Search results for "acetonitrile"
showing 10 items of 1007 documents
Retention-pH profiles of acids and bases in hydrophilic interaction liquid chromatography
2018
Abstract The high proportion of acetonitrile used in many HILIC mobile phases significantly changes the acid-base properties of pH buffers and analytes foreseen from available data in water. In this paper, the recommended stability pH range for chromatographic columns is examined with various acetonitrile/water mixtures, resulting in a significant broadening in the operational pH window with the content of organic solvent. Additionally, the challenge of buffer selection in HILIC is also addressed. Commonly used ammonium acetate shrinks its pH buffering range in acetonitrile-rich mobile phases due to variations in the dissociation constants of the buffer constituents (acetic acid and ammoniu…
Electro- and magneto-electrochemistry of zeolite Y- and MCM-41-associated bipyrylium ion
2005
Abstract The electrochemical response of bipyrylium bication [1,4-bis(3,5-diphenyl-4-pyrylium)phenylene] associated with Y and MCM-41 aluminosilicates (BTP@Y and BTP@MCM, respectively) is described using polymer-film electrodes immersed into Et 4 N + + MeCN and Bu 4 N + + MeCN electrolytes. BTP@MCM provides a solution-like response in all electrolytes consisting in two successive strongly comproportionation mediated one-electron reduction processes near to +0.05 and −0.12 V vs. Ag|AgCl. The response of BTP@Y in Bu 4 N + + MeCN is restricted to a unique reduction process near to −0.40 V, while in Et 4 N + + MeCN, it differs significantly: here, two reduction processes at −0.22 and −0.36 …
Orientation of the acidity probes benzene, acetonitrile and pyridine in SAPO-5 and GaAPO-5 molecular sieves: an FTIR microscopy study
1997
The adsorption and desorption behaviour of benzene, acetonitrile (CD3CN) and pyridine for large crystals of SAPO-5 and GaAPO-5 is studied using FTIR microscopy with polarised IR radiation. From the analysis of the polarised adsorption bands it is concluded that the adsorbates are ordered in the molecular sieves at 373 K. The orientation of molecules interacting with Bronsted or Lewis acid sites and of physisorbed molecules are discussed. Benzene adsorbed at Bronsted sites is oriented with the aromatic ring parallel to the crystallographic c-axis of the molecular sieve, whereas physisorbed benzene is oriented with the aromatic ring parallel to the crystallographic a,bplane. Acetonitrile can …
Sustainable Approach to Waste-Minimized Sonogashira Cross-Coupling Reaction Based on Recoverable/Reusable Heterogeneous Catalytic/Base System and Ace…
2016
In this contribution, we present a chemically efficient and sustainable protocol for the palladium-catalyzed copper-free Sonogashira cross-coupling reaction, based on the use of a heterogeneous catalytic system. This consists in the combination of a palladium catalyst on highly cross-linked thiazolidine network on silica and a polystyrene-supported base. The solid catalyst/base system acts as a palladium scavenger avoiding leaching of the metal and consequent product contamination. The reaction can be conducted in safe and easily recoverable acetonitrile/water azeotrope as reaction medium. This proved to be an efficient greener alternative to the classic toxic aprotic media commonly used in…
Waste-free electrochemical oxidation of alchools in water
2006
We describe a new sol-gel molecular electrode made of a thin layer of organosilica doped with the nitroxyl radical TEMPO (2,2,6,6-tetrame-thylpiperidine-1-oxyl) electrodeposited on the surface of an ITO-coated glass and its employment as a selective and versatile oxidation catalyst in the electrochemical conversion of different alcohols to carbonyl compounds. Environmentally friendly water or a water/acetonitrile mixture buffered with bicarbonate is used as solvent. The electrode is highly stable and it can be reused for a prolonged period of time allowing easy separation from the products.
An E-Factor Minimized Protocol for a Sustainable and Efficient Heck Reaction in Flow
2014
A highly sustainable and waste-minimized protocol for Heck coupling has been defined. Optimal conditions have been defined by exploiting a heterogeneous catalyst based on supported ionic liquid-like phases featuring high Pd loading (10 wt %) and by optimizing its efficiency in a recoverable green reaction medium (acetonitrile/water azeotrope). Pure products 4a–l and 6a–h have been isolated chromatography-free in high yields (74–99%) and with extremely low environmental factor (E-factor) values (2.3–5.0). With the application of flow technology, the selected heterogeneous base and Pd catalyst have been fully recovered and reused, and minimum palladium leaching allowed for isolation of the fi…
A Chemosensor Bearing Sulfonyl Azide Moieties for Selective Chromo-Fluorogenic Hydrogen Sulfide Recognition in Aqueous Media and in Living Cells
2014
A simple chemodosimeter based on a sulfonyl azide dye (1-Az), which displayed a highly selective response toward hydrogen sulfide anion in mixed aqueous media, was synthesised and characterised. Addition of hydrogen sulfide to acetonitrile/HEPES 1:1 solutions of 1-Az induced a clear colour change from red-orange to yellow, which was easily detected by the naked eye, and by an enhancement in the emission intensity. Other common anions, thiol-containing biomolecules and oxidants did not induce any noticeable colour or fluorescence modulation in the probe. The chemodosimeter also showed a good sensitivity, with limits of detection of 11.91 and 0.63 μM by using UV/Vis or fluorescence measuremen…
Interaction Between Amines and N-Haloimides: a New Motif for Unprecedentedly Short Br...N and I...N Halogen Bonds
2011
The complexes of N-bromosuccinimide or N-iodosuccinimide with a halogen bond acceptor, either 1,4-diazabicyclo[2.2.2]octane (DABCO), hexamethylenetetramine (HMTA) or 1,3,5-triazine (TRZ), led to an unprecedentedly strong (CO)2N–X⋯N halogen bond synthon (X = Br or I) determined from crystal structures of [DABCO]·[NBS]22, [HMTA]·[NBS]22, [TRZ]·[NIS]22 and [HMTA]·[NIS]44. The Br⋯N distances with DABCO and with HMTA donors were 2.347 A and 2.414 A being remarkably shorter (31% and 29%) than the sum of the VDW radii of nitrogen and bromide atoms, respectively. The corresponding I⋯N distances with HMTA and TRZ were 2.549 A and 2.596 A (27.8% and 26.4% less than the sum of the VDW radii of N and I…
New Dinuclear Catalysts Rh2(N−O)2[(C6H4)P(C6H5)2]2 with Imidate Ligands: Synthesis and Isomerization from Head-to-Tail to Head-to-Head Configuration…
2001
Two new dirhodium(II) catalysts of general formula Rh(2)(N-O)(2)[(C(6)H(4))P(C(6)H(5))(2)](2) (N-O = C(4)H(4)NO(2)) are prepared, starting from Rh(2)(O(2)CCH(3))(2)(PC)(2)L(2) [PC = (C(6)H(4))P(C(6)H(5))(2) (head-to-tail arrangement); L = HO(2)CCH(3)]. The thermal reaction of Rh(2)(O(2)CCH(3))(2)(PC)(2).L(2) with the neutral succinimide stereoselectively gives one compound that according to the X-ray structure determination has the formula Rh(2)(C(4)H(4)NO(2))(2)[(C(6)H(4))P(C(6)H(5))(2)](2) (1). It corresponds to the polar isomer with two bridging imidate ligands in a head-to-head configuration. However, stepwise reaction of Rh(2)(O(2)CCH(3))(2)(PC)(2).L(2) with (CH(3))(3)SiCl and potassiu…
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…