Preparative regioselective acylation of glycols by enzymatic transesterification in organic solvents

Porcine pancreatic lipase can catalyze transesterification reac tions in organic solvents in a highly regioselective manner. Lipase powder was suspended in solutions of various diols in ethyl carboxylates, and the mixtures were shaken at 30°C; as a result, pri mary monoesters of glycols were produced on a preparative scale.     

Mechanistic studies on the effect of veratryl alcohol on the lignin peroxidase catalyzed oxidation of pyrogallol red in reversed micelles

The lignin peroxidase (LiP) catalyzed oxidation of pyrogallol red (PR) in the absence and presence of veratryl alcohol (3,4-dimethoxybenzyl alcohol, VA) was carried out in bis (2-ethylhexyl) sulfosuccinate sodium (AOT)/ polyoxyethylene lauryl ether (Brij30) reversed micelles to elucidate the role of VA. Results indicated that VA could accelerate the LiP catalyzed oxidation of PR, especially at low H₂O₂ concentrations. Unlike in bulk aqueous medium, the protection of LiP by VA in the present medium was relatively unsubstantial, even at high H₂O₂ concentrations. Analysis of data from a series of experiments showed that the enhancement of the PR oxidation caused by VA was mainly due to the indirect oxidation of PR by VA^+∙ from the LiP catalyzed oxidation of VA. It was also found that at the same protector concentration (40 μM), VA (the physiological substrate of LiP) was less effective than PR (a phenolic compound) in protecting LiP from the H₂O₂ derived inactivation. This novel phenomenon deserves further study.      

水溶性电泳漆溶剂中有机成分的气相色谱分析

异丙醇,正丁醇,乙二醇单丁醚均为水溶性电泳漆溶剂中添加的有效成分,其含量的大小影响金属件着漆效果及经济成本,其中乙二醇单丁醚是电泳漆中高沸点溶剂,用作分散剂、湿润剂[1,2]。本文在文献[3,4]的基础上,考察了三种成分的气相色谱分离,确定了测定条件。1　实验部分1 1　仪器与测试条件日本产岛津GC-9A型气相色谱仪带C-R3A型色谱数据处理机。FID为检测器,1 6m×3 2mm玻璃柱,固定相GDX-103(60 80目),气化温度200℃,检测温度250℃,柱温144℃。载气:氮气50ml/min,氢气40ml/min,空气450ml/min。以保留时间定性,采用内标乙二醇单乙醚…     

Adsorption studies of acetic acid dimers on activated charcoal from organic solvents

Acetic acid exists as dimers in organic solvents like benzene, toluene and xylene. Adsorption of dimeric acetic acid on activated charcoal (AC) at various temperatures from benzene, toluene and xylene solutions have been studied. The system obeys Langmuir isotherm, thus signifying a monolayer adsorption of dimers. Corrections on AC-solvent pore volume fillings, molecular cross sectional surface area of acetic acid dimers, the adsorption equilibrium constants, the free energy change and the enthalpy change values are computed at different temperatures for the three solvents. The adsorption process has been found to be physisorption type. The FTIR measurements show that the adsorbed acetic acid dimer seems to retain the cyclic structure against the open chain non-cyclic structure.     

Kinetics of the oxidation of 1-phenyl ethanols with phase-transferred monochromate in organic solvents

Kinetic studies on the oxidation of 1-phenyl ethanol and its para-methyl, para-methoxy and para chloro derivatives have been carried out using phase transferred chromate as oxidant in pure organic solvents. The inorganic oxidant was transferred to the non polar media using the phase transfer catalyst, tetrabutyl phosphonium bromide (TB PB). The electronic effects of the substituents, effect of varying the temperature on the rate, as well as the effect of varying the dielectric constant of the medium on the rate have been investigated. The rate data fitted well with the Hammett equation.     

Isothermal and polythermal kinetics of depolymerization of C60 polymers

Isothermal depolymerization of the two polymers of C₆₀, i.e. of 1D orthorhombic phase (O) and of “dimer state” (DS) have been studied by means of Infra-red spectroscopy in the temperature ranges 383-423 and 453-503 K, respectively. Differential Scanning Calorimetry (DSC) has been used to obtained depolymerization polytherms for O-phase and DS. Standard set of reaction models have been applied to describe depolymerization behavior of O-phase and DS. The choice of the reaction models was based primarily on the isotherms. Several models however demonstrated almost equal goodness of fit and were statistically indistinguishable. In this case we looked for simpler/more realistic mechanistic model of the reaction. For DS the first-order expression (Mampel equation) with the activation energy E_a = 134 ± 7 kJ mol⁻¹ and preexponential factor ln(A/s⁻¹) = 30.6 ± 2.1, fitted the isothermal data. This activation energy was nearly the same as the activation energy of the solid-state reaction of dimerization of C₆₀ reported in the literature. This made the enthalpy of depolymerization close to zero in accord with the DSC data on depolymerization of DS. Mampel equation gave the best fit to the polythermal data with E_a = 153 kJ mol⁻¹ and preexponential factor ln(A/s⁻¹) = 35.8. For O-phase two reasonable reaction models, i.e. Mampel equation and “contracting spheres” model equally fitted to the isothermal data with E_a = 196 ± 2 and 194 ± 8 kJ mol⁻¹, respectively and ln(A/s⁻¹) = 39.1 ± 0.5 and 37.4 ± 0.2, respectively and to polythermal data with E_a = 163 and 170 kJ mol⁻¹, respectively and ln(A/s⁻¹) = 32.5 and 29.5, respectively.     

Synthesis and analysis of aminochromes by HPLC-photodiode array. Adrenochrome evaluation in rat blood

The catecholamine oxidation process induces cardiotoxicity and neurotoxicity. Catecholamines can oxidize to aminochromes through autoxidation or by enzymatic or non-enzymatic catalysis. Although some toxic effects seem to be related to the formation of aminochromes there is still scarce information concerning the identification and evaluation of these compounds in in vivo models. In this study five catecholamines were oxidized to their respective aminochromes: adrenaline/adrenochrome; noradrenaline/noradrenochrome; dopa/dopachrome; dopamine/dopaminochrome; and isoproterenol/isoprenochrome. The evaluation of the catecholamines oxidation profile was performed by HPLC with photodiode array detection and using either enzymatic (tyrosinase) or non-enzymatic [Ag(2)O, CuSO(4), NaIO(4) and K(3)Fe(CN)(6)] catalytic systems. The NaIO(4) was found to be the most efficient oxidant of catecholamines. An isocratic reverse-phase HPLC method was developed to analyse each pair of catecholamine-aminochrome. The analytical system was then applied to the detection of adrenochrome in rat blood at 490 nm. Thus, adrenochrome was administered i.p. to rats and its concentration in whole blood was monitored after 5, 15 and 25 min. Blood treatment for adrenochrome evaluation consists of an acidification for protein precipitation followed by a rapid neutralization. The results showed a rapid decrease of adrenochrome concentration in blood after its administration. The adrenochrome present in blood was characterized by UV and tandem mass spectrometry.     

Acceleration of bromide mediated benzoylperoxide oxidations of secondary alcohols in aqueous organic solvents

The efficiency of the bromide mediated benzoylperoxide oxidation of 2° alcohols to ketones was greatly improved by the addition of water. The aqueous oxidation protocol allows also the direct use of off-the-shelf benzoylperoxide reagent without an otherwise necessary and potentially dangerous drying procedure. The oxidation of cyclopentanol, cyclohexanol, 1-phenyl-ethanol and three menthol isomers occurred in good to excellent yields. The oxidation reaction tolerated N,N-dimethylacetamide (DMA) as the solvent, which resulted in a slightly lower oxidation rate than acetonitrile. Chemoselective oxidation of vicinal diols to α-hydroxy ketones did not succeed under the aqueous organic conditions employed as over-oxidation and bromination side-reactions were observed. The impact of water content, solvent, oxidant source and type of alcohol substrates employed was investigated.     

Synthesis and cationic ring-opening polymerization of mono- and bifunctional spiro orthoesters containing ester groups and depolymerization of the obtained polymers: An approach to chemical recycling for polyesters as a model system

A spiro orthoester having an ester moiety, 2-acetoxymethyl-1,4,6-trioxaspiro[4.6]undecane (4) was synthesized, and its cationic polymerization and depolymerization of the obtained polymer (5) were carried out. The monomer 4 underwent cationic polymerization with a cationic catalyst to afford the corresponding poly(cyclic orthoester) 5. The obtained polymer 5 could be depolymerized with a cationic catalyst to regenerate the monomer 4 in an excellent yield. Further, bifunctional spiro orthoesters (6, 8, 9) having diester moieties were synthesized from terephthalic acid, succinic acid, and 1,4-cyclohexanedicarboxylic acid, and their acid-catalyzed reversible crosslinking–decrosslinking was examined. The bifunctional monomer 6 derived from terephthalic acid underwent cationic crosslinking to afford the corresponding network polymer (7), which could be also depolymerized to regenerate the original bifunctional monomer 6. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2551–2558, 1999     

Cu催化羟基自由基氧化断裂纤维二糖分子糖苷键反应及其在纤维素低温解聚中的应用

纤维素是葡萄糖通过β-1,4-糖苷键链接而成的高聚物,在木质纤维素中含量最高,结构稳定,较难水解.糖苷键的解聚主要有三种方式:酶水解、酸水解以及碱降解.酶解的优点是反应条件温和、副产物少,但存在成本高、活性低等缺点,限制了其大规模的工业化生产.碱水解纤维素的同时伴随着葡萄糖的peeling-off反应得到异变糖酸,需要消耗大量的碱,并且强碱也存在腐蚀性强和回收难等问题.酸水解是目前工业上常用的纤维素水解方法,在保持较高葡萄糖选择性的同时,通过对反应条件的控制(提高反应温度和酸浓度)来提高纤维素的水解效率,但是硫酸对设备的腐蚀性强,也难以回收,不符合绿色化学的发展要求.固体酸是近年来研究较多的纤维素水解催化剂.固体酸虽然腐蚀性弱、易回收,但是其活性低,水热稳定性较差,目前还不具备大规模生产的条件.本文发展了一种羟基自由基活化断裂糖苷键的方法,利用羟基自由基的高活性在低温下实现糖苷键的选择性断裂,同时羟基自由基与糖苷键作用后转化为无毒无害的水和氧气,将不会对环境造成污染.我们首先以纤维二糖作为纤维素的模型分子,通过羟基自由基能够优先与糖苷键反应得到葡萄糖和葡萄糖酸的实验证实所提出的方法的可行性.实验表明,来自H2O2的·OH自由基能够在铜基催化剂作用下选择性氧化断裂其糖苷键,生成葡萄糖和葡萄糖酸.比如:采用均相CuSO4体系,纤维二糖转化率约为20%时,葡萄糖和葡萄糖酸的选择性分别为28.5%和32.3%.采用多相CuO/SiO2(4 wt%CuO)体系,纤维二糖转化率约为20%时,葡萄糖和葡萄糖酸的选择性约分别为23.3%和25.7%,并且该催化剂具有良好的循环使用性能.与·OH类似,CuSO4催化过硫酸钾生成的·SO4-自由基也能够有效转化纤维二糖,在纤维二糖转化率为20%时,葡萄糖和葡萄糖酸的选择性分别为36.6%和39.9%.利用这种·OH和·SO4-自由基氧化的方法,也能够在较低温度下(333 K)解聚纤维素中的糖苷键.我们发展了H2O2浸渍预处理纤维浸渍预处理纤维素的方法,通过部分破坏纤维素糖苷键,提高了纤维素的水解活性.比如:处理后的纤维素在413 K条件下反应12 h,纤维素转化率和葡萄糖选择性分别达到约36.1%和42.5%.XRD结果表明,处理后的纤维素的晶体结构未发生明显的变化.FT-IR表征结果显示处理后的纤维素表面生成了大量的羧酸基团.     

Enzymatic polyesterification in organic media. Enzyme-catalyzed synthesis of linear polyesters. I. Condensation polymerization of linear hydroxyesters. II. Ring-opening polymerization of ϵ-caprolactone

With the object to synthesize polyesters by enzymatic catalysis in organic media, two directions have been investigated: (1) the condensation polymerization of linear ω-hydroxyesters and (2) the ring-opening polymerization of lactones. The commercially-available crude porcine pancreatic lipase (PPL), suspended in organic solvents, was the preferred enzyme for the reactions. In order to determine the optimal conditions for the condensation polymerization, the bifunctional methyl 6-hydroxyhexanoate was used as a model compound to study the influence of the following parameters: type of the enzymecatalyst, kind of solvent, concentration, temperature, duration, size of the reaction mixture, and stirring. Film-forming polyesters with a degree of polymerization (DP) up to about 100 were obtained from linear aliphatic hydroxyesters in n-hexane at reflux temperature (69°C). Yet concurrently with the intermolecular condensation polymerization, macrolactones were also formed by intramolecular reaction. Two aromatic hydroxyesters did not react under these conditions. For the ring-opening polymerization of lactones the reaction of ?-caprolactone with methanol as the preferred nucleophile, was studied. Polyesters with a DP of up to 35 were obtained in n-hexane at temperatures between 25 and 40°C. The degrees of polymerization of the polyesters were determined by comparative analyses of the end groups in the ¹H-NMR spectra and by determination of molecular weights either by vapor phase osmometry, gel permeation chromatography, or intrinsic viscosity. © 1993 John Wiley & Sons, Inc.     

Contributions of hydrocarbon radicals and functional groups of organic molecules to enthalpies of their solvation in mixed water—tert-butyl alcohol solvents

The contributions of hydrocarbon radicals (−CH₃, >CH₂, >CH−, >C<) and functional groups (−OH, −OCOO−, −NO₂, −CN, >SO) to the enthalpies of solvation of organic molecules in mixed water—tert-butyl alcohol solvents were calculated in the whole range of compositions at 298.15 K. The influence of the composition and properties of the mixture on the solvation of different functional groups is discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1811–1814, October, 1997.     

Isolation of Functionalized Phenolic Monomers through Selective Oxidation and CO Bond Cleavage of the β‐O‐4 Linkages in Lignin

Functionalized phenolic monomers have been generated and isolated from an organosolv lignin through a two‐step depolymerization process. Chemoselective catalytic oxidation of β‐O‐4 linkages promoted by the DDQ/tBuONO/O₂ system was achieved in model compounds, including polymeric models and in real lignin. The oxidized β‐O‐4 linkages were then cleaved on reaction with zinc. Compared to many existing methods, this protocol, which can be achieved in one pot, is highly selective, giving rise to a simple mixture of products that can be readily purified to give pure compounds. The functionality present in these products makes them potentially valuable building blocks.     

Regioselective oxidative polymerization of 1,5-dihydroxynaphthalene catalyzed by bilirubin oxidase in a water–organic solvent mixed solution

Bilirubin oxidase (EC1.11.1.7) was used to catalyze the oxidative polymerization of 1,5-dihydroxynaphthalene to its polymer in a mixed solvent composed of dioxane, ethyl acetate, and acetate buffer. In an aqueous solution, the enzymatic oxidative polymerization hardly occurred and resulted in negligible yield mainly due to the poor solubility of 1,5-dihydroxynaphthalene. In the mixed solvent the conversion proceeded with a yield of ca. 70%. The polymer yield was studied with respect to reaction time and solvent components. Elemental analysis, UV-visible, fluorescent, and FT-IR spectroscopic analyses, proton NMR and electrochemical studies, and solubility in various organic solvents revealed that 1,5-dihydroxynaphthalene is polymerized by the C? C coupling. The molecular weight of the polymeric products solubilized with DMF varied from low molecular weight product to high molecular weight polymer. From the chromatographic studies, the organic solvent–insoluble residue was suggested to be highly polymerized material. Based on these findings a possible mechanism for enzymatic polymerization of 1,5-dihydroxynaphthalene is presented: less stable intermediates produced enzymatically from 1,5-dihydroxynaphthalene undergo coupling and polymerization to ortho-1,5-dihydroxynaphthalene polymer, thereby resulting in a regioselective polymerization of 1,5-dihydroxynaphthalene. © 1993 John Wiley & Sons, Inc.     

Anionic polymerization of caprolactam in organic media. Morphological aspects

Crystalline entities formed during anionic polymerization of caprolactam (CL) in nonpolar solvents were examined, mainly by scanning electron microscopy and wide angle X-ray scattering. The morphological development of these entities is governed by the complex interaction between the competing polymerization and physical processes like phase separation and crystallization. The effect of the efficiency of catalytic systems on their interaction, the mechanisms of the phase separation and the crystal growth under topological restrictions set by the phase separation are discussed. Under reaction conditions, for these ones favouring high polymer yields, the final morphology of the polycaproamide (PCA) particles can be controlled by the efficiency of both catalytic species (activator and catalyst). Despite the large range of particle sizes two typical morphologies, namely – connected globules evolving to large blocks and macroporous powders are obtained using more or less efficient catalytic systems, respectively. An adequate selection of the catalytic pairs allows to control the particles’ size and their internal morphology, which is important for certain specific applications of PCA. Received: 1 August 1997 Accepted: 5 February 1998     

EPR study of the dinitrogen tetroxide dissociation in organic solvents

The dinitrogen tetroxide homolytical dissociation constants K _DIS are determined in organic solvents. The values are the highest in non-donor and the lowest in n-donor solvents. The variations of K _DIS with solvent are interpreted in terms of electron donor-acceptor interactions between dinitrogen tetroxide and electron donor molecules.     

Thermochemistry of copper(II) ion solvation in aqueous organic solvents

The integral heat effects of CuCl₂ dissolution in aqueous DMSO, aqueous ethanol and aqueous acetone solutions at 298. 15 K in the electrolyte concentration range 0.001–0.01M were measured by means of calorimetry. ΔH _sol ⁰ values were obtained by extrapolation to zero electrolyte concentration. Literature data were used to determine the thermodynamic characteristics of Cu²⁺ transfer from water to aqueous organic solvents.     

Characterization of racemization of chiral pesticides in organic solvents and water

Eight chiral pesticides, which were selected to cover different pesticide species and origins of chirality, were investigated to explore their chiral stability in organic solvents and water. Profenophos, fenamiphos, quizalofop-ethyl, dichlorprop-methyl (DCPP-methyl) and acetochlor were showed stable under all test conditions. However, significant racemization was observed for malathion, phenthoate and fenpropathrin in methanol, ethanol and water, but not in n-hexane, isopropanol, acetone or methylene chloride. The kinetic parameters (rate constant k and half-life T_1/2) of the abiotic racemization were calculated through a mathematical model of the first-order reaction. Furthermore, the extent of racemization varied among the solvents and was also affected by temperature dependence. The racemization of malathion, phenthoate and fenpropathrin in water was documented to be pH-dependent and took place more rapidly at pH 7.0 than at pH 5.8. The observed racemization was deduced to occur via a proton exchange process at the chiral center, and the relationship between the abiotic racemization and pesticide structure was further explored. Findings from this study are useful for better understanding enantioselectivity of chiral pesticides in environment and also for proper analysis, formulating or handling of enantiopure products.     

Ionic and coordination diene polymerization and organic derivatives of main group metals

The effects of the nature of an organic derivative of a main group metal (cocatalyst), its composition, the cocatalyst : transition metal compound ratio, and the way of introducing the cocatalyst on the formation and operation of the active sites in the Ziegler—Natta catalytic systems in the polymerization of conjugated dienes are discussed. A correlation between the cocatalyst nature and the number and kinetic heterogeneity of the active sites is shown.