Search results for "SOLVENT"
showing 10 items of 1395 documents
Supercritical Carbon Dioxide: A Promoter of Carbon-Halogen Bond Heterolysis
2013
as the leaving groupdeparts from the carbon atom prior to the entrance of thenucleophile. Polar protic solvents with high dielectric con-stants promote polar bond heterolysis by providing effectiveH-bonding and electron-pair donation interactions to theleaving group and the incipient carbocation, respectively.Then, the solvent captures the carbocation intermediate togive the corresponding S
Phenolic and Antioxidant Analysis of Olive Leaves Extracts (Olea europaea L.) Obtained by High Voltage Electrical Discharges (HVED)
2019
Background: The aim of this study was to evaluate high voltage electrical discharges (HVED) as a green technology, in order to establish the effectiveness of phenolic extraction from olive leaves against conventional extraction (CE). HVED parameters included different green solvents (water, ethanol), treatment times (3 and 9 min), gases (nitrogen, argon), and voltages (15, 20, 25 kV). Methods: Phenolic compounds were characterized by ultra-performance liquid chromatography-tandem mass spectrometer (UPLC-MS/MS), while antioxidant potency (total phenolic content and antioxidant capacity) were monitored spectrophotometrically. Data for Near infrared spectroscopy (NIR) spectroscopy, colorimetry…
Enhancing Bioactive Antioxidants’ Extraction from “Horchata de Chufa” By-Products
2018
During the production of a traditional drink produced from the tubers of Cyperus esculentus L. also known as “horchata de chufa,” a high quantity of by-products are generated. These by-products are rich with valuable biological compounds, hence, there is a need to report their extraction conditions for further use in food production as raw materials. Therefore, the objective of this study was to evaluate and improve the conventional extraction process, applied for recovery of phenolic compounds, total flavonoids, and total antioxidant capacity from the by-products. Independent variables for extraction were: (i) Solvent type (mixtures of ethanol-water (v/v) at 0%, 25% and 50%)
Start-Up of Chitosan-Assisted Anaerobic Sludge Bed Reactors Treating Light Oxygenated Solvents under Intermittent Operation
2021
Quality of the granular sludge developed during the start-up of anaerobic up-flow sludge bed reactors is of crucial importance to ensure the process feasibility of treating industrial wastewater such as those containing solvents. In this study, the microbial granule formation from suspended-growth biomass was investigated in two chitosan-assisted reactors. These reactors operated mimicking industrial sites working with night closures treating a mixture of ethanol, ethyl acetate, and 1-ethoxy-2-propanol. Each reactor operated under different hydrodynamic regimes typical from UASB (R1: <
Small Gold Nanoparticles Synthesized with Sodium Citrate and Heavy Water: Insights into the Reaction Mechanism
2010
5 páginas, 3 figuras, 1 esquema.
Partition Behavior of Anilines in Bulk‐Phase and High‐Performance Liquid Chromatographic Systems: Influence on Correlation with Biological Constants
1992
Abstract The partition behavior of a mixed series of ring‐substituted anilines in reversed‐phase high‐performance liquid chromatographic systems is substantially different from that observed in a classical bulk‐phase partition system with n ‐heptane as the aprotic reference solvent. On the basis of the equivalence of each ring substituent in the p ‐straight‐chain methylene groups (ν value) as a function of the fraction of organic solvent (acetonitrile or methanol) in the mobile phase, the biased partition behavior for imperfect homologues and heterologues is verified relative to that of perfect homologues. This behavior was tentatively attributed, mainly, to differences in the hydrogen bond…
Silver Ion-Selective Electrodes Based on π-Coordinating Ionophores Without Heteroatoms
2002
Ion-selective electrodes (ISEs) were constructed by using spherical hydrocarbons (cyclophanes) as π-coordinating ionophores in solvent polymeric membranes. Four structurally similar cyclophanes, i. e., [2.2.2]p,p,p-cyclophane, [2.2.2]m,p,p-cyclophane, [2.2.1]p,p,p-cyclophane and [2.2.1]m,p,p-cyclophane were studied as ionophores for Ag+. The ion-selective membranes were composed of the corresponding ionophore (1%), potassium tetrakis(4-chlorophenyl)borate (0.5%), 2-nitrophenyl octyl ether (65–66%) and PVC (32–33%). The ion-selective membrane was placed on top of a layer of the conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), working as ion-to-electron transducer. The selectivit…
Conformational mobility of thianthrene-5-oxide.
2005
[reaction: see text] Data on the apparent dipole moment of thianthrene-5-oxide (1) and (1)H NMR spectra in different solvents support the conformational mobility of 1, which flaps between two limit boat conformations with the sulfinyl group in pseudoequatorial and pseudoaxial positions, respectively. The conformational equilibrium of 1 occurs too fast for the (1)H NMR (500 MHz) time-scale even at -130 degrees C, and the equilibrium constant has not been determined. The apparent dipole moments of 1 in n-hexane and 1,4-dioxane and the (1)H NMR spectra of 1 and the model compounds cis- and trans-thianthrene-5,10-dioxides (2) and thianthrene (5) in different solvents and at various temperatures…
Inclusion complexes of triphenylphosphine derivatives and peracetylated-β-cyclodextrin in supercritical carbon dioxide
2008
The supramolecular chemistry of peracetylated-β-CD (perAc-β-CD) as a host for triphenyphosphine derivatives has been studied in supercritical (scCO2) using UV absorption spectroscopy. It was found that the association constant in scCO2 at 40°C and 300 bar is 10 to 1000 times smaller compared to analogous systems in aqueous solvent. Studies of the thermodynamics of the inclusion process found an enthalpy of association of -30 kJ/mole and an entropy of -55 J/moleK. This difference with respect to water is attributed to the absence of the hydrophobic effect in scCO2 due to the much smaller polarity of scCO2 versus water. To further explore the effect of the solvent on the association constant,…
Efficiency of QuEChERS approach for determining 52 pesticide residues in honey and honey bees
2016
A comparison between QuEChERS and other pesticide extraction procedures for honey and honey bee matrices is discussed. Honey bee matrix was extracted by solvent based procedure whereas solid phase extraction was the protocol for the honey matrix. The citrate buffered QuEChERS method was used for both matrices. The methods were evaluated regarding cost (equipment and reagents), time, accuracy, precision, sensitivity and versatility. The results proved that the QuEChERS protocol was the most efficient method for the extraction of the selected pesticides in both matrices. QuEChERS is the most economical and less time-consuming procedure.SPE and solvent-based extraction procedures show equivale…