Search results for "Diethyl ether"

Retention behaviour of volatile compounds in normal-phase high-performance liquid chromatography on a diol column

1993

Abstract Retention data on a diol column for over 300 compounds of the chemical classes usually contained in aroma extracts of plants and foodstuffs are reported. A concept that largely corrects for minor fluctuations of the mobile phase composition and of the flow-rate was used to measure capacity factors. The mobile phase was composed of pentane and diethyl ether. The high volatility of these two solvents makes the method perfectly adaptable to the prefractionation of aroma extracts and the semi-preparative isolation of compounds. Non-polar compounds such as hydrocarbons are not retained on diol. Polar compounds can be readily eluted, with the exception of strong acids and bases.

Separation and identification of piperine and chavicine in black pepper by TLC and GC-MS

2006

Conventional extraction of piperine and its derivatives by stirring the black pepper powder with solvents (ethyl alcohol, chloroform, petroleum ether, diethyl ether, etc.) for 16 to 24 h, or in a Soxhlet device for 16 h, can be replaced by extraction with supercritical fluids (CO 2 , CO + ethanol mixtures) [5, 6], or can be aided by use of microwave irradiation [7]. Separation and identification of the compounds present in pepper (essential oils, alkaloids, etc.) has been achieved by gas chromatography combined with mass spectrometry [8] and by thin-layer chromatography [9, 10]. C. Marutoiu, M.I. Moise, Lucian Blaga University of Sibiu, Faculty of Agricultural Sciences, Food Industry, and E…

Hydrogen: a good partner for rhodium-catalyzed hydrosilylation

2014

The influence of hydrogen pressure on the hydrosilylation of ketones catalyzed by [((S)-SYNPHOS)Rh(nbd)]OTf has been studied. We have notably demonstrated that hydrogen significantly affected the outcome of the reaction while not being consumed as stoichiometric reducing agent. In THF, diethyl ether or toluene, the hydrogen pressure exceedingly accelerated the hydrosilylation reaction and preserved or even improved the enantioselectivity of the process. In CH2Cl2, the rhodium catalyst also showed generally higher catalytic activity under hydrogen pressure. Most serendipitously, several ketones were found to give products of absolute opposite configuration upon performing the hydrosilylation…

1984

An apparatus is presented for the precise measurement of vapour pressures. It is tested with diethyl ether and applied to the system tert-butyle acetate/polystyrene (weight-average molecular weight Mw = 110000) up to polymer concentrations of ca. 60 wt.-% in the temperature range from 10 to 90°C; by means of the Redlich-Kister equation the results can well be described analytically. The data are evaluated to yield the Flory-Huggins parameter in the subsequent article in conjunction with other experimental information.

Determination of caffeine in tea samples by Fourier transform infrared spectrometry

2002

A sustainable and environmentally friendly procedure has been developed for the FTIR determination of caffeine in tea leaf samples. The method is based on the extraction with ammonia and CHCl3 and direct determination of caffeine on the chloroform extracts using peak height absorbance measurements at 1658.5 cm(-1) and external calibration. The method provides a sensitivity of 0.2142 absorbance units mg(-1) mL and a limit of detection of 1 mg L(-1), corresponding to 0.002% m/m caffeine in tea leaves. As compared with a reference procedure, based on UV absorbance measurement at 276 nm after low pressure column chromatography, the developed procedure reduces the consume of CHCl3 by a factor of…

Prefractionation of aroma extracts from fat-containing food by high-performance size-exclusion chromatography

1996

A method for the prefractionation of aroma extracts of fat-containing food using high-performance size-exclusion chromatography is presented. The aim was to obtain a fraction of volatile compounds with a residual triglyceride content as low as possible, in order to allow its direct analysis by gas chromatography. Two different mobile phases, diethyl ether and dichloromethane, were tested and the elution volumes of triglycerides and a large variety of aroma compounds were measured. The quality of separation between triglycerides and volatile compounds as a function of column load was studied. The method was successfully applied to the analysis of goat cheese volatiles.

Reductions of M{N(SiMe3)2}3 (M = V, Cr, Fe): Terminal and Bridging Low-Valent First-Row Transition Metal Hydrido Complexes and “Metallo-Transaminatio…

2021

The reaction of the vanadium(III) tris(silylamide) V{N(SiMe3)2}3 with LiAlH4 in diethyl ether gives the highly unstable mixed-metal polyhydride [V(μ2-H)6[Al{N(SiMe3)2}2]3][Li(OEt2)3] (1), which was structurally characterized. Alternatively, performing the same reaction in the presence of 12-crown-4 affords a rare example of a structurally verified vanadium terminal hydride complex, [VH{N(SiMe3)2}3][Li(12-crown-4)2] (2). The corresponding deuteride 2D was also prepared using LiAlD4. In contrast, no hydride complexes were isolated by reaction of M{N(SiMe3)2}3 (M = Cr, Fe) with LiAlH4 and 12-crown-4. Instead, these reactions afforded the anionic metal(II) complexes [M{N(SiMe3)2}3][Li(12-crown-…

Titanium and zirconium complexes that contain a tridentate bis(phenolato) ligand of the [OOO]-type

2003

Abstract The oxygen-linked bis(phenol) 2-oxapropanediyl-1,3-bis(2-tert-butyl-4-methylphenol), [OOO]H2, was prepared in good yield by the condensation of 2-tert-butyl-6-hydroxymethyl-4-methylphenol at 155 °C. This bis(phenol) reacted cleanly with titanium tetrachloride to give the orange titanium dichloro complex [OOO]TiCl2 in virtually quantitative yield. The solubility in pentane indicates a monomeric structure for [OOO]TiCl2 in solution. The reaction of titanium tetra(isopropoxide) gave the di(isopropoxy) complex [OOO]Ti(OiPr)2 which also adopts a monomeric structure of C2v-symmetry in solution. The reaction of the dichloro complex [OOO]TiCl2 with benzyl Grignard reagent in diethyl ether …

Thin-layer chromatography of chlorinated anisoles and veratroles

1989

The thin-layer chromatography of chlorinated anisoles (methoxybenzenes) and veratroles (1,2-dimethoxybenzenes) has been examined on silica gel G60 and RP-18 thin-layer plates. More than fifty solvent systems were screened and some of them recommended for particular separations. Acetone was shown to be suitable for group separation of both chlorinated anisoles and veratroles on a silica gel G60 stationary phase having a very narrow range of RF values. On the other hand, benzene, dichloromethane and the various mixtures of light petroleum (b.p. 40–60°C) and a more polar eluent (such as diethyl ether, acetone or ethyl acetate) were recommended for separation of certain individual isomers. The …

Identification and quantification of carotenoids including geometrical isomers in fruit and vegetable juices by liquid chromatography with ultraviole…

2004

A method was established for the identification and quantification of carotenoids including geometrical isomers in fruit and vegetable juices by liquid chromatography with an ultraviolet−diode array detector, using a C18 Vydac 201TP54 column. The mobile phase used was the ternary methanol mixture (0.1 M ammonium acetate), tert-butyl methyl ether and water, in a concentration gradient, and a temperature gradient was applied. Retinol palmitate was added as an internal standard. An extraction process (ethanol/hexane, 4:3, v/v) was performed, followed by saponification with diethyl ether/methanolic KOH (0.1%, w/v, BHT) (1:1, v/v) for 0.5 h at room temperature. Seventeen different (cis and trans…