Search results for "liquid"
showing 10 items of 4351 documents
ChemInform Abstract: New Ionic Liquid-Modified Silica Gels as Recyclable Materials for L-Proline- or H-Pro-Pro-Asp-NH2-Catalyzed Aldol Reaction.
2008
L-proline and the tripeptide H–Pro–Pro–Asp–NH2 (1) have been supported, by adsorption, onto the surface of modified silica gels functionalized with a monolayer of covalently attached 1,2-dimethyl-imidazolium chloride, tetrafluoroborate or hexafluorophosphate ionic moieties, respectively. Three different linkers were used to attach the ionic liquid moiety to the surface of these supports. The resulting materials have been used as catalysts for the aldol reaction between acetone and several substituted benzaldehydes. Good yields and enantioselectivities, comparable to or better than those obtained under homogeneous conditions, were obtained. These materials are easily recovered by filtration,…
ChemInform Abstract: Sequential Suzuki/Asymmetric Aldol and Suzuki/Knoevenagel Reactions under Aqueous Conditions.
2012
Here we describe for the first time a sequential Suzuki/asymmetric aldol reaction. Such sequential approach was achieved through the combined use of an ionic liquid supported palladium catalyst and the organocatalyst trans-4-(2,2-diphenylacetoxy)proline. Suzuki and asymmetric aldol reactions were performed under aqueous conditions. The use of a palladium catalyst under basic conditions allowed also the first example of sequential Suzuki/Knoevenagel reaction. Reactions were carried out under aqueous conditions and products were isolated in good to high yields and, in the case of the Suzuki/aldol reaction, with diastereoselectivities up to 91:9 and enantioselectivities up to at least 99 %.
N-Substituierte Imidazole aus Aldehyden, 1,2-Diketonen, primären Aminen und flüssigem Ammoniak. 4. Mitt. über Imidazolsynthesen mit flüssigem Ammoniak
1974
N-substituierte Imidazole 5 konnen aus Aldehyden 1, 1,2-Diketonen 2 und primaren Aminen 3 in flussigem Ammoniak 4 dargestellt werden. N-substituted Imidazoles from Aldehydes, 1,2-Diketones, Primary Amines and Liquid Ammonia N-substituted imidazoles 5 can be synthesized from aldehydes 1, 1,2-diketones 2 and primary amines 3 in liquid ammonia 4.
Identification and quantification of valuable phenolic compounds from red wines from western part of Romania
2019
The aim of this paper is to identify and quantify different phenolic compounds known and appreciated for their antioxidant action from five red wines from the west side of Romania. For the determinations HPLC methods were used, the samples were done in cycles of three for better results. Phenolic acids that drew the attention have different values that ranging from 1.3007 mg/L (elagic acid) to 19.3315 (t-cafftaric acid), some various flavonoids (flavone, flavonoli și flavanoli) the values of which were recorded between 0.9997 mg/L (apigenin) and 56.1617 mg/L (catechin) and the stilbens namely the resveratrol has reached the maximum value of 8.1427 mg/L. The phenolic compounds that were det…
Green Solvents for Analytical Separation and Analyses
2010
The alternatives to the use of organic solvents that have been offered by the scientific literature reviewed. In order to look at the best solvents from both analytical and sustainable view points, the use of water under superheated conditions, supercritical fluids, renewable organics, ionic liquids, and aqueous solutions of amphiphillic compounds, have been evaluated. As a general conclusion, it can be seen that, at present, green alternatives to the traditional organic solvents employed in analytical separations and analysis that are being well explored are the capabilities of the use of alcohols, supercritical fluids, and superheated water; and remain unexplored tremendous possibilities …
[23] Ratio of reduced to oxidized glutathione as indicator of oxidative stress status and DNA damage
1999
Publisher Summary This chapter discusses the ratio of reduced to oxidized glutathione (GSH) as an indicator of oxidative stress status and DNA damage. Several methods have been proposed for the determination of GSH status in biological samples. Accurate determination of this status is largely dependent on the prevention of GSH autoxidation during sample processing. As the disulfide form (GSSG) is present only in minimal amounts with respect to the reduced form, a small GSH autoxidation during sample processing can give erroneously high GSSG level. The chapter describes high-performance liquid chromatography (HPLC) method for determining GSSG. It also presents a method for glutathione determ…
Isobaric Vapor−Liquid Equilibrium for Ethanol + Water + Strontium Nitrate
1996
Isobaric vapor−liquid equilibrium for ethanol (1) + water (2) + potassium nitrate (3) at various concentrations of salt and with ethanol mole fractions from 0 to 0.642 has been measured at 100.0 kPa. The results were correlated by assuming that the salt was in ionic form and it was associated only with the water.
Imidazol-4-carbinole aus Iminoestern und Dihydroxyaceton. 2. Mitt. über Imidazolsynthesen mit flüssigem Ammoniak
1974
Imidazol-4-carbinole 3 mit funktionellen Gruppen am C-Atom 2 lassen sich aus Iminoestern 1 und Dihydroxyaceton (2) in flussigem Ammoniak unter Druck darstellen. Imidazole-4-carbinols from Iminoesters and Dihydroxyacetone Imidazole-4-carbinols 3 with functional groups at C-atom 2 are obtained from iminoesters 1 and dihydroxyacetone (2) in liquid ammonia under pressure.
NMR-Spektroskopie an Heterocyclen, 6. Mitt. Favorskii-Umlagerung von α-Brom-β-methoxy-ketonen bei der Imidazol-Cyclisierung in flüssigem Ammoniak
1979
Bei der Imidazolsynthese aus α-Bromketonen und Formiminoethylester in flussigem Ammoniak werden α-alkylsubstituierte Buttersaure-Amide als Nebenprodukte erhalten, deren Entstehen einer Favorskii-Umlagerung zugeschrieben wird. Die isolierten Verbindungen wurden NMR-spektroskopisch untersucht. NMR Spectroscopy of Heterocycles. VI: Favorskii Rearrangement of α-Bromo-β-methoxy Ketones During Imidazole Cyclisation in Liquid Ammonia. During imidazole synthesis with α-bromo ketones and formiminic ethyl ester in liquid ammonia α-alkylbutyric amides were obtained as by-products. Their formation is attributed to a Favorskii rearrangement. The compounds were investigated by NMR spectroscopy.
Eine quantitative Bestimmungsmethode des Uracilgehaltes biologischen Materials im Nanogramm-Bereich mit Hilfe der Hochdruck-Flüssigchromatografie / A…
1974
Abstract A method is described for the estimation of the uracil content in biological materials by means of high-pressure liquid chromatography. Hydrolysis of the tissues and total liberation of RNA bases are carried out in 70% perchloric acid. Less than 1 mg of the materials are needed for analysis. A pre-purification of the hydrolyzates is carried out by anion-exchange chromatography. Recoveries are estimated by isotope dilution analysis with [2-14C] labelled uracil. The method is highly sensitive - about 6000 pmol of uracil content can at least be estimated quantitatively - and analysis time is short. In routine analysis a single sample needs 4 hours to be completed. When preparing sever…