamine)cobalt(III) perchlorate in acetonitrile(AN), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and propylene carbonate (PC) was studied at 25°C. From the conductivities of these solutions the limiting molar conductivity of the tris(ethylenediamine)cobalt(III) ion and the ion association constant of the ion pair formed between the tris(ethylenediamine)cobalt(III) and the perchlorate ion have been determined. The Walden products of the tris(ethylenediamine)cobalt(III) ion in these solvents were found to be approximately constant. It was concluded from the ion association constants obtained that the degree of ion association was determined by not only the dielectric constant but also the basicity of these solvents. The ion association constants of tris(ethylenediamine)cobalt(III) ion with some anions which were determined from the conductivities of the dilute DMF and DMSO solutions at 25°C were found to increase to a great extent with the decrease in crystallographic radii of anions. The tendency could not be explained by the usual electrostatic theory. The conductance behaviour is discussed from the view point of the solvent effects which influence the ion-ion interaction.     

A study of some intermolecular interactions between organic dye molecules in aqueous solution by fluorescence quenching and difference absorption spectrophotoinetry

Intermolecular interactions between the fluorescent organic dyes Fluorescein, Fluorescein Diiodide, Eosin, Rose Bengal, Erythrosin, Phloxine, Phloxine B, Rhodamine 6G, Lissamine Rhodamine B200 and the non fluorescent Crystal Violet and Malachite Green in aqueous solution have been studied by fluorescence quenching and difference absorption spectrophotometry. Equilibrium constants for the interactions have been determined by the two techniques mentioned and are compared. Absorption and fluorescence spectra and rates of photolysis of solutions obtained by extracting aqueous solutions of the mixed dyes into organic solvents are described.     

Nanofiltrationsmembranen für Trennprobleme in organischen Lösungen

Nanofiltration Membranes for Separation Problems in Organic Solutions . Nanofiltration based on rejection and flux features intermediate between those ultrafiltration and reverse osmosis is one of the technically and scientifically interesting membrane processes with a great future. Moreover, most commercial available nanofiltration membranes are only suitable for separation processes in aqueous solutions. A small number of composite membranes with a highly cross-linked selective layer show a technically interesting resistance towards organic solvents, such as ketones, esters, ethers or alcohols. The present article describes such nanofiltration membranes used for separation of low molecular weight chemical compounds from polar or nonpolar solvents, but also for the removal of organic compound from aqueous solutions. Methods of manufacturing and modifying such solvent stable composite membranes are shown, as are the conditioning of membranes and examples of industrial application.     

Neue Ergebnisse zum Fließverhalten von konzentrierten Polymerlösungen

A variety of measurements mainly using solutions of polystyrene and polyvinylacetate has been made to investigate the correlation between viscosity of concentrated polymer solutions and both the properties of all components of the solution and the experimental conditions. The following parameters have been changed: polymer concentration, molecular weight, temperature, shear and chemical structure of the solvents. In addition some measurements have been made using solutions of ethylene-propylene-copolymer, chlorinated polypropylene, polyvinyl alcohol and methylcellulose. Various polymer systems have also been investigated using mixtures of solvents. Data from the literature are reported supplementary to our measurements. It is shown that the results can be explained qualitatively on the basis of physical considerations. Such considerations allowed to predict new effects, for which experimental evidence could be obtained. New correlations with other material properties have been found. Thus we regard these facts as a strong support for the usefullness of our concept.