Search results for "liquid"

Synthesis, characterization and thermal properties of new aromatic quaternary ammonium bromides

2004

Series of new aromatic R 2R′ 2N +Br - (R=benzyl, 4-methylbenzyl, 2-phenylethyl, 3-phenylpropyl; R′=ethyl, methyl, isopropyl) or RR′ 2NH +Br --type (R=benzyl, R′=isopropyl) quaternary ammonium bromides were prepared by using novel synthetic route in which a formamide (N,N-diethylformamide, N,N-dimethylformamide, N,N-diisopropylformamide) is treated with aralkyl halide in presence of a weak base. The compounds were characterized by 1H-NMR and 13C-NMR spectroscopy and mass spectrometry. Structures of the crystalline compounds were determined by X-ray single crystal diffraction, and in addition the powder diffraction method was used to study the structural similarities between the single crysta…

Chromatographically separable rotamers of an unhindered amide

2014

Surprisingly stable formamide rotamers were encountered in the tetrahydroisoquinoline and morphinan series of alkaloids. We investigated the hindered rotation around the amide bond by dynamic high-performance liquid chromatography (DHPLC) and kinetic measurements of the interconversion of the rotamers which can readily be separated by HPLC as well as TLC. The experimental results of the different methods were compared to each other as well as to results obtained by DFT calculations.

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…

3,6-Bis(2-arylethenyl)-1,2,4,5-tetrazine - Synthese, Fl�ssigkristallinit�t und Photochemie

1995

3,6-Bis(2-arylethenyl)-1,2,4,5-tetrazines - Synthesis, LC Properties and Photochemistry The (E,E)-3,6-Bis(2-arylethenyl)-1,2,4,5-tetrazines 8 were prepared in a synthetic sequence starting with aromatic aldehydes 1 and cinnamic acids 2, respectively (Scheme 1). The rod-like conjugated molecules represent calamitic mesogens as well as extended chromophores. Hence, we investigated the formation of liquid crystals, achieved by the introduction of long flexible side chains, and the photochemical behaviour that is characterized by the fragmentation of the central ring (Scheme 3).

Article 40. Emoluments du liquidateur, Bénéfice du privilège général des frais de justice (non), Priorité de paiement de l'art. 40 (oui)

1998

International audience; (Com. 31 mars 1998, Mahieux ès qual. c/ Banque de Polynésie)

Studies on pathways of ring opening of benzene in a Fenton system

1995

Ring-opened products of benzene metabolism have been postulated to play a role in hematotoxicity and leukemogenesis. The reaction of benzene in the Fenton system was reexamined to determine the presence of compounds which might serve as intermediates in the formation of trans, trans-muconaldehyde (MUC), a microsomal hematotoxic metabolite of benzene. Benzene dihydrodiol (DHD) was found in this system based on coelution with authentic standard, ultraviolet (UV) absorption characteristics, and molecular weight. Incubation of DHD in the Fenton system resulted in the formation of phenol (PH), catechol (CAT), and products which reacted with thiobarbituric acid to form chromogens absorbing at 495…

Drift velocity of free electrons in liquid argon

1999

Abstract A measurement of the drift velocity of free electrons in liquid argon has been performed. Free electrons have been produced by photoelectric effect using laser light in a so-called “laser chamber”. The results on the drift velocity vd are given as a function of the electric field strength in the range 0.5 kV / cm ⩽| E |⩽12.6 kV / cm and the temperature in the range 87 K ⩽T⩽94 K . A global parametrization of v d (| E |,T) has been fitted to the data. A temperature dependence of the electron drift velocity is observed, with a mean value of Δ v d /( Δ T v d )=(−1.72±0.08)%/ K in the range of 87–94 K.

Supported Fullerene C60-Ionic Liquid Hybryds as New Catalytic Materials

2015

Nuovi ibridi [60]fullerene-liquido ionico

2014

Catalytic Synergism in a C60IL10TEMPO2 Hybrid in the Efficient Oxidation of Alcohols

2014

A novel fullerene (5:1)hexakisadduct bearing two 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) radicals and ten 1-propyl-3-methylimida- zolium bromide moieties has been synthesized and characterized. Such an C60IL10TEMPO2 hybrid has been successfully employed as a catalyst in the se- lective oxidation of a wide series of alcohols and is highly active at just 0.1 mol% loading. Moreover, it can be easily recovered by adsorption onto a multi- layered covalently-linked SILP phase (mlc-SILP) through a "release and catch" approach and reused for up to 12 cycles without loss in efficiency. Inter- estingly, a catalytic synergistic effect of TEMPO and imidazolium bromide moieties combined in the same…