System petroleum ether

Solvent - Solvent system petroleum ether (100-140 °C) 2-propanol H20 (100 12 0.25)... 

Solvent methanol Solvent system petroleum ether ethyl acetate (6 4)... 

Solvent system, petroleum ether-dioxane-acetone (70 30 10, v/v/v) Chromatography chamber Metal spatula or clean razor blade... 

The newly introduced HPTLC-LiChrospher Si 60 F254S precoated plates in many cases show a still better separation efficiency than the HPTLC silica gel 60 precoated plates. For example. Fig. 12a (HPTLC silica gel 60) and Fig. 12b (HPTLC-LiChrospher Si 60254s) how the scanned chromatograms of eight pesticides, all in the solvent system petroleum ether 40-60 °C + acetone (70 + 30 ml, without saturation of the chamber) [13a]. Also in the analysis of frankincense (olibanum), better separations were obtained on plates precoated with spherical silica gel than on those precoated with irregularly shaped particles [13b-dj. 

Hexazin, Metoxuron, Monuron, Aldicarb, Azinphos methyl, Prometryn, Pyridat, Trifluralin Sample volume 50 nl, normal chamber without chamber saturation, solvent system petroleum ether (40-60 °C) + acetonitrile (70 + 30 v/v), migration distance 7 cm. 

Sherma et al. (1992) separated chloroplast pigments on silica gel and seven types of bonded silica gel plates. Spinach leaves were extracted in acetone, and the best overall separation was done on a Cig (Whatman) reversed-phase plate using the solvent system petroleum ether-acetonltrile-methanol (2 4 4). The Rf values and wavelengths (in nm) of maximum absorption of selected pigments on the Cjg layers were as follows P-carotene, 0.08, 455 nm pheophytin, 0.24, not available chlorophyll a, 0.36, 420 nm and neoxanthin, 0.75, 440 nm. 

Benzene, which has been used as a solvent successfully and extensively in the past for reactions and purification by chromatography and crystallisation is now considered a very dangerous substance so it hasto be used with extreme care. We emphasise that an alternative solvent system to benzene (e.g. toluene, toluene-petroleum ether, or a petroleum ether to name a few) should be used first. However, if no other solvent system can be found then all operations involving benzene have to be performed in an efficient fumehood and precautions must be taken to avoid inhalation and contact with skin and eyes. Whenever benzene is mentioned in the text an asterisk e.g. C Hg or benzene, is inserted to remind the user that special precaution should be adopted. 

Another issue important to the success of this chiral titanium reagent 31 was the discovery of a marked solvent effect. When the fumaric acid derivative is reacted with isoprene in the presence of 10 mol% of the titanium reagent 31 in toluene, poor optical purity results (36-68% ee). Interestingly the optical purity of the adduct greatly increased in the order benzene, toluene, xylenes, and mesitylene, with 92% ee obtained in the last. Mesitylene is difficult to remove, because of its high boiling point, and other solvents were screened in detail. As a result, the mixed solvent system toluene petroleum ether (1 1) was discovered to be very effective. 

Carotenoids are generally well separated on silica gel layers, and a plethora of data is available in the literature for such separations [24]. The developing solvent systems most commonly used consist of acetone or another polar modifier in a light hydrocarbon, hexane, petroleum ether, etc. Systems involving chlorohydrocarbons have also been reported, but great care should be taken with these to avoid the prior presence of acidic impurities in the solvent and to ensure that radicals are not formed during use, because both of these possibilities will cause rapid destruction of the carotenoids present. 

Note Rp-values (p-carotene = 100) are used for systems 1 to 3 and Rp values for system 4. Solvent compositions by volume, p.e. = petroleum ether (40 to 60°C) DB indicates number of in chain conjugated double bonds FG indicates functional groups E = epoxy, H = hydroxyl, K = ketone. 

Glycosidic anthraquinones may be developed using ethyl acetate-methanol-water systems (100 10 10) with suitable adjustments made for polarity. Similarly, aglycones can be separated using a somewhat less polar solvent such as petroleum ether (40 to 60°C)-ethyl acetate-formic acid (75 25 1). Some chosen retention data may be found in a recent monograph [24]. Pigments may be recovered by extraction of the absorbant with acetone or methanol after removal of the individual zones. 

Furthermore, the mechanism shown in Figure 12.1 considers only the all-tnmv-carotcnoid form as the initial compound however, although the all-tran.v-isomer predominates, d.v-isomcrs are also commonly found in model solutions and even more frequently in food systems, since these isomers are in equilibrium in the solution. Therefore, the initial carotenoid system often contains a mixture of isomers, whose composition changes according to the carotenoid structure, solvent, and heat treatment. For example, the isomerization rate of P-carotene is higher in nonpolar solvents, e.g., petroleum ether and toluene, than in polar solvents (Zechmeister 1944). 

Since petroleum ether was the solvent used in the earlier studies for extracting the DDT from seawater, Wilson and Forester [332] initiated further studies to evaluate the extraction efficiencies of other solvent systems. 

The partition of different lipids between two immiscible solvents (countercurrent distribution) is useful for crude fractionation of lipid classes with greatly differing polarities. Repeated extractions in a carefully chosen solvent pair increase the effectiveness of the separation but in practice mixtures of lipids are still found in each fraction. A petroleum ether-ethanol-water system can be used to remove polar contaminants (into the alcoholic phase) when interest lies in the subsequent analysis of neutral glycerides, which may be recovered from the ether phase. Carbon... 

An unusual tautomerism occurs in the system 56. It, too, is found in two crystal forms. One has a melting point of 108 to 110°C, is insoluble in petroleum ether, and is assigned the zwitterionic structure 56a. The second melts at 77 to 78°C, is soluble in hot petroleum ether, and is assigned structure 56b (118). 

Because of their versatility and simplicity, TLC methods have been frequently applied to the separation and semi-quantitative determination of carotenoid pigments in synthetic mixtures and various biological matrices. The retention of pure carotenoid standards has been measured in different TLC systems. Separations have been carried out on silica plates using three mobile phases (1) petroleum ether-acetone, 6 4 v/v (2) petroleum ether-tert-butanol 8 2 v/v, and (3) methanol-benzene-ethyl acetate 5 75 20 v/v. Carotenoids were dissolved in benzene and applied to the plates. Developments were performed in presaturated normal chambers. The chemical structure and the Rv values of the analytes measured in the three mobile phases are listed in Table 2.1. It was concluded from the retention data that mobile phase 3 is the most suitable for the separation of this set of carotenoids [13],... 

Method A The haloalkane (50 mmol), f-BuOCS2K (10.3 g, 55 mmol) and Aliquat (1.5 g, 3.75 mmol) in H20 (50 ml) are stirred until a yellow oil is produced (ca. 10-15 min). The temperature of the mixture is then raised to 75-80°C over a period of 10 min and maintained at this temperature until the evolution of gas ceases. The mixture is cooled, and petroleum ether (l 00 ml) is added. The organic phase is separated, washed with H20 (2 x 20 ml), dried (MgS04), filtered through silica, and fractionally distilled to give the thiol. MethodB The haloalkane (50 mmol) and Aliquat (1.5 g, 3.75 mmol) in H20 are heated to ca. 50°C and f-BuOCS2K (16.9 g, 90 mmol for sec-bromides and 28.2 g, 150 mmol for chlorides) is added in small portions over a period of l h (2 h for the chlorides) allowing the aqueous phase to become colourless before the next addition. The mixture is stirred for ca. 30 min and the temperature of the system is then raised to 75-80°C and the thiols are isolated as described in 4.1.23.A. 

The conversion of primary alcohols to aldehydes was achieved by using a biphasic system consisting of water and a nonpolar organic solvent such as petroleum ether. Under these conditions, benzylic and allylic alcohols were oxidized with high selectivity to the aldehydes (for example, (16) to (17) in Scheme 4), while aliphatic alcohols were converted to aldehydes with poor selectivity [17]. 

Under dirty operating conditions it is possible for dust deposits to form a crusf in the pump chamber. These contaminants will deposit in part in the pumping chamber and in part on the pump s impellers. They may be removed, once the two connection lines have been detached, either by blowing out the system with dry compressed air or by rinsing with a suitable cleaning agent, such as petroleum ether (naphtha). 

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