Reactivity of base catalysed hydrolysis of 2-pyridinylmethylene-8-quinolinyl-Schiff base iron(II) iodide complexes: solvent effects

Three ligands of 2-pyridinylmethylene-8-quinolinyl (L1), methyl-2-pyridinylmethylene-8-quinolinyl (L2), and phenyl-2-pyridinylmethylene-8-quinolinyl (L3), Schiff bases were synthesised by direct condensation of 8-aminoquinoline with 2-pyridinecarboxaldehyde, 2-acetylpyridine, or 2-benzoylpyridine. They coordinated to Fe(II) ion in a 1: 2 mole ratio followed by treatment with iodide ions affording complexes with a general formula [Fe(L)₂]I₂·2H₂O, (L = L1, L2, or L3). Spectrophotometric evaluation of the kinetics of base catalysed hydrolysis of these complex cations was carried out with an aqueous solution of NaOH in different ratios of water/methanol binary mixtures. Kinetics of the hydrolysis followed the rate law (k ₂[OH^?] + k ₃[OH^?]²)[complex]. Reactivity trends and their rate constants were compared and discussed in terms of ligand structure and solvation parameters. The methanol ratio affects the hydrolysis as a co-solvent which was analysed into initial and transition state components. The increase in the rate constant of the base hydrolysis of Fe(II) complexes, as the ratio of methanol increases, is predominantly caused by the strong effect of the organic co-solvent on the transition states.     

A new solvent system for efficient synthesis of 1,2,3-triazoles

The use of CH₂Cl₂ as a co-solvent with H₂O in the copper(I)-catalyzed 1,3-dipolar cycloaddition of organic azides and alkynes increased reaction rates and provided the corresponding 1,2,3-triazoles in excellent yields compared to other organic co-solvent systems. Moreover, we applied this discovery to prepare the functional multivalent compound in an excellent yield.     

混合溶剂体系中牛肝β-半乳糖苷酶催化5-氟-2'-脱氧尿苷区域选择性半乳糖基化反应

研究了混合溶剂体系中有机溶剂种类和含量对牛肝β-半乳糖苷酶催化5-氟-2'-脱氧尿苷区域选择性半乳糖基化反应的影响.结果表明,在含10%(体积分数)有机溶剂体系中,该酶稳定性差,失活严重.减少有机溶剂含量可显著减轻其对该酶的毒害作用.然而,有机溶剂的添加对酶促糖基化反应的区域选择性的影响很小(均保持在99%以上).牛肝...     

Peculiarities of Mobile Phases Containing Formic Acid

Formic acid is often used for pH adjustment in RP–LC mobile phases. However, under certain circumstances, formic acid can also behave as an organic co-solvent. This study illustrates two scenarios when the effects of formic acid as co-solvent will be most noticeable. One scenario is for water-rich mobile phases, in which the addition of formic acid will cause small but significant decreases in retention of neutral analytes. The other scenario is in gradient chromatography. It is demonstrated that, during acetonitrile solvent gradients, desorption of formic acid from the column stationary phase occurs simultaneously, potentially causing a spike in UV detector baselines at the beginning of gradients. A pK _a value of formic acid obtained in 50% acetonitrile is also reported and the impact of organic solvent on the dissociation of formic acid is discussed.     

Reagent concentration effects in the REM resin solid phase synthesis of tertiary amines

The use of reagent concentration has resulted in increased rates for all stages of the REM resin synthesis of tertiary amines. These increases in rate translate into faster reaction times, higher yields and lower reagent consumption. Of the methods examined, the most successful was the use of perfluorous solvents, either alone or with a small amount of organic co-solvent.     

Spectrophotometric determination of the dissociation constants of methyl yellow in mixed protic solvents

The concentration dissociation constants (pK(a)) of methyl yellow, MY (H(+)In) in mixed aqueous solvents of methanol, ethanol, iso-propanol, tert-butanol have been accurately determined from spectrophotometric measurements at 25 degrees C and a constant ionic strength of 0.1 mol l(-1). It has been shown that in these solvents, the pK(a) values decrease with increasing composition of the organic co-solvent. A linear relationship between pK(a) and the mole fraction (x(2)) of the co-solvent was observed in a limited range of the compositions for each of the solvent systems. The results have been discussed in the light of transfer thermodynamic properties of the species existing in the dissociation equilibrium, solvent basicity and solute-solvent interactions. Furthermore, it was also observed that with the change of the solvents, the absorption spectra of MY shifted apparently and the color transition changed accordingly. The solvent effect on the spectra has been attributed to the isomerization equilibria of MY. A simple application of MY was also shown to the sodium acetate-hydrochloric acid titrations in the mixed solvents.     

Enzyme mediated kinetic resolution of δ-hydroxy-α,β-unsaturated esters as a route to optically active δ-lactones

A novel synthetic route to optically active saturated and unsaturated δ-lactones based on enzymatic kinetic resolution and ring-closing metathesis reactions has been proposed. The influence of temperature, co-solvent, organic additives and the substrate structure on the catalytic behavior of selected hydrolases was studied. The substantial impact of the organic co-solvent and surfactant type on the enzymatic activity and enantioselectivity was observed providing enantiomerically pure δ-hydroxy-α,β-unsaturated esters. The established protocol combining enzymatic kinetic resolution with ring closing metathesis was successfully applied in the synthesis of the enantiomerically pure (6R)-phenyl-5,6-dihydro-2H-pyran-2-one which plays crucial role in the synthesis of the number of bioactive compounds.     

Hydrophilicity and acid hydrolysis of water-soluble antibacterial iron(II) Schiff base complexes in binary aqueous solvents

Kinetics of acid hydrolysis of seven antibacterial iron(II) Schiff base complexes has been studied. The Schiff base ligands were derived from sodium 2-hydroxybenzaldehyde-5-sulfonate and a series of amino acids. The hydrolysis rate is studied by spectrophotometric method and compared with complex hydrophilicity. Addition of the organic co-solvent, dimethylsulfoxide or n-propanol, significantly accelerates the hydrolysis.     

超临界二氧化碳介质中钯催化末端炔烃双羰基化反应的研究

在超临界二氧化碳介质中，钯催化末端炔烃双羰基化反应时需要加入适当量的 醇作为共溶剂，反应才能顺利进行，而且反应规律与常规有机溶剂有所区别．     

离子液体与微波协同促进有机合成反应

介绍了离子液体作溶剂、助溶剂、催化剂和反应试剂与微波协同促进有机合成的研究进展。离子液体与微波协同促进有机合成反应,缩短了反应时间,提高了反应的选择性和产率,对环境更加友好。     

Horse liver esterase catalyzed enantioselective hydrolysis of N,O-diacetyl-2-amino-1-arylethanol

N,O-Diacetyl-2-amino-1-arylethanol can be efficiently resolved by horse liver esterase (HLE). A remarkable organic co-solvent effect on the enantioselectivity of HLE was observed.     

Phase-transfer catalytic determination of phenols as methylated derivatives by gas chromatography with flame ionization and mass-selective detection

A microemulsion electrokinetic chromatographic (MEEKC) method was developed for the separation of six catechins, specific marker phytochemicals of Cistus species. The MEEKC method involved the use of sodium dodecyl sulfate (SDS) as surfactant, heptane as organic solvent and butan-1-ol as co-solvent. In order to have a better stability of the studied catechins, the separation was performed under acidic conditions (pH 2.5 phosphate buffer). The effects of SDS concentration and of the amount of organic solvent and co-solvent on the analyte resolution were evaluated. The optimized conditions (heptane 1.36% (w/v), SDS 2.31% (w/v), butan-1-ol 9.72% (w/v) and 50 mM sodium phosphate buffer (pH 2.5) 86.61% (w/v)) allowed a useful and reproducible separation of the studied analytes to be achieved. These conditions provided a different separation profile compared to that obtained under conventional micellar electrokinetic chromatography (MECK) using SDS. The method was validated and applied to the determination of catechin and gallocatechin in lyophilized extracts of Cistus incanus and Cistus monspeliensis.     

超临界二氧化碳介质中钯催化伯胺羰基化反应的研究

以正丁胺为模板 ,比较了超临界二氧化碳介质和常规有机溶剂中钯催化伯胺羰基化反应的规律。研究结果表明 ,在超临界二氧化碳中钯催化伯胺羰基化反应的化学选择性发生了改变 ,而且助溶剂对反应的化学选择性和产率也有较大的影响     

Effects of different extraction methods and conditions on the phenolic composition of mate tea extracts

A simple and rapid HPLC method for determination of chlorogenic acid (5-O-caffeoylquinic acid) in mate tea extracts was developed and validated. The chromatography used isocratic elution with a mobile phase of aqueous 1.5% acetic acid-methanol (85:15, v/v). The flow rate was 0.8 mL/min and detection by UV at 325 nm. The method showed good selectivity, accuracy, repeatability and robustness, with detection limit of 0.26 mg/L and recovery of 97.76%. The developed method was applied for the determination of chlorogenic acid in mate tea extracts obtained by ethanol extraction and liquid carbon dioxide extraction with ethanol as co-solvent. Different ethanol concentrations were used (40, 50 and 60%, v/v) and liquid CO? extraction was performed at different pressures (50 and 100 bar) and constant temperature (27 ± 1 °C). Significant influence of extraction methods, conditions and solvent polarity on chlorogenic acid content, antioxidant activity and total phenolic and flavonoid content of mate tea extracts was established. The most efficient extraction solvent was liquid CO? with aqueous ethanol (40%) as co-solvent using an extraction pressure of 100 bar.     

High Regioselective Hydroformylation of Higher Olefins Catalyzed by Water-soluble Rhodium Complex

The idea of two-phase (aqueous/organic) catalysis has attracted great attention in recent years due to the easy separation of catalyst from organic products by simple decantation and the environmental benefits. However, in the case of higher olefin hydroformylation, the unacceptable low reaction rate was observed due to its very low solubility in water. In fact many efforts have been devoted during the last years to find efficient means either to improve the mass transfer of the reactants or to maintain the active species at the interface, mainly by using a co-solvent, a cyclodextrin, a surfactant, an amphiphilic ligand, a carbohydrate modified phosphine or by supported aqueous phase catalysis and water-soluble polymer ligand.     

Kinetics of solvolysis of trans-dichlorotetra (t-butylpyridine)-cobalt(III) ions in mixtures of water with ethane-1,2-diol and with 2-methoxyethanol. A contrast with the effect of hydrophobic co-solvents

The kinetics of the solvolysis of the hydrophobic ion, Co(4-t-Bupy)₄Cl₂⁺, have been followed in mixtures of water with co-solvents having a hydrophilic tendency, ethane-1,2-diol and 2-methoxyethanol. The variation of In(rate constant) with the reciprocal of the dielectric constant is nonlinear for both co-solvents. The enthalpy and the entropy of activation are rather insensitive to changes in the solvent composition in both mixtures, but low maxima may exist at mol fractions of co-solvent Ca. 0.10–0.20. The application of a Gibbs energy cycle to the process of the initial state going to the transition state suggest that, in water-rich conditions, the increase in the stability of the emergent solvated Co^III ion in the transition state relative to the increase in the stability of Co(4-t-Bupy)₄Cl₂⁺ in the initial state as the co-solvent content rises is greater for 2-methoxyethanol than for ethane-1,2-diol. © 1995 John Wiley & Sons, Inc.     

丹参中3种丹参酮的超临界二氧化碳萃取及液相分析

 用超临界CO2 流体及共溶剂乙醇萃取丹参中的 3种丹参酮 ,分别采用正交设计法和系统法考察了萃取中的主要影响因素 ;采用高效液相法 (HPLC) ,在甲醇 水 (体积比为 80∶2 0 )溶液为流动相和检测波长为 2 80nm的条件下 ,以外标法检测了萃取产物中 3种丹参酮的含量。实验得到的最佳条件为 :萃取压力 2 0MPa ;萃取温度 4 5℃ ;分离温度 35℃ ;共溶剂 95 % (体积分数 )乙醇 ;流量 1 0mL/min。建立的HPLC测定方法简便快捷 ,准确度高 ,重现性良好 ,相关系数r为 0 9994～ 0 9998,相对标准偏差RSD为 2 37%～ 3 4 7%。     

Solvent denaturation of supramolecular capsules assembled via the hydrophobic effect

The organic co-solvent induced denaturation of a series of capsular complexes formed between trioxolane guests and a water-soluble deep-cavity cavitand was examined. The results obtained demonstrate a wide range of denaturation properties, and suggest the important factors governing capsule stability.     

Catalytic asymmetric carbon-carbon bond-forming reactions in aqueous media

Use of water as a reaction solvent or co-solvent has received much attention in synthetic organic chemistry. Recently, successful examples of catalytic asymmetric carbon-carbon bond formation in aqueous media have been developed. Most of these examples show characteristic features that are realized only in the presence of water. The role of water in these reactions is also discussed here.     

Analysis of catechins in extracts of Cistus species by microemulsion electrokinetic chromatography

A microemulsion electrokinetic chromatographic (MEEKC) method was developed for the separation of six catechins, specific marker phytochemicals of Cistus species. The MEEKC method involved the use of sodium dodecyl sulfate (SDS) as surfactant, heptane as organic solvent and butan-1-ol as co-solvent. In order to have a better stability of the studied catechins, the separation was performed under acidic conditions (pH 2.5 phosphate buffer). The effects of SDS concentration and of the amount of organic solvent and co-solvent on the analyte resolution were evaluated. The optimized conditions (heptane 1.36% (w/v), SDS 2.31% (w/v), butan-1-ol 9.72% (w/v) and 50 mM sodium phosphate buffer (pH 2.5) 86.61% (w/v)) allowed a useful and reproducible separation of the studied analytes to be achieved. These conditions provided a different separation profile compared to that obtained under conventional micellar electrokinetic chromatography (MECK) using SDS. The method was validated and applied to the determination of catechin and gallocatechin in lyophilized extracts of Cistus incanus and Cistus monspeliensis.